Raman scattering in conjunction with photoluminescence spectroscopy were applied to investigate strain relaxation, lattice dynamics and band offsets in ZnSe-ZnSxSe1-x strained-layer superlattices, and the effects of a ZnSe overlayer on the optoelectronic properties of GaAs surfaces in ZnSe/GaAs heterostructures.

Instrumental options for Raman spectroscopy in light of low noise, Si charged coupled device (CCD) detectors are discussed. The unique sensitivity of this detector in the wavelength interval between 0.8 and 0.98 um is shown. The potential advantages of employing diode laser excitation at wavelengths longer than 0.75 um for nonresonant vibrational Raman spectroscopy along with the available high throughput spectrometers at these wavelengths are delineated. The application of detection in this spectral region to quantitative determination of acceptor impurities in bulk semi-insulating GaAs is demonstrated. The improvement over excitation at 1.06 um is shown to exceed 104.

We present the growth and characterization of Ge/Si strained layer superlattices grown on different substrate orientations. Prior to the growth of the superlattices, a relaxed thick GexSi1-x buffer layer is grown on Si substrate to symmetrize the strain distribution and thus maintain pseudomorphic growth of the superlattices. The effective Ge fraction x is used to define the degree of interface mixing of these superlattices. It is found that for samples grown on the same orientaion, the degree of interface mixing is higher for samples with smaller period lengths. The samples grown on (110) and (111) substrates also have a higher degree of interface mixing than those grown on (100) substrates. The thermal stability of these Ge/Si strained layer superlattice samples is also studied.

Raman scattering measurements of zone-folded acoustic phonons in periodic and quasiperiodic superlattices have been performed and analyzed in order to extract values of the structural parameters. The period of either periodic or quasiperiodic lattices can be obtained with an accuracy of 2-3% from analysis of the peak frequencies. The determination of the period can be made accurately even in strained-layer material systems which exhibit misfit dislocation networks. Peak intensity analysis yields an estimate for the individual layer widths, but with considerably more uncertainty than found using x-ray diffraction modeling. In strained-layer lattices intensity analysis is generally limited to structures which exhibit pseudomorphic epitaxy since the presence of misfit dislocation arrays perturb the zone-folded acoustic mode intensities. In lattices grown with intentionally broken symmetry we have observed strong zone-boundary peaks which would normally be symmetry forbidden. Observation of the latter serve as a qualitative indicator of layer width variations in superlattices.

We describe the use of vibrational Raman spectroscopy to characterize ultra-thin crystalline Ge and Si layers grown by molecular beam epitaxy on Si(100) substrates. Samples have been studied where the Ge or Si layer thickness is less than 1 nm. The Ge layers were grown on Si(100) and covered by a thin silicon cap layer. Thin Si layers were grown on thick, relaxed Ge layers deposited on Si(100). The crystalline Si layer was capped by epitaxial Ge and a thin layer of amorphous Si for protection against oxidation. In spite of signals from the substate and the cap layer that are orders of magnitude stronger than the Raman scattering from the buried layer of interest, Raman scattering provides information about the crystalline quality of the epitaxial growth, the abruptness of the interfaces between the different layers, the strain in the layers and the electronic structure of the layers being studied.

The reliability of using commonly employed expressions for extracting the alloy concentration from Raman and photoluminescence peak energies is examined. Study of molecular beam epitaxically grown AlxGa1-xAs alloys shows disagreement in Al% of as large as 20% between the value derived from Raman data and that derived from PL data using these expressions. The atomistic nature of the heterostructure interface imperfection is examined through the study of single quantum well luminescence. Luminescence linewidth as a function of single quantum well width (dw) shows a dw-1 behavior and not the dw-3 behavior as predicted by the well-width-fluctuation model. This measured behavior brought out the importance of the fluctuation in the alloy concentration in both the lateral and growth directions arising from the kinectics of growth.

Raman spectroscopy provides powerful insights into the novel physical properties of the tetrahedrally coordinated diluted magnetic semiconductors, the II-VI semiconductors with group II ions randomly replaced with transition metal ions like Mn2+, Co2+ or Fe2+. The technique is equally fruitful in the context of the special issues which arise in epilayers and superlattices of these semiconductors.

In wide gap II-VI compound semiconductor superlattices, excitons frequently dominate the optical spectra. They can also couple strongly to phonons, the point which we illustrate with a specific example in ZnSe superlattices, where incorporation of ZnTe on monolayer scale induces strong exciton localization effects with the participation of lattice distortion.

Raman and resonant Raman scattering measurements have been performed on two HgTe/CdTe superlattices (SL). HgTe-like and CdTe-like phonon modes were observed, corresponding to layers of Hgl-xCdxTe (x ~ 0.85) rather than of pure CdTe, because of Hg added during the growth process. Pure HgTe phonon modes were also seen. Pure CdTe phonon lines are observed from a HgTe-CdTe SL with a 300 Å CdTe cap. The multiple CdTe phonon outgoing resonances with the E0 + Δ0 gap are studied for this SL and CdTe substrates. An unexplained Raman feature is observed near 430 cm-1.

Raman scattering is a powerful tool for the investigation of II-VI compounds. In particular, scattering by longitudinal optical (LO) phonons shows very strong resonances associated with the increased ionicity and reduced screening in these materials as compared with III-V and group IV semiconductors. In alloys of II-VI compounds, resonance Raman scattering by LO phonons can be used for electronic band structure studies, including the determination of critical points and their broadening. More recently, the fabrication of II-VI superlattices has received much attention. These systems, which range from narrow gap superlattices to wide gap structures, cover an impressive range of possible technological applications. They pose new problems such as interdiffusion, strain distribution, band offsets, interband transition energies, etc. Raman scattering can be used to address all these questions. In this paper, I illustrate the applications of Raman scattering by reviewing resonance experiments on HgCdTe alloys and more recent Raman work on CdTe-ZnTe superlattices.

Raman spectroscopy in Hgl,Cdje (MCT) is a powerful, nondestructive surface probe of alloy composition and crystallinity. The frequencies and the relative amplitudes of the HgTe-like and CdTe-like phonon modes change with Cd fraction; the E1 and E1 + Δl critical points shift with x-value and strongly influence the Raman spectra obtained with the green and blue lines of the argon laser. We have studied the resonance enhancement of the two LO and two TO modes and a "cluster" mode in as-grown samples of MCT for x-values between 0.20 and 0.31. In addition, we have studied the changes which occur in the Raman spectra after exposure of the MCT surfaces to single pulses from a dye laser with pulse energies above the melt threshold. The Raman spectra show clear evidence of compositional changes near the surface when processing occurs in air. However, when the irradiation occurs in an ambient of ~20 atm. of argon, the major effect is a reduction of the peak associated with a cluster mode. The results are consistent with a strong suppression of clustering after pulsed laser annealing.

Cd1-xMnxTe films (thickness ~0.5 micron, x = 0.10 - 0.37) have beengrown Ey metalorganic chemical vapor deposition on commercial GaAs and glass substrates with and without buffer layers of CdTe and CdS for potential use in solar cells. Raman scattering and photoluminescence played an important role in characterizing and optimizing film quality. Raman methods established the relation between film quality and substrate type or growth temperature. Photoluminescence spectroscopy determined the percent of Mn in the as-grown films, displayed stress effects due to lattice mismatch and their dependence on substrate, and indicated the presence of defects.

Raman Scattering Extrema Method (RSEM), originally proposed by author, to determine the orientation of a thin layer with diamond structure, is extented to zincblende structure. The Raman scattering intensities of LO and TO phonons as functions of both the orientation of this layer and the polarization direction of the incident light have been derived for a zincblende-structured thin layer. Then the orientation of the layer is determined by means of the extrema of these functions. The obtained results for GaP wafers using this method is compared with that determined by the X-ray diffraction method.

Fiber-optic light pipes have unique advantages for optical spectroscopy in extreme environments: at low-temperatures where optical windows on cryostats are prohibitive; in small-bore high-field magnets; and in high-pressure cells. Practical applications are described for a variety of techniques including photoluminescence, photoreflectivity, Faraday rotation, optical transmission, and even Raman light scattering. To illustrate the utility of these fiber-optic systems, results are presented for experiments to T=0.1 K and up to B=30 tesla on magnetic semiconductors (Cd,Mn)Te and GaAs quantum well systems.

In this review article technical aspects of high-pressure Raman spectroscopy are discussed. With the advancements-in the diamond anvil cell (DAC) technology and spectroscopic instrumentation, high-pressure Raman spectroscopy has made tremendous advances. It has become possible to study vibrational spectra of micron size (~5μ) samples of solids, liquids and gases to very high pressures--approaching the megabar range--in the 0°, 90°, 135° and 180° scattering geometries. The advantages and problems of Raman measurements in various scattering geometries in the DAC are examined by comparing: (i) the high-pressure spectra of normal deuterium (n-D2) fluid in 0° and 90° scattering geometries, and (ii) micro-Raman spectra of diamond anvils at high pressures in 135° and 180° scattering geometries. It is found that the 90° and 135° scattering modes of high-pressure Raman measurements in the DAC provide better signal-to-noise ratio and less interference from diamond-anvil fluorescence. In addition, the results of high-pressure Raman measurements of Ge02 and Si02 glasses and of crystalline polymorphs of a number of materials, including Ge02, Si02, and TiO2 are summarized.

Surface Enhanced Raman Spectroscopy (SERS) has been demonstrated to be a sensitive probe of the structure of molecules that are at or near the surface of an enhancing metal substrate. We have employed vapor-deposited silver island films as the enhancing medium to study the SERS effect in a variety of thin (<700 Å), vapor-deposited, multilayered organic films. Utilizing sequential depositions, we have intentionally positioned the SERS active metal islands at selected depths within the organic films. Our experiments were chosen to explore the "compatibility" of the silver depositions with several vapor-deposited organic species, to investigate the uniqueness of SERS as a position-sensitive probe in a multilayered system and to study possible chemical and/or physical interactions that may occur at the metal/organic and organic/organic interfaces. Our results indicate that SERS can be used to probe molecular structure at very discrete locations (e.g., near a solid/solid interface) in a multilayered system.

A solid-state two-dimensional charge-coupled device (CCD) is found to offer several advantages to the detection of chemiluminescence from luminol. To study these benefits, measurements of luminol emission with hydrogen peroxide and transition-metal ions were made in a continuous flow mode. A mixture of metal ions separated by cation-exchange chromatography was also observed with chemiluminescence. A new technique, simultaneous variable binning, applied to the transient light emission leads to outstanding dynamic range. Excellent linearity and detection limits are obtained for Co2+, Cu2+, Cr3+, and H202.

The polarity and polarizability of -P=N and P-X bonds in phosphazenes (NPX2)n are influenced by the structure and effective electronegativities of the ligands (X) attached to the phosphorus atoms. The nature of chemical bonding in phosphazenes is revealed through responses of vibrational spectra to perturbations such as external pressure and solvent-hydrogen bonding, as well as chemical and isotopic substitution of the ligands. Raman spectra of a series of cyclic phosphazenes are used to identify and classify the vibrational modes. Changes in vibrational frequencies and Raman intensities are interpreted in terms of the polarized chemical bonding model suggested by recent calculations.

The Raman spectrum is a characteristic signature that identifies diamond carbon, diamond-like carbon, graphitic carbon in various structural states, and possibly another structural family of carbon. The single sharp Raman line at 1332 cm-1 allows cubic diamond to be recognized against a background of other types of carbon. Small shifts in band wavenumber have been related to stress state in deposited films and line width relates to structural order. Impurities in diamond act as luminescence centers. Some of these can be excited by the laser line used for Raman spectroscopy and the Raman spectrometer used as a luminescence spectrometer. Four major centers and several minor ones have been identified in CVD diamond films.

Recent developments in diamond thin film growth using plasma, ion beam or hot filament assisted chemical vapor deposition (CVD) techniques have created the potential for a wide variety of applications for diamond in areas as diverse as cutting tool coatings and high speed electronic devices. In this paper we examine the impurity content of diamond films grown by filament-assisted CVD using photo-luminescence (PL) spectroscopy in the 1.6 - 2.5 eV energy range. We find that the dominant impurity in these films besides hydrogen is nitrogen, as determined by the presence of a strong luminescence peak at ~2.1 eV. This band is attributed to donor-acceptor pair recombination in analogy with a similar feature in the PL of natural diamonds. In films which show a sharp Rama feature at 1332 cm-1 and very little Raman activity in the 1550 cm-1 region, additional emis-sion appears at ~1.7 eV. This is in the vicinity of the 1.673 eV emission observed in natural diamonds, and is ascribed to a neutral vacancy. Other luminescence bands, which overlap the 1.7 eV emission and appear to be unique to CVD grown diamond, have yet to be assigned. We also include data on luminescent emission from a nitrogen vacancy complex which is referred to in the bulk as the H3 center This center was induced in the films by irradiation with 2 MeV He+ ions, with no post-irradiation anneal.

Cathodoluminescence of diamond films has been investigated in the range of 2.0-3.5 eV. The CL spectra of diamond films are very sensitive to impurities such as nitrogen and boron. The main emission peak occurs around 2.8 eV in the films where the content of these impurities are lowered. The shape and behaviour of the spectra of the films are very similar to those obtained in natural type IIa diamond. The boron doping to the films increases the CL intensity. The luminescence is explained by donor-acceptor pair recombination where the acceptor is substitutional boron. In the semiconducting film, electroluminescence has been observed at metal/diamond(p-type) interfaces for the first time. From the CL imaging study, (100) growth sectors of diamond particle are much more luminescent than (111) sectors. This result indicates that the introduction of impurity or defect during crystal growth differs in each sectors.

We report resonance Raman results from amorphous carbon films and graphite. Our experiments confirm the presence of π-states in the amorphous samples, as suggested by theoretical models. The different resonance behavior of the high-energy and low-energy sides of the broad amorphous Raman peak is shown to be related to similar differences we observe in cristalline graphite for zone-edge and zone-center phonons.

Raman and photoluminescence spectra were obtained from diamond and diamondlike carbon films synthesized by plasma enhanced CVD techniques. Depending upon certain synthesis conditions, films exhibited photoluminescence attributed to the GR1 color center known to occur in irradiated natural diamond crystals. Photoluminescence intensity, corresponding to the GR1 centers, increased with increasing diamond content of the films, both in terms of film thickness and ratio of diamond to graphitic bonding.

The recent interest in the growth of thin diamond films has led us to consider the differences between the hexagonal (lonsdaleite) and cubic structures. Both phases have very similar properties, and empirical and theoretical considerations indicate that their structural energies are nearly identical. When thin films are grown the hexagonal phase may compete with the cubic phase, making characterization of the film difficult. Cubic diamond has one Raman active mode, while hexagonal diamond has three. The opportunity thus exists for Raman spectroscopy to differentiate between the two tetrahedrally bonded phases (as well as "amorphous" or graphitic phases). Electronic structure calculations can be used to obtain theoretical Q=0 frequencies of the Raman active modes in both structures. We have used the first principles Linearized Augmented Plane Wave method within the local density approximation to calculate the zone center phonon frequencies. The calculated frequency of the cubic diamond Raman mode is 1336 cm-1, very close to the experimental value of 1333 cm-1. Our calculations indicate that the hexagonal structure A t has a zone-center frequency of 1269 cm-1, the Elg mode is at 1215 cm-1, and the E1g mode is at 430 cm-1. Anharmonic corrections are rather large (2-3%) in the cubic diamond Raman mode and in the hexagonal Al mode, but are not important in the E2g and Elg modes. We will compare our results with the available experimental information.

Raman spectra of the hexagonal phase of boron nitride to temperatures exceeding 2000°C. have been recorded using a pulsed-excitation gated-detection method. Surface temperatures were determined during rapid sample heating from analysis of corrected Stokes/anti-Stokes intensity ratios and from shifts in the resonance frequency of the 1366 cm-1 Eg mode. Successive spectra were acquired at time intervals as short as 33 msec corresponding to the pulse repetition frequency of the probe laser. Using this synchronous detection technique, the time evolution of graphite furnace temperatures was determined from measured spectra. Results indicate nearly complete rejection of sample blackbody radiation from the Raman scattered light at these high temperatures. A nearly linear relationship between the Eg resonance frequency and temperature was found. Phonon linewidths were also found to increase by a factor of three over this temperature range.

The pressure dependences of the Raman active modes in submicrometer films of the anatase and rutile crystalline phases of TiO2 have been determined at pressures approaching 90 Kbar. Films investigated have been prepared by reactive sputter deposition and sol-gel techniques. Band frequency shifts as a function of applied pressure for the rutile phase are in agreement with measurements from single crystal samples. However, sol-gel films (anatase) exhibit larger frequency shifts than powder or single crystal samples, and do not undergo the expected pressure-induced phase transformation to the Ti02-II phase. This anomalous pressure response is discussed in terms of the complex film microstructure evaluated from TEM cross-sectional measurements.

The properties of thin films made of alloys of Si, Ge, and C are investigated with Raman spectroscopy and other, mostly non-optical, techniques. The focus is on the relationship between structural, electronic. and optical properties. Three topics are investigated: the microcrystallinity in A thick (> 1000 Å) doped SiC films, the influence of the substrate on the properties of thin (< 1000 Å ) films, and possible heterogeneities in SiGe alloys. This study is the first step towards a better understanding of the relationship between the growth parameters and the electronic and optical properties that are useful in devices.

There was a time not too long ago when proteins were viewed as static structures. It is now apparent that proteins exhibit a wide variety of local and global dynamics; nevertheless, an understanding of both how proteins move and how these motions influence protein reactivity remains a fundamental, unanswered and illusive problem within biophysics. Most of the recent detailed studies to date have been theoretical endeavors utilizing molecular dynamics simulations. Unfortunately comparable experiments that are structurally specific or detailed are lacking. In this manuscript, several picosecond time resolved resonance Raman studies of hemoglobin and myoglobin are reviewed, explored and compared with the purpose of extracting dynamical information on these well characterized "model" protein systems.

The mechanisms by which structure and structural dynamics modulate reactivity at protein active sites pose one of the fundamental problems of molecular biophysics. During the past decade, it has become increasingly evident that dynamics play an important role in determining the reactivity of heme proteins (1-3). Thus, it is clear that simple determinations of equilibrium structures are often only a first step in addressing this issue. The complexity of the multi-level dynamics of proteins makes it highly desirable to examine systems where both the kinetic rates and the equilibrium structures are very well characterized. In that sense, the ligand binding dynamics of hemoglobins and myoglobins provide a nearly ideal framework in which to explore the biophysical complexities that are at the core of structure-function relationships. The specificity and interpretability of resonance Raman scattering from hemes make it an excellent technique for the structural characterization of the active sites of hemoglobin. Here, we present the results of recent studies in our laboratories utilizing time-resolved resonance Raman spectroscopy that further characterize the structural dynamics occurring at the heme active sites of hemoglobin subsequent to ligand photolysis.

The effects of protein structural inhomogeneities are discussed in the context of ligand binding to Mb. The results of resonance Raman, optical absorption and geminate rebinding kinetics reflect these inhomogeneities. These effects can be divided naturally into proximal and distal interactions that, respectively, spread and shift the barrier height distribution for ligand binding.

The presence of oxo-bridged dinuclear iron clusters has been established in the respiratory protein, hemerythrin (Hr), and in the DNA-biosynthesis regulatory enzyme, ribonucleotide reductase (Rr). For the iron proteins uteroferrin and purple acid phosphatase (PAP) evidence for μ-oxo-bridged centers is less clear. Resonance Raman (RR) spectra obtained by excitation into an 0(2-) → Fe(III) CT band may show strong symmetric and weak antisymmetric Fe-0-Fe vibrational modes. We have investigated the spectra of a variety of μ-oxo-bridged Fe(III) complexes to establish the dependence of Raman scattering intensities upon structural parameters. Intensities were found to relate to the nature of the ligand trans to the oxo group: nitrogen ligands with unsaturation (e.g., pyrazole and imidazole) lead to strong scattering, whereas saturated ligands provide only poor scattering. The Fe-0 bonds in Hr and Rr are strong scatterers; the former is known from x-ray crystallography to have a histidyl ligand trans to the μ-oxo group. On this basis, a similar ligand structure is likely in the reductase. In contrast, PAP shows no oxo-bridge with UV and near-UV excitation. We propose that a different structural framework is necessary to account for this result. Hydrogen bonding of protein side chains to oxo and sulfido ligands is proposed to explain changes in frequencies for samples dissolved in water vs. D20. Differences in hydrogen-bond strengths between 0...(D) and S...(D) systems are transferred to the observed Fe-0 and Fe-S bond vibrations.

Cytochrome c oxidase is known to display a conformational transition from a "closed" to an "open" structure upon partial reduction. In the past exogenous ligand binding kinetic differences and differences in tryptophan fluorescence have been associated with this structural change. We report changes in the resonance Raman spectrum of NO-bound cytochrome as upon this transition. We detect changes in both the heme vibrational modes and in the Fe-N-0 bending mode. Furthermore, we have been able to identify a hydroxide-bound intermediate in the enzyme. Analysis of the conditions for its generation lead to the proposal that it is stable only in the open conformation of the protein. In both of these series of experiments advantage was taken of the photoreducibility of the heme groups by the incident laser beam.

Resonance Raman and Fourier transform infrared spectra of several derivatives of cytochrome ba3, a newly discovered terminal oxidase of the bacterium Thermus thermophilus, are reported. The RR features characteristic of cytochrome a3 are uniquely observed without interference from cytochrome b by subtraction of the analogous cytochrome b5 spectra. The spin state indicator peaks of the a3 heme appear at unusually high frequencies, suggesting a uniquely small heme core size. Multiple C-0 and Fe-N(Im) peaks are observed in the FTIR and RR spectra, respectively. Their relative intensities are temperature-dependent suggesting the presence of discrete interconverting conformers of the enzyme. Thermodynamic parameters for interconversion of these conformers are derived. The C-0 infrared stretching frequencies of the fully reduced carbon-monoxy enzyme show that CO binds to Cue following photodissociation of CO from the heme a3 at all temperatures up to ambient.

Surface-enhanced resonance Raman scattering (SERRS) studies of cytochrome c (cyt c) and cytochrome P450 (cyt P450) as a function of laser irradiation time have demonstrated that the proteins are extremely sensitive to photodegradation. The results suggest that previous SERRS reports of hemoprotein denaturation on Ag surfaces may reflect photosensitivity rather than an effect of the protein-surface interaction. Photodamage was eliminated by submersion of the electrode into liquid nitrogen. This procedure resulted in stable SERRS spectra, even with prolonged irradiation. The use of a diode array detector also substantially reduces the laser exposure period ( < 1 minute) required to observe SERRS spectra of the protein. The application of low temperature SERRS spectroscopy to the study of substrate binding in P450b provided evidence for spin state conversion in the presence of substrate.

Resonance Raman spectroscopy has allowed the direct observation of the Fe(IV)=0 (oxo-ferryl) vibration in activated intermediates of heme enzymes. This mode is markedly sensitive to changes in the heme pocket environment. A study of variations among heme enzyme intermediates is beginning to provide a description of structure and dynamics in the active site during catalysis.

Thyroid peroxidase (TPO) is a membrane-bound heme enzyme that catalyzes iodination and coupling of thyroglobulin tyrosine residues in the biosynthesis of thyroid hormones. The soluble heme enzyme lactoperoxidase (LPO) also iodinates tyrosine efficiently and serves as a functional model for TPO. Whereas horseradish peroxidase oxidizes sulfur-containing compounds, e.g., cysteine and glutathione, these compounds interact with LPO and TPO without oxidation. Indeed, clinical treatment of thyroid disease involves the use of sulfur-containing drugs (goitrogens) to inactivate TPO. Reactions of TPO and LPO with goitrogens result in enzyme inhibition, in a process similar to the conversion of myoglobin to sulf-myoglobin (sulf-Mb). We have examined the electronic absorption and resonance Raman (RR) spectral properties of LPO treated with the potent antithyroid drug methylmercaptoimidazole (MMi). Interaction of LPO with MMi yields a stable, emerald green complex (SLPO (MNi]). The electronic absorption spectra of SLPO [MMi] are similar to those of sulf-Mb (which has a sulfur-modified iron chlorin macrocycle), and to those of the naturally occurring Escherichia coli and Neurospora crassa chlorin catalases. The Soret excitation RR spectrum of the SLPO [DIM] complex is distinct from that of native LPO, but is consistent with the spectral pattern for metallochlorins established by our laboratory. The SLPO [NW RR pattern is also analogous to that of chlorin-containing proteins such as the isomeric sulf-Mb's, myeloperoxidase, and the E. coli and N. crassa catalases. These data strongly suggest that MMi treatment of LPO results in conversion of the porphyrin prosthetic moiety to an iron chlorin. We infer that clinical treatment of thyroid disorders with the goitrogen drug MMi similarly converts the porphyrin prosthetic moiety of thyroid peroxidase to an iron chlorin. Spectral differences between sulf-Mb and SLPO [MMI] are particularly intriguing and suggest structural differences between the two systems. Further investigation of the interaction(s) of sulfur compounds with heme systems is in progress.

The development of holographic gratings has been significantly enhanced with the evolution of Ion-etching techniques to "sculpt" groove shapes in an effort to improve efficiency. In this paper it is shown that it is possible to create both plane and concave gratings with efficiency profiles consistent with classically ruled gratings. Success was achieved with gratings up to 110 x 110 mm in groove densities ranging from 300 to 2400 grooves per millimeter.

An algorithm for determining the bandpass of spectrometric instruments is presented. This algorithm makes use of the results of tracing rays through a concave holographic grating in order to obtain an irradiance distribution which is convolved with the exit slit of a monochromator or a detector element of a spectrograph. The resulting convolution may be interpreted as a function of irradiance vs. wavelength, which we call the instrumental profile. A finite number of rays alone is not enough to establish bandpass of a particular instrument configuration. Smoothing from the convolution and possibly additional filtering of the irradiance data are necessary in order to get a continuous irradiance function from which a single bandpass quantity is determined. Examples of one particular instrument design are used to compare the results of a computer program using this algorithm to actual instrument bandpass measurements.

Spectrometry utilizing a dispersive element and a multi-element detector array poses several challenges to precise calibration. A classical method of wavelength axis calibration using two spectral lines is inadequate due to the non-linearity of these modern systems. The variation of detector response over the span of the detector array is problematic for the intensity axis calibration. A novel approach to calibrating an Optical Multichannel Analyzer is detailed, as well as test results comparing the assigned and calculated positions of the spectral Hines included in the calibration set. The equipment used is an EG&G PARC model III with Spectrograph. The wavelength axis is calculated by determining the centroid wavelength of the spectral lines used in the calibration routine; this method employs a sub-pixel assignment technique. The non-linearity of this axis is compensated by a numerical integration of the centroid data points. The intensity axis involves a standard technique utilizing a calibrated tungsten source. Included is a background discussion of why various lamps with measured brightness temperatures were determined to be inadequate for calibration. The intensity axis calibration is proportional to the photon count rather than energy (joules), the advantage for this method for our implementation is presented.

We describe a novel design for a low-resolution spectrograph that is capable of covering the entire 2.9-13.5 μm region, without scanning, at a resolving power of 20-100. The spectrograph uses two unique curved prisms to disperse radiation onto two 58-element arrays of infrared detectors. It has no moving parts. This spectrograph is an effective replacement for scanning circular variable filter (CVF) spectrometers or for Michelson Interferometers working at low resolution. Because all of the detectors in the spectrograph view an object through the same aperture, time-varying sources introduce no ambiguities into the spectra. The use of BIB detector arrays gives the instrument high sensitivity. We describe a ground-based version of the spectrograph that is currently under construction.

The efficiency of planar gratings, both sinusoidal and blazed, is fairly well documented in theory and experiment. The question of efficiency often arises in conjunction with work we are doing in the area of aberration-reduced concave gratings. Since there is not much reported in the literature in this regard, we decided to study it and report it to the community at large. This is a report on the first of a larger study in progress. We chose to investigate an f/2.1 concave aberration-reduced sinusoidal grating of approximately 800 grooves per millimeter. It is used extensively at Milton Roy Company in color analyzing instruments for the wavelength range 350 - 800 nm. It has the ability to resolve approximately 5 nm across the band and is used in the spectrograph configuration. One question we wished to resolve was whether a small region of a concave grating could be approximated by the performance of a plane grating.

The manufacture of varied line space (VLS) gratings was pioneered by Harada and co-workers of Japan, and Gerasimov and co-workers in the Soviet Union. Ruling engines were modified to allow the groove spacing to vary in a continuous manner, the grooves often remaining straight and parallel. This type of grating can also be obtained in the United States from Perkin Elmer Co. of Irvine, CA. Other VLS gratings involving fan shaped or concentric grooves have been developed by these groups and Hyperfine, Inc. of Boulder, CO. Monochromators using VLS for the UV and higher energy regions have been developed by Hettrick. We review the basic aspects of second order focusing of straight and parallel grooved varied line space gratings in both converging and collimated light in a more explicit and detailed manner that we have found in the literature. The effects of the VLS correction to the location of the focal curve for grazing incidence geometries are found to be very significant.

According to Kirchhoff and Planck's laws, it may be demonstrated that the measurement of the thermal radiation of a source, at n wavelengths, allows the determination of both its emissivity and its true temperature (T); the emissivity being described by an expansion in n-2 wavelengths. The accuracy of both thermal radiation and emissivity measurements, theoretically, grows with n for sources with purely thermal radiation.

A spectrograph with collimator compensated camera chromatism (4C) is presented. It has the following advantages compared to classical designs: The camera is small, inexpensive, and can be easily exchanged. It is based on standard materials. Large aspheres are not needed for the lenses. It appears that there are no problems to scale up the design for beam diameters well over 0.5 m. The instrument is efficient and there is no vignetting. The long slit allows a large degree of spatial multiplexing.

In order to respond to the food industry and agriculture needs of on-line control, a NIR spectrometer was developed and coupled with optical fibers. Silica and fluoride glasses were tested. Different geometrical configurations of the optodes were used and compared. The aim was to measure non-destructively the sugar of the fruit (apples and nectarines) and the humidity of the flour. Good results were obtained on the nectarines (sugar) and on the flour (humidity) but the determination of the sugar content of the apples was not satisfying. The depth of penetration of the light and the influence of fruit firmness on spectral characteristics are also discussed.

The limitations of aberration correction to spectrometer imaging by holographic and variable line-space gratings are addressed in light of recent theoretical analyses. Aberration reduction is discussed for particular mountings, specifically flat-field spectrographs, Rowland circle spectrographs and constant deviation monochromators. For these mounts, it is argued that aberration reduction via modification of the groove pattern alone cannot completely correct even the lowest-order aberrations over an arbitrary wavelength range.

This paper describes the development and usage of a new photodiode array spectrophotometer. The new system incorporates a novel optical technique for sampling an extended wavelength region by the use of multiple entrance slits to divide a spectrum, from 200 to 900 nm, into two segregated sampling components. The new system provides improved wavelength definition over conventional spectrographic array systems. Also described is the development methodology and optical optimization techniques used in design of the system.