SATPC0034980 Tab 07 4 SOW_Redacted.pdf

Statement of Work

1. Objective/Requirements Upgrade the NASA Ames Optical Constants Facility (OCF) F40-UVX microscope by replacing the manual stage with a motorized autofocus stage to allow for more accurate measurements that will enable the determination of optical constants.

2. Characteristics, Scope, and Specs The NASA Ames Optical Constants Facility (OCF) is used to characterize laboratory-generated ORMs produced from gas chemistry and ice chemistry and determine their complex refractive indices (optical constants). The optical constants of a material describe how light is reflected, refracted, and absorbed by the material. They are fundamental input parameters for models used to interpret observational data returned by NASA missions.

Currently, the OCF consists of two instruments:

- a Filmetrics microscope F40-UVX is used to measure the reflection spectra from 0.2 to 1.7 µm, on very small spot size down to 5 µm, of planetary aerosol- and cosmic grain analogs produced in several laboratories at NASA Ames Research Center, NASA Jet Propulsion Laboratory, and NASA Goddard Space flight Center.

The optical constants of the characterized materials can then be determined from these reflection measurements in the UV, visible, and near infrared using a Cauchy model.

- a Thermo Fisher iS50 Fourier Transform Infrared (FTIR) spectrometer is used to measure the transmission spectra from the visible to the far infrared (0.6 to 200 µm) of the same solid materials deposited on different substrates. The optical constants of the characterized solid materials can then be determined from these transmission measurements using a subtractive Kramers Kronig analysis.

A critical step in the data analysis protocol for the mid-IR and far IR optical constants determination from the FTIR spectra is the use of the independent measurement of the optical constants in the visible-near infrared obtained with the F40-UVX Filmetrics measurement to constrain the optical constants at lower wavelengths in the calculation. After conducting this independent measurement for the last 10 years using the services of Filmetrics with their FX-40 UVX, we purchased that instrument in 2023 and installed it in the OCF in early 2024.

Unfortunately, preliminary measurements demonstrated that our F40-UVX which uses a manual stage to focus on the sample was not precise enough to focus on our very specific laboratory-generated solid samples and resulted in reflectance measurements that did not allow calculating the optical constants of the materials accurately.

We therefore need to upgrade our F40-UVX microscope by replacing the manual stage with a motorized autofocus stage like the one we used in the past at the Filmetrics facility.

3. Statement of Work The upgraded motorized autofocus stage of our UV-NIR F40-UVX microscope will allow measuring precise and focused normal incidence reflectance spectra of organic refractory materials produced from gas and ice chemistry from 0.19 to 1.7 µm. From these focused measurements, the optical constants of the samples will be calculated in that wavelength range using a Cauchy model to fit the interference fringes observed in the spectrum. The thickness of the sample will also be determined through the analysis of the reflectance measurements. These optical constants by themselves are a critical input parameter for models used in the interpretation of observational data. The accurate optical constants resulting from focused measurements conducted with the F40-UVX microscope using an autofocus stage at the Filmetrics facility in the past have already been used in the analysis of Titan atmospheric observations from the Cassini mission (Sciamma-O’Brien et al. 2023, PSJ) and Pluto surface observations from the New Horizons mission (Sciamma-O’Brien et al. in prep.)

demonstrating the impact of such measurements.

In addition, the n and k values calculated in the visible and NIR will be critical to constrain the calculation of optical constants from measurements conducted in the NIR to FIR with the OCF FTIR spectrometer. The analytical method involves calculating the k values from transmission measurements conducted with the FTIR from 0.8 to 200 µm then using a subtractive Kramers-Kronig (sKK) calculation to determine n. Our methodology uses machine learning which uses both the n and k values obtained from the OCF F40-UVX measurements to constrain the result on k when fitting the transmission measurements. The sKK method also requires an independent value of n as anchor to constrain the calculation. The n value determined independently with the F40-UVX microscope is used as anchor.

Specifications:

In order to successfully accomplish the measurements required in our research program, i.e., the determination of optical constants in the UV-NIR to (1) provide optical constants in that wavelength range to the community, and

(2) constrain the calculation of optical constants in the NIR-FIR from transmission spectroscopy measurements conducted with the OCF FTIR spectrometer, our OCF reflectance F40-UVX microscope system, which allows measurements in the UV to NIR range and most importantly measurements on very small spot sizes down to 5 µm, needs to be upgraded with a motorized autofocus stage to allow more precise, focused measurements. Because we have successfully used the F40-UVX microscope at the Filmetrics facility for the last 10 years and more recently to confirm the problem we encountered with our instrument came from our manual stage, we know that this upgrade will allow for the accurate measurements needed to determine the optical constants of the materials we want to characterize.

Technical information:

The Filmetrics F40-UVX spectral reflectometer directly measures reflectance of a sample. Based on the material and thickness, an interference pattern is observed. This interference pattern can then be fitted to determine thickness and refractive index. Our F40-UVX manual stage will be replaced with a motorized 10”x10” stage with a 100 mm motorized motion coupled with a motorized autofocus for the objective. A stage arm to adapt microscope objective lens to the stage base will also be put in place. The instrument will then be recalibrated.

Period of Performance: Needed by 06/30/2024

NASA Technical POC: Ella Sciamma-O’Brien Telephone: 408-431-2481 Email: ella.m.sciammaobrien@nasa.gov