Studies On Closed Loop Chirp Compensation System Of Femtosecond Laser Pulses

Femtosecond laser pulse has many irreplaceable features, so it gets to be used inbiological and chemical research more and more widely. However, femtosecond lasermeasurement technology is the premise of its evaluation and application. It’s neces-sary to achieve high quality laser pulse with chirp compensation technology. Based onfiber femtosecond laser system，this thesis contents theoretical and experimentalstudies on measurement setup and chirp compensation system of femtosecond laserpulse. The system is made up of photonic crystal fiber lasers amplifier system,femtosecond laser pulse measurement setup and chirp control setup.In the femtosecond laser amplifier system, an oscillation provides seed light withnonlinear polarization rotation mode-locking. After compression with grating pair,seed light was coupled into a photonic crystal fiber (PCF) to be amplified, achievingaverage power of5W, spectrum width of21nm, repetition frequency of48MHz.Frequency-resolved optical gating (FROG) and its simplified setup have beenintroduced. Simplified FROG components parameters are analyzed and designed.Finally we chose a Fresnel Biprism with a vertex angle of168°and a5mm-thick BBOcrystal. The cage mounting structure was used to fix all of the optical elements andencapsulation of the device was also completed. The device was calibrated with aseparation-known double-pulse and was tested with an unknown femtosecond laser.By contrast to an autocorrelation, it’s proved that the device has a high precision.A4f-system was built with concave mirrors, gratings and liquid crystal spatiallight modulator. The characteristics of4f-system were tested after calibration. Afterthat a femtosecond laser pulse closed-loop chirp compensation system was completedwith the4f-system, simplified FROG and the PCF amplifier. In the experimentgrating was used to compensate linear chirp and SLM was used to compensatenonlinear chirp fed back from simplified FROG. Finally74-fs furrier transformlimited laser pulse was achieved and the entire process took approximately30s. Thefeedback was fast and efficient, providing a theoretical and experimental basis toachieve few-cycle laser pulse further.