Gentec-EO QE and XLE4 - Manual (Page 27)

QE Series Joulemeter Instruction Manual Version 3.0 April 2014 27
light must be directed within the detector aperture and that the transmission loss
through the optical component must be known.
5- Adjust the oscilloscope to trigger on the joulemeter pulse or on the laser sync. signal.
6- Measure the foot to crest peak voltage generated by the joulemeter.
7- Determine the joulemeter Volt/Joule sensitivity from the detector identification label or calibration
certificate. Choose the value stated for the wavelength being used.
8- Calculate the optical energy using the following equation:
Energy = V
peak
/ Calibration sensitivity
Ex:
- V
peak
= 1 volt
- Detector calibration sensitivity (10 Volts / Joule)
Energy = 1 Volt / 10 V/J = 100 mJ
NOTE: Exclude any DC offset from the pulse peak value measurement; this offset is a function
of the repetition rate.
2.2.2 Working at other wavelengths than 1.064µm
For measurements with a QE Series joulemeter at wavelengths other than 1.064µm, a
correction factor must be set to compensate for the change in sensitivity of the joulemeter
caused by the change in absorption of the optical absorber at different wavelengths.
To correct for the change in absorption refer to the spectral curve of the “ Personal
Wavelength Correction
TM “ certificate supplied for the joulemeter and calculate K by taking
the percentage difference between the absorption @1.064µm and that at the desired
wavelength.
 
 
μm 064 . 1 @
1
A
A
K


Energy = V
peak
/ Calibration sensitivity / K
Here
 
1

A = Absorption of the QE @ the desired wavelength.
 
μm
064 . 1 @ A = Absorption of the QE @ 1.064µm
A sample calculation follows:
 
1

A = 92 %.
 
μm 064 . 1 @ A = 94 %
K =
 
 
μm 064 . 1 @
1
A
A

x 100