Spectrally Resolved Near-field of a Broad-Area GaAIAs Semiconductor Laser

Broad-Area (BA) semiconductor lasers are compact and reliable sources of laser radiation in the 780-890 nm wavelength range for high-power applications such as rangefinders, laser pumping and medical treatment . These lasers are characterized by a large e mitting aperture that usually ranges between 20 and 200 micro meter. This relatively wide waveguiding structure favors the oscillation on numerous lateral modes along the emitting window. Our picture clearly illustrates the multimode structure of a typi cal BA laser operated at high injection current. It was taken by imaging the emitting facet (near-field) of the laser onto the entrance slit of a 1-m long grating spectrometer (resolution : 0.01 nm). The output slit was replaced by a monochrome CCD came ra with a pickup area of 6.4 x 4.8 mm and a cell size of 8.4 x 19.5 micro meter. Resolution was improved by adding a cylindrical and a spherical lens to expand the beam on the camera. The image was displayed on a TV monitor and a photograph of the scree n was taken using a standard 35-mm camera. The vertical axis represents the emitting aperture of the diode laser and corresponds to a stripe width of 75 micro meter. The horizontal axis corresponds to the optical spectrum with wavelength increasing from left to right. Five mode groups (each group corresponds to different axial mode of the laser), spaced by 0.2 nm, are displayed. Higher order lateral modes can be easily identified within each group by their shorter wavelength and their multilobed spati al intensity distribution as expected from the standard linear waveguide theory.

Sylvain Mailhot Goals

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