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Dyelasers

Dye solutions/dyes doped in solid matrix(polymers / organic molecules)Liquid lasers/dye doped solid state lasers

Large size organic molecules

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Typical

dyes

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Energy

levels

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Energy levels (simplified model)

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Absorption and

emissionDye absorptionDye emission

Green dye absorption

 Yellow dye emission

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Pumps

1. Flash lamp2. Lasers( N2, excimer, Nd, ion

lasers, Cu vapour etc)

Pulsed systems/ CW systemsPhoto-degradation; dye

“degrades” on absorption of 

light;limits the life of the dye

Continuous circulation for CW

lasers

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Flash lamp pumped dyelaser

Linear/coaxial flash lamp pumped laser, dye solution is made to flow; in low

power dye circulation is under gravity while high power sources it is pumps

are usedAverage power ~ several KW

Pulse energy ~ 100J/10Hz

UV-IR, 1GHz line-width

1-5000µs pulse widths, 1ps pulses have been produced

1-2% wall-plug efficiency

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Schematics of a flash lamp pumped dyelaser

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Laser output of flash lamp dye lasers

Linear/coaxial flash lamp pumped

laser, dye solution is made to flow; inlow power dye circulation is undergravity while high power sources it is

pumps are usedAverage power ~ several KW

Pulse energy ~ 100J/10Hz

UV-IR, 1GHz line-width

1-5000µs pulse widths, 1ps pulseshave been produced

1-2% wall-plug efficiency

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Typical pulsed laser pumped dye laser

Tuningelement

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Schematics of a laser pumped pulseddye laser

Withmagnetic

stirrer

Tuningelement

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N2 laser pumped dye laser

N2 LASER

CYLINDRICAL

LENS

DYE

CELL

OUTPUT

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N2 laser pumped dye laser; ANNIMATION

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Schematics of laser pumped CW dyelaser (linear cavity)

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Dye doped solid statelasers

Rd6G doped LAP

developed at IIT Kanpur

PMMA,MPG (polymers), silicate glass,

phosphate glass, silica gel etc

available commercially

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Q-switching

Quality factor “Q” of a resonator is

the measure of the amount of energythat can be stored in the resonator. Ahigh Q factor corresponds to lowresonator losses per roundtrip, andvice versa.

Q=-ωε/(dε/dt), where ε is the storedenergy; in case of a laser resonator

energy is stored in the form of “population inversion density”.

Q=ν/δν(1/2) 

In lasers we have Q-switching; a

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Q-switching (Contd)

Initially the laser medium is pumped while the Q-switchprevents feedback of light into the gain medium

(producing an optical resonator with low Q). Thisproduces a population inversion, but laser operationcannot yet occur since there is no feedback from theresonator. Since the rate of stimulated emission isdependent on the amount of light entering the medium,

the amount of energy stored in the gain mediumincreases as the medium is pumped. Due to losses fromspontaneous emission and other processes, after acertain time the stored energy will reach somemaximum level; the medium is said to be gain

saturated . At this point, the Q-switch device is quicklychanged from low to high Q, allowing feedback and theprocess of optical amplification by stimulated emissionto begin. Because of the large amount of energy alreadystored in the gain medium, the intensity of light in thelaser resonator builds up very quickly; this also causesthe energy stored in the medium to be depleted almost

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Q-switching techniques

1. Mechanical methods

a.Rotating resonator mirror

b. Mechanical chopper inside lasercavity

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Q-switching techniques (contd.)

Saturable absorber (absorption

changes with intensity)

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Q-switching techniques (contd.)

Electro-optic/magneto-optic/acousto-optic switches

Refractive index is modulated byapplication of voltage / acoustic wave

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Acousto-optic Q-switch

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Electro-optic Q-switch

Polarization is changed onapplication of voltage, so the lasercavity has high loss(low Q). Suddenlyvoltage is switched-off and Q of 

cavity is high and a laser output inthe form of pulse is observed

Q-switching increases peak power.What about the average power?

Does it also increase? Think 

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Mode-locking

Output of a windows

The output is viewed in a planperpendicular to laser-axis (line joiningthe resonator mirrors through the gain

medium); transverse laser modes

Output of a laserwhich hascylindricalsymmetry

Out-put of a laser

with Brewsterwindows