Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science (IBS), Korea University, Seoul 02841, Korea.
Department of Chemistry, Korea University, Seoul 02841, Korea.
Int J Mol Sci. 2022 Oct 31;23(21):13245. doi: 10.3390/ijms232113245.
The spectral range of femtosecond time-resolved infrared spectroscopy is limited by the bandwidth of mid-IR pulses (100~400 cm) generated from the combination of Ti:Sapphire amplifier, Optical Parametric Amplifier (OPA), and Difference Frequency Generation (DFG). To overcome this limitation, we implement a compact continuum mid-IR source producing ultrafast pulses that span the frequency range from 1000 to 4200 cm (from 10 to 2.4 μm), which utilize the mixing of fundamental, second-harmonic, and third-harmonic of 800 nm pulse in the air. After building an IR spectrometer with continuum IR and a monochromator, we found that the distortion of the measured IR spectrum originated from the contamination of higher-order diffraction. We used bandpass filters to eliminate the higher-order contributions and correct the measured IR spectrum. We further characterized the spectral properties of fundamental, second-harmonic, and third-harmonic fields after the plasmonic filamentation process, which helps to improve the efficiency of the continuum IR generation. Using the generated continuum IR pulses, we measured the IR absorption spectrum of a water-benzonitrile mixture, which was found to be consistent with the spectrum obtained with a commercial FT-IR spectrometer. The present work will be useful for the efficient generation of continuum IR pulses for IR pump-probe and two-dimensional IR spectroscopy experiments in the future.
飞秒时间分辨红外光谱的光谱范围受到从中红外脉冲（100~400cm）带宽的限制，这些中红外脉冲是由钛宝石放大器、光参量放大器（OPA）和差频产生（DFG）组合产生的。为了克服这一限制，我们实现了一种紧凑的连续体中红外源，产生超快脉冲，其频率范围从 1000 到 4200cm（从 10 到 2.4μm），利用在空气中的 800nm 脉冲的基频、二次谐波和三次谐波的混合。在构建了带有连续体红外和单色仪的红外光谱仪之后，我们发现测量红外光谱的失真源于高阶衍射的污染。我们使用带通滤波器消除高阶贡献并校正测量的红外光谱。在等离子体细丝化过程之后，我们进一步表征了基频、二次谐波和三次谐波场的光谱特性，这有助于提高连续体红外产生的效率。使用产生的连续体红外脉冲，我们测量了水-苯甲腈混合物的红外吸收光谱，发现其与商用傅里叶变换红外光谱仪获得的光谱一致。本工作将有助于未来的红外泵浦探测和二维红外光谱实验中有效产生连续体红外脉冲。
