6. Conclusion

This article shows that all light-amplifying media are tunable. The potential spectral ranges are highly variable, depending on the type of medium: laser or nonlinear. For laser media, spectral widths are small in gases (in the GHz range) and much larger in solids, with some materials such as titanium-doped sapphire or quantum cascade lasers setting records. Just as there are a multitude of laser media, so there are a multitude of ways to tune a laser. Methods intrinsic to the laser oscillator involve playing on the length of the cavity or the spectroscopic properties of the gain medium. Other methods involve adding spectral filters to the cavity to select the wavelength of interest. Any optical component capable of producing even small losses as a function of wavelength is suitable: refractive, interferential, birefringent or diffractive components. The choice of one component over another...