Wavefront control of subcycle vortex pulses via carrier-envelope-phase tailoring

Abstract

The carrier-envelope phase (CEP) of an ultrashort laser pulse is becoming more crucial to specify the temporal characteristic of the pulse’s electric field when the pulse duration becomes shorter and attains the subcycle regime; here, the pulse duration of the intensity envelope is shorter than one cycle period of the carrier field oscillation. When this subcycle pulse involves a structured wavefront as is contained in an optical vortex (OV) pulse, the CEP has an impact on not only the temporal but also the spatial characteristics owing to the spatiotemporal coupling in the structured optical pulse. However, the direct observation of the spatial effect of the CEP control has not yet been demonstrated. In this study, we report on the measurement and control of the spatial wavefront of a subcycle OV pulse by adjusting the CEP. To generate subcycle OV pulses, an optical parametric amplifier delivering subcycle Gaussian pulses and a Sagnac interferometer as a mode converter were integrated and provided an adequate spectral adaptability. The pulse duration of the generated OV pulse was 4.7 fs at a carrier wavelength of 1.54 µm. To confirm the wavefront control with the alteration of the CEP, we developed a novel $$f$$ f -2$$f$$ f interferometer that exhibited spiral fringes originating from the spatial interference between the subcycle OV pulse and the second harmonic of the subcycle Gaussian pulse producing a parabolic wavefront as a reference; this resulted in the successful observation of the rotation of spiral interference fringes during CEP manipulation.

Vortex plate retarder-based approach for the generation of sub-20 fs light pulses carrying orbital angular momentum

“…Regarding the structure of the intensity, it shows the expected low intensity hole in its center along the temporal axis, as shown in figures 8(b) and (e). Spatio-temporal characterization of ultrashort vortices is a developing field [22, 35, 37, 38] and may present many interesting subtleties, especially when the duration approaches few-cycle [39,40] or additional space-time couplings are present [41] and the platform presented here may prove useful in that context. Nevertheless, from this analysis we can see that the pulse duration is close to the original one before OAM generation.…”