MAGIA
Collaboration:
Laboratory: European Lab. for Non-Linear Spectroscopy - LENS (Firenze)
National Responsible: G. Tino (Firenze)
1. Goal of the experiment
Measurement of the Gravitational Constant G with a new method based on atomic interferometry .
2.
Activities during 2002
General
One
new laser was setup together with a tapered amplifier to enhance its power up to
500mW. This laser will be used to perform Raman-cooling in an optical lattice on
the atoms.
Phase-lock
system:
We reach a locking-bandwidth of 4.5 MHz. The phase noise of the two lasers (from 1kHz to 6MHz) is 0.07 radian. Although quite good, it is not enough for our experiment, and further improvements are on the way. The phase-lock is of crucial importance for the experiment, as the phase-front of the beat of these lasers will be the reference frame for the entire experiment.
A
new locking scheme: born
out of the necessity to find a suitable locking system for our MOT-laser without
modulating the light, we developed a new locking method, which suits well for
our purpose.
The
method can be designated as Doppler-free DAVLL (dichroic atomic vapor laser
lock). The setup has in common with the classical saturation spectroscopy the
pump probe configuration, but differs in the following points: a magnetic field
along the propagation axis of the light changes the absorption behaviour of the s+
and s-
component of the (linearly polarised) probe beam. The s+
and s- components
of the probe beam are shifted in opposite directions and are detected
independently on two different photodiodes. The resulting difference signal
between those two signals is of dispersive character and has a very low offset
and therefore noise. The laser can be directly locked on this signal, which in
addition is insensitive to stray magnetic fields. A publication is in
preparation.
New apparatus:
The following achievements have been obtained:
Construction of the vacuum system and of laser source setup (100 %)
Construction of the system with two lasers phase locked and amplified (100 %)
Preliminary characterization of the atomic interferometer (50 % (*))
(*) The realization of the laser system and vacuum apparatus required more time than expected because of unexpected technical problems. Preliminary characterization of parts of the final interferometer were performed: 1) cooling and trapping of the atoms in a magneto-optical trap, 2) measurement of the temperature by time of flight scheme. This work will be completed in the first half of 2003.
Milestones 2003
Optimization of the atomic fountain | 31-05-2003 |
Evaluation and design of the source mass | 31-05-2003 |
Optimization of the atomic interferometer parameters | 30-09-2003 |
Analysis and reduction of systematic errors | 30-09-2003 |
Design of the support and motion structure for the source mass | 30-09-2003 |
Measurement of small g with the atomic interferometer | 31-12-2003 |
3. INFN contribution in terms of manpower and financial support.
Manpower: 7 researchers (4.9 FTE), 2 technicians (0.7 FTE)
Budget for the Year 2003: 0.7 % of the CSN2 budget for 2003
4. Number of publications in refereed journals (year 2002): 4
5. Conference talks (year 2002): 0
6. Number of undergraduate and doctoral thesis.
7. Leadership role and major responsibilities in the experiment.
8. Innovative instruments
9. Competing experiments
10. International Committee which has reviewed the experiment