In this paper, a high efficient terahertz source based on n-type gallium phosphide crystal via cryogenic process is investigated through collinear difference frequency generation pumper by 1064 nm Nd:YAG laser and its OPO system. Absorption coefficient of this crystal at THz range shows a dramatic decrease from ~ 50 cm-1 to 0.5 cm--1 as the temperature decreases from 300 k to 80 k. Four times enhancement of the terahertz emission power and much more broad spectra range (~ 0.2- 3.8 THz) has been achieved in this kind of 0.5 mm length gallium phosphide crystal during the whole varied temperature difference frequency generation from 300 k to 80 k. These results indicate that cooling down the crystal temperature is an effective way to improve the terahertz source property, such as terahertz output power and frequency range.
We launched into a development of a new stand-off sensing system that can detect atmospheric and hazardous gases in real atmosphere utilizing THz technology. Narrow line width, <0.1 cm-1, long-wave (mid-IR and THz) source based on difference frequency generation (DFG) in collinear configuration in GaSe0.91S0.09:Al(0.03 at. %) using seeded YAG laser and KTP OPO as pump sources was designed. The low optical loss coefficient and large hardness, together with the simplicity of the processing, make GaSe0.91S0.09:Al(0.03 at. %) as a high-reliable and effective THz-wave generator suitable for out-of-door application. We demonstrate incoherent terahertz wave detection by stand-off room temperature Schottky diodes located at over 110 m using open waveguide formed by multitude HPE lenses, mirrors and/or unpolished reflectors.
Mn1.56Co0.96Ni0.48O4 (MCN) films with different layers have been prepared on Al2O3 substrate by chemical solution deposition method. The microstructures, optical and electrical properties of the films are investigated. X-ray diffraction and microstructure analyses show good crystallization and both the crystalline quality and the grain size are improved with the increasing thickness of the films. Mid-infrared optical properties of MCN films have been investigated using transmission spectra. The results show the red shift of absorption with the increasing film thickness and the energy gap Eg decrease from 0.6422 eV to 0.6354 eV. All the MCN films show an exponential decrease in the resistivity with increasing temperature within the measured range. The temperature dependence resistivity can be described by the small polarons hopping model. Using this model, the characteristic temperature T0 and activation energy E of the MCN films were derived. With the film thickness increase, the T0 and E of the MCN films increase. The calculated room temperature coefficient of resistance (TCR) of MCN film with 100 layers is -3.5% K-1. The MCN films showed appropriate resistance and high value of TCR, these advantages make them very preponderant for thermal sensors.