Peter Baum, Stefan Lochbrunner

Phase properties of tunable femtosecond pulses An optical pulse with a duration in the 10 fs regime consists of only a few cycles of the electric field. The phase between the pulse envelope and the carrier wave (carrier-envelope phase, CE-phase) is an important property of few-cycle pulses. Experiments sensitive to the CE-phase are for instance coherent control with a combination of fundamental and SHG pulses optical synthesizers and frequency combs for metrology high harmonic and attosecond pulse generation In addition, when performing multi-color experiments, knowledge about the relative phase and the timing jitter between the different pulse sources is essential in phase-sensitive experiments like photon-echo or CARS. We address the CE-phase and the relative jitter of NOPA pulses by spatial interference techniques and measure the phase for every single shot of our kHz repetition rate system. Together with an envelope characterization with ZAP-SPIDER we obtain an almost complete knowledge about the optical light field. Relative phase jitter between multiple NOPAs To explore the phase jitter between different pulse sources we overlap the beams of two NOPAs tuned to similar center wavelengths and let them interfere on a distant screen. We observe a stable interference pattern that shows a residual jitter of much less than one optical period. The two NOPA pulses are therefore generated with a (relative) timing precision of less than one fs. The residual phase variations are due to fluctuations of the pump power. Similar results are obtained thoughout the full tuning range of the NOPA throughout the visible. A movie of the fluctuations, filmed with a standard digital camera, is available for download (400 kB).   A simple spatial "f to 2-f" interferometer for single-shot CE-phase analysis Tunable pulses with a stabilized CE phase are not easily available. However, if the CE phase shift is recorded for every single laser pulse the outcome of an experiment can be correlated to the measured CE phase value. This is how CE-phase experiments can be performed without phase-stabilized light sources. An "f to 2-f" interferometer measures the interference between the high-frequency components of an octave-broad spectrum with the frequency-doubled low-frequency components. The CE-phase is "contained" once in the fundamental and twice in the second harmonic. Therefore it is directly revealed in the fringe position. The octave-broad spectrum is a whitelight continuum generated in sapphire. It extends from 450 nm to beyond 1.6 µm and is routinely used in our group to seed all kinds of NOPAs. For convenience (signal strength) the NIR part is amplified before frequency doubling. The single shot recordings reveal a high contrast interferogram with a different fringe position from pulse to pulse, revealing the CE phase fluctuations for every single shot.

Former co-workers: Johannes Piel

"Phase-locked ultrashort pulse trains at separate and independently tunable wavelengths" P. Baum, E. Riedle, M. Greve and H. R. Telle Opt. Lett. 30, 2028 - 2030 (2005) Details "Carrier-envelope phase fluctuations of amplified femtosecond pulses: Characterization with a simple spatial interference setup" P. Baum, S. Lochbrunner, and E. Riedle Appl. Phys. B 77, 129 - 132 (2003) Details "Phase coherent generation of tunable visible femtosecond pulses" P. Baum, S. Lochbrunner, J. Piel, and E. Riedle Opt. Lett. 28, 185 - 187 (2003) Details