Palm-Sized All-in-One Backward Terahertz-Wave Parametric Oscillator

We have developed an over 10-W peak-power, continuously frequency tunable backward terahertz (THz)-wave parametric oscillator (BW-TPO) in a palm-sized compact package. The driving pump source of a passively Q-switched 1064-nm Nd:YAG microchip laser, the BW-TPO gain medium of a slant-stripe-type periodically poled lithium niobate (PPLN) crystal mounted on a motorized rotation stage, and all the optical components, including a simple layout for injection seeding to the idler wavelength, were assembled as an all-in-one module. To extract the backward-propagating THz-wave output that overlaps with the pump beam line, a thin LN substrate coated with 1064-nm anti-reflection was used as a dichroic beam splitter with a high reflectivity of more than 90% at 0.3 THz. As a result, the monochromatic THz-wave output with a maximum peak power of 15 W was obtained at 0.33 THz. By tuning the quasi-collinear phase-matching condition via mechanical rotation of the PPLN crystal, continuous frequency tunability from 0.29 to 0.35 THz was achieved. THz-wave reflection imaging measurements were performed using a scan of the whole optical setup including the developed BW-TPO module installed on a 2-axis motorized translation stage. Our results confirm that the stable and robust operation of the robot-mountable compact all-in-one BW-TPO is ready for real-world THz-wave non-destructive sensing applications.