Laser Radiation In Plasma Research Articles

Absolutely calibrated EUV spectra of Xe laser plasma radiation for lithography needs

Spectra of Xe laser plasma radiation were measured using Si/Mo and Mo/Be interference mirrors. The intensity within the 11.0-11.8 nm wavelength band has been shown to be 6-7 times as high than that in the 12.5-14 nm range. The spectra obtained by means of the mirrors are compared with those measured earlier using a spectrometer.

Aperiodic reflection diffraction gratings for soft X-ray radiation and their application

We briefly review the works concerned with the development and experimental use of the spectral instruments based on aperiodic reflection gratings whose spacing varies monotonically across the aperture according to a prescribed law (VLS gratings). The review considers the employment of VLS-grating instruments intended for the spectroscopy of laboratory and astrophysical plasmas, including the diagnostics of relativistic laser plasmas, for measuring X-ray laser linewidths, for recording the high-order harmonics of laser radiation, the radiation of fast electric discharges and other laboratory X-ray sources, as well as in reflectometry, X-ray fluorescence analysis and microscopy with the use of synchrotron radiation and laser-plasma radiation, and in emission spectroscopy combined with an electron microscope. Also discussed are achievements in the recently undertaken design and development of special-purpose VLS spectrometers intended for the investigation of the electronic structure of different materials and molecules by the spectroscopic technique of resonant inelastic X-ray scattering of synchrotron radiation. We describe flat-field grazing-incidence spectrometers with concave VLS gratings, which are compatible with modern CCD detectors, as well as plane VLS gratings, which are the key elements of scanning high- and ultrahigh-resolution spectrometers/monochromators with a constant deviation angle and stigmatic (imaging) spectrometers, which are also compatible with CCD detectors.

Absolutely Calibrated Spectrally Resolved Measurements of Xe Laser Plasma Radiation Intensity in the EUV Range

With the aid of Mo/Be and Si/Mo interference mirrors, measurements of radiation intensity from laser plasma with Xe gas-jet target have been realized within a wavelength interval of 11–14 nm with a spectral resolution of 3–6 A. The results are compared with the spectrum formerly measured with the aid of a spectrograph. The ratio of intensities at wavelengths of 11.2 and 13.5 nm has been found to be about 10 under experimental conditions studied.

Spectral characterisation of aperiodic normal-incidence Sb/B4C multilayer mirrors for the λ < 124 Å range

Three broadband aperiodic Sb/B4C multilayer mirrors were synthesised for the purposes of soft X-ray optics and spectroscopy in the wavelength range beyond the L-edge of Si (λ < 124 Å), and their reflection spectra were measured. The multilayer structures were optimised for maximum uniform reflectivity in the ranges 100 – 120 Å, 95 – 105 Å and 90 – 100 Å. The reflection spectra were recorded using a laboratory laser-plasma radiation source and an electronic detector with a 2D spatial resolution (a CCD matrix with 13 × 13 μm sized pixels). The experimental spectra are compared with theoretical calculations. The effect of lower antimony and B4C layer densities on the reflection spectra is discussed.

A method for determination of spatial distribution of gas concentration in supersonic jets outflowing into vacuum

An experimental method for determination of the spatial distribution of gas concentration in millimeter-sized supersonic jets outflowing into vacuum is proposed. This method is based on jet visualization by its illumination with a laser–plasma radiation source and processing of the obtained intensity distribution of the jet glow. The spatial distribution of the jet glow intensity for the visualized jet is measured. The gas concentration distribution in the jet is determined, and the results of experiment are compared with the calculated data obtained by numerical hydrodynamic simulation.

Analysis of induced stress on materials exposed to laser-plasma radiation during high-intensity laser experiments

In this work, we investigate the damage produced in materials when exposed to a laser-generated plasma. The plasma was generated by interaction of a high-intensity laser with Oxygen. We demonstrate that the stress induced on the target surface of a Tantalum target (typical materials used as Plasma Facing Material) after 10h of plasma exposure is equivalent to the stress induced during 1h of conventional laser ablation using a pulsed 0.5J laser. In both cases we obtain a surface erosion in the tens of μm, and a change in the surface roughness in the tens of nm for the stressed materials. The erosion rate of 1nm/s, explained in terms of surface fragmentation at thermodynamic equilibrium, generates a slow damage to the materials exposed to the plasma. Our method allows indicating safety parameters for the maintenance of materials used in high-intensity laser experiments.

Determination of the reflectivity curve of a spherically bent mica crystal used to diagnose X-ray radiation of relativistic laser plasma

A method for determining the crystal reflectivity curve, based on the use of a broadband X-ray source and an additional spectrometer with preliminarily measured characteristics is proposed. Such a technique does not allow determination of the absolute reflectivity, but makes it possible to measure the dependence of its relative values on the wavelength. Using X-ray radiation of relativistic dense laser plasma, the reflection curve of a spherically bent mica crystal is measured in the range of 6.7–8.7 A. The obtained reflectivity curve is used to correctly interpret X-ray spectra of dense plasma generated during the interaction a petawatt laser pulse with solid targets.

Formation of a fine-dispersed liquid-metal target under the action of femto- and picosecond laser pulses for a laser-plasma radiation source in the extreme ultraviolet range

We report the results of studying the dynamics of deformation and fragmentation of liquid-metal droplets under the action of ultrashort laser pulses. The experiments have been performed to optimise the shape of the droplet target used in extreme ultraviolet (EUV) radiation sources based on the laser-produced plasma using the pre-pulse technology. The pre-pulse is generated by a system incorporating a master Ti : sapphire oscillator and a regenerative amplifier, allowing one to vary the pulse duration from to . The power density of laser radiation at the droplet target, averaged over the pulse duration and spatial coordinates, has reached . The production of liquid-metal droplets has been implemented by means of a droplet generator based on a nozzle with a ring piezoceramic actuator. The droplet material is the eutectic indium – tin alloy. The droplet generator could operate in the droplet and jet regime with a maximal rate of stable operation 5 and , respectively. The spatial stability of droplet position of its diameter is achieved. The size of the droplets varied within , their velocity was depending on the operation regime.

Design of a soft X-ray and extreme UV reflectometer equipped with a high-resolution monochromator and high-brightness laser-plasma radiation source

The design of a reflectometer intended for investigating the reflection and transmission coefficients of components of X-ray optics in the wavelength range of 1–25 nm is described. A Czerny-Turner spectrometer with a planar diffraction grating and parabolic collimators is employed to monochromatize the radiation. The required geometry of the monochromatic probe beam is ensured by means of a toroidal mirror. The X-ray source is laser plasma. The expected average spectral radiation power on the sample under study is on the order of 107 photon/s in the spectral band 0.1 nm. A goniometer provides five and two degrees of freedom of the sample 500 mm in diameter and detector, respectively.

Relativistic theory of inverse-bremsstrahlung absorption of ultrastrong laser radiation in plasma

The nonlinear absorption of laser radiation of relativistic intensities in a plasma by a mechanism of stimulated bremsstrahlung of electrons on the ions/nuclei is investigated in the low-frequency approximation. A nonlinear inverse-bremsstrahlung absorption coefficient is studied for intermediate, as well as at asymptotically large values of laser fields and high temperatures of electrons.

Relativistic Propagation of Linearly/Circularly Polarized Laser Radiation in Plasmas

Paraxial theory of relativistic self-focusing of Gaussian laser beams in plasmas for arbitrary magnitude of intensity of the beam has been presented in this paper. The nonlinearity in the dielectric constant arises on account of relativistic variation of mass. An appropriate expression for the nonlinear dielectric constant has been used to study laser beam propagation for linearly/circularly polarized wave. The variation of beamwidth parameter with distance of propagation, self-trapping condition, and critical power has been evaluated. The saturating nature of nonlinearity yields two values of critical power of the beam ( and ) for self-focusing. When the beam diverges. When the beam first converges then diverges and so on. When the beam first diverges and then converges and so on. Numerical estimates are made for linearly/circularly polarized wave applicable for typical values of relativistic laser-plasma interaction process in underdense and overdense plasmas. Since the relativistic mechanism is instantaneous, this theory is applicable to understanding of self-focusing of laser pulses.

Generation of higher harmonics of laser radiation in plasma formed by pulses with a 1-kHz repetition rate

Studies of higher-order nonlinearities in plasma plumes by the method of higher-harmonic generation (HHG) upon laser ablation of different materials by pulses with a repetition rate of 1 kHz are reviewed. It is shown that an increase in the pulse repetition rate compared to the previous works on HHG in plasma using lasers with a pulse repetition rate of 10 KHz considerably increases the average power of converted radiation in the far-ultraviolet (FUV) region. The review considers the results of works on the interference of quantum trajectories of accelerated electrons, two-color pumping, HHG in graphite plasma, HHG in gases compared to HHG in plasma plumes, resonant enhancement of harmonics, and stabilization of the output parameters of radiation converted in plasma. It is shown that the new methods of optimization of the HHG process considerably increase the potential of the use of coherent FUV radiation owing to the improvement of some characteristics of harmonics in plasma generated by pulses with a high repetition rate.

Laser ablation and ionisation by laser plasma radiation in the atmospheric-pressure mass spectrometry of organic compounds

A new method was developed for the mass spectrometric analysis of organic and bioorganic compounds, which involves laser ablation with the ionisation of its products by laser-plasma radiation and enables analysing gaseous, liquid, and solid substances at atmospheric pressure without sample preparation. The capabilities of this method were demonstrated by the examples of fast pharmaceutical composition screening, real-time atmosphere composition analysis, and construction of the mass spectrometric images of organic compound distributions in biological materials.

碳室约束对激光等离子体辐射的增强效应

By taking soil samples as targets,a small carbon chamber was used to perform the spatial confinement for high energy laser induced plasma to improve the quality of laser-induced breakdown spectroscopy.A high energy laser was used to ablate the soil samples,a spectral analysis system consisting of a modular multifunctional grating spectrometer and a CCD detector was adopted to record the spectral information,and the changes of the radiation intensities of laser-induced soil plasma with and without the small carbon chamber were studied.Then,the electron temperature and electron density of the plasma were measured by the spectroscopic methods to explain the mechanism of irradiation enhancement of the plasma.Experimental results show when the laser plasma is confined by the small carbon chamber,the spectral line intensities of the sample elements Mn,K,Fe and Ti increase about 90.77%,101.71%,104.27%and 60.77%than that without the small carbon chamber,and spectral signal-to-noise ratio raises around 54.29%,55.30%,59.37% and 38.80%,while the electron temperature and electron density of the plasma enhance about 1 684Kand 1.8×1016 cm-3,respectively.These results demonstrate that the spectral intensities and signal-to-noise ratio of the laser-induced plasma can be improved effectively by spatial confinement for the high energy laser induced plasma,which is an effective means for detecting the low-content elements in soil samples.

Normal-incidence multilayer mirrors for the wavelength range

Periodic and aperiodic multilayer structures have been theoretically calculated and synthesised for the first time for the application in soft X-ray optics in the range. The reflection spectra of the periodic multilayer mirrors are measured using synchrotron radiation and laser plasma-generated radiation. The experimental spectra are theoretically interpreted with the inclusion of transition layers and substrate roughness. The density of antimony layers is supposedly , and the thickness of transition layers (if any) in the multilayer structures does not exceed . A peak reflectivity of is attained at a wavelength of . An aperiodic mirror optimised for maximum uniform reflectivity in the range is tested employing the laser plasma radiation source.

Formation of an optical pulsed discharge in a supersonic air flow by radiation of a repetitively pulsed CO2 laser

Results of optimisation of repetitively pulsed CO2-laser generation are presented for finding physical conditions of forming stable burning of an optical pulsed discharge (OPD) in a supersonic air flow and for studying the influence of pulse parameters on the energy absorption efficiency of laser radiation in plasma. The optical discharge in a supersonic air flow was formed by radiation of a repetitively pulsed CO2 laser with mechanical Q-switching excited by a discharge with a convective cooling of the working gas. For the first time the influence of radiation pulse parameters on the ignition conditions and stable burning of the OPD in a supersonic air flow was investigated and the efficiency of laser radiation absorption in plasma was studied. The influence of the air flow velocity on stability of plasma production was investigated. It was shown that stable burning of the OPD in a supersonic flow is realised at a high pulse repetition rate where the interval between radiation pulses is shorter than the time of plasma blowing-off. Study of the instantaneous value of the absorption coefficient shows that after a breakdown in a time lapse of 100 — 150 ns, a quasi-stationary 'absorption phase' is formed with the duration of ∼1.5 ms, which exists independently of air flow and radiation pulse repetition rate. This phase of strong absorption is, seemingly, related to evolution of the ionisation wave.

Harmonic generation of picosecond Nd:YAG laser radiation in ablation-produced plasmas

High-order harmonic generation (HHG) up to the 21st order of picosecond Nd:YAG laser radiation in the plasmas produced on the surfaces of metal targets is reported. The peculiarity of these studies was the observation of enhanced single (11th) harmonic generating from some plasmas in the vacuum ultraviolet range (80–200 nm), which may originate from the resonance-induced growth of the nonlinear optical response of the medium in the vicinity of strong neutral and ionic transitions causing an increase of single harmonic conversion efficiency. Our studies showed that picosecond pulses can be efficiently converted towards the 50–220 nm wavelength range using HHG in plasma. This also allowed high fluencies of harmonic emission to be achieved by application of longer (picosecond) pulses compared with the commonly used femtosecond pulses.

Objectives of Laser‐Induced Energy Deposition for Active Flow Control

AbstractA highly concentrated energy deposition has been proposed for a flow control concept in super‐ and hypersonic transportation. The plasma source can be implemented by laser‐, microwave‐ or DC‐discharge phenomena in the flow field upstream of a blunt body. In a wide range of Mach numbers the thermal modification of the gas condition mitigates the strength of the shock waves and improves the aerodynamic performance. This paper presents a discussion of the methodology and objectives of laser‐induced energy deposition particularly with regard to the generation of laser‐sustained plasma in supersonics. A steady‐state argon plasma is maintained by an intensity field in the focal region of a continuous wave laser. The experimental results using drag, laser energy transmission and plasma radiation measurements determine the requirements for laser‐sustained plasma and validate the control authority of this concept (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Spectral and spatial structure of extreme ultraviolet radiation in laser plasma–wall interactions

Intense extreme ultraviolet (XUV) radiation was observed during the interaction of low-temperature laser plasmas and wall materials. Laser plasmas with electron temperature Te ∼ 40 eV were created on massive solid targets (CF2 and Al) by an excimer KrF laser (248 nm/0.5 J/13 ns/1 Hz). The wall was installed in the path of the laser-produced plasma expansion at distances between 0.5 and 3.5 mm. The spectral and spatial structure of XUV radiation (spectral range of λ ∼ 6–20 nm) was studied using a grazing incidence spectrometer with a back-illuminated CCD camera as a detector. XUV spectra of F and Al ions were analyzed. At large plasma–wall distances three-body recombination was identified as the dominant process responsible for ionic level population and radiation. The experiments demonstrate an effective way of creating low-temperature (Te ∼ 1–10 eV) plasmas interacting with solid surfaces (walls).

X-ray radiation of laser plasma of carbon nanotubes

Experimental results on the spatial distribution of X-ray radiation of the plasma generated by nanosecond laser radiation incident on a target made of carbon nanotubes are presented and compared with the results obtained for solid-state magnesium targets.