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All-optical spatio-temporal metrology for isolated attosecond pulses

Journal of Physics B Atomic Molecular and Optical Physics

September 2022
55(20)

Authors:

Characterizing an isolated attosecond pulse (IAP) is essential for its potential applications. A complete characterization of an IAP ultimately requires the determination of its electric ﬁeld in both time and space domains. However, previous methods, like the widely-used RABBITT and attosecond streaking, only measure the temporal proﬁle of the attosecond pulse. Here we demonstrate an all-optical method for the measurement of the space-time properties of an IAP. By introducing a non-collinear perturbing pulse to the driving ﬁeld, the process of IAP generation is modiﬁed both spatially and temporally, manifesting as a spatial and a frequency modulation in the harmonic spectrum. By using a FROG-like retrieval method, the spatio-spectral phases of the harmonic spectrum are faithfully extracted from the induced spatio-spectral modulations, which allows a thoroughgoing characterization of the IAP in both time and space. With this method, the spatio-temporal structures of the IAP generated in a two-color driving ﬁeld in both the near- and far-field are fully reconstructed, from which a weak spatio-temporal coupling in the IAP generation is revealed. Our approach overcomes the limitation in the temporal measurement in conventional in situ scheme, providing a reliable and holistic metrology for IAP characterization.

(a) Schematic diagram of the experimental set-up for the spatio-temporal measurement of the IAP generated in a tow-color driving field. BS, beam splitter; DM, dichroic mirror; DL, delay line; HWP, half-wave plate; WGP, wire grid polarizer. (b) Spatially-resolved harmonic spectrum driven by the 1300 nm fundamental field alone. (c) Same as (b), but for the two-color driving field synthesized by the 1300 nm fundamental and 800 nm assistant laser fields. (d) On-axis harmonic spectra driven by the one-color (red line) and two-color (blue line) laser field, respectively.

…

(a) Far-field spatial distribution of H35 as a function of time delay of the perturbing laser. (b) Same as (a), but for the PCGPA reconstruction. (c) Reconstructed near-field distribution of the intensity (blue line) and phase (red line) of H35. (d) Reproduced far-field intensity (blue line) and phase (red line) of H35. The cyan dashed line plots the measured far-field intensity of the unperturbed H35 for comparison.

…

(a) On-axis harmonic spectra measured in the two-color driving field as a function of time delay of the perturbing laser. (b) Same as (a), but for the PCGPA reconstruction. (c) Reproduced intensity (blue solid line) and phase (red dotted line) of the unperturbed on-axis harmonic spectrum in the far-field. The cyan dashed line plots the far-field on-axis harmonic intensity measured without the perturbation for comparison.

…

(a) and (b) Spatially-resolved far-field harmonic intensity (a) and phase (b) reconstructed from the measurement. (c) and (d) Same as (a) and (b), but for the near-field result.

…

(a) Spatio-temporal profiles of the electric field of the attosecond pulse in the far-field obtained by synthesizing harmonics in the energy range from 33 eV to 47 eV. The inset shows the corresponding spatio-temporal distribution of the intensity of the attosecond pulse. (b) Temporal profile of the on-axis attosecond pulse in the far field. (c) and (d) Same as (a) and (b), but for the near-field result.

…

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Journal of Physics B: Atomic, Molecular and Optical Physics

J. Phys. B: At. Mol. Opt. Phys. 55 (2022) 205601 (9pp) https://doi.org/10.1088/1361-6455/ac8f01

All-optical spatio-temporal metrology

for isolated attosecond pulses

Lixin He1,2, Jianchang Hu1,SiqiSun

1, Yanqing He1,YuDeng

Pengfei Lan1,2,∗and Peixiang Lu1,2,3

1Wuhan National Laboratory for Optoelectronics and School of Physics,

Huazhong University of Science and Technology, Wuhan 430074, People’s Republic of China

2Optical Valley Laboratory, Hubei 430074, People’s Republic of China

3Hubei Key Laboratory of Optical Information and Pattern Recognition, Wuhan Institute of Technology,

Wuhan 430205, People’s Republic of China

E-mail: pengfeilan@hust.edu.cn

Received 23 June 2022, revised 25 August 2022

Accepted for publication 31 August 2022

Published 20 September 2022

Abstract

Characterizing an isolated attosecond pulse (IAP) is essential for its potential applications. A

complete characterization of an IAP ultimately requires the determination of its electric eld

in both time and space domains. However, previous methods, like the widely-used RABBITT

and attosecond streaking, only measure the temporal prole of the attosecond pulse. Here we

demonstrate an all-optical method for the measurement of the space-time properties of an IAP.

By introducing a non-collinear perturbing pulse to the driving eld, the process of IAP

generation is modied both spatially and temporally, manifesting as a spatial and a frequency

modulation in the harmonic spectrum. By using a FROG-like retrieval method, the

spatio-spectral phases of the harmonic spectrum are faithfully extracted from the induced

spatio-spectral modulations, which allows a thorough characterization of the IAP in both time

and space. With this method, the spatio-temporal structures of the IAP generated in a

two-color driving eld in both the near- and far-eld are fully reconstructed, from which a

weak spatio-temporal coupling in the IAP generation is revealed. Our approach overcomes the

limitation in the temporal measurement in conventional in situ scheme, providing a reliable

and holistic metrology for IAP characterization.

Keywords: isolated attosecond pulse, spatio-temporal characterization, all-optical metrology

(Some gures may appear in colour only in the online journal)

1. Introduction

The advent of attosecond extreme ultraviolet/soft x-ray pulses

via high-order harmonic generation (HHG) is a milestone in

strong-eld physics and attoscience [1–8], which has opened

up new avenues for accessing ultrafast electron dynamics

in atoms [9–12], molecules [13–15], and condensed matter

[16] on its natural time scale. HHG is a highly nonlinear

process during the laser-matter interaction [17–19], accom-

panying with complicated macroscopic effects in the propa-

gation [20–22]. Isolated attosecond pulses (IAPs) produced

by HHG generally have complex spatio-temporal structures,

∗Author to whom any correspondence should be addressed.

which encode both the ångstrom-sized spatial features and

attosecond scale temporal features of the response of the mat-

ters to the laser eld. A complete characterization of the IAP

in both time and space is critical not only for the develop-

ment of new attosecond light sources, but also for its appli-

cations in attosecond pump-probe experiments, as well as for

unraveling the physics underlying the laser-matter interaction

[23–25].

The complete characterization of an ultrashort IAP actu-

ally requires the determination of its spatio-temporal electric

eld E(x,y,t), or its spatio-spectral counterpart ˜

E(x,y,ω).

To date, attosecond streaking technique [26,27] has been

usually used to retrieve the temporal prole of an IAP from

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All-optical spatio-temporal metrology for isolated attosecond pulses

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