Gentec-EO THZ-D - Manual (Page 14)

14
Revision 1.1
THZ-D Series Instruction Manual Gentec Electro-Optics Inc. All rights reserved
Gaussian beam stopped at 1/ e 2 ) applied to a diameter equal to 80% of the
detector aperture. The use of a divergent lens, a Lambertian diffuser such as opal
glass, or any other method of beam spreading, is recommended for this purpose.
Please take note that all of the laser light must be directed within the detector
aperture and that the transmission loss through the optical component must be
known.
6- Adjust the oscilloscope so it triggers on the wattmeter pulse or on the chopper sync signal.
7- Measure the baseline to peak voltage generated by the wattmeter.
8- Determine the wattmeter Volt/watt sensitivity from the detector identification label or calibration
certificate. Choose the value stated for the wavelength being used.
9- Calculate the optical energy using the following equation:
Power = (V
peak
-V
offset
) / Calibration sensitivity
- V
peak
-V
offset
= 1 volt
- Detector calibration sensitivity (100 Volts / watt)
Energy = 1 Volt / 100 V/W = 10 mW
NOTE: Exclude any DC offset from the pulse peak value measurement.
3.3.2 Working at other wavelengths than 10.6µm
For measurements with THZ-D Series detectors at wavelengths other than 10.6µm, a
correction factor must be set to compensate for the change in sensitivity of the wattmeter
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 typical “ Personal
Wavelength Correction
TM “ certificate supplied for the wattmeter and calculate K by taking
the percentage difference between the absorption @10.6 µm and that at the desired
wavelength.
 
 
μm
6 . 10 @ A
1 A
K


Power = (V
peak
-V
offset
) / Calibration sensitivity / K
Here
 
1

A = Absorption of the THZ @ the desired wavelength.
 
μm 6 . 10 @ A
= Absorption of the THZ @ 10.6 µm
A sample calculation follows:
 
1

A = 92 %.
 
μm
6 . 10 @ A = 94 %