Ultraviolet to Short Wave Infrared Spectral Reflectance

1 Page 1 NIST Special Publication 250 NIST SP 250-101 Ultraviolet to Short-wave Infrared Spectral Reflectance Heather J. Patrick Clarence J. Zarobila This publication is available free of charge from: https://doi.org/10.6028/NIST... Open at page → 2 Page 2 NIST Special Publication 250 NIST SP 250-101 Ultraviolet to Short-wave Infrared Spectral Reflectance Heather J. Patrick Sensor Science Division, Physical Measurement Laboratory Clarence J. Zarobila Sensor Science Divisio... Open at page → 3 Page 3 NIST SP 250-101 October 2024 Certain commercial entities, equipment, or materials may be identified in this document in order to describe an experimental procedure or concept adequately. Such identification is not intend... Open at page → 4 Page 4 NIST SP 250-101 October 2024 i Abstract The National Institute of Standards and Technology performs calibrations of spectral reflectance measurements in the ultraviolet (UV) to short-wave infrared (SWIR) spectral regions... Open at page → 5 Page 5 NIST SP 250-101 October 2024 ii Table of Contents 1. Introduction ..................................................................................................................................... 1 2. Scope of Measur... Open at page → 6 Page 6 NIST SP 250-101 October 2024 iii Appendix A. Example Calibration Reports .......................................................................................... 31 List of Tables Table 1. Typical source and detector c... Open at page → 7 Page 7 NIST SP 250-101 October 2024 1 1. Introduction The National Institute of Standards and Technology (NIST) performs SI-traceable spectral reflectance calibrations of spectrally neutral, non-fluorescent samples at room temp... Open at page → 8 Page 8 NIST SP 250-101 October 2024 2 ROSI and the RIS are now the national reference instruments for specular, bidirectional, and directional-hemispherical reflectance measurements. Calibrations are offered for specular reflec... Open at page → 9 Page 9 NIST SP 250-101 October 2024 3 2. Scope of Measurements ROSI and the RIS perform spectral reflectance measurements of spectrally neutral, non-fluorescent samples at room temperature. This publication describes measuremen... Open at page → 10 Page 10 NIST SP 250-101 October 2024 4 over which the reflected light is collected. Sections 2.2.1 and 2.2.2 illustrate the geometries used in specular and diffuse reflectance measurements. Directional-hemispherical reflectance... Open at page → 11 Page 11 NIST SP 250-101 October 2024 5 reflectance can also be made in the generalized out-of-plane geometry shown in Fig. 2 with the conventions for ?????? i, ?????? i, ?????? r and ?????? r. The incident beam illuminates a sma... Open at page → 12 Page 12 NIST SP 250-101 October 2024 6 3. The NIST Measurement System Overview Figure 4 shows a schematic of ROSI and the RIS. The system can be functionally divided into three parts, the tunable light source, the robotic goniom... Open at page → 13 Page 13 NIST SP 250-101 October 2024 7 nm to 2400 nm, and a high-brightness laser-driven Xenon light source (LDLS), Energetiq Model EQ- 99-PLUS-NA, with output from roughly 220 nm into the short-wave infrared. The source is sele... Open at page → 14 Page 14 NIST SP 250-101 October 2024 8 Robot Goniometer and Receiver Figure 5 shows a photo of the robot and receiver arm that are represented schematically in Fig. 4. An industrial 6-axis robotic arm (Staubli TX60) holds the sa... Open at page → 15 Page 15 NIST SP 250-101 October 2024 9 silicon photodiode or the input port of the sphere to be positioned behind the precision aperture and lens assembly at the detector plane located about 90 mm behind the lens. In the origina... Open at page → 16 Page 16 NIST SP 250-101 October 2024 10 Both the silicon and EIGA photodiodes are amplified using preamps with multiple, adjustable gain settings. The 75 Hz AC-modulated signals are collected using lock-in amplifiers. The lock-i... Open at page → 17 Page 17 NIST SP 250-101 October 2024 11 Reference Integrating Sphere The RIS is made of a 10 mm thick shell of sintered PTFE and has a 37 mm diameter input port, a 31 mm diameter top detector port, and two 37 mm diameter sample... Open at page → 18 Page 18 NIST SP 250-101 October 2024 12 4. Operating Procedures Sample Check-in and Handling Typical samples suitable for a calibration measurement include mirrors in the case of specular reflectance, and diffuse reflectors such... Open at page → 19 Page 19 NIST SP 250-101 October 2024 13 The sequence of incident flux and reflected radiant flux measurements at the desired geometries, wavelengths and polarizations are controlled by the run definition. In general, there are t... Open at page → 20 Page 20 NIST SP 250-101 October 2024 14 Common Operating Procedures The supercontinuum source, laser-driven light source, and EIGA detector cooling are turned on at least 30 minutes prior to a calibration. Data are saved in a da... Open at page → 21 Page 21 NIST SP 250-101 October 2024 15 5. Data Analysis and Uncertainties Reflectance Calculation 5.1.1. Specular Reflectance For specular measurements, the sample reflectance is the ratio of reflected to incident flux. The sam... Open at page → 22 Page 22 NIST SP 250-101 October 2024 16 5.1.3. Directional-hemispherical reflectance As described in Section 4.3, the 8/di spectral reflectance factor is determined by comparison to a standard with a known 8/di spectral reflecta... Open at page → 23 Page 23 NIST SP 250-101 October 2024 17 voltages, multiplied by &#3627408453; V. The additional terms in Eq. (5) are as follows. First, because the gain of the receiver preamp between measurements of incident flux and reflected... Open at page → 24 Page 24 NIST SP 250-101 October 2024 18 ??????′= ?????? &#3627408439; 2 ∙&#3627408438; &#3627408467;∙&#3627408438; &#3627408466;∙???????????????????????? &#3627408479; (7) where A is the area of the precision aperture of the ROS... Open at page → 25 Page 25 NIST SP 250-101 October 2024 19 geometries of 0/45 and 0/-45 at each wavelength assuming an isotropic sample. For the 0/45 viewing geometry and an ideal uniform illumination spot, &#3627408438; f = 0.9992. The values of... Open at page → 26 Page 26 NIST SP 250-101 October 2024 20 &#3627408438; e= ?????? eff ?????? (10) In the case of the integrating sphere-mounted EIGA detector, the collection efficiency for diffusely scattered light was about 0.6% higher than that... Open at page → 27 Page 27 NIST SP 250-101 October 2024 21 5.2.4. Additional Uncertainty Components Additional uncertainty components are components that do not affect the value of the measurand, do not appear explicitly in the measurement equatio... Open at page → 28 Page 28 NIST SP 250-101 October 2024 22 The reference values for reflectance factor of pressed PTFE are given in [19] and were originally assigned a wavelength-independent uncertainty of 0.2%. However, over the years concerns ar... Open at page → 29 Page 29 NIST SP 250-101 October 2024 23 equation, but for which there is a measurement dependence, for example, wavelength or sample uniformity. As an example, the combined relative uncertainty for a measurement of BRDF in the 0... Open at page → 30 Page 30 NIST SP 250-101 October 2024 24 Incident Angle 1 ?????? &#3627408479; ???????????? &#3627408479; ???????????? &#3627408470; ??????(?????? &#3627408470;) < 0.0001 Combined Relative Standard Uncertainty ?????? c(?????? r)/... Open at page → 31 Page 31 NIST SP 250-101 October 2024 25 6. Validation and quality control Calibration measurements on ROSI and the RIS comply with the NIST Quality System [13], which in turn conforms to ISO/IEC Standard 17025 [14]. As part of q... Open at page → 32 Page 32 NIST SP 250-101 October 2024 26 Fig. 11. Difference of the data in Fig. 10, and the k = 2 combined uncertainty. Validation of 0/45 Reflectance Factor A white sintered PTFE sample has been measured for its 0/45 reflectanc... Open at page → 33 Page 33 NIST SP 250-101 October 2024 27 Fig. 12. Reflectance factor of a white sintered PTFE plaque measured by ROSI and STARR. Fig. 13. Difference of the data in Fig. 12, and the combined k = 2 uncertainty. Validation of direct... Open at page → 34 Page 34 NIST SP 250-101 October 2024 28 pressed PTFE reference standard, leading to correlated components of uncertainty between the two instruments that would be double counted using the root-sum-squared of the uncertainties fo... Open at page → 35 Page 35 NIST SP 250-101 October 2024 29 References [1] P. Y. Barnes, E. A. Early, and A. C. Parr, “Spectral Reflectance,” NIST Special Publication 250-48 (NIST, 1998). [2] F. E. Nicodemus, J. C. Richmond, J. J. Hsia, I. W. Ginsb... Open at page → 36 Page 36 NIST SP 250-101 October 2024 30 [19] V.R. Weidner and J.J. Hsia, “Reflection Properties of Pressed Polytetrafluoroethylene Powder,” J. Opt. Soc. Am. 71 No.7 (1981). [20] Thomas A. Germer, Joanne C. Zwinkels, and Benjamin... Open at page → 37 Page 37 NIST SP 250-101 October 2024 31 Appendix A. Example Calibration Reports Example calibration reports for spectral specular reflectance, 0/45 spectral reflectance factor, and 8/di spectral directional-hemispherical reflect... Open at page →