michael tanksalvala dmitriy polyakov adam ornstein troy owens john trytko

OPEN-ATMOSPHERE PHASE-SHIFT CAVITY RINGDOWN INSTRUMENT

NOAA’S ARK

Michael TanksalvalaDmitriy Polyakov

Adam Ornstein Troy Owens

John Trytko

OVERVIEW The system measures the phase shift of light

to determine the concentration of particles in the air (higher concentration yields greater phase shift).

This is used in conjunction with other instruments to compute specific concentrations of various aerosols.

The project is being developed in cooperation with the National Oceanic and Atmospheric Administration (NOAA).

Dmitriy John Michael Adam Troy

OBJECTIVES Low Level

Detect optical ringdown on breadboardAutomatic cavity length adjustmentSave data to memory

Mid-LevelDetect optical phase shiftAutomatic cavity alignmentTime stamped data saved to SD card

High LevelBuild self-contained unitRecreate faster-than-light neutrinosAutomatic beam profile correction


MILESTONES Milestone 1

Show ringdown signal on oscilloscopeDemonstrate microcontroller-based beam-steering

and cavity length adjustmentSave sample string to SD card

Milestone 2Demonstrate phase shift detectorAutomated photo-diode signal maximizationCollect and save formatted data to SD card


CAPSTONE EXPOSITION Demonstration 1

Show output of phase shift detector on oscilloscopePlace dry ice near cavity and show phase shift (voltage)

increaseRemove SD card and plot contained data in MATLAB

Demonstration 2Connect camera to monitor and photodiode to oscilloscopeManually misalign mirrors and watch automatic readjustment

Demonstration 3 (if possible) Insert SD card, turn on system, initiate data acquisitionPlace self-contained unit near dry iceTurn off system, take out SD card, plot data in MATLAB


LASER SAFETY

Class 3b (continuous wave, 50 mW)Visible wavelengths (633 or 680 nm)High power/area (~200 mW/cm2)

PrecautionsNever look into laserDo not open testing area designated by curtainLaser safety signs will be posted


FUNCTIONAL DECOMPOSITION

LEVEL 1 DESIGN

Measure and record phase shift over several hours. Send the photodiode output to the phase shift

detector unit. Output the camera data to alignment system. Output phase shift data to the data storage system. Alignment system directly controls mirrors.

Data StorageAnd User I/O

AutomaticAlignment

Atmosphere

User Input

SD Card

SD Card (Data) Clock Display

Optical Generation and Signal Detection


LEVEL 2 DESIGN

ALGNRGB

OS

SD


LEVEL 2 DESIGN (OPTICS)


OPTICAL SYSTEM

Objective: Determine the concentration of aerosol particles within the cavity.

Optical system uses amplitude-modulated laser signal within a cavity to determine the phase shift the cavity introduces.

Ringdown cavity simulates effective length of several kilometers through the use of highly reflective mirrors.

John Dmitriy Michael Adam Troy

OPTICAL MODULES Laser Controller

Input: On if instrument is on. Output: Intensity modulated sine wave (~50 kHz) via laser to

cavity and initial phase shift signal to phase shift detector. Testing: Modulating the laser at a low frequency (~1 Hz) will

be visible on a matte surface. Higher frequencies can be verified with a photodiode and an oscilloscope.

Laser Cavity Resonates laser with two concave mirrors. Outputs ringdown signal to photodiode. Testing: Shine output into photodiode. Connect photodiode

to oscilloscope. Measure photodiode output on scope, and look for a quick rise followed by an exponential decay.


OPTICAL MODULES Photodiode

Input: Laser beam from ringdown cavity, 12 volt bias voltage. Sensitive to both wavelengths we are considering (633, 680

nm) Output: current passed to phase shift detector.

Mirror mounts Front: 99.97% reflection, 0.01% transmission. Rear: .2% T Concave mirrors, 1 m focal length, 6.35 mm thick. Input: One 0-30 V signal per quadrant. To turn mirror to the

left, apply a positive voltage to the right two quadrants. Testing: Aim laser at mirror mount, with the reflection hitting a

far wall. Apply 0 V across one side of the piezo and 30 V across the other. Watch for beam movement.


OPTICAL MODULES (CONT)

Phase shift detectorIntegrates initial phase shift and final phase

shift.Input: Photodiode voltage, initial signal from

laser controller.Output: Voltage (representing phase shift) to

microcontroller.


LEVEL 2 DESIGN (ALIGNMENT)

ALGNRGB


ACTIVE FEEDBACK/ALIGNMENT

Objective: Maintain maximum signal power Keeps beam pointed at photodiode If signal is lost, methodically scans over area

to try to find it Concave mirrors provide small amount of

passive beam alignment Uses PID Controller to maintain beam

location


ALIGNMENT MODULES

CMOS CameraOutputs NTSC Signal on single signal lineOutput must be separated into red, green, and blue

components Signal Extractor

Converts single-channel NTSC to three signals with which the microcontroller and monitor can interface

Implementation: a quadrature detector Mirror Mount Voltage Amplifiers

Input: Microcontroller voltage (0-5 V)Output: Mirror Mount voltage (0-30 V)


RGB

ALIGNMENT MODULES (CONT)

Microcontroller28 x Piccolo C200040-80 MHzReads pixel values from signal extractorThresholded average pinpoints beam locationPID Controller aims beam at desired locationSimpler algorithms maximize signal strength by

optimizing desired beam location.Manual interface to alter desired position and call

basic functionsJohn Dmitriy Michael Adam Troy

ALGN

ALIGNMENT SOFTWAREInitialization


Photodiode (PD) Voltage >

(prev_volts * .9)?

Optimize Beam Position

Beam Missing PD?

Optimize Cavity Length

Beam Sweep

Optimize Beam Position

prev_volts = PD Voltage

Correct Beam Mode

NO

YES

YES

NO

ALIGNMENT SOFTWARE MODULES

Correct Beam Mode Detect the positions of the most intense locations on the beam profile Use lookup table to correlate this to beam mode type and find solution Testing: Connect the camera output to a monitor. Manually induce different

beam modes by altering cavity length and alignment, run function, and watch for the beam profile to turn Gaussian.

Optimize Beam Position Loop: Bump mirror 1 in last successful direction (end on failed_dir==4)

○ If photodiode voltage decreases, reverse the movement and increment last successful direction and failed_dir. else, failed_dir = 0;

Testing: Connect photodiode to multimeter. Point beam at photodiode and run program. Watch for photodiode output increase.

Beam Sweep Move mirror 2 (coarse mirror) in grid pattern, searching for a photodiode

signal. Stop when signal is found. Testing: Connect photodiode output to multimeter. Turn beam away from

photodiode, run the function, and watch for the photodiode output to increase.John Dmitriy Michael Adam Troy

ALIGNMENT SOFTWARE MODULES

Optimize Cavity Length Increase voltage across all quadrants uniformly, searching for

a power maximum. If the function finds no oscillatory behavior, the laser is misaligned. Call Beam Sweep.

Testing: Manually adjust cavity alignment and length to get good signal. Mess up alignment. Call function and watch photodiode output increase.

Beam Missing PD?Goal: see if beam is pointed at photodiode.Essentially the same as Optimize Cavity Length, but alters the

cavity length minimally, to test for voltage fluctuations. If the voltage decreases in at least one direction, output false.


LEVEL 2 DESIGN (OS)

ALGN

OS

SD


OPERATING SYSTEM

Objective: Store data to file in SD Card Reads Timestamp from atomic clock chip Measures phase shift as analog voltage Measures valid bit as analog voltage Stores these to comma-delimited text file

<timestamp>,<phase>,<valid>


DATA FLOW

ValidPhase Time

File Formatted SD Card

BufferSD Card LCD

AlignmentADC External Clock

collectData=START =!

STOP

START /STOP


OPERATING SYSTEMInitialization

collectData == START ?

SD Buffer Empty?

Write to SD Card

NO YES

YES

NO


New Data?

Write to SD Buffer

NO

SD Buffer Full?

Close File If Open

NO

YES

YES

Push Time to LCD

Scheduler

SD CARD

Contains files with gathered data Standardized portable memory FAT32 file system


Image obtained from: http://alumni.cs.ucr.edu/~amitra/sdcard/Additional/sdcard_appnote_foust.pdf/

EXTERNAL CLOCK

AntennaReceives Atomic Clock Signal

ReceiverDecodes Antenna Signal

Microcontroller DecoderOutputs time in RS232


Image obtained from: http://alumni.cs.ucr.edu/~amitra/sdcard/Additional/sdcard_appnote_foust.pdf/

USER I/O

InputsPower SwitchStart / Stop Button

OutputsLCD display – Time

○ Blinking – Not collecting dataGreen LED – WorkingRed LED – Error


POWER SYSTEM

Laser Controller – 3 V, 50 mA Camera - DC 12 V, 50 mA Photodiode - 12 V, 50 mA Phase Shift Detector - 12 V, 50 mA Microcontroller (2x) - Core Supply: 3.3 Volts,

I/O Supply: 1.8 Volts Mirror Mount Voltage Amplifier – 30 V


POTENTIAL ISSUES / CONTINGENCY PLANS Phase shift detector doesn’t work

Plan: Software alternative Not able to integrate OS with optics

Plan: demonstrate the systems separately at Expo Beam size too large for camera to measure position

Plan: Use quadrant detector Beam power too low

For photodiode: Right Bumper to pick up Spartan Laser For camera: Use quadrant detector

Complicated OS doesn’t work Plan: Use previously-developed simple OS

SD card Interface does not work Plan: save to onboard flash memory


DIVISION OF LABORTask Primary Secondary

OS Design and Data Storage Adam Michael

Mechanical Structure/Alignment Dmitriy John

Control Systems Michael Adam

Power System Troy Dmitriy

Board Layout/Construction Troy, Michael John

Optical Construction and Detection

John, Troy, Dmitriy

Design Documentation All

Chief Financial Officer (CFO) Michael


SCHEDULE


PARTS LIST


Equipment Estimated Price Acquired

Laser / Laser Controller Borrowed from NOAA Testing Version

Mirror Mounts/Mirrors Borrowed from NOAA No

Optical Breadboard Borrowed from NOAA Yes

5 x Photodiode 5 x $30 Testing Version

2 x Beam-Splitter 2 x $60 No

4 x MSP430 4 x $25 Testing Version

2 x CMOS Camera 2 x $35 Yes

3 x PCB 3 x $60 No

5 x Piezoelectric Buzzer 5 x $5 Yes

Conductive Glue $20 No

Power Components $50 No

2 x SD Sockets 2 x $5 No

SD Card $10 No

Oscillator $10 No

Final Project Poster $50 No

Dry Ice $50 No

Structure Materials $100 No

Other (replacement parts, shipping, etc.) $200 No

TOTAL $1145

FUNDING AND GRANTS

NOAAProviding optical parts (mirrors, mounts,

laser controller, optical breadboard, laser)Will keep the prototype upon completion

Additional FundingReceived $1,000 from UROPAny necessary additional money will be

gathered from generous donations from team members.


QUESTIONS?


michael tanksalvala dmitriy polyakov adam ornstein troy owens john trytko

Documents

output phase shift data

output of phase shift

initial phase shift

phase shift of light

record phase shift

final phase shift

greater phase shift

phase shift detector