Compression of femtosecond pulses by multiplate continuum generators

During interaction between intense laser pulses and nonlinear medium we often encounter nonlinear optical phenomena such as supercontinuum generation (broadband spectrum radiation). Usually, supercontinuum is generated in a bulk condensed media. But this method by itself has a restriction for maximum energy which can be directed to that media. Usual initial radiation energy is a few μJ. In this work we investigated another technique for supercontinuum generation, so called, multi-plate system which was constructed from UV fused silica (UVFS) plates. This method allows to use higher energy pulses and avoid any optical damage. During experiment there were used seven UVFS plates. Plates had different thickness: five of them there 0,1 mm, other two – 0,2 mm. In experiment were used Ti:sapphire laser whose pulse duration was approximately 55 fs, and central wavelength – 800 nm. During supercontinuum generation pulse energy was 329 μJ. Plates configuration was as following: first five plates were thinner and the last two were thicker. Spectrum was broadened from 755 – 855 nm to 530 – 995 nm. Also, configuration there tested at different powers. Results showed that there is an optimal power which results in the widest and most intense supercontinuum. System had approximately 83 % transmittance. However, pulse after continuum generator is chirped that must be compensated. In a single stage supercontinuum generator setup, pulse will split into two and that will result in pedestal in spectral domain. For temporal pulse compression were used pulses stretched in time (chirped) mirror compressors, due to their low losses. To figure out which chirped mirrors are best for to compress continuum radiation there was performed white light interferometry experiment for all chirped mirrors that we had. From all collected data it was decided to pick four mirrors from eight measured ones. Four mirrors will make two compressor pairs for generated supercontinuum temporal compression. First pair group delay dispersion (GDD) mean value is around -75 fs2, second pair – -125 fs2 Also, these mirrors are suitable to reflect broadband spectrum light. The duration of the pump pulses used in the work, measured by the frequency resolved optical gating (FROG) method, was 55 fs. Then, using a two-stage multi-component continuum generator setup, it is possible to achieve pulse compression few times and generate sub-10 fs duration pulses