lasers - pécsi tudományegyetem · time correlated single photon counting (ns, ps, lasers)...
TRANSCRIPT
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Lasers
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• Conditions of laser operation
• Classification of lasers
• Continuous wave lasers (He-Ne)
• Pulsed lasers (Nd-YAG, Ti:Sa)
• Ultrashort pulse generation
• Extreme energies
• Applications
Lasers
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• Pumping
• Stimulated emission
• Population inversion
• Amplification
Laser operation
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Absorption spontaneous emission Stimulated emission
Absorption and emission
LASER = Light amplification by stimulated emission of radiation
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Stimulated emission takes place in the laser active medium
The emitted photons are reflected from the end mirrors stumulating more photon
emission
A small part of the photons quit the resonator trough the output coupler
R = 100% R < 100%
I0 I1
I2 I3 Laser active
medium
Laser operation
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Population inversion
Why do we need population inversion?
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R = 100% R < 100%
I0 I1
I2 I3 Laser active
medium
I
What do we need for population inversion ?
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Population inversion
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Two level
system
Laser
transition
Pumping
transition
In the best case we
get equal population
Four level
system
Easy laser operation
Laser
transition
Pumping
transition
Fast relaxation
Three level
system
Hitting hard will
result in lasing
Fast relaxation
Two, three and four level systems
Pump
transition
Laser
transition
Fast relaxation
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By energy:
• I. class (harmless, laser pointers, CD players etc. )
• II.class(< 1 mW, no danger due to the blink)
• III. class (needs extra attention, < 500 mW),
• IV. class (extremely dangerous, burning dangers, retina
damage etc.)
Classification of lasers
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By the laser active medium:
• Gas lasers (He-Ne, Ar-ion, CO2, N2, krypton etc.)
• Solid state lasers (ruby, Nd-YAG, Nd-YLF, Nd-glass,
titanium-sapphire)
• Diode lasers
• Dye lasers
• Chemical lasers (I, HF, HBr, stb.)
Classification of lasers
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By operation:
• CW = continuous wave
• Pulsed lasers : Q-switched lasers, mode-locking lasers
Classification of lasers
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694,3 nm
Ruby laser
• The first ever operating laser (Theodore Maiman, 1960 )
• The laser active medium is chromium doped syntetic sapphire
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He-Ne laser
• 7:1 – 10:1 mixture of He and Ne gas
• Low pressure (3-7 mbar)
• Excited helium atoms collide with neon atoms
• Four level laser
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• Q-switched lasers
• Mode-locked lasers
Pulsed lasers
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• Repetion frequency: 15 Hz – 100 MHz
Parameters of pulsed lasers
• Pulse length: ns - fs
• Energy in one pulse: nJ-kJ
• (1.85 MJ @ National Ignition Facility)
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National Ignition Facility
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Rutherford Appleton Laboratory
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Central Laser Facility, UK
ASTRA
• Ultra-high intensity 2.6 kJ in sub-picosecond
pulses, 100 TW → PW
• Fusion and Plasma Research
• Extreme UV generation
• Attosecond pulse generation research
• Smaller scale lasers
• Vibrational
spectroscopy
• Imaging; laser tweezers
and microscopy
VULCAN LSF
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Extreme Light Infrastructure
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Q-switched lasers
• Maximazing the population inversion then switching out a giant
pulse
• Pulse length: 100-200 ns
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Mode-locking
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Superposition of seven modes in random phase (A)
And locked phase (B). (Forrás: Enoch Small,19912
Mode locking
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• The working horse of femtosecond lasers
• Laser active medium: titanium doped sapphire very good termal
properties, wide absorption spectrum)
• Pulse length: 6-150 fs
• Energy: nJ-mJ
• Hungarian input: Femtolasers (Krausz Ferenc), R&D Ultrafast
Lasers (Szipőcs Róbert)
Ultrashort lasers (Ti:sa)
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Titanium-sapphire laser
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Tranziens abszorpció @ Biofizika
BBO
CaF2
Minta
Foto-
dióda
Ch
Monokromátor
St
F
100 fs, 1 nJ,
100 MHz, 800
nm
100 fs, ~ µJ,
1 kHz, 800
nm
A pumpa és próba
impulzus térben (és
időben) átfed a
mintában!
CCD
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Time correlated single photon counting (ns, ps, lasers)
Microscopy : confocal microscopes, super resolution (CW
lasers), two photon microscopy (Ti:sa lasers)
FTIR (Fourier –transformed infrared spectroscopy)
Laser tweezers (CW)
Raman spectroscopy (CW lasers)
Transient absorption
Applications
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LIBS analysis
LIBS = Laser Induced Breakdown Spectroscopy
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Cleaning the Acropolis
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Cleaning the Acropolis
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Laser cleaning
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Laser cleaning in Pécs
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http://www.physik.uni-wuerzburg.de/femto-welt/pulsstart.html
https://www.youtube.com/watch?v=boiQkDon9Fs