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Off-axis three-mirror anastigmat (TMA) telescopes provide excellent correction of aberrations over a large field-of-view in one direction. In a push broom configuration, this lightweight and compact optical configuration enables high-performing imaging. Moreover, passive multi-spectral acquisition can be achieved using a filter stack positioned at the detector vicinity. Stray light is a typical limiting factor for instrument performance and its control is specific to the type of optical configuration. We describe the stray light control and analysis methods in an off-axis TMA. The design intends to control first-order scattering from non-optical surfaces and to block straight shots. This is achieved through usage of elements such as apertures and baffles, both internal and external to the instrument. It will be demonstrated that the aperture stop is a critical element, whose stray light contribution can be controlled with V-groove vanes. Impact of mirrors roughness, a manufacturing physical limitation, is evaluated by modeling the bidirectional scattering distribution function and computing the stray light distribution at the detector for point-like source illumination. We show that the scattering on the different mirrors broaden differently the spot size, as the successive mirrors focus or expand the scattered rays differently. Finally, the ghost reflections inside the filter stack are evaluated and we show that there is no cross-talk between the different channels.

The free-form optical quasilens surface technology was utilized to develop and design a solid transparent plastic optical lens for the LED down light with the narrow angular light distribution requirement in the LED lighting applications. In order to successfully complete the mission, the precise mid-field angular distribution model of the LED light source was established and built. And also the optical scattering surface property of the Harvey BSDF scattering model was designed, measured, and established. Then, the optical simulation for the entire optical system was performed to develop and design this solid transparent plastic optical lens system. Finally, the goals of 40 deg angular light distribution pattern defined at full width half maximum with glare reduced in the areas of interest and the optical performance of nearly 82% light energy transmission optics were achieved for the LED down light illumination.

Over the last two decades, extensive research has been done to improve light-emitting diodes (LEDs) designs. Increasingly complex designs have necessitated the use of computational simulations which have provided numerous insights for improving LED performance. Depending upon the focus of the design and the scale of the problem, simulations are carried out using rigorous electromagnetic (EM) wave optics-based techniques, such as finite-difference time-domain and rigorous coupled wave analysis, or through ray optics-based techniques such as Monte Carlo ray-tracing (RT). The former are typically used for modeling nanostructures on the LED die, and the latter for modeling encapsulating structures, die placement, back-reflection, and phosphor downconversion. This paper presents the use of a mixed-level simulation approach that unifies the use of EM wave-level and ray-level tools. This approach uses rigorous EM wave-based tools to characterize the nanostructured die and generates both a bidirectional scattering distribution function and a far-field angular intensity distribution. These characteristics are then incorporated into the RT simulator to obtain the overall performance. Such a mixed-level approach allows for comprehensive modeling of the optical characteristic of LEDs, including polarization effects, and can potentially lead to a more accurate performance than that from individual modeling tools alone.

Image degradation due to scattered radiation is a serious problem in many short-wavelength (x-ray and EUV) imaging systems. Most currently available image analysis codes require the scattering behavior [data on the bidirectional scattering distribution function (BSDF)] as input in order to calculate the image quality from such systems. Predicting image degradation due to scattering effects is typically quite computation-intensive. If using a conventional optical design and analysis code, each geometrically traced ray spawns hundreds of scattered rays randomly distributed and weighted according to the input BSDF. These scattered rays must then be traced through the system to the focal plane using nonsequential ray-tracing techniques. For multielement imaging systems even the scattered rays spawn more scattered rays at each additional surface encountered in the system. In this paper we describe a generalization of Peterson's analytical treatment of in-field stray light in multielement imaging systems. In particular, we remove the smooth-surface limitation that ignores the scattered-scattered radiation, which can be quite large for EUV wavelengths even for state-of-the-art optical surfaces. Predictions of image degradation for a two-mirror EUV telescope with the generalized Peterson model are then numerically validated with the much more computation-intensive ZEMAX® and ASAP® codes.

We propose a novel interpretation of stray light, which is modeled using a scattering process. For this, a description and simulations based on the bidirectional scattering distribution function (BSDF) are developed. We focus on the particular example of a window closing an optical cavity. Such a window is known to introduce a stray light component that is experimentally very subtle to handle. Our idea is motivated by the uncomfortable observation that for years, the usual estimation of this parasitic contribution (be it for absolute or relative measurements, for visible or IR applications, for field or laboratory experiments, etc.) was based on the rather imprecise and obviously incorrect assumption (nevertheless today a widely used rule of thumb) that the optical window can be approximated by a graybody emitting in its transparency range. This statement obviously goes against Kirchhoff's law of radiation, and can thus not be physically sound. Various typical experimental situations are explored with our model, and a comparison is made with results given by the rule of thumb. This shows some cases of relative concordance. However, the scatter-based model should provide an individually more accurate estimation, as shown by some examples.