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Femtosecond Laser Micromachining of Metal Thin Films
摘要： In this paper the possibilities of femtosecond laser micromachining of thin-film titanium coatings for elements of microelectronics and optoelectronics are considered. Using pulsed laser deposition in vacuum (wavelength λ = 1030 nm, pulse repetition frequency f = 10 kHz, Emax pulse energy ≈ 150 μJ, pulse duration τ ≈ 280 fs), a thin-film titanium coating was obtained on the surface of the quartz substrate. An example of the formation of an element of a given geometry by selective laser ablation of areas of a deposited metal coating is shown.
关键词： ultrashort laser pulses,precision micromachining,laser ablation,thin metal films
更新于2025-09-12 10:27:22
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Influence of laser spot size and shape on ablation efficiency using ultrashort pulse laser system
摘要： Ultra-short pulsed laser systems provide high accuracy and high-quality materials processing for various kinds of applications. However, one of the highest industrial needs is to identify most efficient processes to achieve high throughput. In terms of ultra-short pulsed laser processing of metals, the specific removal rate (ablated volume per time and average power) shows a maximum value i.e. there exists an optimum fluence where the ablation process is most efficient. In this study the influence of spot size and shape (Gaussian and Top Hat) on the ablation efficiency on AISI 304 (1.4301) steel grade was examined using 10 ps and 350 fs laser pulses at wavelengths of 1064 nm and 1030 nm. The investigation revealed a significant drop of the specific removal rate with increasing Gaussian spot size for both pulse duration. While this behaviour is less pronounced for a Top Hat, showing just 8% decrease of specific removal rate for spot sizes bigger than 40 μm.
关键词： ablation efficiency,ultrashort laser pulses,Top Hat,specific removal rate,laser spot size
更新于2025-09-12 10:27:22
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Nonlinear absorption dynamics simulated in internal modification of glass at 532nm and 1064nm by ultrashort laser pulses
摘要： Dynamic ionization process at high pulse repetition rate is analysed based on the model consisting of rate equation for free-electrons, Gaussian beam propagation equation, thermal conduction and thermal ionization, showing the plasma generated near the geometrical focus moves toward the laser source periodically by the contribution of avalanche ionization. The effects of laser wavelength on the ionization process are discussed by comparing the contributions of multiphoton ionization and avalanche ionization. The crack tendency of 532nm and 1064nm is also compared between single pulse and multipulse irradiation.
关键词： thermal conduction model,nonlinear ionization process,glass,internal modificatin,thermal ionization,crack,ultrashort laser pulses
更新于2025-09-12 10:27:22
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Dependence of the Two-Photon Absorption Coefficient of Steel on the Pulse Duration During Its Ablation by Femto- and Picosecond Laser Pulses
摘要： The dependences of the depth of single-pulse ablation of the steel surface on the energy density of ultrashort laser pulses (0.3–12 ps) with a wavelength of 515 nm have the form different from the usual logarithmic one for linear absorption of radiation. Since the density of states of free conduction electrons in the s band is low, and the d band of strongly bound electrons with a high density of states is located around the Fermi level, these dependences have been approximated within the two-photon absorption model. The two-photon absorption coefficient increases almost linearly with the duration of laser pulses, which indicates the saturation of absorption and allows estimating the corresponding parameters of the electronic subsystem.
关键词： picosecond,two-photon absorption,femtosecond,ultrashort laser pulses,steel ablation
更新于2025-09-12 10:27:22
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Influence of surface plasmon polaritons on laser energy absorption and structuring of surfaces
摘要： The accurate calculation of laser energy absorption during femto- or picosecond laser pulse experiments is very important for the description of the formation of periodic surface structures. On a rough material surface, a crack or a step edge, ultrashort laser pulses can excite surface plasmon polaritons (SPP), i.e. surface plasmons coupled to a laser-electromagnetic wave. The interference of such plasmon wave and the incoming pulse leads to a periodic modulation of the deposited laser energy on the surface of the sample. In the present work, within the frames of a Two Temperature Model we propose the analytical form of the source term, which takes into account SPP excited at a step edge of a dielectric-metal interface upon irradiation of an ultrashort laser pulse at normal incidence. The influence of the laser pulse parameters on energy absorption is quantified for the example of gold. This result can be used for nanophotonic applications and for the theoretical investigation of the evolution of electronic and lattice temperatures and, therefore, of the formation of surfaces with predestined properties under controlled conditions.
关键词： Laser energy absorption,Surface plasmon polaritons,Plasmonics,LIPSS,Ultrashort laser pulses
更新于2025-09-11 14:15:04
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Temporal evolution of photo-induced thermal strain in InSb probed by ultra-short laser produced Cu Kα x-rays
摘要： Development and characterization of a wire target based kHz rep rate Cu Kα x-ray source using a Ti:sapphire laser system and its use in time resolved x-ray diffraction (TXRD) of the InSb (111) sample are presented. The observed Kα x-ray photon flux is ～3.2 × 109 photons sr?1 s?1 at a laser intensity of ～3.5 × 1016 W cm?2. TXRD signal from the InSb (111) crystal pumped by an ultrashort Ti:sapphire laser pulse (fluence ～ 13 mJ cm?2) shows a lattice expansion due to heating on a multipicosecond time scale. The crystal gradually cools down and recovers at ～1.5 ns after the laser excitation. The observed strain variation in the crystal matches well with the simulated results. The study of full recovery of the sample will be helpful for the development of InSb based devices.
关键词： Cu Kα x-ray source,time resolved x-ray diffraction,ultrashort laser pulses,thermal strain,InSb
更新于2025-09-11 14:15:04
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All-optical field-free three-dimensional orientation of asymmetric-top molecules
摘要： Orientation and alignment of molecules by ultrashort laser pulses is crucial for a variety of applications and has long been of interest in physics and chemistry, with the special emphasis on stereodynamics in chemical reactions and molecular orbitals imaging. As compared to the laser-induced molecular alignment, which has been extensively studied and demonstrated, achieving molecular orientation is a much more challenging task, especially in the case of asymmetric-top molecules. Here, we report the experimental demonstration of all-optical field-free three-dimensional orientation of asymmetric-top molecules by means of phase-locked cross-polarized two-color laser pulse. This approach is based on nonlinear optical mixing process caused by the off-diagonal elements of the molecular hyperpolarizability tensor. It is demonstrated on SO2 molecules and is applicable to a variety of complex nonlinear molecules.
关键词： ultrashort laser pulses,nonlinear optical mixing,hyperpolarizability tensor,molecular orientation,asymmetric-top molecules
更新于2025-09-09 09:28:46