Tunable laser

A tunable laser is a laser whose wavelength of operation can be altered in a controlled manner. While all laser gain media allow small shifts in output wavelength, only a few types of lasers allow continuous tuning over a significant wavelength range.

There are many types and categories of tunable lasers. They exist in the gas, liquid, and solid state. Among the types of tunable lasers are excimer lasers, gas lasers (such as CO₂ and He-Ne lasers), dye lasers (liquid and solid state), transition metal solid-state lasers, semiconductor crystal and diode lasers, and free electron lasers. Tunable lasers find applications in spectroscopy,, atomic vapor laser isotope separation, and optical communications.

Since no real laser is truly monochromatic, all lasers can emit light over some range of frequencies, known as the linewidth of the laser transition. In most lasers, this linewidth is quite narrow (for example, the 1,064 nm wavelength transition of a Nd:YAG laser has a linewidth of approximately 120 GHz, or 0.45 nm). Tuning of the laser output across this range can be achieved by placing wavelength-selective optical elements (such as an etalon) into the laser's optical cavity, to provide selection of a particular longitudinal mode of the cavity.

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