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36 results on '"Lai, Yu Hang"'

3. High spatial frequency laser induced periodic surface structure formation in germanium by mid-IR femtosecond pulses

Author

Austin, Drake. R., Kafka, Kyle R. P., Lai, Yu Hang, Wang, Zhou, Zhang, Kaikai, Li, Hui, Blaga, Cosmin I., Yi, Allen Y., DiMauro, Louis F., and Chowdhury, Enam A.

Subjects
Physics - Optics, Condensed Matter - Materials Science
Abstract

Formation of high spatial frequency laser induced periodic surface structures (HSFL) in germanium by femtosecond mid-IR pulses with wavelengths between $\lambda=2.0$ and $3.6 \; \mathrm{\mu m}$ was studied with varying angle of incidence and polarization. The period of these structures varied from $\lambda/3$ to $\lambda/8$. A modified surface-scattering model including Drude excitation and the optical Kerr effect explains spatial period scaling of HSFL across the mid-IR wavelengths. Transmission electron microscopy (TEM) shows the presence of a $30 \; \mathrm{n m}$ amorphous layer above the structure of crystalline germanium. Various mechanisms including two photon absorption and defect-induced amorphization are discussed as probable causes for the formation of this layer., Comment: 7 pages total (1 page of supplementary material)

Published
2016
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4. Investigation of high harmonic generation from laser ablated plumes of silver.

Author

Konda, Srinivasa Rao, Lai, Yu Hang, and Li, Wei

Subjects
*SILVER, *LASERS, *LASER pulses, *LASER plasmas, *LASER ranging, *ENERGY consumption, *HARMONIC generation
Abstract

Silver (Ag) is one of the important targets in the studies of high harmonic generation (HHG) in the laser-induced plasma due to the relatively high conversion generation efficiencies and cut-off energy. In this work, we study the dependence of HHG in plasma plumes of Ag as a function of various laser parameters, including intensity of ablation pulse, intensity and ellipticity of driving pulse, and the delay between the two pulses. We identify the type of ion that dominates the measured HHG spectra by comparing the experimental data with strong-field approximation simulations and classical calculations for Ag atoms, Ag+, and Ag2+ ions. We also perform a comparative HHG study between the plasmas of bulk Ag target and the plasmas of a nano-powders target. It is found that the harmonic yields in the latter case are higher over a wide range of the aforementioned laser parameters. The results also indicate that the number of nanoparticles in the plasma generated from a nano-powder sample is indeed significantly greater than that in the plasma from the bulk sample. [ABSTRACT FROM AUTHOR]

Published
2021
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17. Perovskite Monocrystals: Ultrathin Perovskite Monocrystals Boost the Solar Cell Performance (Adv. Energy Mater. 34/2020)

Author

Kong, Wenchi, primary, Wang, Shiwei, additional, Li, Feng, additional, Zhao, Chen, additional, Xing, Jun, additional, Zou, Yuting, additional, Yu, Zhi, additional, Lin, Chun‐Ho, additional, Shan, Yuwei, additional, Lai, Yu Hang, additional, Dong, Qingfeng, additional, Wu, Tom, additional, Yu, Weili, additional, and Guo, Chunlei, additional

Published
2020
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19. Ultrathin Perovskite Monocrystals Boost the Solar Cell Performance

Author

Kong, Wenchi, primary, Wang, Shiwei, additional, Li, Feng, additional, Zhao, Chen, additional, Xing, Jun, additional, Zou, Yuting, additional, Yu, Zhi, additional, Lin, Chun‐Ho, additional, Shan, Yuwei, additional, Lai, Yu Hang, additional, Dong, Qingfeng, additional, Wu, Tom, additional, Yu, Weili, additional, and Guo, Chunlei, additional

Published
2020
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22. Diffractive Imaging of C60 Structural Deformations Induced by Intense Femtosecond Midinfrared Laser Fields

Author

Fuest, Harald, primary, Lai, Yu Hang, additional, Blaga, Cosmin I., additional, Suzuki, Kazuma, additional, Xu, Junliang, additional, Rupp, Philipp, additional, Li, Hui, additional, Wnuk, Pawel, additional, Agostini, Pierre, additional, Yamazaki, Kaoru, additional, Kanno, Manabu, additional, Kono, Hirohiko, additional, Kling, Matthias F., additional, and DiMauro, Louis F., additional

Published
2019
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30. Publisher's Note: Universal pulse dependence of the low-energy structure in strong-field ionization [Phys. Rev. A93, 021403(R) (2016)]

Author

Zhang, Kaikai, primary, Lai, Yu Hang, additional, Diesen, Elias, additional, Schmidt, Bruno E., additional, Blaga, Cosmin I., additional, Xu, Junliang, additional, Gorman, Timothy T., additional, Légaré, François, additional, Saalmann, Ulf, additional, Agostini, Pierre, additional, Rost, Jan M., additional, and DiMauro, Louis F., additional

Published
2016
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33. Laser induced periodic surface structure formation in germanium by strong field mid IR laser solid interaction at oblique incidence

Author

Austin, Drake R., primary, Kafka, Kyle R. P., additional, Trendafilov, Simeon, additional, Shvets, Gennady, additional, Li, Hui, additional, Yi, Allen Y., additional, Szafruga, Urszula B., additional, Wang, Zhou, additional, Lai, Yu Hang, additional, Blaga, Cosmin I., additional, DiMauro, Louis F., additional, and Chowdhury, Enam A., additional

Published
2015
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35. Strong Field Phenomena in Atoms and Molecules from Near to MidInfrared Laser Fields

Author

Lai, Yu Hang

Subjects
Physics, Atomic, molecular and optical physics, Strong field physics, Ultrafast laser
Abstract

Strong field atomic physics is the study of the interaction between an atom and an intense laser pulse such that the field strength is ``not-so-small" compared to an atomic unit (50 V/\AA) and so it could not be treated as just a perturbation to the atomic system. Depending upon the ionization potential of the target, typical laser intensity required to reach this regime ranges from $\sim 10$ to 1000 TW/cm$^2$ (the corresponding peak field strength : $\sim$0.017 - 0.17 V/\AA). In the low frequency limit, the photoionization process can be interpreted as a tunneling process in which the atomic potential is ``tilted" by the laser field allowing the electron to escape via quantum tunneling. The escaped electron wavepacket quivers in the strong laser field whose kinetic energy is characterized by the ponderomotive energy $U_p$ which is proportional to the laser intensity and the square of the wavelength. Electron recollision happens when the ionized electron is driven back towards its parent ion by the laser field and it leads to numerous intriguing phenomena such as high-order above-threshold ionization, non-sequential ionization and high-order harmonic generation. While most of the early experiments were performed in the near-infrared (NIR)(0.8 or 1 $\mu$m) wavelengths, an important advance over the last decade has been the emergence of intense mid-infrared (MIR)($\sim 2-4$ $\mu$m) sources. The quadratic scaling of $U_p$ with wavelength benefits the study of recollision-driven phenomena and also enables the exploration of strong field interaction deep in the tunneling regime. In addition, the MIR regime is of particular interest for studying molecules due to the presence of vibrational resonances. In this dissertation, we explore several strong field phenomena in atoms and molecules with near and mid infrared fields, including:1. A comprehensive experimental benchmarking of strong field atomic ionization theories. We performed a comparative study between experiment and theories of the total intensity-dependent ionization yield for different atom species at different laser wavelengths ($0.4 - 4 \mu$m) at linear and circular polarizations in order to investigate the applicability of two commonly used strong field ionization theories, Perelomov, Popov and Terent’ev (PPT) and Ammosov, Delone and Krainov (ADK) models. 2. Ionization and fragmentation of methane in vibrationally resonant MIR fields. We measured the mass spectra of fragments of methane irradiated by MIR fields which cover the resonant frequency range of the C-H bond stretching mode vibration ($3.2 - 3.5 \mu$m). We observed significant enhancement in ionization and dissociation rate at resonant wavelengths compared with non-resonant wavelengths. 3. Electron recollision in tunnel ionization of C$_{60}$ fullerenes in MIR fields. From the ``soft" recollision for low energy electrons we found an unexpected suppression of the ``low-energy structure” which might be attributed to the induced dipole field; from the ``hard" recollision for high energy electrons we demonstrated the applicability of the ``laser-induced electron diffraction” technique for imaging macromolecule and observed hint of laser induced deformation of the molecular structure.4. Strong field double ionization with circularly polarized NIR fields. We searched for the existence of recollision effects in double ionization of magnesium, zinc and calcium at different wavelength in order to examine the validity of the classical interpretation for the previously observed enhanced double ionization yield in magnesium irradiated by circularly polarized 0.8 $\mu$m fields.

Published
2018

36. High-order harmonic generations in intense MIR fields by cascade three-wave mixing in a fractal-poled LiNbO 3 photonic crystal.

Author

Park H, Camper A, Kafka K, Ma B, Lai YH, Blaga C, Agostini P, DiMauro LF, and Chowdhury E

Abstract

We report on the generation of harmonic-like photon upconversion in a LiNbO 3 -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.

Published
2017
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