This PDF file contains the front matter associated with SPIE Proceedings Volume 12220, including the Title Page, Copyright information, Table of Contents, and Conference Committee Page.

A Light Tube is a geometric arrangement of two areas with their center points separated by a certain distance. These can be of equal or different size; they can be oriented perpendicularly to the center line (i.e. face each other) or can be tilted. There are no physical tube walls, only geometry. Important cases are light tubes formed by object and entrance pupil or source and target areas. Light tubes showed up in various aspects of imaging and nonimaging optics, e.g. K¨ohler’s illumination principle, Hottel’s formula in thermal radiation, Zimmer’s Geometrical Optics, and Ploke’s “Lichtf¨uhrungseinrichtungen” (light guides). Besides presenting such examples, we elaborate on optical design around light tubes: we investigate whether and how imaging or non-imaging systems can connect two equal ´etendue light tubes, and we discuss how optics within a light tube (between a given source and target areas) can maximize collection efficiency.

Tailoring freeform surfaces for illumination with point sources is an established method to generate near-arbitrary illuminance distributions with high detail using a single freeform surface. Real, non-laser sources are not point sources, however. Replacing a point source in a tailored freeform system with an extended source blurs the point-source distribution. Accordingly, extended sources are often treated as a perturbation within a pointsource tailoring algorithm, which may work well for small sources. However, important applications like street lighting, wall-washing and automotive front lighting require some peak intensity in certain directions, which can only be achieved with a given source luminance when nearly the whole aperture contributes to that peak intensity. Then, the tenet of point source tailoring – a one-to-one relation of surface points to target points – breaks down. In this paper, we embrace extended sources instead of treating them as a perturbation: Illuminance at several target points is computed by integrating the luminance of the virtual source image over its finite projected solid angle in a noise-free, non-Monte-Carlo way. The freeform surface is parametrized; the shape of the distorted virtual source image, and thus the illuminance at the target points, becomes a function of the freeform surface parameters, leading to a system of nonlinear equations, which we solve iteratively. Using a solved-example problem, we also give first answers to whether solutions exist and are unique.

A new type of prescribed illumination optic is presented that leverages newly available freeform gradient-index (F-GRIN) media. Using F-GRIN to impart freeform optical in fluence, only plane-parallel surfaces are required, and by additive manufacturing, designs can directly incorporate gradient discontinuities. The design process is surveyed, and several designs are demonstrated for generating both binary and grayscale illumination targets from a point source. Fabricated designs are presented for the first time, verifying that F-GRIN optics present a flexible, new way of generating a prescribed illumination distribution.

Conventional line-focus solar concentrators are limited by the 2D concentration limit, two orders of magnitude lower than the three-dimensional limit. This leads to low concentration ratios and strict manufacturing tolerances. It has been shown that by eliminating the continuous translational symmetry of these systems, it is possible to go beyond the 2D limit while maintaining the linear geometry of a line focus. We demonstrate that one way to break this symmetry is through ´etendue rotation, and we present two new concentrator configurations based on this insight. The first configuration uses an ´etendue rotating retroreflector array to boost the concentration of a parabolic trough. Ray-tracing simulations show that this configuration can achieve very high geometric concentration ratios or very high acceptance angles (1484 x at ±9mrad acceptance angle, or 25 x at −70mrad). However, this configuration requires two-axis external solar tracking. To get around this, we demonstrate a second configuration that uses an ´etendue rotating lens array with tracking integration. We demonstrate a design that achieves a geometric concentration of 146x at a ±9mrad, with a simulated average yearly efficiency of 94.9% when used with conventional horizontal single-axis external tracking at an installation latitude of 30°. The extra constraints of the tracking integration gives this design a more modest concentration ratio, but it is still higher than the 2D concentration limit and more than three times as high as the concentration of a parabolic trough evaluated under the same conditions. We believe that these new configurations show that the design landscape for line-focus solar concentrators can be widened, and that a practical high-concentration line-focus concentrator may be within reach.

Geometrical vector flux ~ J, is a well stablished technique in nonimaging optics. The main properties of the vector ~ J, by one side is that the field lines and flux tubes of ~ J provides the geometry for ideal concentrators and, to other, the components of ~ J at any point P are proportional to the irradiance at that point. The latest one means that, at any point P, the Jz component is proportional to the irradiance incident at P upon the XY plane. Lorentz geometry was applied to nonimaging optics by M.Gutierrez et al.5 were they showed that using Lorentz technique it is possible to obtain the field lines and flux tubes of ~ J. In this paper we shown that it is also possible to obtain the modulus of ~ J and then the irradiance pattern produced by Lambertian sources using Lorentz geometry formalism.

Compound Parabolic Concentrators (CPCs) are non-imaging concentrators designed to focus and intensify incoming light. During high-intensity laser plasma interactions, it is possible to accelerate a high energy (> MeV) electron beam. This electron beam can be used to generate many secondary forms of radiation. The intensity of the laser plays a significant role in many of the key aspects of the electron acceleration, such as the temperature of the Boltzmann-like energy distribution. Here we demonstrate experimentally that CPCs are beneficial to the acceleration of high energy electrons through the process of intensification.

Utilizing flow line or geometric vector field analysis we have arrived at an alternative explanation of why nonimaging optics is capable of achieving solar concentration and effective illumination with close to 2nd law of thermodynamics limit. In this paper we will discuss the minimum setup or configuration of such a nonimaging optics problem and how flow line field provides a different perspective on how nonimaging optics work.

Prism-shaped, light-extraction elements that are removed from—or added to—solid light guides are often used in signal and interior automotive lighting systems. These elements can be optimized to provide spatially-uniform (or other desired spatial distribution) light whose angular centroid is aimed in appropriate directions to meet intensity specification test points [1], [2]. Recent work [3] has also examined the efficiency of these lamps and found that face curvature and prism surface width can significantly affect the shape of the intensity distribution, and therefore be used to increase the lamp efficiency, by matching the shape of the intensity test point distribution more closely. Changing the shape of the intensity distribution can also be used to build in more design tolerance. In this work, we first demonstrate how the efficiency of a Daytime Running Lamp (DRL) luminaire can be improved using a trial-and-error approach and the lessons learned in [3]. Next, we implement an optimization approach for the profile W parameter (to change the prism surface width locally) and spread parameter and demonstrate that the optimizer can find a slightly better solution than the trial-and-error approach using the same starting point (620 required lumens improved to 414 lumens). Finally, we use the optimization approach to design two other important design forms; first without and then with efficiency parameters included in the optimization. In both cases, we demonstrate improved efficiency designs: a symmetric circular DRL improved 394→325 required lumens, and a non-symmetric eyebrow DRL improved 365→245 required lumens.

We have designed a Linear Fresnel Reflector (LFR), with potential applications for solar concentration, by using an exact ray tracing. We have mathematically parameterized the slopes of LFR to provide predefined areas of light concentration. LFR planar mirrors were calculated in such a way that an incident plane wavefront can be focused at minimum absorber area. Finally, prototypes of LFR were manufactured by using a 3D printer, considering a set of small sized mirrors to join up with the aim of producing a linear focus.

We present a miniature freeform lightguide for sensing applications, designed according to the principles of the flow-line method from Nonimaging Optics. The optic is obtained by combining two 2D flow-line concentrators in a curved monolithic piece, achieving 45° half-acceptance angle and 40° beam steering in a very compact volume (about 1.3 x 2.0 x 20 mm³). We show how the initial design has been adjusted after a thorough tolerance analysis and describe its fabrication through plastic injection molding. The design of the mold involves a non-standard 3D-puzzle approach, which allows uniform high optical quality and minimizes the fillet radius on the optic.

This research presents the static flexible concentrator photovoltaics (Static CPV) systems for electric vehicles (EVs). The CPV system includes solid CPC, 3‐junction solar cells, and a crystalline Si cell. Direct sunlight with an incident angle satisfying the acceptance angle of the solid CPC is focused on the 3‐junction solar cells, while diffuse sunlight is collected by crystalline Si cells. When direct sunlight and diffused sunlight have an incident angle greater than the acceptance angle of the CPC, they will leak out of the solid CPC and be collected by the Si solar cell. This structure allows to manufacture of Static CPV with a geometrical concentration ratio of 4× for 3‐junction cells, The module was designed using the commercial optic simulation software LightTools™, the simulation results show that the module can achieve 25% annual efficiency, moreover, it can be flexible to meet the requirement of car roof application.

Concentrating Solar Power (CSP) generation is an attractive option for low-emission power generation; however, the high costs of thermal storage associated with concentrating solar create a large barrier for their use and adaptation into modern life. Lowering their operation costs, while maintaining high thermal storage and transfer performance is essential. Solid particle-based heat exchange systems can reduce CSP cost but are often less efficient. Efforts to increase their performance have led to use of binary size particle mixes. Presented is an optical-based thermal analysis technique used to measure near-wall thermal conductivity of particle beds essential in determining their heat exchanger efficiency. Modulated Photothermal Radiometry is used to make dynamic temperature measurements, allowing for the extraction of the most relevant thermal properties like thermal conductivity, specific heat, and effusivity. The system uses a modulated laser source causing a damped periodic heat flux, resulting in a frequency and thermal property dependent surface temperature, of which is measured using radiometry. Lock-In techniques are used to extrapolate the amplitude of the signal. Plotting the amplitude against the root angular frequency allows for effusivity measurement by ratio to a known sample. Using specific heat measurements from literature and density measurements, the thermal conductivity of the particle mixes can be calculated. The simplicity of MPTR to probe through the depth of the bed is ideal for use in CSP for dynamic thermal performance monitoring.

The regulation of the spatial energy distribution of a light source with high efficiency is a classical and challenging issue in the field of nonimaging optics. In this work we derive the partial differential equation that the metasurface phase function must satisfy to produce a desired illumination pattern by refraction, it is a Monge-Ampére equation, and with the specific boundary conditions, the problem can be solved with a numerical tool.