Constant Power Mode (Cp) - THORLABS LDC200C series Operation Manual

Laser diode controller
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The display shows the injection current "I
With the adjust knob (F8) the laser current can be set continuously between 0 mA and the
selected current limit "I
ð If the injection current "I
"LIMIT" (F5) lights up, a short alert beep is heard, and the laser current is limited to the value
of the current limit "I
specifications for normal operation. However exceeding the set current limit "I
impossible.
ð If the connection to the laser diode is interrupted during operation, the laser diode current is
switched off automatically. LED "LASER ON" (F7) extinguishes, LED "OPEN" (F4) lights up
and a short beep is heard.
ð If the output is switched on while the interlock is closed and there is no laser diode
connected, at first the LED "LASER ON" (F7) lights up and the output is switched on. Then
the LDC2xxC recognizes the missing laser diode and switches the output off. The LED
"LASER ON" (F7) extinguishes and the LED "OPEN" (F4) lights up. Connect the laser and
press "LASER ON" (F8) - the LED "OPEN" (F4) extinguishes and the output switches on.
ð If a photodiode is connected, the display can be set to show the photodiode current "I
the optical power "P
The laser current can be

3.4 Constant Power Mode (CP)

If the laser includes a photodiode (also known as monitor diode), the laser can be operated
also in constant power mode. In contrast to the constant current mode, here the photodiode
current is kept constant by controlling the laser injection current.
· Start operating the LDC2xxC in constant current mode (refer to chapter 3.4)
· Select the display "I
· Check whether an appropriate photodiode current "I
at least the minimum control current must be available for a stable operation of the power
control:
5 µA for LDC200CV,
25 µA for LDC201CU, LDC202C, LDC205C,
50 µA for LDC210C, LDC220C, LDC240C.
Note
If the sign of the photodiode current "I
· Switch off the laser current by pressing the key "LASER ON" (F8) .
· Select constant power mode ("P") by pressing the key "CONST" (F24) until LED "P" (F21)
lights up.
· Set the adjust knob (F9) completely counter clockwise.
· Switch on the output by pressing "LASER ON" (F8). The LED "LASER ON" (F7) lights up,
the output is activated and the current slowly increases (about 1 s) to the set value.
· The photodiode current "I
laser diode increases until the laser current "I
ð If the desired photodiode current "I
range of the knob (F9) can be fitted to the current range of the connected photodiode using
the potentiometer "PD RANGE" (F25) - see below.
ð If no photodiode is connected or the polarity of the photodiode is set wrong, the laser current
© 2015 Thorlabs
LD
".
LIM
" reaches the set current limit "I
LD
". In this case, noise a nd ripple do not longer correspond to the
LIM
" by pressing the key (F17) or (F18).
LD
modulated
via the connector "MOD IN" (R2).
17
" with the key (F17) or (F18).
PD
" is negative, the photodiode must be reversed.
PD
" can be set using (F9) and with that the optical power of the
PD
" cannot be set with a sufficient accuracy (F9), the
PD
".
" is available. A photodiode current of
PD
" reaches the selected current limit "I
LD
3 Operating Instruction
" during operation, the LED
LIM
" is
LIM
" or
PD
".
LIM
15

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