Nonlinear optics for short pulse and mid-infrared applications

自从埃德沃德·迈布里奇第一次能够拍摄到赛马停止的运动以来，光脉冲技术已经发展到现在可以产生53阿秒的短脉冲。这个时间尺度与电子围绕原子核运行的时间相对应。观察电子的运动并不像拍照那么简单。为了看到这些微小的物体，需要使用非线性或多光子技术。该方案旨在产生具有足够功率的超短脉冲，以产生非线性效应。所提出的源将产生峰值功率为千兆瓦的单个飞秒脉冲，并可用于测量分子中原子振动的停止运动。 要产生超短脉冲，需要产生非常宽的频谱。宽光谱是通过使用较长脉冲的非线性光学过程产生的。聚焦到分子气体中的两个具有不同颜色的强激光脉冲将导致分子以与两个激光脉冲频率之差匹配的频率振动。然后，分子的振动频率与光学频率混合，产生新的颜色，其中每种颜色都由振动频率分开。这种颜色覆盖了从红外线泵浦脉冲到紫外线的光谱范围。 这项提议不仅涉及到制作一组超广泛的颜色，而且还涉及到让每种颜色都变得宽泛。以这种方式，当颜色被定时在一起以形成一串光脉冲时，该串中将有非常少的脉冲，并且可以最大化每脉冲的功率。 宽频产生的非线性过程首先要求研制高功率双色激光光源。这种新的双色激光光源还可以用来产生短脉冲源很少的长波长中红外辐射。随着在环境监测和医疗应用中的应用，对于在这些长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。

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.