Alkali-metal-vapor light sources for pulsed applications

Alkali-metal-vapor discharge light sources are efficient sources of near-infrared radiation. The radiation characteristics of wall-stabilized discharges of cesium, lithium, rubidium, potassium, and sodium have been studied as a function of vapor pressure, pulse width, and duty cycle. The tubes were constructed with polycrystalline alumina or sapphire bodies, tungsten electrodes, and niobium end-caps. Keep-alive operation was used for ease of starting at high pressures and to reduce sputtering and thermal shocks. Spectrograms, using synchronous detection techniques, have been made. The spectral output is "gray body" and peaks in the near infrared, from 0.7 to 0.8 µm depending on the vapor. The resonance lines show large inversions. The efficiency of the discharges as light sources has been measured for a wide range of pressure and operating conditions. The output efficiency is proportional to the square root of the pressure from 1 to 200 torr. Over 200 toor, the pressure dependence is less significant. The percent modulation is greater than 90%. On the basis of the results obtained, the design of alkali-metal-vapor pulse light sources for near-infrared illumination applications and as optical pumps for solid-state lasers will be discussed.