Properties and Frequency Conversion of High-Brightness Diode-Laser Systems

Abstract

An overview of recent developments in the field of high-power, high-brightness diode-lasers, and the optically nonlinear conversion of their output into other wavelength ranges, is given. We describe the generation of continuous-wave (CW) laser beams at power levels of several hundreds of milliwatts to several watts with near-perfect spatial and spectral properties using Master-Oscillator Power-Amplifier (MOPA) systems. With single-or double-stage systems, using amplifiers of tapered or rectangular geometry, up to 2.85 W high-brightness radiation is generated at wavelengths around 810 nm with AlGaAs diodes. Even higher powers, up to 5.2 W of single-frequency and high spatial quality beams at 925 nm, are obtained with InGaAs diodes. We describe the basic properties of the oscillators and amplifiers used. A strict proof-of-quality for the diode radiation is provided by direct and efficient nonlinear optical conversion of the diode MOPA output into other wavelength ranges. We review recent experiments with the highest power levels obtained so far by direct frequency doubling of diode radiation. In these experiments , 100 mW single-frequency ultraviolet light at 403 nm was generated, as well as 1 W of single-frequency blue radiation at 465 nm. Nonlinear conversion of diode radiation into widely tunable infrared radiation has recently yielded record values. We review the efficient generation of widely tunable single-frequency radiation in the infrared with diode-pumped Optical Parametric Oscillators (OPOs). With this system, single-frequency output radiation with powers of more than 0.5 W was generated , widely tunable around wavelengths of 2.1 m and 1.65 m and with excellent spectral and spatial quality. These developments are clear indicators of recent advances in the field of high-brightness diode-MOPA systems, and may emphasize their future central importance for applications within a vast range of optical wavelengths. What has attracted scientists and engineers most about lasers is, certainly, that strongly directed and monochromatic light beams can be generated with high power. Such radiation with high spatial beam quality and narrow spectral bandwidth is commonly termed high-brightness radiation. The general properties of diode lasers, i.e. small size, robustness, potentially low costs, and their high wall-plug efficiency have so far been the central issues in designing diode lasers for applications. Diode lasers with low brightness, though with