Efficient collinear frequency tripling of femtosecond laser with compensation of group velocity delay

This paper demonstrates an approach that negative uniaxial crystalhas a relative anomalous dispersion effect which can compensate groupvelocity delay, and applies this approach to nonlinear frequencyconversion of an ultrafast laser field. High efficiency of the thirdharmonic generation is experimentally fulfilled by adopting acollinear configuration of doubing-compensation-tripling system.Through finely adjusting the incident angle and optical axis directionof the compensation plate, it obtains ultraviolet (UV) output energy of0.32~mJ centered at 270~nm with spectral bandwidth of 2~nm wheninput beam at 800~nm was 70~fs pulse duration and 6~mJ pulse energywhich was extracted from Ti:sapphire laser system by a diaphragm,corresponding to an 800-to-270~nm conversion efficiency of 5.3%and a factor-of-1.6 improvement in the third harmonic generation ofUV band in comparison with a general conventional configuration.Furthermore, when the full energy of 18~mJ from a Ti:sapphire laser systemwas used and optimized, the UV emission could reach 0.83~mJ.