Spectral and temporal modulation and characterization of femtosecond ultra-short laser pulses

[摘要] ENGLISH ABSTRACT: Ultra-short laser pulses are useful in materials processing like melting and cutting metals,and medical applications such as surgery and many other fields. In this study, we characterizeand control the temporal shape of the ultra-short pulses generated from a Ti:Sapphirefemtosecond laser. It operates in the near infra-red spectral region, with a centre wavelengthof 800 nm. The 4f pulse shaper is the main setup used to modulate spectral shapeand characterize the laser pulse. The shaper consists of two diffraction gratings, two cylindricallenses and a computer controlled liquid crystal spatial light modulator (LC-SLM).Gratings, lenses and LC-SLM are arranged in a 4f geometry, f being the focal length ofthe lenses. This setup is first analysed analytically and numerically using Fourier transformand the results obtained are then compared to those obtained from the experiment. Thecharacterization of ultra-short pulses was done using three different autocorrelation techniquessuch as the intensity autocorrelation, the interferometric autocorrelation, and thepulse shaping autocorrelation which can act as interferometric autocorrelation when a nonlinearcrystalß-barium borate (BBO) is placed exactly at the position of the experiment.These characterization techniques are based on the interaction between the laser pulse anda replica of it with a nonlinear crystal. The setups were implemented and measurementsusing the last two techniques were successfully conducted, with the pulse duration resultin the range from 80-86 fs.

[发布机构] Stellenbosch University