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Custom Zinc Sulphide

Zinc Sulphide (ZnS) is a widely transmitting IR material. It typically comes in two grades: Multispectral (MS) and Forward Looking Infrared (FLIR) both with their own benefits:

Multispectral grade: After zinc sulphide sheets are formed on graphite susceptors, to produce the multispectral grade, also known as Cleartran® or water-clear, it will then be hot isotopically pressed (HIP). This further treatment, which puts the zinc sulphide under intense heat and pressure, normalises the crystal structure, removing defects and producing a material with minimal scattering and low absorption in the broad 0.35 to 12 µm transmission range.

FLIR grade: also known as regular zinc sulphide, it undergoes no further treatment after forming on the graphite susceptors. Unlike MS grade it does not transmit well in the visible range and is mainly used for the 8 to 12µm thermal band. However, it is not without its benefits, it is harder than MS zinc sulphide, with higher fracture strength and better resistance in harsh environments.
Below is a brief summary of Zinc Sulphides’s optical properties, full data sheets are available for FLIR and MS grade ZnS.

FLIR Grade

Multispectral Grade

Transmission range

1.0 to 13µm

0.37 to 13.5µm

Refractive Index

2.192 @ 10.6µm

2.20084 @ 10µm


4.08 g/cm3

4.09 g/cm3

Melting Point




Knoop 240 with 50g indenter

Knoop 160 with 50g indenter

Knight Optical supplies high quality zinc sulphide components, including windows, lenses and prisms, made to your custom specification. We can offer uncoated and coated optics, including broadband antireflective (BBAR) coatings. Our typical manufacturing specifications are listed below however we are always expanding our capabilities so if your requirements are not mentioned below, please contact our technical sales team who will guide you through your enquiry.


< 5mm to 100mm +

Form error (@633nm)

< 0.25 waves

Centration /parallelism

< 1 arc minute


< 60/40

Typical coatings

Single sided BBAR @ 2-14µm

With our in-house state-of-the-art metrology laboratory you can be confident that your optical components will meet your requirements. You can find out more about our testing facilities here.

Typical Applications

Systems with visible and infrared sensors
  • Multispectral zinc sulphide is often used in systems which have visible and MWIR/LWIR sensors due to its broad transmission band and low absorption.
Military systems
  • FLIR grade zinc sulphide can be used as a front optic in many systems, especially those operating in the 8-12 micron thermal band. With a higher fracture strength and hardness compared to MS grade, it is better suited as a front optic, it is shows better chemical and particle resistance.

Our 2022/2023 Catalogue

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