Dr. Lars H. Erdmann Profile

Dr. Lars H. Erdmann

at Carl Zeiss Jena GmbH

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Publications (8)

PROCEEDINGS ARTICLE | June 15, 2018

Optical gratings with low wavefront aberrations and low straylight for enhanced spectroscopical applications

Proc. SPIE. 10692, Optical Fabrication, Testing, and Metrology VI

KEYWORDS: Optical components, Optical design, Holography, Satellites, Spectrometers, Manufacturing, Wavefront aberrations, Photoresist materials, Optics manufacturing, Diffraction gratings

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The sensing performance of spectroscopic systems can be enhanced by improving their optical core-element: the optical grating. in particular for imaging spectrometers - especially Hyper-Spectral Imagers - beside the polarization sensitivity and efficiency the imaging quality of the diffraction grating is an important parameter. Optical elements within the spectrometer are manufactured while aiming on lowest wave front aberrations. Thus, least imaging aberration quality of the grating is required not to limit the overall imaging quality of the instrument. Different types of spectrometers (Offner, Czerny Turner) lead to different requirements for the grating surface figure. Beside wavefront aberrations the straylight of gratings will impact the optical performance of spectrometers too. Both parameters are crucially influenced by the manufacturing processes. During the manufacturing process of the grating substrate, a sequence of polishing steps can be applied in order to minimize the wavefront aberrations and roughness. Chemical assisted polishing in combination with classical techniques lead to least surface roughness. A good practice for the manufacturing of aspheres and freeform substrates is the generation of an initial figure close to the final shape only by a classical process, followed by a careful applied aspherization. The imaging performance (wavefront and straylight) of the grating is also optimized due to the recording setup of the holography - including all employed optics for the wave forming. Holographically manufactured gratings with adapted wave forming functions are used for transmission or reflection gratings on different types of substrates like prisms, convex and concave spherical and aspherical surface shapes, up to free-form elements. Numerous spectrometer setups (e.g. Offner, Rowland circle, Czerny-Turner system layout) work on the optical design principles of reflection gratings. All those manufactured gratings can be coated with adapted coatings to support their reflection or transmission operation. The present approach can be applied to manufacture high quality reflection gratings for the EUV to the IR. In this paper we report our results on designing and manufacturing high quality gratings based on holographic processes in order to enable diffraction limited complex spectrometric setups over certain wavelength ranges. Most beneficial is an optimization of the grating during spectrometer design phase while regarding the manufacturing as well. However, the initial optical design approach will show that gratings can be tailored to the specific requirements of the spectrometer (in order to enhance the imaging quality). The enhancement of the optical performance may lead to a specific wavefront shape after the grating element. this special capability for aberration reduction can be defined to the grating during the holographic process. In general, holography enables to manufacture gratings with a specific and adapted wavefront error compensation functions. Beside the results of low aberration gratings the results on straylight measurements will be presented. Recent results and optimization will be shown.

PROCEEDINGS ARTICLE | November 17, 2017

Space applications: monolithic diffraction grating elements from EUV to NIR spectral range

Proc. SPIE. 10563, International Conference on Space Optics — ICSO 2014

KEYWORDS: Near infrared, Diffraction, Optical design, Holography, Polarization, Spectroscopy, Manufacturing, Extreme ultraviolet, Optics manufacturing, Diffraction gratings

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PROCEEDINGS ARTICLE | September 29, 2017

Instrument pre-development activities for FLEX

Proc. SPIE. 10423, Sensors, Systems, and Next-Generation Satellites XXI

KEYWORDS: Reflection, Imaging systems, Spectroscopy, Luminescence, Fluorescence spectroscopy, Clouds, Vegetation, Spectral resolution, Lawrencium, Absorption

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The FLuorescence Imaging Spectrometer (FLORIS) is the payload of the FLuorescence Explorer Mission (FLEX) of the European Space Agency. The mission objective is to perform quantitative measurements of the solar induced vegetation fluorescence to monitor photosynthetic activity. FLORIS works in a push-broom configuration and it is designed to acquire data in the 500–780 nm spectral range, with a sampling of 0.1 nm in the oxygen bands (759–769 nm and 686- 697 nm) and 0.5–2.0 nm in the red edge, chlorophyll absorption and Photochemical Reflectance Index bands. FLEX will fly in formation with Sentinel-3 to benefit of the measurements made by the Sentinel-3 instruments OLCI and SLSTR, particularly for cloud screening, proper characterization of the atmospheric state and determination of the surface temperature. The instrument concept is based on a common telescope and two modified Offner spectrometers with reflective concave gratings both for the High Resolution (HR) and Low Resolution (LR) spectrometers. In the frame of the instrument pre-development Leonardo Company (I) has built and tested an elegant breadboard of the instrument consisting of the telescope and the HR spectrometer. The development of the LR spectrometer is in charge of OHB System AG (D) and is currently in the manufacturing phase. The main objectives of the activity are: anticipate the development of the instrument and provide early risk retirement of critical components, evaluate the system performances such as imaging quality parameters, straylight, ghost, polarization sensitivity and environmental influences, verify the adequacy of critical tests such as spectral characterization and straylight, define and optimize instrument alignment procedures. Following a brief overview of the FLEX mission, the paper will cover the design and the development of the optics breadboard with emphasis on the results obtained during the tests and the lessons learned for the flight unit.

PROCEEDINGS ARTICLE | September 19, 2017

Imaging gratings: Technology and applications for spectrometers (Conference Presentation)

Proc. SPIE. 10402, Earth Observing Systems XXII

KEYWORDS: Optical design, Holography, Polarization, Reflection, Spectrometers, Manufacturing, Wavefronts, Wavefront aberrations, Infrared spectroscopy, Diffraction gratings

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PROCEEDINGS ARTICLE | October 8, 2015

Enhanced monolithic diffraction gratings with high efficiency and reduced polarization sensitivity for remote sensing applications

Proc. SPIE. 9641, Optics in Atmospheric Propagation and Adaptive Systems XVIII

KEYWORDS: Optical design, Prisms, Holography, Polarization, Etching, Spectroscopy, Remote sensing, Manufacturing, Binary data, Diffraction gratings

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Spectral imaging systems lead to enhanced sensing properties when the sensing system provides sufficient spectral resolution to identify materials from its spectral reflectance signature. The performance of diffraction gratings provides an initial way to improve instrumental resolution. Thus, subsequent manufacturing techniques of high quality gratings are essential to significantly improve the spectral performance. The ZEISS unique technology of manufacturing real-blazed profiles and as well as lamellar profiles comprising transparent substrates is well suited for the production of transmission gratings. In order to reduce high order aberrations, aspherical and free-form surfaces can be alternatively processed to allow more degrees of freedom in the optical design of spectroscopic instruments with less optical elements and therefore size and weight advantages. Prism substrates were used to manufacture monolithic GRISM elements for UV to IR spectral range. Many years of expertise in the research and development of optical coatings enable high transmission anti-reflection coatings from the DUV to the NIR. ZEISS has developed specially adapted coating processes (Ion beam sputtering, ion-assisted deposition and so on) for maintaining the micro-structure of blazed gratings in particular. Besides of transmission gratings, numerous spectrometer setups (e.g. Offner, Rowland circle, Czerny-Turner system layout) working on the optical design principles of reflection gratings. This technology steps can be applied to manufacture high quality reflection gratings from the EUV to the IR applications with an outstanding level of low stray light and ghost diffraction order by employing a combination of holography and reactive ion beam etching together with the in-house coating capabilities. We report on results of transmission gratings on plane and curved substrates and GRISM elements with enhanced efficiency of the grating itself combined with low scattered light in the angular distribution. Beside of the results of straylight measurement the actual results on improving efficiency and lowering the polarization sensitivity for transmission gratings will be discussed on theoretical simulations compared to measured data over the entire wavelength range.

PROCEEDINGS ARTICLE | September 14, 2015

Optical gratings and grisms: developments on straylight and polarization sensitivity improved microstructures

Proc. SPIE. 9611, Imaging Spectrometry XX

KEYWORDS: Optical design, Prisms, Holography, Polarization, Reflection, Etching, Spectroscopy, Ultraviolet radiation, Manufacturing, Diffraction gratings

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Spectral imaging systems lead to enhanced sensing properties when the sensing system provides sufficient spectral resolution to identify materials from its spectral reflectance signature. The performance of diffraction gratings provides an initial way to improve instrumental resolution. Thus, subsequent manufacturing techniques of high quality gratings are essential to significantly improve the spectral performance. The ZEISS unique technology of manufacturing real-blazed profiles comprising transparent substrates is well suited for the production of transmission gratings. In order to reduce high order aberrations, aspherical and free-form surfaces can be alternatively processed to allow more degrees of freedom in the optical design of spectroscopic instruments with less optical elements and therefore size and weight advantages. Prism substrates were used to manufacture monolithic GRISM elements for UV to IR spectral range. Many years of expertise in the research and development of optical coatings enable high transmission anti-reflection coatings from the DUV to the NIR. ZEISS has developed specially adapted coating processes (Ion beam sputtering, ion-assisted deposition and so on) for maintaining the micro-structure of blazed gratings in particular. Besides of transmission gratings, numerous spectrometer setups (e.g. Offner, Rowland circle, Czerny-Turner system layout) working on the optical design principles of reflection gratings. This technology steps can be applied to manufacture high quality reflection gratings from the EUV to the IR applications with an outstanding level of low stray light and ghost diffraction order by employing a combination of holography and reactive ion beam etching together with the in-house coating capabilities. We report on results of transmission, reflection gratings on plane and curved substrates and GRISM elements with enhanced efficiency of the grating itself combined with low scattered light in the angular distribution. Focusing on the straylight characteristic a measurement of the actual straylight level, preferably with extremely high precision, was performed and will be discussed in this paper. Beside of the results of straylight measurement the actual results on improving efficiency for transmission and reflection gratings will be discussed on theoretical simulations compared to measured data over the entire wavelength range.

PROCEEDINGS ARTICLE | October 7, 2014

Monolithic diffraction grating elements for remote sensing applications

Proc. SPIE. 9241, Sensors, Systems, and Next-Generation Satellites XVIII

KEYWORDS: Diffraction, Holography, Polarization, Remote sensing, Spectrometers, Manufacturing, Imaging spectroscopy, Ion beams, Optics manufacturing, Diffraction gratings

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PROCEEDINGS ARTICLE | September 23, 2013

Fabrication of low straylight holographic gratings for space applications

Proc. SPIE. 8870, Imaging Spectrometry XVIII

KEYWORDS: Diffraction, Optical design, Holography, Polarization, Spectrometers, Manufacturing, Optical testing, Stray light, Optics manufacturing, Diffraction gratings

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