Tracing the phase of focused broadband laser pulses

5 years ago

Tracing the phase of focused broadband laser pulses

A. M. Sayler, Gerhard G. Paulus, Dominik Hoff, Peter Hommelhoff, Lothar Maisenbacher, Michael Krüger

In ultrafast light–matter interactions, the phase of the optical carrier field with respect to the pulse envelope’s maximum—the carrier-envelope phase (CEP, see Supplementary Information)¹⁴—is one of the fundamental controls that allows one to steer chemical reactions¹⁵, the generation of attosecond pulses via high-harmonic generation¹⁶, and electron emission and acceleration from solid surfaces and nanostructures^{7, 9, 17}, among others. Hence, determining and controlling the CEP is mandatory in many fields using lasers, but taking into account the broadband and often intense and ultrashort nature of these pulses is challenging and an active area of research^{18, 19}. Further, nonlinear light–matter interactions usually take place in the focus of a beam where the CEP shows a strong spatial dependence. Thus, for a detailed understanding of and field control over these processes, it is essential to take the focal phase evolution, target position, and target extent into account^{13, 20}. This is as important as controlling the CEP of the input beam itself.

For a focused monochromatic beam, the on-axis phase shift due to diffraction is described by the familiar Gouy phase, which follows a simple arctangent curve^{1, 2}. However, many of today’s coherent light sources, even some as common place as those used in ophthalmological diagnostics, are far from being monochromatic. Rather, they can span close to, and many even exceed, an octave of spectral bandwidth^{12, 21, 22}. Moreover, recent theoretical studies, based on diffraction theory for pulsed Gaussian beams, yielded spatially dependent phases that significantly deviate from the simple Gouy phase and show a much more complex behaviour that is dictated by the wavelength-dependent input beam geometry^{5, 6}. The n

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Publisher URL: http://dx.doi.org/10.1038/nphys4185

DOI: 10.1038/nphys4185