Cleartran ZnS Windows

Overview

Cleartran Zinc Sulfide (ZnS) windows are refined CVD ZnS optical components used when one aperture must support visible, MWIR, and LWIR optical paths. Cleartran is also known as multispectral ZnS and is often reviewed for windows, domes, lenses, beamsplitters, filters, and prisms in demanding optical systems.

Compared with standard CVD ZnS, Cleartran is processed after deposition to improve material purity and normalize the crystal structure. This processing helps reduce absorption and scatter, making the material useful where a single optical path must serve several spectral bands.

Why Cleartran ZnS Matters

Cleartran ZnS is selected when multispectral transmission and mechanical resistance must be balanced in one infrared window. It is chemically inert, non-hygroscopic, high purity, theoretically dense, and practical to machine into custom optical geometries.

• Useful visible-to-infrared transmission for systems combining visible cameras and infrared detectors.
• Higher mechanical robustness than ZnSe in harsh-environment window and dome applications.
• Low absorption and scatter across a broad usable transmission range when grade, thickness, coating, and surface quality are controlled.
• Compatible with diamond turning for windows, lenses, aspheric lenses, diffractive elements, beamsplitters, filters, and prisms.

Key Specification Reference

Parameter	Engineering reference
Material	Cleartran ZnS, also called multispectral Zinc Sulfide
Typical transmission range	0.4-12 µm; broader visible-to-far-IR review depends on grade, thickness, and coating
Refractive index	2.350 at 0.63 µm; 2.289 at 1.06 µm; 2.252 at 4 µm; 2.200 at 10 µm
dn/dT	54.3 × 10^-6/K at 0.6328 µm; 42.1 × 10^-6/K at 1.15 µm; 38.5 × 10^-6/K at 3.39 µm
Density	4.09 g/cm3
Knoop hardness	Approximately 160 kg/mm2
Modulus of rupture	Approximately 8704 psi
Thermal expansion	6.3 × 10^-6/K at 273 K; 7.0 × 10^-6/K at 373 K; 7.5 × 10^-6/K at 473 K

Applications

• Visible imaging combined with infrared detection
• Thermal imaging and FLIR protective windows
• Multispectral sensor apertures
• Astronomy and broadband optical instruments
• Rugged windows and domes for mechanically demanding environments

Manufacturing and Surface Guidance

Topic	Typical guidance
Manufacturable parts	Windows, lenses, aspheric lenses, binary or diffractive lenses, beamsplitters, filters, prisms, CNC-shaped blanks, generated lens blanks, and near-net-shape domes
Surface quality	40-20 scratch-dig is often reviewed for 0.4-3 µm use; 60-40 or 80-50 may be reviewed for 3-12 µm use
Diamond-turned finish	Surface roughness is often specified around 100 Å rms or better depending on geometry and acceptance criteria
Surface figure	Visible and NIR requirements may range from 1/10 to 1/2 wave at 0.6328 µm; IR requirements often range from 1/2 to 2 waves at 0.6328 µm
AR coating options	BBAR coating may be reviewed for 0.8-2.5 µm, 3-5 µm, and 8-12 µm bands; custom bands between 0.4 and 12 µm can be reviewed

Selection Notes

Cleartran ZnS can be a strong candidate when a system needs one optical aperture for visible imaging and IR sensing. It should still be selected against the real wavelength band, environmental exposure, mechanical loading, coating durability, and inspection criteria.

If a project only needs LWIR transmission and does not require visible or multispectral performance, standard ZnS, germanium, ZnSe, or another IR material may be more appropriate. If the part is exposed to dust, airflow, cleaning, impact, humidity, or shock, define the coating and mechanical requirements before quotation.

Request Engineering Review

For custom Cleartran ZnS windows or multispectral apertures, send wavelength band, clear aperture, outside dimensions, thickness, coating target, surface quality, environmental exposure, and drawing requirements through the contact form or email sales@iroptical.com.