We report second harmonic generation (SHG) from thick hexagonal boron nitride (hBN) flakes with approximately 109layers. Surprisingly, the resulting signal is stronger when compared to previously reported few-layer experiments thatshowed the SHG efficiency gradually decreasing with the increasing thickness. This confirms that thick hBN flakes canserve as a platform for nonlinear optics, which is useful because thick flakes are easy to exfoliate while retaining a largeflake size. We also show spatial second harmonic maps revealing that SHG remains a useful tool for the characterizationof the layer structure even in the case of a large number of layers.
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