We introduce the development process of a new headlight module with perfect colour mixing and sharp upper edge for use as an additional module. Light is nearly collimated (<0.5° cone angle) for a variety of high-power automotive LEDs illuminating up to 1000 m street in front of the car. Key to success is an optimization process not only of the optical elements but also the materials and parameters of the injection molding process. A feedback loop of geometry measurement and simulation of real geometries does lead to acceptable tolerance values and geometry deviations. Finally, the optics in the module needs to be optimized with respect to mechanical tolerances and the inevitable fabrication errors. In this case it resulted in an additional element to be added at the entrance and exit surface of the initially designed optical structure. All steps were accompanied or carried out by simulations with LucidShape and FRED.
The accurate simulation of stray light is essential for the verification of the contrast requirements in optical instruments. In a spectrometer, the scattering from reflective gratings is difficult to characterize while contributing significantly to the overall system stray light and reduction of the spectrometer contrast.
Curved gratings also introduce higher straylight and difficulties in the verification of their straylight compliance. Scatterometers have to be adapted to the grating curvature and thus loose some of their performance.
While measuring a curved sample, this becomes part of the optical system of the scatterometer. For the AlbatrossTT and the CASI the system considering the curved sample has to be adapted to refocus the beam onto the detector. Additional aberrations modify the near angle limit, i.e. the smallest angle where the measured BRDF is higher than the system signature. Theoretical analysis of the scatterometer becomes necessary because the signature of the system is no longer directly measureable.
In addition, 2D BRDF measurement is adequate for characterization of a high polished optical surface or black coatings but deems to be insufficient to characterize all features of the grating scatter function.
3D measurement is essential to verify compliancy in all angular directions.
Small errors in the measurement procedure or measurement setup can lead to different results. Also every scatterometer setup has its own design driven limitations effecting near angle limit and resolution. To create reasonable results those limitations have to be carefully considered.
We present a set of measurements in two different laboratories with different scatterometers.
The accurate simulation of straylight is essential for the verification of the contrast requirements in optical instruments.
In a spectrometer, the scattering from reflective gratings is hardly understood and difficult to characterize while
contributing significantly to the overall system straylight and reduction of the spectrometer contrast. In this article we present an experimental setup for, and measurement results from, the characterization of the bidirectional scattering distribution function (BSDF) of a grating in the scope of the FLORIS project of the ESA FLEX Mission. The grating is an Engineering Model and will be subject to further optimization. Measurement of the BSDF showed approximately a Harvey-Shack profile parallel to the grating grooves, consistent with a dominant contribution from roughness scatter and minor distinctive features. Moreover, we observed distinct straylight peaks out of the diffraction plane, which are called “satellites”. The main challenges in the measurement of grating BSDFs arise from the near angle limit, the determination of the instrument signature and the selection of the appropriate sampling (2D or 3D). Theoretical analysis has been performed to investigate the influence of, and limitations introduced by, the measurement setup combined with the convex curvature of the grating. The next step is to introduce these measured BSDFs into straylight simulation. We have done that by fitting appropriate functions to the measured BSDF and defining them in the optical analysis software ASAP as a user-defined BSDF.
The Meteosat Third Generation (MTG) program will ensure the continuity and enhancement of meteorological data from geostationary orbit as currently provided by the Meteosat Second Generation (MSG) system. OHB-Munich, as part of the core team consortium of the industrial prime contractor for the space segment Thales Alenia Space (France), is responsible for the Flexible Combined Imager – Telescope Assembly (FCI-TA) as well as the Infrared Sounder (IRS).
Gary L. Peterson (Breault Research Organization) presented a simple analytical model for in- field stray light evaluation
of axial optical systems. We exploited this idea for more complex optical instruments of the Meteosat Third Generation
(MTG) mission. For the Flexible Combined Imager (FCI) we evaluated the in-field stray light of its three-mirroranastigmat
telescope, while for the Infrared Sounder (IRS) we performed an end-to-end analysis including the front
telescope, interferometer and back telescope assembly and the cold optics. A comparison to simulations will be
presented. The authors acknowledge the support by ESA and Thales Alenia Space through the MTG satellites program.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.