Novel THz-frequency spectrometers by integrating widely-tunable monochromatic THz sources and detectors, or arrays of emitters and detectors, with pho

By continuing teaming up with one of the most reputable university teams in THz science and technology, ArkLight proposes to carry out the tasks set for a Phase-II program following our success in Phase I. We are aimed at the further development of novel spectrometers to analyze chemicals in the vapor phase based on accurate measurements of the emission and absorption spectra due to the molecular inter-rotational transitions in the THz domain (100-1000 µm). The proposed analyzers are characterized by simplicity, reasonably high sensitivity, and high reliability. They are designed to analyze the gas samples taken from the hazardous battlefields or sites to stations or labs. The high reliability (i.e. low error probability) is assured by the fact that we plan to combine the unique sharp peaks determined from the THz emission with absorption spectra of the molecules. In addition, in order to achieve high sensitivities the proposed analyzers utilize 2-D photonic bandgap crystals (PBC’s) as narrowband filters to remove the unwanted background while minimizing the false alarm rate, cavities, and tightly-confined waveguide modes. Compared with other spectrum analyzers, our systems should have lower false alarm rates since we propose to match both the strengths and wavelengths for a large number of the transition peaks measured in an extremely wide wavelength range to those on the known hazardous chemicals stored in our data bank, using a software to be developed during Phase II. To achieve our goal we have taken advantages of our expertise in the tunable THz sources and the state-of-the-art fabrication and characterization. Moreover, our goal is built upon our most recent and preliminary results on chemical analysis including our achievements in the Phase I. We will fabricate and characterize the Bragg gratings and 2-D PBC's for the THz waves. The spatial confinement will be achieved by introducing defects into the PBC's. The next step will be the implementation of a tunable and coherent mid-IR source in the range of 9-11 µm – this range is sufficient to pump the most of the molecules of interest to the first vibrational transitions such that they can subsequently emit THz radiations between the rotational transitions. We plan to develop tunable mid-IR sources using intracavity difference-frequency generation in an optical parametric oscillator. We will implement a THz emission spectrometer after combining a mid-IR source, PBC’s, and a bolometer. We will also investigate a few novel configurations for increasing the conversion efficiencies for the THz generation by using intracavity frequency mixing in a waveguide for the THz wave and external frequency conversion in a THz waveguide combined with a pair of the THz Bragg gratings incorporated into the nonlinear materials through the fabrication. We will then implement an absorption spectrometer by combining an efficient and tunable THz source based on difference-frequency generation in GaP with a pyroelectric detector. In order to explore the ultimate detection limit of the proposed spectrometer, we are going to investigate an up-conversion process in GaP. For the emission spectrometer, we will be able to achieve a sensitivity of better than 1 ppm. On the other hand, for the absorption spectrometer our goal is to be able to measure the absorbance as low as 3 ppm.