bluuebunny/crossref_metadata_2025 huggingface dataset:
All-Optical Femtosecond Electron Acceleration
Authors: Kim J.-K. , Dodd E. , Umstadter D.
Published: February 2023

The recent development of compact high-peak-power lasers has spurred renewed interest in electron acceleration by the use of the ultrahigh-electric-field gradients of laser-driven plasma waves [1]. In fact, the field gradient of a plasma wave has recently been demonstrated to exceed that of an RF linac by four orders-of-magnitude (E ≥ 200 GV/m) and has been used to accelerate electrons with over 1-nC of charge per bunch in a low-emittance beam (1 mm-mrad) [2]. However, the energy spread of such beams is 100%, due to the method of injection, which is self-trapping of background electrons with random phases with respect to the accelerating buckets. In order to reduce this energy spread, it is generally thought that the required pre-acceleration can only be accomplished with a conventional RF linac. The difficulty is that the wakefield accelerating buckets are 30 fs in duration and the injection bunch must be a small fraction of that. The shortest pulses from laser-triggered photocathode RF guns are much longer, currently 0.5 ps in duration, and have jitters of more than a picosecond. Besides, RF linacs are large and expensive.
Backward and multi-echo field ionization by intense non-envelope "superpulses"
Authors: Shkolnikov P. L. , Kaplan A. E.
Published: February 2023

Recently, we have proposed two avenues to generating ultrashort (potentially, subfemtosecond) and intense (up to atomic fields) nonoscillating pulses: a high-repetition train of such pulses can be produced in multicomponent stimulated Raman scattering [1], and a single pulse ("electromagnetic bubble" -- EMB) or several of them can result [2,3] from the propagation of an initially broad unipolar pulse (half-cycle pulse -- HCP [4]) in an appropriate nonlinear medium. Such pulses could cause a substantial "shake-up" excitation or ionization of an atomic system within the time much smaller than any characteristic time of the system. These "superpulses" would open a new chapter in nonlinear optics and atomic and molecular physics, both as a new probing tool and a source of new effects. In the present paper, we consider one of them: backward and multi-echo field ionization [5].
Absorption of high intensity femtosecond laser pulses in solids and the production of suprathermal electrons
Authors: Feurer T. , Theobald W. , Sauerbrey R. , Uschmann I. , Altenbernd D. , Teubner U. , Gibbon P. , Forster E. , Malka G. , Miquel J.L.
Published: February 2023

Femtosecond high power laser systems offer the posibility to create plasmas with high electron densities and short scale lengths at relatively moderate energies. One possible application of such lasers is the recently proposed ’fast ignitor’ [Tab94]. The basic idea of this scheme is to seperate the compression phase from fuel ignition that leads to lower requirements on the driver lasers. After compressing the fuel by a factor of several hundred the ignition is performed by a burst of electrons that are created by an intense subpicosecond laser pulse. Such suprathermal electrons can be produced by several mechanisms. For laser intensities where the quiver energy equals or even exceeds the electron rest energy m
e
c2, relativistic effects become important. Now magnetic fields are no longer negligible and the longitudinal component of the Lorentz force accelerates electrons in the longitudinal direction [Wil92], The experiments were performed with the frequency doubled P102 laser at CEA/L-V in Limeil. The laser delivers up to 8 J in about 300 to 400 fs at 528 nm. The conrast ratio is better than 1012, therefore no preplasma, even at the highest intensity, is created on the target surface before the main pulse. The pulses were focused using an off-axis parabola leading to a minimum focal spot size of 5 μm. The central spot contained about 20 % of the full energy on target, the maximum intensity therefore was about 2 · 1019 W/cm2. The remaining part of the energy is distributed over a large spot.
Control of the X-Ray Emission from High-Intensity Ultrashort Laser Produced Plasmas
Authors: Teubner U. , Altenbernd D. , Förster E.
Published: February 2023

The control of the X-ray emission from high-intensity laser-produced plasmas is a subject of current interest (see, e.g., [1]) and requires an understanding of the laser-pulse absorption, thermal transport and the X-ray conversion processes. Both depend on various factors (i.e., target material, angle of incidence, laser intensity, laser pulse duration etc.) and, in particular, ultrashort laser pulses offer the opportunity to generate ultrashort X-ray bursts of high brightness. Furthermore, these short pulse laser-plasma X-ray emitters are of fundamental interest because they allow to diagnose the laser-plasma interaction under unique conditions.
Strong-Field Ionization of Molecules at 35 fsec.
Authors: Gibson G. N. , Li M. , Guo C.
Published: February 2023

The multiphoton ionization of molecules in strong laser fields has been investigated for over 10 years. However, the interpretation of the experiments has been complicated by the vibrational time scales of the molecules. Specifically, when a molecules is ionized to 2+ or higher, it becomes unstable and starts to dissociation. At pulse durations longer that 100 fsec the dissociation occurs while the laser pulse is still on which complicates the interpretation of the results. Thus, there is great interest in performing these experiments with as short a pulse duration as possible. To this end we have constructed an ultrashort-pulse laser system which delivers 0.5 mJ in 35 fsec with good beam quality. Ensuring the latter required the careful design of a multipass amplifier.
Rare Gas Clusters in Intense Laser Fields
Authors: Lezius M , Dobosz S , d’Olivera P , Meynadier P , Schmidt M , Rozet J-P , Vernet D
Published: February 2023

Recent experimental observations suggest that interaction of intense laser radiation with rare gas clusters jets provides an efficient source of X-rays and highly charged, energetic particles. Concerning the generation of X-rays the most prominent examples are the observation of: (i) Xe(M) an Kr(L) shell transitions with energies E up to 5keV reported by Rhodes and coworkers [1], (ii) non-coherent soft X-rays (E<500eV) on a nanosecond timescale reported by Perry and co-workers [2], and (iii) efficient high harmonic generation from Xenon clusters reported by Ditmire et al. [3], Regarding the production of energetic particles, Ditmire et al. [5] have reported Xeq+-ions with extremely high kinetic energies exceeding 100 keV when using 150fs pulses with intensities up to 1016W/cm2. Interestingly, Snyder et al. [4] were able to detect high charge states such as Xe20+ in a time-of-flight mass spectrometer after applying 350fs pulses at intensities of only 1015 W/cm2 to mixed He-Xe expansions. In a recent study of Argon clusters we have made very similar observations in a moderate intensity regime of 1014W/cm2 [6] using 30ps pulses at 1064nm. Our experimental results suggest that the underlying mechanism is efficient electron-ion collisional heating of cluster-sized nanoplasmas, similar to the interpretation proposed by Perry et al [2].
A debris-less laser-plasma source for EUV and XUV generation
Authors: Torres David S. , DePriest Christopher M. , Richardson Martin
Published: February 2023

We have previously reported the development of a laser plasma EUV source, using mass-limited water droplets, based on the 13 nm and 11.6 nm O5+ lines, for EUV projection lithography [1]. The spectrum from this source is shown in Fig. 1. A vital feature of this approach [2 ,3 ] is the incorporation of a target limited in mass to the minimum number of EUV atomic radiators required. This feature has advantages for EUV lithography and other applications in minimizing the collateral debris and allowing for continuous operation without the need for periodic maintenance of the optics or target material replenishment. Debris effects were quantified by the measurement of the reflectivity of a Mo/Si multilayer mirror, placed 4 cm from the source, for > 105 laser shots, Fig. 2. The < 1 % variation in reflectivity allows us to predict that the system could run for up to 108 shots without any major degradation in performance.
0.125 Terawatt Kilohertz Laser System
Authors: Backus Sterling , Durfee Charles , Murnane Margaret , Kapteyn Henry
Published: February 2023

Recently there has been significant progress in the development of high repetition rate, high peak power Ti:sapphire systems. [1] Many experiments in high field science require peak powers of 0.1-1.0 TW, and therefore this new generation of high-average power lasers will have a great impact on the quality and utility of experiments in this area. For example, recent experiments in high harmonic generation (HHG) have demonstrated that with sufficiently short laser pulses (~ 20 fs), laser energies of 2 - 10 mJ can be used to generate very high order harmonics, with photon energy up to 240 eV. [2,3] However, to date, the lasers used to generate very high-order harmonics have typically been low repetition-rate (10 Hz) systems. A kHz repetition-rate laser with sufficient peak power for high harmonic generation would result in a 100 times increase in x-ray flux, with vastly improved signal-to-noise ratios. In addition, other processes such as low-order harmonic generation in gases[4] become even more efficient with millijoules of laser energy, and will be capable of generating sufficient flux for application experiments in chemical dynamics.
Barrier-Suppression Ionization of Complex Atoms and Diatomic Molecules
Authors: Krainov V.P.
Published: February 2023

Theory of tunneling ionization of atoms and atomic ions by strong low- frequency laser radiation was developed in Ref.[1] (so called ADK- approach). This theory is based on the conception of the quasi-stationary electromagnetoc field producing tunneling ejection of valence electrons. A complex atom or an atomic ion is considered in the frames of quantum defect method; its wave function is an asymptotic wave function at the large distances from the atomic core. In Ref.[2] the angular and energy distributions of ejected electrons in tunneling ionization were obtained.
Precision Tests of Laser-Tunneling Ionization Models
Authors: Buerke B. , Knauer J. P. , McNaught S. J. , Meyerhofer D. D.
Published: February 2023

We have used a 1.5 ps, 1 μm laser with intensities up to 1018 W/cm2 and two electron spectrometers to test laser-ionization models in the tunneling regime.
Dynamic Holographic Method of Imaging Phase Objects
Authors: Brody Philip S. , Leavitt R. P.
Published: February 2023

We describe a new method of imaging phase objects using real-time dynamic holography. In the first step of this process, a volume hologram is produced in a single crystal of barium titanate by a coherent light beam being directed through a thin phase-distortion plate and then into the crystal. After the volume hologram forms, a second beam of short duration is sent into the crystal where it scatters off the hologram, producing a back-scattered beam. This beam, which is the phase conjugate of the original beam that produced the hologram, then passes through the phase-distortion plate after the plate has been shifted a small distance in a direction normal to the optical axis. This shift results in an imperfect removal of the phase aberration [1,2,3] in the back-propagating beam and hence, produces intensity variations in the optical field beyond the plate. These are images which show gradients in the phase object’s optical path length which occur along the direction of the shift. Although in principle these images can be obtained using the methods of off-axis holography, the process we use has no equivalent in conventional holography. In particular, by employing the self-phase-conjugating phenomenon in barium titanate [4,5,6] we are able to use a single beam and the rather simple arrangement shown in figure 1 to generate gradient images of different phase objects.
Holographic Interferometric Study of Heat Transfer in Rectangular Cavities
Authors: Patil N.G. , Prasad C.R. , Arakeri V.H.
Published: February 2023

Optical techniques like interferometry, shadowgraphy and schlieren photography find common use in investigations1 of fluid flow and heat transfer. The change in refractive index of the fluid caused by temperature and density changes is the basis of these methods. These non-intrusive probes have several advantages over mechanical probes such as, very high spatial and temporal resolution, absence of probe induced perturbations, etc. Mach-Zehnder interferometers are frequently employed for analysing heat transfer in fluids. But the need to maintain nearly identical path length in the two limbs (hence requires two identical cells with optically flat windows, one cell being used for compensation) has limited its application considerably. Holographic interferometry, on the other hand is especially well suited to studies with transparent fluids since there is no need for special windows or cells.
Residual Stress Determination Using Holographic Interferometry
Authors: Nelson Drew V. , McCrickerd John T.
Published: February 2023

Residual stresses are present in virtually every part as a result of manufacturing processes such as welding, casting, machining, injection molding, etc.. These stresses can have a strong influence on the resistance of parts to failure by fatigue or stress corrosion cracking or by loss of dimensional stability. In general, such stresses cannot be calculated and must be determined experimentally.
Computer Generated Matched Filters by e-Beam Lithography
Authors: Duthie J. G. , Kennedy L. Z. , Gregory D. A.
Published: February 2023

E-beam lithography as a means of realizing computer generated holograms has been discussed by Freyer et al. (1) and by Athale et al. (2). The main advantages of e-beam techniques are the capabilities of focusing electron beams of very narrow dimensions (typically 0.1 to 10 microns) and positioning these beams very accurately on the writing surface. Ultra flat glass plates, plated with chromium then coated with a thin layer of electron sensitive photo-resist, form the writing surfaces. Exposure of the material to the computer located e-beam is followed by development of the photo-resist, and then by etching of the exposed chromium to produce a binary pattern on the glass substrate. Suitable patterns written in this way on the chromium provide a convenient means of achieving holographic elements.
Phase Manipulations in Synthetic Holography
Authors: Wyrowski Frank , Hauck Richard , Bryngdahl Olof
Published: February 2023

In the construction process of computer-generated holograms (CGHs) it is possible to introduce and influence the phase in several ways: superpostion of a suitable phase variation onto

(1) the object data and/or

(2) the hologram itself.

In contrast to optical holography it is easy to realize any desired phase distribution in computer holography.
Design and Simulation of Synthetic Hologram Lenses in Uniaxial Media
Authors: Turk Harris , Froehlich Fred F.
Published: February 2023

The aberrations of Fresnel type grating lenses immersed in uniaxial waveguides are studied. Lens designs which account for the anisotropy and which are aplanatic are presented.
Systematic design method for holographic zone plates with aberration corrections
Authors: Ono Yuzo , Nishida Nobuo
Published: February 2023

Holographic zone plates are systematically summarized, based on the generalized holographic zone plate proposed to improve holographic laser scanners, including their extension.
Optimized Holographic Scanner with Diode Lasers
Authors: Ishii Yukihiro , Murata Kazumi
Published: February 2023

Diode Lasers are compact and potentially reliable for wide uses of digital audio disk. It is desirable to make a holographic grating scanner on dichromated gelatin (DCG) [1] at a wavelength that is different from the readout wavelength of diode laser because DCG suitable for a volume-phase holographic optical element (HOE) [2] is insensitive to exposures at red Light. The major problems associated with making this HOE are that the aberration due to a recording-readout wavelength shift is seriously existed and that the scan spots diffracted from scanner at different aperture inputs suffer from the aberration.
Maximizing Diffraction Efficiency of Bleached, Time-Integration-Exposure, Silver Halide Holograms
Authors: Rhodes William T. , Stroud Robert , Gaynor Edwin S.
Published: February 2023

Time-Integration holograms, where the exposure pattern is recorded as a sequentially applied sum of individual fringe patterns (either sinusoidal "Young’s" fringes or Gabor zone plates), suffer from poor diffraction efficiency and, consequently, low signal-to-noise ratio on reconstruction [1,2]. The reason is straightforward: The total exposure pattern, as in the case of incoherent holography [3], has a low signal-to-bias ratio when many contributing exposures--each bringing its own bias with it--are applied. Since the recorded signal exposure is low compared to the bias exposure, the signal variations in the wave amplitude transmittance function of the processed hologram are small, and diffraction efficiency is therefore low. At the same time, noise in the reconstruction, determined by such sources as dust- and film-grain-scattered light, remains at an essentially constant level.
Computer Generated Holographic Optical Elements for Optical Interconnections of Electronic Integrated Circuits
Authors: Feldman Michael , Guest Clark
Published: February 2023

As electronic integrated circuit technology advances, problems of signal communication play an increasingly critical role [1]. Transmission of signals within a single chip and between chips presents limitations in power dissipation and timing. Replacing critical electronic signal transmission lines with optical signal paths can result in the following advantages: 1) Fewer layers of metalization and polysilicon on the chip; 2) Elimination of clock skew due to limited electronic signal transmission speed; 3) Faster point to point communication; 4) Reduction of the necessary electrical pinouts per chip; 5) Direct access to locations away from the perimeter of the chip; 6) Access to critical signal injection points for testing; 7) Custom configuration during assembly to bypass failed elements; and 8) A path toward dynamic reconfiguration of processing element connections.
Phase sensitive analysis of electron holograms
Authors: Yatagai Toyohiko , Ohmura Katsuyuki , Iwasaki Shigeo
Published: February 2023

Holography has been used in electron microscopy since the field emission electron microscope was developed.[1] Tonomura et al described the interference microscope based on the electron holography to evaluate microscopic distribution of the magnetic field. [2] To gain high sensitivity the use of the optical phase multiplication technique was discussed so as to obtain 10 time magnification of the reconstructed phase. [3] Recently Takeda et al applied the FFT method of the subfringe analysis for electron holographic fringes.[4] They mentioned phase variations much smaller than 2 π could be detected without recource to optical reconstruction or optical interferometric measurements.
Coaxial Fiber Delivery of Object and Reference Beams for Pulsed Ruby Laser Holography
Authors: Marhic M. E. , Raviv G. , Bjelkhagen H. , Epstein M.
Published: February 2023

The fiber delivery of the reference and/or the object beam may be useful or even required for a number of holographic applications. This is particularly true for endoholography, or holographic recording of internal cavities1,2. The design and utilization of such fiber systems can become rather challenging if single-mode fibers and pulsed lasers are used.
Interferometric Imaging Through Atmospheric Turbulence
Authors: Voelz David G.
Published: February 2023

A variety of unconventional techniques for imaging targets using coherent (laser) illumination have recently been proposed and analyzed.1,2 These techniques were primarily derived and developed for the observation of objects, such as spacecraft, at long distances through atmospheric turbulence. Several of the techniques exploit the idea of making 2-D spatial measurements of the coherent optical wave front at the receiver plane. In this paper we briefly review two laser imaging techniques that utilize wave front measurements and we discuss some of the merits, limitations and application of the techniques. References are provided for further investigation.
Synthetic Aperture Holography for Three Dimensional Incoherent Imaging
Authors: Rosen Joseph , Yariv Amnon
Published: February 2023

The Michelson stellar interferometer (MSI)[1] is used for measuring the shape of planar objects which emit quasi-monochromatic, spatially incoherent light. Its principle of operation is based on measuring interference patterns obtained by two pinholes of the Young experiment. The fringes’ visibility, and phase, versus the gap between the pinholes is equal to the complex degree of coherence. According to Van Cittert-Zernike theorem, the complex degree of coherence is proportional to the Fourier transform of the source’s intensity distribution[1]. Thus, measuring the complex degree of coherence versus pinholes separation and performing inverse Fourier transform yield the image distribution of the source.
A technique for control of crosstalk noise in volume holography
Authors: McDonald Mark , Neifeld Mark A.
Published: February 2023

Volume holographic data storage offers many potential advantages over conventional magnetic mass storage including high parallelism, fast access, and high storage capacity. The high capacity of volume holography is partially attributable to the Bragg selectivity of thick media. For angularly multiplexed uniform gratings in media of finite thickness the Bragg diffraction efficiency has a well known sinc2(ϑ) dependence vs. dephasing (i.e., dephasing ϑ ∝ Δθ reconstruction angle for angular multiplexing). When a desired hologram is read out at a particular reconstruction angle, holograms stored at other angles will also be reconstructed, albeit with much lower efficiency. The superposition of the undesired reconstructions is known as crosstalk and this phenomenon has been investigated by several authors1,2. Such crosstalk will result in noise on the data detected from the desired hologram and can be diminished by reducing the density of the angular multiplexing2. Thus, crosstalk forms an upper bound on volume holographic memory density and capacity in the limit of small fixed noise sources. In this paper, we will consider the storage capacity limit imposed by crosstalk for a grating that is uniform throughout the finite medium and compare this with the limit obtained when the grating is apodized to reduce crosstalk. We will also show experimental verification of the apodization effect.
Characterization of Volume Holographic Associative Searching
Authors: Richling Keith G. , Mitkas Pericles A.
Published: February 2023

Volume holographic memories are a prime candidate for the storage of large relational databases because of their large storage capacities1 and their associative nature2,3. We have successfully used a computer-controlled angular-multiplexing photorefractive-based volume holographic memory to store database records, search through the records, and recall the information stored in the memory. In this paper we present and discuss experimental results where the memory is accessed in its associative mode.
Construction of a Holographic 3D Printer using Silver-Halide Filmplates
Authors: Andreassen R. , Birkeland O. , Grahl-Nielsen T.E. , Olsen K.E. , Singstad I.
Published: February 2023

This paper reports on the production of multi stereo hologram from a series of computer images with different camera views which are copied onto a LCD panel, one image view at a time. The LCD images serves as an object in a conventional holographic set up, and two production methods are considered, two-step reflection hologram, produced from a master hologram and one-step reflection hologram.
Applications of Holography for Femtosecond Time-Domain Processing
Authors: Weiner Andrew M.
Published: February 2023

In this talk we discuss Fourier optics methods for signal processing in the femtosecond time domain [1]. Applications include pulse shaping and waveform synthesis, storage, recall, and matched filtering of ultrafast optical signals, time-to-space and space-to-time conversion, and ultrafast transmultiplexing for data format conversion.
Photopolymer Materials for Holography
Authors: Steijn Kirk W. , Gambogi William J. , Trout T. John
Published: February 2023

Interest in holograms as diffractive optical elements began with the early recognition of the correspondence of transmission holograms and Fresnel zone plates.1,2 Optical designs based on holographically-generated optical elements (HOEs) and the extension of computer-based design programs to holographic gratings appeared in the late 1960s.3,4,5 Use of HOEs in systems was limited, however, in part due to complicated processing and lack of environmental stability in available materials. Recent developments in polymeric materials for holography invite reconsideration of HOEs for emerging applications where unique function, weight, light efficiency and cost are premium considerations. OmniDex® Holographic recording films (HRFs) developed at DuPont provide benefits for the manufacturers of HOEs and optical systems that include excellent optical performance, dry processing, environmental stability, and mass reproduction. This paper reviews the holographic properties of these films and gives examples of simple HOE components.
Holographic Recording Kinetics in Photopolymer Media
Authors: Kovalenko E. , Sharangovich S. , Zelenskya T.
Published: February 2023

Holographic information recording in photopolymer media is of great importance and lately has been under the thorough study [1-3]. It is found that with these materials there are some important features in comparison with the recording in photorefractive crystals. First, it is necessary to take into account the dynamic in behaviour of many medium components, involved into the process of the of the radical polymerization [4]. Second, while describing the kinetics of a holographic recording one should take into consideration medium average parameters changing in time. The diffusion processes of interaction components and also of inert component are of great importance [2]. Finally, the considerable variations of kinetic coefficients such as medium viscosity, diffusion coefficients, break reactions parameters of polymeric chain in polymerization process are also very important for description of kinetics recording [3]. All these effects require complex non-linear equations. In this work the analytical solution of the problem about the holographic information recording in photopolymer media for the cases of relatively small light diffraction on the recorded grating, the effects of self diffraction being neglected and the light field being given.
Modeling Issues for the Design of Volume Holographic and Surface Relief Grating Structures
Authors: Kostuk Raymond K. , Haggans Charles W. , Campbell Eugene , Kim Tae Jin
Published: February 2023

Diffractive optical components are being used in a greater number of micro optical systems for data storage, optical interconnects, and fiber optic applications. The design of diffractive elements not only requires a detailed understanding of vector diffraction theory, but knowledge of the materials and processing techniques used for fabricating gratings. Models and design programs must be modified to include variations from ideal grating structures. Modeling data must also be collated into a form which points to promising solutions and allows for design optimization.
Computer generated holographic photonic band gap structures designed using inverse scattering techniques
Authors: Chang S-M. , Pommet D.A. , Malley L. , Fiddy M.A.
Published: February 2023

Inverse synthesis techniques are important for development of diffractive optical elements. For non-periodic media, approximations can be made which allow estimates of the scattering permittivity distribution to be found. Over the last 15 years [1,2,3] we have moved from trying to interpret the most restrictive yet computationally simple of these approximations, the linearizing first Born and Rytov approximations, to the development of techniques which can be applied to both strongly scattering media as well as nonlinear (e.g. χ3) structures. We have also applied these methods to real experimental data as well as simulated cases, as such work has wide ranging uses in fields as diverse as medical and geophysical imaging, as well as the design of optical components. Emerging from these studies is a clearer understanding as to how the differential cepstral method (see [4]) and distorted wave methods can be integrated in order to synthesize structures which are both strongly scattering and which have prescribed optically controllable scattering patterns.
Ray-tracing Approach to Computer-generated Holography with Detour Phase Coding for Precision 3D Beam Patterns
Authors: Chang Shih-Ming , Pommet Drew A. , Fiddy Michael A. , Lin Freeman C.
Published: February 2023

A ray-tracing method with a detour phase coding scheme [e.g., 1] is developed to design on-axis and off-axis computer-generated holograms (CGHs). To date, the usual Fourier-transform approach and coding schemes published by others has been restricted to designs for the reconstruction of two-dimensional (2D) light patterns or "objects" (e.g., [1-3]). The ray-tracing method presented here is readily employed to design CGHs for both 2D and 3D reconstructions and these objects can be situated in either Fresnel or Fraunhofer regions. The ray-based approach simply calculates the optical path length from any chosen point in the object domain and computes the phase of the spherical wavefront from a coherent point source at the recording plane. This approach also conveniently permits various incident and reference beam functions to be modeled, as well as quite complex beam shapes, such as snake beams in the reconstruction regime. While sometimes computationally more intensive than a Fourier-based method, we will show how this approach is highly flexible and allows for very precise location of original object points. A further advantage is that transparent and semi-transparent objects can be easily specified [4].
High Intensity Picosecond Pulse Interaction Experiments
Authors: Richardson M.C. , Chen H. , Chuang Y-H. , Delettrez J. , Epstein R. , Kessler T. , Meyerhofer D.D. , Uchida S. , Yaakobi B.
Published: February 2023

The development of intense short pulse (⪝ 1ps) laser radiation focusable to extremely high intensities makes possible the investigation of many new regimes in atomic, plasma and nuclear physics. At LLE a high power Nd:glass laser system based on chirped pulse amplification(1) is being assembled for a variety of interaction experiments at focused intensities of up to 1018 W/cm2. Plans are underway to generate even higher intensities with a second laser system having an output energy in the 100 J range, which will also be used to study short-wavelength x-ray laser schemes.
The Interaction of Intense Laser Pulses in Plasmas
Authors: Sprangle P. , Esarey E. , Ting A.
Published: February 2023

The interaction of ultra-high power laser beams with plasmas is rich in a variety of wave-particle phenomena. These phenomena become particularly interesting and involved when the laser power is high enough to cause the electron oscillation velocity to become highly relativistic. Some of the interesting laser-plasma processes which will be discussed include i) the production of large amplitude plasma waves which could be used to accelerate electrons to ultra-high energies; ii) the possibility of modifying the plasma refractive properties in order to achieve optical guiding of a laser pulse, thus preventing the laser pulse from diffracting; and iii) the possibility of producing coherent radiation at harmonics of the incident laser frequency.
Spectral Shifting of Intense Femtosecond Pulses During Strong Field Ionization and Plasma Recombination
Authors: Downer M.C. , Wood Wm. M. , Banyai W.M. , Trisnadi J.
Published: February 2023

Highly amplified femtosecond pulses permit the study of atomic ionization in superintense light fields on a time scale shorter than the escape time of electrons from the interaction region or the recombination of ionized species. Most recent studies of strong field femtosecond ionization have utilized photoelectron spectroscopy at low gas pressures (~10-7 torr)1. We utilize a complementary experimental method with unique capabilities, namely the spectral blue shift which is caused by the ultrafast refractive index decrease which occurs when a plasma is created within 1 to 20 optical cycles during the pulse2,3. Accurate analysis of such blue shifts requires modelling based on ionization rates calculated from a Keldysh theory4. Because of the ultrashort pulse duration (< 90 fs.), atomic collisions and plasma expansion play no role, compared to experiments with picosecond and longer pulses. Moreover, we have shown3 that in a sufficiently tight focus geometry, contributions from non-ionizing χ(3) processes (e.g.white light continuum generation5, self focusing), which cause both red and blue shifts, are suppressed relative to plasma generation effects2. Thus detailed observation of blue shifts provides a clean diagnostic of strong field ionization which complements photoelectron spectroscopy in testing theories of superintense laser-atom interactions. In addition this technique offers two additional capabilities not easily achieved by photoelectron spectroscopy: 1) It lends itself readily to femtosecond pump-probe experiments, which we report here for the first time. Such experiments allow us to map ionization rate within the temporal profile of a strong pump pulse. In addition, they allow us to measure plasma dynamics (e.g. recombination, expansion) following the ionizing pulse, manifested as a time-delayed probe red shift. 2) In addition this technique is compatible with gas pressures ranging from 0.1 atm. to supercritical densities (> 100 atm.), allowing us to study ionization, recombination, and expansion dynamics at densities in the range (1019 to 1022 cm-3) relevant for X-ray recombination lasers6. At supercritical densities, both forward and backward propagating blue-shifted waves, as well as plasma-confined DC magnetic fields, are generated7. In addition plasma heating7 and relativistic loss mechanisms8 become important. Initial results in this high density regime will be presented.
Simulations of Intense Laser Beams Interacting with Gases and Solids
Authors: Olson Gordon L.
Published: February 2023

The Los Alamos Bright Source Lasers (LABS I and II) are discussed else-where in this conference1 and in previous publications.2 LABS I generates subpicosecond pulses of 5 eV photons with peak intensities of a few 1017 W/cm2, while LABS II operates with shorter pulses at 4 eV and reaches intensities one order of magnitude higher. These lasers have been focused onto gas and solid targets. The purpose of this paper is to discuss numerical simulations of these experiments.
Generation of Picosecond Laser Pulse by GEKKO-MII Nd:Glass Laser System and its Application to X-Ray Generation
Authors: Shiraga H. , Yamakawa K. , Barty C.P.J. , Nishio M. , Kato Y.
Published: February 2023

An output power of 13 TW in a 3.5 ps pulse at 1.052µ m was generated by chirped pulse amplification using GEKKO-MII Nd:glass laser facility. Solid targets were irradiated for investigation of x-ray generation at the laser intensity higher than 1017 W/cm2.
Ultra-high Intensity Lasers and Experiments at Los Alamos
Authors: Schappert G. T. , Casperson D. E. , Cobble J. A. , Jones L. A. , Kyrala G. A. , Lee P. H. Y. , Nichols T. D. , Taylor A. J. , Tallman C.R.
Published: February 2023

Recent developments in excimer laser technology have made it possible to achieve irradiances on target approaching 1020 W/cm2. Oscillators capable of generating subpicosecond pulses and amplifiers capable of amplifying these pulses without significant pulse stretching or optical distortion are now available. Hence ultrashort pulses of modest energies, focused to nearly-diffraction-limited spots a few microns in diameter, result in an irradiance in excess of 1019 W/cm2. Such laser systems typically operate at a repetition rate of several Hz, ideal for experimental programs.
Fourier Transform Nonlinear Spectroscopies
Authors: Felker P.M. , Hartland G.V. , Corcoran T.C. , Connell L.L. , Henson B.F. , Venturo V.
Published: February 2023

There exist a variety of Fourier spectroscopies based on linear interactions with light. These can be powerful tools in high resolution molecular spectroscopy. Recently, Fourier transform version of nonlinear Raman-type spectroscopies have also been developed. These methods will be described and experimental results obtained by them will be presented.
High Resolution Fourier Transform Raman Spectroscopy of Gases
Authors: Bendtsen Jørgen
Published: February 2023

Raman spectra of molecules in the gasphase yield information about the energy of the rotational and the rotational-vibrational states. This information may more easily be obtained from absorption spectroscopy in the microwave and infrared region, but the less restricted selection rules governing the Raman transitions yield information not measureable in absorption.
High-Resolution FT Spectroscopy of the Violet Transitions in the Nitrogen Molecular Ion N 2 +
Authors: McDowell Robin S. , Krohn Burton J. , Palmer Byron A. , Hof Douglas E. , Manning Thomas J. , Winefordner James D.
Published: February 2023

The Los Alamos Fourier transform spectrometer has been used to study the following four near-ultraviolet transitions of nitrogen molecules in a helium inductively-coupled plasma torch:

N
2
+

 

1NG: B

2

Σ
u
+

−

X
2

Σ
g
+

(
0
−
0
)

and N22PG: C3Πu- B3Πg (0-2, 0-1, 0-0). Molecular constants for the

N
2
+

band have been determined using combination differences and polynomial fits, and will be compared with published values. These data demonstrate the usefulness of this instrument for molecular spectroscopy.
Monitoring of Stratospheric Trace Gases in the Arctic with a New Mobile FTIR Spectrometer
Authors: Notholt J. , Keens A. , Wang S. , Johnson T. J.
Published: February 2023

Interest in atmospheric chemistry has risen dramatically in the last few years. Topics such as the ozone hole, greenhouse effect with global warming, and climatic change have all become household words. High-resolution FTIR clearly suggests itself as a method of choice for research in this field: The high resolution allows individual rotational-vibrational lines of atmospheric gases to be probed and trace gas concentrations thereby be quantified. Unambiguous quantitative identification of individual species is critical in order to characterize and model the changes in the atmosphere. Also, due to the reduced effect of intermolecular line broadening at lower pressures, the absorption linewidths become narrower at higher altitudes. With sufficient spectral resolution, the composite line profiles can thus be deconvoluted to yield vertical profiles of individual gases.
Subtractive Cancellation of Multiplicative Noise using the Complementary Output Channels of a UV/visible Fourier Transform Spectrometer
Authors: Salit Marc L. , Winchester Michael R. , Wythoff Barry J. , Travis John C.
Published: February 2023

In any spectral domain, the appeal of FTS results from the high resolution available for modest dimensions, the wavelength accuracy, and the simultaneous acquisition of a broad spectral range of data. However, for reasons related to the limiting noise, the "multiplex advantage" enjoyed in the infrared is degraded in the UV/visible to the extent of becoming a "multiplex (or Fourier) disadvantage" for certain combinations of noise source, spectral peak intensity, and spectral density.1
Application of Fourier Transform Optical Spectromety to the Preparation of a Spectral Atlas for Inductively-Coupled Plasma Optical Emission Spectrometry
Authors: Travis John C. , Salit Marc L. , Winge Royce K. , Eckels David E. , Weeks Stephan J.
Published: February 2023

Inductively-coupled plasma optical emission spectrometry (ICP/OES) has become the primary tool of analytical atomic spectrometry over the past two decades.1 The success of the ICP may be largely attributed to a torch design which permits a droplet spray from a sample solution to be injected along the axis of the plasma, and from the ability of the plasma to evaporate the solvent, dissociate most chemical species, and render highly excited populations of free atoms and atomic ions. Species concentrations are determined by ratioing measured spectral line intensities to those for known "standard" solutions, and/or by adding quantitative "spikes" to the sample. Under normal operating conditions, the viewing zone utilized for chemical analysis is near local thermodynamic equilibrium (LTE), with an excitation temperature of about 6300K and an electron density of about 1016 cm-3. The high excitation energy is a mixed blessing, providing high sensitivity for about 70 elements, along with the possibility of spectral interferences from concomitant species. Reasonably high optical dispersion is employed to minimize spectral interferences, and interferences are normally characterized by line profiling and spectral tables.
Emission Spectroscopy of Transient Molecules
Authors: Bernath Peter
Published: February 2023

The CN free radical is commonly observed in flames, in the combustion of propellants and in a variety of astronomical sources. The A2Π-X2Σ+ and the B2Σ+-X2Σ+ electronic transitions were observed in a corona-excited supersonic jet expansion source using methyl azide (CH3N3) in helium. The rotationally cold but vibrationally and electronically hot spectra of CN were recorded at high resolution during the course of our work1 on CH3N.
Making Use of the Argon Lines in Hollow-Cathode Spectra
Authors: Whaling W. , Brault J. W.
Published: February 2023

This work was undertaken to obtain a reasonably complete list of the Ar lines that appear in hollow-cathode (HC) spectra. The older Ar linelists do not have the precision one wants in analyzing FTS spectra, and the available interferometric values - notably the beautiful Fabry-Perot measurements of Norlen1 - include only a selection of identified lines of wavelength <9800 Å.
Plasma-induced cross-phase modulation and its application to visible and VUV femtosecond pulse characterization
Authors: Le Blanc S. P. , Qi Z. , Sauerbrey R.
Published: February 2023

Understanding the interaction of an intense ultrashort laser pulse with
an optical-field-ionized plasma is of fundamental interest for
recently proposed x-ray laser schemes [1] and the guiding of optical
pulses in plasma channels [2]. Because field ionization rates depend
strongly on the laser intensity which varies in both time and space,
both the spatial and temporal properties of field-ionized plasmas must
be considered when characterizing such plasmas by ionization induced
spectral blueshifting. Spectral blueshifting occurs when an intense
laser pulse propagates through a gas and field ionization causes a
rapid increase in the electron density along the propagation path.
Temporal variation in the electron density causes plasma-induced
self-phase modulation, and the spectrum of the laser pulse consists of
blueshifted components [3]. In previous work, we have investigated the
spectral characteristics of spectral blueshifting using a femtosecond
KrF excimer laser pulse focused to peak intensities of 1014
Wcm-2 in high pressure rare gases [4]. Here, we present the
results of two-color pump probe experiments to investigate the
temporal and spatial characteristics of spectral blueshifting, and
demonstrate new techniques for visible and VUV ultrashort pulse
characterization based on plasma-induced cross-phase modulation.
High-Order Harmonics Emitted from Low-Density Gas Targets
Authors: Meyerhofer D. D. , Chaloupka J. L. , Peatross J.
Published: February 2023

The far-field profile of high-order harmonics produced during high-field, laser atom interactions are determined by the atomic response and the phase-matching in the medium.1-5 We have continued our studies of the harmonic far-field profiles which are designed to separate the different phase effects that determine the harmonic far-field profile. The primary phase effects are the phase-mismatch introduced by the radius of curvature of the phase front of the laser and the harmonics in the focus, the phase shifts from the group-velocity dispersion due to the indices of refraction of the atomic medium and of free electrons, the Guoy phase-shift through the focus, and the phase of the atomic dipole response. The Guoy phase-shift dominates the amplitude of the harmonic emission at the exit of the medium, but it is independent of radius and, hence, does not affect the far-field profile. By suitable choice of the experimental parameters, we have separated the atomic response, GVD, and the radius of curvature.
Nonlinear Effects on the Propagation and Absorption of Ultra-Intense, Short Laser Pulses in the Fast Ignitor Fusion Concept
Authors: Wilks S. C. , Kruer W. L. , Young P. , Hammer J. , Tabak M.
Published: February 2023

The Fast Ignitor1 is a novel approach to inertial confinement fusion that employs two types of ultra-intense, short laser pulses.2,3 The basic idea in this approach is to couple the energy available in an ultra-intense laser pulse, via energetic electrons, into a precompressed target in a time short compared to the disassembly time. For electrons with energy ~ 1 MeV, the electron range is about equal to the necessary alpha particle range. These electrons then initiate a localized burn in the core, which can then propagate to the rest of the fuel. The potential benefits of this scheme are the use of less energy for ignition and less stringent requirements on implosion symmetry, relative to currently used ICF schemes. As currently considered, the Fast Ignitor requires two different types of short laser pulses. First, a beam of roughly 10-100 ps in duration and Iλ2 ≤ 1018 W μm2/cm2 is used to create a channel through the corona of a precompressed pellet. Next, an ultrashort pulse is sent down the channel (1-10 ps, Iλ2 ≥ 1019 W μm2/cm2)to generate the energetic electrons which transport to the compressed core.
Electron Energy Distributions In Optically Ionized Helium Plasmas
Authors: Glover T. E. , Falcone R. W.
Published: February 2023

Recently, several authors have proposed that x-ray lasers pumped by rapid electron-ion recombination are feasible if cold electrons can be produced from the interaction of a high-intensity laser pulse with a gas sample [1]. Burnett and Corkum [2] have used a model based on tunneling ionization and the resulting drift energy (the quasistatic model) to predict the form of the electron energy distribution function arising from such an interaction. Initial measurements of electron energy distributions were performed at low gas density (< 1011 /cc) with conflicting results [2,3]. Recombination lasers require relatively high gas density (> 1017/cc) and additional heating mechanisms may modify the distributions measured at low gas density [4].
Forward Ponderomotive Acceleration of Electrons from the Focus of a High-Intensity Laser
Authors: Meyerhofer D. D. , Moore C. I. , Knauer J. P.
Published: February 2023

The quiver motion of an electron in a high-intensity laser field becomes relativistic (β= v/c ~ 1) at high-field strengths. This relativistic motion can lead to the emission of second and higher harmonics of the laser field1 and to forward ponderomotive acceleration of the electrons emerging from the laser focus. We will present the first observations of forward ponderomotive acceleration of the electrons born by field ionization at the center of the laser focus.