Interferometer Design for Attosecond Experiments

Abstract: Resolving fast events, such as electron dynamics, requires short light pulses. To this date the shortest available light pulses are created using High-order Harmonic Generation (HHG) and have a duration of a few hundred attoseconds (1 as = $10^{-18}$ s). When used for pump-probe experiments, these pulses are generated in an interferometer, which needs to be stable for the experiment to yield high quality data. In this project the effect of interferometer stability (seen as uncertainty in the time delay, $\Delta\tau$) on the possibility to extract a phase with high precision from data has been investigated. This was done by simulations in MATLAB. It was found that even with a large error in the time delay ($\sigma_{\Delta\tau} = 0.20T$) it is possible to extract a phase with a small error ($\sigma_{\phi}<0.001T$), if the number of data points is sufficient ($N = $100 000). Furthermore the effect of some aspects of interferometer design on the stability of interferometers was investigated by simulations in the ray tracing program FRED. An interferometer design was modified in one aspect at the time and the stability, in terms of spatial and temporal drift, was measured for each modification. In this way it was found that an interferometer should 1) be small, 2) have equal parity of the number of focusing lenses and mirrors, respectively, in its two arms, 3) have focusing lenses of equal focal length in its arms, and 4) have its mirrors perfectly aligned, to be as stable as possible. For short: a stable interferometer is small and symmetric.