Using the widely-tunable monochromatic THz source developed by us recently, we have directly measured the transmission spectra of a few diatomic and triatomic molecules in the THz region. In addition, using the FTIR acquired from Bruker Optics, we have also measured the transmission spectra of the same molecules. As a result, we have observed distinct ro-vibrational and rotational transitions in two carbon monoxide isotopic variants, nitrogen dioxide, and carbon dioxide. After carefully analyzing these transmission spectra, we have identified a series of the transition peaks for each chemical species. The frequencies of the transition peaks measured by using two different methods agree with each other well. In order to determine the rotational constants for each chemical species, it is essential for us to accurately measure the transmission spectrum of the vapor of the chemical species in both of the mid-IR and THz regions.
We designed the Bragg reflectors and 2-D photonic crystals using the R-Soft BandSOLVE software. Following our initial designs, we fabricated the Bragg reflectors and 2-D photonic crystals on Si wafers by using two techniques, i.e. drilling holes using a UV laser and deep reactive ion etching. We then characterized the fabricated structures by measuring both the reflection and transmission spectra using the widely-tunable monochromatic THz source developed by us as well as FTIR. We analyzed and compared our results based on these two different techniques. We also investigated the dependence of the bandgaps on the fluctuation of the diameters of the air holes using the R-Soft software.