bluuebunny/crossref_metadata_2025 huggingface dataset:
193 nm—Moderately EUV
Authors: Rothschild M.
Published: February 2023

Photolithography at 193 nm is a natural continuation of the progression from 436 to 365 to 248 nm in lithography, dictated by the requirement for continually higher resolution. It is anticipated that 193-nm lithography will enable 0.25-μm patterning and will become the leading volume production technology at 0.18 μm. The main issues related to lithography at this new wavelength are being addressed at Lincoln Laboratory. It has been shown that highly transparent optical materials are available at 193 nm. Also, they are damaged by the laser radiation at a slow enough rate that high-quality projection optics are expected to perform within specifications for 10 years of full-time operation. Consequently, a 193-nm step-and-scan system has been constructed by SVGL, and it has been designed to attain sub-0.25-μm resolution over a 22 by 32.5 mm field. A range of 193-nm photoresist schemes has been demonstrated. They include semitransparent single-layer resists, positive-tone surface imaging (silylation), and negative-tone bilayers using ultrathin silicon-based polymers. In most instances we have demonstrated sub-0.25-μm resolution, high photosensitivity, good exposure-defocus latitude, and very low levels of etch residue (Figs. 1 and 2). In sum, the first successful steps towards a fully engineered 193-nm photolithography have been taken, and no major obstacles are anticipated.
Soft X-Ray Projection Imaging at 4.5 nm using Schwarzschild Optics
Authors: Murakami Katsuhiko , Nagata Hiroshi , Ohtani Masayuki , Hiroaki  , Oizumi  , Yamashita Yoshio , Atoda Nobufumi
Published: February 2023

Soft X-ray projection lithography at 4.5nm using NiCr/C multilayer-coated Schwarzschild optics was examined. Resist performance and pattern fabrication using thick resist are presented.
10x Reduction Imaging at 13.4 nm
Authors: Tichenor D. A. , Ray-Chaudhuri A. K. , Kubiak G. D. , Haney S. J. , Berger K. W. , Nissen R. P. , Wilkerson G. A. , Stulen R. H. , Paul P. H. , Arling R. W. , Jewell T. E. , Tejnil Edita , Sweatt W. C. , Chow W. W. , Bjorkholm J. E. , Freeman R. R. , Himel M. D. , MacDowell A. A. , Tennant D. M. , Fetter L. A. , Wood O. R. , Waskiewicz W. K. , White D. L. , Windt D. L.
Published: February 2023

High-resolution imaging of a reflection mask over a 0.4 mm diameter field of view has been demonstrated using a new extreme ultraviolet (EUV) imaging system. A significant reduction in debris from the laser plasma source (LPS) has extended the life of the condenser to approximately 1000 exposures without condenser maintenance. High EUV throughput of this system demonstrates the precise matching of five multilayer-coated surfaces reflecting at a center wavelength of 13.4 nm.
Point Diffraction Interferometry at EUV Wavelengths
Authors: Goldberg K. A. , Beguiristain R. , Bokor J. , Medecki H. , Jackson K. , Attwood D. T. , Sommargren G. E. , Spallas J. P. , Hostetler R.
Published: February 2023

Point diffraction interferometry is a common-path technique that is suitable for at-wavelength testing of EUV lithography optics. We have constructed and successfully tested such a device at the Advanced Light Source at Lawrence Berkeley Laboratory. Preliminary results on the characterization of the wavefront produced by a Fresnel zone plate lens are presented. Reference wavefront quality and thermal effects are also discussed.
At-Wavelength Metrology of EUV Cameras using Lateral-Shearing Interferometry
Authors: Tan Z. , MacDowell A. A. , La Fontaine B. , Russo J. , Bjorkholm J. E. , Tennant D. , Taylor D. , Himel M. , Wood O. R. , Freeman R R. , Waskiewicz W. K. , Windt D. L. , White D. , Spector S. , Ray-Chaudhuri A. K. , Stulen R. H.
Published: February 2023

We present the development of an extreme ultraviolet (EUV) interferometer for testing EUV lithography optics operating at a wavelength of 13 nm using the U13 undulator beamline at the National Synchrotron Light Source. The design and implementation of a lateral-shearing interferometry test will be described.
Post-polish figuring of optical surfaces using multilayer deposition
Authors: Tarrio C. , Spiller E. , Evans C. J. , Lucatorto T. B. , Clark C. W.
Published: February 2023

We present preliminary results of a technique that uses deposition of
variable-thickness multilayer films to correct optical figure errors.
The multilayer technique offers the potential to make figure
corrections, such as aspherizing high-quality spherical optics,
without adding measurable roughness. Moreover, because the period of a
multilayer can be measured very accurately using x-ray diffraction, we
can easily map test depositions made on inexpensive float-glass
substrates. We have used this technique to reduce large rotationally
symmetric errors by almost an order of magnitude in a single run.
Extension to the correction of non-symmetric errors was performed by
deposition through a two-dimensional mask, which was less successful.
We have identified several sources of error in this type of deposition
and discuss means of improvement. We have devised a method using a
series of rotationally-symmetric masks and a varying-rotation-rate
substrate stage to reduce the two-dimensional problem to a series of
one-dimensional problems.
Improving the Figure of Very Good Mirrors by Deposition
Authors: Sweatt W. C. , Weed J. W. , Farnsworth A. V. , Warren M. E. , Neumann C. C. , Goeke R. S. , Shagam R. N.
Published: February 2023

Mid-spatial frequency errors of near-perfect mirrors can be reduced by deposition through a computer-generated mask without degrading the superpolish. Experimental results are presented.
Preliminary investigation of an additive approach to the fabrication of precision aspheres
Authors: Weber F.W. , Montcalm C. , Vernon S.P. , Kania D. R.
Published: February 2023

We report progress in the aspherization of precision optical substrates via deposition of graded period Mo/Si multilayer coatings using a masking technique. These preliminary results show good agreement between the measured and desired thickness profiles over 85% of the sample, however, thickness deviations of up to 7% are observed in the central area. The errors are attributed to misalignments of the mask relative to the substrate during deposition.
Performance of a Two-Mirror, Four-Reflection, Ring-Field Optical System Operating at λ=13nm
Authors: La Fontaine B. , Gaines D. P. , Kania D. R. , Sommargren G. E. , Baker S. L. , Ciarlo D.
Published: February 2023

The performance of an Extreme Ultraviolet Lithography (EUVL) imaging optic was characterized by printing resolution test images in resist. While features as small as 0.137µm were successfuly printed, a resolution of 0.175µm better represents the performance of the system over the full 0.9mm2 image field. The contrast of the aerial image was estimated to be approximately 40% or less for the fine features printed. This low contrast value is attributed to a degradation of the modulation transfer function (MTF) due to the presence of scattered light in the image.
Debris-free EUVL sources based on gas jets
Authors: Kubiak Glenn D. , Bernardez Luis J. , Krenz Kevin D. , O’Connell Donna J. , Gutowski Robert , Todd Alan M. M.
Published: February 2023

Supersonic gas jets are used to produce a source of large cluster laser
plasma targets for extreme ultraviolet (EUV) generation without direct
production of debris. EUV conversion efficiency measurements at a
wavelength of 13.5 nm yield 58% of a solid gold target or
0.0026 J/eV/JL. Multilayer-coated mirrors placed in
proximity to the plasma exhibit 14% reflectance loss after the
equivalent of 1.4 × 108 pulses, an improvement by a
factor of 105× over unprotected solid target
results and 100× over solid targets with extensive debris
mitigation.
High-repetition-rate droplet target for laser-plasma EUV generation
Authors: Malmqvist Lars , Rymell Lars , Hertz Hans M.
Published: February 2023

A spatially stable liquid-droplet target system for uninterrupted, high-repetition rate and practically debris-free laser-plasma EUV generation is described. The system is based on the continuous liquid jet droplet generation method. System requirements for use in EUV lithography system are analyzed.
Specifications and Metrology of Surface Figure and Finish for Microlithography Optics
Authors: Zernike F.
Published: February 2023

Optical microlithography continues to move to smaller feature sizes. The system requirements are very high, and this stresses the fabrication and the assembly of the components and the attendant metrology. Some examples from present day technology are presented and requirements for EUV systems are discussed.
Phase Shifting Diffraction Interferometry for Measuring Extreme Ultraviolet Optics
Authors: Sommargren Gary E.
Published: February 2023

Extreme ultraviolet projection lithography operating at a wavelength of 13nm requires surface figure accuracy on each mirror to be better than 0.25nm rms. A new type of interferometry, based on the fundamental process of diffraction, is described that can intrinsically achieve the required accuracy. Applying this principle, two independent spherical wavefronts are generated - one serves as the measurement wavefront and is incident on the optic or optical system under test and the other serves as the reference wavefront. Since they are generated independently their relative amplitude and phase can be controlled, providing contrast adjustment and phase shifting capability. Using diffraction from a single mode optical fiber, different interferometers can be configured to measure individual mirrors or entire imaging systems. Measurement of an EUV projection system is described.
Phase-Shifting Point Diffraction Interferometry for At-Wavelength Testing of Lithographic Optics
Authors: Tejnil E. , Goldberg K. A. , Medecki H. , Beguiristain R. , Bokor J. , Attwood D. T.
Published: February 2023

We report on the development of at-wavelength wavefront metrology for evaluation of extreme ultraviolet optics intended for use in projection lithography. Initially, a point diffraction interferometer was used and the experience acquired with this instrument led to the development of a new interferometer, the phase-shifting point diffraction interferometer. In this paper, point diffraction interferometry performed at EUV wavelengths is discussed. The design and implementation of the new phase-shifting point diffraction interferometer are described.
Zonal Placement Errors in Zone Plate Lenses
Authors: Tejnil E. , Goldberg K. A. , Anderson E. H. , Bokor J.
Published: February 2023

Diffractive zone plate lenses are critical elements in extreme ultraviolet and soft x-ray applications that require optical imaging or light concentration. To achieve good optical performance, the zone plate features must be accurately defined over the sizable area of the zone plate. Here the effects of zone placement fabrication errors on the performance of zone plates are investigated. Experimentally observed zone-plate diffraction patterns are compared to calculated profiles for different zone placement error models to estimate the magnitude of zonal placement errors.
Ring-Field EUVL Camera with Large Etendu
Authors: Sweatt W. C.
Published: February 2023

These scanning cameras with large instantaneous fields make efficient use of the new, 300-μm diameter, debris-less laser-plasma sources while printing 100-nm features.
Basic Issues Associated With Four Potential EUV Resist Schemes: Trilayer Organometallic Bilayer, or Plasma Deposited-Plasma & Developed Bilayer, and Silylated Resists
Authors: Wheeler David R. , Kubiak Glenn , Ray-Chaudhuri Avijit , Henderson Craig
Published: February 2023

Four of the better developed resist schemes that are out growths of DUV (248 and 193 nm) resist development are considered as candidates for EUV. They are as follows: trilayer, a thin imaging layer on top of a refractory masking/pattern transfer layer on top of a planarizing and processing layer (PPL); solution-developed, organometallic bilayer where the imaging and masking layer have been combined into one material on top of a PPL; plasma deposited, photo-definable plasma developed organo-refractory material on top of a PPL; and finally silylated resists. They are examined in a very general form without regard to the specifics of chemistry or the variations within each group, but rather as to what is common to each group and how that affects their effectiveness as candidates for a near term EUV resist. In particular they are examined with respect to sensitivity, potential resolution, optical density, etching selectivity during pattern transfer, and any issues associated with pattern fidelity such as swelling.
Characterization of SAL605 Negative Resist at λ=13 nm
Authors: La Fontaine Bruno , Ciarlo D. , Gaines D. P. , Kania D. R.
Published: February 2023

We have characterized the response of the negative resist SAL605 in the extreme ultraviolet (λ=13nm). The sensitivity was found to be ~1 mJ/cm2 for all conditions studied. We have identified processing conditions leading to high (γ>4) contrast. The resist response was modeled using Prolith/2 and the development parameters were obtained from the exposure curves.
Heat-Resistance of Mo/Si Multilayer EUV Mirrors with Interleaved Carbon Barrier-Layers
Authors: Takenaka Hisataka , Kawamura Tomoaki , Haga Tsuneyuki
Published: February 2023

Introducing interleaved carbon barrier-layers improves the heat resistance of Mo/Si multilayers . The soft x-ray reflectivities of the multilayers were calculated, and the effects of heating on both the reflectivities and layer structures of Mo/C/Si/C and Mo/Si multilayers were investigated using x-ray diffraction and transmission electron microscopy. The results show that, for applications using intense soft x-ray beams, Mo/Si multilayers with interleaved carbon barrier-layers are better mirrors than Mo/Si multilayers because they have much better heat resistance and almost the same EUV reflectivity.
Pulsed Nozzle Techniques and Applications for the XUV
Authors: Kung A. H. , Rettner C. T. , Marinero E. E. , Zare R. N.
Published: February 2023

It has recently been shown that the well-defined geometry of a gaseous beam, the cooling that results from a supersonic expansion, and the relative simplicity of a pulsed nozzle make a pulsed supersonic beam source most desirable in providing a simple scheme for gas-phase third harmonic generation of radiation to the extreme ultraviolet. A simple model has since been developed to describe the third harmonic generation process in a pulsed beam. The model employs three basic assumptions: first, that the gas density in the jet has a rectangular profile in the direction of propagation of the laser beam; second, that the length of the profile is determined by the conservation of particle flux through all planes perpendicular to the forward direction of the jet; and third, that the laser field is propagating in the plane-wave regime. Using this model, predictions on the functional dependence of the output on reservoir gas density, nozzle diameter, nozzle distance from the laser focus, and other gaseous medium parameters are obtained and are compared, with results from experiments on frequency tripling to 118.2 nm in a xenon jet. Good agreement is obtained.
Collisionally Excited XUV Laser and XUV Radiation from Autoionizing Levels of Potassium in Discharge
Authors: Papanyan Valery O.
Published: February 2023

The talk will consider the application of quartet states of K to the construction of XUV lasers.
Multiphoton Ionization of Alkali Atoms
Authors: Compton R. N. , Dodhy A. , Stockdale J.A.D. , Klots Cornelius E.
Published: February 2023

Multiphoton ionization (MPI) of alkali atoms has played a pivotal role in our understanding of the interaction of intense electromagnetic radiation with matter. The "hydrogen-like" energy levels and absence of low-lying autoionizing states make the alkali atom theoretically tractable. The low ionization potential of these atomic species and the ease with which one can produce atomic beams of alkali atoms facilitate the experimental studies. Many of the early MPI studies involved high-powered fixed-frequency lasers. Presently, the availability of tunable dye lasers with wavelength extension (i.e., frequency doubling, Raman shifting, etc.) makes it possible to study one- to six-photon ionization of the alkali atom with continuously tunable radiation. Also, harmonic generation in these systems which may be present during ionization can be recorded more easily than in other systems since the radiation generated is in the visible or near ultraviolet spectral region. The ability to tune the laser to high Rydberg states with even or odd numbers of photons accesses electronic states of both parities. Stepwise excitation is capable of selectively producing states of high orbital angular momentum. Experiments in which highly excited states are produced in external electric or magnetic fields allow one to test fundamental ideas about the electron–Coulomb system in the quasi–continuum.3
Multiphoton Ionization of Cesium Atoms Above and Below The Two-Photon Ionization Threshold
Authors: Dodhy A. , Stockdale J.A.D. , Compton R. N.
Published: February 2023

The experimental arrangement consisted of a Nd:YAG pumped pulsed dye laser which was focused and crossed at right angle with a cesium beam. Photoelectrons were energy-analyzed by a spherical sector energy analyzer and detected with a dual multichannel plate.
Multiphoton Ionization Spectroscopy of the Fluoromethyl Radical
Authors: Dulcey C. S. , Bogan Denis J. , Hudgens Jeffrey W.
Published: February 2023

Using mass resolved multiphoton ionization spectroscopy, we have detected the first electronic spectrum of the CH2F free radical. The CH2F radicals were produced in a discharge fast flow reactor1 and introduced into a mass spectrometer’s ion optics where they were irradiated with the tightly focussed output of a Nd:YAG pumped dye laser. CH2F radicals were first produced via the reaction of F + ketene. At laser wavelengths between 345-363 nm a spectrum was observed from m/z 33 ions. To identify the spectrum’s carrier these experiments were repeated with the reaction, F + CH3F. Identical spectra were observed.
Variable Line Space Slitless Spectrometers at Grazing Incidence
Authors: Hettrick M.C.
Published: February 2023

A piano grating consisting of variably-spaced grooves concentric about a common point (fig. 1) provides λ/Δλ ~ 3000 over a simultaneous factor two in soft x-ray wavelength (λ = 10-100 Å). The complete instrument contains a 1 arc sec 1-meter diameter collecting mirror whose 10 meter focal length includes a 1.5 meter spectrometer with an imaging detector having 15 μm pixels. The end-to-end efficiency is approximately 4%, and the grating has a factor 4 variation in line spacing across a 50 cm ruled width.
Photoemissive Materials for 0.35μm Laser Fiducials in X-ray Streak Cameras*
Authors: Hale Charley P. , Medecki Hector , Lee Peter H. Y.
Published: February 2023

The Lawrence Livermore National Laboratory's laser fusion program makes extensive use of soft x-ray streak cameras for the diagnosis of laser irradiated targets. The capability of simultaneously recording the laser pulse and the x-ray flux in the streak camera will enhance the utility of the instrument. A program is under way to identify photocathode materials able to photoemit efficiently for soft x-rays (sub-Kev) and the 0.35μm (3.5ev) wavelength of the future NOVA fusion 1aser facility.
Spectroscopic Study of Xe Dimer Using VUV Laser Excitation
Authors: Lipson R. H. , LaRocque P. E. , Stoicheff B. P.
Published: February 2023

Several studies of the absorption and emission spectra of Xe dimers have been reported using cold vapor and large grating spectrographs1,2,3. Some vibronic structure was discernable in the band systems at 130 and 149 nm associated with the first two resonance lines of Xe. Analysis has led to information on the potential well-depths of both

O
u
+

excited states.
Generation of Coherent XUV Radiation Using Lasers and Relativistic Electron Beams
Authors: Freeman R. R. , Kincaid B. M.
Published: February 2023

Coherent soft x-rays can be produced by bunching a relativistic electron beam with a high-powered visible laser.
Multilayer Optics for the CUV: Synthesis, Experimental Results, and Projected Performance
Authors: Barbee Troy W.
Published: February 2023

Advanced vapor deposition techniques have yielded a new class of multi-layer optics for soft X-rays. Applications of these processes to fabrication of XUV optics promises significant improvements. Synthesis processes, current experimental results, and projected performance are discussed.
VUV Laser Photolithography
Authors: White J. C. , Craighead H. G. , Howard R. E. , Jackel L. D. , Wood O. R.
Published: February 2023

In this paper we describe experiments using a molecular fluorine (i.e., F2 dimer) laser operating at 157 nm as a vacuum ultraviolet (VUV) source for high resolution photolithography. The F2 excimer laser is now the only commercially available laser with high average power at a wavelength as short as 157 nm. Using this laser as a source for contact lithography, we made resist lines as narrow as 150 nm, the smallest features yet reproduced by photolithography.
Tunable Resonant Enhancement in Nonlinear Optical Frequency Mixing
Authors: Smith A. V.
Published: February 2023

The ability to introduce additional resonances in the nonlinear optical susceptibility of a medium by the injection of an additional radiation field is an attractive possibility from the standpoint of efficient tunable frequency mixing processes in the VUV. The possibility of such processes suggest themselves in previous observations in atomic mercury where an enhancement of several orders of magnitude in the third harmonic generation efficiency has been reported when the input frequency is four-photon resonant with the 6S → 6D transition(1).
Generation of VUV Radiation in the Kilowatt Power Range down to 130 nm by Stimulated Raman Scattering in hydrogen
Authors: Döbele H.F. , Röwekamp M. , Rückle B.
Published: February 2023

Raman conversion to shorter wavelengths of visible and UV radiation has been studied by several authors /1,2/. Hydrogen is especially suited because of its large Raman shift and low dispersion. In plasma diagnostics, there exists considerable interest to determine the concentration and eventually the flux of 1ow-Z-materials such as O, C, Si, Be, B and others in the piasma-to-wal1 transition layer by laser-induced fluorescence spectroscopy.
Measured Radiative Lifetime of Rovibronic Levels in A'∏(v = 0) State of CO, and Comparison with Theory
Authors: Maeda M. , Stoicheff B. P.
Published: February 2023

VUV radiation was generated by mixing N2-pumped dye-laser beams (2 ns) in Mg vapor, and LIF used to measure lifetimes of perturbed levels from J′ = 0 to 29.
Time Evolution, Radial and Axial Distributions of the EUV Line Intensities in CO2 Laser Produced Plasmas*
Authors: Skinner C. H. , Keane C. , Milchberg H. , Suckewer S. , Voorhees D.
Published: February 2023

A CO2 laser (1 kJ, 75nS F.W.H.M.) was used to create a plasma from a variety of targets, either solid (e.g. C, Aℓ) or gas (e.g. CO2, Ne) in an experiment to develop a soft X-ray laser. An absolute intensity calibrated VUV duochromater was used to observe line emission from the plasma. A scanning slit assembly limited the field of view of the duochromator to a region 1 mm × 0.1 mm, the long dimension being normal to the target. By scanning the slit and target position the radial and axial distributions of the line intensities were built up on a shot-to-shot basis for the different targets.
Soft X-Ray Spectra, Population Inversions, and Gains in a Recombining Plasma Column*
Authors: Milchberg H. , Schwob J. L. , Skinner C. H. , Suckewer S. , Voorhees D.
Published: February 2023

With the view of developing a suitable medium for soft X-ray lasing action in the strongly recombining phase of a CO2 laser produced plasma, we have concentrated on studying the UV and soft X-ray emissions of hydrogenic carbon (CVI) and the Li-like sequence CIV, OVI, FVII, and NeVIII. These absolutely calibrated spectra, both time integrated and time resolved, have been measured perpendicular and parallel to the plasma column. Plasma density and temperature have been estimated from this data using Stark broadening, recombination continua and dielectronic satellites. Satellites have also been used to estimate self-absorption in lines of interest, especially CVI Lyman α.
Optical Pumping of Short Wavelength Fluorescence in Plasmas Using Line Radiation
Authors: Trebes J. , Krishnan M.
Published: February 2023

We have previously reported [1] enhanced fluorescence of the CII, 5d-3p transition at 213.8 nm, when the 5d-2p transition is selectively pumped by A1III, 56 nm line radiation. The CII ions are produced in a carbon vacuum arc discharge, while the A1III pump ions are created in an adjacent, laser-produced plasma. Collisional coupling of the pumped, 5d level in CII to the 5f level was verified [2] by observation of enhanced fluorescence at 299.3 nm on the CII, 5f-3d transition. This paper reports simultaneous observation of four different wavelengths in CII, in order to characterize the optical pumping process and the subsequent collisional-radiative kinetics. Measurements are described of electron density (ne) and electron temperature (Te) in the C vacuum arc. The measured values of ne and Te are inputs to a time dependent, collisional-radiative model for the CII level populations. Model predictions of the expected fluorescence enhancement, the coupling of the pumped 5d level to other levels in CII, and various loss rates are compared with experiments. The possibility of producing a laser in CII using this scheme is examined. Other candidate pairs for optically pumped, XUV wavelength lasers are presented and discussed.
X-Rays Generated by Laser Irradiated High-Z Targets
Authors: Fortin X. , Babonneau D. , Billon D. , Bocher J.L. , Di Bona G. , Thiell G.
Published: February 2023

The X-ray emission from laser irradiated high-Z targets has received much attention in the recent years. The two main centers of interest were : spectral studies for the determination of plasma parameters and conversion efficiencies for understanding the plasma energetics. We have performed these kinds of experiments at Limeil during the three past years using spherical and planar targets (Glass, Aluminum, Gold, Copper) and modifying irradiation conditions (laser wavelength and flux).
The Excitation of Metastable XUV Levels
Authors: Caro R. G. , Wang J. C. , Young J. F. , Harris S. E.
Published: February 2023

For many applications in VUV and XUV physics, it is desirable to have a technique for creating large densities of highly-energetic atoms or ions. Two techniques for efficiently exciting states with energies in the 10–100 eV range are discussed. Both are based on photoionization of atoms by x-rays from a plasma produced by a laboratory-sized Nd:YAG laser. Inner-shell photoionization by these x-rays has been used to preferentially populate excited ionic states in large densities. For the excitation of atomic transitions, a novel "photoionization electron source" is described which produces high densities (> 1610 cm−3) of hot (~ 45 eV) electrons in a pulse of approximately 600 ps duration.
Experimental and Simulation Studies on Soft-X-Ray Emission from 0.53 μm-Laser Irradiated Solid Targets
Authors: Mochizuki T. , Yabe T. , Yamanaka C.
Published: February 2023

The spectrum-resolved radiant energy in 0.17~1.6 keV range from various plane targets irradiated by a 0.53μm laser at 0.15~1.0 nsec pulse through a f/1.4 lens with a nominal incidence angle of either 54° or 0° were obtained by a mutually complementary use of a transmission grating spectrometer, multi-channel filtered X-ray diodes and X-ray calorimeters. Atomic number dependences of the spectrum and X-ray conversion efficiency are described. Especially the radiation investigated at the Au target is concluded to be significantly deviated from the blackbody radiation at the laser intensity range 2×1013~2×1015 W/cm2. The conversion efficiency increases as laser pulse duration. The increase at normal incidence is infered to be mainly due to the increase in the laser absorption.
Population Inversion and Gain in Expanding Carbon Fibre Plasmas
Authors: Pert G.J.
Published: February 2023

Carbon fibres of a few microns diameter, heated by a Nd:glass laser pulse offer a suitable medium for the generation of gain in the XUV spectral region. Population inversion occurs as recombination is induced by adiabatic cooling in the expansion of the hot fibre. Experimental results and their interpretation using computer modelling have given a good understanding of the underlying physics, and show two regimes of operation: one of high gain places stringent limitations of the uniformity of illumination, the other of lower gain of the length of cylindrical focus.
X-Ray Laser Spectroscopy
Authors: Elton R.C. , Dixon R.H. , Ford J.L. , Lee T.N.
Published: February 2023

Emissions from certain resonance lines which are considered to be promising source candidates for matched-line photoexcitation pumping of plasma x-ray lasers have been measured and are found to be near the saturation level. This is supportive of current numerical modeling and laser experiments. The radiation is emitted from high density plasmas near the surface of laser-heated slab targets of selected materials. Among numerous possible ion combinations to be surveyed, a very promising test case involves Na9+ ions pumping Ne8+ ions for lasing at 23, 7.8 or 5.8 nm wavelengths. Spectra from frozen neon targets which include the Ne6+-Ne8+ ions will be presented.
High Resolution Spectroscopy
Authors: McIlrath Thomas J.
Published: February 2023

High resolution spectroscopy in the vacuum ultraviolet region has, until recently, been limited to work with long focal length grating spectrographs. The best resolution with state-of-the-art instrumentation is approximately 250,000, but the photographic method provides simultaneous measurement of ≈ 3 × 104 data points with modest exposure times. The development of tunable coherent sources in the VUV promises to increase the available resolution by well over an order of magnitude, but tunable coherent sources involve sequential point-by-point data collection with typical scanning ranges of ≈ 102 cm−1.
Spectroscopic Measurements of Sub-Laser Linewidth Autoionization Rates
Authors: Cooke W. E. , Bhatti S. A. , Cromer C. L.
Published: February 2023

If the lifetime of an autoionizing state is much shorter than the pulse length of the laser exciting it, then it is possible, with sufficient laser power, to ionize the entire atomic population. When the laser is tuned off resonance, it may still have sufficient power to ionize almost the entire population. The detuning at which the ionization efficiency will drop to 50% depends on the product of the laser pulse's energy density and the excited state's autoionizing rate.
Atomic H and D Concentrations and Velocities Measured with Harmonically Generated Lyman-α (1215 Å) Radiation
Authors: Dreyfus R. W. , Bogen P. , Langer H.
Published: February 2023

A resonance flourescence scattering system remotely senses H- and D- atom concentrations in the 109 cm-3. range in a tokamak. The Doppler broadening measures temperatures down to 100°K.
An Overview of Lithium Spectroscopy
Authors: Bunge Carlos
Published: February 2023

Summary not available
Direct Generation of XUV Radiation*
Authors: Rhodes Charles K.
Published: February 2023

The technology of high spectral brightness rare gas halogen (RGH) excimer lasers can be readily used to generate bright coherent radiation in the extreme ultraviolet (XUV) range. As demonstrations of this capability, tunable (XUV) radiation at ~ 64 nm and ~ 79 nm has been generated using a high spectral brightness ArF* (193 nm) source by frequency tripling and frequency mixing, respectively. In the case of tripling, it has been experimentally determined that the conversion efficiency is limited by photoabsorption of generated XUV photons by the nonlinear medium. It is shown that a simple flow geometry that confines the nonlinear medium to the conversion zone by a buffer gas of low absorption cross-section sharply reduces these losses and leads to correspondingly enhanced conversion efficiencies. With this apparatus, at 64 nm, 30 W, 10 nsec pulses have been generated corresponding to a conversion efficiency of 10-6. This upconverted radiation is tunable over 0.2 nm, the range determined by the gain profile of ArF* amplifiers. Broad tunability is achieved with the use of a dye laser in a process of frequency mixing. Tunable radiation with peak powers of 200 mW at ~ 79 nm has been generated by frequency mixing 2 ArF* photons and one visible dye photon (420 - 460 nm). Since nonlinear processes generally favor the use of short pulses, 10 psec pulses at 193 nm have been generated by frequency tripling of a pulse amplified, synchronously pumped mode-locked dye laser. Amplified radiation of this source is used to obtain coherent radiation at 64 nm with a power of 20 kW by frequency tripling, a value corresponding to an enhanced conversion efficiency of ~ 10-5. An analysis of the expected limiting performance of RGH systems for the production of XUV and soft x-rays will be given.
Anti-Stokes Scattering as an XUV Radiation Source
Authors: Harris S. E. , Falcone R. W. , Young J. F. , Pedrotti K. D. , Rothenberg Joshua E. , Willison J. R.
Published: February 2023

The paper will describe the use of anti-Stokes scattering as a radiation source for high resolution spectroscopy in the 100 Å to 1000 Å spectral region, and as a flashlamp for the construction of XUV lasers.
Photo-Autoionization Pumped BA ION Laser
Authors: Bokor J. , Freeman R. R. , Cooke W. E.
Published: February 2023

We have studied the selective autoionization process 6p3/2np → 6p1/2 + e­ in atomic Ba, and have achieved inversion in Ba+ via this process. Using two lasers, neutral Ba is first excited from its 6s2 1So ground state to a Rydberg state 6snp1Po, with a tunable laser near 247 nm. Another dye laser, near 455 nm, further excites the Ba to 6p3/2np, where-upon the atom autoionizes. We have studied the excitation spectrum as a function of the wavelength of the second laser, and have found it similar to that observed in Ba 6p3/2ns states.1
Resonant Four-wave Mixing Processes in Xenon
Authors: Yiu Yun Mui , Bonin Keith , McIlrath T. J.
Published: February 2023

Four-wave mixing processes have been widely used to generate coherent VUV radiation. In this paper we report the use of intermediate resonances in Xe to enhance the VUV output below 130 nm.
Vacuum UV laser induced fluorescence of the NO molecule
Authors: Scheingraber H. , Vidal C.R.
Published: February 2023

Tunable narrow bandwidth VUV radiation in the spectral region from 190 - 200 nm was generated by resonant sumfrequency mixing of two flashlamp pumped dye lasers. This radiation was used to excite individual rotational vibrational levels of different electronic states of the NO molecule. Using a multiple reflection cell the effective quantum efficiency was raised and the subsequent fluorescence radiation was spectrally resolved by means of a 1m VUV grating monochromator. This technique allowed a direct measurement of the Franck-Condon factors for the different observed transitions. The measured values show significant discrepancies with calculations of Spindler et al./1/ neglecting the R-dependence of the electronic transition moment.
Excitation and Ionization of Atomic Hydrogen by Narrow Bandwidth Tunable VUV Laser Radiation
Authors: Zacharias H. , Rottke H. , Welge K.H.
Published: February 2023

By frequency mixing in rare gases it is now possible to generate tunable coherent radiation in the entire wavelength region from 105 nm to 200 nm1. This techniques will thus open the way for many applications of tunable VUV radiation to physical and photochemical problems. In this contribution we want to report on results of the excitation of atomic hydrogen in an atomic beam. The tunable VUV radiation excited the 1 2S1/2-- 2 2P Lyman - α transition, and a second tunable UV laser served to excite the (2 2P) - H atoms further to high Rydberg states or the ionization continuum. Preliminary results together with a detailed description of the apparatus has been published2,3.
Direct Observation of Hot Electron Spectra from Laser Illuminated Sodium Vapors.
Authors: Legouet J.L. , Picque J.L. , Wuilleumier F. , Bizau J.M. , Dhez P. , Koch P. , Ederer D.L.
Published: February 2023

Low intensity CW laser was tuned to D2 line in sodium. Large numbers of electrons with kinetic energy 4.2 and 5.4 eV were observed.
Autoionizing and High-Lying Rydberg States of Lutetium Atoms
Authors: Miller C. M. , Nogar N. S.
Published: February 2023

A pulsed-field time-of-flight mass spectrometer was used in conjunction with two XeCl* excimer laser pumped dye lasers to examine the spectroscopy of Lu atoms near the 5.4 eV ionization limit, Fig. 1. A fixed frequency laser, 22125 cm−1, was used to saturate the 5d6s 2 2D3/2 →5d6s6p 2D3/2 transition, while a frequency scanned laser was used to probe transitions from the excited state to high Rydberg or low lying autoionizing levels. Rydberg levels close to the continuum were observed and assigned, as were several autoionizing features not previously reported.1,2
Two-Photon Excitation of the Lowest g-States of Xe2*
Authors: Gornik W. , Matthias E. , Schmidt D.
Published: February 2023

Applying two-photon excitation techniques we have studied atomic and molecular states in the energy region of the 5p56s configuration of Xe I. In this way, states can be selectively populated which cannot be reached by dipole transitions from the ground state.
Review of Unconverted Nd-Glass Laser Plasma Experiments at the Lawrence Livermore National Laboratory*
Authors: Manes K. R.
Published: February 2023

Much has been learned about laser heated disk target plasmas which may find application in diverse technologies.
Electron Spectra of Four-Photon Ionization of NO
Authors: Kruit P. , Kimman J. , Van der Wiel M.J.
Published: February 2023

We are currently engaged in a program on spectroscopy of electrons created in multi-photon ionization. Results on atomic Xe concerning additional absorption of photons in the N-photon continuum have been reported recently [1]. These data were obtained using a novel type of electron spectrometer described in a separate abstract.
Non-Linear Mixing
Authors: Welge Karl H.
Published: February 2023

We report investigations with tunable VUV radiation, employing VUV generation in regions down to the cut-off wavelength of lithium fluorid crystal (~ 110 nm) by frequency tripling of tunable UV from dye laser. -Experiments on multiphoton excitation and ionization of atomic hydrogen with tunable VUV light at Lyman-α, have been carried out with the following objectives: (1) sensitive H and D atom detection by two-photon ionization i. e.

1s

ω

Lyα

→

2
p

ω

uv

→

 ion

, (2) two-photon ionization of H with high resolution at Lyman-α to resolve the hyperfine groundstate doublet, aiming at the production of polarized protons, (3) state selective production of high Rydberg states

(

1
s

ω

Lyα

→

2p

ω

uv

→

 ns, nd

)

, and their ionization, (4) Doppler line shape spectroscopy at Lyman-α applied to recoil energy and momentum distribution measurements of H and D atoms in dissociation processes. -Depending on the objective, different experimental conditions and systems have been employed, for instance atomic beam configuration, mass-spectroscopic ion detection, field ionization in cryogenetic environment, and for Doppler measurements laser induced fluorescence.
Generation of Tunable, Coherent 79 nm Radiation by Frequency Mixing
Authors: Egger H. , Srinivasan T. , Boyer K. , Pummer H. , Rhodes C. K.
Published: February 2023

In this paper, we report on the generation of tunable radiation around 79 nm, using frequency mixing of two ArF* photons and a visible dye laser photon. In contrast to harmonic generation with a rather limited tuning range, this method combines the potential of high power excimer lasers (up to 30 W peak powers have recently been measured1 at the third harmonic of ArF*) with the broad tunability of dye lasers. The ArF* lasers used in the present experiments is a modified version of a system described previosuly.2 The output characteristics of the ArF* laser are energy 200 mJ, bandwidth 0.5 cm−1, pulse duration 7 ns, and wavelength 193.55 nm. The tunable dye laser was operated with stilbene 420, tunable from 416 nm to 458 nm, with an output energy of 5 mJ, bandwidth 0.3 cm−1, and pulse duration 15 ns. With these lasers, up to 200 mW peak power of mixed radiation have been measured with hydrogen as nonlinear medium. This radiation has a bandwidth of less than 0.8 cm−1, if gaussian lineshapes are assumed. In order to demonstrate the usefulness of the system as a spectroscopic tool, the source was tuned across the 2P½ 9d' autoionizing resonance in argon. Fig. 1 shows the measured absorption profile normalized to the data from Hudson and Carter3. The bandwidth of the source can be tested by scanning across the 2P3/2 13d states which have an estimated doppler width of 0.22 cm−1
Upconversion of Laser Radiation to γ-Ray Energies
Authors: Collins C. B.
Published: February 2023

Reviewed here are studies of the general problem of multiphoton processes which might occur at the nuclear level when one of the photons belongs to an intense radiation field from a laser at optical frequencies. It has been predicted that sufficient laser intensities could stimulate a component step involving the nuclear radiations. Transition probabilities have been found which relate the probabilities for γ-ray transitions induced by the optical radiation to the Breit-Wigner cross sections for the absorption or emission of single γ-photons. The most important results have concerned the isolation of the multiphoton Mössbauer channel which preserves the natural linewidth of the process in solid media. This channel was found to have a relative weight comparable to the conventional Debeye-Waller factor for the transition. In emission the induced processes of both Anti-Stokes Raman scattering and two-photon emission have been considered and both are found to lead to the generation of tunable γ-radiation. Transition probabilities are calculated to be large enough to support the production of usable spectral sources that could be tuned over a range of γ-ray energies approximately a thousand times greater than can be realized by conventional Mössbauer techniques. Analogous possibilities for the detection and tuning of nuclear reactions induced by intense optical fields also have been considered in this review.
Free Electron Laser on Higher Harmonics
Authors: Barbini R. , Vignola G.
Published: February 2023

The main goal of FEL experiments, both with recirculating and non recirculating machines, is to reach a stable oscillator by adding two mirrors at the ends of the undulator to form an optical cavity. In any case, it is necessary to achieve enough gain in order to overcome losses due essentially to end mirrors absorptions.
Quantum FEL Statistics: a Critical Review
Authors: Dattoli G. , Richetta M. , Renieri A.
Published: February 2023

The literature on the quantum analysis of FEL is now becoming somewhat conspicuous, despite the fact that classical theories work well in accounting for the available experimental data concerning both amplification and oscillation experiments. No genuine quantum effect has been observed up to now. Therefore, the main goal of such analyses should be to put in evidence observable effects whose interpretation needs quantum mechanics.
A Three Dimensional Analysis of Spontaneous and Stimulated Smith-Purcell Radiation in the X-ray Regime
Authors: Gover A. , Piestrup M. A. , Pantell R. H.
Published: February 2023

The Smith-Purcell (S-P) radiation is examined as a possible source of coherent and incoherent radiation in the x-ray regime. The physical mechanism and radiation pattern is quite similar to that of coherent transition radiation(1). However, since in the S-P radiation the electrons are traversing outside the material (above the grating), coherent interference of radiation from a large number of grating rulings and stimulated emission are more likely to be realized.
Extreme Uv Generation with Two-Stage Free Electron Laser
Authors: Boscolo I. , Colson W.B. , Stagno V.
Published: February 2023

An electron beam travelling through a bending magnet emits radiation in all the components of its Fourier spectrum. The emission on the harmonics depends on the bunching tightening. This emission is enhanced if the beam goes through a wiggler.
FTS Measurements of Aerosols
Authors: Tolbert Margaret A.
Published: February 2023

Heterogeneous reactions on polar stratospheric clouds (PSCs) have recently been implicated in Arctic and Antarctic ozone destruction. Although the chemistry is now well documented, there are still major uncertainties in the chemical composition and formation mechanism for PSCs. PSCs are usually classified as type I or type II, depending on their formation temperature. Type II PSCs are composed of crystalline water ice and form only when stratospheric temperatures drop below about 188 K. These clouds are most frequently observed in the Antarctic winter stratosphere. In contrast, Type I PSCs form at temperatures several degrees warmer than the frost point and are therefore observed in both polar stratospheres. Although type I PSCs are thought to contain HNO3 and water, the exact chemical composition has not been established.
Absorption spectra of cold vapours using FTS and collision cooling
Authors: Ballard J , Newnham D A
Published: February 2023

Spectra of polyatomic molecules, which are often very complex with many hot bands at room temperature , are significantly simplified if the sample can be cooled. The simplification aids analysis of the spectra in terms of rotational constants. Similarly spectral parameters such as line broadening coefficients, are needed to be known at cold temperatures for correct interpretation of many atmospheric measurements. However many polyatomic molecules also condense readily on cooling, so gas phase spectroscopy using conventional absorption cells at low temperatures is difficult, if not impossible due to the large negative temperature coefficient of SVP.
Thermal artefacts in mid to far IR FT spectroscopy
Authors: Johns J. W.
Published: February 2023

At wavelengths longer than about 5 microns thermal radiation arising from room temperature components of the spectrometer and indeed of the sample itself can become modulated and hence contribute to the interferogram. Two situations, which are particularly important for certain types of rapid scan instruments, will be discussed.
Pulsed-Beam Fourier Transform Microwave Spectroscopy: Research and Applications
Authors: Lovas Frank J.
Published: February 2023

The method of pulsed-beam Fabry-Perot cavity Fourier transform microwave spectroscopy (FTMW) was first implemented by Balle and Flygare1. The spectrometer at NIST evolved from a design quite similar to the Balle and Flygare instrument2 into a simpler, more sensitive automated scanning instrument3,4 which will be described here.