COMPONENTS OF OPTICAL
INSTRUMENTS
Chapter 7
UV, Visible and IR Instruments
1
Topics
A.
B.
C.
D.
E.
F.
G.
H.
I.
GENERAL DESIGNS
SOURCES
WAVELENGTH SELECTORS
SAMPLE CONTAINERS
RADIATION TRANSDUCERS
SIGNAL PROCESSORS AND READOUT
FIBER OPTICS
TYPES OF OPTICAL INSTRUMENT
PRINCIPLES OF FOURIER TRANSFORM
OPTICAL MEASUREMENTS
2
A. General Designs
5 components
Absorption
Fluorescence
Phosphorescence
Scattering
Emission
Chemiluminescence
3
B. Sources
General Requirements
• Adequate power
• Stability
• Utility voltage: 115 V ac
– 115 V ac Æ desired/ appropriate dc voltage
– Double polarityÆsingle polarity Æsmooth dc
signalÆconstant dc signal
• These conversions are performed within the
Power Supply.
4
Power Supply
• Components of a Power Supply and their Effects
on the 115-V line voltage
5
Power Supply
• Transformer
– Function: decreases or increases
the 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 its
field.
• A changing current in the primary
winding produces a changing
magnetic field flux in the
seconday coil, which induces a
changing voltage across the
secondary coil.
– Vout = 115 V x N2/N1
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Power Supply
• Rectifier
– Function: convert double
polarity current to single
polarity current
– Components:
semiconductor diodes
– Operational principle:
block current in one
direction while allowing it
to flow in the opposite
direction
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Power Supply
• Filtering
– RC circuit
– C: capacitor
– R:resistor
– Capacitor: two conductors separated by an thin layer of dielectric
substance/ insulator with no mobile current carrying charged species
– Capacitor charging by a dc source
Q=CxV
• Q: quantity of charge
• C: capacitance (farads/F)
• A one-farad capacitor stores one coulomb of charge per applied volt.
– Charge and discharge rate
i = I init e −t / RC
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Power Supply
• Voltage regulators
– Function: maintain output voltage at constant
desired level
– Component: Zener diode
9
B-1& 2 Continuum and Lines Sources
• Line source: emit a few discrete lines
• Continuum source: emit a continuum spectrum
10
B-3 Laser Sources
• Light Amplification of Stimulated 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
11
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 radiative
relaxation
Stimulated emission
– excited species struck
by photons that have
same energies emit
photons that travel in
phse with the
stimulating photon
• Coherence
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Mechanism of Laser Action
• Population inversion
required!
– Normal distribution:
number of particles in
the lower energy
state higher than that
in the higher energy
state
– Population inversion:
number of particles in
the higher energy
state higher than that
in the lower energy
state
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How Population Inversion Methods
• Three levels system
– More than 50% of lasing
species must populate level
Ey
• Four level system
– Because the transition from Ex
to E0 is fast population
inversion is more readily
achieved between Ey and Ex
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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 (Al2O3 + 0.05% Cr(III))
– Nd-YAG
• Gas Lasers
– He-Ne (neutral atom)
– Argon (ion laser) Ar+
– CO2 (molecular)
– N2
• Dye Lasers
– Fluorescent dyes
– Tunable (20 to 50 nm)
• Semiconductor Diode Lasers
– Light Emitting Diodes (LED)
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