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We describe the implementation of precision laser transmission spectroscopy for sizing and counting nanoparticles in suspension. Our apparatus incorporates a tunable laser and balanced optical system that measures light transmission over a wide (210-2300 nm) wavelength range with high precision and sensitivity. Spectral inversion is employed to determine both the particle size distribution and absolute particle density. In this paper we discuss results for particles with sizes (diameters) in the range from 5 to 3000 nm. For polystyrene particles 404 to 1025 nm in size, uncertainties of [+ or -]0.5% in size and [+ or -]4% in density were obtained. For polystyrene particles from 46 to 3000 nm in size, the dynamic range of the system spans densities from ~[10.sup.3]/ml to ~[10.sup.10]/ml (5 x [10.sup.-8] to 0.5 vol. %), implying a sensitivity 5 orders of magnitude higher than dynamic light scattering. [c] 2010 Optical Society of America OCIS codes: 120.7000, 300.6360, 290.5850, 290.2200, 290.4020.

A trace gas sensor for the detection of nitrogen dioxide based on cavity ringdown spectroscopy (CRDS) and a continuous wave external cavity tunable quantum cascade laser operating at room temperature has been designed, and its features and performance characteristics are reported. By measuring the ringdown times of the cavity at different concentrations of N[O.sub.2], we report a sensitivity of 1.2 ppb for the detection of N[O.sub.2] in Zero Air. OCIS codes: 000.2170, 010.1120, 010.0280, 120.6200, 300.6360.

We investigated the effects of operator-applied force on diffuse optical spectroscopy (DOS) by integrating a force transducer into the handheld probe. Over the typical range of contact forces measured in the breasts of eight patients, absorption and reduced scattering coefficients (650 to 1000nm) variance was 3.1 [+ or -] 1.0% and 1.0 [+ or -] 0.4%. For trained operators, we observed OCIS codes: 170.3880, 170.3890, 170.5280, 170.6510, 170.6935, 120.3890.

Logarithmic-conversion data processing used in wavelength modulation spectroscopy (WMS) with a current-modulated diode laser as its source is analyzed and compared with second-to-first ratio detection. Analytic Fourier coefficients of logarithmic-converted residual amplitude modulation (RAM) of a light source are given. An experimental setup for methane absorption detection at 1650 nm is described. It is shown theoretically and experimentally that logarithmic-converted WMS cannot only eliminate the fluctuation of received light power, but also improve the signal-to-noise ratio significantly. OCIS codes: 060.2370, 300.1030, 300.6260, 300.6300, 300.6320, 300.6380.

We investigate the dispersion mechanism of surface magnetoplasmons for periodic layered structures in the Voigt configuration. An analytical dispersion relation that retains a similar form with ordinary surface plasmons is obtained. The splitting of surface plasma frequency is accompanied with unequal field strengths of surface modes at the two interfaces and is characterized by a simple dynamic model that recasts the role of magnetic force on to the effective mass. The underlying mechanism is illustrated with the transverse currents induced by the cyclotron motion of electrons, which appears as the typical feature of the dynamic Hall effect. In particular, the acoustical and optical branches exhibit an anticrossing scheme for small filling fractions, due to the like symmetry of modes in the two branches. As the parallel wave number changes, the two interaction branches experience a transition of mode pattern from symmetry to antisymmetry, or vice versa. OCIS codes: 240.6680, 160.1190, 050.5745.

An update of spectroscopic line parameters for the 3.45-3.92 [micro]m ozone bands is reported. The line list includes the parameters of 15 bands of the main isotopic species and of the [v.sub.1] + [v.sub.2] + [v.sub.3] band of [sup.16][O.sup.16][O.sup.18]O and [sup.16][O.sup.18][O.sup.16]O. The results are based on previous high resolution laboratory studies. Comparisons of experimental spectra with an absorptance simulation of ozone based on the reported line list shows that the latter one is accurate enough for strong, medium, and weak transmittance in the 2550-2900 [cm.sup.-1] spectral range. The data are available on the Web in the Spectroscopy and Molecular Properties of Ozone (S&MPO, http://smpo.iao.ru and http://ozone.univ-reims.fr) and HITRAN (http://cfa-www.harvard.edu/hitran/) databanks. OCIS codes: 010.4950, 300.1030, 300.6300, 300.6320, 300.6340.

In cavity ring-down spectroscopy (CRDS), residual or stress-induced birefringence ([10.sup.-7]-[10.sup.-6] rad) of supermirrors will lift the polarization degeneracy of [TEM.sub.00] modes and generate two new polarization eigenstates in the cavity with small resonant frequency splitting (~0.1 kHz); the new eigenstates are nearly linearly polarized. When both modes are excited simultaneously, the intracavity polarization state will evolve as the energy decays in the cavity. Without polarization analysis, such mode beating would not be observable. However, real supermirrors have a linear polarization-dependent loss (dichroism) that leads to a change in the loss rate as the polarization state evolves and thus to deviation from the expected single-exponential decay. We develop a model for the evolution of the intracavity polarization state and intensity for a cavity with both birefringence and polarization-dependent loss in the mirrors. We demonstrate, experimentally, that these parameters (both magnitudes and directions) can be extracted from a series of measurements of the cavity decay and depolarization of the transmitted light. OCIS codes: 280.3420, 260.1440.

To our knowledge we present the first experiments with a fully reflective external-cavity quantum-cascade laser system at mid-infrared wavelengths for use as a local oscillator in a heterodyne receiver. The performance of the presented setup was investigated using absorption spectroscopy as well as heterodyne techniques. Tunability over [approximately equal to] 30 [cm.sup.-1] at 1130 [cm.sup.-1] was demonstrated using a grating spectrometer. A continuous tuning range of 0.28 [cm.sup.-1] was verified by observing the spectra of an internally coupled confocal Fabry-Perot interferometer and the absorption lines of gas phase S[O.sub.2]. In a second step the output from the system was used as a local oscillator signal for a heterodyne setup. We show that spectral stability and side mode suppression are excellent and that a compact external-cavity quantum-cascade laser system is well suited to be used as a local oscillator in infrared heterodyne spectrometers. OCIS codes: 140.3070, 140.3570, 300.6310, 280.0280.

Maintaining high resolving power is a primary challenge in hard x-ray spectroscopy of newly developed bright and transient x-ray sources such as laser-produced plasmas. To address this challenge, the line widths in x-ray spectra with energies in the 17 keV to 70 keV range were recorded by positioning the detectors on and behind the focal circles of Cauchois type transmission-crystal spectrometers. To analyze and understand the observed line widths, we developed a geometrical model that accounts for source broadening and various instrumental broadening mechanisms. The x-ray sources were laboratory Mo or W electron-bombarded anodes, and the spectra were recorded on photostimulable phosphor image plates. For these relatively small x-ray sources, it was found that when the detector was placed on or near the focal circle, the line widths were dominated by the effective spatial resolution of the detector. When the detector was positioned beyond the focal circle, the line widths were determined primarily by source-size broadening. Moreover, the separation between the spectral lines increased with distance behind the focal circle faster than the line widths, resulting in increased resolving power with distance. Contributions to line broadenings caused by the crystal thickness, crystal rocking curve width, geometrical aberrations, and natural widths of the x-ray transitions were in all cases smaller than detector and source broadening, but were significant for some spectrometer geometries. The various contributions to the line widths, calculated using simple analytical expressions, were in good agreement with the measured line widths for a variety of spectrometer and source conditions. These modeling and experimental results enable the design of hard x-ray spectrometers that are optimized for high resolving power and for the measurement of the x-ray source size from the line widths recorded behind the focal circle. OCIS codes: 300.6570, 300.3700.

A theoretical model of modulation transfer spectroscopy (MTS) that includes pump beam depletion is presented and experimentally verified with data covering visible iodine transitions at 532, 543, and 612 nm. This model is used to determine the values for pressure, interaction length, and saturation intensity that yield maximum MTS signals for frequency locking to iodine transitions. The approach is demonstrated for iodine transitions at 532, 633, and 778 nm, with the results showing that theoretically the frequency instability scales inversely to the absorption coefficient. OCIS codes: 140.0140, 140.3425, 120.0120, 120.3930, 120.3940, 300.6190.

The optical components described here are variable narrow-band transmission filters, where the transmittance peak varies with the position along the surface of the filter itself. They allow the construction of ultracompact and low-weight spectrometers for space applications. The theoretical behavior of graded filters has been already investigated by the authors, for imaging spectrometry of the Earth surface. The application of graded filters to miniaturized instruments for planetary missions (Mercury) is considered. Experimental results on the fabrication of small-dimension variable transmission filters operating over a wide spectrum, from visible to near infrared, are reported. OCIS codes: 310.1620, 230.4170, 310.1860.

Several designs of infrared sensors use a Fabry--Perot interferometer (FPI) to modulate the incident light. In this work we analyze the particular case where the FPI fringes are matched with very well defined rovibrational absorption lines of a target molecule such as C[O.sub.2], CO, [N.sub.2]O, or C[H.sub.4]. In this kind of sensor, modulation is induced by scanning the FPI cavity length over one half of the reference wavelength. Here we present an analytical method based on the Fourier transform, which simplifies the procedure to determine the sensor response. Furthermore, this method provides a simple solution to finding the optimal FPI cavity length and mirror reflectivity. It is shown that FPI mirrors with surprisingly low reflectivity (

As excimer lasers extend to deep-ultraviolet and vacuum-ultraviolet wavelengths at 193 and 157 nm, optical coatings experience the challenge of eliminating possible environmental contamination, reducing scattering loss, and increasing laser irradiation durability. Wide bandgap metal fluorides become the materials of choice for the laser optics applications. To understand the optical properties of nanostructure fluoride films, thin Gd[F.sub.3] films grown on Ca[F.sub.2] (111) substrates were evaluated by variable angle spectroscopic ellipsometry. An effective medium approximation model was used to determine both the film porosity and the surface roughness. Structural evolution of the Gd[F.sub.3] film was revealed with improved ellipsometric modeling, suggesting the existence of multilayer structure, a densified bottom layer, middle layers with increasing porosity, and a rough surface. The nanostructure of the film and the surface roughness were confirmed by atomic force microscopy. The attraction of the nanostructure to environmental contamination was experimentally demonstrated. OCIS codes: 160.4670, 310.0310.

A new fiber sensor system designed for spectroscopic analysis and on-line quality assurance of arcwelding processes is presented here. Although several different approaches have been considered for the optical capture of plasma emission in arc-welding processes, they tend to be invasive and make use of optical devices such as collimators or photodiodes. The solution proposed here is based on the arrangement of an optical fiber, which is used at the same time as the optical capturing device and also to deliver the optical information to a spectrometer, embedded within an arc-welding torch. It will be demonstrated that, by using the shielding gas as a protection for the fiber end, the plasma light emission is efficiently collected, forming a sensor system completely transparent and noninvasive for the welding operator. The feasibility of the proposed sensor designed to be used as the input optics of a welding quality-assurance system based on plasma spectroscopy will be demonstrated by means of several welding tests. OCIS codes: 060.2370, 300.2140, 120.4630, 350.3850.

Accurate recovery of tissue optical properties from in vivo spectral measurements is crucial for improving the clinical utility of optical spectroscopic techniques. The performance of inversion algorithms can be optimized for the specific fiber optic probe illumination-collection geometry. A diffusion-theory-based inversion method has been developed for the extraction of tissue optical properties from the shape of normalized tissue diffusion reflectance spectra, specifically tuned for a fiber probe that comprises seven hexagonally close-packed fibers. The central fiber of the probe goes to the spectrometer as the detecting fiber, and the surrounding six outer fibers are connected to the white-light source as illumination fibers. The accuracy of the diffusion-based inversion algorithm has been systematically assessed against Monte Carlo (MC) simulation as a function of probe geometry and tissue optical property combinations. By use of this algorithm, the spectral absorption and scattering coefficients of normal and cancerous tissue are efficiently retrieved. Although there are significant differences between the diffusion approximation and the MC simulation at short source-detector (SD) separations, we show that with our algorithm the tissue optical properties are well retrieved within the SD separation of 0.5-3 mm that is compatible with endoscopic specifications. The presented inversion method is computationally efficient for eventual real-time in vivo tissue diagnostics application.

We study the local-field enhancement in a nanocavity created by optical nanomanipulation. Recently we showed that a metallic probe can modify the optical force experienced by a metallic particle and generate a material selective trapping potential. We show that the same configuration used for optical forces can be used to control both in magnitude and tune the local-field enhancement around the particle at resonance. The spatial resolution and material selectivity of this technique, allied to its capability to manipulate particles at the nanometric level, may offer a new and versatile way to achieve surface-enhanced Raman scattering spectroscopy at the single-molecule level. OCIS codes: 260.2110, 300.0300, 290.0290.

A continuous-wave (cw) optical frequency synthesizer is demonstrated by using a monolithic-type cw optical parametric oscillator (cw-OPO) and an optical frequency comb. The cw-OPO is phase locked to an optical frequency comb that is phase locked to an atomic clock. The output frequency of the cw-OPO is frequency shifted with an electro-optic modulator, which makes it possible to tune the frequency continuously over 10 GHz. Furthermore, Doppler-free spectroscopy is performed using the optical frequency synthesizer for a cesium D1 line at 895 nm. The observed linewidth of 5 MHz is the natural linewidth of cesium. The center frequency of the line is consistent with a previous report. America OCIS codes: 120.6200, 120.3930.

Spatial heterodyne spectroscopy (SHS) is a Fourier-transform spectroscopic technique that simultaneously records all path differences using a detector array. Compared to conventional Fourier-transform spectroscopy that measures interferogram samples sequentially in the time domain, SHS is insensitive to a changing scene; however, the effects caused by differences in the detector elements and/or the optics for each sample must be addressed with a flatfield correction. The flatfield correction is typically a characteristic of the instrument and does not change with the observed scene. We present three different flatfielding approaches. Each is based on different assumptions and is applicable depending on the instrumental effects dominating the flatfield. OCIS codes: 300.6300, 120.2650, 040.5160.

In fluorescence correlation spectroscopy (FCS) analysis it is generally assumed that molecular species diffuse freely in volumes much larger than the three-dimensional FCS observation volume. However, this standard assumption is not valid in many measurement conditions, particularly in tubular structures with diameters in the micrometer range, such as those found in living cells (organelles, dendrites) and microfluidic devices (capillaries, reaction chambers). As a result the measured autocorrelation functions (ACFs) deviate from those predicted for free diffusion, and this can shift the measured diffusion coefficient by as much as ~50% when the tube diameter is comparable with the axial extension of the FCS observation volume. We show that the range of validity of the FCS measurements can be drastically improved if the tubular structures are located in the close vicinity of a mirror on which FCS is performed. In this case a new fluctuation time in the ACF, arising from the diffusion of fluorescent probes in optical fringes, permits measurement of the real diffusion coefficient within the tubular structure without assumptions about either the confined geometry or the FCS observation volume geometry. We show that such a measurement can be done when the tubular structure contains at least one pair of dark and bright fringes resulting from interference between the incoming and the reflected excitation beams on the mirror surface. Measurement of the diffusion coefficient of the enhanced green fluorescent protein (EGFP) and IscS-EGFP in the cytoplasm of living Escherichia coli illustrates the capabilities of the technique. OCIS codes: 300.2530, 300.6280, 120.2650, 120.3930, 170.6280, 170.1420.

An optimal system for temperature measurements by coherent anti-Stokes Raman spectroscopy (CARS) in turbulent flames and flows is presented. In addition to a single-mode pump laser and a modeless dye laser, an echelle spectrometer with a cross disperser is used. This system permits simultaneous measurement of the [N.sub.2] CARS spectrum and the broadband dye laser profile. A procedure is developed to use software to transform this profile into the excitation profile by which the spectrum is referenced. Simultaneous shot-to-shot referencing is compared to sequential averaged referencing for data obtained in flat flames and in room air. At flame temperatures, the resultant 1.5% imprecision is limited by flame fluctuations, indicating that the system may have a single-shot imprecision below 1%. At room temperature, the 3.8% single-shot imprecision is of the same order as the best values reported for dualbroadband pure-rotational CARS. Using the unique shot-to-shot excitation profiles, simultaneous referencing eliminates systematic errors. At 2000 and 300 K, the 95% confidence intervals are estimated to be [+ or -]20 and [+ or -]10 K, respectively. OCIS codes: 120.1740, 120.6780, 190.1900, 300.6230.

A cavity ringdown spectrometer, based on a continuous-wave swept-frequency laser, enables efficient, rapid recording of wide-ranging absorption spectra as characteristic spectral signatures of airborne molecules. The rapidly swept laser frequency resonates with the longitudinal modes of the ringdown cavity, effectively sampling the absorption spectrum of an intracavity gas at intervals defined by the cavity's free spectral range and generating a full absorption spectrum within a single rapid sweep of the widely tunable laser frequency. We report a new analog detection scheme that registers a single data point for each buildup and ringdown decay event without logging details of the full signal waveform; this minimizes demand on digitizer speed and memory depth, reducing the time scale of data processing. This results in a compact, robust, easy-to-use instrument that offers fresh prospects for spectroscopic sensing of trace species in the atmosphere. OCIS codes: 120.6200, 300.6190, 300.6360.

Cavity ring-down spectroscopy (CRDS) was applied in several fuel-rich, one-dimensional, premixed [C.sub.3][H.sub.6]/[O.sub.2]/Ar flames at 50 mbars (37.5 torr) to measure absolute OH, HCO, and [sup.1]C[H.sub.2] concentration as well as temperature as a function of stoichiometry. Although these flames near the sooting limit present a complex chemical environment, significant spectral interferences were found to be absent. Specific aspects of the CRDS technique for measurement of temperature and radical concentration profiles are discussed; and the results are analyzed in comparison with flame model simulations. OCIS codes: 120.1740, 300.1030, 120.6780.

A sensor based on tunable diode laser absorption spectroscopy was constructed for time-resolved temperature and water vapor concentration measurements in a scramjet combustor. The sensor probed two absorption lines near 1390 nm with two time-multiplexed lasers used to measure temperature and water vapor concentration at up to 20 kHz. A demonstration experiment was performed in the supersonic, expanding exhaust region of the combustor, showing the measurement to be repeatable, able to resolve temporal trends during tunnel operation, and sensitive to changes in combustor operating conditions. OCIS codes: 120.1740, 120.6780, 300.1030, 300.6260, 300.6340.

We report on use of cavity ring-down spectroscopy (CRDS) as a means to detect and quantify ion sputtering of refractory metal species. CRDS measurements are made with a neodymium:YAG-pumped optical parametric oscillator laser system in the 375-400 nm region. CRDS sputtering measurements are presented for argon ions incident on iron, aluminum, molybdenum, and titanium. The measurements are based on absorption from fine-structure levels of the electronic ground-state multiplets. For each species, characteristic spectra are provided, the dependence of sputtered particle number density on the beam current is examined, measured densities are compared with a sputter model, and detection limits are determined. For iron, aluminum, and titanium we probe multiple fine-structure levels within the groundstate multiplet and obtain information on their relative populations. OCIS codes: 300.1030, 120.4290, 120.6780.

A theoretical model for cw laser-induced thermal lens spectrometry of optically transparent surface-absorbing solids is developed. In the model, the sample is represented as a set of discrete layers with certain thicknesses and light absorptivities. The bloomed thermo-optical element in the sample is described with a summation of heat-flux functions for all the layers. The model employs simple mathematical expressions and can be used for both steady-state and time-resolved thermal lens experiments. Good coincidence of the experimental and theoretically predicted signal dependences is achieved. This model is verified for volume-absorbing samples (colored optical glasses) and used successfully to calculate absorbances and concentrations for various surface-absorbing samples. America OCIS codes: 300.6430, 300.6490.

Silicon oxynitride thin films are prepared by ion-beam sputtering, and the optical properties and surface chemical composition are studied by spectrophotometric and x-ray photoelectron spectroscopy, respectively. It is seen that the films sputtered by use of nitrogen alone as the sputtering species from a silicon nitride target are completely transparent (k < 0.005) and have a refractive-index dispersion from 1.85 to 1.71 over the visible and near-infrared spectral regions, and the films show distinct spectral lines that are due to silicon, Si(2s), nitrogen, N(1s), and oxygen, O(1s). Sputter deposition of argon and of argon and nitrogen produces silicon-rich silicon oxynitride films that are absorbent and have high refractive indices. These films have a direct electronic transition, with a threshold energy of 1.75 eV. Electron irradiation transforms optically transparent silicon oxynitride films into silicon-rich silicon oxynitride films that have higher refractive indices and are optically absorbing owing to the presence of nonsaturated silicon in the irradiated films. The degradation in current responsivity of silicon photodetectors, under electron irradiation, is within 3% over the wavelength region from 450 to 750 nm, which is entirely due to the degradation of optical properties of silicon oxynitride antireflection coatings. OCIS codes: 310.1210, 310.1260, 040.6040, 310.1860, 310.6860.

We describe a high-resolution real-time spectroscopy system targeted to ethane gas with sensitivity [greater than or equal to] 70 ppt and response time from [greater than or equal to] 0.7 s. The measurement technique is based on a mid-IR lead-salt laser passing through a Herriott cell through which a gas sample flows. We compare wavelength scanning and locked configurations and discuss their relative merits. The technology has been motivated by clinical breath testing applications, ethane being widely regarded as the most important breath biomarker for cell damage via free-radical-mediated oxidative attack. We discuss preliminary human and animal studies in which ultrasensitive real-time ethane detection offers new diagnostic and monitoring potential. OCIS codes: 170.6280, 300.6380, 300.6340.

We integrate ground spectrometry, imaging spectrometry, and in situ pavement condition surveys for assessment of asphalt road infrastructure. There is strong spectral evidence for asphalt aging and deterioration. Several spectral measures derived from field and image spectra correlate well with pavement quality indicators (e.g., a pavement condition index). However, the potential for mapping is limited by fine spatial resolution requirements (as fine as 0.5 m) and by the spectral confusion between pavement material aging and asphalt mix erosion on the one hand and structural road damages (e.g., cracking) on the other. OCIS codes: 300.6340, 110.3080, 300.6190.

Reflectance spectroscopy is a promising technology for detection of epithelial precancer. Fiber-optic probes that selectively collect scattered light from both the epithelium and the underlying stroma are likely to improve diagnostic performance of in vivo reflectance spectroscopy by revealing diagnostic features unique to each layer. We present Monte Carlo models with which to evaluate fiber-optic probe geometries with respect to sampling depth and depth resolution. We propose a probe design that utilizes half-ball lens coupled source and detector fibers to isolate epithelial scattering from stromal scattering and hence to resolve spectral information from the two layers. The probe is extremely compact and can provide easy access to different organ sites. OCIS codes: 060.2310, 170.3660, 170.3890, 170.4580, 170.6510.

The aerosol extinction measurements in the ultraviolet and visible wavelengths by the balloonborne spectrometer Spectroscopie d'Absorption Lunaire pour l'Observation des Minoritaires Ozone et [NO.sub.x] (SALOMON) show that aerosols are present in the middle stratosphere, above 25-km altitude. These observations are confirmed by the extinction measurements performed by a solar occultation radiometer. The balloonborne Laboratoire de Meteorologie Dynamique (LMD) counter instrument also confirms the presence of aerosol around 30-km altitude, with an unrealistic excess of micronic particles assuming that only liquid sulfate aerosols are present. An unexpected spectral structure around 640-nm observed by SALOMON is also detectable in extinction measurements by the satellite instrument Stratospheric Aerosols and Gas Experiment III. This set of measurements could indicate that solid aerosols were detected at these altitude ranges. The amount of soot detected up to now in the lower stratosphere is too low to explain these measurements. Thus, the presence of interplanetary dust grains and micrometeorites may need to be invoked. Moreover, it seems that these grains fill the stratosphere in stratified layers. OCIS codes: 010.1110, 280.1100.

UV--visible absorption spectroscopy with extraterrestrial light sources is a widely used technique for the measurement of stratospheric and tropospheric trace gases. We focus on differential optical absorption spectroscopy (DOAS) and present an operator notation as a new formalism to describe the different processes in the atmosphere and the simplifying assumptions that compose the advantage of DOAS. This formalism provides tools to classify and reduce possible error sources of DOAS applications. OCIS codes: 300.1030, 070.6020, 010.1290, 280.1120.

A new detection technique for photothermal deflection spectroscopy and photoacoustic deflection spectroscopy is presented. The technique uses a pair of matched multiple slits placed in the path of the probe beam and oriented to block the probe light from the detector in the absence of a deflection signal. Significant improvement in the signal-to-noise ratio and in the frequency bandwidth compared with those available with current techniques is demonstrated. OCIS codes: 300.6430, 120.0120.

A spectrally and temporally programmable light engine can create any spectral profile for hyperspectral, fluorescence, or principal-component imaging or with medical photonics devices employing spectroscopy, microscopy, and endoscopy. Multispectral imaging feasibility was demonstrated by capturing nine images at wavelengths from 450 to 650 mm (25-nm FWHM) with a CCD-camera-equipped bronchoscope coupled to the light engine. Selected wavelength regions were combined to produce a color endoscopy image.

It is currently impossible to consistently predict kidney graft viability and function before and after transplantation. We explored optical spectroscopy to assess the degree of ischemic damage in kidney tissue. Tunable UV laser excitation was used to record autofluorescence images, at different spectral ranges, of injured and contralateral control rat kidneys to reveal the excitation conditions that offered optimal contrast. Autofluorescence and near-infrared cross-polarized light-scattering imaging were both used to monitor changes in intensity and spectral characteristics, as a function of exposure time to ischemic injury. These two modalities provided different temporal behaviors, arguably arising from two different mechanisms providing direct correlation of intrinsic optical signatures to ischemic injury time.

Array detector-based instruments are now fundamental to measurements of ozone and other atmospheric trace gases from space in the ultraviolet, visible, and infrared. The present generation of such instruments suffers, to a greater or lesser degree, from undersampling of the spectra, leading to difficulties in the analysis of atmospheric radiances. We provide extended analysis of the undersampling suffered by modern satellite spectrometers, which include the Global Ozone Monitoring Experiment, Scanning Imaging Absorption Spectrometer for Atmospheric Chartography, Ozone Monitoring Instrument, and Ozone Mapping and Profiler Suite. The analysis includes basic undersampling, the effects of binning into separate detector pixels, and the application of high-resolution Fraunhofer spectral data to correct for undersampling in many useful cases. OCIS codes: 010.1280. 120.4570.280.1120.

Trace explosive residues are measured in real time by surface laser photofragmentation-fragment detection (SPF-FD) spectroscopy at ambient conditions. A 248 nm laser photofragments the target residue on a substrate, and a 226 nm laser ionizes the resulting NO fragment by resonance-enhanced multiphoton ionization by means of its A-X (0, 0) transitions near 226 nm. We tested two probes on selected explosives and modeled their electric field in the presence of a substrate with an ion optics simulation program. The limits of detection range from 1 to 15 ng/[cm.sup.2] (signal-to-noise ratio of 3) at 1 atm and 298 K and depend on the electrode orientation and mechanism for NO formation. OCIS codes: 300.0300, 140.3450, 300.6410, 300.6360, 280.3420.

Although the phenomenon of coherent backscattering (CBS) in nonbiological media has generated substantial research interest, observing CBS in biological tissue has been extremely difficult. Here we show that the combination of low-spatial-coherence, broadband illumination, and low-temporal-coherence, spectrally resolved detection significantly facilitates CBS observation in biological tissue and other random media with long-transport mean-free path lengths, which have been previously beyond the reach of conventional CBS investigations. Furthermore, we demonstrate that depth-selective, speckle-free, low-coherent backscattering spectroscopy has the potential to diagnose the earliest, previously undetectable, precancerous alterations in the colon by means of probing short light paths. OCIS codes: 030.1670, 290.1350, 300.6170, 170.4580.

A new lightweight near-infrared tunable diode laser spectrometer CHILD (Compact High-altitude Insitu Laser Diode spectrometer) was developed for flights to the stratosphere as an additional in situ sensor on existing balloonborne payloads. Free-air absorption measurements in the near infrared are made with an open-path Herriott cell with new design features. It offers two individual absorption path lengths optimized for C[H.sub.4] with 74 m (136 pass) and [H.sub.2]0 with 36 m (66 pass). New electronic features include a real-time gain control loop that provides an autocalibration function. In flight-ready configuration the instrument mass is approximately 20 kg, including batteries. It successfully measured stratospheric C[H.sub.4] and [H.sub.2]0 profiles on high-altitude balloons on four balloon campaigns (Environmental Satellite validation) between October 2001 and June 2003. On these first flights, in situ spectra were recorded from ground level to 32,000-m altitude with a sensitivity of 0.1 ppm [(parts per million), ground] to 0.4 ppm (32,000 m) for methane and 0.15-0.5 ppm for water. OCIS codes: 120.6200, 300.6260, 010.1280.

The detailed analysis of measured interferograms generally requires phase correction. Phase-shift correction methods are commonly used and well documented for conventional Fourier-transform spectroscopy. However, measured interferograms can show additional phase errors, depending on the optical path difference and signal frequency, which we call phase distortion. In spatial heterodyne spectroscopy they can be caused, for instance, by optical defects or image distortions, making them a characteristic of the individual spectrometer. They can generally be corrected without significant loss of the signal-to-noise ratio. We present a technique to measure phase distortion by using a measured example interferogram. We also describe a technique to correct for phase distortion and test its performance by using a simulation with a near-UV solar spectrum. We find that for our measured example interferogram the phase distortion is small and nearly frequency independent. Furthermore, we show that the presented phase-correction technique is especially effective for apodized interferograms. OCIS codes: 300.6300, 120.6200, 120.2650.

The spherical beam volume hologram, recorded by a plane wave and a spherical beam, is investigated for spectroscopic applications in detail. It is shown that both the diffracted and the transmitted beam can be used for spectroscopy when the hologram is read with a collimated beam. A new method is introduced and used for analysis of the spherical beam volume hologram that can be extended for analysis of arbitrary holograms. Experimental results are consistent with the theoretical study. It is shown that the spherical beam volume hologram can be used in a compact spectroscopic configuration when the transmitted beam is monitored. Also, on the basis of the properties of the spherical beam hologram, the response of a hologram recorded by a plane wave and an arbitrary pattern is predicted. The information can be used to optimize holographic spectrometer design. OCIS codes: 090.7330, 300.6190, 070.2590.

A new algorithm for the retrieval of columnar water vapor content is presented. The proposed procedure computes the area of the [H.sub.2]O absorption centered about 940 nm to allow its integrated columnar abundance as well as its density at ground level to be assessed. The procedure utilizes the HITRAN 2000 database as the source of [H.sub.2]O cross-section spectra. Experimental results were derived from radiometrically calibrated hyperspectral images collected by the Airborne Visible-Infrared Imaging Spectrometer (AVIRIS) sensor over the Cuprite mining district in Nevada. Numerical simulations based on the MODTRAN 4 radiative transfer code were also employed for investigating the algorithm's performance. An additional empirical [H.sub.2]O retrieval procedure was tested by use of data gathered by the VIRS-200 imaging spectrometer. OCIS codes: 010.1280, 010.1320, 280.0280, 300.1030, 300.3700.

Fluorescence correlation spectroscopy is a valuable tool in many scientific disciplines. In particular, such a spectroscopic technique has received a great deal of attention because of its remarkable potential for single-molecule detection. It is understood, however, that quantitative measurements can be considered reliable as long as molecular photophysics has been well characterized. To that end, molecular saturation and probe volume effects, which can worsen experimental accuracy, are treated here. These phenomena are adequately incorporated into the well-known three-dimensional Gaussian approximation by a novel method applied to interpret saturated fluorescence signals [Opt. Lett. 28, 2016 (2003)]. Comparisons with literature data are given to show the improvements of the suggested method compared with other approaches. OCIS codes: 300.6280, 300.6410, 180.1790, 180.2520.

We discuss the spectroscopic requirements for a laser absorption spectrometer (LAS) approach to highprecision carbon dioxide (C[O.sub.2]) measurements in the troposphere. Global-scale, high-precision C[O.sub.2] measurements are highly desirable in an effort to improve understanding and quantification of the C[O.sub.2] sources and sinks and their impact on global climate. We present differential absorption sounding characteristics for selected LAS transmitter laser wavelengths, emphasizing the effects of atmospheric temperature profile uncertainties. Candidate wavelengths for lower-troposphere measurements are identified in the C[O.sub.2] bands centered near 1.57, 1.60, and 2.06 [micro]m. OCIS codes: 010.0010, 010.1280, 280.0280, 280.3420, 300.6340.

Near-infrared (NIR) spectroscopic imaging technology provides a new modality for measuring changes in total hemoglobin concentration (HbT) and blood oxygen saturation (SO2) in human tissue. The technology can be used to detect breast cancer because cancers may cause greater vascularization and greater oxygen consumption than in normal tissue. Based on the NIR technology, ViOptix, Inc., has developed an optical device that provides two-dimensional mapping of HbT and SO2 in human tissue. As an adjunctive tool to mammography, the device was preliminarily tested in a clinical trial with 50 mammogram-positive patients at the Massachusetts General Hospital. The results of the clinical trial demonstrate that the device can reach as much as 92% diagnostic sensitivity and 67% specificity in detecting ductal carcinoma. These results may indicate that the NIR technology can potentially be used as an adjunct to mammography for breast cancer detection to reduce the number of biopsies performed. [c] 2003 Optical Society of America OCIS codes: 170.3880, 170.3890, 170.7050.

Laser-induced breakdown spectroscopy (LIBS) was applied for simultaneous measurement of the elements C, H, N, and O in CO(.sub.2)-air, C(.sub.3) H(.sub.8)-CO(.sub.2), and C(.sub.3)H(.sub.8)-N(.sub.2) gas mixtures at atmospheric pressure. A single 7-mm-diameter aperture at the sample chamber was used for 1064-nm Nd:YAG laser irradiation and plasma signal output to an echelle spectrometer. Double-pulse laser bursts of ~8-ns pulse width (FWHM) and 250-ns interpulse separation were applied to increase the plasma signal. Calibration curves of the LIBS signal versus the partial pressure or the atomic abundance ratios were taken by dilution series in intervals that are relevant in the combustion of heptane (C(.sub.7)H(.sub.16)) near an equivalence ratio of 1. OCIS codes: 120.0120, 120.6200, 120.1740, 140.3440, 300.6210.

Laser-induced breakdown spectrometry (LIBS) with multiple pulse excitation has been applied for the multielemental analysis of liquid steel. The laser beam and the measuring radiation are guided inside a moveable lance to gain access to the melt surface from the top. Low-alloy steel grades were investigated with a focus on the light elements phosphorus, sulfur, and carbon by use of emission wavelengths in the vacuum ultraviolet. Calibration curves were determined for the elements carbon, phosphorus, sulfur, nickel, and chromium in steel melts of 100 kg. The estimated limits of detection for the light elements phosphorus, sulfur, and carbon are below 21 [micro]g/g for direct analysis of liquid steel with LIBS. The results demonstrate the potential of the laser-based analysis to fulfill the requirements for a process integrated on-line analysis in the secondary metallurgy of steel works. OCIS codes: 120.0120, 300.0300.

Laser-induced breakdown spectroscopy (LIBS) has been used to study bacterial spores, molds, pollens, and proteins. Biosamples were prepared and deposited onto porous silver substrates. LIBS data from the individual laser shots were analyzed by principal-components analysis and were found to contain adequate information to afford discrimination among the different biomaterials. Additional discrimination within the three bacilli studied appears feasible. OCIS codes: 140.3440, 300.6360, 300.6210.

The technique of laser-induced breakdown spectroscopy has been used for the first time to our knowledge for the identification of metals such as palladium and silver that were dispersed in bacterial cellulose membranes. These results for palladium-dispersed films have been correlated to a calibration curve obtained by use of atomic absorption spectroscopy and were found to be in good agreement. The experiments were conducted by use of wet and dry metal-doped membranes. The metal peaks obtained with a dry membrane are greater than five times higher in signal-to-background ratio than when metals are detected by a hydrated membrane. The advantage of this laser-based technique is that minimal sample handling and sample preparation are needed and measurements are completed in real time (a few seconds). Hence this technique can be used for the detection of metals in dry membranes that would be used in the construction of electrode assemblies. OCIS codes: 300.0300, 300.6360, 300.6500.

The use of laser-induced breakdown spectrometry (LIBS) for the analysis of heavy metals and brominated flame retardants in end-of-life waste electric and electronic equipment (EOL-WEEE) pieces is investigated. Single- and double-pulse plasma excitation as well as the influence of detection parameters is studied to yield a parameter field with improved sensitivity and limits of detection. A LIBS analyzer was set up as an on-line measuring unit to detect heavy metals and brominated flame retardants in moving EOL-WEEE pieces in an automatic sorting line. An autofocusing unit with an adjustment range of 50 mm was incorporated to permit measurements of objects that pass by a LIBS analyzer with their surfaces at various distances from it. Tests with EOL-WEEE monitor housings on the conveyor belt of a pilot sorting system successfully demonstrated the capability of the LIBS analyzer to quantify the concentration of hazardous elements in real waste EOL-WEEE pieces. OCIS codes: 300.6360, 140.3440, 160.5470, 120.0280, 300.6500, 120.1200.

Analyses of iron ore slurries in industrial and laboratory environments showed that many physical and geometric parameters affect the stability and reproducibility of the response to laser-induced breakdown spectroscopy. A thorough reexamination of the sampling strategy led to a revised sampling layout that ensures a true representative sampling of the slurry and significantly improves the sensitivity and repeatability of the sampling method. An examination of the characteristics of slurries revealed that the mean particulate size and the concentration of solids in a slurry influence the measurement of silica, whereas the magnetite content is responsible for a matrix effect. On-line monitoring of iron ore slurries should be practicable, provided that these variables are controlled within a few percent or that some means of correction is implemented. OCIS codes: 000.2170, 120.1880, 300.2140.