Gain Saturation in Neodymium: Glass Laser Amplifiers

Abstract

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 σ_a. From this and the measured value of 3.3×10³ sec⁻¹ for the spontaneous emission rate A, the critical saturable power P_c is calculated to be about 20 kW/cm². P_c is defined as the level that reduces the unsaturated steady‐state inversion density by 3 dB; it is given approximately by Ahv_L/σ_a. 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.