Selection of Materials for UV Optics James Johnson OPTI 521 December 8, 2008
Overview Introduction Considerations for UV Optics Criteria for Selecting a Material Material Properties
UV Optics UV Range: nm Applications including lithography, space science, scanners, medical
Why They are Different Most Materials Strongly Absorb below 300nm Atomic Transitions in this range are common Ideal Materials do Have a Resonance Deep into the UV EgEg EeEe hν
Problems with UV Optics Material Absorption Follows Beer's Law I=I 0 e - αL Damage from high intensities Solarization of Material after Long Exposure
Scattering Larger Scattering needs smoother surface Rayleigh λ -4 λ/10 Surface Error not easily achieved Must be polished
Criteria What to consider – Cut-Off Wavelength – Cost – Transmission at Wavelength – Durability
UV Transmissive Mediums Fused Silica Fluorides Calcium Fluoride Magnesium Fluoride Sapphire
Fused Silica (SiO 2 ) Most common UV material Relatively Inexpensive Most grades will not work below 190nm Strong Sources will cause Compaction From Ultraviolet Radiaion(Koller)
Calcium Fluoride(CaF 2 ) Best Alternative when a Farther Wavelength is Needed Expensive Grown Crystal Difficult to Polish Hygroscopic From Melles-Griot
Magnesium Fluoride(MgF 2 ) Similar Range to CaF 2 Less Transmissive Doesn't Absorb Water Makes good AR- Coating From EKSMA
Sapphire (Al 2 O 3 ) Extremely Hard Making for Good Windows Stable Large bandwidth Chemical Resistant Costly Extremely Difficult to Remove Material From Melles-Griot
Summary It comes down to where you need it and what you can spend Stick with Fused Silica if it works Fluorides offer the widest range, but can cost significantly more Sapphire offers dimensional stability and material strength
Questions?
Overage - Reflectors Most materials that reflect in the visible work in the UV Exception is Silver Metals like Aluminum, SiC are excellent choices