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.It is a laser the output wavelength of which can be tuned (i.e., adjusted) (→ wavelength tuning). In some cases, one wants a wide tuning range, i.e., a wide range of accessible wavelengths, while in other cases it is sufficient that the laser wavelength can be tuned (factory-set) to a certain value. Some single-frequency lasers can be continuously tuned over a certain range, while others can access only discrete wavelengths or at least exhibit mode hops when being tuned over a larger range.
Tunable lasers are usually operating in a continuous fashion with a small emission bandwidth, although some Q-switched and mode-locked lasers can also be wavelength-tuned. In the latter case, one may either spectrally shift the envelope of the frequency comb or the lines in the spectrum. Tunable lasers can continuously change their emission wavelength, or color, in a given spectral range. Tunable lasers are usually operating in a continuous fashion with a small emission bandwidth. Here wavelength tuning occurs
Tunable lasers were discovered by Sorokin and Lankard in 1966. This was the dye laser. At first, the radiation from these organic lasers was in the form of broadband emission. Broadband emission is generally comprised by several transverse modes and a multitude of longitudinal modes in each transverse mode. A significant advance towards emission control was provided with the invention of the continuous wave dye laser by Peterson in 1970. In the area of high-power pulsed dye lasers a most important contribution was the introduction of the telescope-grating oscillator by Hänsch in 1972. The laser cavity introduced by Hänsch utilized most of the principles of wavelength tuning and frequency narrowing essential to practical tunable lasers. However, it was not compact and required a large two-dimensional diffraction grating