We report on recent developments in the characterisation of non-linear lensing in semiconductor disk laser gain samples. We find that there is a significant nonlinear lens present and the magnitude and sign of this depend on the conditions under which it is being observed. Under experimental conditions which are, to date, the closest to intra-cavity conditions, with 350 fs pulses at the same wavelength a mode-locked SDL using that gain chip would operate at we find that the lens is always negative and its magnitude is almost independent of pump intensity. We also report on the experimental observation of different mode-locking regimes in SDLs including dual wavelength mode-locking and pulse molecule formation and compare these experimentally observed modes of operation with predictions from microscopic modelling previously reported in by Kilen et. al. 
Keith G. Wilcox, Adrian H. Quarterman, Conor J. C. P. Smyth, and Shamil Mirkhanov, "Optically pumped semiconductor lasers: from nonlinear lensing to solar lasers (Conference Presentation)," Proc. SPIE 10087, Vertical External Cavity Surface Emitting Lasers (VECSELs) VII, 1008707 (Presented at SPIE LASE: January 30, 2017; Published: 21 April 2017); https://doi.org/10.1117/12.2252079.5387835717001.
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