Custom Infrared Domes: Specifications for an Accurate RFQ

How to Specify a Custom Infrared Dome: An Engineering Guide for OEM Buyers

A custom infrared dome must protect the optical assembly while allowing the system to perform as intended. Achieving both goals requires a specification that connects the dome’s geometry, material, coating and mounting interface to the application.

An enquiry such as “We need a 100 mm infrared dome with high transmission” is a useful starting point. However, it leaves several questions unanswered: Is 100 mm the outside diameter or clear aperture? Which wavelength band must pass through the dome? At what angles should the coating perform?

This guide explains what to include in an infrared dome specification so manufacturers can provide a meaningful feasibility review and quotation.

1. Start with the Application and Operating Band

Describe what the dome will protect and how the optical system will use it.

For example, a stationary industrial thermal sensor may have different requirements from a wide-angle imaging system exposed to weather. A laser application introduces additional questions about absorption, beam propagation and power handling.

Include the following information:

• Sensor or optical-system type.
• Required wavelength band or individual wavelengths.
• Field of view.
• Operating temperature range.
• Indoor or outdoor installation.
• Any visible-light alignment or imaging requirement.

The required band should be stated numerically. Terms such as “infrared,” “broadband” and “thermal imaging” are too broad to serve as acceptance criteria.

2. Define the Dome Geometry Clearly

Outside diameter alone does not fully define a dome.

A hemispherical shell, a shallow spherical cap and a dome with a mounting flange may have the same outside diameter but require different manufacturing methods and inspection arrangements.

Check that the dimensions are consistent. For a concentric spherical shell, the wall thickness follows from the difference between the outside and inside radii.

If a CAD model and drawing are both supplied, identify which document controls manufacturing and include the revision number.

3. Select the Material Against the Complete Requirement

Material selection should consider the operating band, allowable absorption, environmental exposure and manufacturing feasibility.

If the material has already been selected, identify its grade. A designation such as “ZnS” may leave uncertainty about whether standard CVD or multispectral material is required.

If alternatives are acceptable, describe the priorities. For example:

Material alternatives may be proposed, provided the finished dome meets the specified transmission, imaging and environmental requirements.

This gives the manufacturer room to suggest a practical option without changing the performance target.

Avoid treating a material’s published transmission range as a guaranteed transmission specification for the finished dome.

4. Turn “High Transmission” into a Measurable Requirement

A transmission requirement should identify the wavelengths, acceptance limits and measurement conditions.

For illustration, an RFQ could state:

Please propose a finished-component transmission specification covering our operating band, including minimum transmission at the critical wavelengths and the proposed measurement method.

Once the design is established, replace this preliminary request with agreed numerical limits.

Clarify whether the requirement concerns:

• Minimum transmission at every wavelength within a band.
• Average transmission across a defined band.
• Transmission at selected wavelengths.
• The substrate alone or the coated finished component.
• Normal incidence or a range of incidence angles.

These definitions can produce different coating designs and quotation results. Agreeing on them early helps avoid a component passing one interpretation of the specification while failing another.

5. Specify AR Coating for the Dome’s Actual Optical Paths

An anti-reflection coating specification should include more than a wavelength range.

The angles at which rays cross the dome depend on the dome geometry and the position of the optical system. A coating evaluated only at normal incidence may not represent performance across the complete field of view.

Provide:

• Required spectral bands.
• Incidence-angle range on the dome surfaces.
• Polarization requirements, where relevant.
• Surfaces to be coated.
• Transmission or reflection limits.
• Required coating durability and cleaning conditions.

Label the surfaces consistently—for example, S1 for the outside and S2 for the inside—and use the same labels on the drawing and coating specification.

For a wide-angle system, share the relevant optical layout or ray-angle information if available.

6. Separate Surface Appearance from Optical Performance

Scratch-dig requirements describe surface imperfections. They do not, by themselves, establish the dome’s effect on image quality.

Depending on the application, additional requirements may include surface figure, transmitted wavefront error, surface roughness or an agreed system-level imaging test.

Every numerical optical requirement should have a clear inspection basis. For example, a wavefront specification should identify the test wavelength, clear aperture, configuration and reported metric.

Specify the requirements that affect the application. Unnecessary precision can increase cost without improving useful system performance.

7. Define the Mounting Interface and Environment

A dome should be reviewed together with its housing.

The mounting arrangement determines where forces act, how the component is located and which areas must remain free of coating or adhesive.

Provide a housing section drawing when possible, showing the seating surface, retaining arrangement, seals and intended contact areas.

Environmental requirements should also be specific. “Outdoor use” may involve temperature cycling, moisture, cleaning, dust or abrasion, but these are separate conditions and should not be assumed to have the same acceptance test.

If a pressure differential applies, specify the operating and test conditions. Pressure capability must be assessed for the complete geometry and mounting arrangement; it cannot be established from material name or wall thickness alone.

8. Agree on Inspection Before Production

Inspection planning should begin during quotation, especially for curved optical components.

Ask the manufacturer to confirm how critical dimensions and optical requirements will be verified. Where direct measurement of the finished dome is limited, agree on any alternative method before placing the order.

The agreed documentation may include:

• Material identification or certification.
• Dimensional inspection results.
• Surface-quality inspection.
• Spectral transmission results.
• Applicable optical test results.
• Part or batch traceability.

If witness samples are proposed for coating verification, clarify which properties they demonstrate and which requirements still apply to the finished dome.

9. Use Prototypes to Resolve Defined Questions

A prototype order is most useful when it has a clear evaluation plan.

Before ordering, identify what the samples must demonstrate: mechanical fit, spectral performance, image quality, sealing compatibility or another requirement.

After testing, record the results against the drawing revision and sample identification. Any changes should be incorporated into the controlled specification before a repeat or production order.

This creates a clearer path from the first sample to a reproducible production component.

Custom Infrared Dome RFQ Checklist

Before sending your enquiry, check that it includes:

Discuss Your Infrared Dome Project with Felix Glass

A complete drawing is helpful, but an early enquiry can also identify which specifications still need to be defined.

Send Felix Glass your available drawing, operating wavelengths, approximate dimensions and quantities. Include the housing interface and optical requirements where available so the enquiry can be reviewed against the intended application.

Contact: James Fu
Company: FELIX OPTICAL GLASS
Email: james@felixglass.com
Website: https://www.felixglass.com/