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The symmetrical quasi-classical approach for propagation of a many degree of freedom density matrix is explored in the context of computing linear spectra. Calculations on a simple two state model for which exact results are available suggest that the approach gives a qualitative description of peak positions, relative amplitudes, and line broadening. Short time details in the computed dipole autocorrelation function result in exaggerated tails in the spectrum. [ABSTRACT FROM AUTHOR]

In the description of the interaction between electrons beyond the classical Hartree picture, bare exchange often yields a leading contribution. Here we discuss its effect on optical spectra of solids, comparing three different frameworks: time-dependent Hartree-Fock, a recently introduced combined density-functional and Green’s function approaches applied to the bare exchange self-energy, and time-dependent exact exchange within time-dependent density-functional theory (TD-EXX). We show that these three approximations give rise to identical excitonic effects in solids; these effects are drastically overestimated for semiconductors. They are partially compensated by the usual overestimation of the quasiparticle band gap within Hartree-Fock. The physics that lacks in these approaches can be formulated as screening. We show that the introduction of screening in TD-EXX indeed leads to a formulation that is equivalent to previously proposed functionals derived from many-body perturbation theory. It can be simulated by reducing the long-range part of the Coulomb interaction: this produces absorption spectra of semiconductors in good agreement with experiment. [ABSTRACT FROM AUTHOR]

We develop a linear response theory of solvation of ionic and dipolar solutes in anisotropic, axially symmetric polar solvents. The theory is applied to solvation in polar nematic liquid crystals. The formal theory constructs the solvation response function from projections of the solvent dipolar susceptibility on rotational invariants. These projections are obtained from Monte Carlo simulations of a fluid of dipolar spherocylinders which can exist both in the isotropic and nematic phases. Based on the properties of the solvent susceptibility from simulations and the formal solution, we have obtained a formula for the solvation free energy which incorporates the experimentally available properties of nematics and the length of correlation between the dipoles in the liquid crystal. The theory provides a quantitative framework for analyzing the steady-state and time-resolved optical spectra and makes several experimentally testable predictions. The equilibrium free energy of solvation, anisotropic in the nematic phase, is given by a quadratic function of cosine of the angle between the solute dipole and the solvent nematic director. The sign of solvation anisotropy is determined by the sign of dielectric anisotropy of the solvent: solvation anisotropy is negative in solvents with positive dielectric anisotropy and vice versa. The solvation free energy is discontinuous at the point of isotropic-nematic phase transition. The amplitude of this discontinuity is strongly affected by the size of the solute becoming less pronounced for larger solutes. The discontinuity itself and the magnitude of the splitting of the solvation free energy in the nematic phase are mostly affected by microscopic dipolar correlations in the nematic solvent. Illustrative calculations are presented for the equilibrium Stokes shift and the Stokes shift time correlation function of coumarin-153 in 4-n-pentyl-4′-cyanobiphenyl and 4,4-n-heptyl-cyanopiphenyl solvents as a function of temperature in both the nematic and isotropic phases. [ABSTRACT FROM AUTHOR]

Composition fluctuations in GaN:Mg have been investigated by optical transmission spectroscopy, near-field scanning optical microscopy (NSOM), and scanning Kelvin probe microscopy (SKPM). An Urbach tail is observed in the optical transmission spectrum of heavily Mg-doped GaN, with the magnitude of Urbach energy increasing with increasing compositional/potential fluctuations. From the relationship between the Urbach energy and the potential fluctuation magnitude, the spatial size of the compositional fluctuations in GaN:Mg (with the average Mg concentration of ∼4×1019 cm-3) is calculated to be 220 nm. The nanoscale compositional fluctuations are determined by NSOM and SKPM. A spatial variation of the transmission mode NSOM intensity is observed with a characteristic wavelength of ∼300 nm, which is attributed to the inhomogeneous distribution of Mg. The normalized root-mean-square (rms) fluctuation of the transmission mode NSOM intensity for heavily Mg-doped GaN is a factor of 5 greater than that for undoped GaN. Similar microstructure patterns are observed in the NSOM and surface potential images of GaN:Mg as probed by SKPM. The variation of local surface potential (on the order of 100 mV) is attributed to the same compositional fluctuations of Mg, which changes the local surface work function. The local Mg concentrations are calculated from the SKPM image. For GaN:Mg with the Mg concentration of 4×1019 cm-3, a rms value of 5.4×1019 cm-3 of the compositional fluctuations has been observed. [ABSTRACT FROM AUTHOR]

Femtosecond laser ablation of Ti, Zr, and Hf has been investigated by means of in situ plasma diagnostics. Fast imaging was used to characterize the plasma plume expansion on a nanosecond time scale. In addition, time- and space-resolved optical emission spectroscopy was employed to determine the plume composition and the characteristic expansion velocities of plasma species. It is shown that two plume components with different expansion velocities are generated by the interaction of ultrashort laser pulses with metals. The composition and the expansion behavior of the two components have been analyzed as a function of laser fluence and target material. The results are discussed in terms of mechanisms responsible for ablation by ultrashort laser pulses. [ABSTRACT FROM AUTHOR]

Polarized optical spectra of quaterthiophene single crystals are reported over a wide spectral range for different planes and angles of incidence corresponding to either transverse or mixed longitudinal/transverse wave propagation. From the absorbance and reflectance spectra the corresponding absorption coefficients are deduced. In the region of the first molecular transition, polarized exciton states of Frenkel origin are found to be responsible for a strong optical anisotropy and for the modification of the state of polarization during light propagation in the crystal. Transmission measurements with crossed polarizer and analyzer allow to clearly identify Frenkel replica of the principal transition. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The influence of solvent dynamics on optical spectra is often described by a stochastic model which assumes exponential relaxation of the time-correlation function for solvent-induced frequency fluctuations. In contrast, theory and experiment suggest that the initial (subpicosecond) phase of solvent relaxation, resulting from inertial motion of the solvent, is a Gaussian function of time. In this work, we employ numerical and analytical calculations to compare the predicted absorption line shapes and the derived solvent reorganization energies obtained from exponential (Brownian oscillator) versus Gaussian (inertial) solvent dynamics. Both models predict motional narrowing as the ratio κ=Λ/Δ is increased, where Λ and Δ are the frequency and variance, respectively, of the solvent-induced frequency fluctuations. However, the motional narrowing limit is achieved at lower values of κ for the Brownian oscillator model compared to the inertial model. For a given line shape, the derived value of the solvent reorganization energy λ[sub solv] is only weakly dependent on the solvent relaxation model employed, though different solvent parameters Λ and Δ are obtained. The two models are applied to the analysis of the temperature-dependent absorption spectrum of β-carotene in isopentane and CS[sub 2]. The derived values of λ[sub solv] using the Gaussian model are found to be in better agreement with the high temperature limit of Δ[sup 2]/2k[sub B]T than are the values obtained using the Brownian oscillator model. In either approach, the solvent reorganization energy is found to increase slightly with temperature as a result of an increase in the variance Δ of the solvent-induced frequency fluctuations. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have used a multitude of linear and nonlinear cw optical spectroscopies to study the optical properties of water precursor poly(p-phenylene vinylene) (PPV) thin films. These spectroscopies include absorption, photoluminescence, photoinduced absorption and their respective optically detected magnetic resonance, and electroabsorption spectroscopy. We have studied singlet and triplet excitons, polarons, and laser action in PPV films. We found that the lowest-lying absorption band is excitonic in origin. It consists of two absorption components due to a bimodal distribution of the polymer chain conjugation lengths. Electroabsorption spectroscopy unambiguously shows the positions of the lowest-lying odd parity exciton 1B[sub u] at 2.59 eV and two of the higher-lying even-parity excitons, namely, mA[sub g] at 3.4 eV and kA[sub g] at 3.7 eV. From these exciton energies we obtained a lower bound for the exciton binding energy in PPV, E[sub b](min)=E(mA[sub g])-E(1B[sub u])=0.8 eV. The quantum efficiency spectrum for triplet exciton photogeneration consists of two contributions; the intersystem crossing and, at higher energies, singlet fission. From the onset of the singlet fission process at E[sub SF]=2E[sub T], we could estimate the energy of the lowest-lying triplet exciton, 1 [sup 3]B[sub u], at 1.55 eV, with a singlet–triplet splitting as large as 0.9 eV. From photoinduced absorption spectroscopy we measured the triplet–triplet transition, T→T[sup *], to be 1.45 eV. The quantum efficiency spectrum for polaron photogeneration also consists of two contributions: one extrinsic and the other intrinsic. The latter shows a monotonically increasing function of energy with an energy onset at 3.3 eV. The intrinsic photogeneration process is analyzed with a model of free-electron–hole pair photogeneration, which separate more effectively at higher energy. The carrier generation quantum yield at 3.65 eV is estimated to be 0.5%. The quantum... [ABSTRACT FROM AUTHOR]

Studies self-assembled nanocrystalline dots of CdS grown within ZnSe host by steady state and transient optical spectroscopies. Presence of an unusually low density of the dots in the material system; Identification of the excitation transfer of excitons from the host; Efficacy of excitonic energy transfer from the ZnSe host to the dots; Possibility of a large effective capture cross section.

Examines the calculation of optical spectra in liquid methanol using molecular dynamics and the chemical potential equalization method (CPE). Application of the CPE technique as analytic tool for computing the infrared (IR) and Raman spectra of liquid methanol starting from classical trajectories generated by a conventional potential; CPE principle.

Presents information on a study on the spectra of silicon. Researches on the optical data of silicon at elevated temperature; Methodology used in conducting the study; Results.

Presents a study which described a surface-laser light scattering spectrometer that uses optical heterodyne detection to measure the temporal behavior of the thermally generated capillary waves at a fluid/fluid interface. Details of instrumentation; Data analysis; Experimental results.

Presents a technique for the optical spectroscopy of adsorbed molecules. Cause of the Davydov splitting; Structure of the tetracene molecule; Method used to study tetracene molecule in the as-deposited state.

Quantum chemical calculations based on density functional theory have been performed on ruthenocene. Excellent agreement is obtained with ground- and excited-state properties derived from optical spectroscopy. In particular, the energies of the first d–d excitations, the unusually large Stokes shift, the structural expansion of Ru(cp)2 and the substantial reduction of the Ru-cp force constant in the first triplet excited state are almost quantitatively reproduced. The lowest-energy excitation is found to have substantial charge transfer character. [ABSTRACT FROM AUTHOR]

The optical spectra of actinide ions in the compound AnCl3 and doped into single-crystal LaCl3 were interpreted in terms of transitions within 5fN configurations. Energy-level calculations were carried out using an effective-operator Hamiltonian, the parameters of which were determined by fitting experimental data. Atomic and crystal-field matrices were diagonalized simultaneously assuming an approximate D3h site symmetry. Spectroscopic data were taken from the literature but in most cases supplemented by unpublished measurements in absorption and in fluorescence. Data for each ion were analyzed independently, then the model parameters were intercompared and in many cases adjusted such that in the final fitting process the principal interactions showed uniform trends in parameter values with increasing atomic number. Consistent with analyses of the spectra of lanthanide ions in both LaCl3 and LaF3, abrupt changes in magnitude of certain crystal-field parameters were found near the center of the 5fN series. This resulted in two groups of parameter values, but with consistent trends for both halves of the series, and generally very good agreement between observed and computed energies. A new energy-level chart based on computed crystal-field level energies for each trivalent actinide ion has been prepared. [ABSTRACT FROM AUTHOR]

The temperature-dependent optical spectra of the major insulating forms of polyaniline—the fully reduced leucoemeraldine base, half-oxidized emeraldine base (EB), and fully oxidized pernigraniline base (PNB)—and of two oligomeric model compounds for polyaniline are reported. All three forms of the polymer possess a ∼3.8 eV optical absorption assigned to a transition from the valence band to a narrow π* conduction band; in all cases this transition shifts to higher energy and weakens with increasing temperature, T. The oxidized forms also exhibit transitions at ∼2 eV; in EB, this absorption feature has previously been assigned to a ‘‘molecular exciton’’ and is found to increase in energy with increasing T. In PNB, the observed ∼2.3 eV transition is correlated with the expectation of a Peierls dimerization gap in this half-filled band system; in contrast to the ∼2 eV transition in EB, this optical transition energy decreases with increasing T in PNB. These observations are for the most part understood by a simple model which accounts for the steric repulsion between the constituent phenyl rings of the polymer chain. The dependence of the steric potential on ring angle is anharmonic, giving rise to thermal expansion of the average phenyl ring-torsion angles and a concomitant reduction in the bandwidth and average energy of the valence band; the observed thermochromic behavior is generally consistent with these changes in electronic structure. The potential role of other conformational changes—rod-to-coil transitions, order–disorder transitions, bond-length order changes, and structural isomerizations—is discussed. [ABSTRACT FROM AUTHOR]

Vibrationally resolved optical spectra, fluorescence decay times, and fluorescence quantum yields have been measured for all-trans diphenyloctatetraene and all-trans diphenyloctatetraene substituted in the para position(s) of the phenyl ring(s) with an electron donor (MeO) or (and) and electron acceptor (CN). The electronic excitation energies, S0–S1 and S0–S2 transition dipoles and vibrational properties of the spectra provide a detailed picture of the effects of donor–acceptor substitution on the S0, S1, and S2 states. The electronic excitation energies are well fit by a simple parametrized quantum-mechanical model for polyene electronic structure which is used to estimate substituent-induced shifts in π-electron density in the S0, S1, and S2 states. [ABSTRACT FROM AUTHOR]

An approximate solution technique for computing spectra of many-body molecular systems is proposed. We focus for concreteness on 0 K electronic absorption and emission spectra. From a time-domain perspective, it is necessary to propagate a well-defined initial Schrödinger wave packet on a specified potential energy surface in order to extract such spectra. In order to perform this task for systems with many degrees of freedom, we investigate the utility of a time-dependent Hartree factorization, in which the wave packet for the complete system is variationally factorized into a product of wave packets of smaller dimensionality. This method is shown to be both flexible and reliable for prototypical model systems associated with the physical problem of impurity spectra in host crystals. Successful application is made to a recently measured emission spectrum of I2 embedded in an argon matrix. [ABSTRACT FROM AUTHOR]

The optical spectra of the lanthanides doped into single crystal LaF3 have been interpreted in terms of transitions within 4f N configurations. Energy matrices combining free-ion terms with a crystal field for an approximate model which assumes C2v instead of the actual C2 site symmetry were diagonalized. Excellent correlations were obtained between experimental transition energies and the computed level structures. We also report the results of previously unpublished experimental spectroscopic investigations of Nd3+ and Sm3+:LaF3, as well as predicted energy levels for Pm3+:LaF3. The spectroscopic data for each ion were independently interpreted using an effective-operator model, then the model parameters were intercompared. Systematic trends have been identified, and a comprehensive energy level diagram is presented. [ABSTRACT FROM AUTHOR]

Analyzes the manifestations of the Jahn-Teller effect on the optical spectroscopy of the Ag[sup +] ion in sodium fluoride (NaF). Details on the growth of NaF crystals containing Ag[sup +] ions isolated from each other using one- and two-photon spectroscopy; Comparison of Cu[sup +] and Ag[sup +] in NaF to better understand experimental parameters.

Provides information on an experimental investigating the interband optical spectra of the semiconducting beta phase of iron disilicide (beta-FeSi2) in the energy range from 0.5 to 5.0 eV. Methodology used to conduct the experiment; Results of the experiment; Discussion on the results.

Investigates the structure of optical phase change memory alloy, silver-vanadium-indium-antimony-tellurium (AVIST), by using optical reflectivity change, Raman spectroscopy and electron diffraction. Study of Sb, AgSb, AgSbTe and AgInTe films; Reversal of relative intensities for the AVIST films; Indication that the AgSbTe2 crystalline phase dominates.

Studies the origin of picosecond-pulse-induced, degenerate four-wave-mixing signals in KTN crystals. Details on the experiment; Optical spectra of KTN crystals; Information on the degenerate four-wave-mixing measurements.

Optical properties of new polydiacetylene (PDA) crystals substituted with fluorobenzene derivatives have been investigated by reflectance, Raman, and electroreflectance (ER) measurements. The results indicate that these fluorobenzene-substituted PDAs have an intermediate optical character between those of the acetylene-type and butatriene-type PDA chains. One of these PDA crystals, DFMDP, has been found to show an exceptionally high crystalline quality, which has enabled us to make a detailed spectroscopic study. ER studies on this DFMDP crystal have revealed the charge–transfer(CT)-type exciton lying at ∼2.7 eV on the higher-energy side of the lowest 1Bu exciton at ∼2.2 eV. On the basis of experimental results, it is conjectured that two-photon resonance with the CT exciton plays a major role in the third-order nonlinear optical process in PDA chains. [ABSTRACT FROM AUTHOR]

The temperature dependences of the fluorescence intensities and lifetimes of Mn2SiO4 and the results of time-resolved spectroscopy measurements on this material are reported. A model is developed to explain the results in terms of thermally activated migration of Mn2+ excitons terminating on deep trapping centers. Fiber growth techniques are shown to decrease the concentration of fluorescence quenching centers in this material, and dilution with Mg or Ca ions is found to decrease the efficiency of the quenching process. Four-wave mixing results suggest the presence of laser-induced photoionization processes in these crystals. [ABSTRACT FROM AUTHOR]

It is possible to measure luminescence quantum yield in a facile way, by designing an optical spectrometer capable of obtaining electronic absorption as well as luminescence spectra, with a setup that uses the same light source and detector for both the spectral measurements. Employment of a single light source and single detector enables use of the same correction factor profile for spectral corrections. A suitable instrumental scaling factor is used for adjusting spectral losses. [ABSTRACT FROM AUTHOR]

We report a demonstration of a very small microwave atomic clock using the 12.6 GHz hyperfine transition of the trapped 171Yb ions inside a miniature, completely sealed-off 3 cm3 ion-trap vacuum package. In the ion clock system, all of the components are highly miniaturized with low power consumption except the 369 nm optical pumping laser still under development for miniaturization. The entire clock, including the control electronics, consumes <300 mW. The fractional frequency instability of the miniature Yb+ clock reaches the 10-14 range after a few days of integration. [ABSTRACT FROM AUTHOR]

An instrumented and highly integrated biaxial stretching system was designed and constructed to obtain true stress, true strain, and optical behavior of polymeric films during biaxial stretching. With programmable drive motors, any form of temporally varying biaxial deformation profiles, including linear, exponential, logarithmic as well as cyclic, can be applied to a square-shaped films. This machine allows the investigation of mechano-optical behavior of films under profiles captured in industrial processes. To overcome the edge effects, the samples are painted with a dot pattern that is imaged using a high speed video capture system. This system accurately determines the locations of the each dot matrix in subsequent images acquired and calculates the true strains in both directions. The in-plane optical retardation is determined using spectral birefringence method that uses polarized white light and optical spectrometer in the optical train. This is carried out automatically at less than 10 nm in retardation resolution with the light beam passing through the symmetry center of the sample. Out of plane retardation is measured with an identical optical train tilted 45° to the plane of the film with its light beam going through the same spot on the sample as 0° beam. The true stress and birefringences are calculated with the determined instantaneous thickness of the film. With this system, the stress optical behavior of PET's is determined up to very large deformation levels at moderate to high deformation rates. Beyond the initial linear stress optical behavior, these films exhibit sudden positive deviation from linearity and this start of nonlinearity was directly associated with the stress induced crystallization. [ABSTRACT FROM AUTHOR]

Radial profile measurement of Zeff using visible bremsstrahlung (5300 Å) in the Large Helical Device (LHD) has often encountered difficulties because the intensity profile was largely deformed by the nonuniform visible bremsstrahlung emissions from the edge ergodic layer surrounding the core plasma. A space-resolved flat-field extreme ultraviolet (EUV) spectrometer has been newly adopted to measure the Zeff profile using the EUV bremsstrahlung continuum in the wavelength range of 70-75 Å. The EUV bremsstrahlung intensity profiles have been measured and checked for all the magnetic configurations with totally different magnetic field structures in the ergodic layer of LHD. It is found that the nonuniform bremsstrahlung emission from the thick ergodic layer can be entirely eliminated by use of the EUV emission with relatively high photon energy of 170 eV. As a result, the Zeff profile can be successfully measured for most of discharges regardless of magnetic field structures of the ergodic layer. The Zeff profiles measured in the EUV range are compared with those measured in the visible range at a magnetic configuration with the thinnest ergodic layer thickness. The result verifies that the use of the EUV bremsstrahlung continuum is an alternative way for the Zeff measurement in toroidal plasmas with nonuniform bremsstrahlung emissions at the edge. Typical results from the EUV bremsstrahlung measurement are presented showing a fairly flat Zeff profile with error bars of ±14%. [ABSTRACT FROM AUTHOR]

A beam emission spectroscopy (BES) system was developed for density gradient and fluctuation diagnostics in the Large Helical Device (LHD). In order to cover the large Doppler shift of the Hα beam emission because of the high-energy negative-ion-based neutral beam atom (acceleration voltage Vacc=90-170 kV) and the large motional Stark splitting due to the large v×B field (magnetic field B=3.0 T), a grating spectrometer was used instead of a conventional interference filter system. The reciprocal linear dispersion is about 2 nm/mm, which is sufficient to cover the motional Stark effect spectra using an optical fiber with a diameter of 1 mm. [ABSTRACT FROM AUTHOR]

A high-resolution x-ray imaging crystal spectrometer, whose concept was tested on NSTX and Alcator C-Mod, is being designed for the large helical device (LHD). This instrument will record spatially resolved spectra of helium-like Ar16+ and will provide ion temperature profiles with spatial and temporal resolutions of <2 cm and ≥10 ms, respectively. The spectrometer layout and instrumental features are largely determined by the magnetic field structure of LHD. The stellarator equilibrium reconstruction codes, STELLOPT and PIES, will be used for the tomographic inversion of the spectral data. [ABSTRACT FROM AUTHOR]

A high-throughput, broadband optical spectrometer coupled to the Rochester optical streak system equipped with a Photonis P820 streak tube was designed to record time-resolved spectra with 1-ps time resolution. Spectral resolution of 0.8 nm is achieved over a wavelength coverage range of 480 to 580 nm, using a 300-groove/mmdiffraction grating in conjunction with a pair of 225-mm-focal-length doublets operating at an f /2.9 aperture. Overall pulse-front tilt across the beam diameter generated by the diffraction grating is reduced by preferentially delaying discrete segments of the collimated input beam using a 34-element reflective echelon optic. The introduced delay temporally aligns the beam segments and the net pulse-front tilt is limited to the accumulation across an individual sub-element. The resulting spectrometer design balances resolving power and pulse-front tilt while maintaining high throughput. [ABSTRACT FROM AUTHOR]

The temporal dispersion of an optical spectrometer has been characterized for a variety of conditions related to optical diagnostics to be fielded at the National Ignition Facility (e.g., full-aperture backscatter station, Thomson scattering). Significant time smear is introduced into these systems by the path length difference through the spectrometer. The temporal resolution is shown to depend only on the order of the grating, wavelength, and the number of grooves illuminated. To enhance the temporal resolution, the spectral gratings can be masked limiting the number of grooves illuminated. Experiments have been conducted to verify these calculations. The size and shape of masks are investigated and correlated with the exact shape of the temporal instrument function, which is required when interpreting temporally resolved data. The experiments used a 300 fs laser pulse and a picosecond optical streak camera to determine the temporal dispersion. This was done for multiple spectral orders, gratings, and optical masks. [ABSTRACT FROM AUTHOR]

A versatile time-to-digital converter based data acquisition system for a segmented position-sensitive detector has been developed. This data acquisition system was successfully demonstrated to a two-segment position-sensitive detector. The data acquisition system will be developed further to support multisegmented position-sensitive detector to improve the photon count rate capability of the advanced x-ray imaging crystal spectrometer system. [ABSTRACT FROM AUTHOR]

The method for plasma rotation measurement in the tokamak TCABR is reported in this article. During a discharge, an optical spectrometer is used to scan sequentially spectral lines of plasma impurities and spectral lines of a calibration lamp. Knowing the scanning velocity of the diffraction grating of the spectrometer with adequate precision, the Doppler shifts of impurity lines are determined. The photomultiplier output voltage signals are recorded with adequate sampling rate. With this method the residual poloidal and toroidal plasma rotation velocities were determined, assuming that they are the same as those of the impurity ions. The results show reasonable agreement with the neoclassical theory and with results from similar tokamaks. [ABSTRACT FROM AUTHOR]

We describe a Fourier-transform spectrometer appropriate for use in an undergraduate optics laboratory. The modular design, which uses off-the-shelf equipment, is suitable for determining the spectra of ultrashort pulsed and continuous light sources. The spectrometer does not require equal step sizes for the motion of the mirror. An algorithm interpolates the phase of both a reference and an unknown light beam at equal intervals before performing the Fourier transform. The interferometer scan and the phase and spectral analysis are performed in a few seconds, making the apparatus a useful tool for teaching concepts of temporal coherence and Fourier spectroscopy. [ABSTRACT FROM AUTHOR]

The spectroscopic investigation of high temperature laser produced plasmas in general, and x-ray opacity experiments in particular, often requires instruments with both a broad coverage of x-ray energies and high spectral, spatial, and temporal resolution. We analyze the design, model the response, and report the commissioning of a spectrometer using elliptical crystals in conjunction with a large format, gated microchannel plate detector. Measurements taken with this instrument at the Janus laser facilities demonstrate the designed spectral range of 0.24–5.8 keV and spectral resolution E/ΔE>400, resulting in two to three times more spectral data than achieved by previous spectrometer designs. The observed 100 ps temporal resolution and 35 μm spatial resolution are consistent with the requirements of high energy density opacity experiments. [ABSTRACT FROM AUTHOR]

The development of a multiple-channel lock-in optical spectrometer (LIOS) is presented, which enables parallel phase-sensitive detection at the output of an optical spectrometer. The light intensity from a spectrally broad source is modulated at the reference frequency, and focused into a high-resolution imaging spectrometer. The height at which the light enters the spectrometer is controlled by an acousto-optic deflector, and the height information is preserved at the output focal plane. A two-dimensional InGaAs focal plane array collects light that has been dispersed in wavelength along the horizontal direction, and in time along the vertical direction. The data is demodulated using a high performance computer-based digital signal processor. This parallel approach greatly enhances (by more than 100x) the speed at which spectrally resolved lock-in data can be acquired. The noise performance of a working system optimized for the 1.3 μm wavelength range is analyzed using a laser diode light source. Time-resolved absorption traces are obtained for InAs quantum dots embedded in a GaAs matrix, and for dispersed films of PbSe nanocrystals. [ABSTRACT FROM AUTHOR]

A complete optical spectroscopy apparatus has been developed on board of a high gravity chemical vapor deposition facility. The article describes in detail the experimental apparatus and its main features. Preliminary results concern in situ plasma diagnostics under various gravity conditions up to 75g. The developed diagnostic apparatus is found to be a convenient tool for systematic in situ investigation of the influence of high gravity on the plasma composition. Thus, it is an effective means to clarify the most relevant active species playing a role during diamond film growth under high gravity conditions. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present the design, implementation and testing of a high-efficiency, high-resolution transmission grating spectrometer for measurements of near-ultraviolet to visible-range spectra of light from an electron beam ion trap, where geometry is constrained. The system consists of two 5 in. diameter f/4.6 achromatic lenses, a 6 in. diameter transmission grating ion-beam etched in fused silica, and a thinned, backilluminated CCD detector. The simple design minimizes the number of optical components, each with optimal throughput and high efficiency. Using a 30 µm wide entrance slit, a resolving power (λ/Δλ) of 15400 at λ ≈ 3850 Å has been demonstrated. The features and limitations of the instrument have been explored and an in situ calibration technique for use on the Livermore EBIT-II and SuperEBIT electron beam ion traps has been developed. [ABSTRACT FROM AUTHOR]

A high-resolution two-color spectrometer for rotational coherence spectroscopy (RCS) in the picosecond time domain has been developed and applied to several molecular systems. This time-resolved method enables the structural characterization of large molecules and clusters in the gas phase by determination of their rotational constants with high precision. Our spectrometer is based on a well stabilized solid-state chirped pulse amplified laser setup with an adjustable pulse duration in the picosecond range. Two optical parametric generators provide tunable radiation in the UV spectral range, with a pulse duration of 2 ps. An interferometric setup is employed in order to perform pump-probe experiments with up to 8 ns delay between pump and probe pulse. Two different pulse to pulse switching modes and the online monitoring of laser parameters have been integrated to enable the measurement of RCS traces with high resolution and good signal/noise ratio. These modes also permit the identification of weak features that would otherwise not have been observed. The molecular samples are prepared in a supersonic expansion and either the laser induced fluorescence or the photoion current are detected as a function of the time delay between pump and probe pulse. The performance of the spectrometer is demonstrated by recording a high-resolution RCS spectrum of para-difluorobenzene·argon and benzene. From their analysis the rotational constants of the ground state and electronically excited state of both species were obtained with an estimated uncertainty on the order of 10[sup -4] and 10[sup -5], respectively, in excellent agreement with high-resolution frequency-resolved data. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]