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We introduce a scalable temporally modulated long-wave infrared source design. The design makes use of an array of resistive blackbody heating elements which radiate into a custom aluminum integrating cavity. The output of the box is a rectangular slit, built to match the traditional tungsten ribbon profile for an infrared deflectometry source. Temporal modulation allows for signal isolation and improved resilience to background fluctuations in an infrared deflectometry source. Infrared deflectometry measurements using the new source design and a traditional tungsten ribbon, both with similar radiant flux, were compared for a ground glass surface, an aluminum blank, and an aluminum blank under thermal load (150 °C). Signal-to-noise ratio was ∼4 times higher for the new design and demonstrated improved source temporal stability and geometry. Further, the new design successfully measured the previously untestable hot aluminum flat. The new design improves infrared deflectometry and allows for high contrast thermal deflectometry measurements of optics under thermal load.

NIH Biomedical Imaging and Spectroscopy Training Grant [T32EB000809]; SPIE Optical Design and Engineering Scholarship; College of Optical Sciences; Friends of Tucson Optics (FOTO) Boye Family Graduate Student Scholarship in Optical Sciences; SPIE and Photonics Media Teddi Laurin Scholarship

Functional fitting with orthonormal polynomials of point-cloud freeform optics is investigated. The amount of asymmetry of the optic drives the selection of Cartesian and/or polar basis sets. This parameterization allows design refinement, optimization, and tolerancing.

A novel meta-heuristic approach for minimizing nonlinear constrained problems is proposed, which offers tolerance information during the search for the global optimum. The method is based on the concept of design and analysis of computer experiments combined with a novel two phase design augmentation (DACEDA), which models the entire merit space using a Gaussian process, with iteratively increased resolution around the optimum. The algorithm is introduced through a series of cases studies with increasing complexity for optimizing uniformity of a short-wave infrared (SWIR) hyperspectral imaging (HSI) illumination system (IS). The method is first demonstrated for a two-dimensional problem consisting of the positioning of analytical isotropic point sources. The method is further applied to two-dimensional (2D) and five-dimensional (5D) SWIR HSI IS versions using close- and far-field measured source models applied within the non-sequential ray-tracing software FRED, including inherent stochastic noise. The proposed method is compared to other heuristic approaches such as simplex and simulated annealing (SA). It is shown that DACEDA converges towards a minimum with 1 % improvement compared to simplex and SA, and more importantly requiring only half the number of simulations. Finally, a concurrent tolerance analysis is done within DACEDA for to the five-dimensional case such that further simulations are not required. ispartof: Optics Express vol:24 issue:26 pages:29380-29405 ispartof: location:United States status: published

Common illumination systems in short wave infrared (SWIR) hyperspectral imaging (HSI) include direct or indirect tungsten halogen lights. While direct lights provide more radiation onto the samples than dome setups, thus being more energy efficient, the acquired images often suffer from specular reflections and gloss. Glare artifacts in images increase variability in the data limiting the accuracy of machine vision algorithms for defect detection and quality inspection, or even providing false positives. Although domes are known to provide a near Lambertian illumination and glare free images, glossy regions and heterogeneities may remain in the data in practice. More particularly, in the field of fruit and vegetable quality inspection, due to their waxy surface, it remains challenging to design an efficient realistic lighting system. This paper suggests a new approach to optimize the illumination of fruit and vegetables based on measurements of the bidirectional reflectance distribution function (BRDF), shape and Stokes parameters. From these measured values, a BRDF model is loaded into ray-tracing software for realistic illumination engineering in order to determine the most suitable illumination scheme. This concept is applied to apples and a cross polarizer (CP) with freeform optics (FO) optical configuration is proposed, which allows the FO to be optimized to maximize uniformity in the field of view of the imager and removes the parallel polarized gloss on the apples. The performance of this CP illumination system was determined experimentally for a set of apples. This cross polarized (CP) illumination system provided a uniformity (U) of 92% and an efficiency (ν) of 90%, while U = 87% and ν = 14% for an ideal dome configuration when illuminating a rectangular target. The simulated imaged apples with assigned optical properties performed better with CP (U=80%) than when using a dome (U=73%) by 7%. Finally, the sensitivity of the design for the light positioning and spectral tolerance are investigated.

As line scanning short wave infrared (SWIR) hyperspectral imaging (HSI) is a growing field in the food industry, it is important to select efficient illumination designs to image contaminants with high contrast and low noise. Illumination systems can efficiently be compared and optimized through the use of ray tracing simulations. However, these simulations provide illumination patterns in absolute radiometric units while HSI systems typically provide relative measurements. To bridge this gap, a supercontinuum laser and monochromator setup was used in this study to calibrate a SWIR HSI imager in spectral radiometric units. For the radiometric calibration, an integrating sphere (IS) was illuminated with the monochromatic laser light, while both a high sensitivity photodiode and the hyperspectral camera were positioned at different ports of the IS to measure the diffuse light synchronously. For each spectral band, the radiance observed by the imager corresponding to a line was detected using image analysis, while the remainder of the image was used to sample the noise of the sensor. Laser power fluctuations were monitored using a power meter coupled with a thermal sensor, allowing for their correction. As these measurements were time consuming, while InGaAs based sensors are very sensitive to thermal drift, the dark current was sampled frequently to avoid noise time drifts. This approach allowed correcting for 6% of temporal noise fluctuations. A per-pixel linear radiometric model was fitted with an R2 of 0:94±0:3 and used to transfer the measured light distribution of a halogen spot with and without a diffuser into absolute radiometric units. This allowed comparing measurements with the results of ray tracing.

This focus issue highlights contributions from authors who presented their research at OSA’s Renewable Energy and the Environment Optics and Photonics Congress held 3-6 November 2013 in Tucson, Arizona, USA. Published version

Freeform optics are limited to design with simplified source models. With a realistic extended source, the resulting design is limited by the ability to hold the source and optic to the desired tolerances. For example, a design is made around the nominal emitter characteristics, such as an encapsulated LED die. This process is called tailoring. Positioning and spectral output can vary appreciably for these emitters. A method to design optics with extended sources with tolerances taken into account is presented. This method uses targeted ray tracing to specify particular points on optical surfaces. In the method presented here, the source is represented instead as a collection of non-ideal sources, each weighted according to the statistics of the dimensional and color variations that are expected in the source. The design is iteratively developed over its extent where each step accounts for the multitude of tolerances potential ray paths through the optics. The end result is to design optics that are tolerant to the predicted level of error, while maintaining the desired level of efficiency and distribution at the target. This method notably samples the differential etendue aspects of the source as it propagates through the system. Upon solution of the iteratively generated reflector control points, an optimization run can be performed to improve performance. We present a wall-wash example to illustrate the method.

This chapter contains sections titled: Introduction Design Tricks Ray Sampling Theory Optimization Tolerancing References

This chapter contains sections titled: What Is Illumination? A Brief History of Illumination Optics Units Intensity Illuminance and Irradiance Luminance and Radiance Important Factors in Illumination Design Standard Optics Used in Illumination Engineering The Process of Illumination System Design Is Illumination Engineering Hard? Format for Succeeding Chapters References

The designation of the merit function for the design of freeform optics using extended sources while including tolerancing with the technique of ray targeting is discussed. Examples are shown.