Title :
Techniques of non-collinear electro-optic sampling for efficient detection of pulsed terahertz radiation
Author :
Tani, Motoaki ; Kinoshita, T. ; Nagase, Tomohiro ; Ozawa, Seiichi ; Tsuzuki, S. ; Takeshima, D. ; Estacio, Elmer ; Kurihara, Keiichirou ; Yamamoto, Koji ; Bakunov, M.
Author_Institution :
Res. Center for Dev. of Far-Infrared Region, Univ. of Fukui, Fukui, Japan
Abstract :
Cherenkov radiation mechanism is an established technique to achieve phase matching between ultrashort optical pulses and terahertz (THz) waves having a large collinear velocity mismatch, in a nonlinear optical material such as LiNbO3 (LN). Phase matching is achieved with the optical and THz pulses propagating at angle with respect to each other. Recently, we have experimentally demonstrated that Cherenkov phase matching mechanism can also be used for efficient electro-optics (EO) sampling of broadband THz pulses [1]. In the detection case, the phase matching is achieved between an optical and THz pulse propagating non-collinearly at the Cherenkov phase-matching angle θC, satisfying the following equation: equation Here, ngLN is the group index of the EO crystal at the sampling optical wavelength and nTHzLN is the refractive index of the EO crystal in the THz frequency region. An advantage of the non-collinear Cherenkov phase matching is that we can find a corresponding Cherenkov phase matching angle, θC, for any electro-optic crystal at a given optical sampling wavelength. When the EO crystal has a much larger refractive index in THz frequency region compared to that in optical region, a coupling prism is used as illustrated in Fig. 1. Moreover, using a low-loss coupling prism can also reduce absorption in the EO crystal. Silicon is an ideal coupling prism material owing to low absorption losses and is non-dispersive in the THz frequency region. From Snell´s law, the incident angle α of THz wave with respect to the prism- EO crystal interface is given as follows: equation Equation (2) leads to the relation, sin β = cosθC. Therefore, Eq. (1) reduces to the following equation for the apex angle of the coupling prism (α) at the Cherenkov phase-matching condition given by the ratio of the group index of the EO c- ystal at the sampling optical wavelength ngLN, and the refractive index of Si, nTHzSi, in the THz frequency region: equation.
Keywords :
Cherenkov radiation; bow-tie antennas; electro-optical devices; high-speed optical techniques; light absorption; optical materials; optical phase matching; optical prisms; photoconducting devices; refractive index; signal sampling; terahertz wave detectors; terahertz waves; Cherenkov radiation mechanism; EO signal; Snell´s law; THz frequency region; THz source; absorption loss; apex angle; broadband THz pulse propagation; collinear EO sampling; collinear velocity mismatch; coupling prism material; electrooptic crystal; group index; noncollinear Cherenkov phase matching mechanism; noncollinear electrooptic sampling; nonlinear optical material; optical pulse propagation; optical sampling wavelength; photoconductive bowtie antenna; prism-EO crystal interface; pulsed terahertz radiation detection; refractive index; size 4 mm; ultrashort optical pulses wave; wavelength 1.55 mum; wavelength 780 nm; Crystals; Electrooptical waveguides; Optical frequency conversion; Optical pulses; Silicon;
Conference_Titel :
Physics and Engineering of Microwaves, Millimeter and Submillimeter Waves (MSMW), 2013 International Kharkov Symposium on
Conference_Location :
Kharkiv
Print_ISBN :
978-1-4799-1066-3
DOI :
10.1109/MSMW.2013.6622077