Advances in high power high beam quality diode lasers

Abstract

Semiconductor laser enjoys its benefits such as small volume, light weight, long operation life, various selectable wavelength and direct current driving, meanwhile suffers from its beam quality which is making it hard for direct applicdations. Researchers around the world realize that it is beam quality has the same importance as power, and acquiring high power and high beam quality is the key issue in semiconductor laser induxtry. The question of how to improve the beam quality of high power semiconductor lasers is attracting increasing attention from researchers home and abroad. Considering the application fields which require high power high beam quality, such as industry processing and national defense, this paper discussed the research progress on both diode laser unit devices and laser beam combining sources. First of all, the relationships between single laser emitter′s structureand themodeof laser units, including lateral mode, transverse mode and longitudinal mode, are analyzed. Lateral mode is the main factor which limits the high beam quality for high power semiconductor lasers. Ridge waveguide is the main method adopted to realize single lateral mode. A method called longitudinal photonic bandgap crystal is introduced to manipulate the transverse mode of a single laser unit, which can acquire large optical near field and high beam quality even in high current input. To control longitude mode, usually to acquire single longitude mode in single semiconductor laser unit, distribute Bragg reflectors and distribute feedback structures using gratings in fabrication is also introduced in this section. And then we summarize the methods and some results of controlling modeusedinternationalresearchers. Further more, we introduced the lasers beam technology, including beam shaping and beam combining, considering all conditions of single emitters beam combining, mini bar beam combining, centimeter bar beam combining, laser stacks beam combining and laser systems beam combining. In beam combining technology, we introducted the method of traditional beam combining, including polarizetion beam combining and wavelength beam combining. Then the method of using dense wavelength division multiplexing with volume Bragg gratings to realize beam combinign is also introduced. Spectrum beam combining method using a Bragg diffractive grating is then introduced, which may realize a high beam quality of a single emitter′s beam spot with a laser bar′s optical power. Furthermore, coherent beam combining considering each laser unit′s wavelength, polarization and phase to realize high power high intensity farfield is also introduce. Then, the lastest international reported of high power, high beam quality diode laser combining sources are introduced, and characteristics of laser beam technology and development trends arediscussed and analyzed. Finally, the developments of high power high beam quality diode lasers are prospected. Right now, our country still have a distance below internal research in high quality semiconductor laser chip and beam combining source. The semiconductor laser chips′ power and beam quality needed to be improved. The technology of 10 kW level beam combining and optical fiber coupling technology is still urged to be acquired. Grating fabrication in optical beam combining technology and chip fabrication are also needed to be conquered.