Compression and Shaping of Femtosecond Laser Pulses for Coherent Two-Dimensional Nanoscopy

Sammanfattning: Femtosecond pulse shaping is a versatile tool that enables the generation of ultrashort laser pulses with nearly arbitrary temporal shapes. Among others, the technique is of use in ultrafast spectroscopy experiments where it can be employed for dispersion control and the generation of well-defined laser pulse sequences. In this work, a Fourier-transform pulse shaper based on a pixelated liquid crystal spatial light modulator (LC-SLM) was implemented and calibrated. The pulse shaper is designed for phase and amplitude shaping of femtosecond laser pulses in the visible and near-infrared spectral range. A distinctive feature of the setup is the use of a prism to spatially separate the spectral components of the input pulses. For accurate pulse shaping a careful calibration of the setup is required. Procedures for determining the pixel-to-wavelength and the wavelength dependent voltage-to-phase mapping of the LC-SLM were implemented. The phase is retrieved from the measured intensity modulation behaviour of the pulse shaper using an iterative optimisation algorithm. Estimates for the limitations of the pulse shaper were derived from a theoretical analysis of the wavelength calibration results. To validate the calibration results, the pulse shaper was used to arbitrarily shape the spectral amplitude of near-infrared laser pulses. Within the limitations of the pulse shaper, good agreement between measured and desired spectral shape was found, confirming the validity of the calibration procedure. To verify the phase shaping capabilities of the pulse shaper, it was used in combination with a prism compressor to compensate for material dispersion introduced by the dispersive prism in the setup. Dispersion compensation could be successfully demonstrated, albeit bandwidth-limited pulse durations were not achieved. This work provides a platform for pulse-shaper-assisted ultrafast spectroscopy experiments.