Efficient first-order quasi-phase-matched backward second-harmonic generation

We demonstrate first-order quasi-phase-matched backward second-harmonic generation (BSHG) with an efficiency of 18.7%. This represents an increase by two orders of mag-nitude from earlier experiments employing higher-order quasi-phase-matching. The efficient BSHG is demonstrated in bulk periodically poled Rb:KTiOPO4 with a poling period of 317 nm. Using these structures, the frequency doubling in the backward direction is achieved for the fundamental wavelength of 2309 nm. Here we report on the experimental investigation of the BSHG properties such as spectral band-width, temperature tuning, and temperature bandwidth by employing broadband and narrowband fundamental wave-length sources. The BSHG properties are compared with those of co-propagating second harmonic generation to reveal the BSHG potential for novel applications that were proposed theoretically but have not been realized in practice so far. (c) 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement