Few-cycle, Gapless, and Intense Terahertz Source for Nonlinear Terahertz Spectroscopy
Ultrashort energetic terahertz (THz) pulses have opened up exciting new avenues of research in the field of light-matter interactions. For material studies in small laboratories, researchers often require widely tunable femtosecond THz pulses with a peak field strength close to MV/cm. Currently, these pulses can be generated through optical rectification and difference frequency generation in crystals without inversion symmetry. We present in this talk a novel approach for generating THz pulses with no frequency tuning gap. Our method is based on Raman-resonance-enhanced four-wave mixing in centrosymmetric media, specifically diamond. We demonstrate that this technique enables the generation of highly stable, few-cycle pulses with near-Gaussian spatial and temporal profiles. Using a 0.5-mm-thick diamond, we were able to generate THz pulses with a stable and controllable carrier-envelope phase. These pulses carried approximately 15 nJ of energy per pulse at 10 THz, with a peak field strength of about 1 MV/cm at the focus. Experimental measurements of the THz pulse characteristics were in good agreement with theoretical predictions. Furthermore, we discuss additional advantages of our scheme, including the potential for improving the THz output energy to even higher levels.