Deep UV Optics

• UVA (315–400 nm): Often used in UV curing, forensics, and inspection, it is referred to as “near-UV.” 

• UVB (280–315 nm): Known as “middle-UV,” it is commonly associated with specialized machine vision cameras for non-destructive testing (NDT), defect detection, and surface analysis. UV spectrophotometers measure chemical composition and analyze specialized materials in this region. 

• UVC (200–280 nm): “Deep-UV” or DUV, used for sterilization and decontamination. Additional industries are primarily lithography and excimer lasers. 

• Vacuum UV (100-200 nm): ”VUV” contains the highest-energy UV photons and is primarily used in advanced technologies such as semiconductor photolithography, spectroscopy, and scientific research. Because wavelengths below approximately 200 nm are readily absorbed by oxygen in air, VUV optical systems must operate in vacuum or controlled inert gas environments. 

Materials for Deep UV Optics

Traditional optical glasses absorb much of the ultraviolet spectrum, making them unsuitable for deep UV applications. Instead, specialized crystalline and synthetic materials are selected based on their transmission characteristics and physical properties.

UV Fused Silica
UV fused silica is one of the most widely used materials for UV optics, transmitting efficiently down to approximately 180–193 nm. Premium grades are manufactured from ultra-high-purity synthetic silica, providing exceptional index homogeneity, extremely low birefringence, and excellent optical consistency throughout the material. Its combination of performance, durability, and manufacturability makes it a popular choice for many UV optical systems.

Sapphire
Sapphire combines good UV transmission—typically down to 150–170 nm—with exceptional mechanical strength, scratch resistance, and thermal stability. Although its UV transmission is lower than fluoride crystals, it excels in harsh operating environments where durability is critical. 

Calcium Fluoride (CaF₂)
Calcium fluoride provides excellent transmission into the deep UV, extending to approximately 150–160 nm. Its low refractive index, broad transmission range, and compatibility with high-performance optical coatings make it a preferred material for semiconductor lithography, laser systems, and precision UV imaging. 

Magnesium Fluoride (MgF₂)
Magnesium fluoride transmits well into the vacuum UV region, reaching wavelengths near 120 nm. It is commonly used for UV windows, lenses, prisms, and optical coatings, particularly in excimer laser systems and scientific instrumentation. 

Lithium Fluoride (LiF)
Lithium fluoride offers the broadest ultraviolet transmission of the commonly used optical materials, extending below 110 nm into the vacuum UV. This makes it ideal for spectroscopy, synchrotron instrumentation, and specialized VUV and X-ray optical systems.  

Why Band Gap Matters

Selecting the right material for deep UV optics involves more than simply comparing transmission curves. One of the most important material properties is the optical band gap.
 
The band gap is the energy difference between the valence band and the conduction band of a material. It represents the minimum amount of energy required to excite an electron into a conductive state and is measured in electron volts (eV). 
Since ultraviolet photons carry substantially more energy than visible-light photons, they are much more likely to excite electrons within a material. When this occurs, the photons are absorbed instead of transmitted. 

Materials with larger band gaps require even higher photon energies before absorption begins, allowing them to transmit shorter UV wavelengths more efficiently. As a result, band gap serves as an excellent indicator of how well a material will perform in deep UV and vacuum UV applications.