Articles, Blog

QEX10 Quantum Efficiency Measurement System Calibration

December 15, 2019

Hello. I’m Michael Kuhr with PV Measurements. Today I will go through the process of calibrating your QE system up to 1100 nanometers in a
beam down configuration. Calibration of the system must be
performed any time the system is turned on anytime the alignment of the optics is changed or
when changing between beam up beam down or reflectance modes. The
calibration standard used in this wavelength range is a silicon photodiode. This photodiode has been factory
calibrated to a similar photodiode at the National Institute of Standards
and Technology or NIST. Note the placement of the photodiode. The beam is fully contained within the
active area, near its focal point, and the photodiode is flat relative to
the beam. This configuration is used during the factory calibration. Make sure your lamp has been running for
at least 15 minutes before starting this measurement. Before the calibration consider the
wavelength range of your measurement. It is important to have a fresh
calibration data point for every data point in the scan range. If you want to measure your device in 10
nanometer increments starting at 300 nanometers and up to
1100 nanometers, you must perform the calibration of the
system with the same or finer interval so that the system
is calibrated it each wavelength where a measurement is made. If you measure the photodiode starting
at 295 nanometers with 10 nanometer increments the
resulting calibration data points will be 295, 305, 315 nanometers and so on. None of the intended data points such as
300, 310 and 320 nanometers will have
calibration data. A scan starting at 295 with five nanometer increments will give me twice the calibration data
point density that you need, which is fine. Once the scan is complete, click ‘Save’ and then click on ‘Apply as Calibration’.
Note the two lines in the graph: The green calibration line shows the
data for the factory calibration. The blue measured line is the
measurement just performed on the photodiode. Notice that this measurement does not
match up well with the calibration data. This is because this particular system
has not been calibrated for some time. Due to slight changes in the optics and
the bulb, the measure has shifted. That is normal. Click on the ‘Update
Calibration’ button to update the calibration for your
system. The graph does not adjust at this point, but the calibration has been updated. If you’re interested in verifying the
calibration, perform the same scan again. Save the measurement and click on the
‘Apply as Calibration’ button. Notice that the two lines now overlap. This shows that your calibration is
indeed valid. It’s not necessary to perform the second
scan after each calibration, but it’s a good
way to check your calibration. Click on the ‘Update Calibration’ button
and then continue. You’re now ready to measure
your sample. Note that Photodiodes, as any calibration device, should
be recalibrated at a regular interval. PV Measurements recommends having your
photodiode calibrated annually. Photodiodes are factory
calibrated using photodiodes that have been calibrated at NIST. For technical assistance with your
system contact our Technical Support Engineers at: [email protected] And for information on calibrating your
photodiode contact our Applications Engineers at: [email protected]

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