TY - JOUR

T1 - Periodical Ultra-Modulation of Broadened Laser Spectra in Dielectrics at Variable Ultrashort Laser Pulsewidths: Ultrafast Plasma, Plasmonic and Nanoscale Structural Effects

AU - Kudryashov, Sergey

AU - Danilov, Pavel

AU - Gorevoy, Alexey

AU - Kovalov, Volodymyr

AU - Kosobokov, Mikhail

AU - Akhmatkhanov, Andrey

AU - Lisjikh, Boris

AU - Turygin, Anton

AU - Greshnyakov, Evgeny

AU - Shur, Vladimir

N1 - The research funding from the Ministry of Science and Higher Education of the Russian Federation (Ural Federal University Program of Development within the Priority-2030 Program) is gratefully acknowledged. The equipment of the Ural Center for Shared Use “Modern nanotechnology” of Ural Federal University (Reg.# 2968), which is supported by the Ministry of Science and Higher Education of Russian Federation (Project #075–15- 2021–677), was used.

PY - 2023

Y1 - 2023

N2 - Self-phase modulation (SPM) broadening of prompt laser spectra was studied in a transmission mode in natural and synthetic diamonds at variable laser wavelengths (515 and 1030 nm), pulse energies and widths (0.3–12 ps, positively chirped pulses), providing their filamentary propagation. Besides the monotonous SPM broadening of the laser spectra versus pulse energy, which was more pronounced for the (sub)picosecond pulsewidths and more nitrogen-doped natural diamond with its intra-gap impurity states, periodical low-frequency modulation was observed in the spectra at the shorter laser pulsewidths, indicating dynamic Bragg filtering of the supercontinuum due to ultrafast plasma and nanoplasmonic effects. Damping of broadening and ultra-modulation for the longer picosecond pulsewidths was related to the thermalized electron-hole plasma regime established for the laser pulsewidths longer, than 2 ps. Unexpectedly, at higher pulse energies and corresponding longer, well-developed microfilaments, the number of low-intensity, low-frequency sideband spectral modulation features counterintuitively increases, thus indicating dynamic variation of the periods in the longitudinal plasma Bragg gratings along the filaments due to prompt secondary laser–plasmon interactions. The underlying sub- and/or near-wavelength longitudinal nanoscale Bragg gratings produced by femtosecond laser pulses in this regime could be visualized in less hard lithium niobate by atomic force microscopy cross-sectional analysis in the correlation with the corresponding sideband spectral components, supporting the anticipated Bragg filtering mechanism and envisioning the corresponding grating periods. © 2023 by the authors.

AB - Self-phase modulation (SPM) broadening of prompt laser spectra was studied in a transmission mode in natural and synthetic diamonds at variable laser wavelengths (515 and 1030 nm), pulse energies and widths (0.3–12 ps, positively chirped pulses), providing their filamentary propagation. Besides the monotonous SPM broadening of the laser spectra versus pulse energy, which was more pronounced for the (sub)picosecond pulsewidths and more nitrogen-doped natural diamond with its intra-gap impurity states, periodical low-frequency modulation was observed in the spectra at the shorter laser pulsewidths, indicating dynamic Bragg filtering of the supercontinuum due to ultrafast plasma and nanoplasmonic effects. Damping of broadening and ultra-modulation for the longer picosecond pulsewidths was related to the thermalized electron-hole plasma regime established for the laser pulsewidths longer, than 2 ps. Unexpectedly, at higher pulse energies and corresponding longer, well-developed microfilaments, the number of low-intensity, low-frequency sideband spectral modulation features counterintuitively increases, thus indicating dynamic variation of the periods in the longitudinal plasma Bragg gratings along the filaments due to prompt secondary laser–plasmon interactions. The underlying sub- and/or near-wavelength longitudinal nanoscale Bragg gratings produced by femtosecond laser pulses in this regime could be visualized in less hard lithium niobate by atomic force microscopy cross-sectional analysis in the correlation with the corresponding sideband spectral components, supporting the anticipated Bragg filtering mechanism and envisioning the corresponding grating periods. © 2023 by the authors.

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U2 - 10.3390/photonics10121316

DO - 10.3390/photonics10121316

M3 - Article

VL - 10

JO - Photonics

JF - Photonics

SN - 2304-6732

IS - 12

M1 - 1316

ER -