bluuebunny/crossref_metadata_2025 huggingface dataset:
High-intensity subfemtosecond sub-cycle pulses, solitons and shock waves via cascade SRS and "EM-bubbles" generation
Authors: Kaplan A. E. , Shkolnikov P. L.
Published: February 2023

We review here our recent work on the formation of extremely powerful near- and subfemtosecond (sub-
fs
) pulses based on two new principles: □ The phase-locking [1] of multiple components of stimulated cascade Raman scattering (CSRS), that can produce an almost periodic train of powerful sub-
fs
pulses, with pulses as short as ~ 0.2
fs
and spaced by ~ 8
fs
. □ The generation of powerful "EM-bubbles" (EMBs) [2], unipolar very short solitary pulses of EM-radiation propagating in a gas of two-level or classically nonlinear atoms. This effect can generate a single EMB, or a few EMBs with controllabe parameters, easily separable into individual EMBs.
Solid to Plasma Transition in fs-Laser-Irradiated Fe: Collapse of the Spin-Orbit Gap
Authors: Grimes M. K. , Lee Y. -S. , Downer M. C.
Published: February 2023

Quantitative measurements of the optical conductivity of iron under earth core conditions are important in modelling geomagnetism[1]. We approximate such conditions transiently[2] by exciting an Fe, and a control Al, surface in a vacuum or helium environment with 620 nm, 120 fs FWHM laser pulses with 105 peak-background contrast ratio at .6 ps focussed to peak intensities 1011 < I < 1015 W/cm2 on target. Figs. 1 and 2 present p- and s- polarized self-reflectivity R
p,s
(θ,I) for constant incident angle θ and peak intensity I, respectively. Geometric correction for the dependence of spot shape on θ has been made in plotting the data. Using very linear pulse energy reference monitors, reproducibility to within ΔR/R ≤ 0.1% was achieved. This allowed measurement of very slight reflectivity changes, as shown in the inset of Fig. 1. This figure also shows that the reflectivities of Fe and Al in the solid to plasma transition region (1013 – 1015 W/cm2) approach each other as I increases, consistent with their similar total conduction electron densities (ne ≃ 1.8 × 1023 cm−3) when the Fe d-electrons are included. This suggests qualitatively that progressive unbinding of the d-electrons dominates the changes in optical properties of Fe in this regime. Fig. 2 provides evidence that a density gradient develops during the laser pulse. It is well known[3] that θ
min
, the angle at which the minumum p-polarized reflectivity occurs, shifts toward smaller angles as the density gradient scale length grows. Although the largest angle of incidence attainable in the experiment was smaller than θ
min
under these conditions, the data clearly indicate a shift toward smaller values, seen for Fe in Fig. 2 as a crossing of the p-polarized data sets.
Guiding of sub-100 femtosecond pulses in preformed plasma channels
Authors: Nikitin S.P. , Clark T.R. , Milchberg H.M.
Published: February 2023

The guiding of 80 fs pulses over a 1 cm distance in a preformed plasma waveguide has been demonstrated. The guided pulses were produced by a Ti:sapphire laser system. The plasma waveguide was created in a neutral gas by using a separate laser system which consists of a 100 ps Nd:YAG oscillator seeding a Nd:YAG regenerative amplifier and two power amplifiers. In order to achieve stable guiding it was necessary to synchronize these two laser systems so that the time jitter between them is substantially less then time scale over which significant changes in the plasma waveguide can occur.
Infrared Holographic Interferometry
Authors: Cormier M. , Lewandowski J. , Mongeau B. , Ledoyen F. , Lapierre J.
Published: February 2023

Having previously developed techniques for Infrared (IR) holography(1, 2), in order to minimize problems related to vibrations, to relatively large displacement or deformation and to facilitate Real Time Holographic Interferometry, we have reported a method for Real Time Interferometry using IR Holography of low-diffusing surfaces(3). This presentation reports a method to inspect diffusing surfaces which consists in the adaptation to IR of the relatively standard techniques of holographic interferometry.
Measurements of Diffusion Coefficients in Liquids using Holographic Interferometry
Authors: Fenichel Henry , Lohman Gary E. , Will David
Published: February 2023

With the advent of holography, traditional interferometric methods, such as Mach-Zehnder, have been replaced by holographic interferometric techniques. A distinct advantage of the holographic method is that it provides the ability to compare wave fronts that are separated temporally, as well as spatially. This paper describes the application of the technique to measurements of mass and heat transport in transparent liquid mixtures.
Holographic Optical Configurations for Eye Protection Against Lasers
Authors: Magariños José R. , Coleman Daniel J.
Published: February 2023

Holographic notch filters are used for eye protection against laser radiation because they allow high transmission, reflecting only a narrow spectral bandwidth. These narrow bandwidth filters are diffractive optical elements and the notch or wavelength protection will be dependent on the angle of incidence. To obtain large angular protection, a wider bandwidth is required and the advantage of high transmission is lost. This is also typical of multilayer interference notch filters.
HOE's for optical computing with wavelength mux-demuxing and spatial light modulator
Authors: Liegeois C. , Meyrueis P. , Pfeiffer P.
Published: February 2023

Our SLM processor using wavelength mux and demux needs good respectively mux and demultiplexing elements. We describe the principle and realisation of a holographic dichromated gelatin mux and demux as well as its integration in the system.
Holographic Memories
Authors: Psaltis Demetri
Published: February 2023

Summary not available.
Multiphoton ionization rates for atomic hydrogen: Solutions of Schrodinger equation compared with model values
Authors: LaGattuta K. J.
Published: February 2023

Direct solutions of the time-dependent Schrodinger equation, for an electron moving in three spatial dimensions (3D), bound initially (t≦0) by a Coulomb potential, and acted upon by an extrinsic oscillating electric field, have been described in several recent publications1-3. The oscillating electric field models the effect of an incident laser beam on the initially bound electron.
The Dynamics of Dense Plasmas Produced by Ultra-Short Pulse Lasers
Authors: Umstadter D. , Freeman R .R. , Milchberg H. , McIlrath T.
Published: February 2023

The interaction of an ultra-short pulse high intensity laser with a solid target is of current interest because the resulting plasma is also solid density. Such a plasma might be a bright short pulse continuum x-ray source [1] to pump an x-ray laser or probe transient properties such as phase transitions or biological phenomena [2]. Recent experiments [3] have revealed that these plasmas are good continuum emitters and that the continuum x-ray duration is sub-picosecond (streak camera limited). The x-ray pulse width is primarily determined by the rate at which the electrons and the ionization stages cool from the diffusion of heat into the solid and the expansion of material into the vacuum. In the following we report the results of a one dimensional fluid code that models the interaction of an ultra-short laser pulse with a solid target of Aluminum. We describe the dynamics of the mass density, pressure, ionization and expansion velocity. In a related paper we discuss the effects of these quantities on the pulse width of continuum x-ray radiation generated by recombination [4].
High Quality, Ultrahigh Instensity Lasers for Tomorrow's Ultrahigh Field Experiments
Authors: Mourou G. A.
Published: February 2023

The CPA concept has been demonstrated with Nd:glass and alexandrite media. Pulses as powerful as TW have been produced with compact laser systems. In the near future PW pulses will be generated. As the laser power increases to these extreme levels, the temporal quality, i.e. pulse contrast and control of ASE, will have to improve accordingly, propagation in air kept to a minimum. We disucss the fundamental considerations to achieve ultrahigh intensities with the highest spatial and temporal quality necessary to perform experiments in the 1020–1023 W/cm2 regime.
Ultrashort Pulse Laser Heating of Solids
Authors: Falcone R. W. , Murnane M. M. , Kapteyn H. C.
Published: February 2023

Ultrashort pulse lasers have been used to heat solid and near solid density plasmas to several hundred volt electron temperatures. The relevant absorption mechanisms and the behavior of material in these conditions are discussed.
Hot Electron Relaxation in Metals
Authors: Elsayed-Ali Hani E.
Published: February 2023

When a metal is subjected to a transient event (femtosecond lasers, a fast electrical current, or energetic charged particles), energy is initially coupled to the electron gas. Hot electrons then transfer their energy to the lattice by inelastic collisions or exit the surface of the metal by a single-photon or a multi-photon photoemission (Fig. 1). For conditions discussed here, energy loss by photoemission is significantly smaller than that due to inelastic collisions so that it can be neglected. The possibility of creating nonequilibrium heating conditions where hot electrons can be generated in metals during the passage of ionizing radiation was postulated many years ago.1 The advent of ultrafast lasers has made accessible the generation and the study of such a nonequilibrium state.
Modeling of Femtosecond Laser-Plasma Interactions Unsafe at any Speed
Authors: Rosen M. D.
Published: February 2023

We describe the trials and tribulations of using large hydrodynamic/atomic physics simulation codes to model the radiative yields of various Z targets irradiated by high power femtosecond pulses.
FT500: A High Resolution VUV FTS: The Why and the How
Authors: Wheaton John
Published: February 2023

The advantages of the FTS over the classical grating spectrometer are clear - the fundamental gain is increased luminosity, with a consequent increase in the rate at which the spectrometer records basic information. Associated, but less fundamental gains include linearity in both intensity and frequency. An indirect but very real gain is the integration of computer and spectrometer, aiding the rapid and direct analysis of large quantities of data.
A Practical Non-Scanning FTS for Astronomy
Authors: Butcher H. , Douglas N. , Frandsen S. , Maaswinkel F.
Published: February 2023

Astronomical stellar spectrometers have traditionally been based on classical slit/grating designs, which have the considerable advantage of easy incorporation of multi-channel array detectors. With current optical, diffraction grating, and array detector technologies, and for constant optical efficiency, high resolution instruments of this type are found to scale in physical size roughly linearly with telescope aperture. For moderate spectral resolutions and existing telescopes, the ability to record simultaneously a substantial length of spectrum has generally been thought to be an advantage outweighing the inelegant and moderately costly nature of the instruments.
Spectral Shifts of Methane Lines in Collisions with Hydrogen, Helium, Nitrogen, and Argon
Authors: Jennings Donald E. , Fox Kenneth
Published: February 2023

Pressure-induced shifts of rotational-vibrational lines have been measured at ambient temperature and pressures ranging from 100 to 500 Torr. Results are reported here.
FTS Observation of CO Fundamental Bands in Cool Stellar Atmospheres
Authors: Wiedemann Günter , Ayres Thomas R. , Jennings Donald E.
Published: February 2023

The infrared ro-vibration spectrum of carbon monoxide provides a powerful observational diagnostic for the investigation of late-type stellar atmospheres. At temperatures of several thousands of degrees, CO vibrational states up to v=7 and rotational states up to j≈100 are populated. The corresponding lines are formed over, and therefore probe, a large range in altitude. The strongest fundamental lines (Δv=1) originate in the upper photosphere and in the chromosphere, regions which are only inadequately described by present stellar atmosphere theories. Numerical simulations have shown that CO affects the stellar atmospheric structure through cooling in optically thin lines (e.g. Johnson, 1973). CO observations are important, because the model predictions can be tested reliably only from observations of species that are intimately involved. This is particularly true in view of the dilemma posed by the contradicting results of 'conventional' chromospheric diagnostics and first CO Δv=1 observations on the Sun (Ayres and Testerman, 1981) and Arcturus (Heasley et al., 1978). The present study has been conducted to establish CO fundamental bands as an observational diagnostic for the higher layers of cool stellar atmospheres.
Hot Bands of Carbon Dioxide in the 15 Micron Region
Authors: Esplin Mark P. , Hoke Michael
Published: February 2023

The Air Force Geophysics Laboratory (AFGL) high resolution Michelson interferometer has been used to make measurement of the spectrum of CO2 in the 15 µm region. The infrared spectrum of a linear molecule like CO2 is composed of vibrational bands made up of many nearly equally spaced rotation lines. At high temperatures there is a great deal of overlapping of these bands. This overlapping causes the line density in the experimental spectrum to be very high. Since the band systems are spread over hundreds of wavenumbers, a Michelson interferometer with its capability of high resolution over wide spectral ranges is well suited to high temperature measurements.
Branching Ratios of Cerium with the Kitt Peak 1m FTS
Authors: Bisson Scott , Comaskey Brian , Conway John G. , Haynam Chris , Stockdale John , Worden Earl
Published: February 2023

The emission spectrum of cerium was recorded on the 1m Fourier transform spectrometer (FTS) at the National Solar Observatory, Kitt Peak, AZ., using a 140Ce electrodeless discharge lamp (EDL) as a source. The frequency range 4,000 to 27,600 cm-1 was covered in two runs while maintaining the EDL parameters as constant as possible. Large UV diodes were used as detectors for the 9,100 to 27,600 cm-1 range and In/Sb detectors were used for the 4,000 to 14,300 cm-1 range. The instrument was intensity calibrated for both ranges using standard lamp scans. A multiplication factor obtained from the overlap region was applied to bring the two regions to the same intensity scale.
High Precision Fourier Transform Spectrometry: Some Observations on Data Reduction
Authors: Brault James W.
Published: February 2023

Even after years of development, data reduction software remains the weakest link in the chain of events leading from source preparation to published spectroscopic papers. Most of the time is spent there, yet the quality of the published numbers often fails to reflect the quality of the original spectra; the quantity of information is also usually greatly reduced.
Digital Signal Processing of Fourier Transform Spectra on IBM PC-Compatible Computers
Authors: Abrams Mark C.
Published: February 2023

The advent of the Los Alamos National Laboratory Fourier Transform Spectroscopy Facility represents a break with past techniques for reducing Fourier transform data. In contrast to system dependent mainframe reduction packages, the LANL data reduction is performed exclusively on Apple MacIntosh II microcomputers. For scientists involved in Fourier transform spectroscopy there is a need for a unified data reduction package that will accomodate high resolution spectra from both the LANL FTS Facility and the McMath Fourier Transform Spectrometer at Kitt Peak. An adaptation of the Kitt Peak code DECOMP is presented that facilitates the reduction of spectral data from either laboratory on IBM PC-compatible computers.
A Self Contained, Variable Gas Inductively Coupled Plasma
Authors: Manning Thomas J. , Hof Byron A. , Hof Douglas E.
Published: February 2023

Various lamps have been used by spectroscopists to study the electronic structure of their respective species. Two of the more common lamps in use are Electrodeless Discharge Lamps (EDLs) and Hollow Cathode Lamps (HCLs). Microwave and radiofrequency excited EDLs have temperatures in the 400-600 K range, pressures in the 0.1-10 torr range and a common excitation frequency of 2450 MHz. The maximum power is 150 W. They are constructed from quartz tubing measuring 10 mm in diameter and 30 mm in length. HCL's are typified by low gas temperatures (400-500 K) and low pressures (0.1-10 torr). Both EDLs and HCLs are produced commercially.
High Resolution Fourier Transform Spectroscopy from 10 to 1000 cm−1
Authors: Johns J. W.
Published: February 2023

A Bomem DA3.002 Fourier transform spectrometer has been modified by replacing the plane moving mirror with a moving roof-top and a stationary retro-reflector. This simple modification results in a maximum optical path difference of about 4.5m and an apparatus function with full width at half maximum of about 0.0014 cm−1. Doppler limited spectra can now be obtained to 600 cm−1 (depending on the species under study) and the maximum resolution has been observed down to 10 cm−1.
Fourier Transform Spectroscopy of OH and OD in the Infrared
Authors: Davis Sumner P. , Engleman Rolf , Abrams Mark C.
Published: February 2023

We are making a thorough study of the Meinel bands of OH and OD radicals in the spectral region 1900 to 9000 cm−1. Three sources have been used, the ozone-hydrogen flame, the oxygen-acetylene flame, and the inductively coupled plasma (ICP). Differences in the spectra are immediately apparent, as shown in Figure 1. The ozone-hydrogen flame operates at low pressure, the lines are sharp, and the excitation is non-thermal. The oxygen-acetylene flame operates at atmospheric pressure and produces thermal excitation and broad lines. The ICP spectrum is similar to the oxygen-acetylene flame but with lines of intermediate sharpness.
High Resolution FTS in Astronomy at 7 to 15 Microns
Authors: Jennings D. E.
Published: February 2023

Infrared molecular and atomic lines in planets, stars, and dust clouds can only be resolved using the highest available spectral resolution. The Fourier transform spectrometer is presently the only type of spectrometer capable of resolving powers near 105 which can operate at arbitrary wavelengths in the infrared. However, because noise in a spectrum increases with resolution, working at high resolution requires maximum sensitivity. In the thermal infrared, radiation from the sky and warm optics is the dominant source of noise in a spectrum. In order to achieve 105 resolving power on even the brightest sources in the mid-infrared, special techniques must be used to minimize background radiation.
Fourier Transform Observation of Jet Cooled Emission from the CH3N and CCN radicals
Authors: Brazier C. R. , Oliphant N. H. , Bernath P. F , Carrick P. G.
Published: February 2023

The gas phase spectrum of the methyl nitrene radical was first observed by Carrick and Engleking1and subsequently the first rotationally resolved spectrum was obtained by Carrick et al.2The use of the Kitt Peak Fourier transform spectrometer, to detect the emission from a corona excited supersonic expansion of methyl azaide in helium, yielded a rotationally resolved spectrum limited by Doppler broadening of 0.02 cm-1. The transition, assigned as

A
˜

3

E-

X
˜

3

A
2

analagous to the A3∏ −X3∑−band of NH, was still extremely complicated however. Due to the case (a) - case (b) nature of the transition 27 branches are allowed for each subband. Giving a total of 81 branches for the 0-1, 1-0 and 1-2 subbands, the only ones likely to be populated at 15 K the observed rotational temperature. Hence the observed transition is a many line spectrum with few branches discernable.
Fourier Transform Studies of Audio Stimulated Surface Enhanced Scatter (ASSES) in Biological Systems (Insects)
Authors: Callahan Philip S.
Published: February 2023

Michael Faraday in his 1848 Christmas lecture titled “The Chemical History of a Candle” stated: “There is no more open door by which you can enter into the study of natural philosophy than by considering the physical phenomena of a candle. There is not a law under which any part of this universe is governed which does not come into play, and is not touched upon, in these phenomena.”
Transition probabilities using branching ratios determined with the Kitt Peak FTS lifetimes obtained by laser and other techniques - lanthanides and U II.*
Authors: Worden Earl F , Conway John G.
Published: February 2023

Our studies at Lawrence Livermore National Laboratory (LLNL) of lanthanide and actinide spectra with the Kitt Peak National Solar Observatory (KPNO) 1 m Fourier transform spectrometer (FTS) have included both intensity for branching ratio (BR) determination (transition probability) and frequency observations using hollow cathodes (HC) and/or electrodeless discharge lamps (EDLs) as sources. The elements we have observed, the purpose of the study and the sources used are given in Table 1.
Recent Results from High Resolution Infrared Atmospheric and Laboratory Fourier Transform Spectra
Authors: Goldman A. , Murcray F.J. , Blatherwick R.D. , Murcray F.H. , Kosters J.J. , Bonomo F.S. , David S.J. , Murcray D.G. , Rinsland C.P.
Published: February 2023

High resolution (0.002-0.003 cm-1) Michelson type interferometer systems have been used at the University of Denver since 1987 to obtain infrared solar absorption spectra of the stratosphere during several balloon flights (~37 km), as well as ground-based solar spectra and laboratory spectra of molecules of stratospheric and tropospheric interest. The stratospheric spectra cover the 700-2200 cm-1 region and show many new spectral features of important atmospheric gases such as O3 (including 18O and 17O isotopic species), NO2, HNO3, O2, N2, COF2, ClONO2, SF6 and others. The new spectral features are enhanced by the high resolution and long path spectra obtained during sunrise and sunset. Also, new features appear as the concentrations of some trace gases increases in the atmosphere.
Band Centers and Line Positions of Hot Bands of 13C16O2 and 16O13C18O in the 15 Micron Region
Authors: Esplin Mark P. , Hoke Michael
Published: February 2023

A high-resolution interferometer and high-temperature absorption cell have been used in a continuing measurement program of rotation-vibration spectra of the isotopes of carbon dioxide in different spectral regions. This paper covers results for the isotopes 13C16O2 and 16O13C18O with band centers in the spectral region 600 to 800 cm-1.

Only a few experimental details will be given here; additional details may be found in the literature.1 The experimental components include an infrared source, a radiation chopper, a high-temperature single-pass gas-sample absorption cell, a Michelson interferometer with "cat’s eye" mirrors employing a step-and-integrate mirror motion, and two liquid-helium-cooled detectors. A carbon dioxide gas sample was contained in the 1.75 meter single-pass stainless-steel sample cell. The central one meter section of the cell was maintained at a temperature of 800K, with temperature gradients in the end segments of the cell, ending with the cell windows at room temperature. For this study a stepping mirror displacement of 75 cm was used, giving a resolution (FWHM) of 0.006 cm-1 with triangular apodization.
Work In Progress at The LUND VUV-FTS
Authors: Litzén Ulf , Johansson Sveneric
Published: February 2023

A Fourier Transform Spectrometer specially designed for the UV and VUV regions is being used at the Lund University Atomic Spectroscopy Group. The instrument, manufactured by Chelsea Instruments Ltd., UK, was purchased thanks to a grant from the Swedish Natural Science Research Council. In the grant application, particular emphasis was put on the possibility to produce accurate laboratory data for astrophysical research, and investigations with this purpose have accordingly dominated during the first year. More general atomic spectroscopy and atomic physics work will, however, also be carried out at the instrument, and such projects have already been initiated.
Detector nonlinearity in Fourier transform spectroscopy
Authors: Abrams Mark C.
Published: February 2023

Spectral distortion due to the nonlinear response of HgCdTe detectors is well known. Methods for removing such features are discussed.

Nonlinear response in HgCdTe detectors is a well known complication in midir Fourier transform spectroscopy; methods of removing the spectral artifacts created by nonlinearity are less well understood. While the instrument and experiment may be designed so that the desired spectrum is properly sampled, non-linearity introduces spectral features that lie outside the intended bandpass and consequently are undersampled and subject to aliasing. Consequently, in cases where nonlinear response may be expected it is essential that optical filters be chosen with the nonlinear harmonics in mind. Several examples of nonlinearity are considered, with practical examples drawn from the ATMOS data set.
High Resolution Infrared Fourier Transform Emission Spectroscopy and Rotational Spectroscopy of Metal Hydrides: 2Σ+ State of CaH
Authors: Frum C. I. , OH J. J. , Cohen E. A. , Pickett H. M.
Published: February 2023

Calcium hydride is an important astrophysical molecule which has been detected in the Sun [1,2] and other stars [3]. It is also believed that this free radical is an important constituent of the interstellar medium [4]. However, a search for the CaH in interstellar medium is hindered by the unavailability of accurate frequencies for the low-N rotational transitions.
High Resolution Fourier Transform Emission Spectroscopy of Transient Molecules Using a Corona Excited Supersonic Expansion Source
Authors: Carrick Patrick G. , Brazier Chris
Published: February 2023

A corona excited supersonic expansion (CESE) source (1) has properties that are well suited to the study of transient molecular species with a high resolution Fourier transform spectrometer. This source is run with a continuous dc discharge and a high speed Roots pumping system. The source of transient molecules is relatively confined and quite intense when compared to flowing afterglow or hollow cathode sources. The discharge serves not only to produce the transient molecules, but also to excite the desired molecules into high electronic states, which can be observed by emission in the ultraviolet and visible spectral regions. The supersonic expansion of the source rotationally cools the transients, thereby reducing spectral congestion from overlapping bands and reducing the Doppler line width of the rotational transitions.
Spatially-resolved blueshifting of third harmonic and fundamental femtosecond pulses during high intensity ionization of subatmospheric density noble gases
Authors: Siders C.W. , Gaul E. , Downer M.C. , Babine A. , Stepanov A.
Published: February 2023

Previous studies1,2 have demonstrated the utility of ionization-induced self-phase modulation of femtosecond laser pulses for time- and space-resolved measurements of moderately high field (1014 < I < 1015 W/cm2) ionization dynamics in gases at pressures p ≥ 1 atm. At such high gas/plasma densities, strong defocusing of the pulses2 and participation of collisions in ionization dynamics1 degrade the beam quality of the transmitted blueshifted pulses and complicate quantitative interpretation of the results. In this paper, we examine spectral blue shifts induced on single 1.5 mJ., 80 fs., 800 nm. pulses and their third harmonics (3ω) upon ionizing much lower pressure (0.5 < p < 500 torr) gases at higher focused intensity (I ~ 1016 W/cm2) than used in previous quantitative studies of this effect. At tens to hundreds of torr pressure, we find that channeling effects3 in the interaction volume give rise to collimated, pressure- and intensity-tunable 3rd harmonic pulses of good beam quality. At still lower pressures (< 10 torr), the effect of channeling and plasma-induced defocusing becomes negligible, as the interaction region simplifies to a near-vacuum Gaussian focal geometry. In this regime, we reliably measure ω and 3ω blueshifts Δω/ω ≤ 10-4, thus demonstrating the feasibility of quantitative, sensitive time- and space-resolved blueshift diagnostics of collisionless high field ionization fronts or small amplitude Langmuir waves (e.g. laser wakefields)4 without the complication of severe beam distortion.
Multiple Photon Absorption by Quasi-Free Electrons in SiO2 under Strong Laser Irradiation
Authors: Daguzan Ph. , Guizard S. , Krastev K. , Martin P. , Petite G. , Dos Santos A. , Antonetti A.
Published: February 2023

One of the main fundamental point in the behavior of dielectrics under strong laser irradiation is the problem of the energy transfer mechanism between electrons, lattice and the laser field [1,2]. In this paper, we report on a subpicosecond photoemission experiment. Measurements of the kinetic energy of emitted electrons, generated via multiphoton transitions, from a laser-irradiated surface of α-quartz provide direct results on the electron energy distribution and can reveal for example the eventual absorption of photons by the quasi freeelectrons in the conduction band.
Strong-Field Dipole Emission of an Ionized Electron in the Vicinity of a Coulomb Potential
Authors: Fedorov M. V. , Peatross J.
Published: February 2023

We have calculated three-dimensionally in the first Born approximation the interaction with a Coulomb potential of an electronic wave packet oscillating in a strong field. The initial wave packet was chosen to be a Gaussian with a 1/e2 probability-density radius of ro = 1.92ao (ao=Borh radius) which has an overlap of 98% with the hydrogen 1s state. The wave packet was expanded in terms of the Volkov states, and in the zeroth-order approximation it was considered to become suddenly free of the Coulomb potential, evolving in the strong oscillating electric field. The first-order correction to the electron motion was evaluated based on a perturbative treatment of the interaction with the Coulomb potential. Implicit in the calculation are the assumptions of the barrier-suppression ionization (BSI) model1 and the wave-packet-spreading photoionization model.2 The conditions for applicability of this approach are examined.
Coulomb Explosion of Polyatomic Ions Induced by an Intense Femtosecond Laser Field
Authors: Cornaggia C. , Schmidt M. , Normand D.
Published: February 2023

The Coulomb explosion of CO2 into multicharged atomic ions is investigated following the ejection of up to 9 electrons by an intense femtosecond laser field at 790 nm and in the 1014-1016 W/cm2 intensity range. The identification of several fragmentation channels OZ+ + CZ'+ + OZ″+ is performed from triple ion correlation experiments. As already observed for the Coulomb explosion of N2 by a strong picosecond laser field, the measured kinetic energy releases are 50% weaker than the Coulomb repulsion energies calculated at the equilibrium internuclear distances. In addition, there is evidence for bending of the molecule during the explosion around the average linear structure. This experimental observation is assigned to bending vibrations arising from the violent laser-induced alignment of the molecule along the laser polarization direction before the explosion.
K-α spectroscopic measurements of MeV electrons from high intensity, picosecond laser plasmas*
Authors: Hammel B. A. , Beg F. N. , Bell A. R. , Dangor A. E. , Darrow C. B. , Fews A. P. , Glinsky M. , Holden M. , Lee P. , Norreys P. A. , Tafarakis M. , Tallents G. J.
Published: February 2023

In the Fast Ignitor concept, hot electrons generated by short pulse interaction, are absorbed in the compressed core of an ICF capsule, creating a hotspot for ignition.1 This scheme requires fundamental studies of the generation of fast electrons and ions and their transport through the plasma. Previous measurements, from the VULCAN laser, indicate that short pulse/solid target interactions at intensities of 2x1018 Wcm-2 result in 10% of the incident laser energy being transferred to fast ions with a mean energy of 1.3 MeV.2 In recent experiments, these measurements have been extended to intensities up to ~ 1019 Wcm-2. One arm of the VULCAN laser is used to produce short (0.7 - 2 ps) laser pulses of 1.05 μm light, with an energy of up to 30 J. P-polarized light is focused onto the target using an off-axis f/4 parabola, resulting in a ~ 25 μm diam. spot size. In this set of experiments, the energy and number of fast electrons was measured by observing K-α x-ray emission from layered targets, typically 25 - 50 μm of Pd on ~ 50 μn Sn.3 The characteristic K-α emission (20-25 keV) from the two layers was detected with an x- ray CCD camera, operated as a nondispersive spectrometer. These measurements indicated that electrons were generated with energies ~0.5 - 1 MeV. In addition to these spectroscopic measurements, fast ion emission was measured by CR-39 plastic nuclear track detectors, and collimation of the plasma flow was observed by Shadowgraphy and Schlieren optical probing, indicating the existence of large magnetic fields.
Coherence and Polarization of High Order Harmonics
Authors: Salières Pascal , L'Huillier Anne , Lewenstein Maciej
Published: February 2023

The understanding of high-order harmonic generation processes has improved tremendously in the last year, with the two-step semi-classical approximation developed by Corkum and by Kulander et al. [1]. In a high-intensity low-frequency regime, the generation of harmonics occurs through the following process : the electron first tunnels out the barrier of the atomic potential lowered by the intense field. It is then accelerated in the laser field. If its trajectory encounters the nucleus, harmonics can be emitted, following the electron’s recombination to the ground state. A quantum-mechanical theory which recovers and justifies these semi-classical ideas has been formulated by Lewenstein et al. [2]. In addition, this approach, which is analytical to a large extent, allows for a rather simple computation of the harmonic components of the dipole moment. Consequently, it can be easily used as an input to the integration of propagation equations [3], to simulate experimental conditions. In this contribution, we apply this theory to two different problems (1) the study of the spatial coherence (amplitude and phase) of the harmonics, (2) the dependence of the polarization and rotation angle of the harmonics on the ellipticity and intensity of the incident laser field. We compare with experimental results [4,5].
Femtosecond-pulse-driven, 10-Hz, 41.8-nm laser in Xe IX
Authors: Lemoff B. E. , Yin G. Y. , Gordon C. L. , Barty C. P. J. , Harris S. E.
Published: February 2023

In this paper, we report the observation of exponential gain at 41.81 nm on the 4d95d 1S0 - 4d95p 1P1 transition in Xe IX, as proposed in reference 1. A 10-Hz, circularly-polarized 800-nm laser pulse with energy of ~70 mJ and duration of ~ 40 fs is longitudinally focused to a peak intensity of > 3 ×1016 W/cm2 over a length of 8.4 mm in a differentially pumped cell containing 12 torr of Xe gas. Laser amplification was observed with an estimated gain coefficient of 13 cm-1 and a total gain of exp(11).
Generation of Tunable XUV Radiation by High-Order Frequency Mixing
Authors: Eichmann H. , Meyer S. , Nolte S. , Egbert A. , Wellegehausen B.
Published: February 2023

For the generation of tunable coherent radiation in the XUV spectral range nonlinear optical techniques have to be considered, as broadly tunable laser systems for this spectral range do not exist. Starting from tunable visible radiation, very high order processes are needed, which has become possible due to recent progress in non perturbative high-order harmonic generation. These processes have been intensively studied using different pump lasers, recent experiments using a Ti: Sapphire laser are for example given in Ref. 1. Although Ti: Sapphire lasers are broadly tunable, high peak power systems can practically not be tuned due to the complicated chirped pulse amplification scheme. A more flexible approach for the generation of tunable XUV therefore is to mix the radiation of a high power laser (ωP) with a less powerful but easily tunable light source (ωtunable), generating tunable photons at n·ωP ± k·ωtunable. A first high order mixing experiment of Nd:glass laser radiation with its second harmonic has been reported recently [2].
Mode Properties of a High Intensity Plasma Waveguide
Authors: Durfee C.G. , Lynch J. , Milchberg H.M.
Published: February 2023

Recently, we demonstrated a technique for optically guiding intense laser pulses, in which a plasma refractive index channel was produced through the hydrodynamic evolution of a laser breakdown spark in an ambient gas1. Here, we present measurements and calculations showing that our plasma light pipe can support, at high intensity, distinct electromagnetic mode propagation, as well as "leaky mode" propagation. As a reminder of the plasma dynamics involved, Fig. 1 shows a calculation of the response of 30 torr Xe to a pulse of peak intensity I=7x1013 W/cm2, spot size r0=1 μm, and duration τp=100 ps, pulse conditions typical of the ≲ 1 cm long axicon focus of our experiment1. Results from 2.2 cm long channels will be presented in a future paper. It is seen that a shock forms after some delay, after which an electron density minimum develops on axis.
Propagation of Intense, Ultrashort Laser Pulses Through Metal Vapor: Refractive Intensity Limits and Spectral Effects
Authors: Bolton P.R. , Ritchie A.B. , Stewart R.E.
Published: February 2023

Fundamental understanding of high intensity ultrashort laser pulse propagation through media is critical to applications such as harmonic generation and development of recombination type, xuv/x-ray lasers driven by optical field ionization. At relativistic intensities self-induced channeling or waveguiding effects have been predicted for cases of nonionizing or preformed plasma media 1. For many single pulse propagation experiments optical field ionization rapidly forms an ionization front at the leading edge of the pulse envelope traveling at relativistic speeds. It is important to understand formation mechasisms of this front and its effects on propagation of intense laser pulses. Strong field ionization can occur at rates exceeding the laser frequency. Such abrupt alteration of the propagation constant results in significant reduction of transmitted pulse energy on axis and in predominantly 'blue biased' shifts in the incident pulse spectrum2.
Investigation of long-range self-channeling of intense fs laser pulses in air
Authors: Korn G. , Braun A. , Liu X. , Du D. , Squier J. , Mourou G.
Published: February 2023

Laser powers exceeding GW level are easily obtained with chirped pulse amplification systems producing energies in the millijoule range with pulsewidths around 100 - 200 fs. We observed, for the first time, the formation of stable filaments by propagating high peak-power laser pulses in air. These pulses channel into filaments with typical diameters of 70 µm - 100 µm and propagate a distance as large as 30 m. They are the result of the combined effect of diffraction, nonlinear refraction, multiphoton ionization and dispersion. They form spatial and temporal solitons, i.e. light bullets [1]. These light bullets are robust. They can propagate in highly turbulent media without any noticeable change. These filaments may have interesting applications such as laser induced lightning [2] and laser pumped x-ray sources [3,4].
Kinetic effects in the wake of a short intense laser pulse in a tenuous plasma
Authors: Mora Patrick , Antonsen Thomas M.
Published: February 2023

Channeling of intense optical fields is an important challenge, with possible applications in the context of laser plasma accelerators or X-rays lasers. It has been shown in recent papers that self-channeled pulses are subject to severe instabilities of the Raman type which modulate the laser pulse and erode its tail [1-5]. The simulations of Refs. 1-4 were based on laser-plasma fluid models corresponding to a cold plasma, which prevents from treating situations where the plasma oscillations reach the wavebreaking limit. In addition the models contain a mathematical singularity at zero plasma electron density which prevents its use when the electrons are totally expelled from the axis of the laser propagation (electron cavitation). Such features are strong limitations of the fluid models in the high intensity regime.
X-Ray Resonant Two Photon Ionization of Inner Shell States
Authors: Norby J. R. , Edner S.E. , Evans S. H. , Hansch P. , Pawlicki J. R. , Van Woerkom L. D.
Published: February 2023

In recent years, considerable attention has been given to the production and characterization of x-rays bursts generated from solid density, ultrashort pulse laser produced plasmas.[1,2] These x-ray sources are very bright and extend from the VUV to hard x-rays which make them useful as novel light sources for numerous applications in material science, medicine, chemistry and physics. Strict characterization of these light sources is required for routine use.
Generation of Tunable High-Power VUV Radiation by Four-Wave Mixing in Xenon
Authors: Mossavi K. , Fricke L. , Liu P. , Momma C. , Wellegehausen B.
Published: February 2023

Frequency tripling, four-wave mixing and high-order nonlinear interactions of high-intensity laser radiation in rare gases and hydrogen are mechanism considered and used for the generation of coherent VUV, XUV and soft x-ray radiation. Currently, high-power laser systems in the IR, visible and UV spectral range provide the pump laser radiation for these nonlinear interactions. The XUV and soft x-ray spectral range is covered only by high-order interactions with low conversion efficiency. Consequently, considerable improvement could be introduced by high-power laser systems operating at VUV wavelengths, which would permit the generation of coherent radiation below 100 nm by efficient low-order nonlinear optical processes.
Characterization of Laser-Generated Hard X-Rays - Differential Absorption Imaging
Authors: Tillman Carl , Persson Anders , Wahlström Claes-Göran , Svanberg Sune , Herrlin Kristian
Published: February 2023

Tightly focused radiation of ultra-short pulses from a terawatt laser interacting with a high-Z solid target, gives rise to the formation of a hot micro-plasma which radiates x-rays with energies up to the MeV region [1]. We have used the 10 Hz table-top terawatt laser of the Lund High Power Laser Facility [2] to generate x-rays in this way. This laser is based on chirped-pulse amplification in titanium-doped sapphire and yields 150 fs pulses with a maximum power of 1.5 TW. Our experiments aim at the full characterization of the radiation as well as to practical applications.
Application of High-Order Harmonic Generation in Spectroscopy
Authors: Larsson J. , Altucci C. , L'Huillier A. , Mevel E. , Svanberg S. , Wahlström C.-G.
Published: February 2023

High-order harmonic generation, using high-power, short-pulse lasers has been shown to be an efficient way to generate coherent radiation in the extreme ultraviolet (XUV) and soft X-ray spectral regions. The characteristics of this radiation depends on the specifications of the exciting laser. Using, for example, the Ti:Sapphire laser system in Lund, which produces up to 150 mJ in 150 fs, we can generate very high-order harmonics. However, the pulse width of the generated harmonics is shorter than that of the fundamental, and the spectral width is large: e.g., for the 15 th harmonic, the resolution Δλ/λ, is only a few times 10-3.
Breakdown Threshold and Plasma Formation in Femtosecond Laser-Solid Interaction
Authors: von der Linde D. , Schüler H.
Published: February 2023

Matter is ionized and very rapidly transformed into a plasma when subjected to electrical fields exceeding some critical value. Laser-induced breakdown of transparent solids in the nanosecond and picosecond time regime has been studied in detail by Bloembergen and his coworkers [1], who showed that breakdown is caused by avalanche impact ionization. More recently, Downer and coworkers [2] have investigated femtosecond laser-induced breakdown in rare gases and concluded that field or tunnelling ionization is the dominant physical mechanism in gases. There is great current interest in hot, dense microplasmas generated during the interaction of very intense femtosecond laser pulses with solids, because these short-lived plasmas represent an interesting point source of ultrashort x-ray pulses. However, to the best of our knowledge, detailed studies of femtosecond laser-induced breakdown in solids and the initial dynamics of plasma formation are still lacking.
Quantitative Dielectric Properties of Solid Density Plasmas Measured by Femtosecond Ellipsometry
Authors: Ahn H. , Grimes M. , Lee Y. S. , Downer M. C.
Published: February 2023

Intense (1012 - 1014 W/cm2) femtosecond laser pulses create deep earth pressure-temperature conditions at a solid surface before hydrodynamic surface expansion occurs1. Photoexcitation of carbon, silicon, and germanium from melting fluence Fm up to approximately 30 Fm by femtosecond pulses induces a phase transition from their crystalline states to metallic liquid states within 1 ps followed by hydrodynamic surface expansion, with scale lengths much less than the incident probe wavelengths. Quantitative optical properties of the well-characterized fluid surfaces are determined by the time-resolved measurement of s- and p-polarized reflectivity at variable probe incident angles and excitation fluences, and at two different probe wavelengths. The surface expanding dynamics in 20 ps as well as the subpicosecond risetimes of reflectivity responses are important for accurate determination of optical properties of liquid states of materials.
Stimulated Emission Pumping(SEP) Spectroscopy of Propynal: An Example of “Sparse” IVR at High Vibrational State Density
Authors: Rogaski C. A. , Price J. , Wodtke A. M.
Published: February 2023

SEP spectra were recorded for the overtones of the C=O stretch(ν4) up to ν4=5 and one combination band with three quanta of C=O stretch and one quanta of in plane C≡C−C bend(ν9). The experiments were performed in a molecular beam, using two excimer pumped dye lasers with etalons for the PUMP and DUMP steps giving an experimental resolution of 0.04 cm-1. The resulting SEP spectra are simple and assignable to a near prolate asymmetric top. Anharmonic perturbations manifest themselves in the SEP spectra for ν4=4 and 5 as extra transitions. Anharmonic perturbations from unobserved levels appear in the rotational constants for ν4=2 and 3.
Stimulated Emission Pumping (SEP)1 Studies of Energy Transfer in Highly Vibratonally Excited Oxygen
Authors: Mack J.A. , Price J.M. , Wodtke Alec M.
Published: February 2023

Recent results have shown that highly vibrationally excited O2 is formed in significant quantities from the ultraviolet photolyis of ground state ozone. An important question for understanding the balance of O3 in the upper atmosphere is the lifetime of these highly vibrationally excited molecules which are proposed2 to be a photolytic source of odd oxygen atoms. In this work we report the rate constants for the collisional deactivation of SEP prepared O2(v"=18-25) by O2(v"=0), at temperatures of 295 and 395 K. The experiments are analogous to the "Pump", "Dump" and "Probe" studies carried out by Yang et al on NO.3 A pulsed tunable Argon Fluoride laser is used to "PUMP" O2 from

X
3

Σ
u
−

ground electronic state to a specific rovibrational level of the

B
3

Σ
g
−

excited electronic state via the well known Schumann-Runge bands4. A Xenon-Chloride pumped tunable dye laser system then stimulates, or "DUMPS" the O2 back to a specific excited rovibrational level of the ground electronic state. A second tunable dye laser system then "PROBES" the vibrationally excited O2 population by Laser Induced Fluorescence. By varying the time delay between the DUMP and PROBE lasers, the time dependant occupation of the prepared vibrational level is monitored. The collisional quenching rate constant for a given vibrational level is then determined from the pressure dependance of the lifetime. Implications of the measured rates for atmospheric chemical reactions are discussed.