Attosecond transient absorption is one of the promising new techniques being developed to exploit the availability of sub-femtosecond extreme ultraviolet (XUV) pulses to study the dynamics of the electron on its natural time scale. The temporal resolution in a transient absorption setup comes from the control of the relative delay and coherence between pump and probe pulses, while the spectral resolution comes from the characteristic width of the features that are being probed. In this review we focus on transient absorption scenarios where an attosecond pulse of XUV radiation creates a broadband excitation that is subsequently probed by a few cycle infrared (IR) laser. Because the attosecond XUV pulses are locked to the IR field cycle, the exchange of energy in the laser–matter interaction can be studied with unprecedented precision. We focus on the transient absorption by helium atoms of XUV radiation around the first ionization threshold, where we can simultaneoulsy solve the time-dependent Schrodinger equation for the single atom response and the Maxwell wave equation for the collective response of the nonlinear medium. We use a time-domain method that allows us to treat on an equal footing all the different linear and nonlinear processes by which the medium can exchange energy with the fields. We present several simple models, based on a few-level system interacting with a strong IR field, to explain many of the novel features found in attosecond transient absorption spectrograms. These include the presence of light-induced states, which demonstrate the ability to probe the dressed states of the atom. We also present a time-domain interpretation of the resonant pulse propagation features that appear in absorption spectra in dense, macroscopic media. We close by reviewing several recent experimental results that can be explained in terms of the models we discuss. Our aim is to present a road map for understanding future attosecond transient absorption experiments in more complex systems.

http://absimage.aps.org/image/DAMOP14/MWS_DAMOP14-2014-000677.pdf

Theory of strong-field attosecond transient absorption

Non-Hermitian lattice systems with unconventional transport phenomena and topological effects have attracted intensive attention recently. Non-Hermiticity is generally introduced by engineering on-site gain/loss distribution or inducing asymmetric couplings by applying an imaginary gauge field. Here, we extend the concept of non-Hermitian lattices from spatial to frequency dimension and emulate various non-Hermitian transport phenomena arising from asymmetric coupling in synthetic dimension. The non-Hermitian frequency lattice is created by introducing complex gauge potentials through appropriate complex modulations in a slab waveguide. This complex gauge potential can induce asymmetric couplings among spectral modes and give rise to various non-Hermitian transport phenomena such as amplified and decayed frequency diffraction, refraction and non-Hermitian Bloch oscillations. The latter manifest themselves as both power oscillation and asymmetric oscillation patterns, and can be exploited to probe in the bulk the non-Hermitian skin effect. Frequency-domain Bloch oscillations with both exponentially growing oscillation amplitude and energy are also predicted. Our results pave the way towards emulating non-Hermitian transport phenomena and topological effects in synthetic dimension on a photonic platform, with potential applications to spectral manipulation of optical signals and energy harvesting.

/pdf/discrete-diffraction-and-bloch-oscillations-in-non-hermitian-4uy1ba8zbi.pdf

Discrete diffraction and Bloch oscillations in non-Hermitian frequency lattices induced by complex photonic gauge fields

The authors have identified dynamically enhanced Autler-Townes splittings in the photoelectron energy spectrum of atoms in a XUV-pump and XUV-probe protocol.

Enhancing Autler-Townes splittings by ultrafast XUV pulses

When the molecules with degenerate current-carrying orbitals are exposed to the bichromatic counterrotating circularly polarized (BCCP) laser fields, the destructive interference between high harmonics from these orbitals results in a strong suppression of harmonic emission with the selected helicity. As a result, there are large intensity differences between the high harmonics with opposite helicities in a wide spectral range. This interference effect is related to the noncylindrical symmetry of the molecular current-carrying orbitals and therefore depends on the relative orientation between the molecule and the driving laser fields. Furthermore, our results show that this interference can be controlled by adjusting the relative intensity ratio of the BCCP field. Finally, we show that highly elliptically polarized attosecond pulses can be generated by using this interference and their ellipticities can be tuned by controlling the molecular orientation.

Interference effect in high-order harmonic generation from degenerate current-carrying orbitals of polyatomic molecules

Generation of Near‐Circularly Polarized Attosecond Pulse with Tunable Helicity by Unidirectionally Rotating Laser Field

When an atom or molecule is illuminated by a short laser pulse, the intense electric field couples different electronic states promptly and alters the final products. Detecting such interaction processes in a time-resolved way requires techniques with unprecedented time resolution and is important for applications such as coherent chemical reaction control. Here by solving the time-dependent Schr\"odinger equation, we demonstrate that the time evolution of complex amplitudes of bound electronic states during the interaction with an optical laser pulse can be extracted with high accuracy using attosecond streaking.

Probing laser-driven bound-state dynamics using attosecond streaking spectroscopy

We demonstrate an all-optical approach for precise characterization of attosecond extreme ultraviolet pulses. Isolated attosecond pulse is produced from high order harmonics using intense driving pulse with proper gating technique. When a weak field is synchronized with the driver, it perturbs the harmonics generation process via altering the accumulated phase of the electron trajectories. The perturbed harmonic spectrum can be formulated as a convolution of the unperturbed dipole and a phase gate, implying the validity of complete reconstruction of isolated attosecond pulses using conventional frequency resolved optical gating method. This in situ measurement avoids the central momentum approximation assumed in the widely used attosecond streaking measurement, providing a simple and reliable metrology for isolated attosecond pulse.

All-optical frequency resolved optical gating for isolated attosecond pulse reconstruction

We demonstrate an all-optical approach for precise characterization of attosecond extreme ultraviolet pulses. An isolated attosecond pulse is produced from high-order harmonics using an intense driving pulse with a proper gating technique. When a weak field is synchronized with the driver, it perturbs the harmonics generation process via altering the accumulated phase of the electron trajectories. The perturbed harmonic spectrum can be formulated as a convolution of the unperturbed dipole and a phase gate, implying the validity of complete reconstruction of isolated attosecond pulses using a conventional frequency-resolved optical gating method. This in situ measurement avoids the central momentum approximation assumed in the widely used attosecond streaking measurement, providing a simple and reliable metrology for an isolated attosecond pulse.

All-optical frequency-resolved optical gating for isolated attosecond pulse reconstruction

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

Xi Chen

Author Tools

Chat about Author

Papers

Probing laser-driven bound-state dynamics using attosecond streaking spectroscopy

All-optical frequency resolved optical gating for isolated attosecond pulse reconstruction

All-optical frequency-resolved optical gating for isolated attosecond pulse reconstruction