Nonlinear optics for short pulse and mid-infrared applications

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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.