Solid-state and gas lasers have followed largely divergent development paths. Gas lasers are based primarily on direct electrical discharge for pumping (energizing), while solid-state lasers are pumped by flashlamps and semiconductor diode laser arrays.
The alkali-vapor laser's intrinsically high efficiency (80+%) and its compatibility with today's commercially available diode arrays enable fast-track development paths to tactical systems, with mass-to-power ratios that far exceed what is possible with today's other laser systems.
DPAL fires an array of high-powered diode lasers, a type used in consumer gadgets like DVD players, into a cloud of alkali metal atoms. The energy is absorbed by their outer electrons and then released as laser light
William Krupke, WFK Lasers, LLC, proposed the diode-pumped alkali laser (DPAL) concept to benefit from the attractive efficiency and power-scaling properties of high-power pump-semiconductor-laser diodes, while replacing the solid-state gain medium with a gaseous (vapor) medium to recover convective transport of waste heat from the laser resonator.
In previous DPAL experiments the gain medium was static, and waste heat removal from the lasing volume occurred through free convection. Efforts to further increase DPAL average output power have retained static gain media but resort to geometries in which at least one high thermal-conductivity wall is placed close to the pumped active laser volume, as in a circular capillary or a planar waveguide. Calculations suggest that capillaries may be scaled to output powers into the 100W regime, and that 2D waveguides may scale to output powers into the kilowatt range. In scaling to much higher powers, it is anticipated that a flowing DPAL medium will be needed, which will likely be undertaken in the next few years.
New Scientist reported the Alkali laser as a leading contender for anti-missile lasers.
Progress in alkali lasers development (2008)
Diode pumped alkali vapor lasers developed during the last several years have the potential to achieve high power. Efficient operation of Rubidium, Cesium and Potassium lasers has been demonstrated. Laser slope efficiencies higher than 80% have been achieved. A diode laser pumping can provide high overall efficiency of these devices. A diode pumped continuous wave 10 W Cs laser and continuous wave 17 W Rb laser were demonstrated. In this paper we review the main results and recent achievements in high power alkali lasers development, discuss some problems existing in this field and ways to solve them
Slope efficiency is the ratio of pump power to output power after the initial priming of the laser has been completed. (higher slope efficiency is better.