An Experimental Design to Beamshape Ultrashort Pulses

Abstract

The central objective of this thesis is to design a system that allows control over the spatial intensity distribution of an ultrashort light pulse in a target plane, as a useful tool in researching non-linear light-matter interactions. We will use a blazed digital micromirror device as a binary spatial light modulator (SLM). In Section 2 we present exploratory beamshaping results where smooth shaping of the third diffraction order of the SLM is achieved using a 4f setup and a spatial filter placed in the Fourier plane. To generate the correction pattern on the SLM we use a simple intensity-shaping algorithm which assigns a probability to each micromirror to be switched off. In Section 3 we adopt a new setup, using a cylindrical lens to image in one direction and focus in the other. By so collapsing approximately a thousand binary degrees of freedom into a section of about 0.12 mm 2 , we increase the precision of our method and create a flattop with 4.3% rms-flatness. Section 4 concerns the spatial dispersion of the linefocus that is observed for broad input spectra. To simulate the broad spectrum that belongs to an ultrashort pulse, we use a laser diode below its lasing threshold. We find that the orientation of the cylindrical lens can be used to compensate for this dispersion, and we report succesful (flattop) beamshaping using broad spectrum light.