Development of a time-resolved multiplex surface sum-frequency spetrometer

研制了一种可见光探头波长可调的时间分辨多路红外-可见和频光谱仪。光谱仪概述：该光谱仪基于双通道光学参量放大器，产生宽带飞秒红外脉冲和窄带宽皮秒可见脉冲（470-800和401 nm）。激光系统的重复频率为1khz。单次测量可获得400 cm^<-1>光谱区域的SF光谱，分辨率为8-13 cm^<-1>。267 nm的紫外脉冲，800 nm飞秒输出的三次谐波，也可用于光激发样品进行泵-探针型SFG测量。(1)利用400、47、535、633 nm的可见探针，在金衬底上自组装十八硫代酸酯单层上测量了CH拉伸区域的Au -频率光谱。VRSFG光谱中的振动带形状随可见激光波长的变化而急剧变化。我们将这种光谱变化归因于来自金衬底的振动非共振信号与可见探针波长的相位变化。(2) TiO_2上的全反式维甲酸酯离子单层膜（110）采用480 nm可见探针和频谱法对全反式维甲酸酯离子单层膜进行了表征。在1580和1405 cm^<-1>处观测到两条强振动的SFG带。波段的强强度是由于SFG信号的电子共振。1580 cm^<-1>波段主要为视黄醇发色团共轭C=C双键的同相拉伸振动，1405 cm^<-1>波段主要为羧酸离子与TiO_2（110）的对称-COO拉伸振动，其中两个氧原子位于桥键的五重配位Ti原子上。

We have developed a time-resolved multiplex infrared-visible sum-frequency spectrometer with wavelength tunability of the visible probe.An overview of the spectrometer :The spectrometer is based on a two-channel optical parametric amplifier producing a broad-bandwidth femtosecond infrared pulse and a narrow-bandwidth picosecond visible pulse (470-800 and 401 nm). The repetition rate of the laser system is 1-kHz. An SF spectrum over a 400 cm^<-1> spectral region with 8-13 cm^<-1> resolutions is obtainable by a single measurement. UV pulse at 267 nm, a third harmonic of 800 nm femtosecond output, is also available to photoexcite a sample for pump-probe type SFG measurements.Applications of the speterometer :(1)Alkanethiolate monolayer on AuSum-frequency spectra were measured on a self-assembled monolayer of octadecanethiolate on a Au substrate for the CH stretching region with 400,477,535,and 633 nm visible probe. Vibrational band shapes in VRSFG spectra were drastically changed with wavelength of the visible laser. We ascribed this spectral change to the change in the phase of vibrational nonresonant signal from Au substrate with wavelength of visible probe.(2)All-trans retinoate ion monolayer on TiO_2(110)An all-trans retinoate ion monolayer was assessed by sum-frequency spectroscopy with 480-nm visible probe. Two strong vibrational SFG bands were observed at 1580 and 1405 cm^<-1>. The strong intensities of the bands were due to electronic resonance of the SFG signal. The 1580 cm^<-1> band was assigned to the predominantly in-phase stretching vibration of the conjugated C=C double bonds of retinyl chromophore, and the 1405 cm^<-1> band to the symmetric -COO stretching vibration of carboxylate ions attached to TiO_2 (110) with the two oxygen atoms on bridge-bonded fivefold coordinated Ti atoms.