THORLABS MCLS1-CUSTOM User Manual page 18

4-Channel Fiber-Coupled Laser Source
temperature set point. The temperature default is 25.00 C but can be adjusted over a range of 20.00 to
30.00 C with a resolution of 0.01 C.
Note: As above, there is a timeout where the display will revert to the viewing display and lock out adjustment to
the temperature.
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Pressing the control knob again will exit the adjustment mode and revert back to the viewing mode,
locking in the selected parameters. This can also be achieved by allowing the display to time out at any
point in the process. Depending on the magnitude of the change in temperature set point, it will take
anywhere from a few seconds to a few minutes for the system to settle into the new operating
temperature.
Turning the Laser Off
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Standby Mode – By adjusting the control knob fully counterclockwise the power will adjust down to the
threshold current and then to off, or standby mode. The threshold current is the point at which the
internal laser diode starts lasing. Below this it operates in a LED mode. For convenience the system is set
up to adjust from the threshold to the max current. In addition, when adjusting below the threshold, the
current will be set to almost 0 mA. Since the system utilizes a constant current control, there will always
be a minimum current to maintain the current control loop. The output emission is typically very low, or
nonexistent. The laser is still enabled and operating at the minimum possible current. This can be useful
while using the external modulation. The full 5 V can be applied without compensating for the internal set
point. However, the external signal will need to provide a DC offset to bias the laser above the threshold
current for best results. Input signals will see clipping on their lower edges below threshold. Pulse
response time may also be affected since there is typically a time delay during the LED to laser emission
change.
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Disable/Enable Mode – The Laser output should be turned off by pressing and releasing the SYSTEM
ENABLE switch. Outputs can be individually turned off at any time by pressing their ENABLE button. The
laser temperature will be maintained even when the laser is disabled.
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Power Down – When completely powering down an enabled unit, first press and release the SYSTEM
ENABLE switch and then turn the POWER key switch counterclockwise, which will turn OFF the entire unit.
Anytime the unit is turned OFF and then turned back ON, the Laser will be disabled until the SYSTEM
ENABLE switch is pressed and the desired channels are enabled.
Modulating the Laser Output
The MOD IN input can be used to modulate the laser output or set the laser output remotely using a 5 V power
source. The 5 V maximum inputs correspond to the maximum calibrated power of each channel, which operate
using a constant current drive technique. The resulting actual output power is dependent on the set current and
operating temperature. In addition, in order to eliminate a dead zone in the power control knob, the output of
the unit is offset to the threshold current of the coupled laser diode. Adjusting the knob below threshold will
immediately set the current to almost 0 mA, or Standby mode as described in section Error! Reference source not
found.. Therefore, there are two modes of modulation available. First, setting the control to "Standby" allows the
analog modulation to utilize the full 0 to 5 V input range. The drawback is that a minimum voltage will be required
to operate above the threshold current but allows more flexibility by the user. The second mode is to adjust the
control knob so that the laser is at threshold or above. The analog modulation voltage will be limited to less than
5 V, but a DC offset will not be required. This should be kept in mind when using the modulation input since it will
limit the actual input voltage range.
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Connect a signal generator or 0 to 5 V power source to the unit using a BNC type connector.
Page 14
Chapter 4: Operation
TTN182036-D02