4.5 Commands
4 – 25
MODU ON
Example:
Laser Control Mode
SMOD(?)
{
z
}
Set (query) the laser diode control mode
{
to
z
=
(
CC 0
,
CP 1
)
}
.
If the laser is on when an
SMOD
command is issued that changes
the operating mode, the controller performs a “bumpless transfer”
to switch control modes on-the-fly. If the laser is originally oper-
ating in CC mode, and
SMOD
CP
is received, the present value of
the photodiode current (or equivalently, optical power) is measured,
and the CP setpoint is set equal to the measurement. If the mea-
sured photodiode current or power exceeds the setpoint limit (either
PILM
or
PWLM
), the
SMOD
command fails with an execution error;
otherwise, the control mode is switched seamlessly to CP.
If the laser is originally operating in CP mode, and
SMOD
CC
is set,
the present value of the laser current is measured, the CC setpoint
is set equal to that measurement, and the control mode switched to
CC. Note that, by hardware design, the measured laser current can
never exceed the setpoint limit.
Front-panel control is by the [CC
/
CP] button. Note that if the mode
is switched from the front panel while the laser is on, a confirma-
tion message appears on the screen requesting a second press of the
[CC
/
CP] button; after a
∼
3 s timeout, the command expires if not
confirmed.
The remote form of the command
SMOD
does
not
impose any delay
or confirmation request; the control mode is changed immediately.
Regardless of the source of the request, changing control mode while
the laser is on can be inhibited with the
SMLK
command.
SMOD CC
Example:
Laser Modulation Bandwidth
SIBW(?)
{
z
}
Set (query) the laser modulation bandwidth
{
to
z
=
(
LOW 0
,
HIGH 1
)
}
.
Both laser control modes, CC and CP, have a high-bandwidth and
low-bandwith setting, which can be set or queried by
SIBW?
. The
bandwidth setting can be changed at any time.
The analog modulation input is DC coupled, with the –3 dB roll-o
ff
frequency dependent on control mode and
SIBW
:
—
SIBW
—
LOW
HIGH
CC mode
10 kHz
1.2 MHz
CP mode
100 Hz
5 kHz
LDC500 Series Laser Diode Controllers
