lecture 38 lasers final exam next week. laser l ight a mplification by s timulated e mission of r...
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![Page 1: Lecture 38 Lasers Final Exam next week. LASER L ight A mplification by S timulated E mission of R adiation](https://reader036.vdocuments.net/reader036/viewer/2022062714/56649d625503460f94a45049/html5/thumbnails/1.jpg)
Lecture 38
Lasers
Final Exam next week
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LASER
Light
Amplification by
Stimulated
Emission of
Radiation
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Electronic Energy Levels
0
1
2
Ene
rgy
e-
e-
Fluorescence or ‘Spontaneous Emission’
e-
e-
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Stimulated Emission
0
1
2
Ene
rgy
e- e-
The stimulated emission has the same frequency and phase as the incoming photon
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3 level system
0
1
2
e-
‘Short’ lifetime
‘long’ lifetime
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Stimulated Emission Light Amplifier
Pump (does not need to be light)
Gain medium can be gas, liquid, or solid
All light is in phase and has the same frequency
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Laser Cavity
Once the amount of gain is equal to the cavity losses,‘lasing’ happens
Losses can include output coupler, reflectivity, other optics in cavity
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Cavity modes
The mirrors force the amplitude of the wave to zero.
Only integral number of half wavelengths can exist.Every wave exits in phase
2c
vL
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Allowed frequencies
0
1
It is a combination to the energy spread and the cavity modes
0.00 0.05 0.10 0.15 0.20 0.25 0.30
X Axis
0
2
4
6
8
10
12
14
YAxis
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Laser pulse generation
PC
“Q-switching”, ns pulses
“Mode-locking”,fs pulses
Cavity length ~1.5m
Gain medium
Q=2*Energy stored
Energy Lost per cycle
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Transverse modes
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Transverse Modes
The 00 mode is the smallest….
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Types of lasers
Gas: HeNe
Solid-state: Semi-conductor Diode, Crystals (sapphire), nano-particles
Liquid: Dyes,
Chemical laser: CO2, Excimer