A. M. Sayler

Real-time pulse length measurement of few-cycle laser pulses using above-threshold ionization

The pulse lengths of intense few-cycle (4-10 fs) laser pulses at 790 nm are determined in real-time using a stereographic above-threshold ionization (ATI) measurement of Xe, i.e. the same apparatus recently shown to provide a precise, real-time, every-single-shot, carrier-envelope phase measurement of ultrashort laser pulses. The pulse length is calibrated using spectral-phase interferometry for direct electric-field reconstruction (SPIDER) and roughly agrees with calculations done using quantitative rescattering theory (QRS). This stereo-ATI technique provides the information necessary to characterize the waveform of every pulse in a kHz pulse train, within the Gaussian pulse approximation, and relies upon no theoretical assumptions. Moreover, the real-time display is a highly effective tool for tuning and monitoring ultrashort pulse characteristics.

Precise, real-time, single-shot carrier-envelope phase measurement in the multi-cycle regime

Polarization gating is used to extend a real-time, single-shot, carrier-envelope phase (CEP) measurement, based on high-energy above-threshold ionization in xenon, to the multi-cycle regime. The single-shot CEP precisions achieved are better than 175 and 350 mrad for pulse durations up to 10 fs and 12.5 fs, respectively, while only 130 μJ of pulse energy are required. This opens the door to study and control of CEP-dependent phenomena in ultra-intense laser-matter interaction using optical parametric chirped pulse amplifier based tera- and petawatt class lasers.

Momentum-resolved study of the saturation intensity in multiple ionization

(Received 25 September 2014; published 16 March 2015)We present a momentum-resolved study of strong field multiple ionization of ionic targets. Using adeconvolution method we are able to reconstruct the electron momenta from the ion momentum distributionsafter multiple ionization up to four sequential ionization steps. This technique allows an accurate determinationof the saturation intensity as well as of the electron release times during the laser pulse. The measured results arediscussed in comparison to typically used models of over-the-barrier ionization and tunnel ionization.DOI: 10.1103/PhysRevA.91.031401 PACS number(s): 32

Tracing the phase of focused broadband laser pulses

In different applications the Gouy phase is used to describe broadband lasers, but new 3D measurements of the spatial dependence of a focused laser pulse show serious deviations from the Gouy phase. Precise knowledge of the behaviour of the phase of light in a focused beam is fundamental to understanding and controlling laser-driven processes. More than a hundred years ago, an axial phase anomaly for focused monochromatic light beams was discovered and is now commonly known as the Gouy phase1,2,3,4. Recent theoretical work has brought into question the validity of applying this monochromatic phase formulation to the broadband pulses becoming ubiquitous today5,6. Based on electron backscattering at sharp nanometre-scale metal tips, a method is available to measure light fields with sub-wavelength spatial resolution and sub-optical-cycle time resolution7,8,9. Here we report such a direct, three-dimensional measurement of the spatial dependence of the optical phase of a focused, 4-fs, near-infrared pulsed laser beam. The observed optical phase deviates substantially from the monochromatic Gouy phase—exhibiting a much more complex spatial dependence, both along the propagation axis and in the radial direction. In our measurements, these significant deviations are the rule and not the exception for focused, broadband laser pulses. Therefore, we expect wide ramifications for all broadband laser–matter interactions, such as in high-harmonic and attosecond pulse generation, femtochemistry10, ophthalmological optical coherence tomography11,12 and light-wave electronics13.

Waveform characterization of few-cycle laser pulses in real-time using above-threshold ionization

Since the time-dependent electric field dictates strong-field laser-matter dynamics, characterization of the waveform is critical for the understanding and control of these interactions. Moreover, the precise determination of these parameters is especially important for applications in the few-cycle regime, e.g. the production of extreme-ultraviolet (XUV) pulses, which serve as the basis for much of the burgeoning field of attosecond science.