We demonstrate second harmonic generation from a GaAs substrate, well-below the absorption edge. The pump is tuned in the transparency range, at 1064 nm, while the SH is tuned in the opaque spectral range of GaAs, at 532 nm. We work far from the phase matching condition and we find that the phase locked component of the second harmonic propagates trough the opaque material. As expected, we find that the polarization of the generated SH signal is sensitive to the polarization of the pump. We demonstrate different surface and bulk contributions to the SH transmitted signal and we show that the surface-generated SH components can be more intense than bulk-generated SH signals. The experimental results are contrasted with numerical simulations that include these two factors, using a hydrodynamic model, accounting for all aspects of the dynamics, including surface and bulk generated harmonic components.

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L. R. Suñé, J. F. Trull, M. Scalora, and C. Cojocaru, "Surface and bulk harmonic generation in the opaque region of GaAs," Proc. SPIE 11026, Nonlinear Optics and Applications XI, 110260O (Presented at SPIE Optics + Optoelectronics: April 02, 2019; Published: 30 April 2019); https://doi.org/10.1117/12.2520979.