Top 10 FAQs for New Users of Infrared Optics: Lenses, Windows, Materials & Coatings

Infrared optics follow different rules from visible-light glass. Here are the ten questions new buyers ask most, with the numbers and standards that actually decide a specification.

Sep 17th,2026 112 Views

What are the main infrared optical materials and their transmission ranges?

Ordinary optical glass and fused silica stop transmitting near 3 micrometres. Infrared systems use crystalline or glass IR materials instead. The table lists the useful transmission bands most quoted by suppliers.

Material	Transmission (μm)	Key trait	Typical use
ZnSe	0.6 - 21	Low absorption, some visible light	CO₂ lasers, broadband LWIR
ZnS (multispectral)	0.4 - 14	Harder, chemically resistant	Visible + IR, harsh duty
Chalcogenide glass	1 - 12	Mouldable, athermal	Volume LWIR lenses
BaF₂	0.15 - 12	Radiation resistant	Spectroscopy, IR windows
CaF₂	0.18 - 10	Low dispersion	UV - MWIR, spectroscopy
MgF₂	0.12 - 7	Rugged, needs no AR	UV - MWIR windows
Sapphire	0.17 - 5.5	Very hard	High-pressure viewports
Silicon (Si)	1.2 - 8	Lightweight, low cost	MWIR 3 - 5 μm

How do I choose between ZnSe, ZnS and CaF₂?

Pick by wavelength first, then by environment:

- CO₂ laser at 10.6 µm: ZnSe is the standard; choose ZnS where spatter or abrasion is expected.

- Need visible plus infrared in one part: multispectral ZnS or CaF₂.

- Low dispersion or spectroscopy: CaF₂.

- Harsh duty where hardness matters: ZnS grades sit above ZnSe.

What is the difference between an IR window and an IR lens?

A window is a flat, protective element with no optical power. Its job is to seal the environment and pass light, so surface quality and transmission dominate. A lens is curved; it bends and focuses the beam, so it also carries tighter tolerances on radius of curvature, flatness, wedge and wavefront. Windows are usually specified easier than lenses.

Which coatings are used on infrared optics?

Coating	Band	What it does
BBAR (broadband AR)	3-5 & 8-12 μm	Cuts reflection, raises throughput > 95%
DLC (diamond-like carbon)	8-14 μm	Hard coat + AR, > 88% single layer
Protected Au / Ag / Al	Reflective	High-reflectance mirrors

What is DLC, and when should I specify it?

DLC is an amorphous carbon thin film whose hardness approaches diamond. It is chemically inert, low-friction and transparent in the infrared, so it both protects and anti-reflects. It is applied to air-facing surfaces of ruggedized optics, typically 1-2 µm thick by PECVD or PVD. Soft substrates - ZnSe (Knoop 120) and chalcogenide glass (100-170) - should carry DLC wherever they meet weather, sand or repeated cleaning.

What surface-quality grade should I specify?

China's national standard GB/T 1185-2006 (Surface imperfections of optical elements), aligned with ISO 10110-7, defines scratch and dig acceptance by grade. In optical trade the common scratch/dig grades are 60-40 (commercial), 40-20 (precision) and 20-10 (high-end), with 10-5 for demanding parts. Specify the grade that matches the function rather than the finest available - tighter grades raise cost and lead time.

What dimensional and figure tolerances are typical?

Parameter	Typical
Diameter	±0.1 to ±0.05 mm
Center thickness	±0.02 to ±0.1 mm
Wedge (tilt)	≤ 3 - 5 arcmin (windows); tighter for lenses
Flatness	λ/4 to λ/10 (λ = 632.8 nm)
Surface roughness	Ra ≤ 0.1 nm class
Radius tolerance	per GB/T 2831 (curvature-radius tolerance)

Tighter figures are available on request; the drawing should state every tolerance so inspection is unambiguous.

How should I clean and handle IR optics?

Blow loose dust with clean dry nitrogen or oil-free air first. Clean with lens tissue and a small amount of reagent-grade acetone, methanol or IPA; wipe once and do not scrub. Handle with lint-free gloves (ZnSe is toxic on contact). Store in a desiccator - BaF₂ and MgF₂ are mildly moisture-sensitive - and never touch the clear aperture.

What are these components typically used for?

Long-wave infrared windows and lenses serve thermal imaging for industrial inspection, firefighting, predictive maintenance, medical thermography and building diagnostics. CO2-laser optics (10.6 µm) support cutting, welding and marking. Other uses include spectroscopy, environmental and process monitoring, automotive night vision and aerospace sensing.

How do I specify custom IR optics from Peoptix?

Send us: (1) wavelength band, e.g. 8-12 µm; (2) material; (3) outer diameter and center thickness; (4) coating - BBAR band or DLC; (5) surface-quality grade; (6) figure and tolerance; (7) quantity. Peoptix supplies custom ZnSe, ZnS, CaF₂, MgF₂, BaF₂, sapphire, silicon and chalcogenide windows, lenses, domes, prisms and mirrors with AR or DLC coatings, built to GB/T and ISO drawings.

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