Multi-harmonic generator and synthesizer for experiments in tailored, intense femtosecond laser fields

Femtosecond pulses with tailored laser fields are indispensable for studying the control of ultrafast chemical transformations [1] and for uncovering the realms of strong field physics in atoms, molecules, solids [2], and nanoscale targets [3]. For such studies pulses with well-controlled electric field, synthesized from hollow-core fiber compressors, have shown their application potential [4]. More commonly used femtosecond laser systems, however, deliver pulses that span less than an octave in spectral bandwidth, making the synthesis of tailored fields with such pulses highly desirable. Here, we present results from an efficient multi-harmonic generator and synthesizer (see Fig. 1(a)), converting femtosecond pulses delivered from an amplified Ti:sapphire system into a three-color beam with desired field waveform. Recently, the careful 3D-modelling of the propagation of tightly focused, broadband light fields from femtosecond oscillators in nonlinear and birefringent media allowed for efficient third harmonic generation with an efficiency of 30% [5]. Here, we followed the same approach, with a design goal for an efficient conversion of 25 fs pulses into three femtosecond beams centered around 260 nm, 390 nm and 780 nm. Together with the harmonic generator our device permits versatile multi-harmonic field synthesis, where first all three beams are separated, and then combined into a single three-color field. The beam separation and recombination allows for independent modification of each of the beams, where not only temporal delays (with interferometric stability) but also the polarization state of each of the beams can be altered.