Tunable Backward THz-Wave Parametric Oscillator Centered at a High Frequency of 0.87 THz

We present the first demonstration of a “high frequency” backward THz-wave parametric oscillator designed for a center frequency of 0.87 THz by quasi-collinear phase matching in a slant-stripe-type periodically poled lithium niobate crystal when pumped with sub-nanosecond pulsed source of $\lambda=$ 1064.44 nm. Along with the THz wave, an idler wave appears simultaneously with $\lambda=1067.75\mathrm{n}\mathrm{m}$. We also show that the oscillation frequency is tunable by a simple crystal rotation, spanning the range of 0.836–0.905 THz based on the change in the spectral line separation between the pump and idler beams. The threshold pump energy for BW-TPO was determined to be 12.4 mJ, equivalent to a pump intensity of 7.24 $\mathrm{G}\mathrm{W}/\mathrm{c}\mathrm{m}^{2}$ while obtaining a conversion efficiency as high as 8.39% at a pump energy (intensity) of 15.5 $\mathrm{m}\mathrm{J}(9.05\mathrm{G}\mathrm{W}/\mathrm{c}\mathrm{m}^{2})$.