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Portable Optical Tweezers Kit Chapter 6: Setup and Adjustment
Rev B, July 8, 2019 Page 45

It is possible to monitor the laser diode with the included photodiode, see Figure
31. This is not necessary for this kit and should not be enabled.

Once the polarity and the maximum current are set and persisted to the hardware,
you can operate the laser driver with the controls on the controller itself (rather
than controlling it by software). The current can be set by turning the
potentiometer knob at the top of the controller. For that, the “Advanced” settings
should look like in Figure 31.
The current range of the L658P040 laser diode is 75 mA (typical) to 110 mA
(maximum). The actual output for a certain current depends on the diode at hand.
You have two options:

Set the current to approximately 80 mA and measure the output power with
a power meter. Adjust the voltage until you reach 40 mW of output power.

Set the operating current just below 100 mA. According to our test
measurements, this will result in an output power above 50 mW. The
advantage is a stronger optical trap, the downside is that operating a laser
diode above the specified output power may decrease its lifetime.
8
Settings of the Laser Diode Controller
8
So far, we have not seen a significantly increased failure rate with an operating current near
100 mA. However, we cannot guarantee that the diode reaches the typical lifetime when driven near
its current limit.