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ET-3500/ET-4000 Photodetectors
OPERATION:
1. Caution: Eye safety precautions must be followed when utilizing any equipment used in the vicinity of laser beams. Laser beams may reflect from the surface of the detector or the optical mount and caution must be exercised.
2. Mount the detector to an optical stand by the mounting holes on the bottom of the detector housing.
3. Adjust the voltage of the oscilloscope to 100mV/div. before connecting the detector. On models with >3V bias supply, the signal may be large enough to damage the oscilloscope if this is not done.
4. Connect the detector to the oscilloscope using coaxial cable models RG-213, RG-214 and RG-217 can be used, with RG-217 being preferred.
5. Use the 50Ω termination 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 1MΩ input.
6. After being certain that the damage threshold of the detector is not exceeded, place the detector in the center of the laser beam.
TROUBLE SHOOTING:
A. No signal is seen the first time the detector is used.
1. Be certain that the signal is not high off scale on the oscilloscope.
2. Is the wavelength of the laser within the spectral range of the detector?
3. Has a 50Ω termination input been used?
4. Try moving the detector within the laser beam.
5. Is there enough light (see sensitivity spec on the data sheet) incident on the detector to generate a signal?
B. A signal has been previously obtained, but not currently:
1. Try steps listed under A.
2. Inspect the active area of the photodiode for any signs of damage.
3. Try a higher input termination on the oscilloscope, but remember to return to 50Ω if this does not work.
4. Test the batteries. Typically the batteries will operate for several years, but operation with cw or high
rep rate lasers can drain the batteries much faster.
a. Replacement batteries are 3V lithium cells Duracell Model DL 2430.
b. Disconnect the coaxial cable before changing batteries.
c. The positive side of the battery should be facing down in the battery holder.
5. You can terminate the detector into 1MΩ input of an oscilloscope to obtain a higher output voltage signal but this could affect the detector's bandwidth.
C. Increasing the power incident on the detector does not result in a higher voltage signal on the oscilloscope:
1. The detector is probably saturated. You should lower the power incident on the detector to a level below
the saturation point.
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