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Tips and Techniques
they are. When one of them is connected to ground, the following must be
considered:
When the anode is tied to earth ground, this effectively connects earth ground
to up to +15V DC referenced to Laser Diode Analog Ground. When the
BNC on the control source is connected to the instrument input, it biases the
LD Analog Control Input and the control signal range is reduced. Thus, it
may appear that the analog control input is not working properly. Therefore,
it is recommended that the laser diode leads be disconnected from the earth
ground.
7.6
Grounding a Laser Diode
The laser outputs are isolated from earth (chassis) ground. Isolating the laser
diode case avoids damaging the device from multiple ground loop potentials,
AC transients, or static discharge. Since test equipment probes, signal
sources, and package mounts are often partially earth grounded, it is often
necessary to also bond the device case to earth ground. It is strongly
recommended that a single point ground scheme be established, specifically
at the binding post. This will help minimize noise, transients, and ground
loop hazards. Be sure to include any signal generators in your ground circuit.
If you have additional questions about your earth grounding method, contact
a Newport applications engineer.
7.7
V
Measurements
f
The attached laser diode's forward voltage (V
Diode Driver subsystem output connector. This is not the actual V
laser, the difference being the voltage drop in the cables due to the laser diode
current.
Use the Anode and Cathode voltage sense inputs on the SIGNALS I/O
connector (located on the rear panel) to monitor the actual voltage across the
laser diode, in a 4-wire configuration. Note that it is necessary to send the
HWCONFIG command via USB (see Section 5.5) in order for the controller
to monitor and display actual laser diode forward voltage on the front panel
and via USB commands query. It is recommended to use shielded sense
wires, or, at minimum, a twisted pair cable.
) is normally sensed at Laser
f
f
137
of the
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