Electronic resonant multiplex SFG spectroscopy with tunable UV probe

我们已经构建了一个多路IR-UV SFG光谱仪，它具有较宽的UV探测波长可调范围(235-400 nm)。使用棱镜单色器作为可调谐锐切带通滤光器，以减少由于紫外光探头散射引起的杂散光，从而使可调范围内的任何波长都可以被选择为可见探头的波长。红外-紫外SFG光谱仪：探头光源基于工作在1 kHz的钛宝石放大器。利用非线性光学技术对放大器的基波输出进行转换，获得了飞秒宽带(200 cm；-1)的红外脉冲和皮秒窄带宽(10 cm；-1)的紫外光脉冲作为探测光。紫外光脉冲的波长在235-400 nm范围内可调。使用一台光栅多色仪(f=55 cm，4320槽/mm)和棱镜单色仪(f=20 cm)作为光谱仪来分析宽带SFG信号。棱镜单色器作为一个可调谐的锐切带通滤光器，以减少由于紫外光探测器的散射而引起的杂散光。测试测量：测试测量在金衬底上的对巯基苯甲酸(HOOC-C6H4-SH)单分子膜上进行。用289 nm和334 nm的紫外光探针测量了对巯基苯甲酸在金衬底上的SFG光谱。在光谱上确定了两个振动带。这些谱带被归属为苯环伸展(~1590 cm^&lt；-1&gt；)、COOH伸展(~1746 cm^&lt；-1&gt；)。289 nm的拉伸模的SFG强度是334 nm探头的3倍。这种增强归因于电子共振效应，分子在275 nm处有很强的吸收。

We have constructed a multiplex IR-UV SFG spectrometer that has a wide tunable range (235-400 nm) of the UV probe wavelength. A prism monochromator was used as a tunable sharp-cut bandpass filter to reduce stray light due to the scattering of the UV probe so that any wavelength within the tunable range can be chosen as that of the visible probe.The IR-UV SFG spectrometer : The probe light source is based on a Ti : sapphire amplifier operated at 1 kHz. A femtosecond broad-bandwidth (200 cm^<-1>) IR pulse and a picosecond narrow-bandwidth (10 cm^<-1>) UV pulse are obtained as the probe lights by converting the fundamental output of the amplifier with nonlinear optical techniques. The wavelength of the UV pulse is tunable in the range of 235-400 nm. A grating polychromator (f=55 cm, 4320 grooves/mm) combined with a prism monochromator (f=20 cm) is used as the spectrograph for analyzing broad-bandwidth SFG signal. The prism monochromator acts as a tunable sharp-cut bandpass filter to reduce stray light due to the scattering of the UV probe.Test measurements : Test measurements were conducted on a p-mercaptobenzoic acid (HOOC-C_6H_4-SH) monolayer on a gold substrate. SFG spectra of p-mercaptobenzoic acid on a gold substrate were measured with 289 nm and 334 nm UV probes. Two vibrational bands were identified on the spectrum. These bands were assigned to phenyl ring stretch (〜1590 cm^<-1>), COOH stretch (〜1746 cm^<-1>). The SFG intensity of the stretch mode with 289 nm was three times larger than that with 334 nm probe. The enhancement was ascribed to due to electronic resonant effect with a strong absorption of the molecule located at 275 nm.