Gain Saturation in Neodymium: Glass Laser Amplifiers

Gain saturation in an Nd3+:glass (Corning 0580) laser amplifier has been investigated using a normal laser driving signal. The study shows that only the average power of the driving signal need be specified. The experimental results obtained agree with the steady-state theory of Schulz-DuBois on the gain saturation of an amplifier with loss. This leads to a value of 3.5±1.0×10−20 cm2 for the amplifier stimulated-emission cross section σa. From this and the measured value of 3.3×103 sec−1 for the spontaneous emission rate A, the critical saturable power Pc is calculated to be about 20 kW/cm2. Pc is defined as the level that reduces the unsaturated steady-state inversion density by 3 dB; it is given approximately by AhvL/σa. When unsaturated, the steady-state gain of the amplifier studied was 29.3±3.8 dB; correspondingly, the gain coefficient β was 0.34±0.04 cm−1 and the inversion excitation rate W was about 30 sec−1. When driven to saturation by 82.5 kW/cm2 (the maximum normal laser driving power used in the experiment), 3.0±0.2 dB of steady-state gain was measured. The loss coefficient α of the amplifier was found to be 0.011±0.002 cm−1 at 1.06 μ.