The caustic of a set of edge rays is defined as the set of intersection points of adjacent edge rays. For a body having a smooth differentiable contour, the caustic of its edge rays coincides with the contour of the body. Therefore one would assume that by calculating the caustic of the edge rays as they are produced by a 2D concentrator such as a trough, the optimal shape for the absorber, e.g. the minimal surface absorber capable of intercepting all rays, should also coincide with the shape of the caustic. We show that this conjecture is not valid in general, but only if the caustic indeed forms a closed smooth curve. For parabolic trough systems, the caustic intersects and forms closed domains for half rim angles of around 60 degrees and 120 degrees. In both cases the contour is not smooth. Therefore the optimal shape is not given by the domain enclosed by the caustic. We present a general recipe of how to construct minimum surface absorbers for given caustics in 2D and apply this to the case of trough parabolic concentrators. We show practical absorber shapes for parabolic troughs with various rim angles. The optimal contour depends discontinuously on the rim angle. The area of the optimum shape for a rim angle of 90 degrees is 0.72 of the area of the smallest cylindric absorber capable of intersecting all rays.

Cone and trumpet are nonimaging concentrators which do not obey the traditional edge-ray principle. The latter states that edge rays from the source should be transferred to the edge of the target. These concentrators have traditionally been described in terms of the heuristic flow line principle. The edge-ray theorem has been generalized to include nonimaging reflectors with multiple reflections. One includes all multiply reflected rays as an auxiliary domain. The general edge-ray theorem then states that the edge rays to the union of source and auxiliary domain must be reflected to edge of the union of target and auxiliary domain by the first reflection. We show the setup for which cone and trumpet constitute perfect nonimaging concentrators in the light of the generalized edge-ray theorem. We discuss the cases where cones are very good approximations for the solutions of nonimaging problems.

Until now the methods of nonimaging optics have been based on isotropic sources of radiation. In this paper we propose an iterative algorithm that extends the solution of the illumination problem to nonisotropic sources. Suppose the tailored edge-ray design (TED) procedure for the isotropic source S_iso has given us a device with flux map E_iso((theta) ) whereas we really want to achieve the flux map E((theta) ) with the real source S. Now let us multiply the desired flux map by the correction factor f₁((theta) ) proportional to E((theta) )/E_iso((theta) ) and design a new TED for the flux map f₁((theta) ) E((theta) ). The correction factor enhances or reduces the flux map according to the observed discrepancy from the design goal. Repeat the correction procedure until it converges sufficiently close to the desired goal. We test this algorithm in 2D for the case where a nonisotropic virtual source is created by introducing a gap between a tubular real source and an involute reflector. The results show that the iterative algorithm does indeed improve the design; however, the convergence is slow. The iterative algorithm also appears promising for the solution of more complicated problems such as the design of 3D luminaires, designs with reflector materials of imperfect specularity, and designs where edge rays can undergo multiple reflections.

We present a general design method of nonimaging optics that obtains the highest possible concentration for a given absorber shape. This technique, which uses a complimentary edge ray to simplify the geometrical formulism, recovers familiar designs for flat phase space distributions, such as trumpets, and (theta) ₁-(theta) ₂ concentrators. This method is easy to use and handles diverse boundary conditions, such as reflection, satisfying total internal reflection or design within a material of graded index. Presented is a novel two-stage 2D solar collector with a fixed circular primary mirror and nonimaging secondary. This newly developed secondary gives a 25% improvement over conventional nonimaging concentrators.

Using the recently-invented tailored edge-ray concentrator (TERC) approach for the design of compact two-stage high-flux solar collectors--a focusing primary reflector and a nonimaging TERC secondary reflector--we present: 1) a new primary reflector shape based on the TERC approach and a secondary TERC tailored to its particular flux map, such that more compact concentrators emerge at flux concentration levels in excess of 90% of the thermodynamic limit; and 2) calculations and raytrace simulations result which demonstrate the V-cone approximations to a wide variety of TERCs attain the concentration of the TERC to within a few percent, and hence represent practical secondary concentrators that may be superior to corresponding compound parabolic concentrator or trumpet secondaries.

Direct view applications present a number of performance challenges for nonimaging optics. Specific requirements for direct view devices are introduced and several nonimaging components are evaluated in terms of these requirements. Results show that uniformity is the key issue for these applications. Two approaches to improving uniformity are presented.

A small series of nonimaging RXI concentrators designed for concentrating radiation on a 1 mm² photodiode have been manufactured by injection molding of PMMA (polymethyl methacrylate). Their entry aperture diameter is 40 mm and the design acceptance angle is +/- 2.24 degrees. Measurements done at (lambda) equals 890 nm show an optical efficiency of 33.8% and the relative transmission drops from 90% to 10% when the incidence angle varies from 1.2 to 3.4 degrees. A computer model of the concentrator which takes into account the different optical losses shows that optical efficiency is increased up to 57.1 % using silver metallization and (lambda) equals 800 nm. Moreover if photodiode position error is corrected, then the efficiency grows up to 76.2%, and if profile errors are also corrected, then the efficiency reach 88.2%. A more stepped angular transmission requires a most accurate manufacture process.

The analysis of the RX concentrator as an imaging optical system is presented. When the field of view is small (less than 6 degrees full angle), even for concentrations up to 95% of the theoretical maximum, its imaging performance is similar (in MTF terms) to that for normal incidence of an f/3.7 planoconvex spherical lens with optimum defocusing. This imaging capability allows us to use the same RXc with receivers/emitters different from the one of design with no loss of nonimaging quality. Also this feature combined with its capability to concentrate radiation close to the thermodynamical upper bound suggest that the RXc may be an interesting optical device for focal plane array applications.

A new family of 3D ideal nonimaging concentrators with rotational symmetry is presented. The formulation has been done using Lorentz geometry. The flow line concentrator and cone concentrator appear as particular cases with this approach.

The total internal reflection lens has been successfully applied to the efficient collimation of light from incandescent lamps and light-emitting diodes, and it is currently being marketed in several retail products. These circularly symmetric designs operated with relatively small sources. Two new forms of the TIR lens have been designed, and prototypes fabricated, for forming beams from fluorescent lamps. The toroidal fluorescent lamp is formed by circularly sweeping a faceted profile about its outer edge. A 5 inch diameter prototype lens has been diamond turned, and has 80% efficiency. When covering a 2.5 inch toroidal source of 0.25 inch minor diameter, it forms a smooth structureless beam of 40 degrees FWHM. The linear TIR lens has a faceted profile that is extended in cylindrical symmetry. In conjunction with a planar back mirror, a 6 inch diameter lens collects 85% of the light from a 5/8 inch lamp. The full width at half maximum is 30 degrees transversely and 120 degrees longitudinally, in a stripe pattern with twin peaks at +/- 47 degrees parallel to the lamp axis. These designs are applicable to other tubular light sources: discharge lamps, such as aircraft strobes and camera flashlamps, as well as neon lamps. They offer greater efficiency, narrower beamwidths, and much more compact profiles than conventional relfector designs.

Warning lights require very narrow elevation with very good glare control and 360 degree azimuthal coverage. These requirements are ideal for combinations of reflective and refractive nonimaging collectors. The design of such a system is described together with estimates of the required flashlamp power which is quite low compared with existing systems.

The use of two stage optical designs, with reasonably compact devices, is required for being close to the thermodynamic limit to optical concentration of solar collectors. In this work we will present the design and the first test results of a second stage concentrator to be added to the existing primary of the solar furnace of Plataforma Solar de Almeria (PSA), designed to improve the final concentration and to increase its working temperature. Different options have been considered, including CPC, CEC, Trumpet, Cassegrainian, and tailored edge-ray devices. For the geometry of the PSA solar furnace, the tailored edge ray comes closest to the thermodynamic limits. It also is the most suitable from a practical point of view.

Conventional parabolic troughs can be combined with second stage concentrators (SSC), to increase temperature and pressure inside the absorber, making possible the direct production of steam, improving substantially the overall system efficiency and leading to a new generation of distributed solar power plants. To attain this objective, research is needed at the optical, thermodynamic, system control, and engineering levels. In what concerns the receiver of such a system, different practical solutions have been proposed recently and in the past for the geometry of the second stage concentrator: CPC type and others. In this work we discuss these solutions and we propose a new one, 100% efficient in energy collection while reaching a total concentration ratio which is almost 65% of the thermodynamic limit. This SSC has an asymmetric elliptical geometry, rendering possible a smooth solution for the reflectors while maintaining a reasonable size for the receiver.

Often the direction of radiation is important for technological reasons. Melting substances may drip down, or for air receivers, convection may cause instabilities. One obvious solution is to reorient the radiation before concentration with a planar mirror. This is only practical, if the angular spread is considerably less than 45 degrees. Here we propose a section of a torus with reflecting walls to reorient the radiation. The torus, by virtue of its rotational symmetry will not reject any radiation, even if the incoming radiation is close to the thermodynamic limit and thus completely diffuse. A toroid reflector can be easily manufactured from massive material and cooled. It seams a compact and practical device. We calculate the number of reflections and discuss applications of such a device in solar furnaces.

We present an inverse engineering topological-axiomatic approach applicable to nonimaging optical design. The reflective and/or refractive surfaces of the optics are sequentially modified within a given parametrization scheme and a constraint set until performance objective global optimality, evaluated upon a system radiometric model is achieved. This formalism permits the study of non-concave, re-entrant, and piecewise continuous reflector and lens configurations that can constructively exploit multiple reflections for maximal energy transfer, beam shaping, or irradiance redistribution. We derive, under a single-reflection approximation, a new variational principle for constructing axially symmetric reflector forms that maximizes energy transfer and can be extended to provide optimal beam shaping. Our derivation accounts for generally shaped sources with arbitrary radiance distributions and for reflection losses. We compare known edge-ray designs with our solutions and find that the 3D CPC concentrator and the 3D involute CPC reflector (operated in reverse as a projector) can be improved upon. We present a projective design, employing a spherical source which makes use of source re-energization through retroreflection. This design achieves a beam radiance greater than that of the (naked) source and requires a re-entrant component, if a requirement for continuity of the reflective surface is imposed.

The National Renewable Energy Laboratory (NREL) has developed and operates the high-flux solar furnace (HFSF), a 10-kW solar concentrator used for research in solar energy applications. An application of ongoing interest is the heat-bonding of metallic foils to ceramic substrates, a process requiring a highly uniform irradiance distribution over a 10 by 10-cm target area, as well as a mean irradiance of at least 10 W/cm², and a working distance of at least 10-cm from the optics. Science Applications International Corporation (SAIC) and NREL have developed designs for two reflective irradiance redistribtuion guides (IRGs) for use in conjunction with the HFSF, which provide significantly enhanced irradiance uniformity while exceeding the mean-irradiance and working-distance requirements. Irradiance- uniformity levels of 7.2% and 3.1% root-mean-square (RMS) deviation over the target area were achieved by the two IRG designs. The designs were generated using SAICs nonimaging concentrator synthesis code, which employs a global optimization procedure. The HFSF was modeled by means of an optical ray set produced by NREL's solar furnace code. The IRG designs are novel in that they feature re-entrant optics combined with the intentional use of ray paths having different nubmers of multiple reflections within a single reflective optical component in order to achieve the desired irradiance distribution.

Nonimaging optical design techniques have been applied in the illumination industry for many years. Recently however, powerful software has been developed which allows accurate simulation and optimization of illumination devices. Wide experience has been obtained in using such design techniques for practical situations. These include automotive lighting where safety is of greatest importance, commercial lighting systems designed for energy efficiency, and numerous specialized applications. This presentation will discuss the performance requirements of a variety of illumination devices. It will further cover design methodology and present a variety of examples of practical applications for enhanced system performance.

A new simple, compact, and efficient optical device is presented which allows any commercially available laser diode arrays or stacks to longitudinally pump laser materials. A Nd:YVO₄ laser was built and an optical-optical efficiency as high as 50% was demonstrated with a diffraction limited output beam.

The background and idea of a quasi geometrical approach to laser beam propagation in real optical systems was presented. The criterion of laser optics quality based on the concept of M² parameter was proposed and discussed. The appropriate software destined to evaluate laser beam propagation in real optical systems was developed. The scope of the presented work was focused on laser diode optics destined to end pumped solid state lasers. The results of computations were compared with results of intensity distribution measurements in the caustics regions for a few practically realized cases.

The solid core polycrystalline middle infrared region (MIR) optical fiber has no bending loss and has been successfully used as a flexible CO₂ laser guide for medical operations. By using a suitable cooling we have improved the power handling capacity for (phi) 1 mm MIR- fiber to 50 W. However this is far less than the needs for most nonmedical applications, like the 500 W requirements for cork cutting. For this purpose a method was developed to join together several fibers and transmit more power. With a fiber bundle composed of 4 MIR fibers, about 120 W is transmitted (with about 50% efficiency for cw power). Preliminary tests were made to improve the power handling capacity and efficiency, so that, in future, about 500 W CO₂ laser power can be delivered by using a larger fiber bundle.

A new approach to fiber—end microlenses fabrication is described below. The general idea is to combine laser action on glass samples ( for example, fiber ) with such mechanical forces action as stretching, twisting, bending, etc. Several different schemes for combination are suggested and tested'. The next innovation is to observe and to measure microlens geometrical and optical parameters during the laser processing and use the results for control on the microlens production. This allows one to combine producing and measurement ( testing ) operations in time and place , that provide higher productivity and an increase of available elements output. In this way, a number of new fiber—end microlenses such as arc, bulb ( spherical and non-spherical ), and elliptic shapes for beam focusing, various types of side-fiber tools, scatterers ( all—side, half—space, point, etc. ), lens—end fo— cons2 are created. Geometro—optical calculations of these fi— ber optical components ( FOC ) provided the ability to optimize their forms using an optical feed—backs of the laser technological installation.

A compact transversely excited atmospheric nitrogen laser is described. A modified arrangment of an energy storage element in Blumlein excitation circuit significantly decreased the dimensions of the laser. By the use of a small low-inductive sparkgap, an efficiency of energy transfer has achieved value of more than 0.35%. With such a high efficiency the laser may operate at comparatively low charging voltage range of 3kV to 6.5kV, producing pulsed coherent radiation with peak output power of up to 300kW. A low charging voltage has been chosen to avoid electrical breakdown in the air in tropical climates.

The coupling efficiency of light from a GaAs laser into an optical fiber with two-layer spherical end. In this paper, the formulas of calculating the half-acceptance angle of the fiber with two-layer spherical end is derived first. The relationship between the angle (theta) and the refractive angle (gamma) ((theta) ) is derived by ray-tracing techniques. A more complete analysis is done for the restriction by which a ray may not be accepted into the fiber core, namely, waveguide, grazing incidence, and core-aperture restriction. We also calculate the maximum acceptance angle of our fibers and the efficiency of coupling a semiconductor laser beam into an optical fiber with two-layer spherical lens on fiber end. The highly coupling efficiency of up to 80% is arrived.

Fluorescent lamps have been used as a general source of illumination for many years. Today, as LCD technology is growing rapidly, more special fluorescent lamps have been manufactured for use in backlighting of displays, with emphasis on high luminance, corrected color, and long life. Because performance can be significantly affected by many factors during the lamp manufacturing and operation, it is essential to have a better understanding of these factors.