Characterization of liquid crystal on silicon SLMs for in-situ Raman imaging for quality control of processed lunar regolith

In-Situ Resource Utilisation (ISRU) will be of great importance for future space missions. Some mission projects will only be possible through the integration of resources gathered during the mission. The use of lunar regolith as a construction and shielding material is particularly important in this context. Sintering or 3D printing of the material is one option. As a contribution to in-situ quality control, this research proposes to realize spatial scanning of a processed regolith material using Crystal on Silicon (LCoS) as spatial light modulators for laser spectroscopy. These spatial light modulators use liquid crystal technology for their design. Unlike mechanical scanners, it has no moving parts subject to failure from shock and vibration. To extend the capabilities of a Raman spectrometer from point measurements to scanning a target surface to evaluate material properties, point mapping, a scanning of the surface with the focused laser, is an essential technology. Focusing and steering a laser for Raman spectroscopy is possible by using Fresnel zone plates (FZP) superimposed by phase gradients mapped on the LCoS, which is an analytically computable and well understood method. In the presented work, a characterization and modelling of a LCoS is carried out with respect to the requirements of this application. Due to the optical properties of LCoS, optical and electrical anisotropy, it can manipulate the phase, amplitude or polarization of optical waves by a controllable birefringence effect. Because of this and the expected robustness against typical space conditions, a large number of further space related application options arise. To assess the suitability for use and the required operational framework, the relevant parameters on the device side and those driven by the mission and measurement problem were identified and represented in a digital optical functional model. The resulting laser spot shape for Raman spectroscopy and the calculated power density were evaluated as target metrics. The digital optical model was integrated into a wavefront simulation using the Angular Spectrum Method (ASM). The model was verified using an analog optical laboratory setup. By combining results from the model and Raman measurements on vitrified regolith simulant material (LRS), a mission envelope of a sample area with a minimum SNR of the Raman measurement could be determined for a realistic scenario. An analysis of the surface using Raman imaging was performed to detect and map in two dimensions the expected mineral classes and an expected sintering classification of the material.

Author dc:creator

• Ritter, Sebastian

Advisor dc:contributor.advisor

• Stoll, Enrico

Licence dc:rights.uri

• https://creativecommons.org/licenses/by/4.0/

Language dc:language.iso

en

Identifier URI

https://doi.org/10.14279/depositonce-21413

OAI identifier oai:identifier

oai:depositonce.tu-berlin.de:11303/22612