Chapter 5 Tips and Techniques 47
5.5 Noise Specifications
Newport measures the noise on its Laser Driver outputs using a resistive
load and an HP 34401A true-rms ac voltmeter with a bandwidth from 3 Hz
to 300 kHz.
5.6 Intermittent Contact Feature
When a loose wire breaks the connection to your laser, the driver sees a
decrease in current through the laser and attempts to increase it back to the
correct value. When the loose wire regains contact, the current may
momentarily be higher than the set point. If this happens and the current is
10% or more above the setpoint and the intermittent contact feature is active,
the unit will shut down with an “open circuit” error message.
It may be necessary to disable this feature when the following conditions
exist:
1) Operating at extremely low set points. For example, 100mA on a 50
Amp driver.
2) When modulating at high frequencies or with square waves or in pulse
mode.
5.7 V
f
Measurements
The Laser’s forward voltage (V
f
) is sensed at the D-sub connector on the
driver. It is not the actual V
f
of the laser. The difference being the voltage
drop in the cables due to the laser current.
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