OWNERS MANUAL | Cobolt Skyra™ |
D0423-E JANUARY 2018
31 | 45
100% of nominal power in the ON state, in this case the High current level is set to the maximum of 3000 mA. For the
DPL line the low current is determined by visually inspecting the output beam and identifying the minimum current
for emission, then lowering the value by 50 mA to ensure that the current is below the threshold. For the MLD lines
the low current is
0
mA.
DPL Digital modulation @1 kHz MLD Digital Modulation @ 500 kHz
Analog modulation
Analog modulation allows direct control of the laser power by an input signal. This allows the laser to be modulated
with arbitrary waveform at limited bandwidth. To enable analog modulation using the Cobolt Monitor™ software,
select “Modulation Mode”, and “Analog” under Modulation Type. The input signal should be connected to the Analog
male SMB connector on the laser head. An input voltage of 1.0 ± 0.3 gives 100 % of the laser’s nominal power level.
NOTE The laser line may give more power if a voltage larger than 1 V is used. Avoid overdriving the diode!
Specifications and diode lifetime are not guaranteed above nominal power. Measure the input voltage
before connecting to the laser head.
When the laser is modulated from 0 to 1 V, the current through the laser diode is modulated from slightly above zero
to the current that gives the laser’s nominal power. The laser diode has a threshold current below which no laser light
is emitted, and above which the optical power is approximately linear with current. When modulating with an arbitrary
waveform, it is possible use a DC offset on the signal generator such that the laser is modulated from this threshold
point to the desired maximum signal level. The threshold level varies from laser-to-laser. To determine the threshold
level for a given laser apply a variable DC voltage to the analog modulation input and looking for the lowest voltage
where laser light is emitted. The amplitude and DC offset of the input signal should then be set so that it modulates
from this point up to 1 V. Note that although the diode does not emit laser radiation below threshold, it still emits
some light; modulating from
0
V will therefore give the best possible extinction ratio.
Typical analog modulation pulse shape, DPL output on channel 1, function generator input on channel 3 of 0-1 V sinus, 100 Hz.
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