bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of Electron Temperature in Hot, Solid Density Plasmas
Authors: Milchberg H. M. , Freeman R. R.
Published: February 2023

The interaction of ultrashort energetic light pulses with solids is of great interest both as a source of picosecond timescale X-ray pulses1 and as a new and interesting regime of plasma and solid state physics.2,3
X-Ray Generation from Laser Irradiation of a Thin Film Target
Authors: Tom Harry K.
Published: February 2023

Summary not available.
High Intensity Charge Displacement Self Channeling
Authors: Solem J. C. , Luk T. S. , Boyer K. , Rhodes C. K.
Published: February 2023

Summary not available.
Recent Developments in High Resolution Spectroscopy Using the IFS 120 HR
Authors: Simon A. , Rubinovitz R.
Published: February 2023

In order to successfully produce high resolution spectra, a spectrometer must possess qualities such as precision optics, a high degree of optical stability, and sensitivity. Additionally, it is highly desirable that the instrument be versatile with respect to permitting a variety of samples to be scanned in the desired spectral regions. Otter practical considerations such as the time required to obtain the spectrum, and general ease of use should be considered in the spectrometer design. In order to meet such demanding criteria, it is clear that Fourier transform (FT) techniques would be appropriate.
Pulsed Time-Resolved Fourier Transform Infrared Emission Spectroscopy
Authors: Leone Stephen R. , Fletcher T. Rick , Woodbridge Eric L.
Published: February 2023

A variety of time-resolved Fourier transform infrared (FTIR) techniques have been described in the literature.1–11 The basic concept is to trigger a transient event such as a chemical photolysis, for example with a lamp or a laser, and to acquire absorption or emission amplitudes with the Fourier transform interferometer at specific time delays after the triggering event. One method steps the mirror to a new fixed position and takes a time-resolved trace at each position. The difficulty with this method comes in the long-term instrument stability of the mirror position in this "step and stop" mode of operation.2–4 Another method allows the mirror to sweep rapidly and continuously, and data at a number of times after a single triggering event are collected as the mirror sweeps. The point in the interferogram where the trigger occurs is varied, so that data are obtained at all mirror positions and times. These data are then used to construct interferograms at a number of different time delays after the triggering event. This method has sometimes been found to have artifacts if there is Jitter in the sweep speed of the mirror or if the amplitude of the initiating source is not constant.5
Fourier Transform Spectroscopy of Transient Molecules
Authors: Bernath P.
Published: February 2023

An overview of our recent work with the Kitt Peak Fourier transform spectrometers will be presented. All of our laboratory spectra were recorded at the McMath interferometer. However, the infrared absorption spectrum of C3 was detected in atmosphere of a carbon star with the interferometer of the 4 meter telescope.
Fourier Transform Spectroscopy of Free Radicals and Ions
Authors: Vervloet M.
Published: February 2023

DC and microwave discharges are often used to excite emission spectra that can be observed by Fourier transform spectroscopy. Here we report the use of two methods which are less often used but which are particularly well suited to FT recording of spectra of free radicals and ions.
High Resolution Spectroscopy of the CN Violet System
Authors: Engleman Rolf , Brazier C. , Frum C. , Lee A. , Oliphant N. , Bernath P. F. , Brault James W.
Published: February 2023

A number of high resolution spectra of different CN violet sources have been obtained with the Kitt Peak Fourier transform spectrometer. These sources fall into four classes.
The Need for FTS Accuracy in the Analysis of Complex Laboratory and Stellar Spectra
Authors: Johansson Sveneric , Litzén Ulf , Leckrone David S. , Wahlgren Glenn M.
Published: February 2023

Modern telescopes make it possible to obtain spectra in high resolution (Δ/Δλ ≈ 100000) and high signal-to-noise ratio from 120 nm to 5 μm for hundreds of thousands of stars in our own Galaxy. The high accuracy obtainable in these observations puts very strong qualitative and quantitative requirements on the atomic and molecular data to be used in the analysis. Different types of atomic data are needed, and in this paper we will focus on wavelengths, line identifications and oscillator strengths. We will demonstrate the need for FTS accuracy in wavelengths for direct application to stellar spectra as concerns calibration and line identification. The FTS accuracy is also needed in the analysis of a complex and line-rich spectrum in order to establish the term system, which subsequently also leads to line identifications. We will also discuss the use of FTS-intensities for obtaining experimental branching ratios to compare with observed line absorption in stellar spectra.
Characteristics of a High Resolution Fourier Transform Spectrometer to Measure Atmospheric Gas Species in Emission from Space: the MIPAS Mission
Authors: Lamarre Daniel , Giroux Jean , Buijs Henry
Published: February 2023

In this paper we present the characteristics of the MIPAS instrument, its measurement objectives and several unique features related to high resolution emission measurements.
FTS Instrument Characteristics for the Network for Detection of Stratospheric Change
Authors: Murcray F. J.
Published: February 2023

The instrument complement for the network sites will include very high resolution solar FTS systems. Characteristics of the FTS instruments are discussed.
VUV Fourier transform spectroscopy (with imaging)
Authors: Thorne Anne
Published: February 2023

The concepts of VUV FTS and imaging FTS have become somewhat linked by studies of the feasibility of a satellite-borne imaging FTS combining spectral and spatial resolution, primarily for solar physics. In the recent ESA study (SIMURIS) the main target of such an instrument is the chromospheric emission spectrum from the end of the continuum, about 180 nm, to Lyman alpha at 121 nm. Instrumentally, however, the two concepts are almost independent. I shall treat them as such in this paper, but I will conclude it with a brief discussion of the merits of an imaging FTS relative to those of a grating spectrometer equipped with a similar array detector.
Argon I Standards for Emission Spectrometry
Authors: Brault James W.
Published: February 2023

For over a decade, users of the FTS at the McMath Solar Telescope of the National Solar Observatory have had access to a simple but precise working wavenumber standard for absorption spectra in the form of a short sealed cell containing 10 or 20 Torr of N2O. Because of the high pressure, the observed wavenumbers are not those of the unperturbed molecule, but a direct calibration of the 0002 band at 4417 cm−1in this cell against the accurately known P(7) transition in CH4 yielded wavenumbers with a precision of the order of 0.000002 cm−1 and an accuracy thought to be at least 0.00001 cm−1 (Brault [1]). Some years later, this band was observed by Pollock, et al. [2] using laser heterodyne techniques, and when our cell values are corrected using the pressure shift which they observed, the absolute agreement is quite satisfactory: (NSO - Pollock, calculated) = 0.000035 ± .0000035 cm−1; note that the absolute uncertainty in Pollock, et al. is quoted as .000080 cm−1.
Contributions of Fourier Transform Spectroscopy to Molecular Databases
Authors: Smith Mary Ann H.
Published: February 2023

The two molecular spectroscopic databases most widely used in terrestrial atmospheric studies, HITRAN (1) and GEISA (2), have recently released updates which contain extensive revisions of the parameters for many key species. Many of the measurements which contributed to these updates were performed using high-resolution Fourier transform spectrometers. In this paper the updates and revisions to the databases will be summarized, and examples of spectroscopic measurements incorporated in the database updates will be presented. Recent efforts to critically evaluate the spectroscopic databases to meet atmospheric remote sensing requirements will also be reviewed.
Fourier Transform Spectra of the A2Σ+ (v=0) -X2∏ (v=o) Band of OH
Authors: Stark G. , Brault J. W. , Abrams M. C.
Published: February 2023

The hydroxyl radical plays an important role in a variety of atmospheric, astrophysical, and chemical processes. Both absorption in, and fluorescence from, the strong (0-0) band of the A2Σ+ - X2∏ system are widely used in concentration measurements of OH (e.g., Stimpfle et al. 1990; Desgroux and Cottereau 1991).
Revised energy levels for neutral chromium
Authors: Murray J. E.
Published: February 2023

For many years the most extensive analyses of neutral chromium have been those of C.C.Kiess1,2. They represent results accumulated over a period of more than 30 years, dating back to the 1920’s. The energy levels in the compilation of Sugar and Corliss3 are mainly from this early work.
Experimental Isotope Shifts in NI II and FE II
Authors: Rosberg Maria , Litzén Ulf , Johansson Sveneric
Published: February 2023

This work reports about measurements of isotope structure in Ni II and Fe II. We have used spectra from hollow-cathode lamps that have been recorded with the Fourier Transform Spectrometer at Kitt Peak National Observatory. Measurements of isotope shifts yield useful information about atomic and nuclear properties. With high-resolution spectroscopy at modern telescopes it is also possible to observe isotope shifts in stellar spectra (Leckrone et al. 1991). The importance of a general knowledge about isotope structure for studies of the solar spectrum has recently been pointed out (Kurucz 1992). This is especially true for elements having line-rich spectra and a high solar abundance. Ignoring isotope structure when constructing synthetic spectra may introduce systematic errors in the calculation of line profiles and may therefore affect e.g. abundance determinations.
The infra-red spectra of dysprosium, erbium and gadolinium in the 1.1 to 5.4 micron region*
Authors: Conway John G. , Worden Earl F.
Published: February 2023

The emission spectra of Dy, Er, and Gd are reported for the infra-red region 1.1 to 5.4 microns, 8940 to 1835 cm-1. Two sources, a water cooled hollow cathode and an electrodeless discharge lamp, were employed. The spectra were recorded using the National Solar Observatory McMath lm Fourier transform spectrometer (FTS) at Kitt Peak, AZ over the spectral region of 40 000 to 1817 cm-1. Improved frequencies are possible by calibration using argon lines and the frequencies of argon reported by Norlen1. The energy levels published2 in NSRDS-NBS 60 were used to calculate all possible transition energies. These energy values were then matched with the observed frequencies. The neutral (I) and singly ionized atom (II) frequencies were calculated and matched.
Electron Acceleration by Nonlinear Plasma Waves Resonantly Driven with Optimized High Intensity Laser Pulse Trains
Authors: Umstadter D. , Esarey E. , Kim J.
Published: February 2023

The generation of large-amplitude, relativistic plasma waves is a subject of much current interest because of its potential use for ultrahigh gradient electron acceleration [2-5]. While conventional rf-driven accelerators are limited to fields ≤ 1 MV/cm, plasma accelerators have been shown experimentally to support gradients ~ 10 MV/cm [5]. The maximum axial electric field of a relativistic plasma wave, as predicted by 1D cold fluid theory, is the “wave-breaking” field [6],

E

W
B

=

(

m
e

c

ω
p

/
e

)

2

(

γ
p

−
1

)

, which can exceed 1 GV/cm, where ω
p
=(4πe2n
e
0/m
e
)1/2is the electron plasma frequency, n
e
0is the ambient electron density,

γ
p

=

(

1
−

v
p
2

/

c
2

)

−
1
/
2

, and v
p
is the phase velocity.
Stark Modulation of the Transition Frequency of a Degenerate Two-Level Atom and High-Order Harmonics Generation
Authors: Burlon R. , Ferrante G. , Leone C. , Oleinikov P.A. , Platonenko V.T.
Published: February 2023

In recent years several experiments have been performed on the generation of high-order radiation harmonics in gaseous jets, and it, in its turn, has prompted a lot of theoretical efforts aimed at elucidating the basic physics underlying the process.
Stimulated Scattering Caused by Multiphoton Absorption and Control of the Physical Mechanism of Stimulated Scattering
Authors: Karpov Vladimir B.
Published: February 2023

Stimulated scattering (SS) is a well-known way to obtain the radiation phase conjugated to an incident wave [1]. Moreover, the effectivity of such a transformation can approach 90% [2].
Inducing of Gamma-ray Emission without Overconcentration of Excited Oscillators by High Optical Field
Authors: Rivlin L.A.
Published: February 2023

Two separate self-consistent scenarios inherent in achieving induced emission of gamma-rays will be discussed. (A) The stimulation of annihilation of parapositronium atoms in colliding particle and photon beams by external infra-red radiation. It is known, that soft-photon stimulation of two-photon annihilation requires and inadmissible high particle energy (approx. 50 GeV). The new scenario consists of two positronium beams and two infrared photon beams moving in opposite directions and includes three steps : 1) exciting ls-2p transitions of moving relativistic positronium atoms (approx. 80 MeV) by an infrared beam (approx. 80 micrometer) propagating in the opposite direction ; 2) lasing in the beam of these excited atoms, the inversion being achieved as a result of lower-state cleansing due to spontaneous annihilation; and 3) stimulating the annihilation in the opposite positronium beam by Doppler shifted photons from the moving atomic laser realized in the previous step.
Gain and phase control of 10-50 TW femtosecond pulses using shifted narrow amplifying media : theory and experiments
Authors: Blanchot N. , Rouyer C. , Sauteret C. , Migus A.
Published: February 2023

Ultrashort pulse generation and amplification require large gain bandwidth materials. During the last decade a series of such crystalline solid state media have been developed, the most notable ones being titanium-doped sapphire and chromium-doped LISAF. These media have large energy storage capability which, when associated with the chirped pulse amplification (CPA) technique [1], making them appropriate for the generation of femtosecond terawatt pulses. Nonetheless, up to now such crystals could not be grown in very large size while keeping minimal optical quality. On the other hand amorphous materials such as neodymium-doped glasses have large energy delivery capability but a gain bandwidth limited to typically 20nm.
X-ray Emission at High-Power Super-Short Laser Pulse Interaction with Dence Plasmas
Authors: Andreev A. , Kurnin I.
Published: February 2023

Now many laboratories pay a great attention to investigation of ultrashort laser pulse-matter interaction. We consider this interaction with condenced targets in vacuum. In this paper the results of absorption and conversion efficiency into X-ray are presented for a broad range of experimental parameters. The situation is studied when the contrast of laser pulse is sufficiently high. We have developed a simulation code for investigation of this interaction by the solution of Vlasov-Fokker-Planck equation for electron distribution function. Our study of heating process of dense plasma predicts high heating rate of electrons due to heat conductivity inhibition in the regime of anomal skin effect. The most common regim of the normal skin effect with continuous density profile at the plasma-vacuum boundary has been studied via numerical simulations, using our code. We have presented the numerical results and the approximate analytical solutions of the P-polarized radiation absorption problem with the parameters of extinguishing and density lying in sufficiently broad ranges. Our results predict absorption efficiency values, which are in agreement with our and another numerical data and experimental results too. We include full radiation terms (bremsstrahlung, recombination and line mechanisms) in the description of the decay phase high dense plasma targets. The hydrodynamic simulations with radiation transport are conducted to study the X-ray emmission and plasma cooling after the end of the laser pulse. The conversion efficiency into X-rays is shown to fall with laser intensity for light target materials in conditions, when invers bremsstrahlung absorption is dominant. On the other hand, when anomalous absorption prevails and havy target material is used, the conversion efficiency increases with laser intensity.
Observation of an optimum condition for the generation of Li-like solid density plasmas with subpicosecond laser
Authors: Jiang Z. , Kieffer J.C. , Côté C.Y. , Chaker M. , Korn G. , Coe S. , Mourou G. , Peyrusse O.
Published: February 2023

We report on experiments carried out at high intensities with a table top terawatt laser system which employs the chirped pulse amplification technique [1]. High efficiency frequency doubling (85% conversion from 1 pm to 0.53 pm wavelength) is used to generate high contrast pulses. The green beam (1 J in 300 fs pulse with no prepulse) is focused to intensities up to 5 × 1018 W/cm2. At these intensities relativistic effects and ponderomotive pressure [2] are important issues for the interaction. The interaction of a very clean pulse with solid matter allows the production of hot solid density plasmas which offers a unique way to address experimentally, in the laboratory, some problems of great astrophysical interest [3] and of importance for atomic physics. In order to get fully ionized solid density emitting matter, a careful optimisation of the interaction regime is required [4]. On one hand laser intensity must be high enough to overcome, with radiation pressure, the thermal and hydrodynamic mechanisms tending to spread the plasma at low intensity. On the other hand the intensity must be kept below some limit above which we enter the regime of cratering and hole boring problems associated with ultra-high radiation pressures [5], We present and discuss such an optimisation study for the generation of Li-like solid density plasmas. The plasma density and temperature are deduced from line broadening [6] and line ratio calculations (using TRANSPEC code). We observe an optimum at a laser intensity of 1018 W/cm2 for the generation of Al plasmas radiating Li-like emission at solid density. We will discuss the physics of the various interaction regimes for laser intensities between 1017 W/cm2 and 1019 W/cm2 and for various Z material. The implications of these results for the design of an ultra-fast X-ray sources [7] will be outlined.
The ellipticity dependence of atomic strong-field processes
Authors: Dietrich P. , Burnett N. H. , Ivanov M. , Corkum P. B.
Published: February 2023

The interaction of atoms with intense laser radiation (I = 1013 - 1016 Wcm−2) is of considerable interest from both a scientific and a technological perspective. There are a number of new phenomena in this intensity range, such as nonresonant multiphoton ionization (MPI), above-threshold ionization (ATI) and high-harmonic generation. They can be used for new sources of coherent XUV radiation or to produce pulses shorter than the current limit of a few femtoseconds. These processes cannot be described with perturbation theory due to the strong coupling of the atom with the field. Therefore nonperturbative models are needed to gain a better understanding of high-intensity laser-atom interactions and to optimize these processes.
Laser solid interaction at high ponderomotive pressure
Authors: Nickles P. V. , Schlegel Th. , Schnuerer M. , Kalashnikov M. , Will I. , Sandner W. , Demchenko N. N.
Published: February 2023

The interaction of 1.5 ps glass laser pulses with dense plasmas is studied at intensities up to 1018 W/cm2. Measurements of laser light absorption in the plasma, plasma dynamics and of the production of Bremsstrahlung X-rays have been made.
Coherence Properties of High Order Harmonic Radiation
Authors: Ditmire T. , Budil K. S. , Crane J. K. , Nguyen H. , Perry M. D. , Salieres P. , Huillier A. L'
Published: February 2023

The results of a series of experiments to characterize the coherence properties of xuv radiation produced by high-order harmonic generation in helium, neon and argon are reported and compared to predictions from an effective order model. The harmonics exhibit smooth, near gaussian spatial profiles, and have a divergence that is approximately constant (< 12 mrad) in the plateau region and decreases (≈ 4 mrad) in the cutoff for f/17 focusing. For a bandwidth limited, 140 fsec incident pulse, we measure a harmonic line width of Δλ/λ ≈ 2 x 10−3 at 30.3 nm. By reducing the spectral width of the driving pulse, harmonics with Δλ/λ ≈ 2 x 10−4 can be produced. Absolute conversion efficiency as high as 10−2 for harmonic radiation as short as 20 nm has been achieved by using 400 fsec, 526 nm pulses from an Nd:Glass laser.
Time profile of harmonics generated by a single atom in a strong electromagnetic field
Authors: Antoine Philippe , Piraux Bernard , Maquet Alfred
Published: February 2023

It is well established, both experimentally and theoretically, that atoms exposed to a strong laser pulse emit high order harmonics of the driving field. Although this process has been intensively studied theoretically, the main effort has been focused so far on the study of the harmonic spectrum while no attempt has been made to analyse systematically its time evolution. We show that the time profile of each harmonic may be obtained through a time-frequency analysis of the acceleration of the atomic dipole. We show also that such an analysis, which is very sensitive to the details of the dynamics, provides valuable information about the competition between photon emission and ionization processes.
The Driving Mechanisms of Self-Focusing and Self-Modulation of Short Laser Pulse in an Underdence Plasma
Authors: Andreev N.E. , Gorbunov L.M. , Kirsanov V.I.
Published: February 2023

Several recent papers reported that short terawatt subpicosecond laser pulses in underdence plasmas can be highly unstable against longitudinal modulation on the plasma frequency. Here, we report about the first analytical and numerical detail study devoted to the mechanisms that trigger off this self-modulation and to the condition these mechanisms dominate under.
Propagation of intense laser pulses in an underdense plasma
Authors: Monot P. , Auguste T. , Gibbon P. , Jakober F. , Mainfray G. , Miquel J. L. , Louis-Jacquet M.
Published: February 2023

The new generation of short duration lasers provides pulses in excess of the terawatt level, that can be focused up to 1018 W/cm2 [1]. For such an intensity, the quiver motion of a free electron becomes relativistic and numerous new physical effects are expected, such as harmonic generation [2], particle acceleration [3] and relativistic self-focusing [4,5]. In order to observe these effects resulting from laser-electron interaction, a high electron density (Ne) is required. In fact, with regard to the small laser-electron interaction cross-section, a large number of electrons is needed for any significant field emission. Furthermore, using a high density, a collective response of electrons is driven that induces intense longitudinal fields required to accelerate particles. A significant change of the refractive index should also occur that will influence beam propagation if the electron density is large enough.
Rydberg Atoms in a Far Infrared Laser Field
Authors: Noordam L. D. , Hoogenraad J. H. , Vrijen R. B. , van der Meer A. F. G. , van Amersfoort P. W.
Published: February 2023

Among the interesting phenomena of atoms in strong laser fields is the strong deformation of the electron wavefunction due to the laser field. This deformation results in a reduced binding energy and inhibition of photoionization [Gavrilla and co-workers]. Recently this stabilization phenomena was observed using visible light of 600 nm. The relevant parameter in this kind of experiments is the quiver excursion a0 of the electron due to the oscillating e.m. field: (1) α0 = √I/ω2 where I is the intensity and w the angular frequency of the light field.
Measuring the Temporal Duration of High-Order Harmonic Radiation
Authors: Glover T. E. , Schoenlein R.W. , Chin A. H. , Shank C. V. , Falcone R. W. , Mittleman D. M. , Freeman R. R. , DaSilva L.
Published: February 2023

Ultra-short x-ray pulses provide scientists with powerful tools for material diagnostics. Production of coherent, soft-x-ray radiation through the generation of high-order harmonics of (optical) laser radiation has been demonstrated in several laboratories [1]. These high-order harmonics are typically generated using ultra-short laser pulses and are expected to be of short (typically sub-picosecond) temporal duration. While many aspects of harmonic generation have been experimentally investigated, the temporal duration of soft x-rays produced via high-order harmonic generation has not yet been measured. One difficulty is that the temporal resolution achievable with commercial instruments (such as x-ray streak cameras) is limited to approximately 1 ps.
Sub-Femtosecond Pulses in Mode-locked 2π-Solitons of the Cascade Stimulated Raman Scattering
Authors: Kaplan A. E.
Published: February 2023

The shortest to date optical pulse length of 6 fs using pulse compression technique was achieved in [1]. Sub-femtosecond pulses were attained by using a Fourier synthesizer [2] of separate lasers synchronized by nonlinear phase-locking [3]. Here, we propose a new approach based on multi-frequency cascade Raman stimulated scattering (CSRS) whose components are mode-locked within 2π soliton reminiscent to the self-induced transparency solitons [4]. We show that Raman active materials can support solitons consisting of pump laser wave with the frequency ω
L
and many cascade-excited Stocks and anti-Stocks component with their frequencies ω
j
= ω
L
+ jω0, j = ±1, ±2, ±3…, mode-locked to each other through a fast "full-swing" 2π-nutation of population at the Raman transition with the frequency ω0 ≪ ω
L
. Similarly to "bright-bright" 2π-solitons in CSRS with two [5] and three [6] components, these solitons have a new, very simple, Lorentzian intensity profile. Due to the engagement of many mode-locked components, however, their total EM field in the time domain consists of the train of ultra-short pulses (separated by the interval 2π/ω0) with their length being of the same order of magnitude or even shorter than the pump cycle, 2π/ω
L
. The major feature of the proposed effect is that all the frequency components of the new soliton are the so called bright solitons (in contrast to well known bright+dark soliton combination in SRS [7]) locked to each other and propagating with the same group velocity. The high-order CSRS required to observe the proposed effect, has first been observed experimentally in [8] and later in many other experiments, with the total number of components up to -10-15. The lock-in of all these components into "all-bright-SRS" 2π soliton has never been observed in experiment; its feasibility is discussed here.
Above Threshold Ionization of Hydrogen Atom in Strong ac Fields
Authors: Karule E.
Published: February 2023

Using a Sturmian function expansion non-perturbative method is applied to calculate above threshold ionization of hydrogen atom in a laser field.
Pulsewidth-Dependent Damage Measurements of Dielectric Materials
Authors: Stuart B.C. , Herman S. , Shore B.W. , Perry M.D.
Published: February 2023

The application of chirped pulse amplification to short-pulse lasers [1] has led to a dramatic increase in the number of high-power, sub-picosecond laser systems. Accordingly, knowledge of the short-pulse damage thresholds of optical components and the scaling of the damage thresholds with pulsewidth has become increasingly important. The development of high energy, (e.g., kilojoule class) short-pulse lasers is contingent on the ability to produce optical components capable of withstanding high fluence nanosecond and femtosecond pulses. In tins paper, we report on our measurements of the front-surface damage threshold of many different dielectric materials including windows, multilayer mirrors, and diffraction gratings over the pulsewidth range of 0.1 to 3000 ps.
Twist and Strain: A Study in Vibrational Mode-Coupling
Authors: Miller C. Cameron , Li Hao , Philips Laura A.
Published: February 2023

A homologous series of small organic molecules are used to explore the role of low frequency, large amplitude motion in vibrational mode coupling and in photochemically induced isomerization reactions. From the variation in structure in a series of substituted ethanes and strained ring systems, we can begin to link aspects of structure with the propensity for vibrational mode coupling. The molecules to be discussed include 2-fluoroethanol (2FE), 1,2-difluoroethane (DFE), 1-chloro, 2-fluoroethane (CFE), and cyclobutane.
High Resolution Spectroscopy of Ti2 and AlY at Near-Infrared Frequencies
Authors: Arrington Caleb A. , Langenberg Jon D. , Pinegar Jacqueline C. , Morse Michael D. , Doverstål Mats , Lindgren Bo , Sassenberg Ulf
Published: February 2023

High resolution jet-cooled molecular beam spectroscopy has been effective in revealing the bonding between transition metals. One periodic trend that has developed during the study of small transition metal molecules is the relatively weak bond strength in the early 3d transition metals (Sc2, Ti2 in comparison to middle (V2, Cr2) or late (Ni2, Cu2) members of the 3d series. This trend of bond strengths in early transition metals is not so pronounced in the 4d and 5d metals where d-bonding is a major contributor to molecular stability. Low bond strengths in molecules, whether due to poor d overlap or high s ← d promotion energy, provides a challenge to the spectroscopist. It has been shown that diatomic systems with a large density of electronic states, as is usually the case for open d-subshell molecules, undergo a rapid predissociation (τ < 5 ns) when excited above the lowest dissociation limit.1 The extreme density of states responsible for predissociation also precludes isolation of single rovibronic states suitable for high resolution spectroscopy at energies near the dissociation limit of these molecules. The spectroscopist interested in investigating species with low bond strengths and high densities of electronic states, as in our investigation of Ti2 and AlY, is forced to search the low energy near-infrared region for isolated electronic states that are not hopelessly perturbed. In the present near-infrared investigation of Ti2 and AlY we have employed resonant two photon ionization (R2PI) as the detection strategy for obtaining optical spectra in a jet-cooled molecular beam.
Doppler-Free Spectroscopy of Molecular Iodine Near 532 nm
Authors: Arie Ady , Byer Robert L.
Published: February 2023

Molecular Iodine exhibits a very rich absorption spectrum1 near 532 nm. Frequency-doubled monolithic diode laser pumped Nd:YAG lasers, having narrow linewidths and relatively wide tuning range, provide an excellent tool to investigate these transitions. Furthermore, we have recently shown that the Nd:YAG laser frequency can be absolutely stabilized to the Doppler-free lines of Iodine2. In this paper we utilize the ability to lock two lasers to Iodine hyperfine transitions in order to measure precisely the hyperfine frequency splitting by heterodyne spectroscopy. These results are then used to determine the hyperfine constants of the measured transitions.
The Position, Shape, and Polarization Dependence of Resonances in the Laser Photoionization Spectrum of Aligned Ca 4s5p 1P1
Authors: Duquette D.W. , McLaughlin K.W. , Eschliman D.S. , Francis O.P.
Published: February 2023

Two-color spectroscopy using narrow-bandwidth pulsed lasers provides a powerful tool to study the near threshold photoionization spectrum of excited atomic states. By combining the energy and polarization selectivity afforded by pulsed dye lasers, it is possible to probe a number of different continua. Many of these would be unreachable from the ground state because of angular momentum and parity selection rules and also due to the lack of high resolution sources of photons at appropriate energies. Precise positions, shape profiles, and strengths of autoionizing resonances, as well as angular distributions of ejected photoelectrons are necessary for comparison with increasingly sophisticated calculations.
Precise pulsed laser spectroscopy in the visible and far uv region: toward the measurement of the 11S-21S interval in atomic helium
Authors: Gangopadhyay S. , Melikechi N. , Eyler E.E.
Published: February 2023

Precise optical measurements have so far been conducted mainly in the visible and near-uv part of the spectrum. Extension to the far uv region depends on the development of tunable coherent sources that provide high resolution, accurate wavelength metrology, and a large photon flux. As part of our ongoing effort to measure the ionization energy of atomic helium by two- photon excitation at 120.28 nm, we have developed improved methods for generating vuv radiation in the vicinity of 120 nm, and for accurately measuring the systematic frequency shifts that occur during amplification and nonlinear mixing of nanosecond laser pulses.
High Resolution Computed Tomography for Solid Modeling and Computer Aided Design
Authors: Vannier Michael W. , Dye Daniel M. , Knapp Robert H. , Gayou Donald E. , Sammon Meil P. , Dzik Stephen , Butterfield Robert L. , Larson John , Ellingson William
Published: February 2023

Modern high resolution CT scanners can produce geometrically accurate sectional images of solid objects. Computer software has been developed to convert serial CT scans into a data base suitable for analysis using a Computer Aided Design / Computer-Aided Manufacturing (CAD/CAM) system.
Tutorial on Hardware for High-Speed Computed Tomography
Authors: Peschman K.
Published: February 2023

Summary not available.
High-Resolution Tomography of Small Laboratory Animals*
Authors: Seguin Fredrick H. , Burstein Paul , Bjorkholm Paul J. , Homburger F. , Adams Richard A.
Published: February 2023

A high-resolution, low-dose, tomographic x-ray scanner for small objects is being developed for use as a tool in in vivo clinical tests of substances suspected of being carcinogenic. In such tests a large group of animals (typically mice) is exposed to the substance in question, and the animals are then inspected at specified intervals for tumor growth. Non-destructive methods of inspection are desirable, and tomographic x-ray imaging is a natural possibility.
Concepts and Nonmedical Applications of NMR Imaging
Authors: Rothwell William P. , Gentempo Peter P.
Published: February 2023

Nuclear Magnetic Resonance Imaging (NMRI) is based on a fundamental relationship in NMR: where ω is the resonant frequency (in radian/sec), ɣ is the gyromagnetic ratio, and H is the magnetic field strength. Application of a linear field gradient across a sample, therefore, gives rise to a spatially dependent distribution of NMR frequencies.
High Speed Optical Tomography for Flow Visualization
Authors: Snyder Ray , Hesselink Lambertus
Published: February 2023

Optical computer assisted tomographic (OCAT) reconstruction of a three-dimensional unsteady object requires simultaneous acquisition of many line-of-sight measurements (projections). A projection represents a measurement of absorption or index-of-refraction along the pathlength. To acquire one projection a source, often a laser, is used in conjunction with beam steering and recording elements; all necessary projections can be obtained by either rotating the object, by rotating the data acquisition apparatus or alternatively by replicating the system required for making one projection. All these approaches have been investigated in the past for the purpose of making, for instance, measurements of quasi-stationary objects (Ref 1) or time-averaged measurements of complicated turbulent flows (Ref 2). Replication often leads to cumbersome and expensive optical systems and the lack of availability of a simple fast data acquisition system has impeded wide spread use of optical tomography in fluid mechanics research.
Tutorial on Mathematical Foundations of Computed Tomography
Authors: Smith Kennan
Published: February 2023

Summary not available
Scintillation Yield of Thin Polystyrene Films
Authors: Botelho do Rego A. M. , Morais M. I. , da Silva J. Lopes
Published: February 2023

The effects of quenching on the value of the scintillation (prompt plus delayed component) induced by a heavy ionizing particle of energy E and specific energy loss dE/dx are analysed measuring the specific luminescence dS/dx of polystyrene films dopped with different concentrations of DPA. In a previous work1 we deduced the following expression for the delayed specific luminescence Quantities (1 – ϕ1), ϕ2 and (ϕ1 - ϕ2) are the fractions of energy transferred by the incident particle to the track, blobs and spurs respectively. These ones represent the three distinct regions considered in the track model proposed before2.
Photoproperties of DCM (4-dicyanomethlene-2-methyl-6-p-dimethyl amino styrl-4H-pyran)
Authors: Lesiecki Michael , Asmar Federico , Drake Michael
Published: February 2023

The dye DCM(4-dicyanomethlene-2-methyl-6-p-dimethyl amino styrl-4H-pyran) is well known as a broadly tunable efficient laser dye and as an active element in luminescent solar concentrators1,2. Our interest has been to study the primary photochemical and photophysical process that are operative in this system.
Metastable Nitrogen Energy Transfer Emission Spectroscopy: Recent Advances and Applications
Authors: Mitchell J. W. , Wittman P. K.
Published: February 2023

Ultrasensitive operationally easy, on-line analytical techniques are required to monitor the fabrication and processing of ultrahigh purity electronic materials. Where inert atmospheres free of oxygen and carbon contamination are required, metastable transfer emission spectroscopy (MTES) is suited ideally for continuous monitoring of gas purity.
Vibrational Relaxation of N2 Aggregates in Rare Gas Matrices
Authors: Bahrdt J. , Kühle H. , Schwentner N. , Wilcke H.
Published: February 2023

In an experimental investigation of the conversion of electronic energy into vibrational degrees of freedom of a cluster followed by dissipation into matrix phonons it is essential that all intermediate steps of the energy flow can be monitored. For this purpose each vibrational level v'=1 up to v'=6 of the lowest excited electronic state A

3

Σ
u
+

of N2 in a solid Xe matrix has been excited selectively by monochromatized synchrotron radiation. The stepwise relaxation to lower A

3

Σ
u
+

vibrational levels has been derived from luminescence spectra. The large vibrational energy of 174 meV corresponding to 35 matrix phonons inhibits vibrational relaxation in completely isolated N2 molecules within the radiative lifetime of ≈ 10-3s. For N2 pairs and larger clusters a complex relaxation cascade is observed which leads to different steady state distributions for each initial level. The first relaxation steps involve only changes of v' by two quanta. For excitation of v′ ≥ 4 states also intermediate vibrational levels are populated in the end of the cascade. The experimental results indicate the following two basic processes: Radiationless electronic energy transfer between two N2 molecules based on exchange interaction leads to a deexcitation of molecule I from the initially (v')A

3

Σ
u

+

state to the groundstate

(

v
'
'
=
1

)

×
1

Σ
g

+

and the neighbouring molecule II is excited from

(

v
'
'
=
0

)

x
1

Σ
g

+

to 

(

v'
−
2

)

A
3

Σ
u
+

corresponding to a reduction of v' by two quanta.
Photoluminescence from Two-Dimensional Electrons in a Magnetic Field
Authors: Perry C.H. , Petrou A. , Smith M. C. , Worlock J.M. , Aggarwal R.L. , Gossard A.C. , Wiegmann W.
Published: February 2023

We have studied photoluminescence from modulation-doped GaAs/AlGaAs multiple quantum well (MQW) structures, grown by molecular beam epitaxy, in the presence of high magnetic fields. Experiments were performed using a variety of lasers as excitation sources. In zero field, electrons in the valence band (VB) are photo-excited by the incident laser light to conduction band (CB) states, creating VB holes. They radiatively recombine with the holes, producing the infrared luminescence observed in our experiments which is, in general, rather broad and extends from about 12100-12400cm−1.
Picosecond Time-Resolved Spectroscopic Study of Vibrational Relaxation Processes in Alkali Halides
Authors: Knox W. H.
Published: February 2023

The vibrational dynamics of fluorescent defects in alkali halides are interesting for a number of reasons. Information on electron-phonon interactions, relaxation of localized excitations and energy transfer phenomena may be obtained from a detailed study of the fluorescence properties at short times after optical excitation. In particular, the vibrational state, or states, of an impurity center may be directly determined from the time-resolved fluorescence spectrum under certain conditions, revealing details about internal energy relaxation processes. Recent advances such as the modelocked color center laser [1] and the demonstration of vibrational fluorescence [2] have provided increased interest in the vibrational properties of defects and defect systems in alkali halides.
Intrinsic Luminescence in CdF2 Crystals
Authors: Fermi F. , Paracchini C.
Published: February 2023

CdF2 crystals have the fluorite structure and a gap 7.6eV wide. Under X rays excitation pure crystals show, at temperatures lower than 100 K, an intense blue luminescence. The emission spectrum evidences a large band between 300 and 500 nm with a maximum at about 380 nm(1).In doped samples one observes the same luminescence besides that of the intentional impurity. The same blue emission is obtained also in the electroluminescence of pure and doped CdF2 crystals(2).
Emission Spectra of Thallium Bromide Solutions
Authors: Giorgianni U. , Grasso V. , Saitta G. , Grassano U.M.
Published: February 2023

Alkali-halide crystals when doped with heavy-metal ions with the s2 configuration show absorption and emission bands which are characteristic of the impurity(2,3). A close resemblance was observed by us between the absorption spectra of thallium bromide solutions and the spectra of thallium-doped potassium bromide single crystals(3) as shown in fig. 1. Furthermore, the same similarity between doped crystals and solutions was also observed in the luminescence spectra on excitation in the UV absorption bands. Fig. 2 reports the emission spectra at Room Temperature of an alcoholic TlBr solution of polycrystalline powder, for two different excitation wavelengths. The spectra consist almost entirely of two overlapping bands with an energy separation of about 0.5 eV and of several shoulders. The spectral positions of the two main structures are the same as in the solid as one can observe in the figure
On the Mechanisms of Non-Isothermal Relaxation Through Thermally Stimulated Luminescence Processes.
Authors: Ratnam V.V. , Manam Jairarn
Published: February 2023

Non-isothermal relaxation techniques in the form of thermally stimulated luminescence phenomena and processes have been utilised to understand the mechanisms involved in the occurrence of luminescence emission during the formation and subsequent destabilisation (by thermal annealing) of the radiation induced and stabilised defects in pure and doped alkali halide crystals. Techniques like thermally stimulated luminescence (TSL) spectra, monochromatic thermoluminescence (MTL) glow curves, photo-stimulated thermoluminescence (PSTL) glow curves have been successfully utilised in this study. Effects of pre-and post-deformation on the X-irradiated crystals on the above luminescence manifested properties have also been studied.
Kinetics of Radiation Induced Thermoluminescence
Authors: Kulkarni D.M. , Narlikar A.V.
Published: February 2023

Gamma-ray induced thermoluminescence of strontium chloro phosphate Sr10(PO4)6Cl2 is studied from the glow curves, the activation energy, escape frequency factor are determined and the values are given in Table 1.1.
Two-Color Superfluorescence of O 2 ` − Centers in KCl
Authors: Florian R. , Schwan L.O. , Schmid D.
Published: February 2023

If

O

2
`

−

centers in KCl are excited in their fundamental absorption band (at about 250 nm), they yield a fluorescnece spectrum which at low temperatures is dominated by a progression of very narrow zero-phonon lines (Δν1/2≈1cm−1) with a large Stokes shift (roughly 23000 cm−1 or 2.9 eV). At very high excitation intensities (≳ 20 GW/cm2) with single pulses of the fourth harmonic of a modelocked Nd-YAG laser (λ = 266 nm, pulse duration 30 ps, pulse energy ~ 100 μJ) and at low temepratures (T < 30 K) one observes a simultaneous coherent emission at the wavelength of two of the zero-phonon lines (0-10 and 0-11 transition at 594.77 and 629.14 nm, respectively) /1/, which can be identified as two-color superfluorescence fron a three-level system /2,3/.
Luminescence from Adsorbates
Authors: Shinjo Kazumasa , Sugano Satoru
Published: February 2023

Theory1 of multivalency of adsorbates on metal surfaces, taking into account the effect of the image-force stabilization measured by η2 in addition to those of the electron-transfer between the adsorbate and the substrate measured by Γ and Coulomb interaction between the adsorbate electrons, has revealed that the critical lines exist in a parameter space, across which the valence charge of the adsorbate ground state changes discontinuously. Dynamical calculations2 have been made on the line shapes of optical absorption and photoelectron emission spectra of a similar system. It has been found that the lines are broadened when the energy, εa-Ua, of the core-hole-stabilized valence level of the adsorbate goes up across the critical line at –η2/2: the broadening may be considered to be due to a short life-time of the excited neutral configuration from which an electron escapes into the substrate. The broadening of the absorption lines has been discussed in connection with the experiment of Cunningham et al3 concerning persistence or non-persistence of exciton lines in the reflection spectra of rare-gas-atoms on metal surfaces.
Interactions and Energy transfer in Chlorophyll a aggregates studied by picosecond fluorescence spectroscopy
Authors: Keller W.W.A. , Albers B.A. , Strauss E. , Maier-Schwartz K.
Published: February 2023

Chlorophyll a (Chl a) in pure non-polar solvents (e.g. dodecane) interacts via its polar groups and forms dimers1). These aggregates are considered model systems for the study of the primary processes in the photosystem II (P 680)1). Minute nucleophilic traces change the kinetic balance towards solvated monomers. The dimer absorption consists of two redshifted peaks, that of the (nucleophilic) acceptor molecule at 663 nm and that of the donor molecule at 678 nm. This indicates, that the π electron systems of the two molecules are not coupled.
Delayed Fluorescence of Algae
Authors: Gerhardt V. , Krause H.
Published: February 2023

The absorption of photons by the antenna pigment-molecules of plants is the first step of the photosynthesis. This absorption leads to the excitation of the two reaction-centers P700 and P680 of Photosystem I and II and, furthermore, to a charge-separation at both reaction-centers. By means of this charge-separation the energy of photons is transfered to electrons which have a high chemical potential within the electron-transport-chain. The charge-separation process is very efficient: Only about 1 % of the excited reaction-centers re-emit the absorbed photon-energy by prompt fluorescence (allowed S1 → S0-transition). The main part of the excitation-energy feeds the photosynthesis by pumping electrons from water-molecules to NADP-molecules.