Ultrawide-band light wave synthesis in the visible and ultraviolet

Few-cycle laser pulses tunable across the entire visible and ultraviolet spectral ranges have long been desired for site-selective triggering of molecular dynamics. Their coherent addition with adjustable delays would, on the opther hand, provide an electric field variable on the electronic (sub-fs) time scale for steering electrons in excited electronic states (C.2.4, C.2.5). Here we aim at realising both objectives. To this end, waveform-stabilised, few-cycle (~5 fs) near-infrared (~750 nm) pulses will be parametrically amplified to the millijoule level. Subsequently, they first produce attosecond xuv pulses and will then — following separation from the xuv beam — be used for supercontinuum generation in a gas-filled capillary (see Fig. 1).

The continuum generation will be followed by a LiF or CaF₂ prism sequence for dispersion control. In the Fourier plane, a static transparent LiF phase mask will ensure that the delay line is disperson-free to all orders over the entire spectral range of ~130–1300 nm, whereas thin and narrow rotatable LiF plates will permit adjusting the delay between different groups of frequencies to synthesise intense light fields controllable on a sub-femtosecond scale. Alternatively, we may select a quasi-monochromatic pulse of predetermined carrier wavelength by introducing an adjustable slit.

An alternative concept for the compression relies on the separation of regions of the ultra-broadband spectrum, selective phase correction for each part and subsequent recombination with interferometric precision. For all approaches the spectral phase of the pulses and sub-pulses have to be measured as well as the phase properties of newly developed optical elements. ZAP-SPIDER¹⁾ will be used for this purpose. Finally, the synthesis will be completed by measuring the waveform with an attosecond xuv pulse ²⁾.