What a tunable laser allows is not only a stronger beam with more power, but the color can be changed. Since the beam can operate in the infrared and microwave you don't see a color change, although it can be seen with the proper sensors. Don't look directly into the beam of a laser. Tunable lasers allow a range of sensitivity for exploring the physical world, such as biological systems and materials science. A frequency that could destroy the surface of a cell wall could be adjusted to a lower frequency to avoid damage with the tunable device.
All tunable lasers involve formidable problems of stability and reusability.
C.V. Raman and K.S. Krishna. Kirk-Othmer Encyclopedia of Chemistry Technology. Published as part of the Springer Series in Optical Sciences , vol.3. The Raman scattering material which may be indium antimonide crystals shaped as a parallelepiped with dimensions of a few millimeters along each edge. At least two opposite sides are polished planes and parallel to form a Fabry-Perot type optical resonator.