Backward wave optical parametric oscillator pumped by subnanosecond microlaser pulses

Microlaser-pumped subnanosecond pulse duration optical parametric generators have great potential to establish themselves as a compact, simple, and cost-effective option for various tasks that do not require high temporal resolution. However, fundamental limitations of co-propagating three-wave interaction, including broad bandwidth, non-transform-limited pulses, and suboptimal spatial coherence of the output, restrict their suitability for demands of high spectral purity and beam quality. In this report, we address these shortcomings and present the first Backward Wave Optical Parametric Oscillator (BWOPO) pumped by transform-limited subnanosecond pulses from Nd:YAG microlaser. This paper reports a thorough performance investigation of BWOPO setups pumped by the first (1064 nm) and second (532 nm) harmonics of the microlaser. Based on a periodically poled Rb-doped KTiOPO4 crystal with a 427 nm grating period, BWOPO achieved nearly transform-limited pulses and diffraction-limited beams of the signal and idler waves in the near and mid-infrared with 50% conversion efficiency. A degenerate BWOPO operation is also presented. 792.5 nm wavelength pumped, temperature-tuned degenerate BWOPO generated a narrowband counter-propagating signal and idler centered at 1585 nm. This experiment also revealed thermal instability of the ferroelectric domain structure, resulting in a twofold decrease of the crystal’s effective nonlinearity.