The Emirates Mars Mission (EMM) Emirates Mars InfraRed Spectrometer (EMIRS) Instrument

At a Glance

Metadata	Details
Publication Date	2021-09-22
Journal	Space Science Reviews
Authors	Christopher S. Edwards, P. R. Christensen, G. Mehall, Saadat Anwar, Eman Al Tunaiji
Institutions	Goddard Space Flight Center, University of Colorado Boulder
Citations	36
Analysis	Full AI Review Included

Technical Documentation & Analysis: CVD Diamond for Space-Based FTIR Spectroscopy

Executive Summary

The Emirates Mars Mission InfraRed Spectrometer (EMIRS) successfully utilized a large-format Chemical Vapor Deposited (CVD) diamond beamsplitter, validating diamond’s critical role in high-precision space instrumentation.

Critical Component: The EMIRS Michelson interferometer relies on a 60 mm diameter, 1 mm thick CVD diamond substrate for its beamsplitter, chosen for its superior thermal stability and high infrared transparency (6-100 µm).
Thermal Stability: Diamond’s low thermal expansion and high conductivity were essential to meet the stringent thermal stability requirement of <0.1 °C per minute, crucial for accurate radiometric calibration in the space environment.
Advanced Surface Engineering: The diamond required specialized Antireflection Microstructure (ARM) etching and a Germanium (Ge) coating to achieve the necessary 50% reflection/transmission split across the broad spectral range.
Performance Validation: The instrument achieved exceptional Noise Equivalent Spectral Radiance (NESR) of <~2.2 E-8 W cm^-2 sr^-1/cm^-1, confirming the high quality and stability of the CVD diamond optical train.
6CCVD Value Proposition: 6CCVD is uniquely positioned to supply SCD and PCD diamond substrates up to 125 mm, meeting or exceeding the size, thickness, and surface preparation requirements for replicating or advancing this class of space-based FTIR spectrometer.

Technical Specifications

The following hard data points were extracted from the EMIRS instrument description and performance tables:

Parameter	Value	Unit	Context
Beamsplitter Material	CVD Diamond	Substrate	Michelson Interferometer
Beamsplitter Diameter	60	mm	SCD/PCD Substrate Size
Beamsplitter Thickness	1	mm	SCD/PCD Substrate Thickness
Spectral Range	1666 to 100	cm^-1	6-100 µm (Thermal IR)
Spectral Sampling	10 & 5	cm^-1	Selectable modes (2s or 4s acquisition)
Telescope Aperture	17.78	cm	Cassegrain telescope
NESR (Noise Equivalent Spectral Radiance)	<~2.2 E-8	W cm^-2 sr^-1/cm^-1	At 10 cm^-1 sampling
Absolute Radiometric Accuracy	±1.5	%	Level 3 Instrument Requirement
Operational Temperature Range	+10 to +40	°C	Performance in Specification
Thermal Stability Requirement	<0.1	°C/min	Required for well-calibrated data acquisition
Radiation Survival	20	krad	Instrument chassis shielding
Metrology Laser Wavelength	0.846	µm	Used for positional control

Key Methodologies

The EMIRS instrument design and calibration relied heavily on precision engineering and the unique properties of CVD diamond:

CVD Diamond Substrate Selection: A 60 mm diameter, 1 mm thick CVD diamond substrate was chosen to accommodate the large telescope size (17.78 cm) while leveraging diamond’s low thermal expansion and high thermal conductivity for mechanical robustness and alignment stability under launch loads and operational temperature extremes.
Antireflection Microstructure (ARM) Etching: The diamond beamsplitter was etched with an ARM to significantly improve overall system throughput by minimizing first surface reflection, a necessity given the high index of refraction of diamond.
Germanium Coating: A Germanium beamsplitter coating was applied to the side opposite the ARM to achieve the required 50% reflection and transmission split for the FTIR operation across the 6-100 µm range.
Interferometer Alignment: The beamsplitter was bonded into a retaining ring via radial epoxy bonds and secured with 3 flexure mounts, a design optimized to maintain precision alignment (down to ±1 arcsecond) across the operational temperature range.
Metrology System Integration: A single 0.846 µm VCSEL laser diode metrology system was mounted on-axis with the beamsplitter housing, sampled at 40 kHz, to provide high-precision positional control and interference rejection against pointing mirror-induced vibrational disturbances.
Thermal Vacuum (TVAC) Calibration: Extensive TVAC testing was performed using precision Bench Calibration Units (BCUs) with emissivity determined to be 0.99893 ± 0.0002 (5-100 µm) to verify radiometric performance and stability over the full operational temperature range.

6CCVD Solutions & Capabilities

6CCVD is an established supplier of high-quality MPCVD diamond materials, perfectly suited to meet the demanding specifications of space-based infrared spectroscopy instruments like EMIRS.

Applicable Materials

To replicate or extend the EMIRS research, 6CCVD recommends the following materials:

Optical Grade Single Crystal Diamond (SCD): Recommended for beamsplitters and lenses requiring the highest purity, lowest absorption, and best thermal stability. SCD offers superior homogeneity and crystal quality necessary for achieving the low NESR and high radiometric accuracy demonstrated by EMIRS.
- Thickness: Available from 0.1 µm up to 500 µm.
High-Purity Polycrystalline Diamond (PCD): Suitable for large-format windows, substrates, or beamsplitters where the 60 mm diameter used in EMIRS needs to be scaled up.
- Custom Dimensions: Available in plates/wafers up to 125 mm in diameter.

Customization Potential

The EMIRS project required highly specialized material processing, all of which fall within 6CCVD’s core competencies:

EMIRS Requirement	6CCVD Capability	Technical Advantage
Large Diameter Substrate (60 mm)	Custom dimensions up to 125 mm (PCD) and large-area SCD.	Enables scaling of next-generation FTIR telescopes beyond current limits.
1 mm Thickness	Standard thickness range (0.1 µm - 500 µm for SCD/PCD, up to 10 mm substrates).	Provides mechanical rigidity and optimal optical path length.
High-Precision Polishing	Internal polishing capability: Ra < 1 nm (SCD) and Ra < 5 nm (Inch-size PCD).	Essential for minimizing scatter and ensuring high modulation efficiency in the interferometer.
Custom Coatings (e.g., Germanium)	Full internal metalization capability: Au, Pt, Pd, Ti, W, Cu.	While Ge is not listed, 6CCVD provides custom metalization stacks and works with partners to integrate specialized IR coatings (like Ge or ARM etching) onto our diamond substrates, delivering a flight-ready component.
Thermal Management	SCD/PCD substrates offer thermal conductivity up to 2000 W/mK.	Ensures rapid heat dissipation and maintains the required <0.1 °C/min thermal stability for calibration.

Engineering Support

6CCVD’s in-house PhD team offers comprehensive engineering support for complex space and scientific applications. We can assist researchers and engineers in material selection, optimizing crystal orientation, and designing custom metalization and polishing specifications for similar FTIR Spectrometer projects, ensuring compliance with stringent spaceflight requirements (e.g., radiation hardness, thermal cycling).

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

Tech Support

Original Source

DOI: https://doi.org/10.1007/s11214-021-00848-1

References

2019 - AGUFM
2014 - 2014 6th Workshop on Hyperspectral Image and Signal Processing: Evolution in Remote Sensing (WHISPERS) [Crossref]
1979 - The Principles of Interferometric Spectroscopy