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High Energy Detectors Second Semester Report

Spring Semester 2014

-Full Report-

By

Ricky Krahn

Prepared to partially fulfill the requirements for

ECE 402

Department of Electrical and Computer Engineering

Colorado State University

Fort Collins, Colorado 80523

Project Advisors: ____Jorge Rocca Carmen Menoni____

Approved By: _____ Carmen Menoni Jorge Rocca______

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ABSTRACT

The Extreme Ultraviolet Lasers at the Extreme Ultraviolet – Engineering Research

Center (EUV-ERC) lab at CSU pursues state of the art research focused on the development of

extreme ultraviolet lasers and applications of these novel sources in nano-imaging, nano-

patterning and nano-mass spectrometry. Many of these applications require controlled doses of

EUV illumination. Therefore, they rely on the use of detectors that can precisely measure laser

pulse energy in a configuration that does not alter or blocks the beam path. This project

addresses this by developing a method to detect the number of photons in a laser pulse without

blocking the beam.

This problem is solved with the Gas Photoionization Extreme Ultraviolet (EUV)

Detector. The detector uses the concept of photoionization which occurs when high energy

photons collide with atoms. The detector uses a strong electrical field to pull the released

electrons to a charged plate causing a readable current. This current is directly proportional to the

number of photons in the laser pulse. Because this detector relies only on the laser hitting air, it

can be implemented in a way that does not impede the laser pulse.

The Gas Photoionization EUV Detector was successfully implemented showing expected

voltage spikes when the laser is shot. A Gold Photodiode Detector was built to calibrate the

photoionization detector. These two detectors were successfully capable of measuring the energy

in a laser pulse. Future may include further refinement of the calibration and a feedback system

to control the laser with the photoionization detector.

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TABLE OF CONTENTS

Title i

Abstract ii

Table of Contents iii

List of Figures iv

I. Introduction 1

II. Summary of Previous Work 3

III. Mechanical Design of Photoionization Detector 4

A. Detector Design 4

B. Support Structure 5

C. Vacuum Design Factors 7

IV. Circuit Design for Photoionization Detector 7

A. Circuit Design 7

B. Component Selection 8

C. Power Supply Circuit 11

V. Mechanical Design of Photodiode Detector 11

VI. Results and Calibration 15

A. Results 15

B. Calibration 18

VII. Other Considerations 22

VIII. Conclusions and Future Work 22

References 23

Bibliography 23

Appendix A – Abbreviations I

Appendix B – Budget II

Appendix C – Timelines III

Appendix D – Dimensions X

A. Gas Photoionization Detector X

B. Gold Photodiode Detector X

Appendix E – Gold Quantum Efficiency XIV

Appendix F – Parts XV

Appendix G – Code XVI

Acknowledgements XXI

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LIST OF FIGURES

Figure 1: Mass spectrometry imaging and microscope systems that will use the EUV

photoionization detector 2

Figure 2: Previous Detector 3

Figure 3: Detector Design 4

Figure 4: Cap Design 5

Figure 5: Detector Case 6

Figure 6: Detector Image 6

Figure 7: Detector in Laser 7

Figure 8: Circuit 8

Figure 9: PCB Design 10

Figure 10: 1st Circuit 10

Figure 11: Power Supply Controller 11

Figure 12: Detector Physics 12

Figure 13: Mesh Tower 13

Figure 14: Gold Photodiode Blow Up 14

Figure 15: Gold Photodiode Design 14

Figure 16: Gold Detector Head 15

Figure 17: Both Detectors Sensing 16

Figure 18: Photoionization Detector Bias 16

Figure 19: Second Spike in Photoionization Detector 17

Figure 20: Old vs. New Photodiode Detector 18

Figure 21: Energy Measured By Photodiode 19

Figure 22: Ratio Between Energy and Voltage from Photoionization Detector 20

Figure 23: β 20

Figure 24: Pressure Relationship 21

Figure 25: Energy Measured by Both Detectors 21

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CHAPTER I: INTRODUCTION

The Extreme Ultraviolent Engineering Research Center (EUV-ERC) at Colorado State

University (CSU) is a leading researching institution in the field of Extreme Ultraviolet (EUV)

and Soft X-Ray (SXR) lasers. The EUV-ERC has developed table top EUV laser systems that

operate between wavelengths of 7.8-46.9 nm which have reduced the needed power and size of

modern EUV lasers. One of these lasers functions at wavelength of 46.9nm which is in the EUV

and SXR region of the electromagnetic spectrum. Due to the wavelength, these lasers must be

operated in vacuum. At that wavelength, the laser pulse will be dissipated too significantly in air.

These table top lasers operate with a pulse duration of about 1.5ns and can be run at a 12 Hz

repetition rate. They carry about 13µJ of energy per pulse. This will correspond to about 2*1012

photons per pulse. [1]

The table top lasers at the EUV-ERC are used for several different applications in

research. One such application is error free nano-scale printing. If a mask containing a periodic

pattern is illuminated by one of these lasers, it can be shown that a 1:1 replica image of the mask

exists at certain distances from the mask. Using a photoresist-covered substrate placed at these

distances, the image exposes the resist, and after processing a pattern is created on the substrate.

This method has been shown to print nanoscale features without errors even if the mask contains

defects. [2]

Another such application is EUV laser ablation mass spectrometry imaging. This is a

method for determining the chemical composition of a material by analyzing the ions created in

the ablation process. The method uses a focused EUV laser to create by ablation nanoscale

craters. In previous systems used for this application, large amounts of mass were removed from

the object being analyzed. Using the shorter wavelength EUV lasers, it is possible to

significantly reduce the amount of material that is ablated and thus map composition in three

dimensions at nanoscale dimensions [3] [4]. There are some additional applications for these

lasers including microscopy.

Currently, there is no method in use on these EUV lasers to determine the number of

photons being shot in a laser pulse without blocking the beam path, which is problematic for

applications. If a pulse is slightly weaker or stronger than expected pulse, it could change the

expected results from the experiment. It would be preferred to use a detector that can function

while the application is being conducted. With a detector like that, a software feedback loop

could be implemented that would enable to precisely control the amount of photons that are

being emitted in the pulse. That would allow for even more accurate results.

The purpose of this project is to develop an EUV detector that can measure the laser

pulse energy while the experiment is being conducted. Using the concept of photoionization, it is

possible to realize such a detector. Photoionization is the phenomenon that occurs when photons

of enough energy collide with atoms causing electrons to escape. There is a certain probability

for each atom that it will emit an electron. This is called the photoionization cross section. By

creating a strong electrical field across the laser pulse, it is possible to capture these free

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electrons, thus generating a current. This current will be directly proportional to the number of

photons in the laser pulse.

Because of its high photon energy, EUV light can ionize any elements or molecules.

The EUV laser operates in vacuum. The pressure near the laser output where the detector will be

set up is about 1*104 Torr, that is 7 orders of magnitude less than the pressure at sea level. At

this pressure, there are about 1012

atoms or molecules per cm3. In the vacuum manifold that

connects the laser to the experiments, Argon atoms give rise to this background pressure. Due to

the presence of these argon atoms, the laser pulse will be photoionizing Ar across its entire

propagation through the 3 cm long body of the EUV photoionization detector. Since the majority

of atoms are argon, the overall photoionization cross section can be just assumed to be that of

argon which is 3*10-15

cm-3

. By simply putting a large electrical field at a point along the beam,

it is possible to capture these free photoionized electrons to generate a current signal.

This detector will be used to get an accurate reading of the energy in the EUV laser pulse,

and to trigger data acquisition as well. Some of the imaging systems require a delay for

acquisition and with the detector it will be possible to optimize this delay based on the laser

pulse. The detector will be used with the systems shown in Figure 1: mass spectrometry imaging

and microscope.

Figure 1: Mass spectrometry imaging and microscope systems that will use the EUV

photoionization detector.

In order to calibrate the gas photoionization detector, a gold photodiode detector was

built. This detector was designed using the same concepts as previous designs of detectors used

on these systems. Gold does not oxidize like aluminum so it is able to measure energy accurately

every time it is used. This detector is able to accurately calibrate the gas photoionization

detector.

Mass spectrometry imaging

Microscope

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This report contains six chapters discussing the design and implementation of the Gas

Photoionization EUV Detector and the Gold Photodiode Detector. Chapter II discusses what has

been previously done in the field of determining the number of photons in light pulses. Chapter

III discusses the physical design of the photoionization detector. It then continues to discuss the

mounting design used to support the detector. Chapter IV discusses the circuit design used to

send the signal to an oscilloscope. It also describes the difficulties of getting parts that meet the

needs of high voltage systems. Chapter V discusses the design and considerations for the gold

photodiode detector. Chapter VI shows the results gathered and discusses the calibration process.

Chapter VII discusses some other considerations relating to the project including some

discussions about ethics and further manufacturability. Chapter VIII finishes up by concluding

the results and by discussing future work that can be done to follow on this project. All

dimensions for parts are given in Appendix D.

CHAPTER II: SUMMARY OF PREVIOUS WORK

There have been several detectors designed that use a different method for detecting the

number of photons in the laser pulse. These detectors are photocathode detectors that use a

similar concept of photoionization but with solids instead of gas. The laser passes through a

stainless steel mesh and impinges on an aluminum surface. When the laser hits the aluminum, it

frees electrons. The stainless steel mesh has a very high voltage causing the electrons to move to

the mesh. This causes current which can be detected and is directly proportional to the number of

photons in the laser pulse.

There are a few methods for supporting the detector. One method is to attach the detector

to a support piece that is vacuum sealed and can be pulled out of the way of the laser without

removing the detector from the system. The other method is to attach the detector to a flange that

is attached to the end of the laser system. This method is only useful if the laser is not being used

on experiments because it is at the end of the laser system. A picture of the detector in the system

is shown in Figure 2: Previous Detector. From this picture, it can be seen that the detector is in

the middle of the system so when it is being used, the laser cannot run its experiments.

Figure 2: Previous Detector

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CHAPTER III: MECHANICAL DESIGN

Section A: Detector Design

The structure of the detector is designed in such a way that it produces an electric field

the crosses the path of the laser pulse. This is done by shooting the laser pulse through two

concentric cylindrical stainless steel metal tubes. The inner of the two cylindrical tubes is

elevated to high voltage of 1000V. In order for the electric field to cross the laser path, the inner

tube is cut such that the cross section of the tube is a semicircle. By doing this, the electric field

is able to pass from one tube to the other while crossing the laser path. A Solidworks

representation is shown in Figure 3: Detector Design.

Figure 3: Detector Design

The cylindrical design was chosen so that it would be easier to support while providing a

voltage to only one plate. Because the cylinders are concentric, the inner cylinder does not need

to be supported by metal. That way the outside cylinder can be grounded while the inner cylinder

can be charged. It was considered to use two metal plates initially but due the difficulty of

supporting two plates, and the nice geometry of cylinders with respect to the laser pulse, it was

chosen to use the cylinders.

The inner cylinder is supported by both two Teflon caps and the soldered pin for the

MHV connecter that goes to the power supply. The Teflon caps are press fit to be inserted

between the two cylinders with a hole in the center for the laser to pass through. A Solidworks

representation is shown in Figure 4: Cap Design. Due to this cap design, the inner tube needed to

be cut in a specific fashion. The tube had to be cut in half for the detector to function, but with

that design, the cap wouldn’t provide enough support to hold the tube up. As such, the tube had

to remain as a full circle on either end. This was difficult to implement on the milling machine.

The tube had to be carefully cut in such a way that kept the ends intact but removed half of the

center. There is a pin hole in the center of the tube that the tip of the MHV connector is soldered

to adding additional strength to the structure.

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Figure 4: Cap Design

The outer tube had to have a hole cut through the center in order to let the MHV

connector through to the inner tube. The ends of the tube had to be thinned down in order to

allow the press fitting of the cap.

The inner tube had to be sized such that the laser could fit through the center. The

diameter of the laser pulse is approximately 5mm at the detector. In order to allow easy

alignment and to give enough space for the laser, the inner tube was chosen to have a diameter of

0.5 inches. The inner tube had to have a minimum thickness of 0.0375 inches in order to machine

the peace without warping the metal. The outer tube was selected to be 0.75 inches in diameter in

order to fit the inner tube in easily. The tubes had to be short enough to fit into the N50 flange

holes in the laser structure. As such, they were chosen to be about 1.5 inches long.

Section B: Support Structure

In order for the laser to pass through the detector, the detector needed to be suspended in

the laser chamber. This is implemented by attaching the detector with a support beam to the

electrical feed through flange that is directly above the detector. The beam is attached to a small

block that is attached to the flange by a set pin. The detector is supported by block that is

attached to the support beam.

The piece that connects to the flange has a hole through the center that allows the

connector on the flange to fit snug. This is then locked in place by a set pin. On one side, there is

a screw hole that attaches to the support beam. The dimensions of this block are 1” X 1.5” X

0.5”.

The support beam is about 10 inches long and 0.5 inches wide. The initial design had the

beam at a thickness of 0.25 inches but this made the structure too wide to fit through the N50

hole in the laser structure so it had to be reduced to a thickness of 0.0125 inches. On one end,

there is a single hole for the screw that goes to the block attached to the flange. On the other end,

a long slit is cut through the support beam. This is where the detector is attached with two

screws. The long slit allows the height of the detector to be adjusted.

The piece that supports the detector is a box that has the dimensions 1.5” X 1.5” X 1”.

The detector sits in a hole in the center of the piece and is secured by a set pin. There is a hole on

the top for the MHV connector to enter. That hole is surrounded by 4 screw holes to hole the

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MHV connector down. There are two screw holes on the side of the piece for the support beam

to attach to. Figure 5: Detector Case shows a Solidworks representation of the piece.

Figure 5: Detector Case

In Figure 6: Detector Image there is a picture of the entire detector with the support

pieces and coax cable attached. Behind the detector is the laser it is being tested in. Figure 7:

Detector in Laser shows the detector as it is aligned inside of the laser system. The small speck

of light in the center of the detector is where the output of the laser is.

Figure 6: Detector Image

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Figure 7: Detector mounted in the Laser

Section C: Vacuum Design Factors

There were several factors that had to be considered when designing the parts of the

detector because of the vacuum. First, there are certain materials that do not work well in

vacuum. Materials like brass will contaminate the vacuum. Because of this, the materials had to

be restricted to stainless steel, aluminum, and Teflon. Also, the coax cable that connects the

detector and the feed through flange had to be removed of its rubber outside.

The other work that had to be done to prepare the detector for the vacuum was ensuring

that all parts were clean. First they had to be sanded down completely because the vacuum will

take apart rough edges contaminating the vacuum. All of the corners on the pieces had to be

smooth. Second, they had to undergo a deep cleaning in methanol. This was to remove all oils

from the skin that has touched the pieces and to remove and water.

CHAPTER IV: CIRCUIT DESIGN

Section A: Circuit Design

The circuit design for the system is used to provide the voltage to the detector and to

dissipate any surges from the detector to the oscilloscope. In order to maintain signal quality, the

entire circuit has an impedance of 50Ω. This minimizes any reflections in the signal. In order to

meet this requirement, the resistive circuit is designed to have both input and output impedances

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of 50Ω. Also, the PCB board layout is sized such that the transmission parts of the board match

this requirement.

There are three input/output terminals to the circuit. One input has the DC bias voltage to

be sent to the detector. This voltage is 1000v. That voltage is first run through a very large

resistor to protect the rest of the circuit. The resistor is 100MΩ. Following the resistor, the signal

is split. On one side, the voltage is run to the detector. On the other, it is run into a capacitor.

This capacitor is there to remove the DC bias provided by the power supply. It is chosen such

that the RC time constant matches the frequency of the pulse duration. The value chosen for the

capacitor is 220pF. That will allow any short pulse signal through but will remove the dangerous

DC bias.

The portion of the circuit that follows the capacitor is in place to protect the oscilloscope

in the event of electric break down. Despite the system operating in a vacuum, there are still

occasional air pockets that form. If the laser hits one of these air pockets in the high electric field

in the detector, it will cause a huge voltage spike. Because this voltage spike will be very short in

duration it will pass through the capacitor. This voltage spike will break the oscilloscope if it is

allowed to pass right it into it. As such, a resistive T-attenuator is put in place to attenuate the

voltage spike. This is put in with a surge arrestor. The surge arrestor is sent immediately to

ground after the capacitor. The surge arrestor has a high resistance and a low capacitance so it

does not affect the signal significantly. When the arrestor reaches a certain voltage it will short

re-routing the voltage spike to ground. The T-attenuator consists of three resistors in the shape of

a T. There are two top resistors that go through to the oscilloscope and one resistor that is fed to

ground. The attenuator is design to attenuate by 20dB which is a magnitude of 10 times

attenuation. In order to meet this attenuation and to meet the 50Ω resistance the three resistors

are as follows: the top two resistors are 40.909Ω and the bottom resistor is 10.101Ω. A

representation of the circuit in spice is shown in Figure 8: Circuit.

Figure 8: Circuit

Section B: Component Selection

Due to the high voltage nature of the circuit, the components had to be selected with very

specific specifications. The components all had to be voltage rated to high voltage ratings.

Without this, the parts will be destroyed by the high voltage. The parts also had to be small in

R1 100MΩ

R2 40.1Ω

R3 40.1Ω

R4 10.1Ω

C2 220nF

D 300V

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size. The desired size is an SMT 1206 size casing. This size corresponds to the dimensions

0.13 × 0.063 in. This means that the equivalent capacitance and impedance will be small. That

maintains the signal integrity. If the parts get to large, they will introduce more noise into the

system. These two requirements are conflicting. Small components tend to not be capable of

handling high voltage.

In order to match size and voltage requirements for the T-attenuator, it was necessary to

split each resistance value into two resistors in series. By using two resistors of half the

resistance value, it was possible to double the voltage that the resistors could handle. Since the

max voltage is 1000V, the resistors needed to be able to handle 250V each. Most of resistors of

the desired size can only handle 200V so it was necessary to find ones that could handle more

voltage. This voltage requirement was pertaining to the resistors ability to handle small pulses of

high voltage, not long durations. When working in normal conditions, the resistors won’t see

much voltage, but in the event of electric breakdown, a short pulse is sent through them. Most

resistors have higher ratings for short duration voltage pulses than for long duration. The

resistors that were selected are rated for 200V for long term voltage and they are rated for 400V

for short duration pulses so they meet the requirement. Also, due to the path that a high voltage

spike will take, the bottom resistors will not see a high voltage drop so they do not need to be

rated for high voltage.

It ended up not possible to find a capacitor that matched both the voltage requirements

and the size requirements. In normal operations the capacitor has to be able to withstand at least

1000V because it needs to dissipate the entire DC bias. That means it was necessary to find a

capacitor that could handle voltages higher than 1000V so that it won’t wear out quickly. It was

possible to find a capacitor that was rated for 1500V that was a slightly bigger size of SMT 1210

which corresponds to the dimensions 0.13 × 0.098 in.

The surge arrestor didn’t need a high voltage rating because its purpose is to short when

the voltage gets too high. While that made it easier to find a surge arrestor, it was still not

possible to find one that matched the size requirement. The voltage rating that was chosen was

300V. The size was chosen to be SMT 1812 which corresponds to the dimensions 0.18 × 0.13 in.

The resistor that is connected to the voltage supply needed to be able to handle the entire

voltage of the supply. It also had to be very high in resistance. This meant the resistor had to

pretty large in size. This is not a problem though because it does not affect the signal, and it

doesn’t have to be surface mounted.

The power supply and the detector are connected to the circuit using MHV coaxial

connectors and the oscilloscope is connected with a BNC coaxial connector. The power supply

and the detector need the MHV connectors because they need high voltage rating. The

oscilloscope doesn’t need a special high voltage connector because there won’t be a high voltage

run to it.

The PCB board is designed such that its transmission line properties have an impedance

of 50Ω. The dielectric constant of the material PCB boards are made out of is about 4.5 so in

order to reach 50 Ω, the distance between the nodes of the circuit and the ground terminal has to

be about 0.125 inches. The distances between the nodes on the board are defined by the SMT

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1206 and SMT 1210 geometry. Figure 9: PCB Design shows the ExpressPCB representation of

the board. The board is held up by being soldered to the pins on the connectors. Some cardboard

is put under the board to support it up.

Figure 9: PCB Design

In order to acquire data while waiting for parts to arrive, a quick circuit was thrown

together. This circuit was not impedance matched nor did it have minimum capacitance and

inductance so the signal quality is not good, but it allowed testing that the detector head works as

desired. A picture of this circuit is shown in Figure 10: 1st Circuit.

Figure 10: 1

st Circuit

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Section C: Power Supply Circuit

Before testing the detector, a problem with the controller for the power supply to laser

came up. In order to work around the problem, a manual controller circuit had to be designed and

implemented in order to drive the laser. This circuit was based on a suggested circuit laid out in

the data sheet for the power supply. It consists of 8 notification LED’s, a voltage controller, and

a voltage reader. The LED’s are powered by the power supply and grounded when certain events

occur within the power supply. In order to get appropriate current through the LED’s, they are

put in series with 2kΩ resistors. The voltage controller is powered by the 15V output of the

power supply and is controlled down to 10V. Those ten volts is run across a potentiometer which

sends a voltage to the power supply controlling its output. The power supply outputs the input

voltage which is read by the voltage reader. Aside from crossing one of the wires, this controller

was working first thing. An image of the circuit is shown in Figure 11: Power Supply Controller.

Figure 11: Power Supply Controller

CHAPTER V: MECHANICAL DESIGN OF PHOTODIODE

DETECTOR

The purpose of this detector is to be able to get a highly accurate reading of the energy in

the laser. That reading is used to then calibrate the photoionization detector. Another goal for this

detector is to simplify and add robustness to the old photodiode design. The old design uses two

vacuum chambers meaning that two O-rings are needed. The goal with the new detector is to

only use one O-ring. The old detector uses epoxy to seal the connectors. The new detector should

also be sealed without the need for epoxy.

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In addition to making a better body design for the new detector, a different metal is used

for the detector head. The old detector used aluminum for the detector head. The problem with

aluminum is it oxidizes. This means that layers of oxide slowly grow the surface. This is a

problem because when the laser pulse strikes the head, it no longer hits aluminum. It only hits

the oxide layer which will give different results that aluminum would. The new detector uses

gold which does not oxidize so over time, the gold will stay clean and will not change results. A

drawing of how the detector works is shown in Figure 12: Detector Physics.

Figure 12: Detector Physics

The body of the new photodiode detector attaches to the vacuum system with an N50

vacuum flange. The inside of the body is open. The first section is where the support piece for

the screen. The screen is used to provide a high voltage close to the detector head. The support

piece is charged to 1500V so that when the laser pulse excites electrons from the detector head,

the electrons are pulled to it. That flow of electrons is directly proportional to the energy in the

laser pulse. The number of electrons excited per photon is determined from the chart in

Appendix E. [5] The support piece is separated from the grounded body with a few layers of thin

capacitive film. This film creates a capacitance that lets the support piece hold a significant

amount of charge without arcing. An O-ring backup ring is used to prevent the support piece

from being pushed too deep. If the piece is pushed too deep, the piece makes contact with the

grounded body. The mesh is attached to the support piece with silver epoxy. Nickel epoxy was

initially used but the nickel didn’t create a solid electrical connection. It was replaced with silver

epoxy to improve the connection.

The stainless steel mesh is also used to attenuate the signal. If the signal is too strong, the

number of electrons will greater than what can be held by the capacitance on the support piece.

By adding more attenuators, the number of electrons can be reduced unsaturating the detector.

For this detector, 5 attenuators were needed before the detector stopped saturating. That means

that the voltage on the screen can be changed but the output signal doesn’t. In order to have a

total of 5 attenuators, an additional 4 attenuators needed to be placed in front of the detector. In

order to do this without adding more O-rings to support the meshes, a mesh tower was

constructed. The base mesh is big enough that it can be supported by the O-ring and the others

are small enough to fit through an N50 flange. Figure 13: Mesh Tower shows an image of 5

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meshes in the tower. Using a He-Ne laser, it was shown that the meshes sitting that closely

produce the expected amount of attenuation. The refraction off of each mesh is sufficient to

spread the light enough before the next mesh.

Figure 13: Mesh Tower

The support piece is fed the voltage from a connector on the side of the detector body.

The wire is fed through a hole in the body from the well for the connector to the support piece. It

is then fed through a hole on the support piece so that it can come to a screw on the front of the

piece.

The next stretch in the body of the detector is designed to keep a 50Ω impedance for the

transmission of the signal. If the impedance changes, there will be reflections in the signal. The

detector head is wide at 0.7 inches so that it captures the entire laser pulse. It needs to be reduced

to a much smaller size in order to connect to the connector to keep the transition at 50Ω. The

head has a cone shape to reduce its size to meet this requirement. In order to have 50Ω

impedance, the signal from the head must be a certain distance from the ground. The setup is like

a coaxial cable so there are equations that can be used to determine the distance from the signal

terminal to the ground around it based on the dielectric between the two. During the cone

portion, there is only air so the angle that the body is cut at matches the ratio to keep the

impedance. The detector head is supported by a press fit piece of Teflon that is matched to keep

the impedance. In order reduce dramatic changes in impedance when the dielectric switches from

Teflon to air, the Teflon piece is tapered until it hits the cone. This creates a change in impedance

that is smaller than can be adjusted when machining. The angles needed to get it perfect are

within about a degree which is not really noticeable.

The detector head press fits until it hits the connector on the back side of the body. In

order to ensure contact with the connector, a gold spring loaded pin is soldered to the back of the

detector head. The spring loaded pin will push against the connector ensuring contact. In order to

improve the contact, the tip of the connector is electroplated with gold so that it is gold touching

gold.

The connectors are held into place with stainless steel supports. The initial idea was to

weld the supports to the connectors to seal the detector. An O-ring was going to be glued to the

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detector body and it would be sealed by the support piece. It turned out that the amount of space

needed to weld would be too great so this idea was not going to work. The solution to this

problem was to simply wedge the O-rings in with the connector and the support piece. The O-

ring sits in a triangular hole surrounding the main hole. The O-Ring used is a number 206 silicon

O-ring. Once this was set up, it was determined that the seal on the O-ring provided enough

strength to support the connectors without the need to weld. Figure 14: Gold Photodiode Blow

Up shows a Solidworks blow up of the detector and all of its pieces. Figure 15: Gold Photodiode

Design shows a Solidworks representation of the detector put together.

Figure 14: Gold Photodiode Blow Up

Figure 15: Gold Photodiode Design

The detector head is made out of tellurium copper. Regular copper is too difficult to

machine to use but copper is needed to place gold on. The piece became too thin to support itself

so it would break from the heat of cutting when copper was used. The first attempt to place gold

on the head was to electroplate it. That worked but the quality of the surface came out looking

poorly. In order to improve the quality of the surface, gold was evaporated onto the surface.

About 200nm of gold was evaporated. Even though it didn’t change the look of the surface, it

provided the confidence to know that the surface is pure gold. Figure 16: Gold Detector Head

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shows an image of the gold detector head installed in the body. It also shows the back side of the

detector with the connector installed.

Figure 16: Gold Detector Head

CHAPTER VI: RESULTS AND CALIBRATION

Section A: Results

Both detectors were able to be tested and shown to function correctly. They were both

also calibrated to show the energy in the laser pulse. Figure 17: Both Detectors Sensing shows

the signal from both detectors while the laser is lasing. There are a few factors causing the

difference in time between the two signals. First, the photodiode detector is about two feet

farther away than the photoionization detector. That would cause a difference of about a

nanosecond. The bigger cause of the delay is the length of the cable to the oscilloscope. The

photoionization detector is connected to a cable that is less than a meter long. The photodiode

detector is connected to a cable that is over three and a half feet long. That provides for about a

17 nanosecond difference which matches what is seen.

16

Figure 17: Both Detectors Sensing

The testing first semester showed that the photoionization detector was functioning but it

presented a few questions. The first thing that was noticed was a bias that appears in the signal.

This can be seen in the first graph in Figure 18: Photoionization Detector Bias which shows one

of the first tests done on the detector. There is a clear drop in voltage in the signal. The current

theory is that this is caused by the spontaneous emission coming from the laser. There is light

coming from the laser even when it isn’t lasing so that is what is likely causing the drop in

voltage.

Figure 18: Photoionization Detector Bias

17

Since the spontaneous emission diverges much more than the laser pulse, then the bias

should drop if the detector is moved away from the laser. When the detector was moved back

about half a foot, there was a noticeable drop in the DC bias. This can be seen in the second

graph in Figure 18. That shows that the bias is likely caused by the spontaneous emission.

The second thing that is odd in the signal is a spike in the voltage at the same distance in

time from the laser pulse. The spike doesn’t occur every time and it still occurs even if the laser

is not lasing. This spike can be seen in Figure 19: Second Spike in Photoionization Detector.

When the detector was moved back, the time between the laser pulse and the second spike grew.

This can be seen in the second graph in Figure 19. The fact that the time between the laser pulse

and the second spike grew suggests that the spike is caused by matter, not light. The spike seems

to be associated with a large negative current swing in the laser system so it might be caused by

electrons moving from this current. The distance also caused the spike to shrink in magnitude

suggesting that it too diverges more than the laser beam.

Figure 19: Second Spike in Photoionization Detector

The new photodiode detector was able to produce a much cleaner signal than the old

detector. This can be seen in Figure 20: Old vs. New Photodiode Detector. There is a lot of

oscillation after the main laser peak in the old signal which is not present in the new signal. This

is a clear sign of improvement in the new design.

18

Figure 20: Old vs. New Photodiode Detector

Section B: Calibration

The Gold Photodiode Detector can be set straight to an equation that relates energy to the

total voltage in the signal. It relies on a constant that relates photons to electrons. The constant is

found in Appendix E. The value acquired is 0.054 Electrons/Photon. The equation that relates the

voltage with the energy is as follows:

The value Atten is the amount of attenuation that the signal undergoes and is unit less.

Each attenuator allows 27% of the light through and there 5 attenuators. There is also an

electrical attenuator before the scope further reducing the signal down to 10%. That results in

Atten = 0.000143. Using the code shown in Appendix G written by Val Aslanyan, it is possible

to graph the amount of energy in the laser pulse. Figure 21: Energy Measured By Photodiode

shows this graph. The error bars shown a simply error from the Gaussian fit. Since the

oscilloscope doesn’t have a high enough sample rate, the data is a bit chopped off. In order

-0.5

0

0.5

1

1.5

2

2.5

3

-50.00 0.00 50.00 100.00 150.00 200.00

Vo

ltag

e (

V)

Tme (nanoseconds)

Old Detector

-0.5

0

0.5

1

1.5

2

2.5

-50.00 0.00 50.00 100.00 150.00 200.00

Vo

ltag

e (

V)

Time (nanoseconds)

New Detector

E = ∫v(t)dt [V*S] * 26.5[ev/p] * 1.602e-19 [J/ev] a

50[Ω] * 1.602e-19 [C/e] * Atten * 0.054 [e/p]

19

integrate the signal, the curve needed to be fit to a Gaussian. The error bars only show error

caused by that process. The values determined by the equation match expected energy levels

from the laser.

Figure 21: Energy Measured By Photodiode

Using this data, it is possible to calibrate the Photoionization Detector. The energy in the

system can be set to equal to some coefficient times the integral of the voltage signal.

E=α*∫v(t)dt . The coefficient is dependent on pressure in a linear relationship. This is because as

the pressure in the system increases, the more gas there is to photoionize. That means that the

same laser pulse will produce a higher voltage. The coefficient can then be written as another

coefficient divided by the pressure. α=β/P. Using these equations, the calibration coefficient β

can be solved for. Β = E/∫v(t)dt * P. Figure 22: Ratio Between Energy and Voltage from

Photoionization Detector shows the ratio between energy and voltage as pressure is changed.

This ratio is lowest when pressure is highest around shot 200 and it is highest when pressure is

lowest around shot 900.

20

Figure 22: Ratio Between Energy and Voltage from Photoionization Detector

By taking these values an multiplying by pressure, the value for β can be solved for.

Figure 23: β shows this value for different pressures. The values are within 3% of the average.

β=0.004759 (J*Torr)/(V*µs).

Figure 23: β

The value used for pressure is not the actual pressure in the system. It is the pressure

before the output of the laser. A linear relationship exists between the used pressure and the

actual pressure however. This is shown in Figure 24: Pressure Relationship. This means that the

coefficient is still functional. The pressure gauge used in the actual chamber that the detector is

in doesn’t work for higher pressures so it makes more sense to use the pressure gauge.

0

0.005

0.01

0.015

0.02

0.025

0.03

0 200 400 600 800 1000 1200

Ene

rgy

Ove

r V

olt

age

(J/

(V*μ

s)

Shot Number

Energy Over Voltage with Changing Pressures

0.0044

0.0046

0.0048

0.005

0.0052

0.0054

270 290 310 330 350 370

β((

J*

To

rr)/

(V*μ

s))

Pressure (mTorr)

β

21

Figure 24: Pressure Relationship

Using the calibration coefficient, the energy measured by the photoionization detector

can be plotted. Figure 25: Energy Measured by Both Detectors shows both detectors successfully

measuring the energy in the laser pulse.

Figure 25: Energy Measured by Both Detectors

0

0.00005

0.0001

0.00015

0.15 0.2 0.25 0.3 0.35 0.4

Pre

ssu

re A

fte

r O

utp

ut

(To

rr)

Pressure Before Output (Torr)

0.00E+00

5.00E-06

1.00E-05

1.50E-05

2.00E-05

2.50E-05

3.00E-05

3.50E-05

0 200 400 600 800 1000

Ene

rgy

(J)

Shot Number

Laser Energy Measured By Both Detectors

PhotodiodeEnergy

Photoionization Energy

22

CHAPTER VII: OTHER CONSIDERATIONS

There are a few other considerations that came along with this project. The management

system for this project was very much like at an actual business. Professor Rocca and Professor

Menoni functioned as the managers. Mark functioned as the project manager who over looked

his specific project. This project was just a small portion of the greater project. Other people

working in the lab had their tasks to get the laser working. Without their work, the detectors built

in this project would not have been able to be tested.

There are not many ethical concerns related to this project. The biggest concern is the

safety of the detectors. Both detectors operate at 1.5 kV which would be very harmful to humans.

In order to keep it safe, the possible contact points were treated very carefully. Potentials for

shorts were removed from the detectors. Another ethical concern is the documentation of the

designs. As a senior design project, it would be very easy to complete the design and leave

completely. An appendix has been added to the end of this report to alleviate this problem.

These detectors are intended to be used on many laser systems. As such, they are

designed with their manufacturability in mind. Both detectors are pretty easy to build and

specifications have been included so anyone who needs to build more detectors will be able to do

so.

There is not much marketability for these detectors. They have fairly specific uses in their

field. However, if anyone buys one of the laser systems, they would like to have these detectors

to be able to measure the laser energy. The lasers cannot really be sold without these detectors.

CHAPTER VIII: CONCLUSIONS AND FUTURE WORK

Two detectors were successfully built in this project. The Gas Photoionization Detector is

capable of seeing the laser pulse without blocking the path of the laser. It can also see a few other

phenomena occurring inside the laser system giving better knowledge of what is happening in

the laser. The Gold Photodiode Detector measures the energy in the laser very accurately. These

detectors will be of great use to the ERC for further development with the lasers.

There is more work that can be done with these detectors. First, the accuracy can be

improved. This can be done by increasing the sample rate so that the signal can be integrated

directly without a fit. A circuit can be built to do this integration in real time. A system can then

be built to let the photoionization detector drive the laser. This will allow full integration of the

detector into the laser system. There can also be multiples of these detectors built for use on each

laser system as these detectors can be very useful.

Overall, this project was a success. It came with ample learning experiences and it

produced two very useful detectors.

23

REFERENCES

[1] S. Heinbuch, M. Grisham, D. Martz, and J.J. Rocca; “Demonstration of a desk-top size high

repetition rate soft x-ray laser,” Optics Express, vol. 13, No. 11, 2005

[2] L. Urbanski, A. Isoyan, A. Stein, J. J. Rocca, C. S. Menoni, and M. C. Marconi; “Defect-

tolerant extreme ultraviolet nanoscale printing,” Optics Letters, vol. 37, pp 3633 – 3635, 2012

[3] Ilya Kuznetsov1, Jorge Filevich, Feng Dong, Weilun Chao, Erik H. Anderson, Elliot R.

Bernstein, Dean C. Crick, Jorge J. Rocca, Carmen S. Menoni; “ Nanoscale 3D composition

imaging by soft x-ray laser ablation mass spectrometry,”

[4] Ilya Kuznetsov, Jorge Filevich, M. Woolston, Elliot R. Bernstein, Dean C. Crick, D.

Carlton, W. Chao, E.H. Anderson, Jorge J. Rocca, and Carmen S. Menoni; “Composition Depth

Profiling by Soft X-Ray Laser-Ablation Mass Spectrometry,”

[5] R. H. Day, P. Lee, E. B. Saloman, and D. J. Nagel; “Photoelectric quantum efficiencies and

filter window absorption coefficients from 20 eV to 10 KeV,” J. Appl. Phys., Vol. 52, No. 11,

November 1981

BIBLIOGRAPHY

David Attwood, Soft X-Rays and Extreme Ultraviolet Radiation, New York: Cambridge

University Press, 1999.

I

APPENDIX A: ABBREVIATIONS

BNC – Bayonet Neill-Concelman

CSU – Colorado State University

EUV – Extreme Ultraviolet

EUV-ERC – Extreme Ultraviolet Engineering Research Center

MHV – Miniature High Voltage

PCB – Printed Circuit Board

SXR – Soft X-Ray

II

APPENDIX B: BUDGET

Photoionization Detector

Flange: $300

Machining Instruction: $72

Support beam: $13

Approximate cost of additional parts taken from the lab: $150

Circuit Components: $84

PCB: $63

Box: $21

Photoionization Detector Total: $703

Photodiode Detector

Connectors: $77

Spacers: $25

O-rings: $29

Steel: $31

Machining Instruction: $72

Approximate cost of additional parts: $200

Photodiode Detector Total: $434

The total cost of the project came to $1137. Funding is supplied by the EUV-ERC and Senior

Design. A total of $200 will come from Senior Design.

III

APPENDIX C: TIMELINES

Final Timeline – Version 7:

9/11/13: Initial calculations complete -Ricky

9/18/13: Initial website design complete -Ricky

9/23/13: Revised timeline complete -Ricky

9/25/13: Initial photoionization detector design complete, Begin ordering parts -Ricky, Mark

10/7/13: Electronics design complete -Ricky, Mark

10/9/13: Solid Works Tutorial complete -Ricky

10/24/13. Preliminary computations for the design of testing detector initiated -Ricky

10/25/13: Testing Plan Complete -Ricky, Mark, Ilya

11/4/13: Full detector built, ready for testing -Ricky, Mark

11/22/13: Circuit Design Complete -Ricky, Mark

11/29/13: Circuit parts ordered -Ricky, Mark

12/10/13: Detector Tested -Ricky, Mark

12/13/13: Report Complete -Ricky

1/20/14: Begin Photodiode Detector Design -Ricky, Mark

2/13/14: Initial design of Photodiode detector complete -Ricky

4/7/14: Photodiode detector built, ready to test -Ricky

4/8/14: Photodiode detector working. -Ricky, Mark

4/23/14: Calibration of Photoionization Detector Finished -Ricky, Mark

4/23/14: Photoionization Detector integrated into laser system -Ricky, Ilya

IV

Version 6:










11/22/13: Circuit Design Complete -Ricky, Mark

11/29/13: Circuit parts ordered -Ricky, Mark

12/10/13: Detector Tested -Ricky, Mark


1/20/14: Begin Photocathode Detector Design -Ricky, Mark

2/10/14: Initial design of Photocathode detector complete -Ricky

3/3/14: Photocathode detector built, ready to test -Ricky

3/31/14: Photocathode detector working. -Ricky, Mark

4/21/14: Calibration of Photoionization Detector Finished -Ricky, Mark

5/2/14: Photoionization Detector integrated into laser system -Ricky, Ilya

V

Version 5:










11/22/13: Test Detector Complete -Ricky, Mark

12/13/13: Testing Complete -Ricky, Mark


1/20/14: Begin Second Detector Design -Ricky

2/10/14: Initial design of second detector complete -Ricky, May get new group members based

on new detector requiremets.

3/3/14: Second detector built, ready to test -Ricky

3/31/14: Initial testing and fixing complete, begin secondary test -Ricky

4/28/14: Secondary testing and fixing complete, begin final test –Ricky

5/2/14: Final testing complete, both detectors done and implemented -Ricky

VI

Version 4:










11/11/13: Test Detector Complete -Ricky, Mark

11/22/13: Testing Complete -Ricky, Mark

12/2/13: Begin design of second detector -Ricky






4/28/14: Secondary testing and fixing complete, begin final test -Ricky

5/2/14: Final testing complete, both detectors done and implemented –Ricky

VII

Version 3:







10/9/13. Preliminary computations for the design of second detector initiated -Ricky



11/4/13: Updates to design based on testing complete -Ricky

11/18/13: Updates to detector implemented, ready for testing again -Ricky, Mark, Ilya

11/22/13: Secondary Testing complete -Ricky, Mark, Ilya

12/2/13: Updates based on secondary testing complete -Ricky, Mark, Ilya

12/9/13: Updates to detector implemented, ready for final testing -Ricky, Mark, Ilya

12/13/13: Final testing complete, Detector finished, Report Complete -Ricky





4/28/14: Secondary testing and fixing complete, begin final test -Ricky

5/2/14: Final testing complete, both detectors done and implemented –Ricky

VIII

Version 2:

9/11/13: Initial calculations complete

9/18/13: Initial website design complete

9/23/13: Revised timeline complete

9/25/13: Initial photoionization detector design complete, Begin ordering parts

10/7/13: Electronics design complete

10/9/13: Solid Works Tutorial complete

10/9/13. Preliminary computations for the design of second detector initiated

10/21/13: Full detector built, ready for testing

10/25/13: Testing Plan Complete

11/4/13: Updates to design based on testing complete

11/18/13: Updates to detector implemented, ready for testing again

11/22/13: Secondary Testing complete

12/2/13: Updates based on secondary testing complete

12/9/13: Updates to detector implemented, ready for final testing

12/13/13: Final testing complete, Detector finished, Report Complete

2/10/14: Initial design of second detector complete

3/3/14: Second detector built, ready to test

3/31/14: Initial testing and fixing complete, begin secondary test

4/28/14: Secondary testing and fixing complete, begin final test

5/2/14: Final testing complete, both detectors done and implemented

IX

Version 1:

9/11/13: Initial calculations complete.

9/18/13: Initial website design complete

9/23/13: Revised timeline complete

9/25/13: Initial photoionization detector design complete, Begin ordering parts

10/7/13: Electronics design complete, Mechanical design complete

10/9/13: Solid Works Tutorial complete

10/9/13. Preliminary computations for the design of second detector initiated.

10/21/13: Full detector built, ready for testing

10/25/13: Testing Plan Complete

11/4/13: Updates to design based on testing complete

11/18/13: Updates to detector implemented, ready for testing again

11/22/13: Secondary Testing complete

12/2/13: Updates based on secondary testing complete

12/9/13: Updates to detector implemented, ready for final testing

12/13/13: Final testing complete, Detector finished, Report Complete

2/10/14: Initial design of second detector complete

3/3/14: Second detector built, ready to test

3/31/14: Initial testing and fixing complete, begin secondary test

4/28/14: Secondary testing and fixing complete, begin final test

5/2/14: Final testing complete, both detectors done and implemented

X

Appendix D – Dimensions

Section A: Gas Photoionization Detector

XII

Section B: Gold Photodiode Detector

XIV

Appendix E – Gold Quantum Efficiency

The following graph was used to determine the quantum efficiency for gold at 26.5 ev.

The value determined was 0.054 Electrons/Photon. [5]

XV

Appendix F – Parts

MHV Double Ended Feed Through Flange:

http://www.lesker.com/newweb/feedthroughs/instrument_feedthroughs_mhv_doubleend.

cfm?pgid=kf

Capacitor: http://www.digikey.com/product-detail/en/C1210C221KFRACTU/399-3440-

2-ND/721285

Surge Arrestor: http://www.digikey.com/product-detail/en/SG300/F4129TR-

ND/2754503

Large Resistor: http://www.digikey.com/product-

detail/en/ROX100100MFKEL/ROX100-100MF-ND/2713103

5Ω Resistor: http://www.digikey.com/product-detail/en/CRCW12064R99FKEAHP/541-

4.99UTR-ND/2227500

20.5Ω Resistor: http://www.digikey.com/product-detail/en/ERJ-8ENF20R5V/P20.5FTR-

ND/88078

Circuit Box: http://www.digikey.com/product-detail/en/3606/3606PO-ND/745063

Weldable BNC:

http://www.lesker.com/newweb/feedthroughs/instrument_feedthroughs_bnc_singleend.cf

m?pgid=weld

Weldable MHV:

http://www.lesker.com/newweb/feedthroughs/instrument_feedthroughs_mhv_singleend.c

fm?pgid=weld

O-Ring Backup Ring #29: http://www.mcmaster.com/#catalog/120/3511/=rpizj9

Gold Spring Loaded Pin: http://www.digikey.com/product-detail/en/0910-1-57-20-75-

14-11-0/ED90454TR-ND/2242383

O-Ring #206: http://www.mcmaster.com/#o-rings/=rqyvui

XVI

Appendix G – Code

The following is code written by Val Aslanyan that fits the signal to a Gaussian and

integrates the signal to determine the amount of energy in the laser pulse. It is written in Python.

"""

Things that change from run to run:

File indices (lines 33 and 34)

Integral to Energy conversion factor (line 36)

Initial estimate for Gaussian fitting (line 91) - uncomment lines 117 to 124 to see how good the

fit is

"""

#!/usr/bin/env python

# -*- coding: utf-8 -*-

from numpy import *

from scipy.optimize import curve_fit

import matplotlib.pyplot as Plot

import csv

#Gaussian function used for fitting

def gaussian_equation(x,A,const,mu,k):

return A*exp(-((x-mu)**2)/const)+k

#Finds index of maximum value of an array

def maxfinder(x):

if (len(x)==1):

maximum=x

idx=0

else:

maximum=x[0]

idx=0

for i in range(1,len(x)-1):

if (x[i]>maximum):

maximum=x[i]

idx=i

return idx

points_num=7 #Number of datapoints around peak which are considered - must be ODD!

files_num=990 #Number of files, counting down from the last good one

end_good_file=999 #Index of the last good data file

integral_to_energy_conversion=26.5/(5*0.054*(0.27)**5*1E9) #Change if in units of ns or V

etc

### Initializations and internal routines ###

XVII

interp_num=100

time_actual=zeros((points_num,files_num))

time_interp=zeros((interp_num))

intensity_actual=zeros((points_num,files_num))

intensity_interp=zeros((interp_num))

gaussian_params=zeros((4,files_num))

gaussian_errors=zeros((4,files_num))

integral=zeros((files_num))

errors=zeros((2,files_num))

time_actual2=zeros((points_num,files_num))

time_interp2=zeros((interp_num))

intensity_actual2=zeros((points_num,files_num))

intensity_interp2=zeros((interp_num))

gaussian_params2=zeros((4,files_num))

gaussian_errors2=zeros((4,files_num))

integral2=zeros((files_num))

errors2=zeros((2,files_num))

ratio=zeros((files_num))

### ------------------------------------- ###

##Loop over files

for file_idx in range(0,files_num):

if end_good_file-file_idx !=296 and end_good_file-file_idx !=153: # Include indices of

bad files here

if end_good_file-file_idx>99:

filename='20140422-0001_'+str(end_good_file-file_idx)+'.csv'

elif end_good_file-file_idx>9:

filename='20140422-0001_0'+str(end_good_file-file_idx)+'.csv'

else:

filename='20140422-0001_00'+str(end_good_file-file_idx)+'.csv'

print filename #at each run; sanity check, helps identify bad files

raw_data = genfromtxt(filename, delimiter=',') #Read in data

time=raw_data[5:,0] # Change 2nd index here, depending on the column

time/voltage values are in

intensity=raw_data[5:,1]

peak_idx=maxfinder(intensity)

intensity2=-raw_data[peak_idx-50:peak_idx+50,2]

time2=raw_data[peak_idx-50:peak_idx+50,0]

peak_idx2=maxfinder(intensity2)

plateau=-raw_data[peak_idx-65+peak_idx2,2]

XVIII

# For photodiode, fit a Gaussian to voltage data

if intensity[peak_idx-1]>intensity[peak_idx+1]:

time_actual[:,file_idx]=time[(peak_idx-(points_num-1)/2)-

1:(peak_idx+(points_num+1)/2)-1]

intensity_actual[:,file_idx]=intensity[(peak_idx-(points_num-1)/2)-

1:(peak_idx+(points_num+1)/2)-1]

else:

time_actual[:,file_idx]=time[(peak_idx-(points_num-

1)/2):(peak_idx+(points_num+1)/2)]

intensity_actual[:,file_idx]=intensity[(peak_idx-(points_num-

1)/2):(peak_idx+(points_num+1)/2)]

fit_params,

fit_errors=curve_fit(gaussian_equation,time_actual[:,file_idx],intensity_actual[:,file_idx],p0=(16

0.0,3E-7,time[peak_idx],0.0),maxfev=200000) #Important - provide a good starting guess as the

the argument for p0 - arguments are Peak Value, Characteristic Width, [auto], offset

if intensity2[peak_idx2-1]>intensity2[peak_idx2+1]:

time_actual2[:,file_idx]=time2[(peak_idx2-(points_num-1)/2)-

1:(peak_idx2+(points_num+1)/2)-1]

intensity_actual2[:,file_idx]=intensity2[(peak_idx2-(points_num-1)/2)-

1:(peak_idx2+(points_num+1)/2)-1]

else:

time_actual2[:,file_idx]=time2[(peak_idx2-(points_num-

1)/2):(peak_idx2+(points_num+1)/2)]

intensity_actual2[:,file_idx]=intensity2[(peak_idx2-(points_num-

1)/2):(peak_idx2+(points_num+1)/2)]

gaussian_params[:,file_idx]=fit_params

for error_idx in range(0,4):

gaussian_errors[error_idx,file_idx]=sqrt(fit_errors[error_idx,error_idx])

integral[file_idx]=gaussian_params[0,file_idx]*sqrt(3.1416*gaussian_params[1,file_idx]

)

errors[1,file_idx]=(gaussian_params[0,file_idx]+gaussian_errors[0,file_idx])*sqrt(3.1416

*(gaussian_params[1,file_idx]+gaussian_errors[1,file_idx]))-integral[file_idx]

errors[0,file_idx]=(gaussian_params[0,file_idx]-

gaussian_errors[0,file_idx])*sqrt(3.1416*(gaussian_params[1,file_idx]-

gaussian_errors[1,file_idx]))-integral[file_idx]

# For photoionization, take a numerical integral under the peak and subtract a

"plateau" offset

integral2[file_idx]=trapz(intensity_actual2[:,file_idx]-

plateau,time_actual2[:,file_idx])

XIX

ratio[file_idx]=1.0/(integral2[file_idx]/(integral[file_idx]*integral_to_energy_conversion

)))

#Uncomment to debug, this will show a graph around the peak for each value

considered and how good the fit is

#It will also print out the fit values, which can be used to improve p0

"""

print fit_params

Plot.figure(file_idx)

Plot.plot(time_actual[:,file_idx],intensity_actual[:,file_idx])

time_interp=linspace(time_actual[0,file_idx],time_actual[len(time_actual[:,file_idx])-

1,file_idx],interp_num)

intensity_interp=gaussian_equation(time_interp,fit_params[0],fit_params[1],fit_params[2

],fit_params[3])

Plot.plot(time_interp[:],intensity_interp[:])

"""

integral*=integral_to_energy_conversion

errors*=integral_to_energy_conversion

#~~~~~ Various plots ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~#

Plot.figure(9001)

Plot.title('Photodiode')

#Plot.ticklabel_format(style='sci', axis='y', scilimits=(0,0))

Plot.errorbar(range(1,len(integral)+1), integral[::-1]*1E6, yerr=abs(errors)*1E6,

fmt='o',color='red')

Plot.plot(range(1,len(integral)+1), integral[::-1]*1E6,linewidth=3,color='blue')

Plot.xlabel("Shot number",fontsize=20)

Plot.ylabel("Energy $\mu J$", fontsize=20)

Plot.axis([0,files_num+1,0,45])

Plot.figure(9002)

Plot.title('Photoionization')


#Plot.errorbar(range(1,len(integral)+1), integral2[::-1]*1E6, yerr=abs(errors2)*1E6,

fmt='o',color='red')

Plot.plot(range(1,len(integral2)+1), integral2[::-1]*1E6,linewidth=3,color='blue')

#Plot.xlabel("Shot number",fontsize=20)

#Plot.ylabel("Energy $\mu J$", fontsize=20)

#Plot.axis([0,files_num+1,0,30])

XX

Plot.figure(9003)

Plot.title('Ratio')


Plot.plot(range(1,len(ratio)+1), ratio[::-1],linewidth=3,color='blue')

#Plot.xlabel("Shot number",fontsize=20)

#Plot.ylabel("Energy $\mu J$", fontsize=20)

Plot.axis([0,files_num+1,0,0.03])

Plot.show()

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~#

#Output to file, only after closing all the graphs

main_output_file=open('EnergyData.txt', 'w')

for output_idx in range(0,len(integral)):

print end_good_file-output_idx-1

print >> main_output_file, output_idx+1, integral[files_num-output_idx-1],

integral2[files_num-output_idx-1], ratio[files_num-output_idx-1]

main_output_file.close()

XXI

Acknowledgements

This work is sponsored by the Electrical and Computer Engineering Department at

Colorado State University. It made use of facilities of the NSF Engineering Research Center and

XUV Lasers Inc.

high energy detectors - home - walter scott, jr. college of...

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