Nonlinear Optics with Two-Colour Lasers

激光在50年前改变了光学研究，现在已经催生了无数的应用。激光工作在从红外到紫外线的许多波长，但要完全覆盖光谱，需要非线性光学。超短脉冲激光现在可以通过一种名为光学整流的非线性过程产生远红外辐射，并可以通过高次谐波产生将频率非线性驱动到极紫外光。然而，仍然存在一些光谱间隙，这一建议旨在填补从6到25微米的“分子指尖”光谱区域，几乎每个分子在其吸收光谱中都有一个独特的特征。随着在环境监测和医疗应用中的应用，对于在这些波长具有强吸收线的爆炸物的痕量气体检测来说，这一光谱区域变得越来越重要。在滑铁卢，我们正在开发一种双色、短脉冲光纤激光系统，通过在非线性晶体中对两个激光输出进行不同频率的混频，将在指纹区域产生具有足够功率的中红外波长，用于微量气体检测。 自从频闪镜发明以来，通过不断减小光脉冲持续时间，已经观察到越来越快的运动。我们正在提议产生一种高强度、超短(~2ps)脉冲的来源，可以用来制作任何分子振动运动的定格电影。要产生如此短的脉冲，需要一道宽阔的颜色栅栏，横跨从紫外线到红外线的光谱区域。双色钛宝石激光系统将通过多频拉曼产生的非线性过程，产生如此宽的频率梳。我们将首先研究这个非线性过程，以便我们可以优化许多颜色光谱。然后，我们将把所有的颜色连贯地加在一起，以产生观察和测量分子运动所需的超短、高强度脉冲。

Lasers transformed optics research 50 years ago and have now spawned innumerable applications. Lasers operate at many wavelengths from the infrared to the ultraviolet, but to completely cover the optical spectrum, nonlinear optics is needed. Ultrashort pulse lasers can now generate far-infrared radiation through a nonlinear process known as optical rectification and can nonlinearly drive the frequency up to the extreme ultraviolet by high order harmonic generation. However, some spectral gaps still exist and this proposal aims to fill in the "molecular fingerpint" spectral region from 6 to 25µm, where almost every molecule has a distinctive signature in its absorption spectra. Along with applications in environmental monitoring and medical applications, this spectral region is becoming increasingly important for trace gas detection of explosives that have strong absorption lines at these wavelengths. At Waterloo, we are developing a two-colour, short pulse fiber laser system, which will generate mid-infrared wavelengths across the fingerprint region with sufficient power for trace gas detection, by difference frequency mixing the two laser outputs in a nonlinear crystal. Since the invention of the stroboscope, increasingly faster motion has been observed by ever decreasing optical pulse durations. We are proposing to generate a source of high intensity, ultra short (~2 fs) pulses that can be used to make a freeze frame movie of the vibrational motion of any molecule. To make such a short pulse, requires a wide picket fence of colours that spans the spectral region from the ultraviolet to the infrared. A two-colour, Ti:sapphire laser system will be used to generate such a wide frequency comb, through the nonlinear process of multi-frequency Raman generation. We will first study this nonlinear process so that we can optimize the many colour spectra. We will then coherently add all the colours together to create the ultra short, high intensity pulses needed to watch and measure molecular motion.