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We present a method for the measurement of small optical absorption coefficients. The method exploits the deformation of cavity Airy peaks that occur if the cavity contains an absorbing material with a nonzero thermorefractive coefficient dn/dT or a nonzero expansion coefficient [a.sub.th]. Light absorption leads to a local temperature change and to an intensity-dependent phase shift, i.e., to a photothermal self-phase modulation. The absorption coefficient is derived from a comparison of time-resolved measurements with a numerical time-domain simulation applying a Markov-chain Monte Carlo algorithm. We apply our method to the absorption coefficient of lithium niobate doped with 7 mol. % magnesium oxide and derive a value of [[alpha].sub.LN] = (5.9 [+ or -] 0.9) x [10.sup.-4]/cm. Our method should also apply to materials with much lower absorption coefficients. Based on our modeling, we estimate that, with cavity finesse values of the order of [10.sup.4], absorption coefficients of as low as [10.sup.-8]/cm can be measured. OCIS codes: 120.0120, 120.5060, 120.6810.

We apply photon-trap spectroscopy, a generalized scheme of cavity ringdown spectroscopy, to infrared spectroscopy of molecular adsorbates on a solid substrate. The storage lifetime of light in a high-finesse Fabry--Perot cavity provides a high absorbance sensitivity for the substrate sample, which is placed exactly normal to the light beam in the cavity to minimize optical losses. Infrared spectra of the C--H stretching vibration of alkylsiloxane monolayer films on a silicon substrate are measured in three ways, namely by employing pulsed and continuous-wave lasers as well as by conventional Fourier transform infrared spectroscopy. The magnitude of optical absorption is shown to vary by the character of the interacting light used in the measurement, i.e., a standing wave versus a propagating wave. OCIS codes: 120.6200, 300.1030, 300.6250.

The goal of the current study was to introduce a mathematical method to derive hemoglobin, oxyhemoglobin and carboxyl-hemoglobin absorption factors from full spectrum reflectometry measurements of retinal microcapillaries. The mathematical equation that describes the spectral reflectometry function was expressed as a linear combination of several terms of [S.sub.i] ([lambda]) representing the spectral signature functions of hemoglobin, oxyhemoglobin, carboxyl-hemoglobin, ocular media, melanin, and a scattering factor. Contrary to the classical model, where the reflectometry function was expressed as an absorbance Ab([lambda]) = log(incident light([lambda])/reflected light([lambda])), in this model and system, it is proposed to express the reflectometry function from the eye structures as an absorption factor A([lambda])% = incident light([lambda])/ reflected light([lambda]). To increase confidence in the estimation of hemoglobin derivatives, the mathematical model was applied to only a part of the spectral function of reflectometry, while the results of the model were used to explain the other part of the reflectometry function. The results demonstrate that for the visible spectral field, the model that explains the absorption of the light by the blood contained in the microcapillaries of biological structures is not compatible with the Beer-Lambert law. OCIS codes: 170.1460, 170.3890.

We thoroughly and critically review studies reporting the real (refractive index) and imaginary (absorption index) parts of the complex refractive index of silica glass over the spectral range from 30 nm to 1000 [micro]m. The general features of the optical constants over the electromagnetic spectrum are relatively consistent throughout the literature. In particular, silica glass is effectively opaque for wavelengths shorter than 200 nm and larger than 3.5-4.0 [micro]m. Strong absorption bands are observed (i) below 160 nm due to the interaction with electrons, absorption by impurities, and the presence of OH groups and point defects; (ii) at -2.73-2.85, 3.5, and 4.3 [micro]m also caused by OH groups; and (iii) at ~9-9.5, 12.5, and 21-23 [micro]m due to Si--O--Si resonance modes of vibration. However, the actual values of the refractive and absorption indices can vary significantly due to the glass manufacturing process, crystallinity, wavelength, and temperature and to the presence of impurities, point defects, inclusions, and bubbles, as well as to the experimental uncertainties and approximations in the retrieval methods. Moreover, new formulas providing comprehensive approximations of the optical properties of silica glass are proposed between 7 and 50 [micro]m. These formulas are consistent with experimental data and substantially extend the spectral range of 0.21-7 [micro]m covered by existing formulas and can be used in various engineering applications. OCIS codes: 160.6030, 160.4760, 290.3030, 160.4670, 050.5298, 110.5220.

To the best of our knowledge, a combined sensitive technique employing both laser calorimetry and a surface thermal lens scheme for measuring absorption values of optical coatings is presented for the first time. Laser calorimetric and pulsed surface thermal lens signals are simultaneously obtained with a highly reflecting UV coating sample irradiated at 193 nm. The advantages and potential applications of the combined technique and the experimental factors limiting the measurement sensitivity are discussed. OCIS codes: 120.6810, 300.1030, 310.6860, 350.6830.

An improved method used to determine the absorption and scattering characteristics of a weakly absorbing substance containing bubbles is suggested. The identification procedure is based on a combination of directional-hemispherical measurements and predictions of Mie-scattering theory including approximate relations for a medium with polydisperse bubbles. A modified two-flux approximation is suggested for the calculation of directional-hemispherical transmittance and reflectance of a refracting and scattering medium. The complete identification procedure gives not only the spectral radiative properties but also the volume fraction of bubbles and the characteristics of possible impurity of the medium. This procedure is used to obtain new data on near-infrared properties of fused-quartz samples containing bubbles. OCIS codes: 030.0030, 290.4020, 030.5620.

Like pure water, the water incorporated into cartilage and cornea tissue shows a pronounced dependence of the absorption coefficient on temperature. Alteration of the temperature by radiation with an IR free-electron laser was studied by use of a pulsed photothermal radiometric technique. A computation algorithm was modified to take into account the real IR absorption spectra of the tissue and the spectral sensitivity of the IR detector used. The absorption coefficients for several wavelengths within the 2.9-and 6.1-[micro]m water absorption bands have been determined for various laser pulse energies. It is shown that the absorption coefficient for cartilage decreases at temperatures higher than 50[degrees]C owing to thermal alterations of water-water and water-biopolymer interactions. OCIS codes: 170.6930, 120.5630, 120.6810, 140.2600.

We propose and test an inverse ocean optics procedure with numerically simulated data for the determination of inherent optical properties using in-water radiance measurements. If data are available at only one depth within a deep homogeneous water layer, then the single-scattering albedo and the single parameter that characterizes the Henyey--Greenstein phase function can be estimated. If data are available at two depths, then these two parameters can be determined along with the optical thickness so that the absorption and scattering coefficients, and also the backscattering coefficient, can be estimated. With a knowledge of these parameters, the albedo and Lambertian fraction of reflected radiance of the bottom can be determined if measurements are made close to the bottom. A simplified method for determining the optical properties of the water also is developed for only three irradiance-type measurements if the radiance is approximately in the asymptotic regime. OCIS codes: 010.4450, 030.5620, 100.3190, 160.4760, 290.1350, 290.3200.

Si:H alloys are being investigated for the high-index material in an interference filter to provide spectral control in an application of thermophotovoltaic energy conversion. In particular, a multilayer edge filter is being developed to provide high transmission of photons with wavelengths between 1.0 and 2.4 [micro]m and high reflectance for wavelengths outside this range. Thin films of Si:H were deposited by means of rf reactive sputtering. Deposition parameters were varied to optimize the H content in Si:H coatings such that the refractive index was greater than 3. Optical absorption near 1 [micro]m and Si:H infrared absorptions near 5 and 12 [micro]m were minimized. OCIS codes: 310.1860, 310.6860, 350.2460.

A series of three mathematical procedures is derived to discriminate the light absorption by phytoplankton, colored dissolved organic matter, and nonpigmented particulates in waters in which absorption is dominated by factors other than phytoplankton (i.e., case 2 waters). The procedures utilize normalized absorption cross-sectional spectra of the absorption components and matrix inversion to solve for the coefficients that scale the normalized spectra. The procedures differ in the amount of ancillary measurements incorporated to reduce the variability of the estimates. The procedure that incorporates no ancillary information is expected to be unbiased only over long time periods. Application of the procedures to a 15-day time series of continuously monitored data from the Rhode River, Maryland, revealed the presence of large (approximately twofold) changes in absorption at 440 nm over periods of a few hours. Hourly sampling over a 24-h period confirmed that the changes in measured optical coefficients corresponded to changes in water quality. Errors in estimates of absorption components were of a magnitude consistent with those observed in development of the procedures and confirmed the progressive improvement achieved by incorporation of additional information. Over the time period observed, changes in optical properties appeared to be driven by advective processes. OCIS code: 010.4450.

A new technique for determining absorbances of interferenceless (incoherent) layers based on measurements of the ratio of the front and the back reflectivities of a double-layer sample at the Brewster angles is proposed. A double-layer stack must have at least one absorbing layer, and the two layers should be interferenceless and should be thicker than the wavelength of the incident light. We found that under these conditions the ratio of the front and the back reflectivities at the Brewster angle of a sample surface is directly related to layer absorbance. For a layer with a known thickness this means finding the extinction coefficient of the layer material. In comparison with the conventional method for measuring transmittance, the advantage of this approach is that it affords an opportunity to get rid of the influence of surface effects on the measuring volume absorption coefficient. For a thick layer with known thickness, it makes possible the determination of a small bulk absorption on a background with even greater surface effects. We trust that this technique will prove to be powerful for measuring the extinction coefficients of weakly absorbing materials. OCIS codes: 120.4530, 120.5700, 160.4760, 300.1030, 310.6860.

An optical-loss measurement system based on a resonant Fabry-Perot cavity at 1.6 micro m in vacuum has been developed for independent monitoring of the cavity total loss and the optical absorption loss. Maintenance of cavity resonance over a one-month period allows the assessment of long-term degradation of the cavity optics in the presence of outgassing materials, with sensitivities of 5 ppm/yr for total cavity loss and 2 ppm/yr for cavity absorption loss. Test results for light-emitting diodes, Kapton-insulated cable assemblies, and Vac-seal epoxy adhesive are given. Scaling of these results to the optical performance requirements of LIGO is discussed.

The Fresnel diffraction integral is used directly to describe the thermal lens (TL) effect with a mode-mismatched collinear configuration. The TL amplitudes obtained with Gaussian, Airy, and top-hat beam excitations are computed and compared. Numerical results for beam geometries optimized for both near- and far-field detection schemes are presented, and the analytical results developed by Bialkowski and Chartier [Appl. Opt. 36, 6711 (1997)] for a Gaussian beam TL effect are summarized in simplified form. Both the numerical and the analytical results demonstrate that, under a beam geometry optimized for either near- or far-field detection, the Gaussian beam TL experiment has approximately the same maximum signal amplitude as does the photothermal-interference scheme. A comparison between the optimum near- and far-field detection beam geometries indicates that a practical mode-mismatched TL instrument should be based on the far-field detection geometry. The computation results further demonstrate that the optimum beam geometry and the TL amplitude depend largely on the excitation-beam profile. The top-hat beam TL experiment is approximately twice as sensitive as the Gaussian beam TL scheme.

A technique is proposed for the extraction of precise values of field-dependent absorption coefficient [Alpha] and refractive index n from photocurrent and transmittance measurements of optical modulator structures. The technique uses approximate results of [Alpha] and n extracted from a simplified device as the initial input into an iterative procedure that utilizes the consistency between [Alpha] and n to obtain successively better estimates of these parameters. The technique was applied to results that were measured experimentally, and we verified the accuracy by using synthetic data. Errors caused by measurement inaccuracy are also investigated. It is shown that the absorption coefficient has a modest sensitivity whereas the refractive index is insensitive to these errors.

There has been a large effort to relate the apparent optical properties of ocean water to the inherent optical properties, which are the absorption coefficient a, the scattering coefficient b, and the scattering phase function [Rho]([Theta]). The diffuse attenuation coefficient [k.sub.diff] has most often been considered an apparent optical property. However, [k.sub.diff] can be considered a quasi-inherent property [k.sub.diff][prime] when defined as a steady-state light distribution attenuation coefficient. The Honey-Wilson research empirically relates [k.sub.diff] to a and b. The Honey-Wilson relation most likely applies to a limited range of water types because it does not include dependence on [Rho]([Theta]). A series of Monte Carlo simulations were initiated to calculate [k.sub.diff][prime] in an unstratified water column. The calculations, which reflected open ocean water types, used ranges of the single-scattering albedo [[Omega].sub.0] and the mean forward-scattering angle [[Theta].sub.m] for two analytic phase functions with different shapes. It was found that [k.sub.diff][prime] is nearly independent of the shape of [Rho]([Theta]) and can be easily parameterized in terms of a, b, and [[Theta].sub.m] for 0.11 [less than or equal to] [[Theta].sub.m] [less than or equal to] 0.48 rad and 0.5 [less than or equal to] [[Omega].sub.0] [less than or equal to] 0.95. [k.sub.diff][prime] is an asymptotic quantity; that is, a steady-state distribution is reached only after many scattering lengths.

An algorithm is described and evaluated for determining the absorption and backscattering coefficients a(z) and [b.sub.b](z) from measurements of the nadir-viewing radiance [L.sub.u](z) and downward irradiance [E.sub.d](z). The method, derived from radiative transfer theory, is similar to a previously proposed one for [E.sub.u](z) and [E.sub.d](z), and both methods are demonstrated with numerical simulations and field data. Numerical simulations and a sensitivity analysis show that good estimates of a(z) and [b.sub.b](z) can be obtained if the assumed scattering phase function is approximately correct. In an experiment in Long Island Sound, estimates of a(z) derived with these methods agreed well with those obtained from an in situ reflecting tube instrument.

A detailed investigation of the use of time-resolved transmittance for the optical characterization of scattering media by use of different analytical solutions to the diffusion equation has been performed. A femtosecond Ti:sapphire laser working at 800 nm and a streak camera with a time resolution of a few picoseconds were employed. Different latex and Intralipid solutions as well as biological samples were investigated. Reduced scattering coefficients were evaluated, and good agreement with the Mie predictions was found. An estimation of the order of magnitude of the absorption coefficient was obtained for the low-absorbance samples examined. These studies confirm experimentally that time-resolved transmittance can be employed usefully for evaluating [[Mu].sub.s][prime] values of thick scattering samples when a proper theoretical description that takes into account realistic boundary conditions is used.

Photothermal deflection is used for mapping the absorption of bare and coated surfaces. The same area is mapped before and after coating and also after annealing. The great importance of the substrate with respect to the total losses of the coated component is emphasized. First the influence of surface contamination of the bare substrate on the total absorption of the coated substrate is studied for BK7 and fused-silica substrates. Then the mean value of the coated-substrate absorptance is shown to be strongly dependent on the type of substrate. Experimental results show that this effect is associated with a localization of the absorption at the near surface of the substrate and at the interfaces of the film. Key words: Optical coatings, absorption mapping, surface contamination, interface absorption, substrate absorption.

The universal bio-optical algorithm of the Coastal Zone Color Scanner (CZCS) for case I waters implicitly contains an average covariance of the absorption by phytoplankton and colored dissolved organic matter (CDOM) and detritus. We made that covariance explicit by combining the CZCS algorithm with an expression for reflectance. The spectral variation of absorption by CDOM plus detritus for case I waters may be estimated by the expression [a.sub.gd([Lambda])] = 2[a.sub.ph(443)]*chl{exp[-0.013([Lambda] - 443)]}. Key words: Hydrologic optics, absorption covariance, phytoplankton, colored dissolved organic matter, detritus.

A method for measuring the absorption of light with optically turbid media is considered. The method is based on the registration of the temporal shape (leading-edge slope) of the developing optoacoustic signal in a medium that is absorbing a short laser pulse. Results of experiments with a Nd:YAG laser (10 ns) demonstrate the effectiveness of the method for both homogeneous and inhomogeneous optical media.

A method is presented for determining the optical absorption coefficient, or the imaginary refractive index, of particulate material that has been collected from aerosols or hydrosols by means of filtration. The method, based on the Kubelka-Munk theory of diffuse reflectance, is nondestructive and requires no other knowledge of the sample than the amount present, the specific gravity, and an estimate of the real index of refraction. The theoretical development of the method is discussed along with an analysis of photometric and gravimetric errors. We test the method by comparing results obtained for powdered didymium glass with measurements made before the glass was crushed. An example of the method's application to the determination of the absorption coefficient of atmospheric dust at UV, visible, and near-IR wavelengths is also presented.

A distributed-feedback InGaAsP diode laser, emitting near 1.38 micrometers, was used to acquire spectrally resolved absorption profiles of H2O lines in the Upsilon(sub 1) + Upsilon(sub 3) band at a repetition rate of 10 kHz. The profiles were used for simultaneous measurements of flow parameters in high-speed, one-dimensional (1-D) transient flows generated in a shock tube. Velocity was determined from the Doppler shift, which was measured with a pair of profiles simultaneously acquired at different angles with respect to the flow direction. Temperature was determined from the intensity ratio of two adjacent lines. Pressure and density were found from the fractional absorption. From these primary gasdynamic variables, the mass and momentum fluxes were determined. Experiments were conducted with three different gas mixtures in the shock tube: pure H2O at initial pressures lower than 3 Torr, up to 6% of H2O in O2 at initial pressures below 120 Torr, and up to 8% of H2 in O2 at initial pressures below 35 Torr. In the third case, pyrolysis of H2/O2 behind incident shocks produced known yields of H2O. With all three mixtures, results compare well with 1-D shock calculations. This H2O diagnostic strategy shows promise for applications in both ground and flight testing.

Simultaneous and independent lasing on two different atomic lines is achieved with spatial resolution of laser eigenstates in conjunction with intracavity frequency selection. A sensitivity of 0.3 part in 10 to the sixth power meter in the differential detection of methane in 1 atm of air is experimentally demonstrated with this novel dual-wavelength laser. Monitoring the output intensities of the two orthogonally polarized eigenstates permits absolute measurement of methane concentration.

We solve an inverse problem of ocean optics for estimating spatially dependent absorption and scattering coefficients and for determining sources such as fluorescence, bioluminescence, or Raman scattering. The solution requires in situ measurement of the downward and upward plane irradiances and scalar irradiances and a priori estimation of the angular shape of the volume scattering function. Both an explicit algorithm and an implicit one are developed from new two-stream radiative-transfer equations that utilize an asymptotic radiance approximation to close the set of equations. A comparison of numerical tests for the two algorithms is given.

A laser long-path absorption system was developed with a hydrogen Raman shifter pumped by a tunable dye laser. The absorption spectrum of CO2 in the 2-micrometer region was measured in the open air with a retroreflector or a hard target. The concentration of CO2 was determined from the spectrum by the least-squares method. Noise in the system was analyzed, and the propagation of error to the obtained concentration was investigated. The statistical error in the concentration was estimated at approximately 1% for a single spectrum measurement. Comparison with the simultaneous measurements with a nondispersive infrared gas analyzer showed good agreement.

A method of measuring the total reflection and transmission spectra of scattering materials with an integrating sphere and a Fourier-transform infrared spectrometer is studied. The reflectance measurement system is considered in a specific case where the incident beam overfills the back side port of the sphere, and the correction functions for measured spectra are derived for this case. Correction formulas are based on the energy balance between incident radiation and absorbed or escaped radiation in the system. The absorption spectrum of the material is calculated from the corrected spectra. The optical properties of paper samples and radiating surfaces of infrared dryers in the 0.4-20-[mu]m wavelength range are determined. The correction formulas are compared with previous work presented in the literature.

Scattering effects have always been an important systematic problem in absorption measurements. A new integrating cavity absorption meter has been developed that, in principle, is rigorously independent of scattering effects. The theoretical basis for this integrating cavity device is developed and applied to a generic experimental device: a one-dimensional model is described that demonstrates qualitatively the observed deviations from ideal; details of an actual device are provided; and experimental results for the absorption coefficient of aqueous solutions with various absorptions and with various concentrations of scatterers are presented. Key words: Absorption, integrating cavity, scattering, oceanic absorption.

The graphic presentation of relationships between a, b, R, and micron bar in a previously published nomogram on calculation of inherent optical properties (Aust. J. Mar. Freshwater Res. 32, 533 (1981)) are replaced by explicit mathematical expressions.

The absorption coefficients of mixed silver halide crystals and fibers were measured by different laser calorimetric methods: adiabatic for crystals and isothermal for fibers. The composition dependence of the bulk absorption coefficients Beta(sub b) of crystals and polycrystalline fibers at 10.6-micrometer (CO2 radiation) was investigated. It was found that the crystal surface absorption Beta(sub s) is dependent on the surface polishing quality. All experimental results of Beta(sub b) are smaller than those reported in the literature.

The high detection sensitivity available from intracavity laser spectroscopy (ILS) is extended into the near infrared by solid-state laser systems operating with relatively narrow (~0.002 [micro]m) bandwidths for three [CO.sub.2] absorption features of importance to an understanding of planetary atmospheres. The absolute intensities and pressure-broadening properties of the P(12), P(14), and P(16) lines of the [Sigma]-[Sigma] band (12 [degrees] 1-00 [degrees] 0) of [CO.sub.2] (at 2.0129, 2.0136, and 2.0143 [micro]m) are measured quantitatively by ILS with a Tm:YAG laser operating near 2.0 [micro]m. The temperature dependencies of these absolute intensities and collisional-broadening parameters for these three [CO.sub.2] features are also measured over the 110-300 K range. The 3.0-km equivalent absorption path length available from the ILS Tm:YAG system is used to enhance detection sensitivity by more than a factor of 1.5 x [10.sup.4] while maintaining a physical sample cell path length of ~20 cm. The enhanced detection sensitivity of ILS permits absolute intensities and collisional-broadening parameters to be measured from [is less than] 1-Torr [CO.sub.2] over a series of temperatures, conditions that emulate those found in the atmospheres of Mars, Triton, and Venus. [C] 2001 Optical Society of America OCIS codes: 120.1880, 120.4820, 140.3070, 140.3480, 300.6390, 350.1270.

A YAG laser was used to emit nanosecond pulses of light at 532 nm at depths from 1185 to 2200 m in Antarctic ice, corresponding to temperatures increasing from 229 to 249 K. From the timing distributions of photons arriving at phototubes at distances up to 100 m and at similar depths, the scattering and absorption coefficients were measured, and the temperature dependence of absorptivity at 532 nm was determined. Despite the absorptivity being many orders of magnitude lower at 532 nm than in the near ultraviolet and near infrared, the fractional increase of absorptivity, [a.sup.-1]da/dT = 0.01 [K.sup.-1], was the same in the visible, ultraviolet, and infrared. Analysis of published data at other wavelengths shows that [a.sup.-1]da/dT is ~0.01 [K.sup.-1] from 175 nm to ~1 cm, above which it increases strongly from 1 cm to 10 m. That temperature dependence applies only in regions not close to absorption bands. [C] 2001 Optical Society of America OCIS codes: 280.0280, 300.1030.

A model developed recently by Loisel and Stramski [Appl. Opt. 39, 3001-3011 (2000)] for estimating the spectral absorption a([Lambda]), scattering b([Lambda]), and backscattering [b.sub.b]([Lambda]) coefficients in the upper ocean from the irradiance reflectance just beneath the sea surface R([Lambda], z = [0.sup.-]) and the diffuse attenuation of down-welling irradiance within the surface layer [([K.sub.d]([Lambda])).sub.1] is compared with measurements. Field data for this comparison were collected in different areas including off-shore and near-shore waters off southern California and around Europe. The a([Lambda]) and [b.sub.b]([Lambda]) values predicted by the model in the blue-green spectral region show generally good agreement with measurements that covered a broad range of conditions from clear oligotrophic waters to turbid coastal waters affected by river discharge. The agreement is still good if the model estimates of a([Lambda]) and [b.sub.b([Lambda]) are based on R([Lambda], z = [0.sup.-]) used as the only input to the model available from measurements [as opposed to both R([Lambda], z = [0.sup.-]) and [([K.sub.d]([Lambda])).sub.1] being measured]. This particular mode of operation of the model is relevant to ocean-color remote-sensing applications. In contrast to a([Lambda]) and [b.sub.b]([Lambda]) the comparison between the modeled and the measured b([Lambda]) shows large discrepancies. These discrepancies are most likely attributable to significant variations in the scattering phase function of suspended particulate matter, which were not included in the development of the model. [C] 2001 Optical Society of America OCIS codes: 010.4450, 030.5620, 290.5860, 280.0280.

Passive Q switching of a tunable alexandrite solid-state laser with a Cr:[Y.sub.2]Si[O.sub.5] solid-state saturable absorber is numerically studied over a major portion of the alexandrite tuning range. The theory of passive Q switching with a slowly relaxing saturable absorber is studied and utilized for evaluating the performance of the Cr:YSO Q-switched alexandrite laser system. With a typical laser configuration, a Q-switched laser pulse of 262 mJ in 23 ns is obtained. [C] 2001 Optical Society of America OCIS codes: 140.3430, 140.3540, 140.3580, 140.3600.

Analytic equations are developed for the single-scattering properties of a spherical particle embedded in an absorbing medium, which include absorption, scattering, extinction efficiencies, the scattering phase function, and the asymmetry factor. We derive absorption and scattering efficiencies by using the near field at the surface of the particle, which avoids difficulty in obtaining the extinction based on the optical theorem when the far field is used. Computational results demonstrate that an absorbing medium significantly affects the scattering of light by a sphere. [C] 2001 Optical Society of America OCIS codes: 290.5850, 010.1290, 290.1090.

We modify an algorithm for retrieving the absorption (a) and backscattering ([b.sub.b]) coefficient profiles in natural waters by inverting profiles of downwelling and upwelling irradiance so as to include the presence of Raman scattering. For a given wavelength of interest, [Lambda], the light field at the appropriate Raman excitation wavelength [[Lambda].sub.e] is first inverted to obtain the Raman source function at [Lambda]. Starting from estimates of the inherent optical properties at [Lambda], the contribution to the irradiances at [Lambda] from Raman scattering is then estimated and subtracted from the total irradiances to obtain the elastically scattered irradiances. We then inverted the elastically scattered irradiances to find new estimates of a and [b.sub.b] using our original method [Appl. Opt. 37, 3886 (1998)]. The algorithm then operates iteratively: The new estimates are used with the Raman source function to derive a new estimate of the Raman contribution, etc. Sample results are provided that demonstrate the working of the algorithm and show that the absorption and scattering coefficients can be retrieved with accuracies similar to those in the absence of Raman scattering down to depths at which the light field is significantly perturbed by it, e.g., with ~90% of the upwelling light field originating from Raman scattering. [C] 2000 Optical Society of America OCIS codes: 010.0010, 010.4450, 290.3200, 290.4210, 290.5860, 240.0290.

By means of radiative transfer simulations we developed a model for estimating the absorption a, the scattering b, and the backscattering [b.sub.b] coefficients in the upper ocean from irradiance reflectance just beneath the sea surface, R([O.sup.-]), and the average attenuation coefficient for downwelling irradiance, [.sub.1], between the surface and the first attenuation depth. The model accounts for Raman scattering by water, and it does not require any assumption about the spectral shapes of a, b, and [b.sub.b]. The best estimations are obtained for a and [b.sub.b] in the blue and green spectral regions, where errors of a few percent to [is less than] 10% are expected over a broad range of chlorophyll concentration in water. The model is useful for satellite ocean color applications because the model input, R([O.sup.-]) and [.sub.1], can be retrieved from remote sensing and the model output, a and [b.sub.b], is the major determinant of remote-sensing reflectance. [C] 2000 Optical Society of America OCIS codes: 010.4450, 030.5620, 280.0280, 290.5860.

We tested closure between in situ radiometric and absorption coefficient measurements by using a nearly backscattering-independent remote-sensing reflectance model that employs the remote-sensing reflectance at three wavelengths. We show that only a small error is introduced into the closure model when the proper functional relationships of f/Q and the backscattering is taken to be a constant when using the sea-viewing wide field-of-view sensor wavelengths 443, 490, and 555 nm. A method of inverting the model to obtain the absorption coefficient by use of simple linear spectral relationships of the absorption coefficient is provided. The results of the model show that the independent measurements of reflectance and absorption obtain closure with a high degree of accuracy.

Measurement of absorption and reduced-scattering optical coefficients [[Mu].sub.a] and [[Mu].sub.s][prime] is possible when a steady-state backscattered image is used on a sample surface. A new method for processing the backscattered image, acquired with a CCD, has been developed. The image is integrated to decrease sensitivity to noise. The resulting curve is defined as the integral reflectance. The curve is then fitted with a relaxation model to evaluate [[Mu].sub.a] and [[Mu].sub.s][prime]. We have validated the method with calibrated scattering and absorption phantoms. The integral reflectance method is then applied to measurements of the [[Mu].sub.a] and [[Mu].sub.s][prime] coefficients of human skin in vivo.