A new dual-wavelength generator for high-efficiency difference frequency generation of terahertz wave

It has been two decades since the invention of THz wave difference frequency generation (DFG) by using organic crystal DAST. The dual-KTiOPO4 (KTP) optical parametric oscillator (OPO) structure is a kind of quite popular dual wavelength generator since it is convenient for realization. However, the imbalance of both pumping power and efficiency at two KTPs is normal, and it leads to a deviation from ideal 1:1 on the output energy ratio of dual wavelengths. In this paper, on one hand, we find a method to balance the output energy of dual-KTP OPO under most conditions. On the other hand, we propose to use two single-KTP OPOs to replace the dual-KTP OPO. In this way, both the power balance and beam pattern can be guaranteed, and thus the DFG efficiency is significantly improved. Compared with a non-optimized dual-KTP OPO setup (energy ratio 1:5), the DFG efficiency is enhanced by an average factor of 2.59 and a maximum factor of 8.68 (at 18.6 THz).