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Dye Lasers

Excerpt from Field Guide to Lasers

A dye can selectively absorb light with certain wavelengths corresponding to certain electronic transitions. However, it may also emit fluorescence and even exhibit laser gain. A wide range of emission wavelengths—from the ultraviolet to the near-infrared region—is accessible with different laser dyes, most often used in a liquid solution. They offer a broad gain bandwidth and thus broad wavelength tunability as well as the potential for ultrashort pulse generation with passive mode locking (see p. 107). Upper-state lifetimes are typically a few nanoseconds, and the gain per unit length can be rather high (on the order of 103/cm).

dye_laserMost dye lasers use a thin jet (with or without a thin cuvette) of dye solution. The dye molecules are exposed to the pump light only for a short time interval. From time to time, the dye solution has to be exchanged because it degrades during operation. The laser resonator may contain a birefringent tuner (or some other kind of tuner) for adjusting the emission wavelength.

There are also dye lasers that utilize a large volume of dye solution pumped with a flash lamp or a Q-switched laser. Such dye lasers can generate pulses with many millijoules.

While dye lasers have dominated the fields of tunable lasers and ultrashort pulse generation for a long time, they have been largely replaced by solid-state lasers (often based on Ti:sapphire), which avoid the disadvantages of handling poisonous dye solutions, a limited lifetime, and limited output power. However, dye lasers are still used in some areas, such as spectroscopy with wavelengths that are otherwise hard to generate.

Properties of Dye Lasers

important typescontinuous-wave or mode-locked Rhodamine 6G lasers; flashlamp-pumped lasers with various dyes
applicationsspectroscopy; ultrashort pulse generation
pump sourcesother lasers or flash lamps
power efficiencya few percent to an order of 50%
accessible wavelengthsmostly visible and near infrared
wavelength tuningpossible over tens of nanometers
average output powertypically between 10 mW and 1 W, but >1 kW is possible
beam qualitynormally diffraction-limited; worse for pulsed high-power devices
continuous-wave operationyes
nanosecond pulse generationyes, with pulsed pumping
picosecond & femtosecond pulse generationyes, with mode locking

R. Paschotta, Field Guide to Lasers, SPIE Press, Bellingham, WA (2008).

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