A terahertz (THz) radiation source plays an important role in many applications, such as in biophysics, detecting and imaging. However, an effective method to generate coherent THz radiation is still under development. Based on nonlinear optical techniques, a beat-wave laser with THz spectral modulation can be a useful tool to generate a coherent THz wave. We have previously generated a sub-ns coherent THz wave from a difference frequency generator pumped by a THz beat-wave laser near 1.55-𝜇m. On the other hand, highly efficient electron radiation at THz frequencies is achievable from an electron radiation device such as an undulator or a Smith-Purcell grating. However, electron bunching is the key for efficient electron radiation. We intend to generate THz bunched electrons directly from a photocathode electron accelerator by illuminating the photocathode with a UV THz-beat-wave laser. With the THz modulated electrons emitted from the cathode, a highly efficient and compact coherent THz radiation source can be realized.
In this thesis, a beat-wave seed laser was first generated by combining two continuous-wave (CW) diode lasers at telecom ~1.5-μm wavelengths. The combined CW beat-wave is then sent into an optical parametric amplifier (OPA) using a periodically poled lithium niobate (PPLN) crystal as a gain crystal. The OPA is pumped by an amplified passively Q-switch laser at 1064-nm. The OPA amplifies and modulates the seeding signals to further generate frequency sidebands through cascaded frequency mixing process in the PPLN crystal. The generated ~1.55-𝜇m beat-wave laser from the OPA was frequency quadrupled to achieve ~390-𝜇m in the second part of our experiment. In this part, three nonlinear optical crystals are used to triple the frequency of the infrared THz beat-wave laser to a UV one. A type-I PPLN crystal with grating period 20.6-𝜇m can provide a wide phase matching bandwidth for doubling the beat-wave laser at ~1.55-𝜇m to a beat-wave laser at ~780-nm. A LBO crystal is used to double the frequency of the ~780-nm beat-wave laser to obtain a wavelength at ~390-nm. In conclusion, we have demonstrated in this thesis a high power UV THz-beat-wave laser at ~390-nm with a beat frequency tunable from 0.25 THz to 1.5THz. This laser source can be useful to induce periodically bunched electron emission from a photocathode accelerator in the next endeavor.

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