Patrick (Paddy) Hayden

Patrick (Paddy) Hayden
University College Dublin | UCD · School of Physics

PhD, MSc and BSc

About

58
Publications
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February 2013 - March 2014
University College Dublin
Position
  • PostDoc Position

Publications

Publications (58)
Article
Full-text available
It has been well established in the literature that surface contamination can adversely affect the aerodynamic performance of aerofoils and hence the efficiency with which turbines can convert wind to electrical power. Hence it is critical to ensure that turbine blades are kept as free as possible of contaminants. In this manuscript, we discuss LIB...
Article
The purpose of this study is to investigate the possible improvement of the limit of detection of laser induced breakdown spectroscopy using the stagnation layer formed at the centre of an annular plasma. An axicon was used to form an annular plasma on various certified reference targets, the spectra from which were used to construct calibration cu...
Article
Full-text available
The photoabsorption spectrum of Bi + was measured in the wavelength range between 37 and 60 nm, using the dual laser plasma technique in which one plasma is used as the source of vacuum ultraviolet continuum radiation and the other plasma is used as the sample of atoms and/or ions to be probed. A number of features in the Bi + spectrum was identifi...
Article
The dual-laser plasma method has been used to record photoabsorption spectra of Tm, Tm+, and Tm2+ ions. The dominant process is 4d photoexcitation, giving rise to structure in the 140–240-eV region while structure due to 5p excitation is observed in the 27–38-eV region. Due to successive removal of 6s electrons outside a 4f13 core with increasing i...
Conference Paper
Full-text available
List of Scope, Invited Speakers, International Programme, Local Organising Committee are available in this pdf. 24 th International Conference on Spectral Line Shapes (ICSLS 2018) It is commonly accepted that the Europhysics Study Conference on Spectral Line Broadening and Related Topics which was held in Meudon in 1973 was the first in the current...
Article
Full-text available
We present a simplified radiation hydrodynamic model based on the fluid dynamic equations and the radiative transfer equation to rapidly investigate the radiation properties and dynamics in laser-produced tin plasmas. The self-absorption features of EUV spectra measured at an angle of 45° to the direction of plasma expansion have been successfully...
Article
Full-text available
One of fundamental aims of extreme ultraviolet (EUV) lithography is to maximize brightness or conversion efficiency of laser energy to radiation at specific wavelengths from laser produced plasmas (LPPs) of specific elements for matching to available multilayer optical systems. Tin LPPs have been chosen for operation at a wavelength of 13.5 nm. For...
Article
Full-text available
Extreme ultraviolet (EUV) light generation by hybrid laser-assisted vacuum arc discharge plasmas, utilizing Sn-coated rotating-disc-electrodes, was investigated. The discharge was initiated by localized ablation of the liquid tin coating of the cathode disc by a laser pulse. The laser pulse, at 1064 nm, was generated by Nd:YAG lasers with variable...
Article
Full-text available
In this paper, we report results on two-colour above-threshold ionisation, where extreme ultraviolet pulses of femtosecond duration were synchronised to intense infrared laser pulses of picosecond duration, in order to study the laser-assisted photoelectric effect of atomic helium, neon, krypton and xenon which leads to the appearance of characteri...
Article
Full-text available
The use of laser produced plasmas (LPPs) in extreme ultraviolet/soft x-ray lithography and metrology at 13.5 nm has been widely reported and recent research efforts have focused on developing next generation sources for lithography, surface morphology, patterning and microscopy at shorter wavelengths. In this paper, the spectra emitted from LPPs of...
Article
Full-text available
The bi-modal nature of charge integrated ion kinetic energy distributions, which result from ultrafast laser produced plasmas, is discussed in this paper. A negatively biased Faraday cup was used as a charge collector to measure ion distributions from three different solid targets that had been irradiated with an ultrafast laser in the fluence rang...
Article
Full-text available
Much effort has gone into the development of plasmas as sources of radiation in the 2 to 9 nm region in recent times with particular interests in the "water window" region (2.3 to 4.4 nm) and the 6.X nm region. Plasmas were formed on a range of targets of medium to high atomic number (Z) elements using Nd:YAG lasers with various illumination parame...
Article
Full-text available
We present the results of a time and space resolved optical-spectroscopic study of colliding plasmas formed at the front surfaces of flat and inclined Cu slab targets as a function of both the distance and the wedge angle between them for angles ranging from 100° to 180° (laterally colliding plasmas). The key parameters studied are stagnation layer...
Article
Full-text available
Photoionization cross sections and dipole angular distribution asymmetry parameters, β, of 5s and 4d shells of the closed-shell ions (La3+,La9+, and La11+) in the La isonuclear sequence have been studied using the relativistic random phase approximation. The positions of the 5s Cooper minima in La3+ and La9+ ions are found to be extremely sensitive...
Conference Paper
This paper describes the extreme ultraviolet and soft x-ray emission recorded in the 2-12 nm region from Mo, Ru, Rh and Pd ions present in the laser produced plasmas. The spectra were found to be dominated by 3p-3d transitions in the 5-8 nm region, which shift slowly to shorter wavelengths with the increasing atomic number, and by 3d-4p and 3d-4f t...
Article
Full-text available
Colliding plasmas are steadily gaining significance in hohlraum studies, pulsed laser deposition and laser-induced breakdown spectroscopy for a number of reasons, not least the levels of control they o.er over the properties of the slab of plasma that accumulates at the collision front, i.e. the stagnation layer. We present here some results of a t...
Article
Laser Induced Breakdown Spectroscopy (LIBS) in the vacuum ultraviolet (VUV) has been applied to calibrated steel samples for the low concentration level detection of the light elements, carbon and sulfur in steel. Experimental optimization parameters, aimed at enhancing the sensitivity of the technique, included short wavelength spectral detection,...
Article
Full-text available
Ion signals from laser produced plasmas (LPPs) generated inside aluminum rectangular cavities at a fixed depthd¼2 mm and varying width,x¼1.0, 1.6, and 2.75 mm were obtained by spatially varying the position of a negatively biased Langmuir probe. Damped oscillatory features superimposed on Maxwellian distributed ion signals were observed. Depending...
Article
Colliding plasmas produced by neodymium-doped yttrium aluminium garnet (Nd:YAG) laser illumination of tin wedge targets form stagnation layers, the physical parameters of which can be controlled to optimise coupling with a carbon dioxide (CO2) heating laser pulse and subsequent extreme ultraviolet (EUV) production. The conversion efficiency (CE) of...
Article
Time-integrated spatially-resolved Laser Induced Breakdown Spectroscopy (LIBS) has been used to investigate spectral emissions from laser-induced plasmas generated on steel targets. Instead of detecting spectral lines in the visible/near ultraviolet (UV), as investigated in conventional LIBS, this work explored the use of spectral lines emitted by...
Article
The collision of two aluminium plasmas was investigated by combining both time and space resolved spectroscopy and Langmuir probe measurements. Plasma plumes were produced by a Continuum™ Surelite Nd:YAG Laser System with pulse duration of FWHM of 6 ns and wavelength of 1064 nm, at a laser irradiance of 1011 W/cm2 on slab Al targets. By analyzing t...
Article
Full-text available
We report results from the analysis of the shock wave formed following the creation of a laser-produced plasma in a gaseous atmosphere, using both interferometry and shadowgraphy. A Nomarski polarization interferometer and a focused-type shadowgraphy setup were utilized to track the evolution of the shock wave with high spatial and temporal resolut...
Article
Full-text available
We present a systematic study of the photoionization of noble gas atoms exposed simultaneously to ultrashort (20 fs) monochromatic (1–2% spectral width) extreme ultraviolet (XUV) radiation from the Free-electron Laser in Hamburg (FLASH) and to intense synchronized near-infrared (NIR) laser pulses with intensities up to about 1013 W cm−2. Already at...
Article
The collision of two aluminium plasmas was investigated by combining both time and space resolved spectroscopy and Langmuir probe measurements. Plasma plumes were produced by a Continuum TM Surelite Nd:YAG Laser System with pulse duration of FWHM of 6 ns and wavelength of 1064 nm, at a laser irradiance of 10 11 W/cm 2 on slab Al targets. By analyzi...
Article
Full-text available
Measurements of the total ion emission from a pair of colliding laser-produced aluminium plasmas were obtained with the aid of a Faraday cup detector. The energy profile width at half height of the kinetic energy distribution for ions emitted normal to the target was found to be 30% narrower for colliding plasmas compared with a single plasma. Simi...
Article
Intense ultra-short XUV-pulses from the Free Electron Laser in Hamburg (FLASH) were used in combination with the synchronized near-infrared (NIR) radiation from a femtosecond laser to perform two-color experiments on rare gas atoms and small molecules. Results of atomic photoionization in the presence of a NIR dressing field are presented and discu...
Article
Full-text available
Many next generation lithography schemes for the semiconductor industry are based on a 13.5 nm tin plasma light source, where hundreds of thousands of 4d-4f , 4p-4d , and 4d-5p transitions from Sn <sup>5+</sup>– Sn <sup>13+</sup> ions overlap to form an unresolved transition array. To aid computation, transition arrays are treated statistically, an...
Article
Full-text available
Two-color photoionization processes in rare gases have been studied using the combination of XUV pulses from the Free Electron Laser in Hamburg (FLASH) and intense femtosecond pulses from an external synchronized near infrared laser. In the low field regime of the NIR dressing laser (<10¹¹ W/cm²), the partial cross sections of the two-photon ioniza...
Article
Full-text available
We have developed a new laboratory facility to investigate and explore the potential applications of colliding laser produced plasmas. Specifically we have employed optical diagnostics such as laser interferometry, spectrally resolved fast photography and optical emission spectroscopy to investigate the dynamics of the collisions between electrons,...
Article
Full-text available
The current key performance indicators of the pump-probe facility at the Free Electron Laser in Hamburg (FLASH) are described. The temporal and spatial characteristics of both the extreme ultraviolet (XUV) Free Electron Laser and the temporally synchronized optical femtosecond Ti:Sapphire laser are determined by measuring two-color above threshold...
Article
Full-text available
Laser produced plasmas have been used for many years as intense sources of extreme ultraviolet (EUV) and soft x-ray radiation. Depending on the choice and composition of target the EUV spectra can be dominated by line, unresolved transition array (UTA) or continuum emission. Line and UTA emission have found application in various proposed EUV sourc...
Article
Full-text available
Using a noninvasive, electro-optically based electron bunch arrival time measurement at FLASH (free electron laser in Hamburg) the temporal resolution of two-color pump-probe experiments has been significantly improved. The system determines the relative arrival time of the extended ultraviolet pulse of FLASH and an amplified Ti:sapphire femtosecon...
Article
Full-text available
We report results from a combined optical interferometric and spectrally resolved imaging study on colliding laser produced aluminium plasmas. A Nomarski interferometer was used to probe the spatio-temporal distribution of electron densities at the collision front. Analysis of the resulting interferograms reveals the formation and evolution of a lo...
Article
Full-text available
Two-color multiphoton ionization of atomic helium was investigated by combining extreme ultraviolet (XUV) radiation from the Free Electron Laser in Hamburg with an intense synchronized optical laser. In the photoelectron spectrum, lines associated with direct ionization and above-threshold ionization show strong variations of their amplitudes as a...
Article
The 4d photoabsorption spectra of I2+, I3+, and I4+ have been obtained in the 70–127 eV region with the dual laser-produced plasma technique at time delays ranging from 400 to 520 ns. With decreasing time delay, the dominant contribution to the spectra evolves from the I2+ to the I4+ ions, and each spectrum contains discrete 4d-nf transitions and a...
Article
Full-text available
Extreme ultraviolet spectra from a tin laser produced plasma have been recorded over a range of angles between 20° and 90° from the target normal. Absolute intensity measurements are presented of both the 2% band centered on 13.5 nm and the total radiation emitted by the plasma between 10 and 18 nm . The in-band intensity is seen to be relatively c...
Article
Full-text available
In a series of experiments, the dynamics of atomic photoionization in strong bi-chromatic laser fields has been studied. By taking advantage of the unique characteristics of the Free Electron Laser in Hamburg (FLASH), especially its monochromaticity, short temporal width and high number of photons per pulse in combination with a strong synchronized...
Article
Full-text available
Out-of-band radiation emitted from an extreme ultraviolet laser-produced plasma, formed on a solid tin target, was measured over several angles between 25 degrees and 85 degrees with respect to the target normal for six energy bands between 200 and 1000 nm. The optical and target system was rotated with respect to the detector and the intensity of...
Article
Extreme ultraviolet lithography requires a light source at 13.5 nm to match the proposed multilayer optics reflectivity. The impact of wavelength and power density on the ion distribution and electron temperature in a laser-produced plasma is calculated for Nd:YAG and C O <sub>2</sub> lasers. A steady-state figure of merit, calculated to optimize e...
Article
Full-text available
We have performed time of flight (TOF) analysis to determine the intensity of ion distribution from tin based plasma for a range of charged tin ions (Sn1+-Sn10+). A Nd:YAG laser operating at 1064 nm with a full width at half maximum pulse duration of 5.2 ns was used to create the plasma under vacuum with a base pressure of 10−6 Torr. The plasma for...
Article
Extreme ultraviolet lithography schemes for the semiconductor industry are currently based on coupling radiation from a plasma source into a 2% bandwidth at 13.5 nm (91.8 eV ) . In this paper, we consider the case for a laser-produced plasma (LPP) and address the calculation of ionic level populations in the 4p<sup>6</sup>4d<sup>N</sup> , 4p<sup>6<...
Technical Report
Full-text available
This report from the LITH152 project presents the results of cross-calibrating in-band and out-of-band (OOB) measurements using an absolutely calibrated spectrometer in the extreme ultraviolet (EUV) range and calibrated sources in the UV-infrared (IR) ranges against a multilayer (ML)/filter-based energy monitor. Two sets of instruments were cross-c...
Article
An examination of the influence of target composition and viewing angle on the extreme ultraviolet spectra of laser produced plasmas formed from tin and tin doped planar targets is reported. Spectra have been recorded in the 9-17 nm region from plasmas created by a 700 mJ, 15 ns full width at half maximum intensity, 1064 nm Nd:YAG laser pulse using...
Article
Results are reported for tin based laser-produced plasmas (LPPs) formed from slab targets, where resonance transitions from Sn7+ to Sn13+ ions overlap to yield an unresolved transition array (UTA) in the required emission bandwidth to match available multilayered mirror reflectance characteristics. The effect of target orientation, tin concentratio...
Article
Laser-produced Sn plasmas are at present a major contender in the challenge to find a suitable replacement for the currently used excimer-laser technology, which has wavelengths of 248 and 193 nm, and that is utilized in projection lithography. These wavelengths are to be superseded by soft x-ray sources in the 13.5 nm wavelength regime for utiliza...
Article
One key aspect in the drive to optimize the radiative output of a laser-produced plasma for extreme ultraviolet lithography is the radiation transport through the plasma. In tin-based plasmas, the radiation in the 2% bandwidth at 13.5 nm is predominantly due to 4d-4f and 4p-4d transitions from a range of tin ions (Sn7+ to Sn12+). The complexity of...
Article
The ideal source of radiation for extreme ultraviolet lithography will produce intense light in a 2% bandwidth centred at 13.5 nm, while the debris and out-of-band radiation produced will be limited to prevent adverse effects to the multilayer optics in the lithography system. In this study ways to optimise plasma sources containing tin are present...
Article
The photoabsorption spectra of Te I-Te IV have been recorded and analysed in the XUV spectral region using the dual laser produced plasma technique. Photoexcitation from the 4d subshell is the dominant process in the 35-150 eV energy region. For photon energies between 35-45 eV discrete structure corresponding to 4d-np (n>4) transitions were obtain...
Conference Paper
Cited By (since 1996): 9, Export Date: 19 December 2012, Source: Scopus, doi: 10.1063/1.1944698, Language of Original Document: English, Correspondence Address: O'Sullivan, G.; Department of Experimental Physics, University College Dublin, Belfield, Dublin 4, Ireland, References: Silverman, P., (2002) Manufacturing Requirements for EUV Sources, , E...
Conference Paper
The aim of this study is to investigate ways to maximise the efficiency of tin based laser produced plasmas as sources of EUV radiation in the 2% band centered on 13.5 nm. It has been found that targets containing below 15% tin atoms by number emit more brightly in the spectral region around 13.5 nm than pure tin targets. Furthermore, if the remain...
Conference Paper
Full-text available
Conference code: 65985, Cited By (since 1996): 4, Export Date: 19 December 2012, Source: Scopus, Art. No.: 19, CODEN: PSISD, doi: 10.1117/12.604853, Language of Original Document: English, Correspondence Address: Hayden, P.; Atomic and Molecular Physics Group, Experimental Physics Department, University College Dublin, Belfield, Dublin 4, Ireland;...
Article
The time-independent ion distributions of variable composition laser-produced Sri plasmas are studied for a wide range of electron temperatures and atomic number densities, the purpose of which is to elucidate the effect that varying the number density of Sn within a mixed species plasma has upon the steady state populations of Sn and its ions. Par...
Conference Paper
Conference code: 62746, Cited By (since 1996): 7, Export Date: 19 December 2012, Source: Scopus, CODEN: PSISD, doi: 10.1117/12.504715, Language of Original Document: English, Correspondence Address: O'Sullivan, G.; Department of Experimental Physics, University College Dublin, Belfield, Dublin 4, Ireland; email: gosullivan@speclab.ucd.ie, Reference...

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