Chapter 3: Photorefractive Limits
Page 6
Chapter 3
Photorefractive Limits
Lithium Niobate, LiNbO
3
, has an optical transparency range from 320 nm to over 5 µm and can withstand pulsed
power densities up to 1 MW/cm
2
. However, short wavelength operation is limited by photorefractive effects which
lead to color center formation and progressively increasing absorption. Photorefractive damage is noted by
increase scattering and absorption in the optical path along with gray appearance in the crystal (gray tracking).
Photorefractive limits are a concern in the visible region (400 – 700 nm) particularly with frequency- doubled
lasers.
The lithium niobate crystals in Thorlabs’ EO modulators are MgO-doped for increased resistance to
photorefractive damage.
Chapter 4
Cleaning and Maintenance
Under normal operating conditions, the modulator needs very little, if any maintenance.
4.1. Cleaning the Optics
The modulator crystal is recessed inside the housing and under normal conditions, the crystal faces should not
need cleaning. If necessary, use a gentle stream of compressed air (dry nitrogen under low pressure or a can of
compressed air made specifically for cleaning optics).
WARNING
Damage may result from excessive cleaning air pressure of if condensation is allowed to build up from using a stream of
compressed air from an inverted can.
4.2. Cleaning the Compensator Housing
The housing can be wiped clean with a lint free rag wetted with propanol or a commercial window cleaner. Do not
soak the housing – it is not watertight and any moisture introduced inside the modulator may cause condensation
problems.
