Large Optical Windows (Visible, IR and UV)​

Optical windows are flat plates made from optically transparent materials, designed to allow light into optical instruments and protect light sources from external environments. These windows minimize reflection and absorption while maximizing transmission over specific wavelength ranges. Large optical windows provide undistorted light passage, optical flats test surface flatness, and transmission flats assess transmitted wavefront quality. While related, they serve distinct purposes in optical applications: viewing, testing, and calibrating respectively.

Our optical window features include X-ray protection, non-browning to UV light, and light transmission from deep UV to far infrared light. Optical window selection considerations include material transport characteristics as well as scattering, strength and resistance to corrosion, heat shock and damage thresholds in certain environments.

Manufacturing Capability

Standard Specifications

High Precision Specification

Dimensional Tolerance

±0.1 mm


Surface Accuracy

λ/4 @ 633nm

λ/10 @ 633nm

Wavefront Distortion

λ/4 @ 633nm

λ/10 @ 633nm

Surface Quality (S/D)



Parallelism Tolerance




Customized coating according to customers’ request

Customized coating according to customers’ request

Large Optical Window
Large Optical Window

Key Features

Avantier offers > 4 inch fused large fused silica window glass for applications in the near-infrared (NIR) and ultraviolet (UV) spectra and large N-BK7, H-K9L window glass for applications in the visible spectrum.

Avantier offers a comprehensive array of processing equipment, including embryo processing, grinding, polishing, and performance testing instruments. Our facilities feature large CNC edge grinding machines and precision milling machines equipped with high-power grinding spindles, enabling quick cutting and forming of large optical embryos. We utilize ultra-large ring polishing equipment and 40B double-sided polishing equipment for grinding and polishing various specifications and types of precision surfaces. Additionally, our large aperture planar digital laser interferometer ensures accurate surface flatness and wavefront distortion detection for large window glass, achieving a PV accuracy of surface detection up to λ/15 @633nm.

Optical Flats

An optical flat is a meticulously polished flat surface used as a reference to compare the flatness of an unknown surface. We provide both single sided and dual sided optical flats made from Fused Silica and other materials. The flatness of an optical flat is determined in fractions of a reference wavelength, specifically 632.8nm. For instance, a λ/20 flat has a peak to valley deviation of up to 31.64nm (632.8/20). Our single surface flats come in several flatness levels: λ/4, λ/10, and λ/20. Similarly, our dual surface flats are available with 1/4, 1/10, and 1/20 flatness.

Transmission Flats

A transmission flat is essential for verifying the surface flatness or transmitted wavefront of flat surfaces or precision optical components such as mirrors, prisms, and windows, typically using an interferometer. Avantier’s high quality transmission flats consist of a precision optical window mounted, and the representative materials are fused silica, N-BK7, H-K9L and so on. 

Large Optical Windows, Optical Flats, and Transmission Flats

Avantier is a leading manufacturer of high-precision large optical windows, including optical flats and transmission flats. We offer a wide range of materials and sizes to meet your specific application requirements. 


From standard to high-precision specifications, our optical windows offer dimensional accuracy, superior surface quality, surface flatness, and precise parallelism tolerance. Our optical flats are polished to meet the most demanding flatness specifications, making them ideal for applications such as interferometry and laser collimation. Our transmission flats are designed to maximize light transmission with minimal absorption or scattering, making them perfect for use in optical systems that require the highest possible throughput. Whether you need a large optical window for a complex instrument or a small transmission flat for a critical sensor, Avantier has the expertise and capabilities to meet your needs.


With manufacturing capabilities spanning fused silica and N-BK7/H-K9L materials, we deliver high quality solutions for multiple applications including near-infrared(NIR), ultraviolet(UV), and visible spectrum optical components and window applications. Equipped with advanced processing equipment and meticulous quality control measures, Avantier ensures the highest fabrication and performance standards. Our commitment to customization enhances customer satisfaction, guaranteeing optimal functionality and reliability across various optical setups. Avantier’s windows are ideal for applications demanding precision, durability, and performance. Our expertise extends to crafting translucent optical windows and optical flats, ensuring we identify the best solution for your project. Trust Avantier for exceptional optical windows that exceed expectations.


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