10.1007/s11455-008-3003-5

Abstract

The output radiation power of modern laser diodes (LDs) operating in the continuous-wave (CW) generation regime reaches 10 W and above [1], which makes them promising sources for nonlinear optical converters for the yellow-green spectral range. However, a significant disadvantage of high-power edgeemitting LDs with wide stripe contacts is the operation in a multimode and multifrequency regime, which is related to the uncontrolled generation of numerous longitudinal and transverse modes in the p − n junction plane and accounts for a relatively large width of the radiation spectrum (linewidth). At the same time, the spectral bandwidth of conversion in modern nonlinear crystals-for example, that based on periodically poled lithium niobate (PPLN)-does not exceed 0.3 nm. Therefore, it is an urgent task to create a high-power edge-emitting laser that possesses a narrow linewidth.One possible approach to solving the above problem consists in the use of an external resonator in which the spectrally selective element can be based on an interference filter [2], a diffraction grating [3-5], etc. A simple and effective design of the external resonator is offered by a cavity with external grating that operates in the Littrow scheme, according to which a grating and an unbloomed output face of the LD form a spectrally selective laser cavity. The angle of diffraction for the selected wavelength λ is equal to the angle β of radiation incidence on the grating (Fig. 1), so that where d is the grating period. λ 2d β, sin = Abstract -Use of an external cavity with a grating ensures effective narrowing of the linewidth (~0.35 nm) of a high-power multimode semiconductor laser with a broad (100 µ m) stripe contact. An output power of up to 550 mW has been reached with experimental external-grating-cavity laser diodes. It is demonstrated that a 3-mm-long multimode laser diode based on a quantum-dimensional AlGaAs/GaAs/InGaAs heterostructure ( λ = 1.06 µ m) can be used with a directly pumped PPLN crystal waveguide to obtain second-harmonic radiation with λ = 0.532 µ m. PACS numbers: 42.55.Px First diffraction order First diffraction order First diffraction order β β β β β β Cylindrical microlens Microobjective R ഛ 0.05 LD R = 0.95 L = 25 cm Diffraction grating (1/1200) Output beam, zero diffraction orderFig. 1. Schematic diagram of an external-cavity LD ( R is the coefficient of reflection).