APPLICATION NOTE

Selecting Optical Components for High-Vacuum and Cleanroom Environments

Q: What makes an optic 'vacuum-compatible'?

Low outgassing, stable dimensions, vacuum-compatible coatings. Fused silica, sapphire, and most glasses are inherently compatible. Mounting hardware and adhesives must also be vacuum-rated.

Q: Can standard optics be used in Class 100 cleanrooms?

Yes, if properly cleaned and packaged. Specify 'cleanroom compatible' for cleanroom-grade cleaning and packaging.

Q: What is bake-out and which optics survive it?

Heating to 150-300°C to drive off adsorbed gases. Fused silica, sapphire, CaF2 survive standard bake-out. BK7 survives <200°C.

Q: How to prevent contamination in vacuum?

Clean assembly protocols: powder-free gloves, cleanroom wipes, laminar flow hoods. Avoid adhesives near optical surfaces.

Q: What outgassing spec for space optics?

ASTM E595: TML < 1.0%, CVCM < 0.10%. Most glasses and oxide coatings meet this. Request lot-specific test data.

Q: How does vacuum affect optical adhesives?

Standard epoxies outgas significantly. Use space-qualified epoxies (EPO-TEK 353ND-T), glass frit, or mechanical retention.

Guide to specifying optics for vacuum chambers, cleanrooms, and controlled environments. Covers outgassing, bake-out compatibility, and contamination control.

VacuumCleanroomSemiconductorSpace Optics

Published: August 23, 2026By PhotonEdge Engineering Team~8 min read

Why Standard Optics Fail in Vacuum

Every material contains adsorbed gases. In vacuum, these outgas and become contaminants — raising chamber pressure and depositing volatile condensables on nearby optics.

Key Insight: The substrate is rarely the problem — it's coatings, adhesives, markings, cleaning residues, and packaging that introduce contaminants. Specify the entire assembly as vacuum-compatible.

Vacuum-Compatible Materials

Material	TML	CVCM	Bake-out	Verdict
Fused Silica	<0.1%	<0.01%	300°C	Excellent
Sapphire	<0.05%	<0.01%	400°C	Excellent
BK7	~0.3%	<0.05%	200°C	Good
Standard epoxy	5-20%	1-5%	80°C	Not compatible
EPO-TEK 353ND-T	<0.5%	<0.05%	150°C	Space-grade

TML/CVCM per ASTM E595. Request lot-specific data for critical applications.

Cleanroom & Coatings

Oxide coatings (SiO2, Ta2O5, Al2O3, HfO2): Excellent vacuum compatibility. Dense, low porosity.

Fluoride coatings (MgF2, CaF2): Acceptable but more porous. Request post-coating bake-out.

Avoid: Organic coatings, epoxy edge seals, evaporation-deposited coatings without ion assist.

Contamination Control

Wear powder-free nitrile gloves — never bare hands
Clean with electronic-grade IPA, applied with cleanroom wipes
Avoid adhesives within 5mm of optical clear aperture
Pre-bake optics at max rated temperature before assembly
Install optics last, immediately before system pump-down

Summary: Vacuum optics require attention to the full chain — substrate, coating, cleaning, adhesive, and packaging. Fused silica with oxide coatings is the safest choice. Always specify vacuum level and bake-out temperature.

Frequently Asked Questions

Common questions from optical engineers and procurement teams.

What makes an optic 'vacuum-compatible'?+

Low outgassing, stable dimensions, vacuum-compatible coatings. Fused silica, sapphire, and most glasses are inherently compatible. Mounting hardware and adhesives must also be vacuum-rated.

Can standard optics be used in Class 100 cleanrooms?+

Yes, if properly cleaned and packaged. Specify 'cleanroom compatible' for cleanroom-grade cleaning and packaging.

What is bake-out and which optics survive it?+

Heating to 150-300°C to drive off adsorbed gases. Fused silica, sapphire, CaF2 survive standard bake-out. BK7 survives <200°C.

How to prevent contamination in vacuum?+

Clean assembly protocols: powder-free gloves, cleanroom wipes, laminar flow hoods. Avoid adhesives near optical surfaces.

What outgassing spec for space optics?+