bluuebunny/crossref_metadata_2025 huggingface dataset:
Reflecting Multilayer Coatings for EUV Projection Lithography
Authors: Underwood James H.
Published: February 2023

In the past 20 years, a very large effort has been devoted to the
development of multilayer reflecting coatings for the x-ray and
extreme ultraviolet (EUV) spectral regions. Out of this development
arose the concept of EUV projection lithography, and multilayer
coating represents the key technology which enable EUVPL. At the same
time it presents technical challenges to be overcome for EUVPL to
become a production tool. These lie in the physics and chemistry of
the multilayers, in the deposition technology and in the metrology of
the final coatings. In this paper these topics are reviewed, and some
interesting results obtained using the soft x-ray/EUV Calibration and
Standards beamline at the Advanced Light Source are presented.
Reflectance coatings for the vacuum/extreme ultraviolet region
Authors: Duddles N. J.
Published: February 2023

A theoretical examination has been undertaken to evaluate the performance of reflective coatings at normal incidence in the spectral region 40-70nm for applications in lithographic imaging systems. Aluminium based multilayer structures were found to offer the highest theoretical reflectance values in this region but due to the presence of surface oxide layers are of little practical value. Alternative multilayer structures based on silicon are offered as an alternative, were it is suggested that oxide formation may be more easily controlled.
Generation of Coherent Tunable VUV Radiation
Authors: Hilbig R. , Hilber G. , Timmermann A. , Wallenstein R.
Published: February 2023

We report on the generation of narrowband tunable coherent Vacuum ultraviolet radiation by third-order sum- and difference frequency conversion of intense pulsed or continuous-wave dye laser radiation in rare gases or metal vapors.
Tunable Sub-Angstrom Radiation Generated by Anti-Stokes Scattering from Nuclear Levels
Authors: Collins C. B. , DePaola B. D.
Published: February 2023

This work concerns the demonstration of the feasibility of the tuning and perhaps even stimulation of nuclear radiation. Theory [1-3] has indicated that anti-Stokes Raman upconversion of intense but conventional long wavelength sources of radiation produced by scattering from isomeric states of nuclear excitation could lead to significant sources of tunable y-radiation characterized by the natural Mössbauer width of the lines. This would result in lines with sub-Angstrom wavelengths and widths of a few MHz. Further computations [4] have suggested that this type of coherent, as well as a new type of incoherent, optical pumping could even lead to appreciable levels of inversion of the population of nuclear levels that would be capable of supporting the growth of stimulated y-ray intensity. Whether or not these processes can reach threshold depends upon the resolution of basic issues lying in an interdisciplinary region between quantum electronics and nuclear physics that have not been previously addressed. It was the purpose of this work to study these issues experimentally.
Recent Experiments on Soft X-Ray Laser Development in a Confined Plasma Column*
Authors: Suckewer S. , Keane C. , Milchberg H. , Skinner C. H. , Voorhees D.
Published: February 2023

A series of recent experiments were performed with a new focussing system for our CO2 laser, which allowed a significantly smaller focal spot. The plasma was created by the interaction of a 1 kJoule CO2 laser with solid or gas targets. The plasma column was confined by a solenoidal magnetic field (B ≈ 50-100 kG) or was expanding freely (B =0). Spectral line radiations in the VUV region were monitored by two instruments operating initially in the spectrographic mode (spectra) and later in the monochromatic mode (time evolution of line intensities). To increase the cooling rate of the recombining plasma column, higher-Z elements were introduced into the plasma. For example, in case of a gas target, oxygen, argon or xenon were added for faster plasma cooling. For solid carbon targets, Aℓ-blades were used to increase radiation losses. Enhancement of hydrogen-like CVI 182Å line intensity and population inversion in Li-like ions (CIV, OVI, FVII, and NeVIII) were monitored for different plasma conditions. In order to change these conditions we varied the amount of higher-Z elements, CO2 laser power, magnetic field, and in the case of gas targets, we also varied the initial gas pressure. The interpretation of the time evolution, the radial and axial distribution of line intensities, together with computer simulations of the data will be presented.
Anomalous Multi-Photon Processes
Authors: Rhodes C. K.
Published: February 2023

Recent studies of multiphoton ionization1 indicate the presence of an anomalously strong coupling for high Z materials. The principal findings, obtained at intensities up to ~1016 W/cm2, are (1) an unexpectedly strong multiphoton coupling strength resulting in multiple ionization of target atoms, (2) a strong Z-dependence of the coupling, and (3) ion charge state distributions which in some cases resemble those characteristic of Auger cascades. The results of these experiments suggest, for the heavy materials, a multiphoton analog of the collective atomic inner-shell response observed in both single-photon photoionization2 and bremsstrahlung.3 The relatively slow decline observed in the abundance of high ion states as Z increases qualitatively corroborates such an interpretation.
Photoionization of Excited Molecular States using Multiphoton Excitation Techniques
Authors: Dehmer P. M. , Pratt S. T. , Dehmer J. L.
Published: February 2023

Resonantly enhanced multiphoton ionization (REMPI) affords the opportunity to select a specific ionization pathway in order to produce a particular ionic state for further study or to investigate detailed aspects of excited state photoionization dynamics. The production of electronic or vibrational state-selected ions using REMPI can be achieved by first preparing an intermediate Rydberg state that has a potential energy curve similar to that of the final desired ionic state, and then ionizing the Rydberg state with a single additional photon. Under these circumstances, the Franck-Condon factors governing the final ionization step strongly favor the preservation of the Rydberg state core. Here we demonstrate the final electronic and vibrational state selectivity of REMPI by recording photoelectron spectra following single photon ionization of the 2pπu C 1Πu Rydberg state of H2 (Figure 1) and the (1Πu)3(3σg)2 3sσg o3 1Πu Rydberg state of N2 (Figure 2). Both excited states were prepared by resonant three photon transitions from the ground electronic state. In the case of H2, the C 1Πu Rydberg state converges to the ground electronic state of the ion, and photoionization produces vibrational state-selected ions in the ground electronic state. In the case of N2, the o3 1Πu Rydberg state converges to the first excited state of the ion, and photoionization produces vibrational state-selected ions in an excited electronic state.
Two and Three Photon Ionization of Cesium
Authors: Pindzola Michael S.
Published: February 2023

Probabilities for the two and three photon ionization of cesium are calculated using the density matrix formalism.1 We assume a narrow band width radiation field of moderate intensity (108 watts/cm2).
VUV Instrument Calibrations for Laser-Plasma Studies
Authors: Rockett Paul D. , Bird C. Richard , Shepherd Ronnie
Published: February 2023

KMS Fusion has assembled a laboratory soft x-ray calibration system, which enables a quick response to the needs of laser-plasma experiments. Interest in laser-generated VUV sources has grown from the early work of W. Ehler in 1968 to the detailed line identification studies of J. Reader (NBS). Simultaneously, there has been a dramatic growth in the development of instrumentation for both spectroscopy and detection of 50 eV to multi-keV radiation. Calibration of these instruments, however, has frequently lagged behind their introduction, limiting our ability to accurately interpret their data. This has occurred because typical calibration sources are expensive and/or labor intensive and suffer from an inability for fast turnaround. Our source has become both flexible and capable, presently allowing calibrations in wavelength and intensity from 67.4 Å to 2.76 Å with Kα and Lα sources.
A High-Resolution VUV Spectrometer with Electronic Parallel Spectral Detector
Authors: Cromer C. , Bridges J.M. , Lucatorto T.B. , Roberts J.R.
Published: February 2023

We demonstrate a new high resolution VUV spectrometer for applications in the range 50 to 800Å. The instrument is comprised of a laser-plasma VUV source, which provides continuum background illumination, a 1.5m grazing incidence spectrometer, and a 1024-channel VUV optical multichannel analyzer (VUV-OMA). The VUV-OMA is of new design, featuring a special resolution-enhanced channel electron multiplier array in an overall configuration chosen to optimize the spatial resolution of the detector while maintaning single-photoelectron sensitivity.
X-UV Gain Amplification Studies in Laser Plasma Using Normal Incidence Multilayers Mirrors
Authors: Dhez P. , Jamelot G. , Carillon A. , Jaegle P.
Published: February 2023

Progress achieved in X-UV Amplification of Spontaneous Emission (ASE) lead us to look as soon as possible for mirror cavity feasability.
Performance of Transition Metal--Carbon Multilayer Mirrors From 80 To 350eV
Authors: Kania D. R. , Bartlett R. J. , Trela W. J. , Spiller E. , Golub L.
Published: February 2023

We have measured the reflectivity of transition metal (Co, Fe, V, and Cr)--carbon multilayer mirrors between 80 to 350 eV. The multilayer structures were fabricated by electron beam evaporation with in situ monitoring during the deposition process in order to maximize the reflectivity of the coating.1 The effective 2d spacing of all the samples was approximately 150 Å.
Laser Spectroscopy Experiments on Atomic and Molecular Hydrogen
Authors: Rottke Horst , Welge Karl H.
Published: February 2023

The two-step excitation-ionization, has been studied in electric fields (1–8 keV/cm) using linearly polarized (it or a) VUV and UV laser light. Tuning the VUV to selected components in the (n=2) Stark manifold and scanning the UV, the H* excitation energy ranged from ~500 cm-1 below to ~100 cm-1 above the zero-field ionization potential, IPO. Ionization spectra taken for (π,π), (π,σ), (σ,π), (σ,σ) polarization, showed the sharp line structure from states between the field-ionization saddle point energy and the IPO, in agreement with theory (Fig. 1). In the (π,π) case oscillating resonances extending beyond the IPO were observed. As an example, Fig. 1 shows the ionization spectrum for (π,π) excitation at field strength F = 5714 V/cm. The lines are Identified by upper state parabolic quantum numbers |n1,n2,|m|> with n = n1 + n2 + |m| + 1. Lifetimes of the field ionizing states have been measured and the dependence of the oscillations on the electric field has been studied.
State-selective vacuum uv spectroscopy of small molecules
Authors: Vidal C.R.
Published: February 2023

State-selective spectroscopy of the CO and NO molecule is demonstrated using the methods of fluorescence-, of frequency-selective excitation, and of vacuum uv-visible double resonance spectroscopy.
Coherent Radiation Characteristics Of Magnetic Insertion Devices In Modern Storage Rings
Authors: Kim K.J. , Halbach K. , Attwood D.T.
Published: February 2023

We discuss the characteristics of radiation from undulators and wigglers in modern electron storage rings. Of particular interest are the coherence properties of undulator radiation which provides an assured route to tuneable coherent radiation throughout the soft x-ray spectral region. We discuss spectral, angular, spatial, and polarization properties of this radiation.
Diagnostics for XUV/Soft X-ray Laser
Authors: Kauffman Robert L.
Published: February 2023

We have begun investigating the production of an XUV/soft x-ray laser using our high-powered glass lasers as drivers. A major diagnostic for lasing is the measure of the absolute power produced in the lasing line. I have developed a spectrograph to time-resolve lasing lines in the energy range from 50 eV to greater than 200 eV. The spectrograph combines a transmission grating and x-ray streak camera to produce a flat field instrument. A cylindrical mirror is used in front of the grating to image the source and act as a collecting optic. The efficiency of the components are calibrated so that absolute intensities can be measured. I will compare the performance of this instrument with reflection grating systems. I will also discuss planned improvements to the system which should increase total throughput, image quality, and resolving power.
Continuously Tunable Sum-Frequency Generation Involving Rydberg States
Authors: Boyd R. W. , Gauthier D. J. , Krasinski J. , Malcuit M. S.
Published: February 2023

It has recently been shown1 that extremely large values of the second-order nonlinear suceptibility can be obtained through use of Rydberg atomic states perturbed by an external electric field.2 In these experiments a value of χ(2) = 10-9 esu was obtained using a sodium vapor of number density ~1014 atoms cm-3 and a dc electric field of magnitude 1 kV/cm. One laser was tuned close to the sodium D2 resonance line while a second laser completed the two-photon resonance with a Rydberg state. A strong coherent UV beam at the sum frequency was generated in the forward direction. The splitting of the highly excited atomic levels induced by the external electric field created a broad region of overlapping levels, leading to continuous tunability. This technique can be applied to any system displaying a Rydberg series, and should be capable of producing coherent, tunable radiation in the extreme ultraviolet.
Sum Frequency Generation Spectroscopy of Rydberg States
Authors: Schnitzer A. , Hollenberg K. , Behmenburg W.
Published: February 2023

Consider sum frequency generation (SFG) ω3 = 2 ω1 + ω2 in a phase matched metal-noble gas mixture, using two lasers ω1 and ω2, where 2 ω1 is tuned to a two photon transition Ωg2 and ω2 is shifted across Rydberg transitions Ω2n (g groundstate, 2 excited state, n Rydberg state of the metal atom). Then the intensity of the SFG spectrum I3 (ω3)~ |χ(3) (ω3)|2 displays resonances and related antiresonances, separated by (1) which are caused respectively by constructive and destructive interference of resonant and nonresonant parts of the 3. order nonlinear susceptibility χ(3) (ω3 ≃ Ωng) = χR(ω3)+ χNR (3) The products μ2nμng:= xn of the dipole transition matrix elements may then be obtained from a simple measurement of the frequency spacings Δωn at a large number of transitions Ωgn and solving iteratively the coupled equation system (1),(3); neither absolute radiation intensity nor vapour density deter mination is needed.
A Soft X-Ray Source Based on a Low Divergence, High Repetition Rate Ultraviolet Laser
Authors: Crawford E.A. , Hoffman A.L. , Milroy R.D. , Albrecht G.F.
Published: February 2023

The soft x-ray emission of dense plasmas produced by irradiation of solid targets with high intensity lasers has been studied extensively in recent years. Experiments motivated by requirements of the Inertial Confinement Fusion (ICF) program have dominated these studies, but in addition, other experiments have been directed toward the efficient production of soft x-rays for microlithographic and other industrial applications. These experiments have primarily been done using relatively large (E>1 J) lasers operated at low repetition rates.
Measurements of Photoionization Cross Sections of Ions in the Extreme Ultraviolet
Authors: Jannitti E. , Nicolosi P. , Tondello G. , Yongchang Wang
Published: February 2023

Absorption spectra of He-like and Li-like ions of light elements (Be, B, C) have been recorded using two laser produced plasmas [1]; one acts as a background continuum emitting source and the other as the target for the absorption experiment.
Amplification of Spontaneous Emission in Aluminium and Magnesium Plasmas
Authors: Jaegle P. , Jamelot G. , Carillon A. , Klisnick A. , Sureau A. , Guennou H.
Published: February 2023

Experiments performed in recombinating aluminium plasmas have shown, for various conditions of plasma production, that population inversions occur between the levels 3, 4, 5 of lithium-like ions (1-4). In references 1 and 4, inversions between 3d and 4d or 5d levels have been deduced from the analysis of line intensity ratios corresponding to 2p-nd transitions. In references 2 and 3, the evidence of an inversion between the 3d and 5f levels resulted directly from the behaviour of the 3d-5f line for relevant changes in plasma geometry in the line of sight. Numerical modelling, in which rate equations are solved for 22 levels, has suggested that the explanation of these inversions refers to the recombination scheme (5).
Tunable, Coherent Sources for High-Resolution VUV and XUV Spectroscopy
Authors: Stoicheff B. P.
Published: February 2023

About 20 years ago, great strides were made in high-resolution spectroscopy in the VUV with the building of large grating spectrographs which provided resolving powers of ~3 × 105. To-day, with the use of tunable laser sources, resolving powers of ~107 have been reached in limited wavelength ranges, with ~105 available over most of the VUV and XUV regions to as short as ~50 nm.
Optical-Optical Double Resonance Multiphoton Ionization Spectroscopy of NO.
Authors: Seaver M. , Cheung W. Y. , Gauyacq D. , Chupka W.A. , Colson S. D.
Published: February 2023

Resonantly enhanced multiphoton ionization of NO has been investigated using two tunable dye laser beams oppositely directed and having a common focus. The focus lies between two electrodes in a cell containing 4-15 torr of NO. The first laser beam pumps a rovibronic level of either the A or C state by a two or three photon process. The second laser is scanned over a spectral region leading finally to ionization by one or two photons sometimes assisted by field or collisional ionization. We have obtained high resolution data on high Rydberg and non-Rydberg states below and above the ionization limit with special attention to the Rydberg-non-Rydberg perturbations and dynamic processes such as autoionization, predissociation, collisional and field ionization and rotational relaxation. The spectral simplification resulting from the rotational selectivity of the double resonance technique has yielded easily analyzed spectra in cases for which the ordinary one-photon spectrum is hopelessly congested or overlayed by strong, broadened lines. One of many examples is the strongly perturbed v=8 level of the L valence state. Decay processes can yield either peaks or dips often with measurable widths. Thus the N=1, v=1 level of the 5pσ state, which is obscured in the one-photon spectrum is found to have a predissociation width of about 6cm-1. In contrast, the v=3 levels of the 4f, 4d, 6s and 7s Rydberg states, all of which lie above the ionization limit for v=0 or v=1 and hence are subject to vibrational autoionization, are found to have widths < .5cm-1 in agreement with our calculations. We have studied linear and quadratic, static and dynamic Stark effects as well as pressure shifts and broadening of Rydberg states with values of n up to ~35. Pulse delay studies have shown adiabatic following of dressed states under conditions of strong power broadening and A.C. Stark shifts. Resonant structures which appear as either peaks or dips as a function of laser power are explained in terms of Fano theory.
Stimulated Vacuumultraviolet Emission From Rare Gas Crystals
Authors: Schwentner N. , Dössel O. , Nahme H.
Published: February 2023

The advantages of solid state rare gas lasers compared to the gas phase lasers can be a high excimer density at reduced losses from excimer quenching and an efficient energy deposition. Free standing optically clear and 2 cm long rare gas crystals have been excited by an intense electron pulse (400 keV, 3kA, 3 x 10−9s, 3 J). Densities of excited centers of 1017 to 1018 cm−3 have been created in the crystals without reduction of the optical quality. The crystals emit the well known excimer bands at 128 nm (Ar), 145 nm (Kr) and 160 - 180 nm (Xe). Each band consits of two components, the dipole allowed transition

1

∑
u

+
→
1

∑
g

+

which is responsible for amplified stimulated emission and a long living transition

3

∑
u

+
→
1

∑
g

+

.
Multiresonant Two-Photon-Absorption-Induced Four Wave Mixing in Crystalline Rare Earth Insulators
Authors: Cone R. L. , Ender D. A. , Otteson M. S. , Fisher Paula L. , Friedman J. M. , Friedman J. M. , Guggenheim H. J.
Published: February 2023

We report the first observation of intermediate state enhancement of four wave mixing induced by two photon absorption in rare earth insulators. Coherent generation of ω4=ω1+ω2−ω3 exhibits strong intermediate state resonances when ω1 sweeps through a single photon transition to the 5D4 states arising from the 4f8 ground configuration of Tb3+ while (ω1+ω2) is simultaneously resonant with an allowed transition to the excited 4f75d configuration. Measurements are presented for Tb(OH)3 and LiTbF4.
Two-photon Excitation of Argon
Authors: Pindzola Michael S.
Published: February 2023

Multiphoton excitation is describable in terms of rate equations1,2 when the generalized n-photon Rabi frequency and the excited-state photo-ionization rate are much less than the laser bandwidth. This is generally the case when powerful excimer lasers are used to excite atomic levels in rare gases. The two photon excitation rate may be written as where ω1 and ω2 are the frequencies of lasers 1 and 2 respectively, I1 and I2 are the laser intensities, G(ω1, ω2) is the bandwidth-dependent line-shape function and α is the two-photon excitation parameter defined by Eq. (1).
2π Electron Spectrometer for Multi-Photon Ionization Studies
Authors: Kruit P. , Read F.H. , Van der Wiel M.J.
Published: February 2023

In highly focussed nanosecond laser pulses the yield of electrons must be kept below about one hundred per lasershot, otherwise the space charge of the ions in the laser-focus will seriously influence the electron energy spectrum. Especially for the study of electrons produced in multiphoton ionization a spectrometer has been designed which accepts an opening angle of 2π sr. The laser beam is focussed in a region where a magnetic field of 1 T is present. The strong field diverges along the axis of a 50 cm. time-of-flight tube to a weak field of 10−3 T, in which an electron detector is positioned. Photoelectrons with any velocity in the direction of the detector spiral around the magnetic field lines and reach the detector. In the region of the field divergence the spread in forward velocities is reduced to 5×10−4 by an inversed magnetic-mirror principle. The total velocity is unaffected. Experiments show the resolution to be 20 meV for electrons up to 10 eV energy. By applying a retarding potential in the high magnetic field region it is possible to select an opening angle different from 2π sr, thus permitting measurements of angular distributions as well.
High Average Brightness Rare-Gas Halide Laser Technology
Authors: Moody Stephen E. , Mullaney George J. , Grossman William , Cassaday Philip E. , Byron Stanley
Published: February 2023

Discharge pumped rare-gas halide lasers are attractive pump sources for non-linear UV generation techniques such as multiwave mixing and Raman conversion because of their high peak power. To extend the performance of these lasers to much higher average powers, we have used high velocity closed loop gas flow systems that allow both 100 and 1000 Hz operation at average powers ranging from 1 to greater than 100 Watts at 308 nm. At the highest powers, active heat exchangers and sidewall acoustic wave dampers using lossy materials are required, careful design of flow bends and the laser head interface is also required to prevent flow separation.
Analysis of vuv and Soft x-ray Lasing Based on Charge-Exchange Mechanisms
Authors: Bellum J. C. , Chow W. W. , Drühl K. , Scully M. O.
Published: February 2023

We report theoretical investigations of long-wavelength laser mechanisms based on efficient formation of electronically excited atoms or ions by charge exchange. In one promising practical arrangement a plasma containing the ions clashes with a vapor containing the neutral-atom collision partners. If charge transfer wins over competing photo-chemical processes, then inversion of population in an electronically excited state appropriate for lasing results. We present a systematic procedure for determining whether and under what conditions lasing occurs for given collision partners. Via rate equations describing ionic and neutral populations we assess in a first approximation the roles of charge transfer, spontaneous emission from the excited specie, and plasma and vapor pulse shapes in achieving population inversion. We next investigate basic laser action by extending the rate equations to include stimulated emission and photoionization of the excited specie by laser radiation. Our refined analysis is based on detailed studies of the other photo-chemical processes to determine their relative effects on laser action. Where necessary, we perform cross-section calculations for various processes to assess their importance.
Resonantly Enhanced Multiphoton Ionization and Third-Harmonic Generation in Carbon Monoxide Gas*
Authors: Glownia James H. , Sander Robert K.
Published: February 2023

Multiphoton ionization (MPI) and third-harmonic generation (THG) in gaseous carbon monoxide (CO) have been studied using photons generated from a Nd:YAG-pumped tunable dye laser (Quanta-Ray). The MPI and THG were studied in a static-gas ionization cell with a vacuum ultraviolet (VUV) radiation detector as shown in Fig. 1. In both experiments the dye laser output was focused to give a power density on the order of 109 W/cm2.
A Laser Produced Plasma as an Extreme Ultraviolet Continuum Source for absorption Experiments
Authors: Jannitti E. , Nicolosi P. , Tondello G.
Published: February 2023

For experiment of absorption of highly ionized species, produced in a pulsed regime, a background source emitting continuum in the XUV region with high brightness is needed. The spectral output of plasmas produced by focusing a ruby laser pulse of 10 J of energy and 15 ns duration on plane targets of various light materials has been studied.
Multiphoton Ionization of Atoms and Molecules
Authors: Compton R. N. , Miller John C.
Published: February 2023

Recent studies of resonantly enhanced multiphoton ionization (MPI) and third-harmonic generation (THG) in the rare gases Xe, Kr, and Ar, will be discussed. In particular, the disappearance with increasing pressure of the MPI signals resonant with the three-photon allowed 6s, 5s, and 4s states, respectively, of the rare gases is correlated with the appearance of THG. At certain laser wavelengths the THG signal is partially quenched by self absorption.
First Observation of Photoionization of Laser-Excited Atoms by Synchrotron Radiation (SR)*.
Authors: Bizau J.M. , Wuilleumier F. , Dhez P. , Ederer D. , Legouet J.L. , Picque J.L. , Koch P. , Ederer David L.
Published: February 2023

In a triple, orthogonal crossed beam experiment, we have studied photoionization of excited Na atoms. A cw ring dye laser (few W/cm2) locked to the D1 or D2 absorption lines produced a steady-state fraction up to 20% of excited Na(3p2P1/2 or 3p2P3/2) atoms in a weakly collimated Na(3s2S1/2) beam with density ≲ 1013 cm−3. Monochromatized SR from the ACO storage ring provided the photoionizing radiation. A cylindrical mirror electron spectrometer was used to measure photoelectron spectra. First measurements of photoionization from the 2p subshell with the 3p orbital occupied were obtained. Transitions to autoionizing resonances hνSR+Na(2p63p2PJ)→Na(2p53s3p)1 were driven near hνSR≃31 eV from either J=1/2 or J=3/2 levels. A comparison of the results for the 2p63p →2p53pεd and 2p63s→2p53sεℓ' ionization channels will be given.
Multistep Excitation of Alkaline Earth Atoms to Autoionizing States
Authors: Gallagher T. F.
Published: February 2023

Using a multistep laser excitation of alkaline earth atoms in an atomic beam we are able to excite autoionizing states in which one of the electrons can be in a state of almost arbitrary n and 1. The multistep approach uses all single photon transitions in which one electron is excited at a time, as shown in Fig. 1. In addition to the technical simplification of requiring low energy photons, exciting one electron at a time simplifies the observed spectra and their interpretation.
Generation of Coherent Radiation Below 100nm in Hg Vapor
Authors: Freeman R. R. , Bokor J.
Published: February 2023

We have studied two-photon resonant third harmonic generation of coherent radiation below 100nm in Hg. Output near 93 nm was produced with input radiation from a frequency doubled dye laser tuned near the 6s2-6s6d two-photon resonance in Hg at 280.3nm, and output near 83nm was produced with radiation from a tunable KrF excimer laser tuned near the 6s2 -6s10s two-photon resonance in Hg at 248.8nm.
Spectroscopy of CO and NO Using Coherently Generated VUV
Authors: Vidal C.R.
Published: February 2023

Summary not available
Generation of Narrowband Tunable VUV Radiation
Authors: Hilbig R. , Wallenstein R.
Published: February 2023

Nonresonant sum- and difference-frequency mixing of the fundamental (ωL) and the second harmonic (ωuv) output of a powerful narrowband pulsed dye laser excited by a Nd-YAG laser has been investigated in Xe and Kr. The sum-frequency ωvuv = 2ωuv + ωL is tunable in spectral regions of negative dispersion between 110 nm, and 130 nm. The maximum VUV pulse power exeeds 20 W (5 1010 photons/pulse). The difference frequency ωvuv = 2ωuv − ωL provides VUV light pulses with up to 60 W (2.3 1011 photons/pulse) at wavelengths between 185 nm and 207 nm. Coherent VUV light of shorter wavelength (159.5 nm to 186.6 nm) is obtained by mixing the UV dye laser radiation with the infrared output (ωIR) of the Nd-YAG laser (ωvuv= 2ωuv − ωIR). With UV light of shorter wavelength

(

ω

uv

′

=

ω

uv

+

ω

IR

)

the difference frequency conversions

ω

vuv

=
2

ω

uv

′

−

ω
L

and

ω

vuv

=
2

ω

uv

′

−

ω

IR

allow the generation of VUV light with wavelengths between 122.6 nm and 160 nm. Thus with a single dye laser which is operated in the most efficient operating range of Nd-YAG laser pumped dye lasers (ωL = 550 − 670 nm) the investigated conversion schemes generate intense coherent VUV light which is continuously tunable between 110 nm and 210 nm.
General Characteristics and Requirements of XUV Storage Ring FEL's
Authors: Madey John M. J.
Published: February 2023

Adequate gain appears available to operate storage ring FEL oscillators at wavelengths at least as short as 100 Å. Operation at these wavelengths will require a flat, low emittance electron beam and a long interaction region.
Electron Storage Ring Design
Authors: Krinsky Samuel
Published: February 2023

We review the Chasman-Green approach to the design of low-emittance storage rings having dispersion-free straight sections for the placement of undulators. The matching of undulator magnets to the storage ring lattice is considered, as are limitations on the achievable peak current and transverse emittance. A brief discussion of the operation of a free electron laser in a storage ring is presented and some comments are made on the optimization of the storage ring design.
New Technologies: Permanent Magnet Undulators
Authors: Halbach K.
Published: February 2023

Following a discussion of the circumstances under which permanent magnets have a performance that is superior to magnets that are excited by coils (room temperature or superconducting), the properties of two specific types of linear permanent magnet undulators are described. The discussion of the performance limitations of these undulators is complemented by a description of design details to the extent necessary to appreciate the importance of some seemingly unimportant features. Effects of tolerances are clearly important and will be even more important for the very long undulators that one might build in the future. It is shown what has been done in the past, and what one may want to do in the future, to reduce the detrimental effects of tolerances. In addition to these discussions of linear undulators, a conceptual design of a helical permanent magnet undulator (with adjustable length, if desired) is shown, and the performance limitation of this device is discussed.
Multilayer Mirrors and Optics for Low Energy X-Ray and Extreme Ultraviolet Regimes
Authors: Barbee Troy W.
Published: February 2023

During the past decade techniques for the synthesis of multilayer structures of quality sufficient for application as x-ray and extreme ultraviolet dispersion elements and optic devices have been developed. Physical vapor deposition techniques have been applied to the sequential deposition of layers of two materials having optical constants appropriate for the spectral range of interest. These layers are of extremely high uniformity and vary in thickness from less than 1 nanometer to 100 nanometers. This work follows the early efforts of Dumand and Youtz and the work of Dinkledge and Frericks. More recently Spiller and his coworkers have been working on the development of normal incidence multilayer mirrors specifically for the low energy x-ray domains.
Coherent Soft X-Rays in High Resolution Imaging
Authors: Howells Malcolm , Kirz Janos
Published: February 2023

To illustrate the coherence problems in X-ray imaging we shall examine

- scanning X-ray microscopy

- holography, and

- soft X-ray diffraction

as illustrative examples. We show that only X-rays from within the emittance xx'yy' < (2.44λ)2 have the necessary spatial coherence to yield diffraction- limited images. The degree of temporal coherence required depends on the nature of the imaging system, and the size of the specimen. In conventional X-ray systems, spatial coherence is generated by collimation, while temporal coherence is achieved with monochromators. In these systems, then, one filters out a minute coherent fraction of an intense incoherent beam. Aside from the inefficiency of the procedure, there is a practical limitation of the temporal coherence length of about 103λ that one can generate this way in the soft X-ray regime.
Laser harmonics from 2000 Å to 100 Å
Authors: Kincaid B. M. , Freeman R. R.
Published: February 2023

It is possible to bunch a relativistic electron beam in a storage ring using a powerful laser in conjunction with a periodic undulator magnet. Such a spatially bunched beam passing through a periodic undulator magnet radiates much more strongly than a normal unbunched beam. This optical klystron effect also generates significant harmonic output, much as in a conventional microwave klystron, only in this case, the output wavelengths are in the extreme ultraviolet (XUV). It is useful to think of the relativistic electron beam in the storage ring as a kind of non-linear medium for generating harmonics. Conversion efficiencies from laser power to harmonic output in the range 2000 Å to 100 Å vary from 10−3 down to 10−8 for a practical experiment using the National Synchrotron Light Source (NSLS) 700 MeV storage ring at Brcokhaven. This exceeds by several orders of magnitude any other technique for generating tunable coherent light in the XUV region, and will make possible a practical coherent light source for high resolution spectroscopy, microscopy, lithography, and holography. The physics of the bunching and harmonic generation process will be discussed, as well as some details of a computer simulation of the proposed NSLS Brookhaven experiment. In addition, a proposal for a tunable XUV light source based on this technique will be presented.
Are There Quantum Mechanical Effects on Free Electron Laser Operation in the X-ray Regime?
Authors: Gover A.
Published: February 2023

The question of whether quantum mechanical effects may have a significant roll in the free electron laser (FEL) gain mechanism and the oscillation build-up process is considered in detail. In particular, we consider two important aspects: The effect of electron quantum recoil on the FEL gain formula and the effect of quantum field fluctuations on the FEL operation1.
Generation of Intense Coherent Soft X-rays by Laser Induced and Subsequently Frozen Electron Microbunching
Authors: Yu L. H.
Published: February 2023

The Transverse Optical Klystron (TOK) has been described by many authors1. An important recent development is the proposal to use the TOK to generate radiation from the vacuum ultra-violet to the soft X-rays2,3. In this paper, a new and improved method to generate intense coherent radiation of short wavelength is described.
Precise Emission Spectroscopy with the FTS
Authors: Learner Richard C.
Published: February 2023

Summary not available.
High Resolution, Calibrated IR Emission Spectra from 80°N
Authors: Olson J.R. , Van Allen J. , Fogal P.F. , Murcray F.J.
Published: February 2023

The need to study Arctic ozone depletion phenomena similar to that experienced over the Antarctic, has led to the installation of a 0.1 cm-1 resolution, absolutely calibrated, emission interferometer known as the Extended Atmospheric Emission Radiometric Interferometer (AERI-X). Earlier instruments of this type had a resolution of 1 cm-1, and while these instruments performed quite well, it was felt that higher resolution would benefit both stratospheric chemistry and radiative transfer measurements.
Submillimeter Fourier Transform Spectroscopy of Astronomical Sources
Authors: Serabyn E. , Weisstein E.
Published: February 2023

From the 4000 m altitude of Mauna Kea, submillimeter wavelength astronomical observations are often possible at frequencies up to nearly 1 THz. To measure broadband astronomical and atmospheric spectra in the available atmospheric transmission windows between 150 GHz and 1 THz, we have built a moderate resolution (λ/Δλ < 5000) Fourier Transform Spectrometer for use at the Caltech Submillimeter Observatory (CSO). The instrument is a dielectric-beamsplitter rapid-scan FTS which uses the CSO’s facility bolometer as its single detecting element. Five bandpass filters are used to match to the available atmospheric transmission windows, in order to limit the background flux on the detector. The maximum path difference is 45 cm, yielding a spectral resolution of 200 MHz. The instrumental field of view is defined by a Winston cone light concentrator. Observations with this instrument have now begun to yield high quality astronomical spectra, several of which are described in the following.
Fourier Transform Spectra of the N 2 + C 2 Σ u + − X 2 Σ + g System
Authors: Stark G. , Learner R. C. M. , Thorne A. P.
Published: February 2023

The

N
2
+

C-X electronic system, extending in emission from about 137 - 207 nm, has a number of unusual features which have been the focus of spectroscopic studies for many years. When produced in an electric discharge, the intensities of individual vibrational bands are extremely sensitive to excitation conditions. In discharges through helium with a trace amount of nitrogen, bands with v' ≥ 3 are readily excited whereas bands with v' < 3 are absent. Discharges through pure nitrogen, or trace amounts of nitrogen in neon or argon produce emission only in bands with v' < 3. In addition, there are irregularities in the vibrational structure of the

C
2

Σ
+

u

state as well as weak rotational perturbations. Predissociation in vibrational levels with v' ≥ 3 is thought to be centrally involved in the character of the emission spectrum, although the mechanism has never been fully explained.
The Remote Molecular Monitor - Real-Time FTS Using Neural-Net Processing
Authors: Walter William T.
Published: February 2023

AIL Systems Inc. and MIDAC Corporation have teamed to win an ARPA-TRP award to develop an Air Quality Monitoring System Using a Neural-Network FTIR Spectrometer. Initiated by the White House, the Technology Reinvestment Project (TRP) has encouraged the applications of defense technologies to non-defense needs. Of 2,860 proposals submitted, 152 were awarded in 1993. AIL Systems has been awarded two of the five awards in the environmental monitor focus area. The Remote Molecular Monitor (RMM) has evolved from the present MIDAC FTIR instrument after undergoing both hardware and software improvements. Environmental testing has directed a hardening and ruggedizing for outdoor dual-use applications. Improved signal processing utilizing AIL’s neural network technology has been incorporated to provide more sensitive detection in real time. Improved detection sensitivity has been shown in three tests: 1. In the laboratory1 where > 50-times improvements were measured over FFT processing alone of interferograms taken at various concentrations. Sulfur hexafluoride, SF6, and dimethyl methylphosphonate (DMMP) were examined as test candidates having single and multiple absorption features, respectively. 2. At field tests at the U.S. Army Dugway Proving Ground in Utah2, where all four simulants for chemical agents utilized were detected including triethyl phosphate (TEP) at 600 ppb-m in an outdoor vapor chamber 3m x 3m x 6m. Syringes were used to drop successively-larger measured amounts of liquid TEP, 0.1 to 10 mL, at 3-minute intervals into a beaker placed on a hot plate inside the vapor chamber. The staircase curve in Figure 1 shows detection of each of the injected samples. A point monitor inside the vapor chamber indicated a TEP vapor density of 800 µg/cm3 during the smallest syringe injection, 0.1 mL, which corresponds to a path-averaged concentration of 100 ppb over the 6-m chamber length. TEP was also detected during the open-air release as well as SF6 at 15 km 3. AIL’s analysis of helicopter data supplied by the U.S. Army Edgewood Research, Development and Engineering Center (ERDEC) from an overflight of an SF6 line source found SF6 in 16 additional scans1. Identification of 22 SF6-containing scans in the 815-data record had previously been provided by ERDEC.
Time-resolved Fourier spectroscopy for energy-transfer studies in laser crystals
Authors: Weidner H. , Peale R. E.
Published: February 2023

Advances in compact solid-state lasers using diode-laser pump sources have renewed interest in rare-earth activated insulating crystals. A variety of schemes have been developed for creating new laser wavelengths throughout the near IR and visible. Many of these involve frequency conversion via energy transfer between ions of the same or different species. In such systems, changes in luminescence lines with < 1 cm-1 widths occur simultaneously over a range of thousands of wavenumbers in time scales in the range of 1 µs to 1 ms. Hence, there is a need for a single technique which captures these changes in the form of spectral "movies" having adequate time resolution, frequency resolution, and frequency range. An immediate practical return from such a technique would be in facilitating the optimization of dopant concentrations, since a variety of concentration-dependent processes compete with the desired energy-transfer phenomena. A benefit of fundamental interest is in revealing complex transfer phenomena which test existing models.
Reanalysis of 6Li I and 7Li I transitions using hollow cathode Fourier transform spectra
Authors: Engleman R. , Radziemski L. J. , Brault J. W.
Published: February 2023

The spectrum of neutral lithium remains of considerable interest to both theorists and experimentalists. There have been attempts to calculate from first principles the energy levels, hyperfine parameters and isotope shifts (see for example Ref. 1); thus, good experimental values are important for comparison. The abundance of lithium is a key indicator for the age of a star; thus, accurate information on the stronger lithium lines becomes important in certain astrophysical problems.
A Method for Phase Determination from Highly Asymmetric Interferograms Developed for the FIRS-2
Authors: Johnson David G. , Traub Wesley A. , Jucks Kenneth W. , Chance Kelly V.
Published: February 2023

The FIRS-2 is a far- to mid-infrared Fourier transform spectrometer, designed and built at the Smithsonian Astrophysical Observatory for the purpose of measuring stratospheric emission spectra. The instrument and data reduction system have been described elsewhere [Johnson et al., 1994]. We present here the method we have developed for phase recovery from highly asymmetric interferograms in the presence of an out-of-phase background signal.
Modulated Source FTS for Atmospheric Pollution Measurements
Authors: Kagann Robert H. , Walter William T.
Published: February 2023

Most active open-path FTIR measurements are made using a bistatic configuration in which an infrared source is set up in the field at one side of the parcel of atmosphere to be measured and the Michelson interferometer and detector is placed on the other side. In order to maintain efficient collection of light at the detector, the source may be placed at the optical focus of a transmitting telescope and a receiver telescope may be optically coupled to the interferometer and detector. In this configuration, the infrared radiation emitted from objects in the field of view of the detector (objects behind or around the source, the receiver optics and the interferometer beamsplitter) passes through the interferometer and contributes to the interferogram and thus to the Fourier transformed single beam spectrum. The gray-body emission curve for the terrestrial temperature range (260 °K to 315 °K) extends through the entire fingerprint window of the atmospheric infrared spectrum (700 to 1200 cm-1).
Extracting Atmospheric Profiles from Space Shuttle Spectra
Authors: Abrams Mark C.
Published: February 2023

During the third flight of the Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS) in 1994, telemetry data were transformed and processed into atmospheric profiles in near-real time. Spectroscopic, computational and database techniques are discussed in the context of streamlining high data-rate remote sensing.
IR Retrieval Algorithms Intercomparison for the NDSC
Authors: Zander R.
Published: February 2023

The validation of spectral forward calculations and retrieval algorithms is a fundamental task for ensuring correct interpretation of remote spectrometric observations. This is particularly important when analyzing high-quality measurements to determine relative differences and changes occuring within the frame of a network, and the codes adopted are to be commensurate with the precision and data flow of the measurements.
Issues affecting the photometric accuracy of a FTS
Authors: Delbouille L.D.
Published: February 2023

When photometric accuracy is of prime importance, FTS is widely recognized as ranking well above most of the other spectrometric techniques. That does not mean, however, that FTS gives always perfect, (or even near-perfect) results.
Seismology with an FTS: Application to Giant Planets and Stars
Authors: Maillard J.P.
Published: February 2023

A new method for detecting the acoustic spectrum of celestial bodies is based on a step-by-step FTS. First results are on Jupiter, Saturn and Procyon.
New results in atomic FT spectroscopy and applications to HST
Authors: Johansson Sveneric
Published: February 2023

The most fundamental branch of atomic spectroscopy is the study of atomic structure, as other basic research in atomic physics involves studies of the properties of energy levels or transitions between energy levels in atoms or ions. In spite of that, laboratory work on atomic spectra has often been initiated or motivated by its applications, in particular the needs for atomic data in astronomy. The most striking examples are the Tables of LS-multiplets and of Atomic Energy Levels compiled by Charlotte Moore partly for the purpose of analysing the solar spectrum recorded at groundbased telescopes.
Digital Array Scanned Interferometer: Instrument and Results
Authors: Smith Wm. Hayden
Published: February 2023

Digital array scanned interferometers or DASIs (also, HFTS, fixed FTS, or SMIFTS), blend characteristics of a grating spectrometer and a two-beam interferometer for acquisition of hyperspectra.