About

Andreas Becker is a Distinguished Professor and Fellow at JILA within the Department of Physics at the University of Colorado Boulder. His research focuses on the analysis and simulation of ultrafast phenomena in atoms, molecules, and clusters, particularly attosecond electron dynamics, coherent control, and molecular imaging. He is interested in the theoretical analysis and numerical simulation of ultrafast phenomena involving interactions with intense laser pulses, which generate light pulses with field strengths exceeding that of the Coulomb field within an atom or molecule, with durations as short as a few femtoseconds or less in the attosecond regime. His group pursues theoretical studies on the coherent control of chemical reactions, the observation of correlated electron dynamics, the imaging of molecular dynamics, and the propagation of ultrashort intense laser pulses, often collaborating closely with experimental groups.

Research topics

• Computer Science
• Physics
• Nuclear physics
• Quantum mechanics
• Atomic physics
• Optics

Selected publications

• Generation of elliptically polarized high-order harmonics in cross-polarized bichromatic laser pulses: mechanism and control

  Journal of Physics B Atomic Molecular and Optical Physics · 2025-11-10 · 1 citations

  articleOpen accessSenior authorCorresponding

  Abstract We present an analysis based on results of numerical model simulations of microscopic high-order harmonic generation in a cross-polarized laser set-up using the time-dependent Schrödinger equation. The set-up consists of an intense laser pulse at the fundamental frequency corresponding to a wavelength of 800 nm and a weaker second harmonic pulse. In qualitative agreement with the observations in an experiment (Lambert et al 2015 Nat. Commun. 6 6167) the results of the simulations show that at pulse durations in the regime of 3–8 cycles full-width-at-half-maximum (FWHM) high ellipticities of the even harmonics (scaled in terms of the fundamental frequency) at the cut-off of the spectrum can be achieved. In the long pulse limit (beyond 20 cycles FWHM) those harmonics are close to linearly polarized, consistent with earlier predictions (Shafir et al 2009 Nat. Phys. 5 412; Shafir et al 2010 New J. Phys. 12 073032; Neufeld et al 2019 Nat. Commun. 10 405). In contrast, ellipticities of odd harmonics remain rather small independent of the pulse duration. In the further analysis of the results we discuss the impact of the relative intensities of the two pulses, their relative carrier-to-envelope phase and the pulse duration on the ellipticity of the harmonics.

  PublisherDOI

• Pulse characterization via two-photon auto- and cross-correlation

  Optics Express · 2024-08-27 · 2 citations

  articleOpen accessSenior author

  We present the application of a previously proposed multiple-Gaussian approach to characterize ultrashort vacuum (VUV) and deep ultraviolet (DUV) pulses via auto- and cross-correlation methods. The knowledge of the temporal variation of amplitude and phase of such pulses is important for spectroscopic and dynamical imaging techniques. The method, which is an extension of the single Gaussian autocorrelation technique, is based on the expansion of the pulse in a series of Gaussian functions at different frequencies and the use of analytic solutions for two-photon ionization of atoms by Gaussian pulses. Using this approach we compare the characterization of a pulse via the auto- and the cross-correlation techniques and find that an accurate characterization even in the case of more complex pulse forms can be achieved. Furthermore, the comparison of the application of unchirped and chirped Gaussian pulses reveals some specific advantages in the use of pulses with a linear chirp. Finally, we quantify our conclusions from the qualitative comparisons by defining errors and using results from information theory.

  PublisherDOI

• Enabling elliptically polarized high harmonic generation with short cross polarized laser pulses

  2024-01-01

  articleSenior author

  Based on results of numerical simulations we shed new light on a controversy between experiment and theoretical predictions on the generation of harmonics with large ellipticity using cross-polarized bichromatic laser pulses.

  PublisherDOI

• Tuning the conversion efficiency of high-order harmonic signals via variation of the Porras factor

  2024-01-01

  articleSenior author

  We investigated the effects of a novel phase term for short driving laser pulses on optimizing the macroscopic HHG process. We theoretically analyze the HHG yield, resulting in an increase of the harmonic yield by a few orders of magnitude.

  PublisherDOI

• A multi-technique detection of an eccentric giant planet around accelerating star HD 57625

  arXiv (Cornell University) · 2024-12-09

  preprintOpen access

  The synergy between different detection methods is a key asset in exoplanetology, allowing for both precise characterization of detected exoplanets and robust constraints even in the case of non-detection. Recently, the interplay between imaging, radial velocities and astrometry has produced significant advancements in exoplanetary science. We report a first result of an ongoing survey performed with SHARK-NIR, the new high-contrast near-infrared imaging camera at the Large Binocular Telescope, in parallel with LBTI/LMIRCam in order to detect planetary companions around stars with significant proper motion anomaly. In this work we focus on HD 57625, a F8 star for which we determine a $4.8^{+3.7}_{-2.9}$Ga age, exhibiting significant astrometric acceleration and for which archival radial velocities hint at the presence of a previously undetected massive long-period companion. We analyse the imaging data we collected with SHARK-NIR and LMIRCam in synergy with the available public SOPHIE radial velocity time series and Hipparcos-Gaia proper motion anomaly. With this joint multi-technique analysis, we aim at characterizing the companion responsible for the astrometric and radial velocity signals. The imaging observations result in a non-detection, indicating the companion to be in the substellar regime. This is confirmed by the synergic analysis of archival radial velocity and astrometric measurements resulting in the detection of HD 57625 b, a ${8.43}_{-0.91}^{+1.10}$M$_{\rm Jup}$ planetary companion with an orbital separation of ${5.70}_{-0.13}^{+0.14}$au and ${0.52}_{-0.03}^{+0.04}$ eccentricity. HD 57625 b joins the small but growing population of giant planets in outer orbits with true mass determination provided by the synergic usage of multiple detection methods, proving once again the importance of multi-technique analysis in providing robust characterization of planetary companions.

  PublisherOA PDFDOI

• Pulse characterization via two-photon auto- and cross-correlation

  2024-01-01

  articleSenior author

  We present the application of a multiple-Gaussian approach to characterize ultrashort vacuum and deep ultraviolet pulses via auto- and cross-correlation methods. We compare characterizations obtained via both methods with chirped and unchirped Gaussians.

  PublisherDOI

• Tuning the conversion efficiency of high-order harmonic signals via variation of the Porras factor

  Physical review. A/Physical review, A · 2024-11-01

  articleSenior author

  High-order harmonic generation in atomic gases is important for several applications in ultrafast strong-field physics, ranging from attosecond pulse generation to ultrafast spectroscopy and imaging of different forms of matter. In the case of the generation with focused short Gaussian pulses, recent theoretical studies indicate that the conversion efficiency depends on the spatial phase distribution of the driving laser pulse which scales with the Porras factor. Using theoretical analysis and the results of numerical simulations, we find that for positive Porras factors the contribution of the Gouy phase to phase matching can be balanced and the conversion efficiency can be significantly enhanced as compared to a standard laser setup. Specifically, our results indicate that for a Porras factor of ${g}_{0}\ensuremath{\simeq}1.2$, the conversion efficiency as well as the cutoff of the harmonic spectra can be optimized while the harmonic lines remain narrow, which may be interesting for spectroscopic applications.

  PublisherDOI

• Photoelectron spectra in circularly and elliptically polarized laser pulses

  Physical review. A/Physical review, A · 2024-02-27 · 4 citations

  articleOpen accessSenior author

  We present results of numerical simulations of the time-dependent Schr\"odinger equation and theoretical analysis concerning the interaction of a rare gas atom with circularly and elliptically polarized laser pulses. In agreement with recent observation in circularly polarized fields, the photoelectron energy spectra for counterrotating electrons are peaked at lower kinetic energy than those for corotating electrons. We show that this difference can be interpreted as being due to the additional pathways to ionization that are available for the counterrotating electrons only. Furthermore, our results show, in agreement with earlier work, that the offset angle by which the emission of electrons is rotated in an elliptically polarized field increases with each successive above-threshold ionization (ATI) order and is larger for the emission from counterrotating states as compared to that from corotating states. A simple model based on the interference and relative phase difference between just three continuum states provides remarkable agreement and once again emphasizes the importance of the additional ionization pathways available for the counterrotating electrons.

  PublisherOA PDFDOI

• Performance of the CMS High Granularity Calorimeter prototype to charged pion beams of 20–300 GeV/c

  Journal of Instrumentation · 2023 · 13 citations

  • Computer Science
  • Physics
  • Nuclear physics

  Abstract The upgrade of the CMS experiment for the high luminosity operation of the LHC comprises the replacement of the current endcap calorimeter by a high granularity sampling calorimeter (HGCAL). The electromagnetic section of the HGCAL is based on silicon sensors interspersed between lead and copper (or copper tungsten) absorbers. The hadronic section uses layers of stainless steel as an absorbing medium and silicon sensors as an active medium in the regions of high radiation exposure, and scintillator tiles directly read out by silicon photomultipliers in the remaining regions. As part of the development of the detector and its readout electronic components, a section of a silicon-based HGCAL prototype detector along with a section of the CALICE AHCAL prototype was exposed to muons, electrons and charged pions in beam test experiments at the H2 beamline at the CERN SPS in October 2018. The AHCAL uses the same technology as foreseen for the HGCAL but with much finer longitudinal segmentation. The performance of the calorimeters in terms of energy response and resolution, longitudinal and transverse shower profiles is studied using negatively charged pions, and is compared to GEANT4 predictions. This is the first report summarizing results of hadronic showers measured by the HGCAL prototype using beam test data.

  PublisherOA PDFDOI

• Storage Ring Cross Section Measurements for Electron Impact Single and Double Ionization of Fe13+ and Single Ionization of Fe16+ and Fe17+

  Columbia Academic Commons (Columbia University) · 2023-03-15 · 14 citations

  articleOpen access

  We report measurements of electron impact ionization (EII) for Fe^13+, Fe^16+, and Fe^17+ over collision energies from below threshold to above 3000 eV. The ions were recirculated using an ion storage ring. Data were collected after a sufficiently long time that essentially all the ions had relaxed radiatively to their ground state before data were collected. For single ionization of $\fethirteen$ we find that previous single pass experiments are more than 40% larger than our results. Compared to our work, the theoretical cross section recommended by Arnaud & Raymond (1992) is more than 30% larger, while that of Dere (2007) is about 20% greater. Much of the discrepancy with Dere (2007) is due to the theory overestimating the contribution of excitation-autoionization via n=2 excitations. Double ionization of Fe^13+ is dominated by direct ionization of an inner shell electron accompanied by autoionization of a second electron. Our results for single ionization of Fe^16+ and Fe^17+ agree with theoretical calculations to within the experimental uncertainties.

  PublisherDOI

Recent grants

• Correlated Electron Dynamics in Few-body Systems

  NSF · $210k · 2009–2013

• Theoretical Concepts for Generation and Characterization of Ultraviolet Laser Pulses

  NSF · $300k · 2022–2026

Frequent coauthors

• Agnieszka Jaroń-Becker

  244 shared

• Carlos Hernández-García

  110 shared

• Henry C. Kapteyn

  University of Colorado Boulder

  82 shared

• Margaret M. Murnane

  75 shared

• Joel Venzke

  48 shared

• K. Spruck

  Max Planck Institute for Nuclear Physics

  45 shared

• Tenio Popmintchev

  44 shared

• Camilo Ruíz

  Universidad de Salamanca

  41 shared

Labs

• Becker GroupPI

Awards & honors

• Fellow - JILA