Dissertation
Fabrication of next-generation reflection gratings for use in ultraviolet astronomy
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2025
DOI: 10.25820/etd.008016
Abstract
Observations of ultraviolet (UV, 900 – 2000 Å) spectra are imperative to the continued pursuit of a complete, multi-wavelength understanding of the Universe. To enable better measurements for future science goals, technology developments in all components of UV space missions are required. This thesis is motivated, in particular, by the requirements defined for future UV diffraction gratings. Gratings are a critical spectrometer component and are a limiting factor on the maximum possible resolution and efficiency of an instrument. Improvements to UV diffraction gratings can enable observation of important molecular and atomic absorption lines which are historically challenging to observe due to the density of their spacing and the reduction of signal via attenuation through space. Thus, the primary objective of this dissertation is to determine the most appropriate method for fabricating large-area, high-resolution, and highly efficient blazed gratings for use in UV astronomy. To accomplish this goal, fabrication techniques borrowed from the semiconductor industry including electron beam lithography (EBL), nanoimprint lithography (NIL), and potassium hydroxide (KOH) wet-etching were employed. Metrology, both conventional in the field of fabrication (SEM, AFM, and optical microscopy) and unconventional (interferometry) were used. Through an iterative fabrication and metrology process, a wide parameter space of techniques was explored and the most effective methods for data preparation, patterning, and etching were determined. The primary deliverable of this thesis is a cm $\times$ cm grating which is patterned via EBL, transferred, and blazed into silicon to a UV relevant angle via KOH etching. The grating will be characterized via interferometric metrology to determine its limiting resolution and delivered to collaborators for at-wavelength UV efficiency measurements. Results on replication of gratings for large missions via NIL are also detailed. Finally, efforts to model imperfectly fabricated gratings via Fourier optics are reported.
Details
- Title: Subtitle
- Fabrication of next-generation reflection gratings for use in ultraviolet astronomy
- Creators
- Cecilia Fasano
- Contributors
- Casey DeRoo (Advisor)Thomas Folland (Committee Member)Aditi Bhattacherjee (Committee Member)Jasper Halekas (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Physics
- Date degree season
- Spring 2025
- DOI
- 10.25820/etd.008016
- Publisher
- University of Iowa
- Number of pages
- xx, 162 pages
- Copyright
- Copyright 2025 Cecilia Fasano
- Language
- English
- Date submitted
- 04/23/2025
- Description illustrations
- illustrations (some color)
- Description bibliographic
- Includes bibliographical references (page 124-136).
- Public Abstract (ETD)
In order to expand our understanding of the various physical processes occurring across the Universe, astronomers need observational data across a wide domain of energies. Many processes associated with star formation, planetary atmospheres, and the interstellar medium create light that radiates in the ultraviolet (UV) band pass (900 - 2000 A˚ ). In order to parse the information encoded in observed UV light, astronomers often use spectrometers. Spectrometers contain dispersive elements, such as a prism or grating, which take white light and spread it out into its rainbow of colors. In the UV band pass, technological advances to these dispersive elements are required to adequately spread the light and maintain enough signal to draw data-driven conclusions about physical processes occurring throughout the Universe. In particular, the diffraction grating is a technology ripe for improvement.
The following work details the production of next-generation reflection gratings for use in UV astronomy. It makes use of microfabrication and metrology techniques borrowed from the semiconductor industry in order to enable high-resolution and highly-efficient diffraction gratings. Results of these efforts as well as work to model perfect and imperfect diffraction gratings are reported.
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984830923602771
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