Emission spectroscopy of laser ablation plume: Composition analysis of a target in water

Emission spectra of the laser ablation plume formed by the irradiation of Cu65/Zn35 binary alloy in water at the room temperature with 150-ns pulsed laser were measured. The spectra were analyzed by comparing with the theoretical calculation based on the assumption that self-absorption effect is negligible and that the same temperature can be applied to Cu atoms and Zn atoms in the plume. The calculation reproduced the spectra very well and gave reasonable temperature as a best-fit parameter. However, the best-fit value of the Cu atomic density relative to Zn is significantly low compared with the target composition. Care should be taken to perform in situ LIBS in liquid due to the complicated plume formation mechanism and dynamics of material intake into the plume.     

Influence of Laser Wavelength on Laser-induced Breakdown Spectroscopy Applied to Semi-Quantitative Analysis of Trace-Elements in a Plant Sample

Laser-induced breakdown spectroscopy （LIBS） as a powerful analytical technique is applied to analyze trace- elements in fresh plant samples. We investigate the LIBS spectra of fresh holly leaves and observe more than 430 lines emitted from 25 elements and molecules in the region 230-438nm. The influence of laser wavelength on LIBS applied to semi-quantitative analysis of trace-element contents in plant samples is studied. The results show that the UV laser has lower relative standard deviations and better repeatability for semi-quantitative analysis of trace-element contents in plant samples. This work may be helpful for improving the quantitative analysis power of LIBS applied to plant samples.     

Study of the plasmas produced during the deposition of TiC/SiC thin films in a hybrid magnetron-laser system

Time- and spatially-resolved optical emission spectroscopy was performed to characterize the plasma produced in a hybrid magnetron-sputtering-laser deposition system, which is used for TiC or SiC thin films preparation. A graphite target was ablated by a KrF excimer laser (λ=248 nm,τ=20 ns) and either Ti or Si targets were used for DC magnetron sputtering in argon ambient. Spectra were measured in the range 250–850 nm. The evolution of the spectra with varying magnetron powers (0–100 W) and argon pressures (0.3–10 Pa) was studied. Spectra of the plasmas produced by a) the magnetron alone, b) the ablation laser alone, and c) the magnetron and the ablation laser together, were recorded. Spectra (a) were dominated by Ar atoms and Ar⁺ ions. Emission lines of Ti and Si were detected, when Ti target and Si target was used, respectively. Spectra (b) revealed emission of C, C⁺, C₂, Ar, Ar⁺. Spectra (c) showed presence of all previously mentioned species and further of Ti⁺ ions emission was detected. The research was supported by Grant Agency of the Czech Republic No. 202/06/02161, GA ASCR project number A1010110/01 and Institutional Research Plan AV CR No. AV0Z 10100522.     

Substrate dependence of ion motion in femtosecond laser ablation cloud observed by planar laser-induced fluorescence

We have observed the motion of Sm⁺ ions as well as Sm atoms produced by femtosecond laser ablation of a solidified samarium solution sample on substrates by using a planar laser-induced fluorescence method. Kinetic energies of both Sm⁺ ions and Sm atoms increase as the electrical conductivity of the substrate decreases, which suggests the effect of surface charging. The kinetic energy of Sm⁺ ions is larger than that of Sm atoms for a variety of substrates due to the further electrical acceleration by the surface charge. The knowledge of ion motion will be the key information for the optimization of femtosecond laser simultaneous atomization and ionization of organic and inorganic samples on substrates.     

Femtosecond laser-induced cleaving of protein crystal in water solution

For precise X-ray diffraction (XRD) measurement giving the three-dimensional structure of proteins, it is important to prepare high-quality single crystals with suitable shape. As a new processing technique to obtain such protein crystals, we employed femtosecond laser-induced cleaving of protein crystal in a growth vessel containing water solution. An intact protein crystal was precisely processed without mechanical contact in its sealed growth vessel by focusing femtosecond laser pulses. We confirmed that three-dimensional processing of the crystal in its supersaturated solution was realized using multiphoton absorption and that the processing was efficiently enhanced by the cleaving behavior attributed to a photomechanical mechanism of the femtosecond laser ablation.     

Effect of ionization on laser-induced plume self-similar expansion

The dynamics of a laser ablation plume during the first stage of its expansion, just after the termination of the laser pulse is modelled. The one-dimensional expansion of the evaporated material, considered as an ideal fluid, is governed by one-fluid Euler equations. For high energetic ions, the charge separation can be neglected and the hydrodynamics equations solved using self-similar formulation. Numerical solution is obtained, first when the laser fluence range is low enough to deal with a neutral vapor, and in a second stage, when ionization effects on the expansion are taken into account, for different material targets. As a main result, we found that the presence of ions in the evaporated gas enhances the self-similar expansion.     

Nano- and microdot array formation by laser-induced dot transfer

Fabrication of FeSi₂ nano- and microdot array was performed by utilizing droplet ejection through laser-induced forward transfer, which we named laser-induced dot transfer (LIDT). An amorphous FeSi₂ alloy source film on a transparent support was illuminated from the support by a nanosecond excimer laser pulse patterned into migcrogrid form, resulting in size- and site-controlled dot deposition. Micro-Raman spectroscopy confirmed β-FeSi₂ semiconducting crystalline phase even on unheated substrates. Moreover, the microdots exhibited near-infrared photoluminescence at the peak wavelength of 1.57 μm, which comes from the β-FeSi₂ crystalline phase precipitated during the LIDT process. The dot size was successfully reduced to approximately 500 and 300 nm in diameter and height, respectively. This technique is useful for integrating functional nano- and microdots under atmospheric room-temperature conditions.     

Modulation-free acetylene-stabilized lasers at 1542 nm using modulation transfer spectroscopy

We report frequency stabilization of diode lasers using modulation transfer spectroscopy of an acetylene transition (¹³C₂H₂, ₁+₃, P(16)) at 1542 nm. We realize modulation-free acetylene-stabilized lasers with a frequency stability of about 10^–11 and an absolute frequency accuracy of about 20 kHz.This revised version was published online in March 2005. In the previous version, the published online date was missing     

Ultrahigh-resolution saturation spectroscopy using slow molecules in an external cell

We present the narrowest molecular lines so far recorded in the 10 µm spectral region. A linewidth of 80 Hz (HWHM) has been obtained for theP(39)A ₁ ³ (–) line of OsO₄, by selecting slow molecules (T _eff=0.6 K) in saturation spectroscopy at low laser fields (30 nW) and low pressures (2 × 10^–6 Torr). In these conditions, the contribution of the fast molecules is greatly reduced because of the finite size of the beam. This method, applied previously to methane at 3.39 µm, is used for the first time in an external cell and improves by a factor 8 the best resolution of our spectrometer. Heterodyne detection and double frequency modulation have been necessary to extract a signal at a contrast of only 10^–6. The physical ideas concerning this regime are described and a detailed analysis of the line shape is given.     

Formation of TiN-Ir particle films using pulsed-laser deposition and their electrolytic properties in producing hypochlorous acid

Using sintered TiN and TiN-Ir (Ir contents: 5.9-14.2 at.%) targets, pulsed-laser deposition (PLD) was carried out to produce thin films composed of nanoparticles and particulates in the presence of nitrogen gas. The size (2-100 nm) of the produced crystalline TiN nanoparticles increased as nitrogen pressure was increased in the range from 1.33 to 1.33 × 10² Pa. At a pressure of 1.33 × 10³ Pa, amorphous TiN nanoparticles combined in the form of chains. Large Ir particulates with diameters of up to 2 μm were particularly prominent in TiN-Ir films. Size distributions of the Ir particulates were dependent on ablation laser wavelength; that is, the diameter decreased at laser wavelength shortened. The TiN-Ir films with different Ir contents and morphologies on Ti substrates were evaluated as electrolysis electrodes for water disinfection. The highest current efficiency was 0.45%, which is comparable to that of conventional Ti-Pt electrodes, for a chloride-ion concentration of 9 mg dm⁻³.     

Drilling enhancement by nanosecond-nanosecond collinear dual-pulse laser ablation of titanium in vacuum

Laser ablation of titanium in vacuum was performed using single- and dual-pulse regime in order to study crater formation. Crater profiles were analyzed by optical microscopy. It was found that the repetition-rate plays an important role in a process of laser ablation. The drilling is most effective for the highest repetition-rate. For the same total number of laser pulses clear drilling enhancement was achieved by dual-pulse regime of ablation in comparison to single-pulse regime. The strongest ablation rate in dual-pulse regime was achieved for the delay time between the pulses τ = 370 ns. Results are discussed in terms of decreased ablation threshold due to continuous heating of the target during the experiment.     

Nanoparticle injection to single animal cells using femtosecond laser-induced impulsive force

An impulsive force, which was generated by focusing tightly a femtosecond laser into a cell culture medium, was applied to inject nanoparticles into local areas of a single mouse fibroblast NIH3T3 cell. When the impulsive force was induced near the cell, the nanoparticles adhering on the cell membrane were introduced, which was directly confirmed by confocal fluorescence microscopy.     

High-resolution VUV spectroscopy using pulsed laser sources

The resonance spectroscopic techniques - level-crossing, optical double resonance and quantum-beat spectroscopy - have been employed following pulsed laser excitation. The use of pulsed lasers has enabled spectroscopic studies of atomic structures and radiative lifetimes in the UV/VUV spectral region.     

Measurement of UV absorption of single living cell for cell manipulation using NIR femtosecond laser

Optical UV absorption of single human living cells ranging from 200 nm to 360 nm was measured in situ for the study of cell manipulation using the near-infrared (NIR) femtosecond laser. Human breast living cells of MCF-10A, MCF-7, and MDA-MB-231 were used in this experiment. The selective photo-disruptions of single living cell and its sub-organelle (nucleus) were also demonstrated using the tightly focused 790 nm wavelength femtosecond laser with pulse duration of 110 fs. It was found that each living cell has its own absorption spectrum in UV wavelength ranges. It was also inferred that intrinsic absorption spectrum is attributed to the amount of DNA and protein of living cell. For the study of photo-disruption of single cell using the multi-photon absorption excited by the NIR femtosecond laser pulse, the origin UV absorption spectrum of targeted living cell is important and fundamental information to understand nonlinear interaction between NIR ultrashort, high-intensity laser light and transparent living cell.     

Single-shot laser-induced fluorescence imaging of formaldehyde with XeF excimer excitation

Single-shot formaldehyde laser-induced fluorescence (LIF) imaging measurements in a technical scale turbulent flame have been obtained using XeF excimer laser excitation in the ?¹A₂-˜X¹A₁ transition at 353.2 nm. Measurements have been carried out in a 150 kW natural gas swirl burner where formaldehyde distribution fields have the potential, in combination with OH concentration fields, to visualize the heat release distribution and therefore give an optimal visualization of flame-front positions. The extended areas where formaldehyde was detected in the swirl flame indicates the presence of low temperature chemistry in preheated gas pockets before ignition. Received: 31 January 2000 / Revised version: 2 March 2000 / Published online: 5 April 2000     

Degenerate four-wave-mixing spectroscopy in NaH

We performed DFWM spectroscopy on X ^–1+–A ¹⁺ transitions in NaH produced in an indirect photochemical reaction between Na(3p) and H₂ and detected v=1, 2 and 3 ground state vibrational levels of NaH molecules, whereas with resonance enhanced CARS, we observed v=0 levels only. This different sensitivity can be explained by considering the Franck-Condon-factors and the relevant damping coefficients for the corresponding transitions in the NaH molecule. Time resolved DFWM spectroscopy showed that NaH(v=1) molecules effectively live much longer than Na(3p) atoms which merely follow the laser excitation pulse.     

Tritium recovery from co-deposited layers using 193-nm laser

Recovery of tritium from co-deposited layers formed in deuterium–tritium plasma operations of the TFTR (Tokamak Fusion Test Reactor) was investigated by the use of an ArF excimer laser operating at the wavelength of 193 nm. At the laser energy density of 0.1 J/cm², a transient spike of the tritium-release rate was observed at initial irradiation. Hydrogen isotopes were released in the form of hydrogen-isotope molecules during the laser irradiation in vacuum, suggesting that tritium can be recovered readily from the released gases. In a second experiment, hydrogen (tritium) recovery from the co-deposited layers on JT-60 tiles that had experienced hydrogen-plasma operations was investigated by laser ablation with a focused beam of the excimer laser. The removal rate of the co-deposited layers was quite low when the laser energy density was smaller than the ablation threshold (1.0 J/cm²), but reached 1.1 μm/pulse at the laser energy density of 7.6 J/cm². The effective absorption coefficient in the co-deposited layers at the laser wavelength was determined to be 1.9 μm^-1. The temperature of the surface during the irradiation at the laser energy density of 0.5 J/cm² was measured on the basis of Planck’s law of radiation, and the maximum temperature during the irradiation decreased from 3570 K at the initial irradiation to 2550 K at the 1000th pulse of the irradiation. Received: 5 August 2002 / Accepted: 7 August 2002 / Published online: 28 October 2002 RID="*" ID="*"Corresponding author. Fax: +81-29/2825917, E-mail: shu@tpl.tokai.jaeri.go.jp     

Deep drilling of metals by femtosecond laser pulses

Results of recent investigations on deep drilling of metals by femtosecond laser pulses are reported. At high laser fluences, well above the ablation threshold, femtosecond lasers can drill deep, high-quality holes in metals without any post-processing or special gas environment. It is shown that for high-quality drilling of metals, the following processes are important: (1) laser-induced optical breakdown of air containing metal vapor and small metal particles (debris) generated by multi-pulse femtosecond laser ablation, (2) transformation of laser pulses into light filaments, and (3) low-fluence finishing. Received: 15 November 2002 / Accepted: 20 January 2003 / Published online: 28 May 2003 RID="*" ID="*"Corresponding author. Fax: +49-511/2788-100, E-mail: ch@lzh.de     

2D imaging of laser wing effects and of soot sublimation in laser-induced incandescence measurements

The distribution of Laser-Induced Incandescence (LII) signal in sooting flames along the laser beam is imaged using two directions of observation: one counter to the propagation direction of the incident laser (backward LII) and one at right angles. It is shown that the effective probe volume, in which the LII signal is observed, is highly dependent on the laser irradiance profile. At high fluence, the LII from the central part of the beam decreases because of soot sublimation. This decrease can be compensated by an increase in the LII from the wings of the laser beam. This interaction is particularly important in the extraction of quantitative information in the backward LII case, which is the configuration best suited to the practical application of LII for in-situ particle concentration measurements in the exhaust of aero-engines.