Pulses In The Mid Infrared

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Introduction ANU researchers have developed a technique for generating ultra-short pulses. The process uses a high gain optical parametric amplifier where the pump pulses undergo a single pass through a relatively long optical parametric amplifier crystal. Background The mid-infrared is an exceptionally important wavelength range since in this range all molecules can be identified through their characteristic absorption spectra. In addition the mid infrared is the region where thermal sources can be identified by their characteristic emissions and hence is important for sensing and defence. Currently several different coherent optical sources exist in this region including quantum cascade lasers, infrared diode lasers, gas lasers notably CO2 and CO and optical parametric oscillators and optical parametric generators. For many of these systems the output is in the form of continuous emission or relatively long pulses in the picosecond or nanosecond range. Sources of sub-picosecond pulses in this wavelength range are relatively few and are restricted to complex system based on synchronously pumped optical parametric oscillators (OPO) where the pump powers need not be very high, or optical parametric generators (OPG) which need to be pumped by very powerful ultrashort pulse lasers. What is needed is an alternative way of generating ultra-short pulses that permits vastly simplified hardware compared with the techniques described above. Opportunity We have developed a technique that uses a high gain optical parametric amplifier in which the pump pulses undergo a single pass through a relatively long optical parametric amplifier crystal such as periodically poled lithium niobate. T he key to the technology is the recognition that in certain conditions the deleterious effects of the different group velocities of the interacting pulses can be eliminated and the conditions that best achieve this also provide an advantage of improved efficiency of the optical parametric amplifier.