bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser Induced Degeneracies
Authors: Kylstra N J , Latinne O , Dörr M , Joachain C J , Purvis J , Burke P G , Terao-Dunseath M , Noble C J
Published: February 2023

Atomic states may be embedded in the continuum by dressing the atom by an intense laser field. This is often referred to as a laser induced continuum structure (LICS) [1]. This continuum, in general, also has a natural structure due to the doubly excited states, or autoionizing states, of the atom. We have considered the situation in which a complex atom or ion is subjected to an intense laser field such that the LICS states and autoionizing states occur simultaneously. We have have found that, by tuning the frequency and intensity of the field, the states can become degenerate, i.e. have the same position and width.
Rapidly Ionized Atoms as a Tunable Source of Ultra-Short Coherent VUV Radiation
Authors: Sergeev A.M. , Kim A.V. , Vanin E.V. , Downer M.C.
Published: February 2023

Our paper addresses the problem of nonlinear conversion of high
intensity femtosecond laser pulse spectra, during the process of rapid
multiphoton gas ionization. Previously, various modifications of laser
spectra resulting from the nonlinear response of media have been
observed in investigations of intense laser beam interactions with
rarefied gases. The observed "elemental” modifications include
blue shifting of the pulse frequency produced by temporal variations
in the refractive index due to gas ionization [1-3],
superbroadening of the focused laser pulse spectrum caused by
avalanche gas ionization [4,5], and high-order optical
field harmonic emission [6-9]. In investigations of
the last process, the atom ionization has usually been treated as a
negative effect that breaks the phase matching conditions between the
fundamental and excited waves. However, in the recent paper of Corkum
[10] and in our paper [11] it has been
demonstrated that ionization itself is precisely the mechanism which
is responsible for high-order harmonic coherent pulse generation.
Hence, atoms ionized in the strong laser field constitute a. nonlinear
medium which has attractive potential for producing supershort
(spectrum broadening), tunable (blue-shifting), ultrashort wave
(higher harmonics) radiation. The question arises: can these
possibilities be exploited simultaneously to create a unique source of
coherent radiation? Our paper proves theoretically this possibility
and defines the relevant conditions for experimental
demonstration.
Possible Applications of the Self-Channeled Propagation of Powerful Ultra-Short Laser Pulses in Matter
Authors: Borovskiy A.V. , Korobkin V.V. , Prokhorov A.M.
Published: February 2023

One of the most interesting physical effects having much promise is the relativistic and charge-displacement self-channeling of the ultra-short laser pulse.
X-Ray Lasers Pumped by Ultrashort Pulse Optical Lasers
Authors: Eder D. C. , Amendt P. , DaSilva L. B. , Donnelly T. D. , Falcone R. W. , London R. A. , Moon S. J. , Strobel G. L. , Rosen M. D. , Wilks S. C.
Published: February 2023

X-ray lasers have been available for almost ten years with the majority still being pumped by high energy (≈ 1 kJ) modest duration (≈ 500 psec) optical lasers. The recent availability of ultrashort pulse (≈ 100 fsec) optical lasers with modest energies (≈ 1 J), has renewed the interest in x-ray laser schemes that could be pumped by these relatively inexpensive, compact lasers. In one x-ray laser scheme, the ultrashort pulse, high intensity laser ionizes the target gas via the electric field of the laser with subsequent recombination and lasing between the first excited state and the ground state. In contrast with collisional ionization, this ionization mechanism may result in nearly complete emptying of a given ionization stage and has the potential of leaving relatively cold free electrons. There is potential for lasing down to wavelengths of order 100Å, e.g. Li-like Ne at 98Å, using lasers with energies of order 1 J.1 Lasing at significantly shorter wavelengths, e.g. Li-like Al at 52Å or H-like B at 48Å, appears to be very difficult because of excessive heating associated with Raman instabilities.2 There have been recent experimental results showing possible evidence of lasing in H-like Li at 135Å.3,4 We discuss theoretical efforts on this approach to lasing and modeling efforts to understand the recent data. A second approach to x-ray lasing using ultrashort pulse lasers is based on innershell photoionization which has the potential of reaching short wavelengths, e.g., 15Å in Ne. The indirect ionization process of this scheme, where incoherent x rays emitted from a nearby plasma ionize the innershell electron, results in higher energy requirements. For example, lasing in Ne is calculated to require a pump laser with approximately 10 J in a 100 fsec pulse. The energy requirements are significantly reduced by considering longer wavelengths, e.g., 45Å in C, but a rapid rise time (≈ 50 fsec) for the x rays is still required to minimize collisional ionization. For both approaches the use of modest energy ultrashort pulse lasers allow for much higher repetition rates than available with conventional x-ray lasers pumped by high energy laser drivers. We discuss new applications appropriate for such high-repetition-rate x-ray lasers.
Application of X-ray Lasers as Imaging and Plasma Diagnostics
Authors: Wan A. S. , Da Silva L. B. , Barbee T. W. , Cauble R. C. , Celliers P. , Lee H. R. , Libby S. B. , London R. A. , Matthews D. L , Mrowka S. , Moreno J. C. , Ress D. , Trebes J. E. , Weber F. , Van Wonterghem B.
Published: February 2023

Since the first demonstration of a soft x-ray laser (XRL) at the Lawrence Livermore National Laboratory1, XRLs have been considered for applications in the fields of microscopy, holography, material science, and plasma physics. With its short wavelength, controllable short pulse duration, high brightness and coherence, the XRL is ideally suited as a plasma diagnostic to image rapidly evolving (< 1 ns) laser-driven plasmas with high electron density (1021 cm-3 < ne< 1024 cm-3). Over the past 2 years, we have made significant progress in the development of short-wavelength multilayer mirrors and beam splitters in the soft x-ray regime and are pioneering the development of XRLs as an imaging diagnostic for laser plasmas. We have used XRLs as high fluency monochromatic radiographic sources2. We have also used XRLs to measure 1-D density gradients of laser plasmas using the Moiré deflectometry technique2. We have began testing a 2-D XRL interferometer, in the Mach-Zehnder configuration, which will allow us to measure absolute 2-D plasma density profiles. The demonstration of the 2-D interferometer and the application of this interferometer to understand the physics of laser plasmas will be our primary focus for the near future. We are also working on the development of enhanced-coherence, high-brightness XRLs. During the past year we have experimentally and theoretically characterized shaped XRLs3 as part of our research on adaptive spatially filtered XRLs to develop a single-mode oscillator which has application beyond the 2-D interferometer and can yield a 3-D hologram of an imploding inertial confinement fusion (ICF) capsule.
Stimulated Ionization Scattering in Plasmas Produced by High Intense Ultrashort Laser Pulses
Authors: Kim A.V. , Abramyam L.A. , Sergeev A.M.
Published: February 2023

The paper deals with the structural instability of a focused high-power short laser pulse capable of producing rapid field-induced ionization of a dense gas. This is a key problem in proposed applications of intense subpicosecond lasers, including the creation of dense cold plasmas for X-ray lasing, the laser-driven particle acceleration schemes and the processes of laser frequency up-conversion. This problem has actively been discussed recently (see, e.g., [1-3]), but the main attention has been payed to the analysis of the defocusing properties of "smooth" emerging plasma objects. In our consideration the emphasis is layed on electrodynamics, or more precisely, on the joint evolution of the wave field and plasma for a specific nonlinearity law, assuming the field ionization (tunneling or multiphoton) rate for the issues of interest to be a known function of the field amplitude. As has been shown in a previous paper [4], strong electromagnetic waves propagating in media with ionization nonlinearity may cause the development of various types of ionization instabilities. The main role under the discussed conditions is played by the instability of the stimulated ionization scattering. We demonstrate that the dynamics of the interaction between ionizing short laser pulses and gases may be accompanied by the stimulated forward ionization scattering at small angles to the propagation direction, which completely changes the structural and temporal characteristics of the laser field and produced plasma.
A 21.5 Å X-ray Laser Pumped by a 500 fs Laser Pulse*
Authors: Maxon S. , Dalhed S. , Osterheld A. , London R. , Alley E.
Published: February 2023

With the development of short-pulse lasers,1 applications occupy a position of prime importance. In this paper we investigate the possibility of pumping short-wavelength collisional x-ray lasers.
Stimulated Brillouin Backscatter Driven By A Short- Pulse Laser
Authors: Hinkel D. E. , Williams E. A. , Berger R. L.
Published: February 2023

The interaction of a short-pulse laser with plasma[1],[2], where the pulse length is short compared to the plasma length and the Rayleigh length, drives stimulated Brillouin backscatter (SBS) in a qualitatively different manner than when the pulse length is long compared to the plasma length [3]. In the latter case it is well-known that if the damping rate is less than the absolute growth rate, the instability is absolutely unstable. In the former case, SBS is not absolutely unstable even in the absence of damping.
Leaky Mode Propagation in a High Intensity Plasma Waveguide
Authors: Lynch J. , Durfee C.G. , Milchberg H.M.
Published: February 2023

The finite thickness of the electron density barrier in the shock driven plasma waveguide1 (see Fig. 1 of paper Mode Properties of a High Intensity Plasma Waveguide, this conference) implies that formally, there are no bound modes (ie. no discrete spectrum of channel propagation wavenumbers) since all fields leak to some extent. For sufficiently large ΔNe and rm (where ΔNe = Ne(rm)-Ne(0) is the electron density difference between the peak and on-axis electron density and rm is the radius to the electron density peak), low order leaky waveforms are effectively indistinguishable from eigenmodes of a channel having Ne(r)= Nemax for r>rm (idealized channel). As an example of this, Fig. 1 compares leaky waveforms from a model channel (consistent with predictions of our laser-plasma hydrodynamics code1) to eigenmodes of the corresponding idealized channel. In this case, the field attenuation in the walls is sufficient to result in little tunneling or leakage of the lowest order p=0, m=0 mode (where p and m are radial and azimuthal mode indices). The p=1, m=0 mode, however, is sensitive to the finite barrier thickness in this case.
Observation of laser-assisted Auger decay in argon
Authors: Schins J.M. , Breger P. , Agostini P. , Constantinescu R. , Muller H.G. , Grillon G. , Antonetti A. , Mysyrowicz A.
Published: February 2023

We investigated the effect of an intense dressing field on the energies of electrons ejected in an Auger process by means of electron spectroscopy. An amplified Ti:S laser provides infrared (800 nm) pulses of 40 mJ ranging from 150 femtoseconds to 8 picoseconds.[1] Part of the infrared beam is focused onto a liquid metal (gallium) target to produce broadband X-radiation. Auger electrons resulting from the X-induced LMM transition in argon[2] are detected in a time-of-flight electron spectrometer. When the X-ray beam and the infrared dressing beam overlap in space and time, sidebands appear around the Auger peaks, corresponding to absorption or emission of photons from the dressing field.
Photoelectron Spectroscopy of Laser Excited Surfaces Using Synchrotron Radiation
Authors: Long J.P. , Itchkawitz B.S. , Kabler M.N.
Published: February 2023

For over a decade, laser pump-probe photoelectron spectroscopy (PES) has proven unique in its ability to determine the energy, momentum, and population dynamics of surface and near-surface excited states in solids.1,2 Practitioners most often generate the requisite probe UV pulse with laser upconversion techniques. The broader and continuous tunability of synchrotron radiation (SR) make it also an attractive source, albeit with reduced ultimate time resolution, and, in fact, SR is employed for time resolved spectroscopies spanning the far infrared to the hard x-ray regimes.3 We have developed a laser-pump, SR-probe PES system with nanosecond resolution at the National Synchrotron Light Source, and here we summarize results from GaAs, C60 films, and Si. This work anticipates specific areas where new photon probes, particularly femtosecond high harmonic generation4, UV-FEL’s, and 3rd generation SR sources, will find important applications.
High Resolution Stimulated Brillouin Gain Spectroscopy
Authors: Grubbs W. Tandy , MacPhail Richard A.
Published: February 2023

Brillouin spectroscopy has been an important source of information about the collective dynamics of molecules in liquids.1,2 In a conventional Brillouin experiment, a Fabry-Perot interferometer is used to measure the spectrum of laser light scattered at an angle θ by spontaneous density fluctuations in a sample. The Brillouin peaks in the spectrum arise from the acoustic wave component of these density fluctuations, and accordingly the shift of the Brillouin peaks from the elastic Rayleigh scattering peak corresponds to the acoustic frequency, while the width of the Brillouin peaks corresponds to the acoustic damping rate. By varying θ, and thus the scattering wavevector, one can determine the dispersion in the speed of sound and the acoustic attenuation, which in turn characterize the elastic and viscous responses of the fluid. A more detailed analysis of the spectral lineshape with the aid of generalized hydrodynamic theories allows one to determine the values of transport coefficients that describe the molecular dynamics.1
Spectroscopy of Jet-Cooled Ag2Au
Authors: Pinegar Jacqueline C. , Langenberg Jon D. , Morse Michael D.
Published: February 2023

While the electronic structure of metallic atoms can be calculated accurately using ab initio quantum chemistry, and infinite metallic solids are rather well understood through the methods of solid state physics, metallic clusters ranging in size between these two extremes are understood to a much lesser extent. The study of these small metal clusters provides fundamental information about bonding in metals, such as the contribution of the various orbitals to the bonding and the effect this has on bond strengths and other properties.
Study on isotope mass difference (16O, 18O) effect on CO2 laser oscillation spectra
Authors: Saito Yasuyuki
Published: February 2023

It is difficult to explain continuity between12C16O2−12C16O2−12C18O2 laser oscillation spectra due to only oxygen isotope–mass–difference (16O, 18O) effect on rotation energy level of fine structure for 00°1 to 10°0 of transition of CO2 molecules. In order to explain fine structure interval of CO2 laser oscillation spectra, it is necessary to consider CO2 molecule shape of smaller O=C bond length (this means smaller rotation inertia moment of a CO2 molecule) through nuclear characteristics (for example, gravity center, shape, spin) in a CO2 molecule.
FTIR Spectra and Torsion-Vibration Coupling in 13CD3OH
Authors: Xu Li-Hong , Lees R.M.
Published: February 2023

Methanol is one of the simplest molecule capable of large amplitude torsional motion. This couples with the vibrational motions and has significant effects on the infrared spectrum, illustrated at low resolution in Fig. 1 for the 13CD3OH isotopomer in the 950-1450 cm-1 region. The complex torsion-vibration energy structure of 13CD3OH is shown in Fig. 2. Level crossings occur among a variety of states giving numerous Fermi and Coriolis interactions. Thus, methanol offers a good test platform for the study of intramolecular vibrational relaxation (IVR) with torsional effects. Furthermore, the ready availability of different isotopomers allows us to seek insight into individual torsion-vibration interaction mechanisms through the substantial changes in symmetry coordinate mixing and vibrational interaction which occur upon isotopic substitution. So far, different bands of 13CH3OH, CH318OH, CD3OH and 13CD3OH as well as the normal 12CH316OH species have all been studied by several groups around the world.1-7
Intermolecular Interactions in the Fluorene Dimer
Authors: Highstrete Lt. Clark , Wessel John
Published: February 2023

Excited state interactions in molecular dimers and higher clusters are of increasing spectroscopic interest because the interactions reveal the nature of the intermolecular potential and provide geometrical information about clusters. Cold clusters were prepared in a supersonic beam and studied by fluorescence excitation and photoionization and spectroscopies. Past studies revealed that benzene dimers are characterized by weak intermolecular interactions in the first excited state, whereas naphthalene dimers undergo strong excimer formation that results in broad electronic spectra. Prior reports2 indicated that fluorene dimers fluoresce efficiently from a lower energy excimer state.
b-Dipole Transitions in X ˜ 2A' t-HOCO Observed by FIR Laser Magnetic Resonance
Authors: Sears Trevor J. , Radford H. E. , Moore Mary Ann
Published: February 2023

The HOCO radical is crucially important in combustion chemistry as the intermediate in the reaction between hydroxyl radicals and carbon monoxide. Studies of the temperature dependence of the rate constant for this reaction implied the existence of the radical intermediate1 but only very recently was HOCO detected in the gas phase2,3. Both the infrared spectrum3, which is due to the perturbed C=O stretching fundamental (v2), and the observed rotational spectrum2 consist only of a-dipole transitions. Such transitions obey the selection rule ΔKa = 0 in this near prolate top rotor and as such contain no direct information on the spacings between energy levels of different Ka. The high precision of the millimeter wave data allowed an approximate value for the A rotational constant to be derived2 however the accuracy with which it is known is much less than for B and C. Nonetheless, when combined with data for DOCO, it was possible to unequivocally attribute the spectra as due to the trans- geometrical isomer of the radical2.
High Resolution Spectroscopy on Single Molecules
Authors: Sepiol Jerzy , Güttler Frank , Pirotta Marco , Renn Alois , Wild Urs P.
Published: February 2023

Single particle spectroscopy has become a source of valuable information on fundamental interactions between light and matter. Whereas trapping and cooling of ions and atoms has been sucessfully achieved, single molecules, because of their multilevel structure (high number of internal degrees of freedom) have not been observed in electromagnetic traps so far. However due to the presence of zero phonon lines in conjunction with inhomogeneous broadening the spectroscopic isolation and detection of single molecules ‘trapped in solids at very low temperatures' is made feasible [1,2]. Single molecule spectroscopy allows to study the distribution of molecular properties and not only the statistical average which is generally observed.
Measurement of Collision Cross Section and Line Broadening Coefficient for 2p8 → 4d4 Transition in Neon
Authors: Kumar P R Sasi , Harilal S S , Nampoori VPN , Vallabhan CPG
Published: February 2023

The collision cross section and broadening coefficient for 2p8 → 4d4. transition in neon has been evaluated by high resolution optogalvanic spectroscopy using a single mode ring dye laser.
Production of the High-Intensive Beans of Ultracold Atoms for High Resolution Spectroscopy
Authors: Korsunsky E. , Kosachiov D. , Rozhdestvensky Yu
Published: February 2023

The characteristic feature of the transversal cooling with OPT is that light pressure force F
z
is of constant sign in a whole range of velocity variation [1,2]. Therefore, decelerating the atoms with v
z
< 0, the same force accelerates the atoms with positive velocities, that leads to the considerable loss of final intensity of the atomic beam.
Flame Temperature Measurement by Infrared Ray Emission Computed Tomography
Authors: Uchiyama Hiroki , Nakajima Masato , Yuta Shinichi
Published: February 2023

Noncontact and Nondestructive measurements in determing flame temperature distribution are currently under investigation.
The Applications of Gamma Ray Tomography to Gas Fluidised Beds
Authors: MacCuaig N. , Seville J. P. K. , Gilboy W. B. , Clift R.
Published: February 2023

Gamma-ray tomography is a powerful technique for the accurate measurement of time-averaged density in both single and multi-phase systems. The fact that it is also non-invasive makes it particularly well-suited to the elucidation of internal structure in both stationary and mobile granular systems, an example of the latter being the gas-fluidised bed.
Temperature sensing by means of NMR
Authors: Waller M. , Fiddy M.A. , Leeman S.
Published: February 2023

During the last decade, techniques have been developed for obtaining tomographic images of three dimensional objects by means of NMR1-5. Their common feature is the use of magnetic field gradients (static or oscillating) to spatially encode the detected signal.
Abel Inversion from Noisy Data: An Optimal Filtering Approach
Authors: Hansen Eric W. , Law Phain-Lan
Published: February 2023

In many cross-sectional imaging situations, the object is axisymmetric, ie, a function of radius alone. Examples include plasma spectroscopy and refractive index profiling of optical fibers. In such cases, one projection suffices for reconstruction, and the object f(r) and projection g(R) are related by the Abel transform pair [1]: (1) (2) where prime denotes differentiation.
Quantum Size Effects and the Surface Photochemistry of Small Semiconductor Crystallites
Authors: Brus L. E.
Published: February 2023

Time resolved Raman scattering studies of the surface reactions of organic molecules adsorbed on colloidal semiconductor (TiO2 and CdS) crystallites, following optical excitation of the crystallite, show that single electron redox reactions occur.1 The vibrational structures of the initial transient species show negligible distortion due to adsorption on the crystallite surface. TEM micrographs of the CdS crystallites (zinc blende cubic) directly image the crystallite internal lattice. The crystallites are essentially excised fragments of the corresponding bulk lattices. As diameter decreases in the range 50 to 20Å, CdS and ZnS crystallites show an increasing blue shift of the optical absorption edge (exciton peak), by as much as 0.8 eV.2,3 The exciton peak intensity also increases relative to the above gap absorption, as it shifts to higher energy. CdS crystallites of = 45Å average dimeter show corresponding exciton shifts in the LO phonon Raman excitation spectra, and the relaxed fluorescence spectra. We interpret these observations as quantum size effects. That is, these crystallites are too small for the bulk band gap to completely form. The size dependence of the crystallite lowest excited state is modelled, without adjustible parameters, at the same level of approximation as in the Wannier bulk exciton Hamiltonian.4 The exact Coulomb interaction between an electron and hole in a polarizable small crystallite is derived. The size dependences of the ionization potential and chemical redox potentials are also modelled.5 Materials with strong chemical bonds involving the valence electrons, and hence small effective masses for holes and electrons at the band edges, should show significant quantum size effects.
Circularly Polarized Luminescence of (-)D-[Cr(R-Pn)3]3+ and Related Chiral Chromium(III) Complexes Using a Microcomputer-based Digital Spectrophotometer System
Authors: Morita M. , Eguchi K. , Shishikura M. , Nishikawa H. , Inoue M.
Published: February 2023

Circularly polarized luminescence (C.P.L.) spectroscopy has been recently accepted as a unique technique which detects a difference in intensities between left- and right-circularly polarized emission and thereby elucidates chirality of optical active molecules in the emitting state[1]. This spectroscopic means is complementary to circular dichroism(CD) spectroscopy in which information in the ground state is obtained. We have been interested in studying vicinal effects of chiral rare earth cmoplexes by CPL spectroscopy[2]. In order to investigate conformational and configurational effects, we have extended our work to tris chelate chromium (III) complexes of D3 symmetry. Since chiral fluorescent molecules are easily damaged by photolysis, we have also constructed a very sensitive and stable digital instrument based on an Apple II microcomputer for the measurements of CPL spectra.
Luminescent Properties of Bis(n5-pentamethyl-cyclopentadienyl)ytterbium Derivatives
Authors: Thomas Alan C. , Ellis Arthur B.
Published: February 2023

Several adducts of (n5-Me5C5)2Yb(II) (1) and (n5-Me5C5)2 YbCl(III) (2) have been found to exhibit photoluminescence (PL) at 295K. The mono-THF adducts of 1 and 2 have served as the parent complexes for this study;1,2,3 they are orange-red (λmax ~ 445, 505 and 790 nm)4 and purple (λmax ~ 520 nm), respectively. Electronic spectra of the adducts are sensitive to the Lewis base coordinated to the Yb(II) or Yb(III) center. Excitation into any of the visible absorption bands of 1 at 295K in toluene yields a broad (FWHM ~100 nm) PL band with uncorrected λmax ~935 nm. Solutions of 1 in THF, compositionally dominated by the bis-THF adduct, exhibit a band of similar character, but possessing, in addition, a shoulder at ~900 nm. Solid-state PL spectra of the mono- and bis-THF adducts of 1 display band maxima at ~960 and 910 nm, suggesting that the shoulder observed in THF solution is due to the bis-THF adduct. The THF data suggest that excited-state adduct dissociation competes favorably with other decay routes of the bis-THF adduct. Other adducts studied by dissolving 1·THF in the corresponding solvent include Et20, for which PL at 875 nm is found, and CH3CN and pyridine, for which no PL between ~700-1000 nm is observed. In THF, 2 exhibits the sharp PL bands characteristic of f-f transitions between ~950-1000 nm; spectra are compared to those previously observed for adducts of (n5-C5H5)3 Yb(III).5
Optically Detected Magnetic Resonance Studies of Triplet Cyclopentanone*
Authors: Lynch W. B. , Pratt D. W.
Published: February 2023

Neat cyclopentanone (CYP), when cooled to ⩽4.2 K and irradiated with ultra­violet light, exhibits a sharp zero-field optically detected magnetic resonance (zf-ODMR) spectrum. Three transitions were initially found [1,2]; however, Shain and Sharnoff [3] subsequently detected six additional resonances (two "satellite" triads) of much lower intensity separated from the "normal" triad by 9-214 MHz. A double resonance experiment using two microwave fields to excite transitions in different triads seemed to indicate some communication between them. For this reason, it was suggested that different electronic and/or nuclear configurations of the isolated molecule are responsible for the different triads, and that these communicate via a rapid exchange process, perhaps enhanced by tunneling. But later CW and pulsed ODMR experiments [4] failed to reveal the existence of such a process, thus casting doubt on this interpretation.
Optically Detected Chlorine Nuclear Quadrupole Resonance in Organic Molecular Crystals
Authors: Borczyskowski C. v.
Published: February 2023

Some years ago an optical pumping cycle has been designed to transfer via the solid state effect electron spin alignment to nuclei such as bromine and chlorine /1/. The obtained nuclear spin alignment can be destroyed by nuclear quadrupole resonance (NQR) transitions in the ground state of the molecule resulting in phosphorescence intensity changes. By this method the sensitivity of optical detection of magnetic resonance (ODMR) is obtained and NQR on quadrupole nuclei with concentrations as low as 10-5 molar is feasible.
Photoluminescent Properties of the Conducting Polymer Poly-(Para-Phenylene)
Authors: Heim A. , Leising G. , Kahlert H.
Published: February 2023

Recently a whole class of conjugated organic polymers has been discovered, the members of which undergo a transition to a conductive state on doping with electron acceptors or donors. One of the most prominent members of this class is poly-(paraphenylene) (PPP), which exhibits a conductivity increase as high as 18 orders of magnitude on appropriate doping [1]. The basic chemical unit of PPP is shown in Fig. 1. Doped PPP and similar polymers in many respects show transport and optical properties reminiscent of those of conventional semiconductors like silicon. Undoped PPP-type polymers composed of coupled aromatic rings are very heat resistant and have already been used as materials which must stand against high temperatures. We have performed measurements of the excitation and emission spectra of the photoluminescence of PPP in the wavelength region between 200 nm and 800 nm. Samples have been prepared by two different methods, the one designed by Kovacic et al. [2], which is known to yield material with a higher degree of polymerization, and by the Yamamoto [3] method. Both synthetical routes not only result in high-molecular weight insoluble PPP, but also in products which are soluble in toluene and exhibit a much lower molecular weight. The emission spectra for the Kovacic-product show a series of three bands in the blue region of the spectrum and a broad maximum around 625 nm, whereas the Yamamoto-samples show similar bands in the blue region and an additional band around 505 nm. A comparison of these spectra with photoluminescence spectra of the commercially available oligomer p-terphenyl is shown in Fig. 2 together with the excitation spectra for p-terphenyl (dashed curve a) and for PPP (dashed curve b), which coincide for both types of samples. These measurements on two differently produced kinds of PPP allow a critical discussion of the role of impurities for the strong photostimulated luminescence of PPP.
Multiple Fluorescence in 1,8-dihydroxy, 6-methoxy, 3-methyl anthraquinone and 8-hydroxy, 1,6-dimethoxy, 3-methyl anthraquinone
Authors: Sharma Ashutosh
Published: February 2023

Environment dependent fluorescence spectroscopy has proved to be a
valuable tool in studying primary photochemical processes. It is well
established that excited state properties of a molecule may differ
drastically from the corresponding ground state properties, due to the
difference in charge distribution in the two combining states.
On the Dynamics of Excitons in Molecular Crystals
Authors: Cortes Emilio
Published: February 2023

The description of exciton dynamics in molecular aggregates at finite temperatures has recently been shown to require the inclusion of dissipative contributions that have heretofore not been taken into account1,2. The specific model considered so far has been the usual one of an exciton coupled to a bath of harmonic oscillators as described bv the Hamiltonian Here

a
h
+

(

a
k

)

creates (destroys) an exciton of wave vector k and energy Ek,

b

qα

+

(

b

q
α

)

creates (destroys) a phonon in branch α of wave vector q and energy ℏωqα, and Γkqα is a coupling constant. The dynamics of the excitons is then desceibed by the exact equation of motion1,2
Determination Method of The Characteristic Parameters of Different Interaction Potentials From Energy Transfer Measurements
Authors: SIPP Bernard , VOLTZ René
Published: February 2023

In many cases, the characteistic parameters of the microscopic distance dependent transfer rate between an excited donor and an acceptor molecule are unknown. Quite generally, the transfer rate expression can be expressed as

1
τ

f

(

r

r
o

)

where r0 is the interaction range and 1/τ a frequency factor.
The Usefulness of Sensitized Luminescence as a Probe for Exciton Motion in Molecular Crystals
Authors: Kenkre V. M. , Parris P. E.
Published: February 2023

Despite considerable work done in the field of energy transfer via sensitized luminescence, 1-3 serious questions4 remain concerning the relationship between the primary experimental observable and microscopic parameters which govern exciton transport. We present a quantitative analysis of these questions as they pertain to several specific excitontrap systems, particularly tetrachlorobenzene, naphthalene and anthracene. On the basis of a general theory5 which treats the capture process on an equal footing with motion, we address quantitatively the concept of time-dependent energy transfer rates. We find that the time dependence depends strongly on the effective dimensionality, becoming more pronounced as the dimensionality decreases and that for fixed dimensionality the time dependence becomes less marked as the capture process is slowed down.
Luminescence of Tetracene Crystals
Authors: Kurik M.V. , Piryatinskii Yu. P.
Published: February 2023

Electron spectra of molecular crystals are quite sensitive to the structural changes of a lattice. It allowed to establish by spectrum that at cooling of tetracene crystals lower than 160K it was observed that phase transition of the first kind occurs [1-2]. It is assumed that at the phase transition, a weak tricli­nic lattice transits into a monoclinic one. Increased concentration of structural defects is observed in tetracene crystals subjected to the phase transition. These defects in tetracene lattice are the places of localization of singlet and triplet excitons and they make an essential influence on the energy transfer and luminescence spectra. We carried out investigations of luminescence by spectroscopy method with the time resolution that allowed at low tempered spectra to observe bands responsible for luminescence of free excitons and excitons localized on defects [3]. It has been determined that values of free excitons lifetime in tetracene crystals at 4,2K lies in the range from 1 to 2,5 nanoseconds.
Is the S2↝S0 Internal Conversion an Important Pathway for Radiationless Decay of the S2 State of Azulene?
Authors: Sobolewski A.L. , Prochorow J.
Published: February 2023

The rates of the S1⇝S0 and the S2⇝S0 internal conversions in azulene were both estimated to be almost of three orders of magnitude greather than expected for internal conversion in aromatic hydrocarbons with equivalent energy gaps (see [1] and references therein). According to Hirata and Lim [1] the S2 ⇝S0 internal conversion is already competitive with the S2⇝S1 internal conversion in radiationless decay of S2 of azulene. This picture is in accordance with the experimental results of Griesser and Wild [2] who didn’t find a simple correlation between energy gaps of S2, S1 and S0 states and the rate constants of radiationless transitions from S2 state in azulene and its derivatives. It must be emphasized, however, that up to now all correlations and interpretations of radiationless transitions from S2 state in azulene were based on two-electronic-state model, which seems to be particularly inadequate in this case. We may expect that besides a direct couplings S2⇝S0 and S2⇝S1 also coupling between S1 and S0 is of importance in the kinetic of deactivation of S2 state.
How Isolated is Nitrogen in a Matrix?
Authors: Creuzburg M.
Published: February 2023

The doubly forbidden

A
3

Σ
u
+

→

X
1

Σ
g
+

(Vegard-Kaplan,V-K) emission of the N2 molecule can serve as a probe for its interaction with the neighborhood. While the radiative lifetime in noble-gas matrices is affected only by the host, the vibrational relaxation rates in the A state depend strongly on the proximity of other imperfections.
Is the Barrier Height of Exciton Self-Trapping Evaluated So Far Correct ?
Authors: Sumi H.
Published: February 2023

It has theoretically been shown that in the course of self-trapping exciton surmounts a potential barrier made by lattice distortion (or penetrates it by quantum-mechanical tunneling at low temperatures). Then, how high the potential barrier is has been investigated so far by analyzing the temperature dependence of the quantum yield η (or simply, the indensity) of free-exciton luminescence in many crystals. Three examples of it for RbI measured by Nishimura et al.1 are shown in the figure of the next page, η decreases with increasing temperature T. This is regarded as originating from the increase of the self­trapping rate W of a free exciton with increasing temperature. Then, assuming that the temperature dependence of W was determined by a factor exp(-EB/kBT) describing the classical behavior of surmounting the potential barrier with height EB, and moreover that other nonradiative and radiative decay processes had a rate independent of temperature, many people have analyzed η by a formula proportional to 1/[C+exp(−EB/kBT)] with a constant C. For example, this analysis gives EB=17~18 meV for RbI.1 However, the temperature region (15 ~ 30K in RbI) where η most decreases is considerably lower than the Debye temperature (~100K). In such low temperatures, lattice distortion making up the potential barrier cannot be regarded as classical, and the self-trapping process must be intermediate between the classical surmounting and the quantum-mechanical tunneling with rate almost independent of temperature. Therefore the EB value evaluated so far must be reconsidered: It has been evaluated small.
Study of M 0 X Band in Indirect-Gap GaAs1−xPx by Resonant Excitation
Authors: Lai Shui T. , Klein M.V.
Published: February 2023

Two basic characteristics of localized excitons in GaAs1−xPx are depicted in this study. They are: (1) the density of state extends into the band gap, and (2) the effective range of the wave-function is a sensitive function of its binding energy.1 The photoluminescence (PL) properties of the

M
0
X

band in indirect gap GaAs1−xPx has been reported.2,3 The origin of the Mg band has been attributed to the exciton localized by the potential fluctuation in the GaAs-GaP solid solution. In n-type GaAs1−xPx, the excitons bound at the donor centers

(

D
0
X

)

are located at a lower energy (8~13 meV) than those at the

M
0
X

(Fig. 1, top trace). Inelastic tunneling to the short-lived

D
0
X

centers is the dominant quenching process for the localized excitons Since the probability of the tunneling is related to the spatial extent of the wavefunction, the exciton wavefunction can be studied through the tunneling processes. Sharp phonon structures appear as the excitation energy is in resonance with the

M
0
X

band excitons (Fig. 1, λL⩾5920Å). The most prominent feature, labelled LAX, is the LA phonon sideband of the localized excitons at the laser energy. It's narrow linewidth derives from a small energy portion of the localized exciton population which is selectively and resonantly excited by the narrow-width laser. A PL peak M' (Fig. 1, λL = 5924Å) occurs at ~3 meV below the laser energy. This "Raman-like" peak persists even at excitation energy well below the

M
0
X

band (λL = 5963Å). The M' band results from excitons created at the laser energy, tunneling to more deeply localized states. The fact that it has a peak rather than a portion of the

M
0
X

lineshape indicates that the effect of tunneling processes has a dominant role in the exciton luminescence lineshape. Localized exciton at higher energy has a lower fluorescence quantum efficiency due to its more spatially extended wavefunction. Rapid variation of the fluorescence lifetime across the

M
0
X

band lineshape has also been observed.2 The ratio of M' peak intensity to that of the LAX increases as the laser energy is tuned below the

D
0
X

peak. This increase is consistant with our model that

D
0
X

center is the energy sink for the localized exciton.
Photoluminescence in Liquid Phase Epitaxially grown Hg0.3Cd0.7Te and its CdTe Substrate at 4.2 and 77K
Authors: Feldman Bernard J. , Bajaj J. , Shin S. H.
Published: February 2023

The photoluminescence spectra of liquid phase epitaxially (LPE) grown Hg0.3Cd0.7Te and its CdTe substrate have been measured. The CdTe spectra at 4.2 K consist of two band edge sets of lines, B and C, while the Hg0.3Cd0.7Te spectra consist of one set of lines, A. From the temperature dependence of both the integrated intensity and peak position, we determined that the A line is unrelated to the C line but is very possibly related to the B line. The B line in CdTe is due to recombination of electrons and holes bound to a neutral donor or acceptor. This suggests that the same neutral donor or acceptor may be present in both materials, whereas the impurity or defect responsible for the C line in CdTe is undetectable in LPF grown Hg0.3Cd0.7Te. In contrast the photoluminescence spectra of both Hg0.3Cd0.7Te and CdTe at 77 K consist of a single narrow, high energy line with a free exciton lineshape and a broad, low energy line due to a deep level. From binding energy considerations, the origin of the observed deep level in Hg0.3Cd0.7Te is unrelated to that in CdTe.
Temperature Dependence and Asymmetry of Exciton-Lineshapes
Authors: Becker K.W. , Grötsch H. , Rössler U.
Published: February 2023

Exciton-phonon coupling and electronic overlap (excitation transfer) are known as the competing mechanisms in the exciton-phonon problem, which become apparent in the optical lineshape of excitons. A phenomenological treatment of this problem yields a Lorentzian lineshape for weak exciton-phonon coupling and a Gaussian for strong coupling.1 We have studied the lineshape of excitons by evaluating Kubo's expression for the optical susceptibility using the projection-operator formalism. In general, this theory yields asymmetric lineshapes due to a frequency-dependent memory function.
Nonequilibrium Steady States of Electrons and Holes in Semiconductors
Authors: Shrivastava K.N. , Tripathy G.S.
Published: February 2023

We report an interesting instability in the excitation of pairs of electrons and holes in semiconductors by light absorption. The distribution of electrons and holes is bistable as a function of input power. As the nonequilibrium electrons and holes emit light, the total light intensity is a multivalued function of input power. This effect is of interest to study the electron-hole drops.1
Emission properties of quantized excitonic polaritons in a thin GaAs layer
Authors: Schuitheis L. , Ploog K.
Published: February 2023

Excitonic polaritons in a thin semiconductor layer have discrete wave vectors perpendicular to the layer. The eigenstates are standing polarization waves (Fabry-Perot modes). Previous investigators /1/ have reported interference structure from these modes in the reflectance spectra of thin II-VI semiconductors platelets.
Two-Center Optical Transitions in Condensed Matter
Authors: Stavola Michael
Published: February 2023

The absorption of a single photon by the simultaneous excitation of two rare-earth ions was first reported by Varsanyi and Dieke in 1961.1 D. L. Dexter explained this unusual observation by including the electron-electron interactions (that also give rise to energy transfer) between the rare earth ions with perturbation theory.2 In the 70's Dexter became interested in electronic-vibrational coupling. A theory of two-center optical transitions was developed for a rare-earth ion weakly coupled to a high energy, internal vibrational mode of a near-lying ion.3 Using theoretical techniques that had been developed for rare-earth ion pairs, intensities and selection rules could be determined.
4f-Electron-Phonon Interaction and Davydov-Splitting in PrF3
Authors: Dahl M. , Schaack G.
Published: February 2023

In the ionic Rare Earth compound PrF3 we studied several interaction effects between the system of the low lying 4f-electron excitations and the optical phonons, which could be interpreted by a Jahn-Teller type interaction Hamiltonian between the two systems.
Measurement of Exciton Absorption Spectrum in KI Using New Method
Authors: Nishimura H.
Published: February 2023

Detailed information about optical absorption is very important in understanding the optical processes such as luminescence, excitation, reflectance and absorption itself. However, the information for alkali halides is poor compared with the detailed information about other processes which have been reported recently.1,2) For alkali halides the measurement of optical absorption in crystal is impossible on account of the very high absorption coefficient and as a consequence one has to use other (substitutional) methods. The spectrum of thin film, however, is very broad and shifts to low energy, and the imaginary part of the dielectric constant derived from reflectance spectrum also deviates from the real spectrum of absorption because of the difficulty in measuring the reflectance over the whole spectral region. Besides, in general the imaginary part often does not show structures which are observed but weakly in absorption and excitation spectra. Therefore, we have to find new method to know real information about absorption.
Excitons in CuCl microcrystals embedded in NaCl
Authors: Itoh Tadashi , Kirihara Toshio
Published: February 2023

In heavily Cu+-doped alkali halides, microcrystals of Cu= halides having the size less than 0.1 μm are known to be formed due to the coagulation of Cu+[1-3]. The present paper reports the optical properties of CuCl microcrystals (1 mol% in NaCl) in order to study the crystal size effect upon their exciton states. Figure 1 shows two exciton absorption bands, Z3 and Z1,2, which are located at the higher energy side with more broadened band= width compared with those in the bulk CuCl on account of the size effect: the smaller the size of the microcrystal, the larger the exciton energy [3]. Under the band-to-band excitation a broad emission band appears with the Stokes shift of ~30 meV from the Z3-absorption band.
Dependence of emission properties on the counter-ion in crystalline [Ru(bpy)3]X2
Authors: Yersin H. , Gallhuber E. , Hensler G. , Schwan L. O. , Rettig W.
Published: February 2023

During the past decade [Ru(bpy)3]2+ complexes have been investigated intensively.[1-4] From measurements with dissolved complexes it has been concluded that the second coordination sphere (solvent sphere) strongly influences the spectroscopic behavior. Thus, it is near at hand to analyze crystalline compounds with different counter-ions, leading to a more defined variation of the second coordination spheres. Such investigations are presented here for the first time. Fig. 1 reproduces the emission spectra of two compounds and Table I summarizes spectroscopic data for different counter-ions and crystal water contents. These results show that counter-ions and/or crystal water strongly influence the emission spectra and their temperature behavior, the decay properties, and the emission intensities and their temperature dependence. For instance, the intensity of the PF6-salt is at 300 K appreciably larger than that for other salts. However, with temperature reduction all compounds seem to come to a comparable value. This can be understood on the basis of an electronic state strongly coupled to lattice vibrations, only accessible over an activation barrier. An equivalent behavior has also been found for dissolved complexes.[4] The corresponding quenching state has been assigned in [4] to a charge-transfer-to-solvent state and in [2] to a Ru 4d state. Our results indicate the significance of the counter-ion redox potential. This suggests - in analogy to [4] - that a charge-transfer state coupled to the second coordination sphere (counter-ion) is responsible for the quenching properties.