Towards the carrier-envelope phase stabilization of a16 TW 4.5 fs laser system

Abstract: In the last decades the scientific development has made it possible to produce pulses with durations below the femtosecond time scale (1 fs = 1015 s), reaching to attoseconds (1 as = 1018 s). This is the time scale of electronic motion inside atoms and molecules. One way to produce isolated attosecond pulses is through high harmonic generation in gases with intense few-cycle laser pulses. This process depends strongly on the electric field shape relative to the pulse envelope, which is characterized by the so called carrier-envelope phase (CEP).The goal of this master’s thesis is to measure and investigate the possibility to improve the CEP stability of sub-two-cycle laser pulses from the laser, Light Wave Synthesizer 20 (LWS-20). The first step of the master’s thesis was to modify a Labview program used to evaluate the CEP change to be able to reevaluate the already acquired raw data. The measurements are done with an f-to-2f interferometer, whichis a spectral interference device, which measures the CEP difference between two pulses. The CEP change of the laser system was measured at three positions: after the multi-pass amplifier of the laser front end (MP), after a hollow-core fiber (HCF), which is used for spectral broadening, and at the end of the laser system. The stability is determined as the RMS error (standard deviation) of the phase change overall shots in one sample (lower RMS is better stability). The measurements show an average stability of 160±20 mrad RMS after the MP, 280±31 mrad RMS after the HCF and 560±53 mrad RMS at the end of the system. The stability at the end of the system could be improved to 475±40 mrad RMS after a scan of the pump energy for one of the amplifier stages. The HCF appears to provide a lower limit in stability and influences it only if it is very good after the MP. The alignment of the HCF does also seem to influence the CEP stability and the best stability appears to coincide with maximum output energy. An acousto-optic modulator (Dazzler) has been used to manipulate the CEP change at the end of the system and can thereby compensate for long-term drifts, but the source of the CEP stability degradation at the end of the system should be further investigated.