Herbert Legall

Herbert Legall

Dr. rer. nat.

About

43
Publications
7,469
Reads
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505
Citations
Additional affiliations
March 2017 - August 2021
Bundesanstalt für Materialforschung und -prüfung (BAM)
Position
  • Researcher
June 2016 - February 2017
Laserkern GmbH
Position
  • Project Manager
January 2014 - July 2015
Optigraph GmbH
Position
  • Project Manager

Publications

Publications (43)
Article
Full-text available
Interactions between ultrashort laser pulses with intensities larger than 10 13 W/cm 2 and solids during material processing can lead to the emission of X-rays with photon energies above 5 keV, causing radiation hazards to operators. A framework for inspecting X-ray emission hazards during laser material processing has yet to be developed. One requ...
Article
Full-text available
Laser processing with ultra-short laser pulses enables machining of materials with high accuracy and throughput. The development of novel laser technologies with laser pulse repetition rates up to the MHz range opened the way for industrial manufacturing processes. From a radiological point of view this evolution is important, because X-ray radiati...
Article
Full-text available
Irradiation with ultra-short (femtosecond) laser beams enables the generation of sub-wavelength laser-induced periodic surface structures (LIPSS) over large areas with controlled spatial periodicity, orientation, and depths affecting only a material layer on the sub-micrometer scale. This study reports on how fs-laser irradiation of commercially av...
Article
Ultrashort pulse laser processing of materials allows for precise machining with high accuracy. By increasing the repetition rate to several 100 kHz, laser machining becomes quick and cost-effective. Ultrafast laser processing at high repetition rates and peak intensities above 10¹³ W/cm² can cause a potential hazard by generation of unwanted x-ray...
Article
It is well known that the use of ultrashort (fs) pulsed lasers can induce the generation of (quasi-) periodic nanostructures (LIPSS, ripples) on the surface of many materials. Such nanostructures have also been observed in sample’s surfaces irradiated with UV lasers with a pulse duration of 300 ps. In this work, we compare the characteristics of th...
Article
Full-text available
During ultra-short laser material processing at high laser pulse repetition rates unwanted X-ray radiation can be generated in a quantity that may constitute a potential risk for health. An adequate X-ray radiation protection requires a thoroughly understanding of the influence of the laser processing parameters on the generation of X-ray radiation...
Conference Paper
The industrial use of ultrashort laser pulses has made considerable progress in recent years. The reasons for this lie in the availability of high average powers at pulse repetition rates in the several 100 kHz range. The advantages of using ultrashort laser pulses in terms of processing precision can thus be fully exploited. However, high laser in...
Article
Full-text available
In laser machining with ultrashort laser pulses unwanted X-ray radiation in the keV range can be generated when a critical laser intensity is exceeded. Even if the emitted X-ray dose per pulse is low, high laser repetition rates can lead to an accumulation of X-ray doses beyond exposure safety limits. For 925 fs pulse duration at a center wavelengt...
Article
Full-text available
Highly annealed pyrolytic graphite (HAPG) is an advanced type of pyrolytic graphite that, as a mosaic crystal, combines high integral reflectivity with a very low mosaicity of typically less than 0.1°. When used as dispersive X-ray optics, a high resolving power has been observed, rendering HAPG very suitable for applications in high-resolution X-r...
Chapter
Nanoscale imaging of biological samples in the lab as well as mask inspection in extreme ultraviolet lithography near the production line with sub 30 nm resolution require high spectral brightness soft x-ray sources. Laser produced plasma (LPP) sources and plasma based X-ray lasers (XRL) emit soft X-ray radiation in the wavelength region of interes...
Article
Measurements were carried out on high pressure treated (HPT) bacterial endospores of the Bacillus subtilis strain PS832 by means of laboratory (LTXM) and synchrotron based transmission soft X-ray microscopy (SynchTXM). Using LTXM at 500 eV HPT spores could be identified by a higher transparency, due to dipicolinic acid (DPA) release from the spore'...
Conference Paper
Full-text available
In the development of optimum ceramic materials for plastic forming, it is of fundamental importance to gain insight into the compositions of the clay minerals. Whereas spectroscopic methods are adequate for determining the elemental composition of a given sample, a knowledge of the spatial composition, together with the shape and size of the parti...
Conference Paper
Full-text available
In the water window (2.2 – 4.4 nm) the attenuation of radiation in water is significantly smaller than in organic material. Therefore, intact biological specimen (e.g. cells) can be investigated in their natural environment. In order to make this technique accessible to users in a laboratory environment a Full-Field Laboratory Transmission X-ray Mi...
Article
Full-text available
Ultrafast X-ray absorption spectroscopy (UXAS) offers the opportunity to investigate function-structure relationships of complex organic molecules or biological functional subunits without the need of crystallization. Of special interest from the viewpoint of structural biology is the region of K-edges of transition metals between 5 and 10 keV. Reg...
Conference Paper
Full-text available
X-ray microscopy in the water window has become a valuable imaging tool for a wide field of applications with a resolution in the nanometer regime. The emergence and the development of laboratory based transmission X-ray microscopes (LTXM) can be of great benefit to users, since LTXM provides access to a method previously limited to synchrotron fac...
Article
Laboratory water window cryomicroscopy has recently demonstrated similar image quality as synchrotron-based microscopy but still with much longer exposure times, prohibiting the spread to a wider scientific community. Here we demonstrate high-resolution laboratory water window imaging of cryofrozen cells with 10 s range exposure times. The major im...
Article
Full-text available
We present a laser plasma based x-ray microscope for the water window employing a high-average power laser system for plasma generation. At 90 W laser power a brightness of 7.4 x 10<sup>11</sup> photons/(s x sr x μm<sup>2</sup>) was measured for the nitrogen Lyα line emission at 2.478 nm. Using a multilayer condenser mirror with 0.3 % reflectivity...
Article
Full-text available
Different metal targets were investigated as possible source material for tailored laser-produced plasma-sources. In the wavelength range from 1 to 20 nm, x-ray spectra were collected with a calibrated spectrometer with a resolution of λ/Δλ = 150 at 1 nm up to λ/Δλ = 1100 at 15 nm. Intense line emission features of highly ionized species as well as...
Article
X-ray optics with high energy resolution and collection efficiency are required in X-ray spectroscopy for investigations of chemistry and coordination. This is particularly the case if the X-ray source emits a rather weak signal into a large solid angle. In the present work the performance of a spectrometer based on thin mosaic crystals was investi...
Conference Paper
Because the photon flux of laser-based X-ray sources is considerably lower than that of synchrotron radiation sources and radiation is emitted isotropic in all directions, focusing optics with a large solid collecting angle and high integral reflectivity are required. For these requirements crystals of Pyrolytic Graphite (PG) arc of particular inte...
Article
The feasibility of the realization of a HOPG-based von Hamos spectrometer with a high energy resolution is discussed on the basis of the acquired theoretical and experimental data. The spectrometer makes use of HOPG films, which can be deposited on a mould of any shape, including the cylindrical form. In this way focusing geometry of a von Hamos sc...
Article
Peridinin-chlorophyll a protein (PCP) is a unique water soluble antenna complex that employs the carotenoid peridinin as the main light-harvesting pigment. In the present study the near edge X-ray absorption fine structure (NEXAFS) spectrum of PCP was recorded at the carbon K-edge. Additionally, the NEXAFS spectra of the constituent pigments, chlor...
Article
Soft X-ray laser have recently shown a dramatic reduction in the pump energy needs. Grazing incidence pumping geometry constitutes the last achieved milestone on the way to real repetitive soft X-ray lasers. We present the results of the experimental investigation on such a laser scheme using Mo as a slab target. The preplasma conditions are discus...
Article
Full-text available
Thin films of highly oriented pyrolytic graphite (HOPG) give the opportunity to realize crystal optics with arbitrary geometry by mounting it on a mould of any shape. A specific feature of HOPG is its mosaicity accompanied by a high integral reflectivity, which is by an order of magnitude higher than that of all other known crystals in an energy ra...
Conference Paper
Full-text available
Highly Oriented Pyrolytic Graphite (HOPG) is a mosaic crystal, which consists of a large number of small nearly perfect crystallites. The unique structure of HOPG crystals enables them to be highly efficient in diffraction in an energy range between 2 keV up to several 10 keV. The mosaicity of the crystal is responsible for the dramatic increase of...
Conference Paper
Full-text available
In this contribution we present results on near edge x-ray absorption fine structure spectroscopy (NEXAFS) at 284 eV (carbon K-edge) using a compact laser-plasma x-ray source. The spectrometer works with a single x-ray optical element in grazing incidence configuration called off-axis reflection zone plate. Using different sample foils we were able...
Conference Paper
Thin films of highly oriented pyrolytic graphite (HOPG) give the opportunity to realize crystal optics with arbitrary geometry by mounting it on a mould of any shape. A specific feature of a HOPG is its mosaicity accompanied by mosaic focusing and high integral reflectivity. These characteristics are of interest for compact x-ray diagnostic tools a...
Conference Paper
Full-text available
Technological reasons stimulated enormous interest in the spectral range between 10 nm and 15 nm. One of the most important, apart from the potential to be applied in the microlithography, was the existence of the high-efficiency, spectrally highly selective (narrow-band) reflective multi-layer (ML) optics in this spectral range. Applying these opt...
Article
Full-text available
We characterize and compare four different types of focusing optics for hard X-rays, suitable for femtosecond X-ray diffraction experiments, usinga tabletop femtosecond laser-based plasma source. We demonstrate a 23 μmfocus with a toroidally bent Ge single crystal. A maximum flux of 7 108 photons/(s mm2) is generated in a 32 μm focus using a multi-...
Article
We present a laser produced plasma (LPP) source optimized for metrology and the results of its radiometric characterization. The presented (LPP) source can be used for reflectometry and spectroscopy in the soft x-ray range. For these applications, stable operation with high spectral photon yields high reliability in continuous operation and, to rea...
Article
In this article we present a setup of a spectrometer for near edge x-ray absorption spectroscopy at the carbon K-edge (284 eV). The spectrometer works with a laser produced plasma as x-ray source and a single x-ray optical element in grazing incidence configuration called off-axis reflection zone plate. Using different sample foils we were able to...
Conference Paper
Radiometric characterization of a laser produced plasma (LPP)-source, newly developed at MBI Berlin was carried out. The source was characterized regarding spectral photon flux, source size and source point stability. Two independently calibrated instruments, an imaging spectrometer and a double multilayer tool for inband power measurements were us...
Conference Paper
The quality assurance for production of optical components for EUV lithography strongly requires at-wavelength metrology. Presently, at-wavelength characterizations of mirrors and masks are done using the synchrotron radiation of electron storage rings, e.g. BESSY II. For the production process of EUV optics, however, the immediate access to metrol...
Conference Paper
Summary form only given. In recent years the development of semiconductor devices like SESAMs has led to a substantial progress in the generation of ultrashort pulses in solid-state lasers. The use of semiconductor materials makes it possible to combine strong nonlinear properties with short recombination times. In this work we describe a novel mod...
Article
Photoinhibition under aerobic and anaerobic conditions was analyzed in O2-evolving and in Tris-treated PS II-membrane fragments from spinach by measuring laser-flash-induced absorption changes at 826 nm reflecting the transient P680+ formation and the chlorophyll fluorescence lifetime. It was found that anaerobic photoinhibitory treatment leads in...

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Projects

Project (1)
Archived project
ERULAS systematically investigates the emission of X-ray radiation during the materials processing with ultrashort laser pulses. It aims to improve the knowledge of potential hazards. The ERULAS project is part of the network „Scaling Ultrafast Laser Productive Precision Processing Technology (SCULPT, 10.01.2017-31.01.2019)“ https://www.photonikforschung.de/foerderung/lasertechnik/projekt/sculpt.html https://www.researchgate.net/project/Scaling-Ultrafast-Laser-Productive-Precision-Processing-Technology within the initiative „Effiziente Hochleistungs-Laserstrahlquellen (EffiLAS, 01.02.2016-31.12.2019)“ [Efficient high-performance laser beam sources], https://www.photonikforschung.de/foerderung/lasertechnik/foerdermassnahme/effilas.html as part of the funding program „Photonics Research Germany“. https://www.photonikforschung.de/ The ERULAS project is supported by German Federal Ministry for Education and Research (Bundesministerium für Bildung und Forschung, BMBF) in the funding program Photonics Research Germany under contract number 13N14249.