chapter 7_part 1_one slide per hand out

8/13/2019 Chapter 7_Part 1_one Slide Per Hand Out

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Topics

A. GENERAL DESIGNSB. SOURCESC. WAVELENGTH SELECTORSD. SAMPLE CONTAINERSE. RADIATION TRANSDUCERSF. SIGNAL PROCESSORS AND READOUTG. FIBER OPTICSH. TYPES OF OPTICAL INSTRUMENTI. PRINCIPLES OF FOURIER TRANSFORM

OPTICAL MEASUREMENTS


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B. Sources

General Requirements

Adequate power Stability Utility voltage: 115 V ac

115 V ac desired/ appropriate dc voltage Double polarity single polarity smooth dc

signal constant dc signal

These conversions are performed within thePower Supply.


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Power Supply

Components of a Power Supply and their Effectson the 115-V line voltage


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Power Supply

Transformer

Function: decreases or increasesthe ac voltage Components: induction/ inductor

coils Primary inductor coil Secondary inductor coil

Principle of operation A varying magnetic field induces a

voltage in any conductor in itsfield.

A changing current in the primarywinding produces a changingmagnetic field flux in theseconday coil, which induces achanging voltage across thesecondary coil.

V out = 115 V x N 2/N1


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Power Supply

Rectifier Function: convert double

polarity current to singlepolarity current

Components:semiconductor diodes

Operational principle:block current in onedirection while allowing itto flow in the oppositedirection


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Power Supply Filtering

RC circuit C: capacitor R:resistor

Capacitor: two conductors separated by an thin layer of dielectricsubstance/ insulator with no mobile current carrying charged species

Capacitor charging by a dc sourceQ = C x V Q: quantity of charge C: capacitance (farads/F) A one-farad capacitor stores one coulomb of charge per applied volt.

Charge and discharge rate RC t

init e I i /

=


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Power Supply

Voltage regulators Function: maintain output voltage at constant

desired level Component: Zener diode


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B-3 Laser Sources

Light Amplification of S timulated Emission of

Radiation Useful characteristics

High Intensity Narrow bandwidth Coherent

Applications

High-resolution spectroscopy Kinetic studies of short lived events (10 -9 to 10 -12 sec) Low concentrations Raman FT IR


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Components of lasers Lasing medium

Gas (He-Ne, Argon) Solid (ruby) Solution (dye)

Pumping system (radiation, electrical discharge) Mirrors (amplifying cavity)


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Mechanism of Laser Action Pumping-Excitation Population of a Metastable

Excited State Spontaneous emission

Normal radiativerelaxation

Stimulated emission excited species struck

by photons that havesame energies emitphotons that travel in

phse with thestimulating photon

Coherence


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Mechanism of Laser Action Population inversion

required! Normal distribution:

number of particles inthe lower energystate higher than thatin the higher energystate

Population inversion:number of particles in

the higher energystate higher than thatin the lower energystate


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How Population Inversion Methods

Three levels system More than 50% of lasingspecies must populate levelE y

Four level system Because the transition from E xto E 0 is fast populationinversion is more readilyachieved between E y and E x


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Laser cavity

Optical Cavity Lasing is an optical feedback Wave is amplified as it moves back and forth within

the cavity All lasers cavities are types of interferometer

100% refelecting < 5-90%reflecting


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Examples of Lasers Solid State Lasers

Ruby (Al 2O 3 + 0.05% Cr(III)) Nd-YAG

Gas Lasers He-Ne (neutral atom) Argon (ion laser) Ar +

CO 2 (molecular) N 2

Dye Lasers Fluorescent dyes Tunable (20 to 50 nm)

Semiconductor Diode Lasers Light Emitting Diodes (LED)

chapter 7_part 1_one slide per hand out

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