This PDF file contains the front matter associated with SPIE Proceedings Volume 11485, including the Title Page, Copyright information, and Table of Contents.

This conference on Reflection Scattering and Diffraction from Surfaces is the 7th in a series that have highlighted new progress, developments and applications in a key area of the field of optical properties of materials. A brief welcome, introduction and summary is provided.

The Generalized Harvey-Shack (GHS) surface scatter theory claims to predict scatter from surfaces over a wide domain but has not been widely implemented or tested. The focus of this talk is to provide experimental validation of the GHS theory for the prediction of the BRDF from real surfaces. First, the GHS theory was implemented in software. Next, a BRDF measurement system was designed, built, and validated. Smooth, moderate, and rough surfaces were characterized via AFM as inputs to the GHS theory. The BRDF of each surface was measured and simulated. In nearly all cases, GHS simulations matched well with experimental results.

An experimental and theoretical study of the scattering and diffraction properties of nanopatterned dielectric structures is presented. The samples consist of periodic arrays of silicon disks over a flat layer of silicon dioxide on a silicon substrate. The samples produce far-field scattering patterns that display a series of well-defined circular fringes that modulate the intensity of the diffraction orders. Simple models of the physical mechanisms that give rise to the observed phenomena are proposed. Measurements of the angular scattering distribution produced by the samples are presented and compared them with the results of numerical calculations.

The improved anomalous diffraction approximation for particle cross sections requires the induced polarization response to the incident electromagnetic field as an input. Solutions to Maxwell’s equations are developed for the induced polarization vector response for spheroidal particles. The emphasis is on near infrared wavelengths and micron sized particles. The model agrees with published results in the static limit. There is no published literature on the optical frequency dependence. General spheroidal shapes are examined. The goal is to apply the result to obtain the Muellar matrix.

Bidirectional Scattering Distribution Function (BSDF) measurements of selected specular samples were made using the Table-Top Goniometer (TTG) in the Diffuser Calibration Lab (DCL) at NASA GSFC in the support of NASA remote sensing instruments and programs. The same TTG system has also been used in the BRDF measurements for diffuse samples. The tunable laser-based TTG possesses the advantages of small incident beam profile and configuration flexibility and is able to meet various BSDF test requirements on specular samples with flat and curved surfaces. It also has a useful capability in characterizing instrument straylight due to surface roughness and in determining the scattering light distribution function of optical surfaces. The BSDF measurements on specular samples can be performed over 8 orders of linear dynamic range with correction of instrument signatures. In this paper, we present BSDF results on two types of specular samples: a witness flat fold mirror for the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) project and four Multi-Layer Insulation (MLI) samples for the Restore project at NASA GSFC. BRDF measurements in the viewing angle range of ± 90° were acquired at 500 nm, 700 nm, and 2000 nm and at incident angles of 0°, 8°, and 25° for the PACE sample, and at 500 nm, 633 nm, 700 nm, 900 nm, 1000 nm, 1550 nm, and 1800 nm at incident angles of 10° and 25° for the MLI samples. For both types of samples, the ABg model was applied to fit the BSDF data to generate the parameters for optical modeling. The ABg model is able to fit the BSDF data on the polished surface of the flat mirror very well. However, two scattering components were seen in the MLI BSDF fitting results attributed to wrinkle and surface morphology issues. Total Hemispherical Reflectance (THR) and Total Integrated Scatter (TIS) measurements were also made on the samples and were compared to the BSDF results. The details of the BSDF measurement setup and the methodology for realization of the BRDF scale for the specular samples are also described.

For a given material, the bi-directional reflectance distribution function (BRDF) spatially describes how much light from any given incident direction reflects into each possible scattered direction. One common simplification in both BRDF measurement and modeling is to assume that material reflectance is isotropic throughout the scattered hemisphere with respect to the azimuthal direction. However, in reality, many materials with directionally-dependent surface characteristics, such as milled metals, are likely to exhibit anisotropic BRDFs, particularly noticeable near specular peaks. Scatter measurement devices similar to the modified Complete Angle Scatter Instrument® (CASI®) operated at the Air Force Institute of Technology (AFIT) are capable of direct specular measurements with high spatial resolution, but constrained within the plane of incidence. Anisotropic measurement techniques often sacrifice spatial resolution, particularly near specular peaks. In this work, AFIT's CASI® is augmented by installing a scientfic-grade monochrome charge-coupled device (CCD) camera on the detector arm, whose pixel array captures both in-plane and out-of-plane specular scatter measurements with high spatial resolution. Camera mounting and alignment processes are presented, including required beam attenuation for the visible red helium neon laser source used. The beam signature is measured and characterized, and the camera's effective dynamic range is extended using various exposure times. Beam signature is converted from raw digital counts to BRDF values, providing the baseline for an idealized perfectly specular material. Ultimately, this work is expected to lead towards improvements in measuring and modeling BRDFs for materials exhibiting anisotropic or out-of-plane reflectance properties for a range of radiometric remote sensing applications.

We describe an algorithm to extract the complex refractive index of a material from reflectance and transmittance measurements commonly taken by spectrophotometers. The algorithm combines Kramers-Kronig analysis with an inversion of Fresnel's equations to provide a direct method of solving for the refractive index which is accurate, even for weakly absorbing materials. We discuss the details of the uncertainty analysis of the algorithm. The algorithm is validated by extracting the complex refractive index of polydimethylsiloxane between 2 μm and 18 μm and comparing against existing literature.

We map the weak modal transformation of a polarized optical Gaussian beam reflected o a surface using an optical confocal scanning setup, designed to detect the resonance fluorescence of a quantum emitter. Such challenging measurements require the suppression of laser background by several order of magnitudes. Normally, high quality commercial crossed polarizers allows a laser suppression down to 5 to 6 orders of magnitudes. Surprisingly, when used in combination with a reflecting surface, the extinction ratio is boosted up to 9 order of magnitudes. This unexpected but very welcome enhancement finds its origin in the Imbert-Fedorov effect, which manifests itself in the reflectivity of a Gaussian laser beam off a mirror. In this work, we note that this effect give rise to a cross-polarized component carried by a TEM₀₁ Hermite-Gaussian spatial mode which we imaged using a confocal scanning technique for the first time

Mueller matrix polarimetry (MMP) is a technique capable of determining a material’s effect on polarized light. However, there are limiting factors that can be optimized to improve the quality of information that is collected using traditional MMP. One such issue lies in the full-field assessment of samples which gives a bulk assessment of a sample’s polarimetric properties and disallows specific structures to be distinguished between different depths as there would be in any non-uniform or multilayered sample. Spatial Frequency Domain Imaging (SFDI) is a well-documented technique that can be used to manipulate depth of penetration of an investigating light source through use of different [sinusoidal] frequency patterns. Higher frequency patterns can be used to restrict the depth of penetration for more superficial structure. The combined technique was used to investigate and differentiate between birefringent samples with varied depth-dependent structure.

We report the results of ex vivo studies of different types of human tissue (colon, uterine cervix, brain) with the custom-built multi-wavelength wide-field imaging Mueller polarimeter for medical diagnostics. Any type of pathology has impact on tissue microstructure at the very early stage of disease development. Consequently, it modifies optical properties of tissue. Apart from changing the scattering of light by tissue, disease progression also leads to the loss of tissue linear birefringence by breaking its fine fabric and erasing optical anisotropy. These structural changes can be detected early with polarized light by estimating the degree of depolarization of backscattered light, as well as the retardance of non-depolarized fraction of backscattered probing light beam. We demonstrate that polarization (scalar retardance and azimuth of optical axis) and depolarization parameters can serve as the optical markers of tissue pathology.

Microfacet BRDF models describe how light reflects off surfaces. Previous analysis found unpolarized data fitted to a microfacet BRDF model that approximated wave optics factor, Q for Fresnel reflectance and geometric attenuation terms was found to be more physically accurate. This work builds on those findings to examine pp and ss polarization cases individually, discovering that pp parameters fit the data better than ss parameters in 13/14 cases. This is accomplished for a variety of materials at different incident angles, and trends are determined to guide future work in refining microfacet pBRDF models.

Microfacet BRDF models based upon geometric optics and used in computer graphics and remote sensing commonly account for surface scatter and Lambertian volume scatter. These models agree well with forward scatter observations, but lack accuracy in backscatter observations. This work proposes directional volume scatter modeling for enhanced BRDF performance. Five directional volume models are incorporated into the modified Cook-Torrance model. A reduction in model error by as large as 53% overall, and 64% in backscatter modeling, is demonstrated. Using our novel semi-empirical model reduced error in 13/15 materials, and incorporating the Sandford-Robertson directional volumetric term reduced error in 14/15 materials.

The first version of the SCATMECH polarized light scattering C++ class library was released in 2000. This software provides a large number of models for Mueller matrix bidirectional reflectance distribution function (BRDF), models for free-space scatterers, rigorous coupled wave (RCW) analysis of diffraction gratings, reflectance and transmittance of thin film coatings, and manipulation of polarimetric and optical properties. In 2004, the Modeled Integrated Scatter Tool (MIST) was developed to provide a front-end application for calculating integrated reflectance. While SCATMECH provides efficient codes for modeling, it requires experience with C++ to use, and MIST has limited functionality for many applications. As a result, we have developed a Python interface that provides an intermediate level of access to the SCATMECH library, allowing faster development of applications and test simulations. In this paper, we demonstrate the functionality and use of pySCATMECH using the example of an interference bandpass filter and calculations of scattering by roughness, particles, and volume scattering within that filter.

Additive manufacturing involving layer-wise selective laser melting of a powder material, or laser powder bed fusion (LPBF), is a fast-growing industry. At the Additive Manufacturing Metrology Testbed (AMMT) at the United States National Institute of Standards and Technology (NIST) an integrating hemispherical reflectometer has recently been developed to facilitate measurements of spatially resolved reflectance of the laser-melting heat affected zone (HAZ) during the LPBF process. Reflectance is then used to determine spatially resolved emissivity. The design features of the hemispherical-directional reflectometer are discussed. Then, the reflectometer performance and measurement uncertainties are detailed. A two-dimensional map of emissivity and emissivity uncertainty of the HAZ around a meltpool of high-purity nickel are presented. It is found that emissivity measurements are in good agreement with literature values at the melting point of high-purity nickel with acceptable uncertainty.

We developed a new measurement system for bidirectional reflectance distribution functions (BRDF). The system can obtain simultaneously isotropic BRDF of all scattering angles utilizing a semicircular ring and an image sensor. First, we predicted the performance of our measurement system using integrated ray tracing simulation. The light path is as follows: the light from the light source at 635 nm is reflected off the target material, and the light is reflected back at the semi-circular ring. The image sensor records the light reflected from the semicircular ring. The results show good agreement with original and simulation BRDF, but detailed analysis suggested. The system improves significantly measurement time and resolution of reflection angles. Furthermore, the system is not only more cost effective than other traditional measurement systems, but also eliminated the temporal fluctuation of the light source intensity.

Advances in the semiconductor industry have led the wafer inspection technology to the limit of nanometer-scale defect detection, which is far beyond the diffraction limit. In this regime, the signal-to-noise ratio (SNR) is the figure-of-merit to determine whether the optical system can detect a single nanometer-scale defect. In this paper, we investigated the SNR properties of various line defects using the dark-field inspection with tailored polarized illumination by simulation and experiment. Conventional crossed Nicols configuration with linear polarized illumination and crossed analyzer can minimize background scattering noise and maximize line defect signal only for a specific kind of line defect such as gap or bridge due to strong polarization dependence on a line and space (L/S) pattern. The nulling elliptically polarized illumination is optimized to suppress background scattering noise moderately and maintain defect signal intensity at the same time. We confirmed SNR improvement for both 10 nm open and bridge defects on 40 nm line and space silicon pattern with 40 nm depth. There was a good agreement between our simulation results and experimental results. We experimentally confirmed SNR ~ 4 for both line gap and bridge defect detection on 40 nm L/S patterned wafer with the fixed nulling illumination.

A high-dynamic-range reflectivity measurement instrument has been developed with a dynamic range in excess of 100 dB and sensitivity below 1 pW. It can measure the angle-dependent back-scattered reflectivity of static surfaces up to 80º incidence angle over any orientation without the need for physical contact with the part. It has been designed to operate at both 800 nm and 1550 nm. The system operates through lock-in detection of amplitude-modulated laser light in a bi-static probe architecture, specially designed to minimise the effects of unwanted scattering and stray light. This development has been designed for on-site characterisation of the reflectivity of components of the ITER nuclear fusion reactor whose size, radioactivity or toxicity are inappropriate for insertion in traditional BRDF measurement instrumentation. Measuring the reflectivity of these components is critical for the development of tools for in-service inspection of ITER’s reaction chamber, a key element for the safety of the machine. The reflectivity of beryllium blanket module components and tungsten divertor components has been measured to vary over a range of up to 50 dB from normal to 80º incidence angle, to values below 10^-5 /sr. Strong anisotropy of the reflectivity is also observed. This data has been matched with the inspection system performance in a custom simulator to confirm that inspection is possible over < 95 % of the ITER reactor plasma facing components.

In this paper, we propose and evaluate a wavelength division multiplexing passive optical network (WDM-PON) architecture with a centralized light source (CLS). The use of only one 10 GHz band reject filter at the remote node (RN) allows WDM-PON to have a minimal value of the optical interferometric noise, which is induced by Rayleigh backscattering (RB), in the main lobe of each downstream (DS) optical signal. Utilizing this filter achieves an optical interferometric noise reduction in the upstream (US) direction and the simulation results indicate an enhancement in the performance of a bit error rate (BER) to be 10^-11 and in the Q-factor to be above 6.0. Owning to the US signal modulation without extra light source, this architecture successes in power saving and efficient utilization of the wavelength.