We developed a reflection type ultra-broad band terahertz time-domain spectroscopic ellipsometry covering the frequency range from 0.5 to 30 THz. The system utilizes two nonlinear optical crystals of GaP and GaSe as terahertz and mid-infrared sources, respectively, and employs a detector based on a photoconductive antenna switch using a low temperature grown GaAs (LT-GaAs) epitaxial layer transferred on Si substrate. By switching the emitter, the measurable frequency range can be easily changed from the 0.5-7.8 THz range to the 7.8-30 THz range without additional optical alignment. We measured the dielectric function of a p-type InAs wafer and the complex optical conductivity of an indium tin oxide (ITO) thin film. The obtained carrier density and the mobility of the ITO thin film show good agreement with that obtained by the Hall
We report the experimental results of physiologically active substances including hormones utilizing Terahertz (THz)
spectrum technology. Various analytical techniques have been employed for the determination of physiologically active
substances. Most of methods used oxidation reagent and sodium sulfite stabilization reagent or fluorescent reagent.
These methods had a good selectivity, but the stability of samples was not satisfactory. The direct detection method has
not been advanced yet. In this study, the THz characteristics of physiologically active substances were measured directly.
We found all of samples have their vibrational features like signature peaks either in pellet and/or sample solution. A
membrane device was used to hold the sample solution in this study. This device allows samples to be prepared in
solutions and measured easily with THz measurement system after dried. Results suggest that this membrane device is
sensitive for detecting the physiologically active substances in THz ranges. THz spectrum technology has the potential to
be a useful tool in clinical applications. This approach promotes the understanding of the relationships between
biomolecules with THz radiation.
Recent progress in the field of terahertz (THz) imaging is overviewed. First, various THz-wave sources developed and recently improved in our group are described. Second, imaging of samples can be achieved in different modes, of which we discuss here the transmission mode and the reflection-scattering mode. An emphasis in placed on the latter, which can be used to detect and determine for example the distribution of powders inside THz-transparent containers and packages. One-frequency or wide-spectrum imaging can be extended to chemical imaging, a technique by which images acquired at different THz frequencies can be combined to allow the identification of the chemical composition of the target at each spatial position. Other THz imaging applications are also discussed.
We have studied the generation of terahertz (THz) waves by optical parametric processes based on laser light scattering from the polariton mode of nonlinear crystals. Using parametric oscillation of LiNbO3 or MgO-doped LiNbO3 crystal pumped by a nano-second Q-switched Nd:YAG laser, we have realized a widely tunable coherent THz-wave sources with a simple configuration. We report the detailed characteristics of the oscillation and the radiation including tunability, spatial and temporal coherency, uni directivity, and efficiency. A Fourier transform limited THz-wave spectrum narrowing was achieved by introducing the injection seeding method. Further, we have developed a spectroscopic THz imaging system using a TPO, which allows detection and identification of drugs concealed in envelopes, by introducing the component spatial pattern analysis. Several images of the envelope are recorded at different THz frequencies and then processed. The final result is an image that reveals what substances are present in the envelope, in what quantity, and how they are distributed across the envelope area. The example presented here shows the identification of three drugs, two of which illegal, while one is an over-the-counter drug.
High-sensitivity terahertz direct detectors using superconducting tunnel junctions were fabricated. They were designed for detecting terahertz radiation in the frequency range of 0.4 and 0.65 THz with the fractional bandwidth of above 10 percent. The results of their performance evaluation of five detector elements are presented. We show the results of the frequency response as well as that the absolute efficiency ranged from 10 to 30 percent and that the the
sensitivity was 1.9 x 10-16 W Hz-0.5 in noise equivalent power.
We have proposed and demonstrated a nondestructive and non-contact inspection method for electrical faults using laser-Terahertz (THz) emission microscopy (LTEM). By measuring the position dependence of the amplitude of the THz emission from integrated circuits (IC) excited with femtosecond (fs) laser pulses, it is possible to investigate the electrical faults in IC. By improving the spatial resolution of the system, we successfully observed the THz emission
image of a microprocessor on standby mode. The LTEM system has a spatial resolution about 3µm and it can localize electrically defective sites in the chip to within a ten square microns.