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