Diffraction corrections are required in radiometric measurements in remote sensing. In this work, I will discuss the capabilities that we have developed to calculate them accurately and efficiently. Several aspects will be considered, namely, (1.) diffraction effects for a single aperture, for spectral power and total power in the case of radiation thermometry, including asymptotic behavior a small wavelengths and high temperatures; (2.) diffraction effects specific to multi-staged optics trains; (3.) applications in remote-sensing applications in test chambers use to simulate observation of remote objects in outer space; and (4.) solar radiometry.
The Advanced Baseline Imager (ABI) is the next-generation imaging sensor for the National Oceanic and Atmospheric Administration’s (NOAA’s) operational meteorological satellites in geostationary orbit. One pathway for traceability to reference standards of the visible and near-infrared radiometric response for ABI is to a 1.65 m diameter integrating sphere source standard of spectral radiance. This source illuminates the full entrance pupil via the ABI Earth-view port, thus determining the absolute spectral radiance responsivity in the visible and shortwave infrared. The spectral radiance values of the large sphere are assigned by Exelis using a double monochromator and a 15.24 cm diameter integrating sphere source standard that is calibrated by NIST. As part of the ABI program, Exelis was required by NASA to have the spectral radiance values assigned by Exelis to the large sphere be validated by NIST. Here we report the results of that activity, which took place in April, 2013. During the week of April 8, Exelis calibrated the 1.65 m diameter sphere at all 24 levels that correspond to the ABI calibration protocol. During the week of April 15, the NIST validation exercise for five selected levels took place. NIST deployed a portable spectral radiance source, a filter radiometer restricted to the visible and near-infrared, and two spectroradiometers that covered from 350 nm to 2500 nm. The NIST sphere source served as the validation standard. The comparison results, which are reported at the ABI bands, agreed to within the combined uncertainties. We describe the methodology, results, and uncertainty estimates related to this effort.
We describe the characterization of a group of NIST spectral irradiance lamps at longer distances and larger angles than are typically issued by NIST. The spectral irradiances from the FEL lamps were measured from 50 cm to 150 cm at 8 different distances using a cosine-corrected filter radiometer to determine if the lamps adhere to the inverse square law. Using the filter radiometer, the spatial uniformities of the FEL lamps were also mapped over a 20 cm square area at 135 cm, 143 cm and 151 cm. In the NIST gonio-spectroradiometer facility, selected lamps were also mapped for the angular dependences of the spectral irradiances at a distance of 123 cm using a spectrograph which measures from 300 nm to 1100 nm for comparisons to the filter radiometer measurements. Using these measurements, an uncertainty budget for the distance and the angular uniformity correction of the FEL lamps was developed.
Scales of spectral irradiance are disseminated by NIST using assignment of values to FEL lamp standards for defined
conditions. These lamp standards can be used for absolute calibrations of irradiance radiometers, or more typically, be
used in conjunction with a diffuse reflectance standard to establish a scale of spectral radiance and for subsequent
absolute calibrations of radiance radiometers. The NIST FEL standards are valuable artifacts requiring special care.
Many users optimize resources by in-house transfer of their primary standard to working standards. There are a number
of sources of uncertainty in utilizing FEL lamps, e.g., lamp current, alignment, distance setting, instrument aperture size,
drift, scattered light, and interpolation in the wavelength grid for the specified irradiance values. In this work, we
validated the transfer activity by ITT of their primary, NIST-traceable FEL lamp standards. A portable irradiance bench
that had kinematic mounts for an FEL lamp, on-axis baffle, and three different irradiance radiometers was built, tested,
and deployed to ITT in Rochester, NY. We report the results of this comparison activity. An uncertainty budget was
developed and it was found that the results agreed well within the combined uncertainties of 1.5% to 1.6% (k = 2).
Optical imaging has the potential to achieve high spatial resolution and high functional sensitivity in wound
assessment. However, clinical acceptance of many optical imaging devices is hampered by poor reproducibility, low
accuracy, and lack of biological interpretation. We developed an in vivo model of ischemic flap for non-contact
assessment of wound tissue functional parameters and spectral characteristics. The model was created by elevating
the bipedicle skin flaps of a domestic pig from the underlying vascular bed and inhibiting graft bed reperfusion by a
silastic sheet. Hyperspectral imaging was carried out on the ischemic flap model and compared with transcutaneous
oxygen tension and perfusion measurements at different positions of the wound. Hyperspectral images have also
been captured continuously during a post-occlusive reactive hyperemia (PORH) procedure. Tissue spectral
characteristics obtained by hyperspectral imaging correlated well with cutaneous tissue oxygen tension, blood
perfusion, and microscopic changes of tissue morphology. Our experiments not only demonstrated the technical
feasibility for quantitative assessment of chronic wound but also provided a potential digital phantom platform for
quantitative characterization and calibration of medical optical devices.
We report on our comprehensive survey of high-index UV optical materials that may enable extension of immersion lithography beyond a numerical aperture of 1.45. Band edge, refractive index, and intrinsic birefringence (IBR) at 193 nm determine basic viability. Our measurements of these properties have reduced the list of potential candidates to: ceramic spinel, lutetium aluminum garnet, and a class of germanium garnets. We discuss our measurements of the intrinsic properties of these materials and assess the present status of their material quality relative to requirements. Ceramic spinel has no significant IBR, but transmission and scatter for the best samples remain at least two orders of magnitude from specifications. Improving these would require a major development effort. Presently available lutetium aluminum garnet has material quality much closer to the specifications. However, the IBR is about three times the required value. The germanium garnets offer the possibility of a lower IBR, but a suitable candidate material has yet to be established.
193 nm immersion lithography optical projection systems using conventional UV optical materials and water as the immersion fluid, with planar lens/fluid interfaces, have a practical numerical aperture (NA) limit near 1.3. The bottleneck for pushing the NA further is the refractive index of the final lens element. Higher-index immersion fluids cannot alone give much improvement, because the NA is limited by the lowest material index. In this paper we consider the possibility of using novel high-index materials in the last lens element to get around this bottleneck and to push the NA limit to at least 1.5, while containing the lens system size and complexity. We discuss three classes of high-index (n>1.8), wide-band-gap, oxide-based materials that have the potential for being fabricated with optical properties appropriate for lithography optics: group-II oxides, magnesium-aluminum-spinel-related materials, and ceramic forms of spinel. We present theoretical calculations and experimental measurements of the optical properties of these materials, including intrinsic birefringence, and we assess their prospects.
We discuss a first-principles method to compute electronic optical excitation spectra of solids over energy ranges varying from 20 eV to 70 eV. We discuss the principal components of the method that is used, which centers around solving the coupled electron-hole Bethe-Salpeter equation. Results are presented for the 1s edge of Si in silicon and F in LiF, as well as valence excitation spectra of BeO and MgO. We conclude by noting areas for future improvement.
The discovery of a significant spatial-dispersion-induced birefringence (intrinsic birefringence) in CaF2 at ultraviolet wavelengths has had a major impact on the design of 157 nm lithography systems, requiring complete redesign of the optics to take account of the imaging aberrations resulting from the birefringence and the accompanying index anisotropy. This intrinsic birefringence phenomena results from a symmetry-breaking effect of the finite wave vector of the photon on the symmetry of the light-matter interaction in fluorite-structure cubic crystals. As a follow-up to our original concise report of measurements and theory of the effect in CaF2 and BaF2, we present here a more detailed analysis of the theory, focusing on the symmetry and its consequences. We also provide the full directional dependence of the effect in useful closed forms. We analyze the implications for precision optical design with CaF2 optical elements, and discuss qualitatively the approaches being considered to compensate for it.
Collimated infrared sources covering the 2 micrometer to 30 micrometer range of wavelengths are necessary to simulate infrared radiation from distant objects. This is important because on-orbit servo and tracking systems make extensive use of infrared radiation for remote sensing. Collimators are used to calibrate infrared detectors in terms of absolute power within a given spectral range. The National Institute of Standards and Technology (NIST) operates and maintains the Low Background Infrared Calibration (LBIR) facility, which uses a 2 K electrical substitution radiometer, the Absolute Cryogenic Radiometer (ACR), that is the primary national standard for broadband and infrared spectral measurements. At this facility, users can calibrate blackbody sources with at most 1% uncertainty. However, users must then rely on optical systems at their own facility to collimate the radiation from the blackbody. The effect of the optics on the output of the beam must then be calculated from models. For this reason, NIST is developing a portable transfer radiometer (BXR) that can be taken onsite to directly measure the spectral output, thus eliminating intermediate steps in the calibration chain. NIST is also developing a source having 1 cm diameter collimated beam, for a preliminary calibration of the BXR at the LBIR facility from 2 micrometer to 8 micrometer. The source must fit into a volume of about 0.03 m3 (1 cubic foot), have an angular divergence of less than 700 (mu) rad, a power output greater than 10 nW, and demonstrate 1% repeatability or better. The development and characterization of this source is the main topic of this paper.