A novel THz spectrophotometer by integrating a widely-tunable monochromatic THz source with a detector based on up-conversion process

This SBIR Phase I project focuses on the implementation of a novel THz spectrophotometer. Such a goal is built upon the recent success of the implementations of widely-tunable monochromatic THz sources and the characterizations of Bragg reflectors and bio tissues. During the Phase-I period, we propose to reduce the linewidths of a Nd:YAG laser and OPO down to 0.003 wave numbers and 0.075 wave numbers, respectively, using an etalon and increase the output peak powers. We will investigate how to antireflection-coat a GaSe crystal near 2.128 µm and test the performance of the crystal by measuring its reflectivity. We plan to design, fabricate, and test a beamsplitter to efficiently split a THz wave from the 1.064-µm beam using a THz Bragg reflector. We will also achieve an up-conversion process by mixing a THz wave with a 1.064-µm beam. We continue to carry out our Phase-I tasks by designing and testing a THz cavity formed by a pair of the Bragg reflectors and fabricated on a zinc germanium phosphide crystal. We will test a mini spectrometer for separating two optical beams with their frequencies very close to each other. Finally, we plan to design a novel THz spectrophotometer based on a widely-tunable THz source and a detector based on the up-conversion process and then to perform the preliminary testing. After completing the above objectives, we will be ready to study the performance of the THz spectrophotometer for the point and remote detections of biological agents. We plan to perform the preliminary testing during Phase I and carry out the comprehensive investigations during Phase II. During Phase I Option period, we propose to optimize our initial design of the spectrophotometer including every single component. Moreover, we plan to carry out calculations on the performance of the optimized system and come up with modifications to further improve the performance. Furthermore, we will set up experiments to carry out the tests on the modified components. Finally, we will also study issues of how to make the THz spectrophotometer compact, portable, and suitable for battlefield deployment. To achieve these goals, we plan to investigate the issues of packaging, robustness, and required operating powers for the system. The efforts described above are considered as the initial Phase II activities.