bluuebunny/crossref_metadata_2025 huggingface dataset:
Persistent Photon-gated Spectral Holeburning In A New Donor-Acceptor Electron Transfer System
Authors: Tian Mingzhen , Luo Baozhu , Li Wenlian , Huang Shihua , Yu Jiaqi
Published: February 2023

Due to the interest in the frequency-domain optical storage application, recent researches on spectral holeburning concentrated on the two-colour photon-gated persistent holeburning[1,2]. Some organic systems have been investigated [3-7]. A representative one is TZT as a donor and CHCl3 as an acceptor in PMMA film undergoing donor-acceptor electron transfer, which offered a significant mechanism for persistent holeburning in organic system [4,5]. But there is an insurmountable problem in the system. As CHCl3 is volatile at room temperature, its concentration can not be controlled and the sample is difficult to further study. Here we report the holeburning system composed of metal-tetrabenzoporphyrin derivatives (MTBP) as the donors and a solid electron acceptor, p-hydroxybenzaldhyde (PHBA), which can easily be made into a stable "dry" film and in which the concentration of each component can be modified easily.
Hole Burning in the Vibrational Spectrum of Crystals and Glasses
Authors: Sievers A. J.
Published: February 2023

Persistent IR spectral holes can be generated in the vibrational degrees of freedom of small molecules matrix isolated in crystals(1) and glasses(2,3) even though no electronic excitation is involved, i.e., a non-photochemical process. The union of the IR lead salt diode laser and broad band FT interferometric methods has produced a new high resolution spectroscopic technique for investigating both the statics and dynamics of molecules in solids. These low power single mode diode lasers (~10 to 100 μW) provide a near ideal cw source for investigating persistent IR spectral holes (PIRSHs). They can be produced and probed with a single laser, focused to an intensity at the sample typically up to 100 mW/cm2. Persistent spectral changes which occur far from the laser line can be monitored with an FTS probe beam at 60 MHz resolution.
Linear electron-phonon interaction in dye-doped polymers: Boson peak frequencies in polymers
Authors: Saikan Seishiro
Published: February 2023

This talk presents a review of our recent experimental results on femtosecond accumulated photon echo in dye-doped polymers. The aim of this research is to clarify the parameter that is most important in affecting seriously the linear electron-phonon coupling in these samples, and to find the materials which have extremely weak linear electron-phonon coupling. The latter research is needed for the improvement of the PHB memory materials. We have so far demonstrated experimentally that Fourier-transform spectroscopy [1] based on the femtosecond accumulated photon echo is most useful for these studies. Furthermore, the detection sensitivity for the accumulated photon echoes has been improved significantly with the use of the phase modulation technique [2].
Stark Effect on Persistent Spectral Holes Measured by Electric Field Modulation Technique
Authors: Shimada Toshiyuki , Suzuki Hiroyuki
Published: February 2023

An external field applied to dye doped polymers which have inhomogeneous dispersion in their absorption spectra causes a shift in the absorption of the dye molecules. This, in turn, changes the line shapes of persistent spectral holes1). The Stark effect has been applied to optical storage2) and optical computing3). It has been also used as a powerful tool for investigating such physical profiles of materials as the difference between the effective molecular electric dipole moments in the host matrix in the ground and excited states which is related to hole burning4),5).
Effect of Intersystem crossing enhancement on the hole-burning process of metal-free porphyrin
Authors: Sakakibara Youichi , Tani Toshiro , Kaizu Youkoh
Published: February 2023

The photochemical reaction in the hole-burning process of metal-free porphyrins has been ascribed to the photoinduced tautomerism of central two protons through the triplet state1). For further understanding of the reaction mechanism, one of the useful approachs is to modify the lifetimes of the excited states without changing energy levels. The population of electronic states under laser-excitation will be influenced considerably, but the electronic structure itself will not change so much. The quantum yield of the hole-formation will be also influenced if it depends mainly on the population of the state where the reaction starts. In this study, we modified the lifetimes by enhancing the intersystem crossing rates with a paramagnetic effect of copper(II) atom. The starting point of the reaction will be discussed with the quantum yields and the population of the states.
Crystalline Model Systems Probing Dynamics and Electric-Field Effects
Authors: Attenberger T. , Bogner U.
Published: February 2023

Recently in studies of fluorescence excitation and persistent spectral hole burning (PSHB) of single molecules in crystalline environment spectral jumps have been observed at 1.5 K providing new insights into the low temperature dynamics of the condensed phase [1]. The connection between PSHB and the phonon-induced dynamics in asymmetric double-well-potentials (DWP) has been used in a photophysical model of PSHB explaining also phonon detection by refilling of a spectral hole observed after irradiation with nanosecond heat pulses [2]. These DWP have been originally introduced in order to explain anomalous acoustic and thermal properties of amorphous materials by the socalled two-level systems, the existence of which is due to tunneling in DWP with appropriate parameters. The photophysical model is based on spectral shifts (matrix-shift-variations) caused by phonon-induced crossing of the barriers which can occur in all DWP if the phonon frequency is high enough.
Accumulated photon echoes as a probe of radiationless relaxation processes in Nd-doped glasses
Authors: Ver Steeg Keith W. , Reeves Roger J. , Powell Richard C.
Published: February 2023

Accumulated photon echoes (APE) were used to measure the dephasing rates of Nd3+ in various inorganic glasses as a function of excitation wavelength, sample temperature, and laser power. Although dephasing processes of optical transitions in solids are of considerable interest, they are poorly understood, largely due to the lack of experimental data on femtosecond and picosecond time scales. The APE technique using sub-picosecond laser sources has made it possible to measure in the time domain dephasing rates of inhomogeneously broadened transitions in amorphous systems.1,2
Fluorescence Excitation of Single Molecules
Authors: Orrit M. , Bernard J.
Published: February 2023

A few years ago, many people would have deemed the optical observation of single molecules nearly impossible. Yet, new experiments at room [1] and at liquid helium temperatures [2,3] have started to remove this psychological barrier. Several applications to trace detection and sensing, to spectroscopy of localized neighborhoods and to optical addressing of local spots in solids may now be envisioned. The purpose of this presentation is to show that single molecules can be studied at helium temperatures by means of a fairly simple setup, at least in the very favorable case of pentacene in terphenyl crystal. We thus hope to stimulate further work either on this model system or on more difficult ones with more sophisticated detection methods.
Observation of Spectral Diffusion in Solids Using a Single Molecule
Authors: Ambrose W. P. , Basche' T. , Moerner W. E.
Published: February 2023

Recent advances in high-efficiency fluorescence excitation spectroscopy of pentacene in p-terphenyl crystals1-3 have improved the signal to noise ratio for the detection of single pentacene defects, thus confirming single pentacene detection using absorption techniques.4 Using 1-10 μm thick crystals, tightly focused laser beams, and high collection efficiency, background emission noise is significantly reduced below the fluorescence emission rate of single pentacene defects. To observe single molecules, the laser is tuned out into the wings of the pentacene O1 site inhomogeneous line until the number of defects per homogeneous linewidth is less than 1. With the improved detection sensitivity, we have observed two classes of pentacene defects present in both the red and blue wings of the inhomogeneous line: class I consist of stable, time-independent defects with lifetime limited homogeneous linewidths below 4 K, and class II have time varying resonance frequencies.
Time Dependent Hole Burning and Optical Coherence Experiments as Probes of Spectral Diffusion in Low Temperature Glasses
Authors: Fayer Michael D.
Published: February 2023

Dynamics and interactions in low temperature glasses can be studied with optical line narrowing techniques applied to chromophores embedded in glassy hosts. Prior to the use of optical methods, a wide variety of classical methods, such as heat capacities, were applied to the study of glasses. Results have been successfully interpreted in terms of a model of the glass potential surface described in terms of Two Level Systems (TLS). Because of the very large extent of inhomogeneous broadening in glassy systems, it is necessary to apply line narrowing methods to provide information on the dynamics and interactions of atoms and molecules with their environments.
Photon Echo and Time-Resolved Fluorescence Anisotropy Measurements of Organically Doped Sol-Gel Glasses
Authors: L’Esperance Drew M. , Crowell Robert A. , Chronister Eric L.
Published: February 2023

We present time resolved measurements of homogeneous dephasing of organic dopants in inorganic sol-gel glasses. A variety of organically doped sol-gel glasses have been synthesized and their dynamics investigated by time-resolved photon echo and fluorescence anisotropy measurements. The homogeneous dephasing rate of the chromophore is determined from photon echo measurements at low temperature (T = 1.4 K), while thermally activated homogeneous dephasing mechanisms are investigated by temperature dependent photon echo measurements. Our results are contrasted with recent hole-burning experiments on doped sol-gel glasses. Aluminosilicate (ASE) and tetraethoxy silane (TEOS) glasses have been doped with rhodamine dyes, polyaromatics, cresylviolet, resorufin and a wide range of chromophores with different nonradiative electronic relaxation rates. A small list includes naphthalene (170ns), rhodamine 6G (2ns), Rose Bengal (500ps), stilbene (70ps), azulene (2ps), as well as quinizarin and chlorin. The visible absorption spectra of some organically doped sol-gel glasses is shown in Figure 1. The low temperature homogeneous dephasing rate for chromophores doped into TEOS and in ASE solgel glasses has been measured utilizing photon echo measurements, as shown in Figure 2.
Ultrafast Dephasing of Resorufin in D-Ethanol Glass from 1.8 - 35 K Studied by Incoherent Photon-Echo
Authors: Gruzdev N.V. , Vainer Yu.G.
Published: February 2023

Optical dephasing studies of organic glasses and polymers provide the valuable information about an amorphous system’s dynamics. In the recent years hole-burning and two-pulse picosecond photon-echo were widely used for these purposes. These methods have different characteristic times: minutes and more - for hole-burning, picoseconds - for two-pulse picosecond photon-echo. As a result, in the case of amorphous systems, data obtained by using of these methods correspond to different time scales and are not equivalent [1]. The comparison between the results obtained by these different methods can provide additional information about a dynamical processes in amorphous systems (for example, about spectral diffusion).
Hole-Burning and External Field Effects: Principles, Recent Results and New Systems (Superfine Films)
Authors: Personov R.I.
Published: February 2023

The possibility to investigate the influence of external electric and magnetic fields on complex molecules in amorphous solids is essentially limited by a large width of their spectral bands (Δν=102-103 cm−1 even at liquid helium temperature). Hole-burning opens up new excellent opportunities for using the Stark and Zeeman effects in spectroscopy of molecules and solids and their different applications [1]. Owing to the small hole width (Δν=10−1-10−2 cm−1 at 2-5 K) the sensitivity of measurements increases by several orders of magnitude.
Spectral Holes Under Pressure: Proteins and Glasses
Authors: Zollfrank J. , Friedrich J.
Published: February 2023

Pressure tuning of spectral holes /1/ provides, in a way, a link between gas–phase and solid state spectroscopy. Generally speaking, the shift of a spectral hole under isotropic pressure conditions, allows for a determination of three system parameters. These are: the vacuum frequency νvac of the molecular probe, the solvent shift νs which the probe experiences when embedded into a lattice and the compressibility κ of the host material.
Layered Optics for Nuclear Monochromatization of Synchrotron Radiation
Authors: Alp E. E. , Witthoff E. , Mooney T. , Homma H. , Kentjana M.
Published: February 2023

The insertion device based third generation synchrotron radiation sources currently under construction in Europe, USA, and Japan brings new opportunities and challenges in the design and manufacturing of x-ray optics. These high brightness sources demand more stringent parameters on the quality of multilayered optics in terms of size, uniformity, and surface and interface roughness.
Stability of the Long Period Modulated Structures in Ordering Systems
Authors: Andreev S.S. , Polushkin N.I. , Salashchenko N.N. , Shinkarev S.I.
Published: February 2023

The anomalies in diffusion behavior of compositionally modulated structuresin ordering systems W/Sb and Co/Pt are discussed. There are stable subnanometer modulated structures in W/Sb alloys. It has allowed to construct normal incidence X-ray mirrors. Co/Pt alloys are characterised by arising of self-organizated modulated structures with d=3.8 - 4.2 nm.
Application of in-situ ellipsometry to the study of ultrathinn layers and soft x-ray multilayers
Authors: Yamamoto Masaki
Published: February 2023

Ellipsometry is an accurate tool to study surface and thin-film phenomena[1]. It gives information of the dielectric boundary structures causing diffractions or reflections at the probed area of a surface down to the escape depth of the probe light. With a He-Ne laser light of a wavelength of 633nm, the probed depth for most metals are of an order of a few tens nm, being equivalent to several periods of a soft x-ray multilayer The accuracy achieved for the single layers is at least a few tenths of nm in thickness[2,3].
Pulse Laser Deposition of Layered Synthetic Microstructures
Authors: Gaponov S.V. , Kluenkov E.B. , Platonov Yu. Ya. , Salashchenko N.N.
Published: February 2023

The deposition technique of LSM's efficiently reflecting in the soft x-ray region (SXR) should satisfy the following requirements: to be capable of depositing continuous superthin layers up to 5Å thick, to control thickness and crystal structure of superthin layers, to sustain the period thickness at the LSM depth with an accuracy to hundredth fractions of the period. Thus, the admissible rms height of interfacial LSM roughness should not exceed 2-5Å, while the accuracy of sustaining the period thickness in the shortwave part of the SXR region (where the structure period d=15-25Å and the number of efficiently reflecting periods 100) amounts to fractions of Ångstrom.
Comparison of Microstructure and Thermal Stability of Short Period X-Ray Multilayers
Authors: Nguyen Tai D. , Gronsky Ronald , Kortright Jeffrey B.
Published: February 2023

detail studies of x-ray multilayer microstructures and stability are essential to a complete understanding of these nano-scali metastable materials, and may lead to synthesis of multilayers of improved performance. The microstructures and phases inside the layers depend upon the period, and show different behaviors for different materials systems.1,2 Their response to thermal treatment likewise depends on the materials combinations and the period. In this project, the microstructures and their thermal stability of various period W/C, WC/C, Ru/C and Ru/B4C multilayers are investigated by High-Resolution Transmission Electron Microscopy (HRTEM) and x-ray diffraction.
Theory of Nonspecular X-ray Scattering from Multilayer Structures
Authors: Stearns D.G.
Published: February 2023

One important type of structural imperfection that can affect the properties of multilayer (ML) structures is interfacial roughness. In x-ray optical ML, roughness both decreases the reflectivity and introduces a background halo that can degrade the resolution of imaging optics. A promising technique for characterizing the roughness of surfaces and interfaces in ML structures is x-ray scattering. The use of x-ray scattering as a structural probe has several important advantages. It is inherently a non-invasive technique, well-suited for dynamic measurements including in situ growth studies. The penetration of x-rays allows both surfaces and buried interfaces to be directly probed. Furthermore, due to the short wavelength of x-rays, x-ray scattering can provide structural information on spatial scales ranging down to atomic dimensions. There is increasing interest to use nonspecular x-ray scattering to study the roughness of interfaces in x-ray ML structures. The first experimental results indicate that the x-ray scattering can exhibit a rich variety of behavior associated with the structural correlations between interfaces1-4. We present a simple theory that, within the limitations imposed by certain simplifying approximations, can provide a straightforward means of relating realistic interface structures to measurements of nonspecular scattering.
Experimental and Theoretical Soft X-Ray Reflectivities for Mo-B4C Multilayer Structures
Authors: Brown D.B. , Gilfrich J.V. , Freitag R.K. , Rosenstock H.B. , Konnert J.H. , D’Antonio P. , Burkhalter P.B. , Dozier C.M.
Published: February 2023

The use of artificial multilayer structures (MLS) as wavelength dispersive elements has proven of great importance in soft x-ray (2 to 15 nm) spectroscopy. Much of the early work in this field has concentrated on structures consisting of alternating layers of a pair of materials, one of high atomic number (most commonly tungsten) and one of low atomic number (most commonly carbon). Although the ideal performance of multilayer pairs can be calculated,1 the performance of a MLS can be substantially degraded by imperfections introduced in their manufacture. In particular, it has become clear that optimum performance of MLS is strongly dependent upon the quality of the interfaces (roughness, interdiffusion, etc.) between the two materials. These interface properties are dependent upon the chemical-metallurgical properties of the materials chosen. Since such properties are typically not amenable to theoretical prediction, the choice of good layer pairs is typically an Edisonian process. The purpose of this paper is to explore the soft x-ray diffracting properties of the material pair Mo-B4C. We will concentrate on the ways in which the measured diffraction behavior deviates from ideality and, especially, possible reasons for this non-ideality.
Gradient index multilayers for X-ray reflection
Authors: Schlatmann R. , Keppel A. , Bultman S. , Verhoeven J.
Published: February 2023

Energetic ions penetrating a solid lose their energy by nuclear interaction with one or more target atoms as well as by electronic excitation of the target atoms. The energy loss by nuclear interaction can be described in the classical ballistic way. Target atoms, put into motion by a primary collision, can exchange momentum with surrounding target atoms. This results in implantation of primary ions and damage in the target structure. A part of the momentum exchange is reversed in the direction of the target surface. This can give rise to the release of surface atoms, which is known as sputtering. Momentum transfer at an interface of two different materials will give rise to intermixing as demonstrated by van der Weg1). Fundamental research2) revealed that ion beam mixing could not only be explained by ballistic effects, but that also thermodynamic and chemical effects play a role. These effects are expected to take place in the end of a cascade formation, when the average energy is smaller than 1 eV. Further experiments have shown the importance of radiation enhanced diffusion, which shows up as a temperature dependent effect for a temperature higher than a critical value. The physics of this effect is based on vacancy enhanced diffusion.
X-ray reflectivity by surfaces and multilayers: A comparison of exact and approximate solutions
Authors: Caticha Ariel
Published: February 2023

Novel synthetic multilayered materials have useful properties which are strongly correlated with the structure of the surfaces and interfaces. Reliable theories of x-ray scattering by complex surfaces are therefore essential to the successful control and engineering of these properties; either the x rays are used as a non-invasive structural probe, or else the multilayer is used as an optical device to manipulate x rays.
A Facility for the Measurement of the Soft X-ray Reflectivity Spectrum of XUV and Soft X-ray Mirrors
Authors: Villoresi P. , Jannitti E. , Nicolosi P. , Perin M. , Tondello G.
Published: February 2023

The spectrally resolved reflectivity coefficient of multilayer mirrors is measured in the EUV-soft X-ray spectral region. A laser produced plasma (LPP) acts as a bright source of continuous spectrum radiation, and it is used to light the multilayer mirror under test. The reflected rays are collected by a grazing incidence toroidal mirror and focused in the entrance slit of a grazing incidence spectrograph, where the spectrum is detected. The ratio of such spectrum with that obtained with the direct collection of the LPP spectrum, corrected for the higher diffraction orders contributions, is the spectrum of the absolute reflectivity coefficient for the mirror[1].
Microstructure, Stress and Optical Properties of Ge/C Multilayers
Authors: Lu Xiang , Nguyen Tai D. , Soufli Regina , Gullikson Eric M. , Underwood James H.
Published: February 2023

Recent studies of x-ray multilayers have focused on understanding and controlling the roughness at the interfaces to achieve high reflectivity. In general, the structure at the interfaces depends on the microstructure inside the layers, and on the interactions between the layer materials. Presumably, in systems in which the components do not react with each other, such as Ru/C and Ge/C, minimum intermixing and diffusion should allow relatively sharp and well-defined interfaces. For this reason, the germanium and carbon pair is studied as a potential candidate for the x-ray multilayer mirrors. Some early materials studies showed that no compounds of Ge and C were detected up to 3170 °C [1]. Early measurements also indicated virtual insolubility of C in Ge, or Ge in graphite [2]. These materials science properties suggest that Ge/C may be able to form sharp multilayer interfaces and hence may provide significant specular x-ray reflectance, especially at wavelengths just above the carbon K edge (4.4 nm), where interfacial microstructure and morphology play a critical role in the determination of reflectivity. In this paper, we present results from a systematic study of the microstructure, stress, and optical properties of as-prepared and annealed Ge/C multilayers having periods and relative individual layer thicknesses typical for soft x-ray applications.
Stress Characteristics in Periodic Multilayer Structures for X-Ray Optics
Authors: Nguyen Tai D. , Lu Xiang , Underwood James H.
Published: February 2023

Sputtered x-ray multilayers usually exhibit the presence of intrinsic stress in the structures. Stress in multilayer mirrors are undesirable in many x-ray optical applications where flat mirrors, or precise control of curved mirrors, are designed. Controlling of the stress in these multilayers requires understanding of stress characteristics in multilayers and thin films.
SOFT X-RAY REFLECTANCE AND SURFACE ROUGHNESS OF VAPOR DEPOSITED THIN FILMS
Authors: Yanagihara M. , Sasaki T. , Furudate M. , Yamamoto M.
Published: February 2023

For application to soft x-ray multilayers we have so far determined optical constants of thin-film materials in the soft x-ray region using reflectance measurements.1-3 The optical constants are determined by least-squares fitting analysis for the reflectance vs angle-of-incidence curves. The Fresnel reflection coefficients are corrected with the so-called Debye-Waller factor, where only the rms surface roughness is included as a parameter characteristic to the sample surface. From the curve-fitting analysis we obtain rms surface roughnesses as well as the optical constants.
In-Situ Structural Characterization of Ultra-Thin Epitaxial Metal Films and Multilayers Observed with Grazing Incidence X-Ray Scattering
Authors: Clemens B. M. , Bain J. A. , Lairson B. M. , Daniels B. J. , Payne A. P. , Rensing N. M. , Brennan S.
Published: February 2023

The flexibility of physical vapor deposition allows fabrication of near ideal structures which can be used to investigate fundamental aspects of the mechanics of materials. One important phenomena which can be addressed is the deformation which occurs during relaxation of epitaxial strains. We have developed a unique sputter deposition system capable of performing in-situ structural characterization using grazing incidence x-ray scattering (GIXS). This gives us the ability to accurately measure lattice parameters of films in the monolayer thickness regime. Using this capability, we have investigated epitaxial orientation relations and coherency stress relaxation in several epitaxial film systems, including Cu on Fe (001), and Co on Pt (111).
Multilayer Coated Echelle Gratings for Soft X-rays
Authors: Malek C. Khan , Underwood J. H. , Gullikson E. M.
Published: February 2023

Recently there have been many experimental and theoretical studies of diffraction gratings coated with short-period multilayers to enhance their reflectivity in the extreme ultraviolet and x-ray regions. Much of this work has been focussed on lamellar gratings, but there is also considerable interest in multilayer coated blazed gratings. Until now, these blazed gratings have been made by traditional ruling. In an interferometrically controlled ruling engine this leads to very accurate groove placement, but the quality of the groove surfaces may be poor because the grooves are burnished into a soft material such as gold. This leads to low multilayer reflectivity because the substrate roughness (in this case the groove surface) is an important factor in determining its performance. In addition the gratings can be used only in low orders, since operation in higher orders requires excellent groove profile.
Detection and Localization of Quantum Limited Events from Radionuclide Labeled Materials by Computer Enhanced Video Microscopy
Authors: Traub RK , Pressman NJ , Frost JK , Gupta PK , Showers RL , Gill GW , Cook DL , Frost JK
Published: February 2023

Enhanced microscope-video acquisition of radionuclide decompositions quantitatively determines single events. High spatial resolution of nuclide distribution has been demonstrated.
Subpicosecond Light Scattering With a Micro-channel Plate Photomultiplier
Authors: Kash J. A. , Tsang J. C
Published: February 2023

We have used time-resolved Raman spectroscopy to study the energy relaxation of non-equilbrium carriers in semiconductors such as GaAs. Since the initial transfer of energy from the carriers to the lattice occurs within a few picoseconds, these experiments require a temporal resolution of less than a picosecond. We discuss in this paper the constraints on such experiments, their rationale, and the results obtained using a micro-channel plate photomultiplier.
Imaging a Randomly Translating Object Using the Triple Correlation
Authors: Dainty J C , Northcott M J
Published: February 2023

The triple correlation function I(3)(x1,x2) and its Fourier transform, the bispectrum Ĩ(3)(u1,u2), of a one dimensional intensity distribution I(x) are defined by [1], (1) and (2) where Ĩ(u) is the Fourier transform of I(x). Lohmann and Wirnitzer [1] have shown that it is possible to recover a signal I(x) from its triple correlation or bispectrum. The recovered signal is unique except in certain cases of no practical significance in the present study.
Origins of linear and nonlinear recursive restoration algorithms
Authors: Meinel Edward S.
Published: February 2023

In a recent paper Frieden1 unified the theory behind many nonlinear image restoration methods. He proposed that these methods be implemented using the Newton-Raphson iterative approach. Although this approach is fast, exhibiting quadratic convergence, it requires complex programming and large core storage capabilities even for modest image sizes, unless the problem can be reduced to line-by-line processing2. By contrast, recursive or replacement formulas permit interactive processing with modest storage requirements, albeit with slower convergence. They can also be implemented on a specialized image processing computer since the formulas use only simple algebraic operations. These recursive algorithms also have the capability of immediate display of intermediate images, which is especially useful in interactive processing.
An Opto-Electronic Parallel Interferogram Processor for Enhanced SNR Efficiency In Infrared Spectroscopy
Authors: Ramamoorthy P.A. , Pace Phillip E.
Published: February 2023

An opto-electronic interferogram processor for real-time FT-IR spectroscopy is presented which leads to an enhanced SNR efficiency by eliminating the serial scanning and free-space me­chanical aberrations associated with the frequently used Michelson interferometer. The parallel interferogram processor consists of an array of properly balanced Mach-Zehnders which can be conveniently integrated with electronic digital processing for improved performance high SNR spectroscopy applications. Design analysis is given and a near infrared example is detailed.
Knox-Thompson Imaging at Low Light Levels
Authors: Nisenson Peter
Published: February 2023

Speckle interferometry is proving to be an important tool for astronomical research, allowing measurements of a wide range of scientifically interesting objects that can be made in no other way. Most speckle scientific results to date have been on sources which are bright and have relatively simple geometries These results include the determination of close binary star orbits and the measurement of stellar angular diameters. Many astronomical problems require the study of faint, complex, extended sources. At the Center for Astrophysics (CfA), we have been developing detectors and algorithms for this application. The Knox-Thompson (K-T) algorithm (Knox, 1976) is one of a class of approaches which preserves the phase in the speckle process, allowing true image reconstruction. K-T has proven to be a robust and accurate approach to phase recovery, due to several improvements in the technique since Knox's original implementation. These improvements include the averaging of complex vector differences rather than phase differences and the application of a least squares error distribution in the phase estimation process.
AIGaAs/InGaAs/GaAs Multiple Quantum Well Voltage Tunable Bragg Reflector with Inter-digitated Contacts
Authors: Blum O. , Zucker J. E. , Wu X. , Gulden K. , Gustafson T. K.
Published: February 2023

Future developments in optical communications, interconnects and information processing rely on availability of integratable, tunable, surface-normal geometry mirrors and filters. In this paper, we present the first tunable multiple quantum well (MQW) distributed Bragg reflector (DBR) with inter-digitated contacts. This contacting scheme, shown in Fig. 1, allows us to apply large fields across MQW λ/4 layers producing electro-refraction and electro-absorption associated with the quantum confined Stark effect. Compared to our previous MQW DBR [1], where the applied voltage dropped across the entire mirror stack, in this work we obtain similar changes in reflectivity with nearly 20 times lower voltages.
Femtosecond Dynamics of Exciton Gain in (Zn,Cd)Se/ZnSe Quantum Weils
Authors: Hagerott M. , Ding J. , Nurmikko A.V. , Gan Y. , Grillo D. , Han J. , Li H. , Gunshor R.L.
Published: February 2023

The recent proof-of-concept demonstration of a blue-green diode laser in 1991 [1],[2] relied in part on the useful optical properties of the (Zn,Cd)Se/ZnSe and (Zn,Cd)Se/Zn(S,Se) quantum wells. These included large exciton effects to room temperature and beyond [3], a particularly unusual circumstance in wide gap II-VI semiconductors, given the large exciton-LO phonon interaction. However, due to quantum confinement, the binding energy in a ZnCdSe QW can exceed the LO-phonon energy so that excitons can in principle dominate also spontaneous emission to device temperatures. So far, most of the characterization of the new diode lasers has been performed at T = 77K, a temperature where the 2D excitons are particularly robust. The role of excitons in providing gain has been argued by us to be a physical reality in the ZnCdSe/ZnSe system [4], a feature which takes additional potential significance in terms of future diode laser design and development.
Fast optical switching and amplification in a multiple quantum well vertical microcavity
Authors: Raj R. , Oudar J. L. , Bensoussan M.
Published: February 2023

A major advance in the processing of optical signals in recent years has been the development of innovative devices based on vertical microcavity structures such as surface emitting lasers, bistable optical switches and modulators. These devices have attracted a lot of attention as they are highly suitable for bidimensional integration allowing fast parallel processing of information[1]. However such a bidimensional optical processing could be performed much more easily if another important function i.e amplification could be achieved in a practical way.
Asymmetric Gain in a Vertical-Cavity Surface-Emitting Laser
Authors: de Colstoun F. Brown , Lowry C. W. , Khitrova G. , Gibbs H. M. , Paul A. E. , Koch S. W. , Brennan T. M. , Hammons B. E.
Published: February 2023

The gain spectrum of a semiconductor can be locally modified by a strong nearly resonant laser field through population pulsations.1,2 Rayleigh-gain, an asymmetric modification of the gain profile of an atom, has been investigated previously.3,4 Laser diode longitudinal modes have been used to show gain asymmetry1,5, but the mode spacing (75 GHz5) has limited the observation to the periphery of the curve. Mapping the more closely spaced gain peak and dip is important because they can significantly modify the output spectrum of a laser (creating new lasing lines at the new gain peak and extinguishing the original lasing with the gain dip). Pump/probe experiments in traveling wave amplifiers (TWA)6 have shown the gain to be asymmetric, but the gain peak and dip were broadened because the injected signal grew in power (from ≃ 87 μW to 4.4mW6) during propagation. Using a high Q vertical-cavity surface-emitting laser (VCSEL) as the gain medium we have intracavity powers at the injected frequency that do not grow with propagation and are much higher than the TWA experiments (up to 75 mW in a 5 μm spot), pushing the gain peak as far as 36.5 GHz from the injected frequency. Rather than using longitudinal modes to probe discretely the gain asymmetry, when the gain extrema are within 10 GHz of the injected frequency we directly observe localized dips and peaks in the continuous ouput spectrum of the VCSEL. As increased injected power pushes the gain extrema out further, we observe modification of the line shape and pushing of the lasing. We find that the detuning of the gain extrema from the injected frequency increases linearly with the intracavity intensity at the injected frequency (in contrast with relaxation oscillations and other effects that scale with the field level). Understanding local modifications of the cw gain profile is of crucial importance to elucidate instabilities in semiconductors lasers.
Highly Non-degenerate (>1THz) Four-Wave Mixing in Multi-Quantum Well Laser Structures
Authors: Tatham M.C. , Sherlock G. , Seltzer C.P.
Published: February 2023

Carrier dynamic processes in semiconductor lasers, such as spectral holeburning and dynamic carrier heating, give rise to nonlinear gain. This affects many of the important static and dynamic laser characteristics, including the bandwidth and damping of high speed lasers. Recent time-domain pump-probe experiments1 have shown that several ultrafast processes contribute to nonlinear gain in InGaAs/InGaAsP laser structures with time-constants varying from sub-100fs to 1ps, but these are not yet fully understood. Here we describe measurements of ultrafast carrier dynamic processes in InGaAs/InGaAsP laser amplifiers using the technique of highly non-degenerate four-wave mixing2,3 (FWM), with pump-probe detunings of >1THz capable of measuring effects with time-constants of <200fs. We have used the technique to make quantitative measurements of both the time-constants and nonlinear gain parameters for the dominant processes.
Laser-Diode Based Scanning Force Microscope and Ultrafast Sampling Probe
Authors: Nees John , Craig Douglas , Hama Soichi , Wakana Shin ichi
Published: February 2023

New discoveries in fabrication technology and in device physics have open the way for a class of electronic and optoelectronic devices with nanometer-scale dimensions. These devices offer the opportunity to work with electrons confined to 2-D, 1-D and 0-D in space. In an effort to understand how individual devices work it will be necessary to interrogate individual submicron structures. Aside from the fine dimensions of the contacts used for such measurements it will be necessary to make measurement with very low invasiveness and increasingly, with higher speed. To meet the challenges of new nano-technologies we have developed a probe which demonstrates high impedance voltage measurement using a 0.1-micron contacting tip. The voltage of the tip is photoconductively sampled allowing waveforms to be measured with picosecond resolution [1]. In this paper we describe the operation of the probe using a gain switched laser diode to make measurements which extract only a few fC from the device under test. We also show the probes value as a high-speed, high sensitivity probe for millimeter-wave circuits.
A Record Low Threshold InGaAs/GaAlAs Vertical-Cavity Surface-Emitting Laser
Authors: Hayashi Y. , Mukaihara T. , Hatori N. , Ohnoki N. , Matsutani A. , Koyama F. , Iga K.
Published: February 2023

An index-guided InGaAs/GaAlAs vertical-cavity surface-emitting laser with a native oxide confinement structure has been proposed and fabricated. A record threshold current of 70μA was achieved by a 5μmϕ core device. The proposed structure provides both strong electrical and optical confinements.
II-VI Semiconductor Nanocrystals as Isolated Quantum Dots and in Complex Structures
Authors: Bawendi Moungi G.
Published: February 2023

Semiconductor crystallites which are 10's of Angstroms show a striking evolution of electronic properties with size.1 These particles (quantum dots) are large enough to exhibit a crystalline core, but small enough that solid state electronic and vibrational band structure is not yet developed. We use a recently developed synthetic method for the fabrication of high quality nanometer size (1-10 nm) II- VI semiconductor crystallites with narrow size distributions (σ<5%), emphasizing CdSe.2 Optical characterization of their electronic structure reveals both molecular and bulk-like characteristics as well as properties which are unique to nanometer size crystallites. We observe a number of discrete electronic transitions, assign them as coming from the creation of delocalized "particle-in-a- sphere" states using the theory of Ref. 3, and study their dependence on crystallite diameter.4
Blue-green laser diodes with improved crystal quality by using a strained-layer superlattice for the optical guiding layer
Authors: Gotoh Jun , Nakatsuka Shinnichi , Mochizuki Kazuhiro , Momose Masayuki , Taike Akira , Kawata Masahiko
Published: February 2023

Blue-green laser diodes (LDs) are attractive for such novel media applications as high- density optical recording systems and full color display devices. ZnSe-based II-VI semiconductor LDs have been developed in recent years1), and room temperature continuous- wave operation has been achieved2). These developments have enabled us to examine the various laser structures using this II-VI semiconductor, e.g., a separate-confinement heterostructure (SCH) gain guide laser1,2), and a ridge-waveguide laser3).
Exciton Confinement in Organic Multiple Quantum Wells
Authors: Forrest S. R. , Haskal E. I. , Shen Z. , Burrows P. E.
Published: February 2023

It has recently been shown that ordered, organic thin films of planar stacking molecules can be grown with monolayer uniformity and control over large substrate distances by the ultrahigh vacuum process of organic molecular beam deposition (OMBD). Due to this ability to grow films with such a high degree of order, it was demonstrated by So, et al1
,
2 that multiple quantum well stacks consisting of alternating layers of the archetype compounds, 3,4,9,10 perylenetetracarboxylic dianhydridc (PTCDA) and 3,4,7,8 naphthalenetetracarboxylic dianhydride (NTCDA) exhibit exciton quantum confinement That is, energy shifts in the absorption spectrum, as well as time resolved photolumincscence indicates systematic changes with layer thickness, as the thickness is reduced from 500Å to 10Å. While these early data were compelling, they opened up many questions as to the nature of excitons in closely packed organic molecular systems. Hence, in this work, we have extended this early investigation by measuring the electroabsorption, the absorption and the fluorescence spectra of organic MQW stacks consisting of PTCDA+NTCDA, as well as 3,4,9,10 peryleneietracarboxylic-bis-benzimidazole (PTCBI)+NTCDA. These new investigations provide further information essential to understanding the nature of excitons in these van der Waals-bonded molecular solids.
Strained InGaAs Quantum Disk Laser with Self-organized Nano-scale Active Region
Authors: Temmyo Jiro , Kuramochi Eiichi , Sugo Mitsuru , Nishiya Teruhiko , Nötzel Richard , Tamamura Toshiaki
Published: February 2023

Although there have been controversial discussions about the validity of quantum box lasers [1-2], few experimental results have been reported because of the difficulty of fabricating a quantum box structure suitable for laser application [3].
Fabrication and Optical Characterization of GaAs Nano-whiskers
Authors: Katsuyama T. , Hiruma K. , Sato T. , Ogawa K. , Shirai M. , Haraguchi K. , Yazawa M.
Published: February 2023

In recent years there has been considerable interest in the quantum effects of dimensional confinement on the optical properties of semiconductor materials. These confinement effects provide a means of artificially tailoring the optical properties of materials, offering the possibility of producing new optoelectronic devices. For example, modification of the carrier density of states makes it possible to produce semiconductor lasers with lower threshold currents and higher gains[1].
Realization of large subband separation and high power light output in GaAs/AlGaAs two-dimensional quantum well wire laser arrays
Authors: Qian Yi , Chen Lianghui , Zhang Jingming , Wang Qiming , Zhen Lianxi , Hu Xiongwei
Published: February 2023

Incorporating lower-dimensional structures such as quantum well wires (QWWs) and dots into semiconductor laser structures is expected to result in improved laser performance1. The technique of fabrication QWWs on nonplanar substrates by metal-organic chemical vapor deposition (MOCVD) is much potential due to formation of defect-free interfaces entirely during the epitaxial growth process2. With this approach, enhanced optical gain3,4 and ultralow threshold current2,5 have been demonstrated in QWW lasers. However, large QWW subband separation greater than thermal energy kBT at room temperature (~25meV) is still desirable, which should be realized by reducing wire sizes. The small wire volume, however, is disadvantageous for achieving high power light output of QWW lasers for some practical applications.
Spontaneous Emission Coupling to the Lasing Mode in a Fabry-Perot Microcavity with High Contrast AlxOy/GaAs Bragg Reflectors
Authors: Deppe D.G. , Huffaker D.L. , Deng H. , Shin J. , Deng Q.
Published: February 2023

There has been recent interest in studies of the influence of controlled spontaneous emission on the operating characteristics of lasers and light emitting diodes. Most cavity designs used in such work can be distinguished as either planar and of the Fabry-Perot type, or as possessing additional confinement in the lateral direction. For both cavity types the mirror design based on distributed Bragg reflectors (DBRs) plays an important role. Since the actual cavity length is set by light penetration into the mirrors, both the cavity length and the mirror reflectivity are set by the DBR design, which in turn sets the lateral mode profile for the planar cavity. In this talk we will present data characterizing the operation of a Fabry-Perot microcavity laser fabricated using high contrast DBRs of AlxOy/GaAs. The mirrors are formed by the selective conversion of AlAs into AlxOy using "wet oxidation" [1], resulting in the laser structure as illustrated in Fig.1. Four AlxOy/GaAs pairs are used on both the top and bottom (substrate) sides to form the laser cavity. In the actual laser cavity the oxidized mesa as illustrated in Fig.1 is 100μm in diameter while the lasing mode area is less than 10μm, so that the laser cavity is in fact planar. The resulting lasing characteristics of this cavity with high contrast DBRs are compared with those of a similar planar cavity design which uses the more typical AlAs/GaAs Bragg reflectors. For this second laser the upper reflector consists of sixteen pairs of AlAs/GaAs while the lower reflector (substrate side) consists of twenty-four pairs of AlAs/GaAs.
Strained InGaAs/AlAs MQW pin Modulator with Ultrafast Recovery
Authors: Wang H.S. , LiKamWa P , Ghisoni M , Parry G , Stavrinou P N , Roberts C , Miller A
Published: February 2023

The lattice mismatched, InGaAs/(GaAl)As multiple quantum well (MQW) system is currently of interest for optical modulator applications around 1μm. Most work to date has concentrated on the low barrier, InGaAs/GaAs system1,2. Here we investigate, InGaAs/AlAs using time resolved ultrashort pulse laser techniques in order to assess the suitability of this system for applications as high speed modulators based on the quantum confined Stark effect (QCSE) and saturable absorbers for mode-locked lasers. It is shown that this material system may offer advantages for optical modulator applications because an ultrafast recovery can be combined with low photocurrent to reduce power dissipation in a material which retains strong excitonic absorption features and clear QCSE.