THORLABS LDC200C series Operation Manual Download

Page: 17 / 38

3 Operating Instruction

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

LIM

If the injection current "I

" reaches the set current limit "I

LIM

" during operation, the LED

"LIMIT" (F5) lights up, a short alert beep is heard, and the laser current is limited to the value
of the current limit "I

LIM

". In this case, noise a nd ripple do not longer correspond to the

specifications for normal operation. However exceeding the set current limit "I

LIM

" is

impossible.

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.

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.

If a photodiode is connected, the display can be set to show the photodiode current "I

" or

the optical power "P

" by pressing the key (F17) or (F18).

The laser current can be

modulated

via the connector "MOD IN" (R2).

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

" with the key (F17) or (F18).

Check whether an appropriate photodiode current "I

" is available. A photodiode current of

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

" is negative, the photodiode must be reversed.

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

" can be set using (F9) and with that the optical power of the

laser diode increases until the laser current "I

" reaches the selected current limit "I

LIM

If the desired photodiode current "I

" cannot be set with a sufficient accuracy (F9), the

range of the knob (F9) can be fitted to the current range of the connected photodiode using
the potentiometer "PD RANGE" (F25) - see below.

If no photodiode is connected or the polarity of the photodiode is set wrong, the laser current