Gentec-EO UM-B - Manual (Page 14)

14
Revision 2.1
UM-B Series Instruction Manual Gentec Electro-Optics Inc. All rights reserved
4 DAMAGE TO THE OPTICAL ABSORBER MATERIALS
At any time, the beam’s incident area should not be less than 10% of the detector’s aperture.
Please check with Gentec-EO to make measurements with such small beams.
Damage is usually caused by exceeding the manufacturer is specified maximum tolerances:
- Average Power Density
- Peak Power Density
- Single Pulse Energy Density
Refer to the UM-B Series wattmeter specifications pages. Damage can also be caused when using
a detector with a contaminated absorber or attenuator surface.
The damage thresholds specified in the specifications section refer to a visible alteration of the
absorber surface. In practice, a slight alteration will not affect the wattmeters response. Consider
the wattmeter to be damaged and/or out of calibration when large-scale damage is evident or you
can see the metal electrode beneath the coating
5 .
In the case of a TEMoo (Gaussian) beam, the maximum peak power and energy density can be
calculated using the following equation:
Density (power or energy)

2Io

W
2
Where Io is the total beam power or energy
W is the beam radius at 1/e
2 and 
= 3.1416
NOTE: The beam waist for a TEMoo beam is the radius of a circle centered on the beam axis and
containing 86 % of the beam energy. Ref.: SIEGMAN, A.E., An Introduction to Lasers
and Masers, p. 313 (Mcgraw-Hill Series in the Fundamentals of Electronic Science).
Example of energy density;
Io = 1 joule (total energy)
W = 1 cm
Energy density = 2 x 1 joule = 0.64 joule/cm
2

x (1 cm)
2
Example of power density calculation;
Io = 1 MegaWatt (total power)
W = 1 cm
Power density = 2 x 1 MegaWatt = 0.64 MW/cm
2
5 Contact Gentec-EO for evaluation, repair, recalibration, or replacement (refer to the WARRANTY
instructions).