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Dye 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.

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