OWNERS MANUAL | Cobolt 06-01 Series | D0136-K DECEMBER 2018
201
31 | 52
Continuous wave operation
The laser has two continuous-wave operating modes: constant power and constant current. The default mode for
Cobolt 06-MLDs when shipped is constant current. For 06-MLD lasers being used in continuous-wave operation it is
recommended to operate in constant current mode. It may be necessary to adjust the output current to reach the
desired output power if the laser is operated for more than 8 hours.
The default mode for Cobolt 06-DPLs is constant power. In constant current mode the laser runs at a set current level.
In constant power mode the power is monitored on an internal photodiode, and this is used to regulate the current to
maintain a constant power level.
Modulation mode operation
06-MLD
Which modulation type to use?
The Cobolt 06-MLD has three different modulation types: on/off, digital and analog. These three modulation types
aim to cover most applications the user may have, and they each have very different specifications.
•
On/off modulation
is quick to set up and requires no computer connection. It allows for the highest
extinction ratio. Use this mode if you are modulating at speeds below 500 kHz in a square wave.
•
Digital modulation
allows for extremely fast modulation speeds of up to 150 MHz with a rise time of under
2.5 ns. Use digital modulation if you are modulating at high speeds in a square wave.
•
Analog modulation
is not as fast as digital (2 MHz), but has the advantage that the user can drive the laser
with arbitrary waveforms. Use this mode if you require arbitrary waveform.
These types of modulation can be used simultaneously in any combination to give complicated output shapes such
as pulse bursts. These combinations are dealt with separately at the end of this section. Switching between
modulation types can be done using the Cobolt Monitor
™
software or with RS-232 commands; except for on/off
modulation, which is activated automatically when connected.
On/off modulation
On/off modulation is the simplest modulation type, and can be used out of the box with no connection to a computer.
It allows the user to completely shut off the diode between pulses, giving it a theoretically infinite extinction ratio. It
does however have the narrowest bandwidth and slowest switching times of the three modulation types. The on/off
modulation feature can be accessed via a socket on the key control box (CDRH model) or pin 11 on the laser head’s D
-
SUB (OEM model).
The on/off modulation socket is connected to a floating voltage line. When this line is grounded or forced to zero, the
laser automatically enters on/off modulation mode in the off state. The laser will remain in on/off mode until the laser
is restarted. Note that only a very small current (< 500 μA) must flow in order to ground the circuit. A
0-5 V TTL signal
