Radiation Budget Instrument (RBI) is a scanning radiometer that measures earth reflected solar radiance and thermal emission at the top-of-atmosphere. RBI has three radiance channels that cover 0.25-5μm, 5-100μm and 0.25-100μm spectral bands respectively. To ensure highly accurate measurement throughout mission life, RBI is equipped with two internal calibration targets to routinely calibrate the radiance channels on orbit. A highly stable Electrical Substitution Radiometer (ESR) based Visible Calibration Target (VCT) is used to calibrate RBI short wave and total channel; A 3- bounce specular trap blackbody Infrared Calibration Target (ICT) with high emissivity, High accuracy temperature measurement is used to calibrate the RBI long wave channel. Prior to launch, RBI will undergo a comprehensive ground calibration campaign in a thermal vacuum chamber developed for RBI at the Space Dynamics Laboratory (SDL). A set of calibration targets developed by SDL, including short wave radiance source (SWRS), long wave infrared calibration source (LWIRCS), and a space view simulator (SVS) were used for RBI ground calibration. The plan is to characterize RBI absolute radiance measurement accuracy and repeatability, tie internal calibration targets to ground calibration, to carry the ground calibration to orbit. In fall 2017, the RBI Engineering Development Unit (EDU) went through the ground calibration campaign, as the pathfinder for flight unit. A large discrepancy was observed between the SDL target based calibration and RBI internal target based calibration. In this paper, we describe the discrepancy observed, the root cause analysis, and some lessons learned.
A full-spectral monitoring (FSM) system utilizing (charged coupled device) CCD array spectroradiometer and optical fiber has been developed and implemented for accelerated laboratory weathering instruments. The system provides in-situ, real-time irradiance monitoring and control. Compared to the conventional photo diode and fixed band pass interference filter radiometer used for irradiance measurement and control, FSM represents a revolutionary step forward for the weathering industry. Additionally a calibration process utilizing an identical xenon lamp used for testing has been developed for the FSM system. This calibration process greatly simplifies the traditional Mercury plus FEL lamps based calibration process. The total measurement uncertainty of this FSM is also analyzed and discussed in the paper.
Phase shifting based measurements have been well established for use in both interferometry and structured light based
measurements. The use of modern LCD, DLP or LCOS based projectors to create and shift projected patterns for use in
phase shifting systems has provided new capabilities such as pattern masking, adjustable resolutions and active
preprocessing, along with many challenges. Now the latest consumer projection technology has made available low
cost, pocket-sized projectors, some with built in memory. These small projectors open up the possibility of mini-phase
shift systems, as well as the possibility of portable measurement systems. This paper explores some of the possibilities
for systems made with pocket size pattern projectors, and what some of the limitations may be that will need to be
overcome. Experimental data will be presented that illustrates some of these challenges.
CdZnTe is a high efficiency, room temperature radiation detection material that has attracted great interesting in
medical and security applications. CZT crystals can be grown by various methods. Particularly, CZT grown with the
Transfer Heater Method (THM) method have been shown to have fewer defects and greater material uniformity. In this
work, we developed a proof-of-concept dual lighting NIR imaging system that can be implemented to quickly and
nondestructively screen CZT boule and wafers during the manufacturing process. The system works by imaging the
defects inside CZT at a shallow depth of focus, taking a stack of images step by step at different depths through the
sample. The images are then processed with in-house software, which can locate the defects at different depths, construct
the 3D mapping of the defects, and provide statistical defect information. This can help with screening materials for use
in detector manufacturing at an early stage, which can significantly reduce the downstream cost of detector fabrication.
This inspection method can also be used to help the manufacturer understand the cause of the defect formation and
ultimately improve the manufacturing process.
Current spectroscopic detector crystals contain defects that prevent economic production of devices with sufficient
energy resolution and stopping power for radioisotope discrimination. This is especially acute for large monolithic
crystals due to increased defect opportunity. The proposed approach to cost reduction starts by combining stereoscopic
IR and ultrasound (UT) inspection coupled with segmentation and 3D mapping algorithms. A "smart dicing" system
uses "random-access" laser-based machining to obtain tiles free of major defects. Application specific grading matches
defect type to anticipated performance. Small pieces combined in a modular sensor pack instead of a monolith will
make the most efficient use of wafer area.
The fabrication of new optical materials has many challenges that suggest the need for new metrology tools. To this
purpose, the authors designed a system for localizing 10 micron embedded defects in a 10-millimeter thick semitransparent
medium. The system, comprising a single camera and a motion system, uses a combination of brightfield and
darkfield illumination. This paper describes the optical design and algorithm tradeoffs used to reach the desired detection
and measurement characteristics using stereo photogrammetry and parallel-camera stereoscopic matching. Initial
experiment results concerning defect detection and positioning, as well as analysis of computational complexity of a
complete wafer inspection are presented. We concluded that parallel camera stereoscopic matching combined with
darkfield illumination provides the most compatible solution to the 3D defect detection and positioning requirement,
detecting 10 micron defects at a positioning accuracy of better than +/- 0.5 millimeters and at a speed of less than 3
minutes per part.
A review is given of recent theoretical and experimental studies on the liquid crystal (LC) infiltration of 3D photonic crystal (PC) structures so as to obtain tunable Bragg reflection and transmission characteristics. It is shown that large-pore and non-close-packed inverse opals formed by sintering, or by a multiple-layer conformal deposition technique, provide a simple and effective dielectric scaffold for liquid crystal infiltration. The dynamic optical properties are strongly dependent on the scaffold structure and the dielectric contrast between the scaffold and the LC. Experimental structures were fabricated using precise, conformal, low temperature atomic layer depositions of Al2O3 and TiO2 to create inverse opals and non-close-packed inverse opals, which were subsequently infiltrated with the nematic liquid crystals 5CB and MLC2048. The dependence of the visible/infrared reflectance and transmittance were investigated as functions of applied electric field amplitude and frequency for applications in optical modulation and switching.
We studied the electro-optical property and photorefractive effects in a semiconductor CdSe nanorod doped neamtic liquid crystal [NLC] system. The nonlinear index coefficient is measured to be n2=2.05×10−2cm2/W, which is 10 times larger than that of an equivalent pure liquid crystal system. Electro-optical switching investigation shows that the Freedericksz transition voltage of this system is also noticeably lower than that of un-doped NLC. These enhanced electro- and nonlinear optical properties are attributed to the photoconductivity of CdSe nanorods and the enlarged electric conductivity and dielectric anisotropies of the doped system. An AC field assisted photorefractive effect in CdSe nanorod doped liquid crystal system has also been studied.
We have fabricated 1-, 2- and 3-D photonic crystalline structures in polymer dispersed nematic and isotropic phase liquid crystals. It is observed that a particular mixture of isotropic liquid crystals and the photo-polymer will also polymerize and phase separate, forming high quality optical gratings, just as typical nematic liquid crystals. Liquid crystal droplet sizes obtained could be as small as a few 10’s of nm, i.e., nano-droplets. The resultant structure exhibits excellent optical qualities, and high efficiency Bragg diffraction properties.
We report theoretical and experimental studies of supra-photorefractive nematic liquid crystals doped with C60 and/or Carbon nanotubes. Theoretical estimate shows that the nonlinear refractive index change coefficient n2 in such systems can be >> 1 cm2/Watt. Experimentally, we have observed n2 of ~ 10 cm2/W, with typical nematic response times.
We report theoretical and experimental studies of 1-D and 2-d tunable nonlinear photonic crystals made of liquid crystal or liquid crystal infiltrated periodic structures. Theoretical modeling shows that such structures exhibit tunable bandgap, and sugar-prism effect. Experimentally, we have demonstrated the possibility of writing dynamic or permanent [but switchable] index gratings to dye-doped LC films that act as planar waveguides.
We report optical and photoresponsive behavior of nonlinear liquid crystals in two-dimensional (2D) periodic structure. 2D structure made of photoresist and titania is constructed by interference photolithography using grating mask. Then azobenzene-doped nematic liquid crystal is infiltrated into these arrays, and photoresponsive behavior of the azobenzene-doped liquid crystal in the periodic structure is investigated. In particular, we show that the diffraction from these liquid crystal infiltrated grating structures can be optically modulated by an Ar+ laser at 488 nm.
We have studied the optical nonlinearities of aligned nematic liquid crystalline films in the near IR communication spectral region (1.55 micrometers ). The measured refractive index coefficients are on the order of 10-3 cm2/W. The origins of the refractive index changes are thermal indexing effect and director axis reorientation. Phase modulation of several (pi) s can be generated with mW-power near IR lasers in micron thick films.