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For more than 45 years, L3Harris divisions in Hilton Head, SC and Orlando, FL have pioneered the development of erbium/ytterbium (Er/Yb) co-doped phosphate laser glass and Q-switches in “eye-safe” laser transmitters for range finding and illumination/tracking/targeting applications. In this paper we will present how varying the Er to Yb ratio in high-gain phosphate laser glass media has innovation in small laser transmitters emitting at 1.54µm and capable of operating over a wide temperature range from -40°C to 85°C without active cooling. We focused on three different doping ratio regimes: The first ratio – medium Er/high Yb – enabled slightly larger laser 3mJ per shot with a repetition rate of 5Hz. The second ratio – low Er/medium Yb enabled the development of a high repetition rate of 100Hz laser emitting 1mJ of energy in each shot. The third ratio – high Er/ relatively low Yb – was used to produce a very small lightweight laser with an energy output greater than 200μJ per shot with a repetition rate of 10Hz and triple pulse output. In this paper, we will provide a theoretical model for calculating the output from our Er3+ mini lasers depending on the Er to Yb co-doping ratio and energy transfer efficiency in phosphate laser glass. The model takes into account the major laser parameters such as number of pump diode, their efficiency, pump time, diode wavelength, optical density of the pump wavelength in the laser gain medium, pump volume (absorption length, pump length, pump width), cavity mirrors, Co2+ Spinel Q-switch initial transmission, maximum energy output, and “expected” energy output etc. The pump structure of the laser transmitter and the laser cavity design will be illustrated. The laser output energy over temperature, its pulse width, output beam quality, and shot-to-shot beam pointing stability will also be presented.
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