Overview

One of the newer additions to the commercial laser world is a family of solid-state lasers with tunable wavelength. Their tunability originates from their operation on vibronic transitions in which the active species (an atom in a solid host) changes both electronic and vibrational states. Dye lasers operate on similar transitions. Solid-state tunable vibronic lasers are much easier to use than dye lasers, which has stimulated their rapid commercial development. However, tunable solid-state lasers cannot yet generate all wavelengths available from dye lasers. Their fundamental wavelengths are in the near infrared; visible and near ultraviolet light can be produced only by harmonic generation or other nonlinear processes.

The first tunable solid-state laser to reach the market was alexandrite, chromium-doped BeAl ₂O ₄, which can be tuned between 701 and 826 nanometers (nm) at room temperature, although not across the entire range under the same conditions. It has since been joined by titanium-doped sapphire (Al ₂O ₃), which is tunable from 660 to 1180 nm, the broadest tuning range of any single conventional laser medium. (Dye lasers can be tuned across a broader range only by switching dyes.) Titanium-sapphire lasers gained rapid acceptance at the end of the 1980s and are displacing dye lasers from the market for near-infrared tunable lasers. Indeed, one company which makes both dye and Ti-sapphire has advertised that dye is dead for the nearinfrared. Other vibronic solid-state lasers are in development or offered commercially on a small scale, including cobalt-doped magnesium...