Download - 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)