High-repetition-rate THz parametric oscillator based on an electro-optic Q-switched laser

A high-repetition-rate and high-peak-power terahertz parametric source based on the stimulated polariton scattering in MgO: LiNbO₃ crystal has been demonstrated using an electro-optic Q-switched nanosecond Nd: YAG laser. The high-repetition-rate 1064 nm pump laser under 1 kHz was built with a L-shape cavity, where the maximum average power reaches 7.26 W with the pulse width of 12 ns. By optimizing the diameters and position of pump beam waist in MgO: LiNbO₃ crystal, the maximum average THz-wave output power reaching 29.69 µW has been obtained at 1.78 THz, corresponding to the THz-wave peak power of 4.2 W. The tunable THz-wave frequency was in the range of 1.06-3.18 THz. The THz-wave beam quality factor M² was estimated to be 1.81 × 4.32 in the x and y directions, respectively. Furthermore, this THz parametric source is used to characterize KDP and its deuterated counterpart DKDP crystals. A clear fingerprint peak was observed at 2.3 THz in DKDP but not in KDP. This work demonstrates the potential of this THz parametric source's potential in characterizing and imaging crystalline materials with subtle structural variation.