Master-Oscillator Power-Amplifier Diode Lasers

Abstract

The inability of edge-emitting gain-guided (Chap. 5) and most laser-array oscillators (Chap. 6), as well as surface-emitting laser arrays to operate single frequency, and at brightness and power level above single-element diode lasers, provided an impetus to researchers to investigate alternative structures. In recent years, the Master-Oscillator Power-Amplifier (MOPA) architecture, which was already well known in the fields of large high-power gas, dye, and solid-state laser systems [1.272, 2.32, 2.37, 2.38, 4.16][8.1]–[8.3], as well as optical telecommunications [8.4]–[8.7], has emerged as a preferred approach for obtaining high-power, single-frequency, beam-quality, diode-laser sources. The mode discrimination can be considerably simpler in a MOPA diode-laser array, as compared to a diode-laser array oscillator. In a MOPA architecture, the output of a low-power, single-frequency laser oscillator is injected unidirectionally into an optical amplifier of greater output-power capacity. Here, what is meant by unidirectional coupling is that a negligible light level from the amplifier is injected back into the oscillator. This is also referred to as nonreciprocal coupling. In principle, the unidirectional coupling means that the frequency characteristics and power output levels can be set independently of each other. Of course, the advantage here is that the spectral-and spatial-mode instability with drive current, which is pervasive in diode-laser array oscillators, can be avoided. A critical requirement for all MOPA designs is that the light levels injected back into the oscillator from the amplifier be sufficiently low that the frequency stability of the oscillator is maintained and self oscillation of the power amplifier is avoided.