Half Cycle Terahertz Pulse Generation by Prism-Coupled Cherenkov Phase-Matching Method

Abstract

Nonlinear optical terahertz wave generation is a promising method for realizing a practical source with wide frequency range and high peak power. Unfortunately, many nonlinear crystals have a strong absorption in the terahertz frequency region. This limits efficient and widely tunable terahertz wave generation. The Cherenkov phase-matching method is one of the most promising techniques for overcoming these problems. We propose a prism-coupled Cherenkov phase-matching method, in which a prism with a suitable refractive index at terahertz frequencies is coupled to a nonlinear crystal. We demonstrate prism-coupled Cherenkov phase-matching terahertz generation using the DAST and LiNbO 3 crystals. With a DAST crystal, we obtain a spectral flat tunability up to 10 THz by difference frequency generation. With a LiNbO 3 crystal, we observe a spectral flat broadband terahertz pulse generation up to 5 THz pumped by a femto second fiber laser. The obtained temporal waveform is an ideal half cycle pulse suitable for reflection terahertz tomography.

Waveguided Approach for Difference Frequency Generation of Broadly-Tunable Continuous-Wave Terahertz Radiation

“…Generally, the THz frequency range, achievable with a DFG setup, coincides with the phase-matching (PM) bandwidth of the process, which, in accordance with Heisenberg's uncertainty principle, is limited by the finite interaction area within the nonlinear material [30]. Several different PM geometries have so far been adopted, including tilted-front-pulse generation [31], collinear and non-collinear quasi-PM in periodically-poled LN crystals [29], and Cherenkov generation [32,33]. The intensity-dependent self-beam-defocusing effects in LN [34,35], incompatible with the achievement of an adequate PM, have hampered the possibility to produce broadly-tunable and spectrally pure CW THz radiation by means of bulk nonlinear crystals.…”

Broadband terahertz wave generation from ridge waveguide

“…The THz radiation emanated as spherical waves from each point of the waveguide and was enhanced 50° from the pump-beam axis. Based on the PCC-PM method, a Si prism was used to cancel the total internal reflection and bring out the generated THz waves [10]. The incident beam entering the waveguide was monitored by an infrared vidicon camera (C2741 , Hamamatsu Photonics).…”

Nonlinear optical THz generation and applications

“…From the point of view of applied researches using terahertz-waves, there is a growing demand for sources that are simple and compact and provide a high-power output. In our laboratory, we have been developing several kinds of terahertz-wave sources using nonlinear optical effects [2][3][4][5][6][7][8][9][10]. Among them, we have recently focused on the improvement of the output of the THz parametric sources.…”