Widely-tunable, Compact, and Portable Terahertz Source Based on Intracavity Difference-Frequency Generation in Dual-Frequency Yb:YAG Laser for Identification and Detection of Biological Agents

摘要

Report developed under topic No. A10-076, contract W911NF-11-C-0044. The purpose of the work is to make a proof-of-concept demonstration on THz generation by using a dual-frequency laser in a nonlinear crystal. We have achieved all the objectives set for Phase I. In particular, we designed CW and Q-switched Yb:YAG lasers, purchased all the components necessary, assembled them into laser systems, optimized the setups, and tested the performances of the CW and Q-switched laser systems. Such laser systems were pumped by diode lasers at 940 nm. We achieved the broadband emission from the CW laser system. By placing an etalon in the laser cavities, we generated a pair of the output wavelengths around 1 micron from the CW and Q-switched laser systems. As a result, we successfully demonstrated the dual-frequency operation of the CW and Q-switched laser systems. Using the Q-switched dual-frequency laser, we generated THz pulses in a GaP crystal based on difference-frequency generation. We also confirmed the polarizations of the THz output pulses. Based on our calculations, the THz output powers can reach 8.5 mW through optimizations. We developed a concrete plan for identification and detection of biological agents, which is regarded as the major application of the THz spectrometer.