Abstract-The effect of an optical pump on the absorption coefficient of magnesium-doped near-stoichiometric lithium niobate in terahertz range

Zuo Zhi-Gao (左志高)1,2, Ling Fu-Ri (凌福日)2, Ma De-Cai (马德才)3, Wu Liang (吴 亮)4, Liu Jin-Song (刘劲松)1 and Yao Jian-Quan (姚建铨)1,4

http://iopscience.iop.org/1674-1056/22/10/107802;jsessionid=7FFAC9924135B52A23278DDB2468455C.c2
ingfuri@163.com

1 Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China
2 School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China
3 Sino-French Institute of Nuclear Engineering & Technology, Sun Yat-Sen University, Guangzhou 510275, China
4 College of Precision Instrument and Optoelectronics Engineering, Tianjin University, Tianjin 300072, China 

The absorption coefficient of magnesium-doped near-stoichiometric lithium niobate crystal is measured by terahertz time-domain spectroscopy in a frequency range of 0.2 THz–0.9 THz at room temperature. The absorption coefficient is modulated by external optical pump fields. Experimental results show that the absorption coefficient of near-SLN:Mg crystal is approximately in a range of 22 cm−1–35 cm−1 in a frequency range of 0.2 THz–0.9 THz and tunable up to nearly 15%. Further theoretical analysis reveals that the variation of absorption coefficient is related to the number of light-induced carriers, domain reversal process, and OH−absorption in this crystal.

Abstract-Observation of suppressed terahertz absorption in photoexcited graphene

http://graphenetimes.com/2013/01/observation-of-suppressed-terahertz-absorption-in-photoexcited-graphene/

Authors: A. J. Frenzel, C. H. Lui, W. Fang, N. L. Nair, P. K. Herring, P. Jarillo-Herrero, J. Kong, N. Gedik

When light is absorbed by a semiconductor, photoexcited charge carriers enhance the absorption of far-infrared radiation due to intraband scattering. We observe the opposite behavior in monolayer graphene, a zero-gap semiconductor with lin- ear dispersion. By using time domain terahertz (THz) spectroscopy in conjunction with optical pump excitation, we observe a reduced absorption of THz radiation in photoexcited graphene. The measured spectral shape of the differential optical conductivity exhibits strongly non-Drude behavior. We discuss the influence of hot optical phonons, thermally broadened carrier distribution, and stimulated emission of THz radiation on the low-frequency non-equilibrium optical response of graphene.

arxiv.org