Experimental setup for temporal coherence mapping of few-cycle vortex pulses with two subsequently arranged spatial light modulators.
Ultrashort pulses from a Ti:sapphire laser (6.5 fs, 800 nm, 80 MHz) are reflected from a first spatial light modulator (SLM1, generation part) to shape a pulsed vortex beam (Inset: schematic of a twisted pulse). This beam is coupled into a Michelson interferometer containing a beam splitter (BS) and producing phase-locked pulse pairs with variable delay (mirrors M1, M2). Wavefront and local temporal coherence are analysed by a nonlinear Shack-Hartmann sensor consisting of axicons programmed in a second spatial light modulator (SLM2, characterisation part), a 10-μm thick nonlinear crystal (BBO) for second harmonic generation, a filter to suppress the fundamental light and a matrix camera detector (EMCCD). By modifying this modular setup, two geometrical configurations with (a) single vortex beams and (b) multiple vortex beams were studied. Dispersion is compensated by 4 double chirped mirrors (DCMs) and a pair of thin CaF2 wedges. For reasons of simplicity, only one DCM mirror is shown in the figure.