bluuebunny/crossref_metadata_2025 huggingface dataset:
Saddle Toroid Arrays: Novel Grazing Incidence Optics for Synchrotron X-Ray Lithography
Authors: Rosser R. J. , Wormell P. M. J. H.
Published: February 2023

Replacing the scanning mirror in a synchrotron lithography beamline with a fixed saddle-toroid array mirror will give uniform illumination over wafer-size fields, without the problem of moving parts in the high vacuum section of the beamline, the constraints of oscillating the electron beam in the storage ring or the engineering difficulties of moving the entire wafer alignment system.

Ray tracing results for one and two saddle-toroid systems are presented, showing that a single saddle-toroid mirror provides a satisfactory alternative to the scanning cylindrical mirrors used in existing lithography beamlines, if the input beam is uniform. A two element system, comprising a saddle-toroid and a cylindrical mirror, can be used to give a nearly rectangular patch of illumination, closely matched to the needs of lithography. However the total usable flux through the such a device is lower, because of the extra reflection.

Both designs require a uniform input beam and are not suitable for the gaussian profiled synchrotron beam. By using the techniques developed to produce micro-lens arrays, saddle-toroid arrays can be made which spatially average the beam. These provide outputs that are uniform, even from a synchrotron beam.

Though designed with storage ring x-ray lithography in mind, saddle-toroid arrays may have applications in expanding undulator and free-electron laser output.

Patents are pending.
Parabolic Mirror Electron Energy Analyzer for Multiphoton Photoemission Spectroscopy
Authors: Van Woerkom L. D. , Trevor D. J. , Freeman R. R.
Published: February 2023

We report the use of a new, extremely efficient electron energy analyzer for recording high resolution electron spectra from multiphoton photoemission. The analyzer uses an electrostatic parabolic mirror and has a collection solid angle in excess of 2π sr with an energy resolution of 35 meV at 1.8 eV. We have used this detector to record the above threshold ionization spectra emitted in xenon using a 275 fsec, 616 nm, 2 × 1014 W/cm2 laser pulse.
Time-resolved study of surface recombination at Si(111) surfaces
Authors: Halas N. J. , Bokor J.
Published: February 2023

At present, the technologically important phenomenon of nonradiative surface recombination at semiconductor surfaces and interfaces is very poorly understood. Since the phenomenon was initially described by Shockley, Bardeen, and others over 30 years ago, knowledge of the basic physics has progressed surprisingly little. We have endeavored to obtain a complete microscopic understanding of surface recombination at a semiconductor surface, including knowledge of the surface-state electronic structure and the detailed kinetics of the bulk-surface transfer of charge carriers. The Si(111) cleaved surface is an excellent model system for this study since the surface electronic structure is extremely well known experimentally and theoretically. There is a single intrinsic mid-gap state at 0.45 eV above the bulk valence band maximum (vbm) which is labelled π*. Previously, infrared radiation was used[1] to selectively excite the π* state without exciting the bulk and the details of its decay kinetics were measured. We have now directly observed the role played by this state in surface recombination of bulk electrons and holes.
Ultra-High Resolution VUV-XUV Laser: Application to the Hyperfine Study of Krypton
Authors: Kung A. H. , Trickl T. , Cromwell E. , Vrakking M. J. J. , Lee Y. T.
Published: February 2023

A near-transform-limited VUV-XUV laser source with 210 MHz resolution has been constructed and used to study the hyperfine splitting, isotope shift, and lifetime of the three lowest ns (n=5,6,7) Rydberg states of Krypton.
Non-Reciprocity of Autoionizing Interferences: Lasers Without Inversion
Authors: Harris S. E.
Published: February 2023

Interferences of autoionizing lines may reduce or eliminate absorption of lower level atoms. Stimulated emission shows no such interferences, thereby allowing laser gain without population inversion.
Narrow Line X-Ray Transition Radiation by Electron Beam Traversing a Solid-State Superlattice
Authors: Kaplan A. E. , Law C. T.
Published: February 2023

Soft x-ray can be generated by low energy electron beams traversing a periodic layered medium with very short spatial period as was shown previously by Kaplan and Datta. We show that a combination of materials with high and low atomic number can produce an intense x-ray radiation with very narrow spectral peaks at the vicinity of K, L, … atomic absorption edges of each of the materials. We propose selection rules for materials constituting the solid-state superlattice. Our results demonstrate that an inexpensive x-ray source with mega (or submega) electron volt energy of electron beam can be used to generate narrow-line x-ray radiation.
Intense Coherent Radiation in the VUV and XUV Region with Electron Beam Pumped Rare Gas Excimer Lasers
Authors: Sasaki Wataru , Kurosawa Kou , Herman Peter R. , Yoshida Kunio , Kato Yoshiaki
Published: February 2023

Rare gas excimer lasers are attractive sources for applications in laser spectroscopy, plasma diagnostics and photolytic pumping of other lasers. Since 1981, we have developed high-power rare-gas excimer lasers pumped by a pulsed electron beam and studied their performance using tunable cavities [1,2].
Prepulsing to Increase the Efficiency of Laser-Produced-Plasma Pumped Lasers
Authors: Sher M. H. , Benerofe S. J.
Published: February 2023

We have demonstrated the use of a low energy prepulse to enhance the soft-x-ray emission of laser produced plasmas in a parameter range which has been used to pump photoionization lasers. We present data on conversion efficiency and output pulse duration as a function of input intensity, pulselength, and prepulse conditions. Our goal in these studies is to allow the design of more efficient short-wavelength photoionization lasers, and to achieve high repetition rate operation of these lasers in the near future.
Harmonic Generation in Laser-Free Electron Scattering Reconsidered
Authors: Puntajer Anna K. , Leubner C.
Published: February 2023

For zero electron drift velocity, the corrected version1 of
Vachaspati's classical cross sections1-2
deviates strongly from a semi–classical one by
Ehlotzky3 and from an unpublished quantum electrodynamical
cross section by Jafarpour.4 Therefore, the cross section
is recalculated within classical electrodynamics, which suffices for
the experimental configurations in question.5 This
classical cross section, derivable more simply and with fewer
approximations than the semi–classical one, nevertheless
agrees perfectly with Elotzky's result3 for all harmonics,
but only to some extent with Vachaspati's earlier version2
of the classical second harmonic cross section, and not at all with
his corrected one,1 nor with Jafarpour's quantum
electrodynamical one.4 Moreover, it also incorporates
relativistic Thomson scattering as envisaged by
McDonald.6
Ionization and Dissociation of Molecular Hydrogen by Ultrashort Light Pulses.
Authors: Zavriyev A. , Schumacher D.W. , Weihe F. , Bucksbaum P.H. , Squier J. , Salin F. , Mourou G.
Published: February 2023

Much research has been done lately to investigate the interaction of intense coherent light with molecules. Even simple homonuclear diatomic molecules exhibit very complicated behavior in an intense light field, including multiphoton ionization and dissociation, multiple ionization, above-threshold ionization (ATI), and bondsoftening, which has also been called above-threshold dissociation (ATD).1
Resonantly-Enhanced Harmonic Conversion at High Laser Intensity
Authors: Budil K. , Perry M.D. , Glover E. , Falcone R.
Published: February 2023

In much the same way that intermediate states shifted through resonance by a strong field influence the electron spectrum in above threshold ionization (ATI),1,2 so too can these states influence the nonlinear dipole responsible for high order harmonic generation.3 However, because of the additional propagation effects (phase matching), such field induced resonances can have an even more important effect on the harmonic spectrum.
High Damage Threshold Gratings using Coated Silicon Substrates.
Authors: Tom H.W.K. , Sher M. H. , Wood O. R. , Mansfield W. M. , Mohideen U. , Freeman R. R. , Bokor J.
Published: February 2023

We are currently investigating the manufacture of high damage threshold gratings using a novel idea. We are placing high reflectivity coatings on holographically patterned Silicon grating blanks. This approach provides four principle advantages compared to current gratings made by placing a thin metallic layer over holographically patterned photoresist on glass substrates. First, groove shapes can be optimized because lithographic and etching techniques for Si can make almost any arbitrary profile while retaining holographic registry across large surfaces. Second, photoresist which damages at 100-200° C is replaced with metal-silicide or silicon with much higher damage thresholds. Third, Si efficiently conducts heat away from the surface whereas the glass substrates prevent cooling. Fourth, enhanced metallic and dielectric coatings, which can be made nearly 99% reflecting, can be used when the groove profile is blazed with flat surfaces (ie., triangular groove). These four advantages make us believe damage thresholds comparable to those of bulk metals (~ 300 mJ/cm2) are obtainable.
Plasma Reflectivity and Propagation Effects in a Femtosecond Laser Pulse
Authors: Rae Stuart C. , Burnett Keith
Published: February 2023

The development of table-top terawatt lasers, producing intensities of 1015−1018 W/cm2 in pulses of duration on the order of a picosecond or less, has opened up a whole new regime for plasma physics. The interactions occurring in a femtosecond-pulse laser-produced plasma differ in a number of important respects from the traditional mechanisms observed in, for example, an ICF plasma. Much of the interest in the field of femtosecond plasma physics centres on the production of ultrashort pulses of x-rays [1], and there has also been a considerable amount of work devoted to studies of energy absorption, in an attempt to characterise the hot, near-solid-density plasmas produced [2-4].
Nonlinear Compton Scattering in a Pulsed Focused Laser Beam
Authors: Mohideen U. , Tom H.W.K. , Freeman R.R. , Bokor J. , Bucksbaum P.H.
Published: February 2023

We have calculated the radiation emitted from free electrons in an ultrashort pulsed laser focus. For low electron densities, where space charge is negligible, we find that ponderomotive forces limit the effective volume where the radiation is emitted to a region much smaller than the waist at the focus. For typical focal parameters, the emitting region is significantly smaller than the fundamental wavelength. Nonetheless, constructive inteference plays a significant role in the collective radiation spectrum. Phase mismatch becomes important only for the higher harmonics. These studies are intended as a prelude to experiments with high intensity ultrashort laser pulses.
Recombination Lasers Pumped by Multi-Photon Ionization
Authors: Burnett N. H. , Brunel F. , Corkum P. B. , Enright G. D. , Capjack C. E. , Rankin R.
Published: February 2023

Recent advances in ultra-short pulse visible and uv laser technology make it practical for the first time to consider the production of multiply ionized laboratory plasmas in which ionization is moderated by an external optical field rather than by electron collisions. Such plasmas will be remarkable for the high degree of disequilibrium that can be achieved between the distribution of ionization and the electron energy distribution. In particular it should be possible to produce plasmas in which the electron energy distribution is much cooler (either locally or over a distance comparable to an electron mean free path) than the ionization temperature. This leads naturally to consideration of the use of these plasmas for short wavelength recombination lasers.
X-ray Generation by High Irradiance Subpicosecond Lasers
Authors: Kyrala G. A. , Fulton R. D. , Casperson D. E. , Wahlin E. K. , Jones L. A. , Schappert G. T. , Cobble J. A. , Taylor A. J.
Published: February 2023

The pumping of short wavelength x-ray lasers requires very large power. The most widely used method for recombination schemes utilizes direct heating of the lasant with laser irradiation followed by relaxation to the desired levels. We prefer to use selected x-ray lines to pump the x-ray laser in a manner similar to dye lasers. This selective method reduces the x-ray pump energy requirements as well as the extraneous heating that accompanies the pumping, but requires high irradiance. We have been studying the generation of intense x-ray pulses using the interaction of a subpicosecond uv laser pulses with appropriate solid targets.
A Search for Gain on 2p-2s Transitions in a Collisionally Excited Ge Plasma
Authors: Enright G.D. , Baldis H.A. , Dunn J. , La Fontaine B. , Villeneuve D.M. , Kieffer J.C. , Pépin H. , Chaker M.
Published: February 2023

Soft x-ray amplification in collisionally excited Ne-like Ge plasmas has been extensively studied. Gains in excess of 4 cm-1 have been reported for the 3p-3s transitions. Significant gains have been observed over a wide range of irradiance conditions. The present experiments make use of a novel focusing arrangement[1] that employs a segmented wedge array (SWA) to overlap several line foci to produce a highly uniform linear plasma. The reproducibility of the XUV spectra was improved allowing gain to be inferred on a core-excited 2s2p63d-2s2p63p J=2-1 transition[2]. The 3d-2s quadrupole (E2) emission from the upper state of this transition was also identified in the L-shell emission spectrum. These measurements have now been extended into the 60-80 Å region where gain on 2s2p63s-2s2p53s and 2s2p63d-2s22p63d transitions is expected. Observation of gain on these Ne-like transitions would be significant as it would allow Ne-like lasers to scale to shorter wavelengths, into the "water window".
Radiation Cooling in Photopumped C VI Inversion
Authors: Pakula Ricardo A.
Published: February 2023

The idea of generating inversion and gain by photoionization followed by three-body recombination was first stated by Bunkin1 et al., and further analized by Goodwin and Fill2. The application of this scheme for the specific case of a hydrogen-like C VI plasma, exposed to the soft x-ray emission of a titanium-laser-produced plasma was considered in Ref. 3. Necessary conditions for the achievement of inversion are a low plasma temperature (~10 eV) , and a high electron density (~1019cm−3). Both are required for the establishment of a strong collisional-recombination regime, favouring the cascading of electrons towards the upper excited levels, leaving the lower levels almost unpopulated. Radiative cooling was originally proposed as a means to reach the desired temperature in similar recombination schemes4, however posterior work has shown that this regime was not attainable for low-Z materials5. In this paper we consider in detail the hypothesis of radiative cooling for the case of C VI pumped by the Ti-plasma.
High Resolution Soft-X-Ray Projection Imaging
Authors: Wood O. R. , Bjorkholm J. E. , Bokor J. , Eichner L. , Freeman R. R. , Jewell T. E. , Mansfield W. M. , MacDowell A. A. , Szeto L. H. , Tennant D. M. , Waskiewicz W. K. , White D. L. , Windt D. L. , Bruning J. H.
Published: February 2023

The principal motivation for carrying out projection imaging with soft-x-rays instead of with visible or ultraviolet light lies in the dramatic improvement in resolution that can be obtained (while maintaining a usable depth of focus). Although there are many reports of soft-x-ray imaging in the literature,1-6 soft-x-ray imaging with truly high resolution has only recently been demonstrated.7 In this talk we describe the results of several experiments which have demonstrated projection imaging in the soft-x-ray spectral region with a resolution approaching the Rayleigh limit, 1.22λ/2NA where λ is wavelength and NA is numerical aperture of the imaging system.
Soft X-ray reduction lithography using a reflection mask
Authors: Kinoshita H. , Kurihara K. , Mizota T. , Haga T. , Torii Y. , Takenaka H. , Ishii Y.
Published: February 2023

We have conducted the research work on X-ray projection lithography and have already demonstrated a 0.5 μm replicated pattern using a reflection mask. To obtain smaller features, we have designed a Schwarzschild typed demagnifying objective with a numerical aperture size of 0.1 and fabricated a Mo/B4C multilayer very precisely on its optics.
Proximity X-ray Nanolithography
Authors: Smith Henry I. , Schattenburg M. L.
Published: February 2023

The use of x-ray lithography in the fabrication of integrated electronics at 0.5 μm minimum feature sizes, and its extension to 0.1 μm features, is well documented in the technical and popular literature. The primary advantage of x-ray relative to optical-projection lithography in the 0.5 to 0.25 μm range is process latitude, which follows from a high contrast aerial image and absence of coherent scattering (e.g., standing waves). The potential of x-ray lithography in the nanometer domain (i.e., sub-100 nm features) has been appreciated since the late 70's when 18 nm lines and spaces were demonstrated by Flanders [1]. Over the past 5 years, a concerted effort to develop a reliable, manufacturing-compatible technology for sub-100 nm lithography has been persued at MIT; our motivation being the eventual manufacture of quantum-effect electronic systems. A number of options were considered. Our results indicate that x-ray nanolithography using 1 to 1 masks will meet all the needs of manufacturing down to 50 nm features, and probably also from 50 down to 10 nm. The techniques of x-ray nanolithography will be reviewed and the factors that limit resolution and drive mask architecture described.
Spectrum of Radiation Emitted by a Resonantly Driven Hydrogen Atom
Authors: LaGattuta K. J.
Published: February 2023

The spectrum of scattered radiation was computed for an electron, bound initially in the 2s-state of a hydrogen atom, and driven resonantly by the sinusoidal field of a moderately intense linearly polarized laser. A numerical solution of the time-dependent Schrodinger was performed for the duration of a several femtosecond laser pulse. The radiation which emerged from this transient state was characterized by the spectrum of the autocorrelation function of the electronic acceleration. Copious radiation, near the second harmonic, was emitted prior to ionization.
Subpicosecond, Far Infrared Radiation from High-Intensity Laser Plasmas
Authors: Hamster H. , Sullivan A. , Gordon S. , White W. , Falcone R. W.
Published: February 2023

Laser pulses with terawatt intensities and 100 femtosecond duration are focused onto gas and solid targets. Strong emission of coherent terahertz radiation is observed. The most intense radiation is detected from solid density targets and is correlated with the emission of MeV x-rays and electrons.
Ultrafast Spectroscopy of Plasmas Generated by Intense Femtosecond Laser Pulses
Authors: von der Linde D. , Schüler H. , Engers T.
Published: February 2023

Plasmas generated on glass targets by laser pulses of 80 fs duration with peak intensities around 1016 W/cm2 are studied by means of optical pump-probe techniques. Femtosecond time-resolved measurements of optical reflectivity and second harmonic generation reveal the dynamics of the formation of the plasma and of the subsequent plasma expansion.
Simple Model of Suprathermal Electron Transport
Authors: Glinsky Michael E. , Kruer William L. , Tabak Max , Hammer James H.
Published: February 2023

A simple two-fluid 1D model is developed from the collisional Vlasov equation, using a Fokker-Planck collision operator. This model is used to study the penetration of a population of suprathermal electrons into a cold background plasma. This is a situation which could result from the absorption of a short-pulsed (100 fsec, 1 μm, 1018 W/cm2) laser beam by a solid density target. The relative importance of J•E cold background heating, suprathermal collisions, and cold thermal conduction are determined at different temporal stages of the evolution. Simple scaling relations for how the width and temperature of the heated layer of cold electrons evolve with time are presented. The implications of these relations for fast ion generation is also examined.
Electron-Ion Mean-Free-Path for Short-Pulse Laser Plasmas
Authors: Li Chi-Kang , Petrasso Richard D.
Published: February 2023

A new electron-ion 90° scattering mean-free-path is calculated based on a modified Fokker-Planck The effects of large-angle scattering (ignored in the conventional Fokker-Planck equation) as well as small-angle binary collisions are properly treated. For the first time this calculation manifests the l/lnΛ
b
corrections, where lnΛ
b
is the Coulomb logarithm and is a measure of the importance of small-angle collisions to large-angle scattering.
Design of a Quintic-Phase-Limited Amplification System for Production of Multi-Terawatt 20-fs, 800-nm Pulses
Authors: Lemoff B. E. , Gordon C. L. , Barty C. P. J.
Published: February 2023

Design of a multi-terawatt amplification system based on reflective optics and capable of supporting sub-20 fs pulses is presented. Tests of a quintic-phase-limited expansion and compression system, which is key to this design, are also discussed.
Independent Adjustment of the Higher Order Frequency Dependent Phase in Chirped Pulse Amplification Systems
Authors: White W. E. , Patterson F. G. , Combs R. , Seppala L. , Price D. , Shepherd R.
Published: February 2023

We have developed a system that allows compensation of higher order phase terms that limit chirped pulse amplification systems. Results indicate phase can be compensated by a properly adjusted air-spaced doublet within the stretcher.
Resonant Frequency Transformations of Shortwavelength Coherent Radiation in Plasma
Authors: Shkolnikov P. L. , Kaplan A. E.
Published: February 2023

We have found and evaluated plasma media for efficient multiple-resonant nonlinear frequency transformations of X-ray and XUV laser radiation. Realized experimentally, these nonlinear transformations may result in new short-wavelength coherent sources and in both "line-by-line" and continuously tunable short-wavelength lasing.
Optical Alignment for Lithography
Authors: Bobroff Norman , Rosenbluth Alan E.
Published: February 2023

The total overlay budget in semiconductor lithography has many components, including mask dimensional accuracy, tool-to-tool printing distortion, and process bias, but historically alignment registration has been the most critical. Yet progress in alignment has not kept pace with the exponential increases in printing resolution achieved during the last 10 years. In manufacturing, it is difficult to overlay lithography levels better than 200 nm at the 3 σ confidence level. Registration accuracy is limited by the complex interaction of the alignment optics with wafer registration marks at different process levels. Recent experimental and analytical work has led to an understanding of how to design optical alignment systems with reduced sensitivity to mark structure, coatings and processing. However, it is possible that no single alignment system can be optimized .for all process layers encountered in the fabrication of DRAMS or bipolar logic.
Schwarzschild microscope at λ =7 nm
Authors: Tanaka K. A. , Kado M. , Daido H. , Yamanaka T. , Nakai S. , Yamashita K. , Kitamoto S.
Published: February 2023

X-ray imaging optics have been essential diagnostics in inertial confinement fusion (ICF) research. A micro pellet (<1mm dia.) is irradiated by a giant multi-beam laser system. This pellet is imploded to create a thermonuclear fusion condition, making use of the inertia of the imploding pellet wall. It is of critical importance for ICF to measure nonuniformities at the implosion core(~ 100μm) or the laser spot in order to drive the pellet to a very high density. Such measurements require a spatial resolution of less than 1μm. We have chosen to build a Schwarzschild type x-ray microscope with a magnification of 15. This x-ray microscope can be applied to fields other than laser fusion, such as lithography, biology’ and medicine. This can be a powerful tool when coupled with laser plasma x rays(LAPLAX), since the high brightness and temporal resolution (<1ns) of LAPLAX is added to the high spatial resolution.
Multilayers for Soft-X-Ray Optics
Authors: Namioka Takeshi , Koike Masato
Published: February 2023

Soft-x-ray (SXR) multilayers havé been successfully applied to various optical elements and systems, and their technology seems to have been nearly perfected. However, many problems fundamental to multilayers have to be solved for further development. This paper presents results of our studies on some of these problems.
XUV Conversion Efficiency in a Low Intensity Krf Laser-Plasma for Projection Lithography
Authors: Rockett Paul D. , Hunter John A. , Kubiak Glenn D. , Berger Kurt W.
Published: February 2023

The efficiency of XUV production from a laser-plasma directly relates to the cost of fielding such a source for projection x-ray lithography (PXRL). Measurements of the radiated conversion efficiency were made on the Sandia National Laboratories Laser Plasma Source (LPS), a bright reliable point x-ray source. The LPS was designed for use as a prototype XUV source for PXRL, and included a Lambda Physik KrF laser focussed weakly onto a rotating target drum. The laser produced 1.1J pulses at 248nm in 27ns and could be operated up to 100Hz. Focal intensities on target were in the low 1010 W/cm2 using a 1m focal length simple lens.
Surface-Imaging Lithography
Authors: Hartney Mark A.
Published: February 2023

Surface-imaging lithography is a technique which was first described by Taylor et al. nearly ten years ago. In this approach, a pattern is defined at the surface or near-surface regions of a resist rather than throughout the entire resist thickness. Surface-imaging can eliminate problems such as reflectivity variations due to different substrates or topography in optical lithography and backscattering in electron-beam lithography.2 The use of surface-imaging has also proven beneficial for deep-UV optical lithography, where the high absorbance of most resists necessitates such an approach.
Throughput estimate of an X-ray projection lithography system
Authors: Itou Masaaki , Terasawa Tsuneo , Moriyama Shigeo
Published: February 2023

A recent feasibility study on X-ray projection lithography (XRPL) has demonstrated an extremely high resolution reaching 0.1 µ m1). For practical manufacturing of integrated circuits, however, a high throughput is also necessary. Although the throughput of an XRPL system was already estimated at a wavelength of 4.5nm2), this system is difficult to build owing to low performance of actual multilayers. We discuss the throughput of an XRPL system using 13nm radiation for which good quality multilayers can be fabricated3).
On the feasibility of X-ray nonlinear resonant effects in plasma
Authors: Shkolnikov P. L. , Kaplan A. E.
Published: February 2023

Recent developments in x-ray laser research resulted in the experimental observation of laser amplification at many wavelengths in soft x-ray domain [1] ranging from λ=280 Å to λ = 42 Å. There is no doubts that within next few years powerful sources of coherent x-ray laser radiation at those wavelengths will also be available. This sets a stage for the research on the interaction of intense coherent x-ray radiation with a matter, in particular on x-ray nonlinear optics. The first obvious choice of the environment and frequency for the nonlinear effects to occur and to be experimentally observed, is the same plasma of ionized atoms that gives rise to the laser action itself, with the nonlinear interaction occurring at the frequency of lasing transition. The nonlinear effects in such a situation are essentially expected to be the same as in any other resonantly-enhanced nonlinear interaction of light with matter in a visible optical domain and could approximately be evaluated using basically two (or three) level model. In order to demonstrate the feasibility of this kind of nonlinear effects both in active and passive x-ray laser medium, we present here evaluations of the characteristic parameters pertinent to the resonant nonlinearity: the saturation driving intensity and nonlinear change of refractive index. We use simple and yet realistic model based on the neonlike Mo XXXIII plasma; observation of soft X-ray amplification in such a system has recently been reported [2].
Radiation Cooling in Photopurnped C VI Inversion
Authors: Pakula Ricardo A.
Published: February 2023

The idea of generating inversion and gain by photo-ionization followed by three-body recombination was first stated by Bunkin1 et al., and further analized by Goodwin and Fill2. The application of this scheme for the specific case of a hydrogen-like C VI plasma, exposed to the soft x-ray emission of a titanium-laser-produced plasma was considered in Ref. 3. Necessary conditions for the achievement of inversion are a low plasma temperature (~ 10 eV) , and a high electron density (~ 1019 cm–3). Both are required for the establishment of a strong collisional-recombination regime, favouring the cascading of electrons towards the upper excited levels, leaving the lower levels almost unpopulated. Radiative cooling was originally proposed as a means to reach the desired temperature in similar recombination schemes4, however posterior work has shown that this regime was not attainable for low-Z materials5. In this paper we consider in detail the hypothesis of radiative cooling for the case of C VI pumped by the Ti-plasma.
The State of Soft X-ray Projection Lithography in Japan
Authors: Ogura Shigetaro
Published: February 2023

Soft X-ray projection type Lithography has been expected to be most atractive technology in future electronics device production, paticularly since the realization of normal incidence soft x-ray mirror [1]. For instance, Kinoshita et al [2] and other groups [3,4] have already shown the feasibility of this technology, adopting a Schwartzschild optical system composed of normal mirrors. If neglecting process speed or throughput, it is widely accepted the projection type lithography is the one of most fascinateing candidate for future excess 1 G electronics device fabrication. For realizing this technology as a successor of Excimer and/or proximity x-ray lithography, a long range research and development have already started in Japan, at first individual necessitate component such as conpact SR source, typically SiC substrate mirror and multilayer mirror fabrications, including optical design works [5] for this purpose.
XUV Projection Lithography System Design Based on Single-Surface Reflecting Optics*
Authors: Newnam Brian E. , Viswanathan V. K.
Published: February 2023

Optical projection lithography using exposure wavelengths less than 100 nm is being developed to produce integrated circuits with feature sizes less than 0.2 µm while providing a total depth of focus (DOF) of ~1 µm. With such short wavelengths, all-reflective projection systems with reflective masks will be required. Since six to seven reflections at normal incidence will be necessary to attain large, diffraction-limited images ≥1 cm2, high mirror reflectance is very important for future high- volume production. As a result, present attempts to develop soft-x-ray projection lithography are focused mainly around 13 nm [1-3] where relatively high reflectance ~60% has been attained with Mo/Si multilayer mirrors.
X-ray Plasma Source Design Issues
Authors: Cerjan Charles
Published: February 2023

The optimization of soft x-ray production from a laser-produced plasma source is an important issue for several current lithography schemes. Recent experiments at Lawrence Livermore National Laboratory by R. Kauffman, D. Phillion, and R. Spitzer, indicate that the required conversion efficiency can be achieved using moderate laser intensities for a few select materials. Computer simulations of these experiments delineate the critical phenomena underlying these high conversion efficiencies, especially the role of the coupled hydrodynamic expansion and radiation flow in the plasma. By driving the plasma emission out of local thermodynamic equilibrium, photon output in the desired spectral region can be much greater than the black-body emissivity. These conditions can only be achieved under certain conditions which are determined by the incident laser intensity, essentially the electron temperature, and the excited electronic state populations within each ionization stage. Reliable simulations of the experiments require fairly detailed atomic physics databases since the prediction of photon output occurs in such a narrow spectral range. The computer program LASNEX is capable of coupling the hydrodynamic motion and a radiation field described by detailed atomic physics rates for laser produced plasmas. Two-dimensional simulations using this code are compared to the experimental results and are shown to be reliable in their interpretation of these results.
Conceptual Design Of a 60-nm Free-Electron Laser for XUV Projection Lithography*
Authors: Sheffield Richard L. , Carlsten Bruce E. , Dominic Chan K. C. , Goldstein John C. , Lynch Michael T. , Newnam Brian E. , Nguyen Dinh C. , Prono Daniel S. , Warren Roger W.
Published: February 2023

We present the design and calculated performance for a 20-W XUV-FEL source for 60-nm projection lithography. The compact design features an 85-MeV rf linear accelerator with photoinjector, and a pulsed microwiggler with multifacet resonator optics.
Simulation of Soft-X-Ray Images from a 1:1 Ring-Field Optic
Authors: Wood O. R. , D'Souza R. M. , Himel M. , Bjorkholm J. E. , Early K. , Fetter L. A. , Freeman R. R. , Szeto L. H. , Tennant D. E. , Taylor D. W. , Jewell T. E. , Lee D. , Neureuther A. R. , Newmark D. M. , MacDowell A. A. , Eichner L. , Waskiewicz W. K. , White D. L. , Windt D. L. , Williamson D. M. , Zernike F.
Published: February 2023

Using a recently extended version of the two-dimensional aerial image simulator, SPLAT 1 , we show that annular illumination of a soft-x-ray 1:1 ring-field camera at 13 nm increases image contrast for features with spatial frequencies immediately above the coherent cutoff and that surface figure errors are responsible for the asymmetric, spatially-shifted images that have been observed experimentally.
A Migration Path to Nano-Meter Lithography: From the viewpoint of VLSIs
Authors: Takeda Eiji
Published: February 2023

The "VLSI revolution" that is opening a new epoch in the electronics industry has made such remarkable progress that now 108 - 109 transistors can be fabricated on a single chip. VLSI microfabrication technologies are being pushed to new extremes by the DRAM community, thereby expediting research on 256 Mbit DRAMs using the 0.2 μm design rule. Giga-bit DRAMs and sophisticated ULSI processors using 0.1 μm Si-MOSFETs could possibly appear in the latter half of the 1990s. Recently, a very high speed ring oscillator has achieved 10 psec/gate for 77 K operation[1]. In the field of advanced bipolar transistors, a 64 GHz cut-off frequency has been reported[2]. These speeds are comparable to those of conventional quantum devices such as HEMTs (High electron mobility transistors)[3], JJs (Josephson junction devices)[4], and STrs (Superconducting transistors)[5] as shown in Fig. 1. In addition, device operation of 7-10 nm Si-MOSFETs (corresponding to 1-16 Tera-bit memories) [6] and single electron transistors (SET) [7] have been confirmed, which implies an increased importance for nano-meter fabrication technology. Si devices have a promising future, which will pave the way to the 21st century.
Computational Analysis of Debris Formation in SXPL Laser-Plasma Sources
Authors: Trucano Timothy G. , Grady Dennis E. , Olson Richard E. , Farnsworth Archie
Published: February 2023

Laser generated extreme ultraviolet sources applicable to soft x-ray projection lithography (SXPL) are undermined by target debris formation. This debris, in the form of vapor and condensed ejecta, can coat and damage the optical systems that direct and focus the emitted radiation for the lithographic application [1]. The purpose of this paper is to present ongoing work to develop a computational methodology for understanding and predicting the debris formation process in these laser sources.
Effects of Microstructure and Interfacial Roughness on Normal Incidence Reflectivity of Ru/C and Ru/B4C Multilayers at 7 nm Wavelength
Authors: Nguyen Tai D. , Gronsky Ronald , Kortright Jeffrey B.
Published: February 2023

Recent developments of x-ray multilayers have focused on understanding and controlling the roughness at the interfaces to achieve high reflectance at wavelengths below 10 nm. The structure at the interfaces in generaldepends on the microstructures inside the layers, and on the interactions between the layer materials in multilayers. Studies of the microstructure-interfacial roughness relationship, and their effects on the reflectance performance are hence important in design of the multilayers.
The Use of Zone Plate Arrays in Projection X-Ray Lithography
Authors: Feldman M.
Published: February 2023

Projection X-ray lithography has demonstrated the ability to print very fine features, (1,2) but the technical requirements of useful versions of the proposed systems are beyond the present state of the art. However, X-ray projection lithography using zone plates as the imaging elements is well within the state of art (3,4). We discuss two systems: a simple 1:1 imaging system utilizing existing X-ray masks, and a more mechanically complex reduction system.
Procedure for Calculating Optical Pulse Compression from Fiber-Grating Combinations
Authors: Stolen R. H. , Shank C. V. , Tomlinson W. J.
Published: February 2023

An optical pulse can be compressed by a dispersive grating pair after first inducing a frequency chirp in a single-mode optical fiber.1,2 It is of interest to know how much compression is possible and what will be the necessary fiber length and grating separation given some particular initial optical pulses. This is not immediately obvious because the achievable pulse compression and the quality of the compressed pulse are sensitive functions of the input pulse parameters and also depend critically on fiber length and grating separation.
Theory of the Soliton Laser
Authors: Islam M. N. , Haus H. A.
Published: February 2023

An analytic theory of the soliton laser has been developed to describe the steady state operation of the recent experiment by Mollenauer and Stolen[1]. The theory focusses on the fiber as the key element in shaping the pulse, and shows that the synchronously pumped laser section acts as an injection locked, modelocked amplifier, providing slightly dispersive, time-dependent gain to the soliton (Fig. 1). In contrast to active and passive modelocking, where pulse shortening is achieved by resistive means, the pulse shortening mechanism in the soliton laser is reactive. By studying the propagation and perturbation of the soliton in its passage through the laser and invoking a closure condition, several experimental observations have been explained: (a) the pulsewidth is determined by the fiber length; and (b) in general, the N = 2 soliton is favored over the N = 1 soliton.
Femtosecond Transient Anisotropy in the Absorption Saturation of GaAs
Authors: Oudar J.L. , Migus A. , Hulin D. , Grillon G. , Etchepare J. , Antonetti A.
Published: February 2023

Ultrafast linear dichroism induced by femtosecond pulses near the band-edge of GaAs has been observed. The anisotropy of carrier momentum distribution was found to decay in 190 fs.
Energy Flow from Highly Excited CH Overtones in Benzene and Alkanes
Authors: Sibert E. L. , Hutchinson J. S. , Hynes J. T. , Reinhardt W. P.
Published: February 2023

Simple classical and quantal models of the ultrarapid ( 50 to 250 fs) flow of energy from CH (CD) overtones in benzene (perdeuterobenzene) and in terminal alkyl methyl groups are shown to account for experimental variation in linewidths, including isotopic effects.
High-Yield Picosecond Photon Echoes by Photochemical Hole-Burning
Authors: Kaarli R. , Rebane A. , Saari P.
Published: February 2023

The phenomenon of stimulated photon echo [1] has already been investigated in a variety of molecular systems but in all cases the magnitude of echo signals has been limited to a small fraction of the pumping pulses intensity. The main reason for that lies in a rapid relaxation of nonequilibrium population of molecular states, which hinder the formation of spectral population gratings responsible for the stimulation of retarded optical pulses.
Picosecond Multiphoton Laser Photolysis and Spectroscopy of Liquid Benzenes
Authors: Miyasaka Hiroshi , Masuhara Hiroshi , Mataga Noboru
Published: February 2023

Measurement of transient absorption spectra by means of ps laser has been one of the most useful methods to investigate photophysical and photochemical primary processes. The high peak power of the ps pulse, however, induces easily nonlinear phenomena such as multiphoton excitation as well as multiphoton ionization and decomposition of molecules. Therefore, it is possible by using this ps multiphoton laser photolysis to excite or ionize various kinds of neat liquids and investigate the transient species by time-resolved absorption measurements. We have already demonstrated the measurements of excimer formation processes by 355 nm two photon excitation of neat benzene1 and solvated electron formation processes by 266 nm multiphoton excitation of water and alcohols.2 Solvated electron formation in liquids has been studied by means of ps pulse radiolysis as well as by ps laser ionization of solute molecule in the liquid solvent. Comparison of the results of these investigations with those of the 266 nm multiphoton ionization of pure liquids will be an interesting problem. In this report, results of investigations on the mechanism of excimer formation in neat benzene and alkyl substituted benzenes induced by multiphoton excitation will be given.
Chemical Reactions in Condensed Media
Authors: Statman D. , Jalenak W. A. , Robinson G. W.
Published: February 2023

Chemical reactions in condensed media can be thought of as consisting of four steps: 1) relative diffusion to the local reaction regime ("microenvironment"), 2) dynamics in the microenvironment ("microdynamics"), 3) electron and nuclear rearrangements, and 4) energy relaxation. Any or all of these steps may occur on picosecond timescales. The cis-trans isomerization problem omits step 1) and concentrates primarily on steps 2) and 3). Typical photochemical quenching reactions are primarily concerned with steps 1) and 2), while the I+I→I2 recombination problem has mainly focussed on steps 3) and 4). Except for the latter type of problem, actual experimental examples of condensed phase chemical reactivity are fairly complex, and this complexity hides the very aspects of the problem that one would like to probe. Because of this, it is fair to say that almost nothing is known about the important steps 2) and 3) in the above scheme.
The Generation of 0.41 Psec Pulses By the Single-Stage Compression of Frequency Doubled Nd:YAG Laser Pulses
Authors: Johnson A. M. , Stolen R. H. , Simpson W. M.
Published: February 2023

The technique of optical pulse compression utilizing self-phase modulation (SPM) to chirp the pulse in a single-mode fiber followed by a grating-pair dispersive delay line has been very successful in compressing dye laser pulses. A 3X single-stage compression of the colliding pulse modelocked laser has resulted in optical pulses as short as 0.03 psec [1]. A 65X two-stage compression of a synchronously modelocked dye laser has resulted in optical pulses as short as 0.09 psec [2]. We report an 80X single-stage compression of 240W, 33 psec duration optical pulses from a cw modelocked frequency doubled Nd:YAG laser to 1.2 kW, 0.41 psec duration optical pulses. The compression of these 0.532 µm optical pulses has resulted in the largest single-stage compression factor reported to date. These results demonstrate the production of subpicosecond optical pulses directly from relatively long optical pulses without the use of a modelocked dye laser.
Femtosecond Dephasing Measurements Using Transient Induced Gratings
Authors: Weiner A.M. , Ippen E.P.
Published: February 2023

Transient four-wave mixing techniques have been developed in the past several years for the investigation of ultrafast dephasing of electronic transitions in condensed matter [1,2]. These experiments involve self-diffraction of two noncollinear pulses from an optically induced absorption grating. We have recently reported an improved scheme utilizing three separate input pulses [3]. Similar three pulse transient grating experiments [4] can be used to study processes such as spatial diffusion, orientational relaxation and excited state relaxation; but the applicability to dephasing studies had not been previously recognized. Compared to the two pulse scattering, our three pulse experiment provides several important advantages, including resolution below the pulse width, clear demarcation between homogeneous and inhomogeneous broadening, and automatic separation of energy relaxation (T1) effects from the phase relaxation (T2) effects. In this paper we will first describe the three pulse scattering theoretically and then present new experimental data taken with a colliding-pulse-modelocked (CPM) ring dye laser [5].
Phase Conjugation of Picosecond Light Pulses in Organic Dyes Solutions
Authors: Kabelka V.J. , Mikhailov A.V. , Bondarenko S.V. , Ivakin E.V. , Rubanov A.S.
Published: February 2023

We report the experimental observation of the 5,9 GHz hypersonic wave generation by interferention of picosecond light pulses during degenerate four-wave mixing (DFWM) in organic dyes solutions. Phase conjugation on standing hypersonic waves and the one by DFWM have been observed. Phase conjugation quality and backward wave (BW) signal dependence on pump energy have been measured both for DFWM and diffraction by hypersonic wave (DHW).
Picosecond Pulse Multiphoton Coherent Propagation in Vapors
Authors: Diels J.-C. , Vanherzeele H.
Published: February 2023

We present a novel method for the study of multiphoton excitation by intense picosecond pulses in vapors. The technique, based on interferometric cross correlations of the multiphoton stimulated reradiation with the pulse itself, requires an interferometric delay line to generate accurately phased pulse sequences. Experimental data obtained with our method for two photon coherent propagation in lithium vapor, are in excellent agreement with a theoretical model.
Stimulated photon echo for elastic and depolarizing collision studies
Authors: Keller J.-C. , Le Gouët J.-L.
Published: February 2023

Among various photon echo phenomena which have been predicted and observed in vapours [1], stimulated photon echo (three pulse echo) is a very attractive tool to investigate angular dependence of collisional processes. Already applied to the study of small angle elastic scattering [2] this method may also prove adequate for studying quasi-resonant inelastic processes involving excited species such as depolarizing collisions, collisional transitions between hyperfine, fine or rotational sublevels, energy pooling collisions. For all these processes total cross sections have already been obtained in the past by different experimental ways. However they deserve to be reexamined in the perspective of their angular dependence.
Colliding Femtosecond Pulses Propagation in Dyes With Account of Their Amplitude and Phase Nonlinear Response
Authors: Vishchakas J. , Daugvila A. , Kabelka V. , Milyauskas A.
Published: February 2023

During the last decade many studies appeared on colliding pulse mode-locking lasers. These lasers are generating femtosecond pulses with a wide bandwidth. Due to this factor the phase and amplitude dispersional properties of matter are evident.