[14p-211-1~17] 3.9 テラヘルツ全般

▲ [14p-211-17] Saturated absorption of vibrational band in antibiotic via an intense terahertz emission generated by tilted-pump-pulse-front scheme

〇(P)Ali Khumaeni^1,2、Hideaki Kitahara¹、Daiki Gotoh¹、Takashi Furuya¹、Kohji Yamamoto¹、Jessica Afalla¹、Masahiko Tani¹ (1.Research Center for Development of Far-Infrared Region, University of Fukui、2.Department of Physics, Diponegoro University, Semarang, Indonesia)

キーワード：Terahertz generation based on nonlinear optics, Tilted pump pulse front scheme, Saturated absoprtion in antibiotic

Nonlinear phenomena via high-intense terahertz have been observed in various materials including semiconductors. The nonlinear response of vibrational bands in material informs us the existence and strength of hydrogen bonding and the anharmonicity. In this study, saturated absorption of vibrational potential in antibiotic was observed via an intense terahertz (THz) emission generated by tilted-pump-pulse-front scheme (TPPF). The sample used in the experiment was chlortetracycline hydrochloride (CTCH), which is usually used as an antibiotic in veterinary medicine. The sample was provided in the pellet with a thickness of 1 mm and a diameter of 10 mm. Figure 1(a) shows the experimental setup used to generate high-intense THz emission. A femtosecond laser system (800 nm, 100 fs, 1 kHz, maximum pulse energy ~ 3 mJ) was used as the optical source for the generation and detection of THz emission. THz radiation is guided with four off-axis parabolic mirrors of different focal lengths to the EO detection optics consisting of ZnTe crystal (t=1 mm) and a balanced photodetector. The maximum THz electric field E_max at the focal point of THz beam was estimated to be 460 kV/cm. The terahertz electric field was varied by using a pair of wire-grid polarizers. The time-domain THz waveform was obtained in a standard THz-TDS scheme. The sample was placed at the focal point of THz beam in the four parabolic mirror system. All the measurements were conducted at room temperature at around 20^OC. Figure 1(b) shows the transmittance spectra of CTCH sample at various THz electric fields. The inter-molecular absorption band observed at 0.76 THz [2] shows saturation of absorption with increasing the THz electric field. However, their frequency shifts and broadening of the absorption bands are small, indicating the anharmonicity of these vibration modes are not strong.