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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).
Most 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.
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 types||continuous-wave or mode-locked Rhodamine 6G lasers; flashlamp-pumped lasers with various dyes|
|applications||spectroscopy; ultrashort pulse generation|
|pump sources||other lasers or flash lamps|
|power efficiency||a few percent to an order of 50%|
|accessible wavelengths||mostly visible and near infrared|
|wavelength tuning||possible over tens of nanometers|
|average output power||typically between 10 mW and 1 W, but >1 kW is possible|
|beam quality||normally diffraction-limited; worse for pulsed high-power devices|
|nanosecond pulse generation||yes, with pulsed pumping|
|picosecond & femtosecond pulse generation||yes, with mode locking|