Continuous System-Level Scale for Comparing Laser Gain Media

Report No. ARL-TR-4682
Authors: Jeffrey O. White
Date/Pages: December 2008; 24 pages
Abstract: Several quantities are proposed for facilitating a quantitative comparison of laser gain media, operating temperatures, pump, and laser wavelengths. They are based on the occupation probability of absorbing and emitting pump and laser levels. The "system level," l, has a numerical value coinciding with conventional usage of the terms two-, three-, and four-level system. The "occupation factor" f0 has a value from -1 to +1, and is appropriate for describing an optical amplifier in the small signal regime. f1 also ranges from -1 to +1, and is appropriate for describing an amplifier in the large signal regime, e.g., a laser. The physical significance is that for l > 2 , f0 > O, or l > O, the laser beam gains photons at the expense of the pump beam, in steady state. For l < 2 , f0 < O, or l < O the opposite occurs. The proposed definition is general enough to apply to many types of gain media, but is particularly useful for comparing systems with discrete levels, pumped with a narrow-band source, in near-resonance with the laser wavelength. Several low-quantum-defect combinations of pump and laser wavelengths are analyzed for Er3+, Nd3+, and Yb3+ in YAG, as a function of temperature.
Distribution: Approved for public release
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Last Update / Reviewed: December 1, 2008