Optics for Earth Observation Instruments
Doctoral thesis, 2019
A free-form three-mirror off-axis telescope was developed for the limb instrument on board the MATS satellite. The f/7.3 (D = 35 mm) design achieved diffraction-limited performance (at 270-772 nm) over a wide field (5.67° × 0.91°) by applying a new design method that corrects for linear astigmatism. Single point diamond turning was used to fabricate the free-form mirrors, which resulted in a telescope with a modulation transfer function of 0.45 at 20 lp/mm. Simulations and measurements were used to assess stray light rejection of the limb instrument. Measurements of a breadboard front baffle with a new type of extremely black coating showed a point source transmittance down to 10-6, which was in excellent agreement with simulations. Detailed modeling predicted a stray light rejection of 10-10-10-4 in the most critical region below the nominal field of view.
Two 874 GHz Schottky mixer receivers with integrated low noise amplifiers, spline horns and low-loss dielectric lenses were developed for ISMAR, which exhibited record-low receiver noise temperatures of 2260-2770 K. Radiation patterns were measured between 868.7-880.0 GHz in a setup capable of resolving side lobes down to 25-30 dB below the main peak. The main beam full-width-half-maximum was in good agreement with simulations and well below the required 5°.
Spline horn antennas at frequencies 120-340 GHz were also developed. An efficient optimization algorithm based on mode matching in circular waveguides was used for all designs, which exhibited Gaussicity values of 98% over bandwidths up to 19%. Far field radiation patterns were measured using a setup for spherical and planar scanning geometries.
A mechanical tolerance analysis was performed for the optical system of STEAMR, which consists of two polarization-separated focal plane arrays, a four-reflector anastigmatic relay optics chain and an off-axis Ritchey-Chretien telescope. Using Monte-Carlo simulations based on ray-tracing and physical optics, an overall reflector alignment accuracy requirement of 100 μm was obtained. Surface distortion analyses of the 1.6 m × 0.8 m primary reflector highlighted the need for an optical system with small mechanical variations in orbit (<30 μm). A relay optics demonstrator showed that alignment accuracies down to 50 μm could be obtained.
In conclusion, the methods for design, manufacturing and characterization presented in this thesis can be used to develop new instruments for Earth observation and related fields.
Chalmers, Microtechnology and Nanoscience (MC2), Terahertz and Millimetre Wave Laboratory
Wide-field off-axis telescope for the Mesospheric Airglow/Aerosol Tomography Spectroscopy satellite
Applied Optics,; Vol. 58(2019)p. 1393-1397
Stray light suppression of a compact off-axis telescope for a satellite-borne instrument for atmospheric research
Proceedings of SPIE - The International Society for Optical Engineering,; Vol. 10815(2018)
Paper in proceeding
Low noise 874 GHz receivers for the international submillimetre airborne radiometer (ISMAR)
Review of Scientific Instruments,; Vol. 89(2018)
A 874 GHz Mixer Block Integrated Spline Horn and Lens Antenna for the ISMAR Instrument
9th European Conference on Antennas and Propagation, EuCAP 2015, Lisbon, Portugal, 13-17 May 2015,; (2015)
Paper in proceeding
THz smooth-walled spline horn antennas: Design, manufacturing and measurements
2016 IEEE Antennas and Propagation Society International Symposium, APSURSI 2016, Fajardo, Puerto Rico, 26 June - 1 July 2016,; (2016)p. 1341-1342
Paper in proceeding
Optical Tolerance Analysis of the Multi-Beam Limb Viewing Instrument STEAMR
IEEE Transactions on Terahertz Science and Technology,; Vol. 4(2014)p. 714-721
Atom and Molecular Physics and Optics
Other Physics Topics
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4569
Chalmers University of Technology
Opponent: Christopher Groppi