What is the alexandrite laser?

Alexandrite crystal, a rare gemstone, is named after the Russian tsar Alexander II. The most sensational feature about this stone, however, is its surprising ability to change its color. Green or bluish-green in daylight, alexandrite turns a soft shade of red, purplish-red, or raspberry red in incandescent light. An alexandrite laser is a solid state laser in which chromium ions (Cr⁺³), at the amount of 0.01% to 0.4%, are embedded in a BeAl₂O₄ crystal. Ions of chromium are contaminants in the crystal. Both Q-switched and flashlamp-pumped alexandrite lasers are available. These lasers deliver a wavelength of 755-nm light.