Sapphire Dome for EO/IR Thermal Imaging

Topic: Sapphire Hemispherical Dome, MWIR Transmission, Thermal Shock, EO/IR Sensor Protection

Overview

Sapphire optical domes are the preferred protective window for mid-wave infrared (MWIR) EO/IR thermal imaging systems. With excellent mechanical hardness, high thermal shock resistance and stable transmission across 0.3–5 μm, sapphire domes defend internal optical sensors from high-speed airflow, sand erosion, rain impact and extreme temperature cycling.

Core Material Advantages

• High Mohs hardness (9): superior abrasion resistance compared to ZnS, ZnSe and fused silica
• Wide transmission band: UV, visible and MWIR infrared
• Low thermal expansion coefficient, strong resistance to rapid temperature change
• Pressure-resistant, suitable for airborne, missile and high-speed surveillance platforms

Common Form Factor & Coating Options

Most sapphire domes are manufactured in hemispherical or hyper-hemispherical geometry. Single-layer or broadband AR coatings for MWIR are widely applied to reduce surface reflection and boost system signal-to-noise ratio. DLC hard coatings can be added for extra anti-erosion performance in harsh outdoor environments.

Typical Application

• Airborne infrared search and track (IRST) systems
• UAV thermal payload protective domes
• Missile seeker EO/IR windows
• Ground-based high-performance thermal surveillance cameras

Key Design Notes for RFQ

When ordering sapphire domes, confirm clear aperture, outer diameter, wall thickness, wavelength band, wedge tolerance, scratch-dig surface grade and coating requirements. Wall thickness must be balanced between mechanical strength and optical distortion.

Dome Wedge Tolerance & Surface Quality Specs

Topic: Dome Wedge Error, Scratch-Dig, Optical Homogeneity, Wavefront Distortion Control

Overview

Wedge tolerance is one of the most critical specifications for hemispherical optical domes. Uncontrolled wedge introduces beam deviation, boresight error and image shift, which severely degrade the pointing stability of EO/IR tracking systems. Surface quality (scratch-dig) determines background noise and laser scatter performance.

Dome Wedge Tolerance Explained

Wedge describes the thickness variation between two sides of the dome wall. It is usually specified in arcseconds. For high-precision seeker domes, typical wedge tolerance ranges from 10 arcsec down to 2 arcsec. Tighter wedge control increases polishing difficulty, inspection cost and lead time.

• General surveillance dome: 10 ~ 30 arcsec wedge
• High-precision tracking seeker dome: 2 ~ 10 arcsec wedge

Scratch-Dig Surface Quality Standard

Scratch-Dig (S/D) follows MIL-PRF-13830B, the dominant standard for military and aerospace optical components. Common grades:

• Commercial grade: 60-40, 40-20
• Aerospace / EO-IR grade: 20-10, 10-5

Smaller scratch and dig numbers mean fewer surface defects and lower stray light inside the optical system.

Related Specs You Need To Match

• Surface figure / irregularity: controls wavefront error
• Optical homogeneity: avoids internal refractive index variation
• Subsurface damage: critical for high-power laser and thermal cycling scenarios

Inspection Method

We test dome wedge with interferometer and goniometer, inspect scratch-dig under darkfield microscope, and provide formal inspection reports for aerospace projects.