bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal Design of Lens Duct for End-Pumped Solid-State lasers
Authors: Fu Rulian , Wang Guangjun , Zhang Lingqian , Wang Zhaoqi , Ba Enxu , Mu Guoguang , Hu Xinhua
Published: February 2023

For a typical laser diode bar, in slow axis plane its length is 10mm and the divergent angle is about 10°, while in fast axis plane the width is about 1 μm and the divergent angle is about 30° ~ 50°.So when LD acts as a pumping source, a coupling system is necessary to deliver the pumping light into laser rod. Coupling method currently adopted include: aspheric lens series[1], gradient index lens[2], optical fiber[3] and directly[4] coupling. But their efficiencies are normally lower. A new type of coupling system—lens duct[5,6,7] was used in recent years , we optimized its parameters with geometry optical method.
Study of Kilowatt Pulsed Laser with Tuning Pulse Width and Pulse Rise Time
Authors: Yao J.Q. , Yu Y.Z. , Wang X.L. , Wu F. , Zhang R. , Zhou G.H. , Xiao Y. , Yang Y.M. , Li J.K. , Yu Y.P.
Published: February 2023

The high power pulsed Nd:YAG laser is very useful for material processing and other applications. Different applications need different laser pulses with different pulse widths and rise times. A high power pulsed Nd:YAG laser were successfully designed , it includes three big YAG rods (ϕ10 × 150mm), six Krypton lambs and six power supplies with different pulse width and rise times .Here we use Krypton lamb instead of Xenon lamb because it has better spectrum match feature , high conversion efficiency and suited to long pulse operation. The power supplies have resonant and switched types(VDMOS and IGBT). Cooling system has internal and external circular systems. Whole system has a laser light fiber delivery device which can be transmitted high energy. Table shows the light shapes of Krypton lamp and shapes of laser pulses. The pulsewidth can be tuning from 0.3 to 6 ms, the rise time can be tuning from 0.2 to 0.8ms.
Single-frequency Operation of a Q-switched Nd:YAG Laser by Injection Seeding
Authors: Hao Hongxu , Gao Chunqing , Wei Guanghui , Li Jaize
Published: February 2023

Injection seeding is a convenient and reliable method for achieving single-frequency operation. Injection seeding is accomplished by introducing light from a low-power stable single-frequency oscillator (referred to as a seed laser) into a high-power laser cavity (referred to as power oscillator) during the laser pulse buildup period.
Organic Optical Materials: An Overview of Scientific Issues and Applications
Authors: Dalton Larry R.
Published: February 2023

Although historically, organic materials have not been thought of as optical materials, organics are experiencing increased use as both passive and active optical components. Applications range from passive elements such as gratings, fibers, interconnects, lens, and prisms to active components such as light emitting diodes, electro-optic modulators, solid-state lasers, frequency doublers, optical memories, and sensor protection elements. The utilization of organic materials has typically involved competition with established technology based on inorganic materials. For example, polymeric optical fibers must compete with established silica fiber technology, polymeric electro-optic modulators must compete with established lithium niobate technology, organic light emitting diodes with a host of inorganic light emitting materials, etc. Unless organics offer special advantages, they have little chance of market penetration. A frequently quoted putative general advantage of organics, and particularly polymeric materials, is their processibility and low cost. In areas such as discrete passive components, this advantage clearly comes into play and has resulted with wide commercial use. Indeed, inorganic materials such as sol-gel glasses have major difficulty in competing with polymeric materials in the manufacture of passive discrete optical components. For applications, such as electro-optic modulators and light emitting diodes, the success of organics depends on a number of properties other than materials cost or processibility although even here processibility can be an important consideration for issues such as integration with semiconductor VLSI electronics.
Progress in Co-Directional Second Harmonic Generation in Poled Polymers
Authors: Jäger M. , Canva M. , Stegeman G. I. , Wirges W. , Yilmaz S. , Brinker W. , Bauer-Gogonea S. , Bauer S. , Ahlheim M. , Stähelin M. , Zysset B. , Lehr F. , Diemeer M. , Flipse M. C.
Published: February 2023

Polymers, even with attached, non-centrosymmetric, side groups are amorphous due to the random orientation of the chromophores and therefore are not second-harmonic active. They can be made macroscopically non-centrosymmetric by applying strong electric fields (poling) near the glass temperature of the host polymer to align the side groups which normally have large dipole moments.[1] The side groups can be engineered to have large non-resonant nonlinearities so that the poled polymers can have d(2)s of the order of 50-100 pV/m.[1] This has made poled polymers interesting doubling media, especially in channel waveguides which can be easily fabricated using a number of polymer techniques. We have been exploring poled polymers for second harmonic generation (SHG) for operation with 1550 nm inputs for potential application to cascading, WDM frequency shifting, etc.[2,3] Here we report our progress using the modal dispersion phase-matching technique.
A Computer-Controlled Tunable Pulsed Ti:Al2O3 Laser
Authors: Qiao J. Y. , Li X. F. , Yao J. Q. , Wang P. , Song F.
Published: February 2023

Ti:Al2O3 laser is one of new solid state tunable lasers. We developed a pulsed Ti:Al2O3 laser, which is pumped by an EO Q-switched frequency doubled pulsed Nd:YAG laser from two ends. It is shown in Fig.1. A prism is inserted into the resonator that uses as tunable element. By rotating HR(13) mirror, output wavelength can be tuned.
Calculation of optimum parameters in single frequency LDP intracavity frequency doubled Nd:YAG laser
Authors: Yao J.Q. , Yang J.B. , Sheng W.D. , Zheng Y.
Published: February 2023

The experiment setup of the laser is shown in Fig. 1. The bireffequent effect of KTP crystal, together with the Brewster-plate(B-plate) function in the cavity as a loss modulator. Define δ-phase delay angle, γ-angle between the polarization orientation of the slow ray in KTP crystal and the P-plane polarization direction of the B-plate. P-polarization is the polarization direction along which the loss that a light wave passes through the B-plate is zero. Previous calculation results from many other literatures show that the optimum value of γ is 45°, with the mode selecting ability of the crystal reaching the peak value.
LD tightly pumped compact green laser
Authors: Feng Song , Jianquan Yao , Weidong Sheng , Xiaobo Cheng , Guangyin Zhang , Jia Yang
Published: February 2023

Green lasers can be used in many fields such as colour display, optical storage, laser medicine. The main requirements for the green lasers in the applications are compact, stable, high beam quality. It is one of the most efficient way to obtain green lasers by frequency doubling of Nd:YVO4(or Nd:YAG) lasers pumped by LD, which have been researched widely.
Retracing Behaviors of Phase-matching Angle in Non-collinear Phase-matched BBO Optical Parametric Oscillators
Authors: Hsu Chih-Wei , Huang Shen-Dean , Huang Ding-Wei , Yang C. C.
Published: February 2023

The retracing behaviors of phase-matching angle, which are the key phenomena for realizing multiple-wavelength optical parametric oscillators (MWOPO), have been observed in a LBO crystal [1] and also studied in other crystals in the collinear phase-matching configurations. However, based on collinear phase-matching the implementation of MWOPO is limited by the specific ranges of pump wavelength, particularly for the widely used BBO crystal. In this paper, we, on the one hand, present the results of theoretical study on the retracing behaviors of a BBO crystal based on non-collinear phase-matching configurations. On the other hand, we demonstrate our experimental results of the retracing behavior of a BBO optical parametric oscillator (OPO) pumped by the second-harmonic of a Q-switched Nd:YAG laser. Particularly, we discovered that near the turning point of the retracing curve, there was an angle around which a broad wavelength range could be simultaneously phase-matched. Based on this observation, we have implemented an OPO with an extremely broad signal and idler spectra.
Potassium Titanium Oxide Phosphate (KTP) Optical 'Parametric Oscillator Pumped at 0.532 and 1.064μm
Authors: Baoquan Yao , Youlun Ju , Qiang Liu , Xin Yu , Yuezhu Wang
Published: February 2023

Optical paranetic oscillators (OPO) are attractive sources of coherent radiation in application for which laser sources are unavailable or for which wide tunability is needed. For samples, they can be used as mid-IR. countermeasure sources in military applications and can be applied into difference absorption lidar operating in the range of 2 ~ 14 μ m to monitor environment, medical diagnosis and treatment, material processing, scientific instrument, optical communication, low-light imaging, atmospheric aberration for astronomy and satellite tracing, optical signals processing, communication and imaging in water, remote sensing and identification biological materials. Many nonlinear frequency-conversion crystals such as lib3O5(LBO), KTiOPO4(KTP), β-BaB2O4 have been used in OPO devices. KTP is one of the best nonlinear frequency-conversion crystals, and it has high nonlinear coefficient, high damage threshold, easily-polished surface, and a broad transparency range[1,2]. So, Here, we focus our interest to KTP OPO.
Rectangular pulse Nd:YAG laser pumped Ti:Sapphire laser and optical parametric tunable laser
Authors: Liu Huang , Li Wang , Yu Zhao , Jinfeng Zhou , Yong Tian , Jing Liu
Published: February 2023

We report a rectangular pulse Nd:YAG laser pumped Ti:Sapphire laser and optical parametric tunable laser, worked in high stability and high transform efficiency. The highest pulse energy is 125mj, the highest repetition rates is 30Hz. A microcomputer and single-chip computer is used for wavelength tuning, the tunable range of 532nm pumped Ti:Sapphire laser is from 680nm to 860nm; the tunable range of 355nm pumped BBO crystal optical parametric tunable laser is from 440nm to 2600nm.

Three high power rectangular laser pulses of 1064nm, 532nm and 355nm are offered by the multifunction wide band tunable laser respectively.
Analytical vs. Numerical Methods for Rough Surface Scattering
Authors: Thorsos Eric I.
Published: February 2023

The integral equation method can be used to obtain exact solutions for scattering from one-dimensional surfaces. Scattering cross sections for randomly rough surfaces can then be found by averaging scattered intensities for many surface realizations. The accuracy of analytical methods for rough surface scattering can then be examined. Traditionally, the perturbation and Kirchhoff approximations have been the most commonly used analytical methods—the former for surfaces with small roughness and the latter for surfaces with smooth roughness. These approaches can be extended systematically to obtain the perturbation series and the multiple scattering series, respectively. The first few terms in the perturbation series can be formally averaged, extending the range of analytic perturbation theory. The terms in the multiple scattering series beyond the lowest order (the Kirchhoff approximation) have not yet been formally averaged. The multiple scattering series is thus implemented as an approximate numerical method. Numerical results will be presented showing the accuracy and limitations of these two series approaches. These results will also clarify how the two complementary series apply when the surfaces have both small and smooth roughness. The relationship of the multiple scattering series to shadowing phenomena and a major shortcoming with the multiple scattering approach will also be addressed. Recently, several new approximations to rough surface scattering have been developed which reduce properly to the perturbation and Kirchhoff approximation limits. These new approaches will be briefly reviewed and their accuracy discussed.
Oxidation Stacking Faults (OSFs) in Silicon Crystals Detected by Light Scattering Topography
Authors: Abe Takao , Takeno Hiroshi , Ushio Satoshi , Iba Kunio
Published: February 2023

It is well known that particles on a silicon wafer may have a large influence on the yield of high - density devices. Such particles have been reliably detected only by light - scattering methods. Recently, light scattering has been used to attempt to measure the surface roughness of a silicon wafer, but reasonable results have not yet been obtained.
Design Review of a Unique Out-Of-Plane Polarimetric Scatterometer
Authors: Stover John C. , Schiff Tod
Published: February 2023

This presentation reviews a unique out-of-plane scatterometer designed and built at TMA. Features which make it unique include the ability to measure liquid samples, a vertical optical table devoted to constructing custom laser or broadband sources, software that allows complete automation, and the option for complete polarization control and analysis (Stokes Vectors, Mueller matrices, etc.) of laser sources and received signal.
Progress Toward an RF-Linac Free-Electron Laser for the Extreme-Ultraviolet Spectral Region*
Authors: Newnam B. E. , McVey B. D. , Goldstein J. C. , Elliott C. J. , Schmitt M. J. , Lee K. , Wang T. S. , Carlsten B. E. , Fraser J. S. , Sheffield R. L. , Scott M. L. , Arendt P. N.
Published: February 2023

Los Alamos National Laboratory is pursuing a research and development program leading to eventual establishment of a free-electron laser (FEL) facility, based upon a single rf linear accelerator, for production of coherent radiation extending from the visible spectrum to the extreme untraviolet (XUV) and soft X-ray wavelengths as short as 10 nm. (Figure 1 illustrates such a multi-oscillator configuration.) Several key areas have been identified for concentrated attention over the next two years, particularly to assure feasibility at the short-wavelength end of this range. First, theoretical studies are directed toward maximizing the single-pass gain and output power from FEL oscillators using realistic electron beams produced by rf linacs. Since electron beam emittance is the primary concern for ultraviolet wavelengths, a unique three-dimensional code (FELEX) has been developed for numerical simulation of FEL parameter variations. Accelerator calculations of the influence of single-bunch beam loading on longitudinal energy spread are being performed with an advanced version of PARMELA. Also, to project further into the XUV and soft X-ray regions, methods to maximize the conversion efficiency to coherent optical harmonics of the fundamental lasing wavelength are being evaluated.
Scanning Soft X-Ray Microscopy at the National Synchrotron Light Source
Authors: Jacobsen C. , Kirz J. , McNulty I. , Rosser R. J. , Buckley C. , Burge R. E. , Browne M. T. , Cave R. , Charalambous P. , Duke P. J. , Kenney J. M. , Michette A. B. , Morrison B. , Cinotti F. , Rarback H. , Pine J.
Published: February 2023

In scanning soft X-ray microscopy a quantitative map of specimen absorptivity is obtained. Sharp changes in the spectrum at absorption edges provide contrast and are the basis for elemental analysis by comparison of images taken at differing wavelengths. We have developed an instrument that uses monochromatized synchrotron radiation as its source. A collimated portion of this source is focused with a Fresnel zone plate to a submicron spot, across which the specimen is scanned under computer control.
Suppression of Multiphoton Ionization with Circularly Polarized Light
Authors: McIlrath T.J. , Bashkansky M. , Bucksbaum P. , Freeman R.R.
Published: February 2023

Above threshold ionization is one of the fundamental new phenomena revealed in the study of atoms in very intense light fields ( > 1013 W/cm2). ATI is the production of photoelectrons at a number of discrete energies above the ionization limit. The electron energies appear to closely follow the relation E =(Nħw–E
ionizanon
)+Sħω; that is, they correspond to absorption of an additional S photons more than the minimum number N needed to ionize the neutral atom or molecule. Understanding ATI is essential to determining the role of coherent and incoherent processes when the radiation field forces become comparable to atomic forces. The work reported here supports the interpretation of ATI as a coherent rather than a stepwise process.
Optical Gain at 185 Nanometers in a Laser Ablated, Inner-Shell Photoionization-Pumped Indium Plasma
Authors: Lacy Robert A. , Silfvast William T. , Svanberg Sune , Wood Obert R. , Byer Robert L.
Published: February 2023

Inner-shell photoionization of In+ ground state ions by a laser-produced-plasma broad-band soft X-ray pump source has created a large population inversion on the 185 nanometer 4d9 5s2 2D5/2 → 4d10 5p 2P3/2 transition in In++. A small signal intensity gain of exp(0.5) was measured in a path length of ~4 millimeters, yielding a gain coefficient of a ≈ 1.25 cm-1. The initial population of ~1016 cm-3 In+ ground state ions is prepared by ablating a liquid indium target with a 10 nanosecond, 100 millijoule, 532 nanometer laser pulse yielding a highly ionized indium plasma. The expanding plasma cools and recombines to give the required In+ 4d10 5s2 population, at which time a 100 picosecond, 40 millijoule, 1.06 mm laser pulse, incident on a nearby tantalum target, generates a hot plasma radiating broad-band soft X-rays. The soft X-rays photoionize inner shell 4d electrons from the In+ ions, populating the 4d9 5s2 In++ state, which is inverted with respect to the nearly empty 4d10 5p state.
X-Ray Laser Experiments Research at the Nova Laser Facility
Authors: Matthews D. L.
Published: February 2023

I will review our research program which studies the lasing phenomena and its applications at soft x-ray wavelengths. Included will be a description of our soft x-ray laser demonstration experiments at 20.6, 20.9 and 15.5 nm for optical laser pumped collisional excitation laser schemes, our physics understanding of the phemonema, our new 10TW 2-beam facility at the Nova laser and our near-term experiment's program. Ultimately, we are hoping to achieve efficient lasing at 3 to 5 nm at MW output power levels, with low-divergence highly-coherent beam properties. Near term our research will be performed at 20 to 15 nm wavelengths and will focus on achieving saturated output from our ASE amplifier and characterizing the beams divergence and mode structure.
High-Gain VUV and Visible Inversions in He+ and Ar+ Produced by Two-Electron (Shakeup) Photoionization
Authors: Silfvast W. T. , Wood O. R. , Al-Salameh D. Y.
Published: February 2023

Emission from 100 psec laser-produced plasmas has been used to excite two-electron (shakeup) photoionization processes and produce large population inversions in He+ with gain at 164 nm and in Ar+ with gain at 428 and 477 nm. Shakeup processes have recently been used to identify autoionizing levels1 in Cd+ and proposed as an excitation source2 for VUV lasers m Li+.
Electron angular distributions in above threshold ionization of xenon
Authors: Bashkansky M. , Bucksbaum P. H. , Freeman R. R. , McIlrath T. , Dimauro L. F. , Custer J.
Published: February 2023

We have measured angular distributions of the electrons produced in above threshold ionization of xenon by 100 psec 1.06 μm and .532 μm laser pulses. We find that the electrons are generally emitted along the polarization direction for linearly polarized light. However, the angular distributions differ for electrons emitted with different kinetic energies, corresponding to different numbers of photons absorbed in the photoemission process. Furthermore, for a given electron energy, the angular distribution is dependent on laser intensity. We have also measured the intensity dependence of electrons photoemitted by circularly polarized light. Results are discussed in terms of atomic theory and ponderomotive potential scattering.
Multi-Electron Multi-Photon Ionization
Authors: L'Huillier Anne
Published: February 2023

The interaction of a many-electron atom with a strong laser field (>1012 W.cm-2) induces the removal of several electrons (up to Xe8+ at 193 nm). We briefly review the main experimental results obtained so far1-3 and we analyze in some details the result obtained on Xenon using a 50 ps Nd-YAG laser at 532 nm1. We show that the mechanism responsible for the formation of highly charged ions (e.g.Xe5+) is probably a sequence of 1-electron multiphoton ionizations taking place during the rise of the laser pulse. It is essential to take into account both the temporal and spatial distributions of the laser pulse to understand the experimental data.
The Stark Effect in Atoms at Extremely High Intensities: Ponderomotive Potentials and All That
Authors: Freeman Richard R.
Published: February 2023

Recent measurements of the kinetic energies of photoelectrons produced in multiphoton ionization of the rare gases for ultra-short (≤ 250 femtosec), high intensity (≈1014W/cm2) light near 616 nm reveals a complex spectra, rich in structure with some features so narrow in energy that they are limited by the spectrometer resolution. In this paper I show that this thoroughly unanticipated result is a signature of a general phenomena, one that is present (but often hidden) in all multiphoton experiments regardless of the pulse length employed in the particular experiment. Further, I argue this phenomena is directly related to the ponderomotive potential associated with the "wiggle" motion that an electron executes under the influence of an intense optical field.
Characteristics of a Non-Equilibrium Picosecond Laser Plasma
Authors: Gibson G. , Rosman R. , Luk T. S. , McIntyre I. A. , McPherson A. , Wendin G. , Boyer K. , Rhodes C. K.
Published: February 2023

VUV spectra of a highly ionized argon plasma produced by a high-power subpicosecond laser are analyzed to determine the electron temperature. The calculated electron temperature is too low to support the highest observed charge state, showing the plasma charge state distribution to be out of Saha equilibrium.
Multiphoton Spectroscopy of Multielectron Atoms and the Quest for Direct Two-Electron Ejection
Authors: Lambropoulos P.
Published: February 2023

I present a brief review of recent high intensity experiments showing the participation of multiphoton resonances with bound atomic states. The results compare favorably with some of our calculations on rare gases and alkaline earths.
X-Ray Holographic Microscopy: Improved Images of Zymogen Granules
Authors: Jacobsen Chris , Howells Malcolm , Kirz Janos , McQuaid Kenneth , Rothman Stephen
Published: February 2023

Soft x-ray holography has long been considered as a technique for x-ray microscopy [1]. It has been only recently, however, that sub-micron resolution has been obtained in x-ray holography [2-4]. This paper will concentrate on recent progress we have made in obtaining reconstructed images of improved quality.
Reflectance of Aluminum Reflectors in the Extreme Ultraviolet
Authors: Scott Marion L.
Published: February 2023

We have investigated a new concept in retro-reflectors for use in the extreme ultraviolet, namely, UHV aluminum coated, multi-facet, grazing-incidence mirrors. Our results indicate that this type of mirror, which utilizes total-external-reflectance, works very well in the wavelength range from 35 nm to 100 nm (89 ± 3% measured retroreflectance at 58.4 nm for a 9-facet mirror). However, the coated mirror surfaces must not be allowed to oxidize after deposition, which implies that the retro-reflector must be coated and used in situ or the oxide layer must be removed in a ultra-high vacuum (UHV) system.
Large Holographic Diffraction Gratings Made by a Multiple Exposure Technique
Authors: Wosinski L. , Breidne M.
Published: February 2023

The maximum size of a holographic grating that can be manufactured in a specific set-up is, in principle, limited by the size of the collimating optics (mirrors) in this set-up. A technique, which permits to circumvent the limitation set by the mirrors and fabricate large holographic gratings, is described. The accuracy of phase agreement, when two gratings are bound together, is better than λ/20.
Proposed Method for the Measurement of the Spatial Coherence of Laboratory X-Ray Lasers
Authors: Trebes James , Barbee Troy , Nathel Howard , Szoke Abraham
Published: February 2023

A proposed method of measuring the spatial coherence length of laboratory x-ray lasers is described. The method is based on the coherence dependent interference pattern produced by double slit arrays. The neon-like Se laser at 208Å is used as an example.
X-Ray Optics for X-Ray Laser Research Applications
Authors: Ceglio N. M.
Published: February 2023

State of the art capabilities in soft x-ray lenses, multilayer mirrors, beamsplitters, and synthetically generated holograms are reviewed. Application of these capabilities in recent x-ray laser cavity experiments, and to the development of a soft x-ray interferometer and a high intensity (≳1013 watt/cm2) soft x-ray laser are discussed.
Sub-Nanosecond, Photon Counting, Imaging, X-Ray Camera
Authors: Whelan D. A. , Carter M. R. , Price D. F. , Stewart R. E.
Published: February 2023

A high temporal bandwidth x-ray detector has been developed for time resolved one dimensional x-ray imaging experiments. The detector serves as a high gain, high quantum efficiency preamplifier for a streak camera, and consists of a reflective x-ray photocathode, an active microchannel plate, optional electrostatic optics, and a sub-nanosecond phosphor. The optional electrostatic optics allows the detector to be used for either two dimensional imaging with a 100 picosecond framing (without focusing optics), or as a high gain one dimensional imaging detector, with either a 100 picosecond gated Reticon camera, or a streak camera. Other versions of the one dimensional detector have been developed, in which the microchannel plate which employs a reflective photocathode on the front surface of the microchannel plate, is replaced with a transmission photocathode consisting of a photocathode deposited on a thin polypropylene foil. The detector exhibits a time resolution of 400 picoseconds FWHM, a spatial resolution of 350 pm with an electron compression of ten to one (100μm resolution without compression). Quantum efficiency of 40% have been achieved, and effective quantum efficiency greater than 100% have been achieved with the one dimensional electrostatic optics. Data will be presented on the efficiency, time response and spatial resolution of the one dimensional detectors.
Nuclear Bragg Diffraction using Synchrotron Radiation
Authors: Ruffer Rudolf
Published: February 2023

Nuclear Bragg diffraction in combination with synchrotron radiation will become a powerful new X-ray source in the Å-region. This new source exceeds already Mossbauer sources in brilliance giving Mossbauer scattering experiments further impetus. With the planned dedicated storage rings synchrotron radiation, filtered by measures of the Mossbauer effect, will not only allow new types of Mossbauer experiments but offers also a new X-ray source for yeV resolution and long coherence length X-ray optics.
All short pulse multiphoton ionization is resonant ionization
Authors: Cooke W. , Freeman R.R. , Mcilrath T.J.
Published: February 2023

Energy resolved photoelectron spectra of multiphoton ionization taken with a 300 fs laser pulse at 616 nm shows that the ionization probability is highly structured as a function of laser intensity. The spectrum is consistent with all of the ionization occurring at intensity resonances.
Observation of Extreme Ultraviolet Amplification in 3-2 (42~46Å)/ 4-3(130.5Å) and 5-4(305Å) Transitions in Laser Produced He-like Al Plasma
Authors: Kuroda H. , Muroo K. , Naito K. , Tanaka Y.
Published: February 2023

To demonstrate the XUV stimulated emission process in plasma produced by 100ps glass-laser pulse, close to the water window region, XUV and X-ray spectroscopic measurements are done by adopting He-like Al 3-2, 4-3 or 5-4 transition scheme. This scheme is simple and predictable by the spectroscopic analysis, and suitable to demonstrate the induced emission of the shorter wavelength than any other transition ever attained.
Soft X-Ray Lasing of Li-like Ions in Laser-Produced Plasmas*
Authors: Lee Yim T. , Howard W. M.
Published: February 2023

Several demonstrations of lasing in the extreme–ultraviolet (XUV) wavelength region have been successfully achieved using either collision or recombination pumping. The first successful demonstration was reported for the 3p–3s transitions in Ne–like selenium ions. Laser transitions at shorter wavelengths have also been achieved by using the 4d–4p transitions in Ni–like ions. These schemes are based on collisional excitation pumping, while in other successful schemes the upper lasing levels are populated directly by recombination processes.
Ultrahigh Peak Power Pulses Produced by Chirped Pulse Amplification
Authors: Maine P. , Strickland D. , Bado B. , Mourou G.
Published: February 2023

Chirped Pulse Amplification (CPA)1 allows the amplification of short laser pulses in amplifying media with good storage properties (low transition cross section) like Nd:glass1,2 or Alexandrite.3-4 In these media, straight amplification cannot be performed well, because of the large input flux necessary to reach efficient energy extraction. This condition leads to unacceptable peak powers. To minimize the intensity effects, the pulse is stretched, amplified, and recompressed. This technique allows an efficient energy extraction while maintaining a good beam quality. The intensity is kept below the onset level of small-scale focusing, occurring when values of the B integral are larger than three. We recall that the B integral is given by the expression.
X-Ray Emission Studies of Sub-Picosecond Laser Produced Plasmas
Authors: Murnane M. M. , Kapteyn H. C. , Falcone R. W.
Published: February 2023

We report on both experimental and theoretical studies of high-temperature, high-density plasmas produced when a solid is illuminated with intense, 160 femtosecond laser pulses. Time resolved measurements have determined the x-ray pulsewidth from the plasma to be 2 ± 2 psec in all spectral regions up to a kilovolt. Spectroscopic observations demonstrate that the x-ray emission comes from regions of density higher than those found in a conventional laser produced plasma. Finally reflectivity measurements indicate that the laser is absorbed at the surface of the solid before it expands.
X-Ray Laser Experiment with Double Pass Device and Long-Recombing-Plasma Column
Authors: Jaegle P. , Carillon A. , Dhez P. , Gauthe B. , Gadi F. , Jamelon G. , Klisnick A.
Published: February 2023

The results reported here, are time integrated measurements of soft X-ray amplification obtained with our new experimental set-up involving a single normal incidence multilayered mirror, put at the rear of a 60mm laser-plasma column. After a brief description of the experimental system, we report the first results obtained at 10.57nm by comparing intensities of single-pass ASE and of double-pass with the mirror. The target is a thin aluminum layer with a thickness optimizing the population inversion on lithium-like Al+10 ions. The pumping is produced by recombination mechanisms during the plasma cooling.

From the single to the double pass X-ray beam, the lines exhibit significant differences, both in peak intensities and widths. First, double-passing enhances the 10.57nm line intensity much more than mirror reflection would do without any amplification by the plasma. Secondly, and concomitantly, one observes a line width decreasing of about 30%.

This is supposed due to a core size decreasing of the zone emitting the line. To explain how the cross-section of the double pass beam can be reduced during propagation trough the plasma column we suggest to consider the focussing effects due to the gain coefficient profile.
Short Wavelength Lasers: Something New, Something Old
Authors: Hagelstein P. L.
Published: February 2023

Significant amplification in the EUV and soft x-ray spectral regimes have been demonstrated recently at a number of laboratories using very high power ICF class lasers as pump sources. We discuss in this paper the possibility of developing short wavelength lasers on a smaller scale by scaling the electron collisional scheme in nickel-like ions to lower Z. Additionally, we examine population inversions in neodynium-like ions as an alternate route towards a small scale soft x-ray laser.

We consider specifically the design of a transient nickel-like molybdenum collisional laser based on a 4d – 4p transition near 194 Å. Such a laser could be driven by a 10 Joule Nd:glass pump laser system. In addition we consider the extension of the electron collisional scheme to neodynium-like U, in which the monopole-excited 5f – 5d transition occurs near 71 Å.
Population Inversions between n = 5, 4, 3 and 2 levels of He-like Al Plasma Observed by Spatially Resolved X-ray Spectroscopy
Authors: Kuroda H. , Katsuragawa M. , Muroo K. , Tanaka Y.
Published: February 2023

Population inversions between N=5, 4 and 3 levels are observed in a 100ps Laser-produced plasma. As a results/ XUV of 42Å~46 Å, 130Å and 305Å corresponding to 3-2, 4-3 and 5-4 transitions are observed experimentally. Relative population densities are determined by measuring the intensities of spatially resolved X-ray line spectra of 6.635Å, 6.314Å and 6.18Å corresponding to the 3-1, 4-1 and 5- 1 transitions, which are normalized by their oscillation strengths. Careful absorption was paid to rule out the effect of reabsorption. Populations were inverted at the region located 50~100μm from the target surface. Laser light was focused into 50μm diameter and amount of inversion was clearly increased when laser intensities was increased. As to the 5-4 and 4-3 inversion, similar result was observed in silicon target, however inversion between n=3 and 2 was not confirmed at these laser intensities. XUV gains are very promising especially as to 5 4 and 4-3 transitions in both target.
Probability of Soft X-Ray Radiation for 3p-3s Transition in Neon-Like Iron
Authors: Peng Huimin , Zhang Guoping , Sheng Jiatian , Shao Yunfeng
Published: February 2023

Using 1-D non-LTE radiative hydrodynamic code JB-19 we simulated the interactions of basic and double frequency neodymium-glass laser beam which is focussed into a line onto target, with thin Formvar-iron foils. The values of population inversions and gains are calculated using steady rate equations. The profiles of laser-produced plasma conditions and the probabilities for 3p-3s transition in neon-like iron at peak intensities 5TW per square centimeter to 20TW per square centimeter and FWHM 800-1000ps are shown.
Reversible Multiphoton Ionization of Gases Observed by a Femtosecond Pump/Probe Schlieren Imaging Technique
Authors: Geindre J.P. , Audebert P. , Gauthier J.C. , Benattar R. , Mysyrowicz A. , Chambaret J.P. , Migus A , Antonetti A.
Published: February 2023

Using femtosecond time-resolved Schlieren imaging, we observe a light-induced reversible plasma-like change of the refractive index of a gas during optical irradiation by 80 fs pulses.
Competition between Above-Threshold Ionization and High-Order Harmonic Generation
Authors: Perry M.D. , Allendorf S. , Crane J.
Published: February 2023

Both above threshold ionization and high-order harmonic generation are the result of atomic excitation in a manner which cannot be described by lowest-order perturbation theory. By high-order harmonic generation, more correctly, strong-field harmonic generation, we are referring to the generation of harmonic radiation (typically greater than the 7th harmonic) which is not a monotonically decreasing function of harmonic order. This was recently observed by MacPherson, et al1 and later by Ferray, et al.2 On the other hand, above-threshold ionization, the process by which an atom absorbs more photons than the minimum required to ionize, is now a well established phenomena in the interaction of intense radiation (>1013W/cm2) with atoms.3
A new approach to solving the time-dependent Schrodinger for an atom in a radiation field
Authors: Pont Marcel , Proulx Daniel , Shakeshaft Robin
Published: February 2023

The time-dependent Schrodinger for an atom in a radiation field has a very special form, at least within the dipole approximation: The time-dependence of the Hamiltonian is contained entirely in a c-number which appears as a factor in the interaction, V(t), of the atom with the radiation field. In the velocity gauge this factor is the vector potential, A(t), of the field — we have V(t)= − (e/µc)A (t) • p, where e, µ, and p are the charge, reduced mass, and canonical momentum (in the center of mass frame) of the electron — while in the length gauge this factor is the electric field vector F(t) — we have V(t) = –eF(t) • x, where x is the position coordinate. To our knowledge, this factorization property has not been fully exploited in previous approaches to solving the timedependent Schrodinger equation1. As we show here, in an application to multiphoton ionization of atomic hydrogen, it is an extremely useful property; and although at first sight it would seem to be a unique feature of the atom-radiation system, this is not so, for, as Solov’ev2 has pointed out, the time-dependent Schrödinger equation for colliding atoms or ions can be transformed into a form in which a scaled time-dependence also appears only in c-number factors of the (transformed) interactions.
Temperature Determination in X-ray Laser Plasmas by Thomson Scattering
Authors: Villeneuve D. M. , La Fontaine B. , Baldis H. A. , Dunn J. , Enright G. D. , Rosen M. D. , Young P. E. , Matthews D. L.
Published: February 2023

One of the outstanding uncertainties in modelling x-ray laser experiments lies in determining the actual plasma parameters which crucially affect the prediction of laser performance. Electron temperatures are commonly inferred experimentally from x-ray emission spectra or from the Landau damping cutoff of stimulated Raman scattering, neither of which directly measures the temperature with sufficient precision at the location where lasing occurs.
Efficient Coupling of High-Intensity Sub-Picosecond Laser Pulses into Solid Grating Targets
Authors: Mumane M. , Kapteyn H. , Bokor J. , Mansfield W. , Gnall R. , Glytsis E. , Gaylord T. , Falcone R.
Published: February 2023

We have experimentally observed very efficient laser-solid coupling of high-intensity (1016Wcm–2) sub-picosecond (150 fsec) laser pulses into grating targets.1 This behavior is in contrast to the very high reflectivities observed from flat targets,2 where we have recently extended our measurements of normal-incidence flat-target reflectivities up to incident intensities exceeding 1016 W cm–2. The average flat target reflectivity observed was 86% - the peak reflectivity at the center of the focal spot and peak of the laser is therefore ≥ 90%. This data is shown in Fig. 1.
Characteristics of Sub-100-ps Laser Irradiation of Cylindrical Cavities
Authors: Balmer J.E. , Soom B. , Ellenberger U. , Weber R.
Published: February 2023

Laser Irradiation of cylindrical cavities has attracted considerable interest in the context of soft x-ray laser experiments because the confined plasma may act as an x-ray waveguide.1) Waveguiding requires a concave, radially symmetric density profile and thus uniform plasma ablation inside the cavity. In the case of transverse irradiation presented in this work, the uniformity of plasma ablation is primarily determined by the mechanisms which redistribute the energy from the initial location of plasma generation by the incident laser. Among the mechanisms to be considered are x-radiation, hot electrons, and laser light reflected at the primary spot. Experimentally, evidence was found that for short-pulse, long-wavelength, high-irradiance conditions, the redistribution of energy is dominated by reflected laser light.
Differential Phase Contrast Imaging in the Scanning Transmission X-ray Microscope
Authors: Palmer J R , Morrison G R
Published: February 2023

In the scanning transmission x-ray microscope (STXM) the specimen is scanned in a raster by an x-ray probe formed with a Fresnel zone plate. To achieve near diffraction limited resolution it is necessary to have a coherent source, even when forming an incoherent brightfield image by measuring the x-ray intensity transmitted by the object. This has so far been the only imaging mode used in the STXM and for hydrated biological specimens is well suited to soft x-ray wavelengths within the “water window” (2·33 to 4·36 nm) where carbon absorbs much more strongly than water. However, by the use of phase contrast rather than amplitude contrast, it is possible to form images at wavelengths where the absorption is low, resulting in lower radiation dose for the same level of contrast. Calculations made by Howells [1] and Rudolph and Schmahl [2] have demonstrated very clearly the advantages of phase contrast imaging at wavelengths outside the water window.
Optical Wiggler Free-Electron X-Ray Laser as a Two-Level Quantum, Generator with Fully Inverted Medium
Authors: Belenov E.M. , Grigoriev S. V. , Nazarkin A. V. , Smetanin I. V.
Published: February 2023

Recently the possibility was widely discussed of creation of an X-ray free-electron laser (FEL) using a high-power laser pulse as the undulator (optical wiggler FEL) [1]. Optical wiggler FEL is characterized by relatively small energy of the used electrons (ε ~ 1÷10 MeV). In order to achieve high values of the gain for X-rays it is necessary to use rather monoenergetic electron beams (Δγ/γ ~ 10–4) and the wigglers with a large number of periodic elements (N ≥ 104). In such FEL the energy of X-ray quantum can exceed the induced emission Cabsorption) linewidth: ωX > max {εΔγ/γ, ε(4N–1)}. We have shown that in this case the electrons interacting with the fields in FEL behave as two-level particles (the energies of these two levels are defined by energy and momentum conservation laws in an elementary act of stimulated Compton backscattering). The electron beam injected into the region of interaction with the energy close to the energy of the upper level represents a fully inverted medium for the amplified X-ray emission. The possibility is shown of FEL lasing with full extraction of inversion.
Coherent X-Ray Generation Via Laser Pumping of a Relativistic Ion Beam - Feasibility Assessment
Authors: Bogacz S.A.
Published: February 2023

The efficiency of most popular approach to generating short wavelength radiation involving particle beams, FEL1, is limited by the Thomson scattering cross section. If one were to use a beam of particles having a resonant scattering cross section for some frequency, a greatly enhanced gain might be expected. A natural candidate is a hydrogenic positive ion, having Z > 2, with a single bound electron. The fact that the ion is charged allows the beam to be accelerated to relativistic energies (γ≫ 1), therefore one can exploit the properties of relativistic kinematics which dictate that the back scattered radiation will have its wavelength shortened by a factor (2γ)2.
Soft X-ray Projection Lithography Technology*
Authors: Ceglio N. M. , Hawryluk A. M. , Stearns D. G. , Gaines D. P. , Rosen R. , Vernon S.
Published: February 2023

Recent analyses of critical system issues in Soft X-ray Projection Lithography are discussed. An overall system design provides detailed requirements (specifications) for x-ray mirror reflectivity, source power and parameters, resist sensitivity, etc. A cost analysis for SXPL systems leads to important requirements for x-ray mirror technology. An analysis of power loading limitations on precision SXPL imaging optics has important implications for source power and x-ray mirror reflectivity requirements.
Inertially Confined Molecular Ions
Authors: Corkum P.B. , Dietrich P. , Laberge M.
Published: February 2023

With high power pulses now shorter than the dissociation time of even highly charged molecular ions, a new molecular species, inertially confined molecular ions are available for study by optical means. Such studies may be important for short wavelength sources. For example, plasmas formed from inertially confined ions will be far from equilibrium. Non-equilibrium plasmas formed from atomic precursors have already lead to new approaches to short wavelength generation.
Search for Strong-Field Direct Two Electron Ionization using Coincidence Spectroscopy
Authors: Agostini P. , Mevel E. , Breger P. , Walker B. , Yang B. , DiMauro L. F.
Published: February 2023

We report on our progress in detecting two-electron ionization using electron-electron and electron-ion coincidence measurements. The coincidence techniques have been applied to the multiphoton ionization (MPI) of xenon atoms with 0.527 µm excitation. The results show that direct two electron ionization is not occurring which is in variance with an earlier report. We also present a polarization study on the MPI of helium at 0.62 pm and discuss these results in context of existing models.
H 2 +: Harmonic Generation
Authors: Bandrauk A. D. , Chelkowski S. , Zuo T.
Published: February 2023

H2+, due to its integrability for fixed nuclei serves as an exact model of molecular orbital theory [1]. In the presence of an intense laser pulse, the molecule-field system becomes nonintegrable and no exact solution of the time dependent problem is known. We have recently developed a new numerical method for solving the time-dependent Schroedinger equation(TDSE) for
H3++ in the presence of an intense subpicosecond laser pulse [2], allowing us thus to calculate the competition between ionization, dissociation and the production of high order harmonics. We shall compare the present results in the series H,
H2+, He+, and H++ in order to elucidate the properties of single electrons in multiple nuclear and laser fields.
Calculations of Femtosecond Optical Solitons from the Vector Nonlinear Maxwell’s Equations
Authors: Goorjian Peter M. , Joseph Rose M. , Taflove Allen
Published: February 2023

We present first-time calculations from the vector nonlinear Maxwell's of femtosecond temporal soliton and spatial soliton scattering, including carrier waves, in two dimensions.
Achieving Uniform Multilayer Coatings on Figured Optics
Authors: Waskiewicz W. K. , Windt D. L. , Bjorkholm J. E. , Eichner L. , Freeman R. R. , Jewell T. E. , Mansfield W. M. , MacDowell A. A. , Simpson W. M. , Szeto L. H. , Tennant D. M. , Taylor D. , Taylor G. , White D. L. , Wood O. R.
Published: February 2023

Spatial uniformity of the multilayer coatings deposited onto figured optics for soft x-ray projection lithography optical systems must be accurately controlled in order to maintain high throughput, and to preserve the imaging quality of the substrate. Controlling the uniformity with the desired accuracy can be quite challenging however, due to the nature of the deposition process.