bluuebunny/crossref_metadata_2025 huggingface dataset:
Light Absorption and X-Ray Emission Measurements From 100 Femtosecond Laser Produced Plasmas
Authors: Price D. F. , Guethlein G. , Shepherd R. L. , White W. E. , Stewart R. E. , Walling R. S. , More R. M.
Published: February 2023

The net absorption for a 100 femtosecond, 400 nm laser pulse's interaction with a wide range of solid density target materials is determined by measuring the total reflected and scattered light signals from the target. Absorption is determined over the intensity range of 1013 to 1018 W/cm2, a range is sufficiently broad to observe the transition in absorption from a low intensity region dominated by the cold material's electronic band structure, to an absorption at the highest intensities marked by a convergence to a nearly universal, material independent value.
Interference in climbing a quantum ladder system with frequency chirped laser pulses
Authors: Balling P. , Maas D.J. , Noordam L.P.
Published: February 2023

Major bottle-necks in climbing a vibrational ladder in a molecule are the anharmonicity of the binding potential and the short time scale on which added vibrational energy is redistributed over all the bindings.
Contradictions between Strong-Field Theories
Authors: Reiss H. R.
Published: February 2023

The theoretical method based on the Kramers-Henneberger (KH) transformation, championed principally by M. Gavrila[1] is the first and most widely known method for predicting the stabilization of atoms. Stabilization is that predicted property of atom photoionization wherein, beyond a certain level of intensity of an applied laser field, the atomic photoionization transition probability begins to fall with increasing intensity. An alternative theory of stabilization[2], while superficially similar in some respects, exhibits a major qualitative difference in its predictions. This second theory is called the strong field approximation (SFA). When applied to ionization by high frequency fields, the KH method predicts that the single-photon ionization process, obviously the only important photon order at low intensity, remains the dominant process even for extremely intense fields. By contrast, the SFA predicts that “channel closings”, of the type observed in low frequency strong-field experiments[3], will continue to occur even at high frequency. That is, the single-photon process is predicted to become energetically forbidden beyond a certain intensity, and then successively higher orders also become forbidden as the intensity rises still further.
Effects of Intensity-Dependent Intrinsic Phases in High-Order Harmonic Generation
Authors: Peatross J. , Chaloupka J. , Meyerhofer D. D.
Published: February 2023

An interesting phenomenon associated with high-order harmonic generation is the development of an intrinsic phase variation at the atomic level between the phase of the laser field and the phase of the emitted harmonic light. We created experimental conditions where the harmonics could be thought of as emerging from a single plane rather than a 3-dimensional volume.1,2 The appearance of broad wings (carrying ~75% of the energy) in the harmonic farfield angular profiles under such conditions indicates the presence of strong intensity-dependent intrinsic phases. The diffraction of the individual harmonics which causes the wings occurs because intrinsic phases translate into radial phase variations in the laser focus according to the intensity distribution.
Optimization of High-Order Harmonic Generation
Authors: Altucci C. , L’Huillier A. , Mevel E. , Starczewski T. , Wahlström C.-G.
Published: February 2023

High-order harmonic generation of an intense, short-pulse laser, provides a way of generating high-intensity radiation in the extreme ultraviolet (XUV) and soft X-ray spectral regions. Using the Ti:Sapphire terawatt laser in Lund (150 mJ, 150 fs at 794 nm), we have observed up to the 105th harmonic (7.6 nm) generated in He. This short-wavelength radiation has unique properties of short pulse length (~100 fs), high peak power and high spectral brightness. By focusing the harmonic radiation with suitable X-ray optics, it should be possible to obtain very high peak intensities. In this respect, high-order harmonic generation complement conventional sources of tunable XUV radiation, such as synchrotrons and laser-produced plasmas. To obtain the highest possible intensity after refocusing, it is important to maintain good temporal and spatial characteristics of the radiation as well as to optimize the number of harmonic photons generated.
Two-Color Photo-Associative Ionization Collisions between Sodium Atoms
Authors: Bagnato V. , Marcassa L. , Tao C. , Wang Y. , Weiner J.
Published: February 2023

Collisions of ultracold trapped atoms ( T< 1mK) have opened a new field of atomic collisions with abundant opportunities for theory and experiments. Photo-associative ionization (PAI) in sodium atoms has been the first two-body collision Studied in optical traps3. In this process two ground state Na atoms absorb two photons during the course of the collisional encounter. The first absorption at long range put the colliding system on an attractive C3/R3 potential curve, and the two atoms begin to accelerate toward each other. A second absorption promotes the system to a doubly excited Na(3p)+Na(3p) potential curve from which the PAI process takes place at short range.
Infrared Laser Spectroscopy of Jet-Cooled Carbon Clusters: The Structure and Spectroscopy of 3Σ c6
Authors: Hwang Hyun-Jin , Van Orden Alan K. , Tanaka Keiichi , Kuo Erica W. , Heath James R. , Saykally Richard J.
Published: February 2023

Carbon clusters have been of interest for many years due to their astrophysical importance and their role in the chemistry of high temperature, carbon-rich environments.1 Recent experimental and theoretical studies have been highly successful in elucidating the structure and bonding of small carbon clusters containing an odd number of atoms. The picture which has emerged is that odd clusters of three to nine atoms possess linear ground electronic states with cumulenic bonding. One of the most fascinating characteristics of these odd clusters is their unusual bending motion. C3, for example, has long been known to possess an extraordinarily low frequency, high amplitude bending mode, and indeed all of these linear chains are characterized by low bending frequencies.
Conformational Interchange in the 10 µm and 3µm Infrared Spectra of Propargyl Amine
Authors: Andrews Anne M. , Fraser Gerald T. , Pate Brooks H.
Published: February 2023

The propargyl amine spectrum was observed using an electric resonance optothermal spectrometer coupled to a CO2 laser-microwave sideband system for measurement of 10 µm spectra and to a color center laser for 3 µm spectra. Three bands were recorded in the 10 µm region; all were characterized by doubling of the transitions with a 3:1 intensity ratio, which is attributed to a torsion-inversion tunneling motion interchanging the two amine hydrogen atoms. The 3 µm band was greatly fractionated due to IVR. From double resonance experiments, each IVR component could be associated with one of the two tunneling states observed in the 10 µm spectrum.
Dynamics in Glasses and Liquids: Optical Non-Linear Line Narrowing Experiments
Authors: Fayer Michael D.
Published: February 2023

Molecules in condensed phase systems are coupled to their environments through intermolecular interactions. These interactions influence the internal electronic and vibrational states of molecules. At any finite temperature, solvent molecules are in constant motion, even in a low temperature glass. Since intermolecular interactions are distance and orientation dependent, the motions of the solvent make the intermolecular interactions with solute molecules inherently time dependent. These time dependent interactions result in fluctuations in the solute's electronic and vibrational energy levels. Energy fluctuations are responsible for processes such as thermal activation of a chemical reaction.
Velocity Selection Technique for High-Resolution Spectroscopy
Authors: Korsunsky E. , Kosachiov D. , Rozhdestvensky Yu.
Published: February 2023

It is known [1-3], that the samples of atoms with a velocity spread much lower than the recoil velocity uR= ħk/M (k is the wave number of exciting light field, M is the mass of atom) can be obtained by use of velocity selection with stimulated Raman transitions. A theoretical analysis of the velocity selection method is presented in [2,3]. So, it was shown in [2] that the formation of such narrow velocity structures is performed not only by the counterpropagating, but also by co-propagating light waves. This fact allows to form the two-dimensional velocity distribution of the widths δvx,y « uR by the velocity selection technique using laser configuration as in Fig. 1b.
The Spatial Response of Source-Collimator-Detector Systems
Authors: Taylor T.
Published: February 2023

Although the tomographic reconstruction technique assumes that the projections correspond to sets of line integrals, the measurements are, in fact, made with beams having a finite width and height. This has important implications for the design of tomography systems. Artifacts may be generated by variations in the beam profile across the slice [1]. Furthermore, the spatial resolution that can be achieved with a given beam geometry is limited to the full-width at half-maximum (FWHM) of the beam profile [1]. (Image restoration can improve spatial resolution but only at the expense of contrast discrimination [2].) Therefore, a detailed knowledge of the spatial response associated with various beam geometries is essential for the design of tomography scanners.
In Vivo Tissue Measurements with an Imaging Electron Spin Resonance Spectrometer
Authors: Halpern Howard J. , Nelson Alan , Teicher Beverly A.
Published: February 2023

Both an advantage and a limitation of current nuclear magnetic resonance techniques is the sensitivity of relaxation times to various chemical and physical environmental conditions. Thus accurate determination of flow is foiled by the similar order of magnetude sensitivity of relaxation measurements to molecular oxygen concentrations. Resolution of the ambigarty that results would occur if it were possible to perform measurements far more sensitive to molecular environment effects and less so to physical factors. Unpaired electrons and spectra that can be gathered from them electron spin responce spectra - fulfill this criterion. Not only do they allow resolution of ambiguities from high spatial resolution nuclear magnetic resonance scans but promise chemically and physiologically interesting measurements in and of themselves.
Numerical Simulations in Limited-Aperture Tomography with Application to Crosswell Acoustics
Authors: Terry Darrell A. , Albright James N.
Published: February 2023

Acoustic imaging techniques for studying the structure and properties of rock between wells are being explored at Los Alamos National Laboratory. A major objective of this work is to develop, validate, and apply tomographic methodology for the two-dimensional image reconstruction of the acoustic velocity structure between wells.
An Impedance Computed Tomography Algorithm and System
Authors: Wexler A. , Fry B. , Neuman M.
Published: February 2023

This presentation is to describe a method and apparatus for imaging the interior of a structure, such as a mineral or human body, having regions of differing electrical impedance.
Coherent Optical Tomography
Authors: Devaney A. J.
Published: February 2023

The methods of conventional (X-ray) tomography have, in the past, been employed in a number of applications in optics such as combustion diagnostics [1] and con-destructive evaluation of strongly refracting objects such as optical fibers [2]. In these applications a laser is employed much in the same way as an X-ray source is employed in X-ray tomography [3]. For example, in combustion diagnostics [1] a narrow laser beam is made to scan through the object of interest and a photo detector records the transmitted light intensity thereby yielding a "projection" of the object’s attenuation profile. The algorithms of X-ray tomography such as ART or the filtered backprojection algorithm [3] can then reconstruct a cross-section of the attenuation profile from the measured data. In the case of strongly refracting objects [2] the goal is to reconstruct the object’s velocity profile from optical path length measurements of the transmitted optical field. These measurements yield a "generalized projection" of the real part of the object’s complex index of refraction profile. Although the reconstruction algorithms of X-ray tomography cannot be employed due to the refraction of the probing optical field, generalized reconstruction algorithms based on a ray model of the optical field have been developed [2] that can yield reconstructions of the real part of the index of refraction from the "generalized projections".
Relaxation and Predissociation of Exciplex in a Supersonic Jet
Authors: Prochorow J. , Castella M. , Tramer A.
Published: February 2023

An exciplex system of perylene with N,N-dimethylani1ine (DMA) with strong exciplex fluorescence in liquid solution and no indication of complex formation in the ground state is studied in this work in a supersonic jet. The aim is to get insight into the dynamics of vibrational energy redistribution in extremly large excited complex characterized by a number of low-frequency vibrations. Furthermore, a problem of a non-bonding (or repulsive) ground state of exciplex vs. van der Waals complex formation is examined.
Photo-Oxidation of Tetracyanoplatinate Single Crystals
Authors: Pfab W.A. , Gerhardt V.
Published: February 2023

Mex [Pt(CN)4]y nH2O (Me = Sr, Ca, Ba, Mg, Lu, ...)-type crystals show highly anisotropic properties. The strong binding between the CN-ligands and the Pt2+-ion of the [pt(CN)4]2--complex-molecule is well preserved in the crystal (1). This is the reason for the demixing of Pt-d3-electrons (Ham-effect) and, additionally, there is formed a nearly one-dimensional dz2-valence-band for the Pt-Pt-binding within the crystal.
High-density excitation and Raman Spectroscopy of the Bound-Exciton Complex (A°,X) in CdS
Authors: Broser I. , Gutowski J.
Published: February 2023

Luminescence and Raman spectroscopy using high-density tunable laser sources in the bound exciton region of CdS yield new informations about excitation channels and excited states of the four-particle (A°,X) complex. Excitation spectroscopy of the I1 luminescence due to the recombination of the (A°,X) complex with two A-valence-band holes in its electronic ground state led to the identification of four fine structure levels of the (A°,XB) complex with one hole from the second B valence band. Excitation with light of polarization

E
⇀

‖

c
⇀

and of an energy which coincides with one of these four levels, split off by hole-hole and electron-hole exchange interaction, is followed by a B-A hole conversion and subsequent I1 recombination of the complex. The sharp and strong excitation resonances due to the (A°,XB) levels allow measurements in a magnetic field giving detailed informations about the nature of these states and the interaction mechanisms involved. Investigations of a resonant electronic Raman effect due to hole scattering from the B to the A valence band within the (A°,X) complex supported these results. Four Raman lines showing resonance behaviour successively at the four (A°,XB) levels with distinctly different properties from known low-density Raman spectroscopy1 could be observed. Polarization and magnetic field dependent measurements were used to identify the Raman mechanism to be a one-photon resonant electronic scattering process within the (A°,X) levels while gain measurements and the observation of a mode structure in the high-density excitation spectra supported the excistance of stimulated Raman transitions. High-density excitation spectra of the I1 bound exciton with polarization

E
⇀

⊥

c
⇀

showed resonances due to first order forbidden electronic excited states2 of the (A°,XA) complex. Extremely high excitation intensities led to the observation of vibration like resonances of the I1 luminescence. Intensity, temperature and magnetic field dependent measurements enabled us to develop a theoretical model to explain these resonances to be vibrations of the particles within the (A°,X) complex analogous to the case of a diatomic molecule.
Donor-Acceptor Pair Line Luminescence in ZnSe Re-Visited
Authors: Neumark G.F.
Published: February 2023

Donor-acceptor (DA) pair line luminescence in semiconductors1 is both useful as a materials probe, and, in view of the analogy of the pairs to diatomic molecules, it is also of interest as a quantum chemical system. In the present paper we consider, for ZnSe, both aspects: using an improved value of the dielectric constant obtained from a re-analysis of literature data, we check agreement with quantum models.
Luminescence of Selective Optical Pumping of Excitons in GaSe
Authors: Capozzi V. , Caneppele S. , Montagna M.
Published: February 2023

The conduction band of the layer semiconductor Gallium Selenide has an indirect minimum at the M point of the Brillouin zone which is very closed (25 meV) to the higher direct conduction edge. The coexistance of these two minima largely influences the features of the photoluminescence spectra in the range from 580 to 800 nm. At low temperatures the emission spectra show intrinsic lines due to free -as well bound- direct and indirect excitonic recombinations and extrinsic bands at lower energy /1/. We measured spontaneous luminescence of GaSe Bridgmann grown crystls at He and N2 temperatures, exiting selectively (with a dye laser) a wide region of wavelengths on the excitonic absorption structures. In the same energy range we also recorded the excitation spectra of the prominent features appearing in the luminescence spectrum. Flourescence line narrowing effect on the direct free excitonic emission is observed even up to 80 K where localization of excitons, due to random microscopic lattice disorder, is not espected to occur /2/. This anomalous behaviour is interpreted in terms of macroscopic strains in our crystals, probably due to stacking faults which easily form in growing semiconductor layered compound.
High Luminescence due to Exciton Complex with Closed Hole Shell around Zinc in Germanium
Authors: Nakata H. , Otsuka E.
Published: February 2023

A new complex, two excitons bound to a neutral double acceptor, was first observed in photoluminescence (PL) measurement of Zn doped Ge samples with extremely low concentration of other impurities. The complex, which we call a bound-double exciton complex (BDEC), has a novel feature of the closed hole shell structure and provides an extraordinarily strong PL intensity. Such a complex has been neither proposed nor observed in semiconductors. The PL spectra from our least doped sample (NA = 1.2 x 1014 cm−3), denoted Ge/Zn-1, are shown in Fig. 1. The peaks α are unambiguously assigned to radiative recombination of BDEC by strong dependence of their PL intensity on excitation intensity. The spectra also contain another kind of luminescence arising from a single exciton bound to the double acceptor, that we will denote (BE)da. Existence of (BE)da was originally predicted by Hopfield and first detected for unidentified double acceptor in GaSb.1 To our knowledge, there are no reports on (BE)da in Si or Ge. The broad peaks γ were assigned to (BE)da by their weak dependence on excitation intensity.
Luminescent Fractal Reactions: Exciton Annihilation on Percolation Clusters
Authors: Anacker L.W. , Kopelman R. , Klymko P.W.
Published: February 2023

We report here the first complete study of fractal reaction kinetics.1-3 This fractal reaction is a prototype of heterogeneous chemical kinetics and is of potential application to chemical catalysis and biological molecular energy transport. We note that for the binary reaction the classical (Euclidean space) kinetic equation is: However, on fractal spaces, the equation is where h=1-ds/2 and ds is the spectral dimension of the fractal space.
Fluorescence Properties of (Ho,Ln)P5O14 Crystals
Authors: Szafraṅski C. , Stręk W. , Jeżowska-Trzebiatowska B.
Published: February 2023

In last decade of years the class of stoichiometric lanthanide pentaphos­phate (LnP5O14) crystals has been extensively investigated. This class of lan­thanide crystals has attracted much attention because of their application to miniature lasers as well as because of their unusual fluorescence properties. Among of lanthanide pentaphosphates the spectroscopic properties have been reported for Ln = Pr, Nd, Eu, Tb, Er ions [1].
New computed radiography utilizing photostimulated luminescence of BaFX:Eu2+ (X=Cl,Br,I) phosphors
Authors: Miyahara Junji , Takahashi Kenji , Kato Hisatoyo
Published: February 2023

New computed radiography utilizing the phenomena of photostimulated luminescence (PSL) was developed to resolve the essential problems of the conventional radiography utilizing the intensifying screen-film combination. The basic constituents of the system are "Imaging Plate", in which photostimulable phosphors are used as the memory material for temporarily storing X-ray image; "Image Reader", which converts the latent image on the plate into digital time-series signals; "Image processor", which manipulates the image digitally with a high speed computer; "Image Recorder", which records the processed signals on a photographic film. The plate can be used repeatedly to store X-ray image simply by flooding it with light to erase the residual energy.
f-f Electric Dipole Intensity Mechanisms for Rare Earth Ions
Authors: Reid Michael F. , Richardson F. S.
Published: February 2023

Transitions within the fN configurations of rare-earth ions are parity forbidden and only became allowed by virtue of external perturbations. A general parametrization of the intensities of transitions between crystal-field levels requires a set of parameters

{

A

tp

λ

}

(
λ
=
2
,
4
,
6
;
t
=
λ
−
1
,
λ
,
λ
+
1
;
p

determined by symmetry).1 However, if the 'superposition' approximation, that the rare-earth-ligand interactions are cylindrically symmetric and independent, is valid, the t=λ parameters are unnecessary and the parametrization reduces to the usual Judd-Ofelt parameter set {Atp Ξ (t,λ)}.
Up conversion of U4+ in ThBr4
Authors: Hubert S. , Song Chong Li , Genet M. , Auzel F.
Published: February 2023

Up to now, most of the experimental examples involving the anti-Stokes fluorescence called up-conversion were dealing with rare earth ions [1]. For the first time we have found that tetravalent uranium as a doping ion in single crystal as well as in microcrystalline powder form of thorium tetrahalides acts as an up-converter. In the case of ThBr4 : U4+, infrared excitation with λ > 0.82 µ at room temperature gives an emission band in the red between 0.67 and 0.72 µm |2|. The power law of the red emission with respect to the infrared excitation is found to be quadratic ; this is the evidence that excitation is obtained by a two-photon process. Furthermore, we found that the 0.69 µm emission follows a linear law with the U4+ concentration for a concentration range from 0.006 % up to 0.05 % in weight. From this result, we can conclude that the up-conversion process takes place in one uranium ion. For higher concentration a quenching effect is observed. We found that the efficiency was optimized using microcrystalline powder with grain size of about 0.2-0.3 µm and a concentration of 0.05 %. In this case the efficiency is multiplied by a factor of 20 in comparison with the same sample single crystal. This is believed to be due to photon trapping as demonstrated by life time variations with sample shapes. The red emission from 3P0 is obtained by the absorption of photons at 0.95 µm 3H4 → 3H6 and 1.17 µm 3H4 → 3F6 as shown by the double beam [1] excitation spectra of figure 1. The level diagram (fig. 2) of U4+ shows that the 3P0 fluorescence can be obtained by different ways such as summation of two photons (0.95 µm plus 1.17 µm or 2 × 0.95 µm or 2 × 1.17 µm) with phonon assistance, followed by a multiphonon relaxation.
"A Theoretical Scheme for 4f←→4f Intensity calculations. Optical absorption intensities in YAℓO3:Pr3+."
Authors: Malta O.L. , Gouveia E.A. , de Sá G.F.
Published: February 2023

The Judd-Ofelt theory [1] has been successfully used in the interpretation of rare-earth 4f↔4f intensities. It is a common practice in this theory to express the oscillator between two J-manifolds, belonging to the ground 4fN configuration, as a function of three intensity parameters Ωλ (λ= 2, 4, 6). If these parameters are treated phenomenologicaly, besides the eletric-dipole mechanism other contributions are automaticaly absorved making it impossible to distinguish between them. Among these contributions, the Pseudo-Multipolar Field has been shown to be of particular importance [2,3]. Vibronic as weel as correlation effects may also be of relevance. It is, therefore, of interest to perform theoretical calculations in order to assesss the relative contribution of each of these mechanisms.
Measurement of Quantum Efficiencies in Laser Crystals by Compensation Calorimetry
Authors: Danielmeyer H.G. , Stark E.
Published: February 2023

Nonradiative decay processes decrease the quantum efficiency and increase the pump threshold of lasers. We present a simple measurement method for quantum efficiencies adapted to the problem of small crystals of arbitrary shape and new results on sources of nonradiative decay.
Electromodulation Reflection Method for Study of the Forming Process in DC Electroluminescent ZnS:Mn,Cu
Authors: Wu Boxi , Chen Jianning , Hong Xiuxia , Liu Far
Published: February 2023

It is well known that the forming process is critical to the operation of DC electroluminescent ZnS:Mn,Cu powder panel.(1)(2) However, the mechanisms of the forming process have not yet been completely known.
Copper-Catalyzed Low-Voltage Cathodic Electroluminescence at Anodized Aluminium Electrode
Authors: Haapakka K. , Kankare J. , Kulmala S.
Published: February 2023

Electroluminescence is observed at several semiconductor-electrolyte interfaces during the reduction of hydrogen peroxide, persulphate and oxygen.1-3 This luminescence is presumably caused by the electron-hole recombination in a semiconductor.
Laser Induced Gratings in CdS
Authors: Kalt H. , Lyssenko V.G. , Bohnert K. , Klingshirn C.
Published: February 2023

The diffraction from laser induced gratings is investigated in CdS at low temperatures in the spectral region close to the absorption edge. The coherent, monochromatic laser beams of about 3 nsec temporal halfwidth coincide on the sample under an angle of 1,6° forming a grating with a period of 17,4 μm. The sample thickness is about 7 μm, so we are dealing with a "thin" grating. The intensities of the beams are varied from about 50 W/cm2 to 106 W/cm2, either by simultaneously attenuating both beams (so keeping their ratio constant) or by changing only one intensity, while the other is fixed.
Relaxation of Localized Excitons in KCl:I and RbCl:I
Authors: Arimoto Osamu , Sasaki Kazuaki , Nakatani Hiroyuki , Kan’no Ken-ichi , Nakai Yoshio
Published: February 2023

Recombination luminescence in alkali halides is originated from the relaxed exciton in the form

(

X
2
−

+
e

)

, where

X
2
−

means halogen molecular ion. Similar situations have been recognized also in the cases of localized excitons in alkali halides containing heavier halogen impurities. Excitation into the absorption bands due to isolated halogen impurities gives rise to broad emission bands in the region of blue-green light (BG emission). They are attributed to the radiative decays from relaxed excited states with a configuration (XY− + e) of two-center type, where XY− means a heteronuclear diatomic molecule consisting of a host (X) and an impurity (Y) halogen ion.1)
Luminescence of amorphous and crystalline Ca3Cr2Si3O12
Authors: Szymczak H. , Pajączkowska A. , Pataj K.
Published: February 2023

Luminescence spectroscopy is essentially sensitive to local environments. Consequently, it can be one of the most useful methods for elucidation of the short-range structure of the amorphous material. The luminescence studies of amorphous materials are not very common in literature. We report here on a comparative study of the luminescence spectra in amorphous insulating Ca3Cr2Si3O12 and its corresponding crystalline counterpart. The amorphous Ca3Cr2Si3O12 compound has been obtained by a fast cooling of the liquid solution. The amorphous state was confirmed by x-ray diffraction analysis. The chemical composition of the specimens was determined by electron-probe microanalyser. In the crystalline state this compound has garnet structure and exhibits long-range antiferromagnetic order with the Neel temperature of 12 K. According to our magnetic and EPR measurements no magnetic long-range order has been found in amorphous Ca3Cr2Si3O12. Below 20 K this compound has to be considered as insulating spin glass with large antiferromagnetic interactions. The luminescence spectra of both considered compounds have been measured at 1.7 K. The emission decreases strongly with increasing temperature and disappears above 10 K. In both cases the luminescence spectra consist of the sharp lines followed by a number of broad bands. The emission which is observed in garnet crystal is not intrinsic but results from 2E - to - 4A2transitions of impurity-perturbed Cr3+ ions. The bound-exciton lines are not observed in luminescence spectrum. Several very sharp lines, found at energies lower than intrinsic 4A2-to-2E absorption, are attributed to the magnon assisted transitions. The luminescence spectrum of amorphous Ca3Cr2Si3O12 is interpreted in terms of spin-wave-like excitations. The spin-wave-like excitations in spin-glass state have been predicted theoretically and confirmed experimentally in number of neutron scattering experiments. In the luminescence spectrum of amorphous Ca3Cr2Si3O12 the sharp line near 13240 cm-1 is interpreted as zero-phonon-zero-magnon transition and strong line near 13025cm-1 is attributed to magnon-assisted transition. Second broad band at 12840cm is identified as a vibronic transition. Analysis of the magnon-assisted transition yields value of the average nearest-neighbour exchange interaction between chromium ions of about 20cm-1. This result is in agreement with our EPR data. In the case of antiferromagnetic garnet the value of the exchange interaction is estimated to be equal 0.6cm-1. This surprising difference can be explained by considerable change in distance between magnetic ions in garnets after amorphization. Analysis of the emission line shape leads to the conclusion that the distribution of the crystal field acting on Cr ions in amorphous Ca3Cr2Si3O12 is narrow in contrary to that observed by Mössbauer spectroscopy in amorphous Y3Fe5O12 [1].
Phonon Assisted Energy Transfer in SrF2:Er3+ 1)
Authors: Wietfeldt John , Moore David , Wright John C.
Published: February 2023

Er3+ doped SrF2 has been investigated using site selective laser spectroscopy.3 Several distinct crystallographic sites have been observed, including clusters, where 2 or more charge compensated Er3+ ions are associated with a unique separation between Er3+ ions are associated with a unique separation between Er3+ ions. It has been shown that in one particular dimer, where the two ions are not in identical environments, energy transfer from one ion to the other can occur.
Optical Spectral Diffusion Processes in Organic Glasses on a Logarithmic Time Scale
Authors: Friedrich J. , Breinl W. , Haarer D.
Published: February 2023

A photochemical hole, burnt into the lowest absorption band of quinizarin in an alcohol glass, was used as an optical detector for structural relaxation processes of the glass. The hole burning photochemistry is due to a light induced breakage of an intramolecular hydrogen bond between the dye molecule and the solvent (1). The stability of the photoproduct is determined by the local conformation of the solvent cage. Hence, one expects a wide distribution of back transfer rates R from the product to the reactant state. As a probe for the number of relaxed molecules we use the area of the photochemical hole. Fig.1 shows the normalized hole area as a function of probing time. The recovery dynamics of the hole occurs on a logarithmic time scale and is subject to a remarkable deuteration effect. In a similar way, the width of the optical transition increases on a logarithmic time scale. To find a quantitative interpretation of the measured logarithmic slopes we introduced the concept of photochemically induced tunnel systems. We consider the product and the educt state as a special two level system, with a distribution of tunneling rates R given by the well known distribution of the TLS states of glasses (2, 3).
Low Dimensional Chaos in Simple Forced Laser Systems
Authors: Arecchi F.T.
Published: February 2023

The laser dynamics arising from quasi-resonant interaction between a single mode field and a medium with a homogeneously broadened gain line is described by the equations coupling five variables, namely, the complex field amplitude E, the complex medium polarization P and the real population inversion D. At resonance, E and P are real and the equations reduce to where k, γ1 and γ11 are the relaxation rates of field, polarization and population, respectively, and D0 is the population imposed by the pump.
Laser with modulated loss: A complete description of its periodic and aperiodic behaviour.
Authors: Poggi A. , Puccioni G. P. , Gadomski W. , Arecchi F. T. , Tredicce J. R.
Published: February 2023

We report new and detailed studies of a CO2 laser system with modulated losses. It has been shown previously both experimentally and theoretically that such a homogeneously broadened laser [1] (and other similar systems [2]) can display instabilities and eventually chaotic behaviour when a parameter is modulated. We have improved the stability of our previous system and using a fast transient recorder we were able to characterize the period-doubling transition to chaos, including a stable f/8 subharmonic. We find periodic windows inside the chaotic region which do not follow the predicted sequence of the well-known logistic map. We present the time behavior, Poincare sections, phase-space portraits and power spectra that permit unequivocal Identification of a transition to chaos. We present other measures of the dynamical behaviour such as bifurcation diagrams showing generalized multistability and phase diagrams in the parameter space which localize the unstable regions. Dimensionality tests on digitized time series show the formation and evolution of a strange attractor as parameters are varied. It was possible to measure the dimension before and at the accumulation point of a Feigenbaum cascade and then into the chaotic region. The results are in good agreement with general theory on nonlinear dynamics [3]. For the first time return maps have been obtained from an experimental system and they reveal the breakdown of an analogy with the Feigenbaum model for a map with a quadratic maximum when we enter into the chaotic region.
Subharmonic oscillations and chaos in a laser diode coupled to an external cavity
Authors: Otsuka Kenju , Mukai Takaaki
Published: February 2023

The first clear evidence of oscillatory instabilities leading to optical chaos is found in a compound cavity laser diode (LD). The intermode interaction through a third-order nonlinearity provides adequate explanation.
On the Stability of Counter-Propagating Waves in a Nonlinear Kerr Medium
Authors: Silberberg Yaron , Bar-Joseph Israel
Published: February 2023

Two plane waves interfering in a nonlinear optical Kerr medium, in one of the geometries shown in Fig. 1, were shown to display self-oscillations, period doubling and chaos as the light intensity is increased [1]. The system contains no external feedback in the form of an optical resonator, and its steady state solution is almost trivial, predicting no energy transfer between the two waves, and the light intensity emerging from the two ends of the system is the same as the incident intensity. Nevertheless, the time dependent behavior of the two waves beyond the instability threshold contains many of the interesting features usually found in more complicated optical systems. The interfering beam system is attractively simple, and it is presented here as a demonstration for the strength of a model suggested recently [2].
Perturbations and Instabilities in Laser Mode-Locking Dynamics
Authors: New G.H.C. , Catherall J.M.
Published: February 2023

In this paper, we present a range of theoretical results that relate to the dynamical properties of mode-locked lasers, discussing perturbations induced by stochastic background fluctuations and instabilities arising from self-pulsing effects in hybrid systems.
Mode-Mode Competition in a Homogeneously Broadened Ring Laser
Authors: Narducci L.M. , Tredicce J.R. , Lugiato L.A. , Abraham N.B. , Bandy D.K.
Published: February 2023

We have analyzed the stability and temporal behavior of a multimode homogeneously broadened ring laser and identified multiple steady state solutions and a low threshold for pulsing behavior.
Longitudinal Mode Competition in Semiconductor Injection Lasers
Authors: Ogasawara Nagaatsu , Ito Ryoichi
Published: February 2023

In transverse-mode stabilized injection lasers, a low frequency intensity noise arises at certain ranges of temperature and bias current, where an oscillation mode jumps to a neighboring mode1); random switching1,2) takes place between these modes and the laser power switches between two distinct levels since output power is different between different modes. There is a general rule in the power change at random switching; a power level PS for a shorter wavelength mode (s-mode) is always higher than a power level P1 for a longer wavelength mode (1-mode).1,2
Steady State and Stability Properties of a Multimode Inhomogeneously Broadened Laser
Authors: Narducci L.M. , Tredicce J.R. , Abraham N.B. , Bandy D.K. , Lugiato L.A.
Published: February 2023

We analyze the multiple steady states of a multimode inhomogeneously broadened ring laser and their linear stability. From these results, we predict hysteresis and pulsations for appropriate control parameters.

The effects of the inhomogeneous broadening on the unstable behavior of single-mode lasers have been documented extensively, both theoretically and experimentally1. Only limited attention, however, has been paid to the multimode extension of this problem2, in spite of the fact that the earliest multimode analysis for a homogeneously broadened ring laser appeared more than 15 years ago3.
Effects of Time-Dependent-Pararameter Variation on the Period-Doubling Route to Chaos.
Authors: Kapral Raymond , Mandel Paul
Published: February 2023

A common method for investigating bifurcation points in physical systems consists in slowly changing a control parameter and observing the state of the system as a function of the instantaneous value of the parameter. The main reason for adopting this procedure is it’s convenience: An entire bifurcation diagram can be constructed in a single sweep of the bifurcation parameter. The literature on laser instabilities contains many examples of such studies.1
Instrinsic Dynamical Instability in Optical Bistability with Two-Level Atoms
Authors: Rosenberger A. T. , Orozco L. A. , Kimble H. J.
Published: February 2023

Self pulsing due to the single-mode instability has been observed in optical bistability.1 This self-pulsing instability has its roots in corresponding instabilities first analyzed for the homogeneously broadened laser. It shares a common physical origin in the intrinsic mechanism by which a strong intracavity field alters the absorption profile of the intracavity medium to produce amplification at frequencies offset from that of the strong field.
Universal Properties and Universal Numbres and their Measurments in Experiments on Chaotic Dynamical Systems*.
Authors: Procaccia Itamar
Published: February 2023

The number of carefull experiments that exhibit a transition to low dimensional chaotic motion has been growing steadilly in recent years.1 Techniques to characterize strange attractors and to measure important invariants like dimensions 2,3, entropies 4,5 and Lyapunov exponents were prposed and widely implemented.There has not been however sufficient experimental stress on universal properties. To my knowledge, the only experimental verifications of universal behviour to date pertained to the subcritical regime (on the way to chaos) and right at threshold. These include measurements of the accumulation rate of period doublings, the spectrum at onset of chaos via period doubling, and recently some universal numbers and spectra pertaining to the transition via quasiperiodicity.8 In the chaotic regime one is still coming up with numbers for the invariants that are not related to any universal properties.In this lecture I plan to review the recent theoretical results on universal behaviour in the chaotic regime, in addition to some novel methods for seeing universality at threshold. Most of these predictions have not been corroborated experimentally yet.
The Dynamics of Line Competition and Line Selection in Off-Resonantly Pumped Systems
Authors: Dupertuis M.A. , Salomaa R.R.E. , Siegrist M.R.
Published: February 2023

Off-resonantly pumped systems emit radiation predominantly on line center or at the Raman shifted frequency. We will discuss line competition for the lambda, vee, cascade, combined vee-lambda and parallel configurations.
Regular and Chaotic Dynamics of a Single- or Multimode Ruby NMR Laser
Authors: Broggi G. , Brun E. , Derighetti B. , Meier P.F. , Ravani M. , Stoop R. , Badii R.
Published: February 2023

The solid state, nuclear spin-flip, ruby nuclear magnetic resonance (NMR) laser with its operating frequency in the rf-range has a variety of ordered (steady, oscillating, pulsing) and chaotic dynamic states. It behaves as a low-Q, lowely pumped, homogeneously broadened nonlinear laser system which may be modeled by Bloch-Kirchhoff equations [1]. Due to the five different NMR frequencies the ruby NMR laser can operate as a single- or multimode device. It can be driven by an external rf-field either tuned or detuned to NMR frequencies. A low frequency modulation, typically of the order of 100 Hz, of one of the system parameters adds another degree of freedom to the system which can be used to study systematically the various roads of chaotic modulation response.
Low-Dimensional Attractors for a Single-Mode He-Xe Ring Laser
Authors: Abraham N. B. , Albano A. M. , Bandy D.K. , Das B. , deGuzman G. , Isaacs T. , Tarroja M. F. H. , Yong S. , Adams S. P. , Gioggia R. S.
Published: February 2023

Calculations of the order-2 information dimension, D2, and the order-2 Kolmogoroff entropy, K2, from digitized intensity versus time sequences from experimental measurements of an unstable, unidirectional, single-mode, inhomogeneously-broadened He-Xe ring laser indicate that the dynamical evolution of the laser can be characterized by an attractor of relatively low dimensionality. Clear states of periodic and period-doubled pulsations give an attractor dimension of one. Pulsations corresponding to broadband Intensity power spectra yield a fractal dimensionality larger than two, confirming that the origin of the irregular pulsations is deterministic chaos. This behavior, which is similar to that found in an earlier analysis of data from a Fabry-Perot laser using the same lasing medium, is deemed rather surprising in view of the fact that inhomogeneously broadened lasers are usually modelled in phase spaces of very high dimensionality.
Resonatorless Optical Bistability
Authors: Bowden Charles M.
Published: February 2023

Intrinsic (mirrorless) optical bistability (MOB) has been predicted independently by a number of authors1. Recent experiments have demonstrated at least one major aspect of this phenomenon, i.e., MOB due to increasing absorption2. Other categories of MOB which have been predicted from theoretical models are caused by: interatomic correlation in a many-body quantum model, the anharmonic contribution in a classical Duffing oscillator, the local field correction in the macroscopic Maxwell-Bloch formulation, and coherent dipole-dipole interaction in a microscopic semiclassical model of a finite number of damped, two-level atoms driven by an external field3. All of these models share a single common characteristic which causes MOB in some region of the parameter space of each model. The characteristic is simply: an interaction-dependent nonlinearity which causes a renormalization of the resonance frequency. In each case, the sign and magnitude of the incident field detuning from the unrenormalized resonance is a crucial parameter.
Squeezed-coherent State Generation via Wideband Four-wave Mixers
Authors: Yurke B.
Published: February 2023

Four-wave mixers have been investigated theoretically as potential sources of squeezed-coherent radiation 1,2 and there are a number of experimental efforts underway to demonstrate the production of squeezed-coherent radiation via such devices.3,4,5 Here the results of some wideband calculations of the output of cavity four-wave mixers is presented. The wideband squeezed-coherent radiation generated by such devices may be detected via a wideband homodyne detector.6 Wideband squeezing will manifest itself in the noise-power spectrum of the homodyne detector's output as regions where the noise is reduced below the level that is observed when no light enters the input port of the homodyne detector. Wideband homodyne detection allows one to look for squeezing at frequencies far from d.c. This gives the experimentalist the freedom to look for squeezing in the frequency range where his detector performs best.
Four-wave-mixing Processes in Multiple-pump Multiphonon Systems: Effects of Coherence Length
Authors: Lin J. T.
Published: February 2023

The effects of four-way-mixing (4WM) and the generation of high-order Stokes (HOS) in a single pump single phonon system have been studied previously.1 In the present paper we shall develop a general theory which provides the equations of motion in a multiple pump multiphonon system which includes all pair field interactions via both Raman and 4WM. The effects of the coherence length of the pump pairs and of the 4WM on the generation of HOS will be investigated analytically and numerically. Pump depletion and the feedback effects due to the high-order processes will be included. The dephasing of the phonon modes will be derived via the phonon-phonon interaction in the Markovian approximation.2
Quantum Stochastic Theory of Optical Bistability
Authors: Carmichael H. J. , Sarkar Sarben
Published: February 2023

Quantum-statistical theories attracted considerable attention in the early history of optical bistability.(1) More recently, there has been less activity in this area; perhaps due partially to the lack of experimental work, and partially to the increasing interest in instabilities and chaos. It has now been demonstrated, however, that experiments which come very close to realizing the theoretical ideal—two-level homogeneously broadened atoms in a ring cavity— can be performed with quantitative precision. (2) Moreover, the rising importance of optical chaos is reason for directing attention towards, rather than away from, quantum-statistical studies, since there questions concerning quantum chaos might be addressed.
Observation of Squeezed Light in an Optical Cavity
Authors: Slusher R. E. , Hollberg L. , Yurke B. , Mertz J. C.
Published: February 2023

We report the observation of squeezed light noise at power levels near the vacuum fluctuation level using nondegenerate four-wave-mixinq in an optical cavity.(1-4) The light at cavity resonances is observed using a balanced homodyne detector with a portion of the pump beam serving as a local oscillator.(5) The noise power is amplified by a factor A at a particular phase and attenuated by 1/A at a phase shift of 90°. This is a basic identifying characteristic of squeezed 1ight.