1. Introduction
The
MOGL
abs
FSC
provides the critical elements of a high-bandwidth
low-latency servo controller, primarily intended for laser frequency
stabilisation and linewidth narrowing. The
FSC
can also be used for
amplitude control, for example to create a “noise-eater” that stabi-
lises the optical power of a laser, but in this manual we assume the
more common application of frequency stabilisation.
Feedback frequency stabilisation of lasers can be complicated. We
encourage readers to review control theory textbooks [1, 2] and lite-
rature on laser frequency stabilisation [3].
The concept of feedback control is shown schematically in figure 1.1.
The frequency of the laser is measured with a
frequency discrimi-
nator
which generates an
error signal
that is proportional to the
difference between the instantaneous laser frequency and the de-
sired or
setpoint
frequency. Common discriminators include optical
cavities and Pound-Drever-Hall (PDH) [4] or H¨
ansch-Couillaud [5]
detection; offset locking [6]; or many variations of atomic absorption
spectroscopy [7–10].
+–
0
Servo
Laser
Frequency
discriminator
Error
signal
Control
signal
dV/df
Figure 1.1:
Simplified block diagram of the
FSC
.
The key common feature is that the error signal should reverse sign
as the laser frequency shifts above or below the setpoint, as in
figure 1.2. From the error signal, a feedback servo or
compensator
generates a
control signal
for a transducer in the laser, such that
the laser frequency is driven towards the desired setpoint.
1
Summary of Contents for FSC100
Page 1: ...Fast servo controller FSC100 Version 0 1 2 Rev 2 4 hardware ...
Page 4: ...ii Contents ...
Page 14: ...10 Chapter 1 Introduction ...
Page 22: ...18 Chapter 2 Connections and controls ...
Page 36: ...32 Appendix B 115 230 V conversion ...
Page 39: ......
