Spectroscopy in the Terahertz Region

Prof. Hitoshi Odashima

Department of Physics, Meiji University, Japan

孙振东 教授

2015-11-04 16:10

知新楼C702 量子报告厅

The terahertz region (1-10 THz) is sometimes called “the gap in the electromagnetic spectrum”, because it is difficult to produce tunable coherent terahertz radiation. However, several techniques have been developed for spectroscopy in this region. One of them uses the difference frequency of two CO2 lasers generated in a metal-insulator-metal (MIM) diode and covers the region up to 6.5 THz, limited by the maximum frequency difference between two CO2 lasers. This technique is extended to 9.1 THz by replacing one of the two CO2 lasers with a 15NH3 laser and enables us to perform high-resolution spectroscopy in all the terahertz region. Unfortunately this technique is used by only a few groups because a good MIM diode is very difficult to make and easily broken by a mechanical shock.

Recently a GaAs photoconductive antenna was developed and is used for the time-domain spectroscopy (THz-TDS). This device provides the terahertz radiation by generating the difference frequency of two semiconductor near-infrared lasers and enables us to observe terahertz spectra. Since the spectrometer consists of solid state devices such as a photoconductive antenna and semiconductor lasers, it is easy to operate and successfully used to observe the spectra of water vapor and methanol in the 1-3 THz region. When the GaAs photoconductive antenna is excited by the femtosecond pulse from a Ti:sapphire laser, it generates a pulse of terahertz radiation. This pulse is detected after transmitting the sample and then the observed signal is Fourier transformed to give the absorption spectrum of the sample in the 1-5THz region. The THz-TDS is applied to observe the spectra of amino acids and the observed spectra are compared with the calculations based on the density functional theory.

1962.8 Born in Kawasaki, Japan

1991. 3 Ph.D. from Tokyo University

1991.4 ~ 2004.3 Department of Physics, Toyama University

2004.4 ~ present Department of Physics, Meiji University

1996.4 ~ 1997.3 Guest Researcher at National Institute of Standards and Technology (U.S.A )

2009.4 ~ 2010.3 Guest Researcher at Fritz-Haber Institute of Max Planck Society (Germany )