Frequency Controlled Terahertz wave Parametric Generation by a Spectral Drill Cavity

We demonstrated terahertz wave parametric wavelength conversion between frequency-controlled infrared (stabilized pumping and tunable seeding) beams and terahertz wave in a nonlinear crystal. The frequency stabilized pumping beam is amplified by an injection-seeded PPLN-OPG and KTAOPA pumped by a Nd:YAG MOPA system. The seeding beam is stabilized 1.5$\mu$ m beam as traceable to the national standard. The master laser of the MOPA system is a SLM Nd:YAG laser with duration of about 1 ns. The frequency of tunable seeding beam is monitored by using a “spectral drill” cavity. The cavity provides a continuous one-way sweep of the axis modes in a Fabry-Pérot cavity without sweeping the cavity length. When a geometric phase shifter composed of fixed and rotating phase plates is arranged within the cavity, the frequencies of the axis modes are controlled by the angle of the phase plate. The frequency of seeding beam is observed as intensity error signals. We used a nonlinear MgO:LiNbO
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crystal with a Si-prism as an efficient output coupler for the terahertz wave. The output terahertz wave was measured using a pyroelectric detector. We speculate that the frequency-controlled terahertz wave could be powerful tools not only for solving real world problems but also fundamental physics. We expect that these methods will open new fields.