Recent Publication

Single-Shot Multi-Stage Damage and Ablation of Silicon by Femtosecond Mid-infrared Laser Pulses

Kevin Werner, Vitaly Gruzdev, Noah Talisa, Kyle Kafka, Drake Austin, Carl M. Liebig, Enam Chowdhury
Scientific Reports volume 9, Article number: 19993 (2019)
Abstract: Although ultrafast laser materials processing has advanced at a breakneck pace over the last two decades, most applications have been developed with laser pulses at near-IR or visible wavelengths. Recent progress in mid-infrared (MIR) femtosecond laser source development may create novel capabilities for material processing. This is because, at high intensities required for such processing, wavelength tuning to longer wavelengths opens the pathway to a special regime of laser-solid interactions. Under these conditions, due to the λ2 scaling, the ponderomotive energy of laser-driven electrons may significantly exceed photon energy, band gap and electron affinity and can dominantly drive absorption, resulting in a paradigm shift in the traditional concepts of ultrafast laser-solid interactions. Irreversible high-intensity ultrafast MIR laser-solid interactions are of primary interest in this connection, but they have not been systematically studied so far. To address this fundamental gap, we performed a detailed experimental investigation of high-intensity ultrafast modifications of silicon by single femtosecond MIR pulses (λ = 2.7–4.2 μm). Ultrafast melting, interaction with silicon-oxide surface layer, and ablation of the oxide and crystal surfaces were ex-situ characterized by scanning electron, atomic-force, and transmission electron microscopy combined with focused ion-beam milling, electron diffractometry, and μ-Raman spectroscopy. Laser induced damage and ablation thresholds were measured as functions of laser wavelength. The traditional theoretical models did not reproduce the wavelength scaling of the damage thresholds. To address the disagreement, we discuss possible novel pathways of energy deposition driven by the ponderomotive energy and field effects characteristic of the MIR wavelength regime.


Nonlinear manifestations of photon acceleration in time-dependent metasurfaces: tunable broadband harmonics generation

Authors: Maxim R. ShcherbakovKevin WernerZhiyuan FanNoah TalisaEnam ChowdhuryGennady Shvets

AbstractTime-dependent nonlinear media, such as rapidly generated plasmas produced via laser ionization of gases, can increase the energy of individual laser photons and generate tunable high-order harmonic pulses. This phenomenon, known as photon acceleration, has traditionally required extreme-intensity laser pulses and macroscopic propagation lengths. Here, we report on a novel nonlinear materialan ultrathin semiconductor metasurfacethat exhibits efficient photon acceleration at low intensities. We observe a signature nonlinear manifestation of photon acceleration: third-harmonic generation of near-infrared photons with tunable frequencies reaching up to 3.1ω. A simple time-dependent coupled-mode theory, found to be in good agreement with experimental results, is utilized to predict a new path towards nonlinear radiation sources that combine resonant upconversion with broadband operation. △ Less

Accepted for publication

  • Kevin Werner and Enam Chowdhury, Extreme Sub-Wavelength Structure Formation from Mid-IR Femtosecond Laser Interaction with Silicon, Nanomaterials 2021, 11(5), 1192;
  • Sara M Mueller, Dongjoon Kim, Stephen R McMillan, Steven J Tjung, Jacob J Repicky, Stephen Gant, Evan Lang, Fedor Bergmann, Kevin Werner, Enam Chowdhury, Aravind Asthagiri, Michael E Flatte and Jay A Gupta, Tunable tunnel barriers in a semiconductor via ionization of individual atoms, Journal of Physics: Condensed Matter (2021)


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