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Theoretical and Experimental Study of Near-Field Beam Properties of High Power Laser Diodes

We present laser beam astigmatism results obtained by Near-field Scanning Optical Microscopy. Measurements made with this technique on the high reflecting facet of a Graded Index Separate Confinement Heterojunction laser diode indicate the lateral beam waist is outside of the device structure, seemingly in contradiction to far-field measurements made on the low reflecting output facet of the device. Our attempts to resolve the discrepancy by invoking thermal lensing due to a temperature gradient across the mirror facet is capable of partly generating the focusing required to explain the difference in observed beam waist position for the two separate measurements. Simulations which include inhomogeneities along the length of the device cavity may resolve the apparent discrepancy. This paper is eligible for best student paper. Keywords— near-field scanning optical microscopy, astigmatism, laser diode