Introduction

This is a time of significant efforts in the development and investigation of physical and technical problems related to laser diodes (LD) and their applications. During the last few years astonishing progress in the performance of a wide set of parameters has been achieved. The output of laser diode bar on a level of more than 100 watts was demonstrated, different schemes of efficient phase locking have been investigated, and perspective approaches in realization of various optical configurations of LD pumped solid state lasers (SSL) were introduced. At the same time the existing level of development still is far from physical limits. The capability of semiconductor advanced technologies, heat transfer modes realization, and wide spectral range SSL materials development appears to be very promising. The task of this Focus Issue of Optics Express is to show the contemporary status of the above-mentioned problems and to attract the attention of the laser community to the new opportunities with wide range of applications.

This focus issue includes four papers that display the guidelines of the LD technology. The achievements in the development of powerful LD bars mounted on either conductively cooled or microchannel heat exchangers are presented in the paper submitted by M. Jansen et al. from the Coherent Semiconductor Group. Employment of the LD for solid state laser pumping is illustrated and the high slope efficiency of the laser is demonstrated in the joint work of the group of K. Ueda et al. from the Institute for Laser Science, University of Electro-Communications, Tokyo, Japan. Two papers contributed by V. Apollonov et al. (General Physics Institute, Russian Academy of Sciences) reveal a theoretical comparison of the thermal resistance of the microchannel and porous heat exchangers and experimental results of both 1D and 2D phase-locking which display the possibility of powerful LD bars application allowing for diffraction limited beams, corresponding to the synthesized aperture size.

I would like to thank each of the contributing authors for their participation in making this special issue a success.