Constant Current, High Bandwidth Mode; Constant Current, Low Bandwidth Mode; Figure 21 - Constant Current - High Bandwidth Mode - Newport 8000 User Manual

42 Chapter 3
3.6.9

Constant Current, High Bandwidth Mode

This mode of laser operation is shown in Figure 21. In this mode, current feedback is
used to control the laser output. The bandwidth is between 50 kHz and 500 kHz,
depending on the model.
3.6.10

Constant Current, Low Bandwidth Mode

This mode of laser operation is shown in Figure 22. In this mode, current feedback is
used to control the laser output.
In this mode, capacitors are switched into the circuit. These capacitors act as a filter
and therefore prevent the laser output from changing too rapidly. This gives added
laser diode protection. This also limits the laser output bandwidth to about 10 kHz.
In the Low Bandwidth - CW mode, the bandwidth is further limited to 30 Hz.
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Laser Diode Driver Module Operation
Modulation
Input Port
Current Set Point

Figure 21 - Constant Current - High Bandwidth Mode

Unregulated DC
Voltage
Regulator
Pass
Transistor
Output
Shorting
Laser Diode
Current
Sense