Nonlinear optics for short pulse and mid-infrared applications

自从 Eadweard Muybridge 首次能够拍摄赛马的停止运动以来，光脉冲技术已经发展到现在可以产生 53 阿秒的短脉冲。 这个时间尺度对应于电子绕原子核运行的时间。 观察电子运动并不像拍照那么简单。 为了看到这些微小物体，需要非线性或多光子技术。 该提案旨在产生具有足够功率的超短脉冲来产生非线性效应。 所提出的源将产生具有千兆瓦峰值功率的单个飞秒脉冲，可用于测量分子中振动的原子的停止运动。 为了产生超短脉冲需要生成非常宽的频谱。 宽光谱是通过使用较长脉冲的非线性光学过程产生的。具有不同颜色的两个强激光脉冲聚焦到分子气体中将导致分子以与两个激光脉冲的频率之间的差异匹配的频率振动。然后，分子的振动频率与光学频率混合并产生新的颜色，其中每种颜色由振动频率分开。 这些颜色跨越了从红外泵浦脉冲到紫外光的光谱。 该提案不仅涉及制作一组超广泛的颜色，而且还涉及使每种颜色变得广泛。 这样，当颜色一起计时以形成一串光脉冲时，该串中的脉冲将非常少，并且每个脉冲的功率可以最大化。 宽频产生的非线性过程首先需要开发高功率双色激光源。 这种新型双色激光源还可用于在短脉冲源很少的情况下产生长波长中红外辐射。 随着环境监测和医疗应用的应用，该光谱区域对于在这些长波长下具有强吸收线的爆炸物的痕量气体检测变得越来越重要。

Since Eadweard Muybridge was first able to photograph the stopped motion of a racing horse, optical pulse technology has evolved to now create pulses as short at 53 attoseconds. This timescale corresponds to the time electrons orbit a nucleus. Watching the electron move is not as simple as taking a photograph. In order to see these tiny objects, nonlinear or multi-photon techniques are needed. This proposal aims to create an ultrashort pulse with sufficient power to create the nonlinear effects. The proposed source would produce single femtosecond pulses with gigawatt peak power and could be used to measure the stopped motion of an atom vibrating in a molecule. To produce the ultrashort pulses requires the generation of a very broad frequency spectrum. The broad spectrum is created through a nonlinear optical process using longer pulses. Two intense laser pulses having different colours focused into a molecular gas will cause the molecules to vibrate at a frequency matching the difference between the frequencies of the two laser pulses. The molecule's vibrational frequency then mixes with the optical frequency and creates new colours, where each colour is separated by the vibrational frequency. The colours span the optical spectrum from the infrared pump pulses out to the ultraviolet. This proposal is concerned with not only making an ultrabroad set of colours, but making each of the colours broad. In this way, when the colours are timed together to make a train of optical pulses, there will be very few pulses in the train and the power per pulse can be maximized. The nonlinear process of broad frequency generation first requires the development of a high power two-colour laser source. This new two-colour laser source can also be used to generate long wavelength mid-infrared radiation where there are very few short pulse sources. 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 long wavelengths.