Types of lasers Flashcards
Name the 4 types of gain media
Gas/vapour
solid state
liquid and dye
semiconductor
TYpical excitation for 4 types of gain media
Everything can basically always be optically pumped,but often electrical pumping used except solid sate(only optical)
Gas/vapour - electric, optical, chem, non them equil
solid state - optical
liquid and dye - optical
semiconductor - electrical (sometimes optical)
What is optical pumping
Mainly used for solid state, semi conductor, dye lasers
Spectral dist of pump match absorption spectrum of pumping band
Light sources: arc and flash lamp, lasers (NdYag)
Electrical pumping
gas and semiconductor lasers
1)discharge pumping - electron collisions
2)current thorugh PN junction
Chem pumping
Gas lasers
-photodissociation, exchanges and recoombinations are used in chemistry to cause excited molecules and pop inv
Eg of non equil thermal pumping
Not common
high pressure conditiosn can achieve pop inv
How is laser action achieved in an eximer laser
Excimer is gas
rare gas /nobel gas very inert, excited state very reactive with group 1 elements or with group 7 form stable rare gas halogen molecules XeF, ArCl, KrF
energy landscape means that pop inversion is possible but requires pump power densities of 100kW/cm^3 so e beam excitation or very high V discharge
Large elec discharge -> Excited ions -> combine with halogen to form rare gas halogen molecule -> Harpooning reaction reaction cause lasing
One pass through, very high gain
CO2 laser
Gas
virbrational and roational levels act as lasing levels
linewidth dominated by pressure breaodening
How is solid state laser pumped
Optically
flashlamp (cna be coiled around rod or //)
or arc lamps
or diode laser
How do solid state lasers work
material like crystal or galss doped with small amounts of transition metal and rare earth elemets posses required transitions
-sharp fluoro lines, strong abs bands, high quantym efficientcy
required host properties of solid state lasers
homogenous index of refraction
strong, thern conductivity
lattice sites that accept dopant ions
crystal growth must be stable
Typical solid state combos
host and dopant:
Glass and Nd
Sapphore and Ti.Ruby
Garnets Yttriuum Aluminium (YAG) and Nd, Er Ho
a crystal laser rod is grown
typically output in NIR/IR
Nd:YAG and Ruby laser summary
Nd:YAG 2% efficiency for flash lamp 23% efficiency for diode laser piumped
4 level laser system
high quantum eff absoroption in NIR
strong and durable, hard clear crystal with high thermal conductivity
pumped by laser diode often matching abs peaks very well to get max efficiency of pumping
Ruby
pumped by flashlamps
pump light in 400 and 550 blue green VIS
very ard almsot as much as diamond
4 ways to generate single well defined laser pulses and not erratic pulse trains
gain switching
q switching *pulse >10ns, slow pulse build up)
cavity dumping (h1-2ns, cavity lenbth limits, mirror refl 100-0%)
mode locking(1ps) maybe fs using Kerr lens modelocking and dispersion compensation
q switching
q switching
quality of a resonant cavity
(introduce large losses in cavity untile amplifier gain reached a val then decrease the lsoses and allow lasing)
4 types
active, mechanical (roating mirrowm chopper wheel)
active, electrooptic (pockers or kerr)
active, acoustooptic (standing waves and bragg angle diverge by 0.5 deg)
passive, saturabnle absorber
what limits fs pulses
Determined by time gain bandith producture
rewuire gain media with very large bandwidth -< Ti:Saphhire 230nm bandwidth
has very rich vibraonic manifold in excited and gorup states forming broad bands
Tisaph very good with Kerr olens mode locking for ultra short pulses
Prism pairs
Blue light deflects mroe in a prsim than red so setup prisms such that blue goes through less g;ass in 2 prisms than the red effectively correcting the path length by creating negative dispersion
Typical modern fs pulsed regime
Pumped by frequency doubled CW Nd based solid state lasers
direct amplification not possible due to damage -> CPA
oscillator produces short pulse
stretched
amplified
compressed
Common lasers list type and wavlength ish
HeNe
XeCl
TiSaph
NdYag
InGaAs
CO2
HeNe - gas, 632
XeCl - excimer (UV), 308
TiSaph - SS, 800
NdYag (1064), nd glass, er glass- SS
InGaAs - Semicond/(diode) (980)
CO2 - gas 10.6um (IR)
Diode lasers
direct current injecting into PN junction - electrically pumped
ot flash laps or lasers
electronic transitions between valence and conduction band (2 level system) electron hole recombination releases photons
GaAsIn comvinations 630-1650 even down to NUV 360 diode lasers
Edge emitting diodes
Lasing emitted from rectangular thin active layer and causes ellibtial pattern. asigmatism corrected by cylindircal lenses, but beam divergence still laser
didoe laser variations
LED -> high current -> diode
optinally pack into array laser bar or 2d stack for high power
very temperature sensitve, mode hppping , heterojunction layers and confinement lead to better temp stability
VCSEL
Vertical cavity surface emittin glaser
symmetric output beam and good beam quality
Advtanges of diode lase
High efficiency
low threshold current and energy consumption
high reliability
small weight and volume
cheeeap
can have nice spectral width
bad:
poor mode quality, poor beam shape
temp instability
