Recent Developments in High Power Semiconductor Diode Lasers

Due to a number of advantages of diode lasers, such as small size, light weight, high efficiency etc., it has been the focus of the laser field from the beginning of the birth and has been widely used in industrial, military, medical, communications and other fields. Especially, to a great extent, a tremendous growth in the technology of solid-state lasers has been complemented by laser diode array designs for pumping such solid-state lasers. Significant applications continue to exist at common solid state laser systems such as yttrium aluminum garnet doped with neodymium or ytterbium (Nd:YAG or Yb:YAG, respectively) requiring pump light in the 780 nm to 1000 nm range. Driven by the increasing demands of high-performance high-power laser pumping source and direct industrial processing applications, tremendous breakthrough have been realized in the main opticalelectronic performances of high power semiconductor diode lasers, such as ultra-high peak power, super-high electro-optical conversion efficiency, low beam divergence, high brightness, narrow spectrum linewidth, high operation temperature, high reliability, wavelength stabilization and fundamental transverse mode operation etc. These achievements are attributed to a combination of the maturity of semiconductor material epitaxy, the optimization of the laser waveguide structure, the cavity surface-passivation technology as well as the high effective cooling and packaging technologies. The Occident and Japan keep ahead in this field with several large corporations actively engaged in this market, for example, Coherent, IMC, SDL, OPC, HPD, Spectrum-Physics of the U.S., OSRAM, JOLD, Frauhorf of Germany, THALES of France, SANYO, SONY of Japan, and ATC of Russia etc. The wavelength of these industrial products ranges from 630 nm to 1550 nm, and optical output power levels from several W to 10 kW class. In China, prominent progresses have also been made at a rapid rate. Advances in the design and manufacture of the bars, together with effective means of stacking and imaging monolithic semiconductor laser arrays (bars), have enabled the production of robust sources at marketcompetitive costs. In particular, the diode lasers for these systems have to meet high demands in relation to efficiency, power, reliability and manufacturability, which following the desire for reducing the cost per watt and the cost per hour’s lifetime for the customer. However, with the enhancement of the power and beam quality, a series of new practical problems arise in the aspect of engineering, such as high cost of the high-current and low-