Supercontinuum Injected Optical Parametric Amplification Method To Generate Ultrashort Mid-infrared Laser Pulses

Near infrared and Mid-infrared ultrashort laser pulses in the 1μm and 3μm～5μm spectral region are very important.The seeded 1.053μm pulse can be amplified in Nd;glass amplification system; on the other hand,Mid-infrared ultrashort pulse in the 3μm～5μm spectral range can provide valuable information on the vibrational dynamics in numerous physical,chemical,and biological systems.It is also applicated in the field of fundamental research,optical spectroscopy,remote sense,medical,environmental,detection,military and etc.After presented the definition and application of Mid-infrared laser briefly,the producing methods are introduced in detail and the comparison is done among these methods.At present, the Optical Parametric Amplification(OPA)is in common use.Collinear phase matching OPA model and non-collinear phase matching OPA model in MgO;LiNbO₃ crystal are built, spatial and temporal walk-off of the two models are analyzed too.In order to avoid the three waves' temporal walk-off,pump wavelength and seeded signal wavelength are tuned simultaneously,and the result is that it can't be avoided in the collinear phase matching OPA. For the purpose of compensating the group velocity's mismatching,phase matching angles, non-collinear angles and the best amplified signal wavelength which is changing with the pump wavelength are optimized in the non-collinear phase matching OPA.Permiting bandwidth of the signal light,the pump light and the idler light are all simulated,the result turned out to be that the bandwidth of the signal light's is larger,the Mid-infrared idler light's is enormous,but the pump's is less than 5nm.Both the bandwidths of the seeded light and the pump light are all several tens of nanometers when Mid-infrared spectral range signal is pumped directly.Optimized result is showen for different pump intensities,different seeded signal's intensities,and different crystal lengthes.In order to achieve precise synchronization of femtosecond pulses and a wider tuning bandwidth,experiment is done to produce ultrashort Mid-infrared laser pulse with super continuum light seeded OPA in MgO;LiNbO₃ crystal.Average output of the signal and the Mid-infrared is up to 520uJ,energy conversion efficiency is about 15.7%.The energy of the Mid-infrared light from 3.2μm to 4.1μm is about 126uJ.At present,this result is excellent for it's largest energy and the shortest pulse in China, it's also the largest energy generated by the same method in the world.