Zinc Sulfide is a polycrystalline infrared optical material produced by chemical vapor deposition (CVD). It offers broad transmission from the visible edge (~0.4 μm) through the LWIR (14 μm), making it one of the few materials suitable for multispectral applications.

Two main grades are available: regular ZnS (amber/yellow, better MWIR transmission) and Cleartran ZnS (water-white, optimized for multispectral 3–12 μm performance). Both offer excellent moisture resistance and good mechanical durability.

Machinability

Relatively soft material, easy to machine. CVD-grown Cleartran grade machines cleanly.

Polishing

Good polishability. Standard optical polishing methods produce high-quality IR surfaces.

Environmental Sensitivity

Low moisture absorption, chemically stable in most environments. Good durability for field-deployed IR optics.

Cost & Availability

Moderate cost. CVD process limits maximum blank size. Multi-spectral grade costs more than standard.

ZnS covers broader range (MWIR+LWIR) but is softer. Ge is harder and has higher index for stronger optics.

ZnS has better multispectral performance; ZnSe has better transmission in specific bands and is preferred for CO₂ laser

ZnS covers IR; Sapphire covers UV-VIS-NIR. Different application domains.

What is the difference between regular ZnS and Cleartran?

Regular ZnS is amber-colored and optimized for MWIR. Cleartran is water-white with optimized multispectral performance from 3 to 12 μm.

Can ZnS be used for CO₂ lasers?

Yes, ZnS transmits at 10.6 μm. However, ZnSe is often preferred for CO₂ laser due to lower absorption at that wavelength.

How does ZnS compare to Germanium?

ZnS covers both MWIR and LWIR (broader range), while Ge is limited to 2-14 μm but is harder and has a higher refractive index.

Is ZnS durable?

ZnS has moderate hardness (4 Mohs). It is less scratch-resistant than Ge or Sapphire. Protective overcoats (DLC) are recommended for exposed surfaces.

What is the thermal performance of ZnS?

Excellent. ZnS has very low dn/dT (6×10⁻⁵/K), making it nearly athermal — ideal for systems operating across wide temperature ranges.

BK7 Optical Glass

BK7 is the most widely used optical glass for visible and near-infrared applications. A borosilicate crown glass, BK7 offers excellent optical clarity, good homogeneity, and reasonable cost — making it the default choice for many general-purpose optical components.

• Excellent visible transmission (>92% per surface uncoated)
• High material homogeneity and consistency
• Good chemical resistance and stability
• Cost-effective — widely available in stock sizes
• Suitable for most visible and NIR applications

• Not suitable for UV below 350nm
• Higher thermal expansion than fused silica
• Lower LIDT than fused silica for high-power lasers
• Hygroscopic under extreme humidity conditions
• Limited IR transmission beyond 2μm

Imaging lenses and objectives

Beam splitters and prisms

General-purpose windows

Spectrometer optics

Machine vision systems

When you need Extreme mechanical wear or scratch-prone environments

→ Consider: Sapphire (if applicable) or hard-coated ZnS

ZnS is relatively soft (Mohs ~3.5) and scratches easily. In field-deployed optics, consider hard-coat protection or sapphire where its transmission range allows.

When you need Short-wave IR only (1-3μm)

→ Consider: Silicon or Sapphire

If your application only requires SWIR performance, silicon is cheaper and harder. Sapphire also transmits well in SWIR with far better durability.

When you need Budget-sensitive MWIR/LWIR projects

→ Consider: Germanium (where temperature allows)

Multispectral ZnS (Cleartran) is expensive. For moderate-temperature MWIR work, germanium may be more cost-effective if thermal limitations are acceptable.

When you need High-power laser applications

→ Consider: Consider coated alternatives

ZnS has moderate laser damage threshold. For very high-power IR lasers, evaluate whether the coating or substrate will be the limiting factor.