External Photodiode Measurement; Grounding Considerations; Temperature Measurement - ILX Lightwave LDX-36000 Series User Manual

External Photodiode Measurement

If a photodiode has been configured to measure the output of the laser, the
photocurrent may be fed into the LDX-36000 so the instrument can display power.
Details on how to configure the instrument to measure power may be found in this
chapter under Power Setpoint.
The photodiode and laser connections are electrically isolated from ground and
each other. To measure photocurrent from an external photodiode, the
photodiode anode and cathode must be connected to two pins on the back panel
9-pin connector labeled Sense. Refer to Figure 3.2 for the pinout. Shielding of
the photodiode connections is recommended to reduce measurement noise. A
common connection between the laser anode or cathode and photodiode will
cause measurement errors. This condition should be avoided.

Grounding Considerations

The laser outputs are isolated from chassis ground allowing either output terminal
to be grounded at the user's discretion. If the output circuit is earth grounded at
some point, such as through the laser mount, care must be taken to avoid multiple
earth grounds in the circuit.

Temperature Measurement

Two pins are available on the back panel connector labeled Sense for the
measurement of laser mount temperature via a thermistor. It is recommended that
a 10 k thermistor be used as this will provide the best accuracy and resolution
for normal operating temperatures of 10°C to 60°C. The thermistor should be
mounted as close as possible to the laser diode with thermal epoxy for a
permanent connection or with thermal grease and a clamping arrangement for
temporary connection. This will provide the most accurate temperature
measurement.
03_10
Note: The instrument measures forward voltage, photodiode current and temperature in
CW and QCW modes. In QCW mode, measurement accuracy is achieved by measuring in
the last 15 s of the pulse and throughout the pulse at pulse widths > 1ms.
O P E R A T I O N
Connections for General Operation
3
C H A P T E R
29
LDX-36000 Series
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