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Amplified Photodetectors
OPERATION:
1. Mount the detector to an optical stand by the insert hole on the bottom of the detector housing. An 8/32 nylon standoff is included to isolate the detector from the optical stand if noise is generated due to grounding through the stand.
2. Adjust the voltage of the oscilloscope to 100mV/division before connecting the detector.
3. Connect the detector to the oscilloscope using a standard RG-58 coaxial cable. If more than 4 feet of coaxial cable is required models RG-213, RG-214 and RG-217 can be used with RG-217 being preferred.
To avoid the loss of high frequency components, coaxial cable lengths should be kept as short as possible.
4. Use the 50Ω input of the oscilloscope. If the oscilloscope does not have a 50Ω input, connect the coaxial cable to a 50Ω terminator and connect this to the oscilloscope's 1 megaohm input.
5. When possible, use a scatter plate (white paper works) to integrate the laser beam. Focus on the active area only if you need increased sensitivity.
6. If the full bandwidth of the detector is not needed, use lowpass, bandpass or highpass filters to remove excess noise.
TROUBLESHOOTING:
1. Is the AC power supply plugged in?
2. Is the detector terminated into 50Ω at the oscilloscope?
3. Is the wavelength being viewed within the spectral range of the detector?
4. Is the signal high off the scale on the oscilloscope?
5. Inspect the diode for possible damage.
6. If increasing the incident power does not result in a higher voltage output, the detector is probably saturated. Check the amplified photodetector data sheet for Maximum Undistorted Output Voltage specification.
7. Are all the connectors securely in place?
8. Is the bandwidth you are trying to measure below the low frequency cutoff of 75kHz?
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