Oct 28, 2004 - R Schilling a. , A Rüdiger a. ,. D Robertson c. , O Jennrich d. , U Johann b and K Danzmann a a. Max-Planck-Institut für Gravitationsphysik ...
The LTP interferometer and Phasemeter
G Heinzela, V Wanda, A Marina, C Braxmaierb, R Schillinga, A R¨ udigera, D Robertsonc, O Jennrichd, U Johannb and K Danzmanna a Max-Planck-Institut f¨ ur Gravitationsphysik (Albert-Einstein-Institut),
Callinstrasse 38, D-30167 Hannover, Germany. b Astrium GmbH, 88039 Friedrichshafen, Germany c Dept. of Physics and Astronomy, University of Glasgow, UK d ESTEC, Noordwijk, The Netherlands
Journ´ ees du GREX 2004, Nice 28/10/2004. 1
Laser
AOM
f0
f0+f1
Photocurrent
Heterodyne Mach-Zehnder interferometer
∆φ
PD1
f1
AOM f2
f0+f2 f1−f2 = f het
PD2
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
∆φ
0
2
4
6
8
10
time
It has constant sensitivity over a range of > ±100 µm. The heterodyne frequency fhet is a few kHz (1.6 kHz in the EM).
2
-2
10
10-9
µrad/√Hz 170 pm/√Hz
-10
SMART2 mission goal
-11
9 pm/√Hz
10 10
interferometer budget 1 pm/√Hz
-12
10
each interferometer contrib.
10-3
10-3
1000
10-4
54
-5
10
6
10-2 frequency [Hz]
10-1
interferometer phase noise [rad/√Hz]
optical pathlength noise [m/√Hz]
Interferometer budget
The frequency dependence of all interferometer-related budgets is y(f ) = y(30 mHz) ·
v u u t
1+
3 mHz f
!4
,
√ and all budgets in the following are given at 30 mHz (such as 9 pm/ Hz for the interferometer). 3
4 interferometers:
Frequency Fiber Inputs
x1 Reference
x1−x2
x1 − x2 provides the main measurement: the distance between the two test masses and their differential alignment. x1 provides as auxiliary measurement the distance between one test mass and the optical bench and the alignment of that test mass. Reference provides the reference phase for x1 − x2 and x1. Frequency measures laser frequency fluctuations with intentionally unequal pathlengths.
