Publications by authors named "Yu Hang Lai"

8 Publications

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Resonance-enhanced high harmonic in metal ions driven by elliptically polarized laser pulses.

Opt Lett 2021 May;46(10):2372-2375

Resonance enhancement of a single order harmonic has been a main attractive feature in high-harmonic generation from laser ablated plumes of metals. Although it has been extensively investigated experimentally and theoretically, studies so far have focused only on linearly polarized driving fields. In this Letter, we study the dependence of the resonant harmonic yield in tin ions on the driving laser ellipticity. We find that the resonance leads to a less rapid decay of the harmonic yield as a function of driving ellipticity, and it is qualitatively reproduced by quantum mechanical simulations. To the best of our knowledge, our findings provide a new type of evidence for supporting previously proposed mechanisms for enhancement.
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http://dx.doi.org/10.1364/OL.425495DOI Listing
May 2021

Diffractive Imaging of C_{60} Structural Deformations Induced by Intense Femtosecond Midinfrared Laser Fields.

Phys Rev Lett 2019 Feb;122(5):053002

Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA.

Theoretical studies indicated that C_{60} exposed to linearly polarized intense infrared pulses undergoes periodic cage structural distortions with typical periods around 100 fs (1  fs=10^{-15}  s). Here, we use the laser-driven self-imaging electron diffraction technique, previously developed for atoms and small molecules, to measure laser-induced deformation of C_{60} in an intense 3.6  μm laser field. A prolate molecular elongation along the laser polarization axis is determined to be (6.1±1.4)% via both angular- and energy-resolved measurements of electrons that are released, driven back, and diffracted from the molecule within the same laser field. The observed deformation is confirmed by density functional theory simulations of nuclear dynamics on time-dependent adiabatic states and indicates a nonadiabatic excitation of the h_{g}(1) prolate-oblate mode. The results demonstrate the applicability of laser-driven electron diffraction methods for studying macromolecular structural dynamics in four dimensions with atomic time and spatial resolutions.
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http://dx.doi.org/10.1103/PhysRevLett.122.053002DOI Listing
February 2019

Femtosecond laser damage of germanium from near- to mid-infrared wavelengths.

Opt Lett 2018 Aug;43(15):3702-3705

Femtosecond laser-induced damage and ablation (fs-LIDA) is a rich field in extreme non-perturbative nonlinear optics with wide ranging applications, including laser micro- and nano-machining, waveguide writing, and eye surgery. Our understanding of fs-LIDA, however, is limited mostly to visible and near-infrared wavelengths. In this work, we systematically study single-shot, fs-laser ablation (fs-LIA) of single-crystal germanium from near- to mid-infrared wavelengths, and compare the fs-LIA wavelength scaling with two widely used models. We show that these models are inadequate, particularly at mid-infrared wavelengths. Instead, a hybrid model is proposed involving Keldysh ionization rates, a constant free-carrier density threshold, and multi-band effects, which yields good agreement with experimental observations. Aspects of this model may be applied to understanding other strong-field non-perturbative phenomena in solids.
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http://dx.doi.org/10.1364/OL.43.003702DOI Listing
August 2018

The roles of photo-carrier doping and driving wavelength in high harmonic generation from a semiconductor.

Nat Commun 2017 11 22;8(1):1686. Epub 2017 Nov 22.

Department of Physics, The Ohio State University, Columbus, OH, 43210, USA.

High-harmonic generation from gases produces attosecond bursts and enables high-harmonic spectroscopy to explore electron dynamics in atoms and molecules. Recently, high-harmonic generation from solids has been reported, resulting in novel phenomena and unique control of the emission, absent in gas-phase media. Here we investigate high harmonics from semiconductors with controllable induced photo-carrier densities, as well as the driving wavelengths. We demonstrate that the dominant generation mechanism can be identified by monitoring the variation of the harmonic spectra with the carrier density. Moreover, the harmonic spectral dependence on the driving wavelength is reported and a different dependence from the well-known one in gas-phase media is observed. Our study provides distinct control of the harmonic process from semiconductors, sheds light on the underlying mechanism and helps optimize the harmonic properties for future solid-state attosecond light sources.
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http://dx.doi.org/10.1038/s41467-017-01899-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5698516PMC
November 2017

High-order harmonic generations in intense MIR fields by cascade three-wave mixing in a fractal-poled LiNbO photonic crystal.

Opt Lett 2017 Oct;42(19):4020-4023

We report on the generation of harmonic-like photon upconversion in a LiNbO-based nonlinear photonic crystal by mid-infrared (MIR) femtosecond laser pulses. We study below bandgap harmonics of various driver wavelengths, reaching up to the 11th order at 4 μm driver with 13% efficiency. We compare our results to numerical simulations based on two mechanisms: cascade three-wave mixing and non-perturbative harmonic generation, both of which include quasi-phase matching. The cascade model reproduces well the general features of the observed spectrum, including a plateau-like harmonic distribution and the observed efficiency. This has the potential for providing a source of tabletop few femtosecond ultraviolet pulses.
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http://dx.doi.org/10.1364/OL.42.004020DOI Listing
October 2017

Tunable mid-infrared source of light carrying orbital angular momentum in the femtosecond regime.

Opt Lett 2017 Oct;42(19):3769-3772

We report on a tunable intense femtosecond mid-infrared (mid-IR) light source carrying orbital angular momentum (OAM). Our setup is based on an optical parametric amplification system with an 800 nm pump shaped with a spiral phase plate. We confirm the anisotropic OAM transfer from the pump to the idler through stimulated difference frequency generation by measuring the diffraction patterns of a triangular aperture illuminated by the signal, pump, and idler beams. The tunability of the setup is demonstrated by performing measurements at 3.0 and 3.6 μm idler wavelengths. This result provides a robust method of controlling OAM in strong field physics and designing secondary sources carrying OAM in the extreme ultraviolet spectral range through high-order harmonics generation.
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http://dx.doi.org/10.1364/OL.42.003769DOI Listing
October 2017

Laser induced periodic surface structure formation in germanium by strong field mid IR laser solid interaction at oblique incidence.

Opt Express 2015 Jul;23(15):19522-34

Laser induced periodic surface structures (LIPSS or ripples) were generated on single crystal germanium after irradiation with multiple 3 µm femtosecond laser pulses at a 45° angle of incidence. High and low spatial frequency LIPSS (HSFL and LSFL, respectively) were observed for both s- and p-polarized light. The measured LSFL period for p-polarized light was consistent with the currently established LIPSS origination model of coupling between surface plasmon polaritons (SPP) and the incident laser pulses. A vector model of SPP coupling is introduced to explain the formation of s-polarized LSFL away from the center of the damage spot. Additionally, a new method is proposed to determine the SPP propagation length from the decay in ripple depth. This is used along with the measured LSFL period to estimate the average electron density and Drude collision time of the laser-excited surface. Finally, full-wave electromagnetic simulations are used to corroborate these results while simultaneously offering insight into the nature of LSFL formation.
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http://dx.doi.org/10.1364/OE.23.019522DOI Listing
July 2015

Diffraction using laser-driven broadband electron wave packets.

Nat Commun 2014 Aug 8;5:4635. Epub 2014 Aug 8.

Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA.

Directly monitoring atomic motion during a molecular transformation with atomic-scale spatio-temporal resolution is a frontier of ultrafast optical science and physical chemistry. Here we provide the foundation for a new imaging method, fixed-angle broadband laser-induced electron scattering, based on structural retrieval by direct one-dimensional Fourier transform of a photoelectron energy distribution observed along the polarization direction of an intense ultrafast light pulse. The approach exploits the scattering of a broadband wave packet created by strong-field tunnel ionization to self-interrogate the molecular structure with picometre spatial resolution and bond specificity. With its inherent femtosecond resolution, combining our technique with molecular alignment can, in principle, provide the basis for time-resolved tomography for multi-dimensional transient structural determination.
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http://dx.doi.org/10.1038/ncomms5635DOI Listing
August 2014