Efficient Rydberg positronium laser excitation for antihydrogen production in a magnetic field

1
Efficient Rydberg positronium laser excitation
for antihydrogen production in a magnetic field

• Marco G. Giammarchi
• Istituto Nazionale Fisica Nucleare - Milano

S. Cialdi, F. Castelli, I. Boscolo, F.
Villa Dept. of Physics, Milano University
D. Comparat Lab. Aimé Cotton CNRS Univ. Paris
Sud, Orsay
In the frame of the antimatter AEGIS experiment
at CERN
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Moire deflectometer and detector
AEGIS experimental strategy
1) Produce ultracold antiprotons (100 mK) 2)
Accumulate e 3) Form Ps by interaction of e
with a porous target 4) Laser excite Ps to get
Rydberg Ps 5) Form Rydberg cold (100 mK)
antihydrogen by 6) Form a beam using an
inhomogeneous electric field to accelerate the
Rydberg antihydrogen 7) The beam flies toward the
deflectometer and introduces a spatial modulation
in the distribution of the Hbar arriving on the
detector 8) Extract g from this modulated
distribution
Cold antiprotons
Porous target
e
3
Ps excitation

• Motivations
• Cross section
• Final state distribution better defined

• Conditions
• 1 mm Ø beam spot
• 100 K temperature
• 1 T Magnetic Field

Ps Excitation Laser Light 1 n
Target
e Bunch
Ps
AD
4
Ps excitation scheme two laser pulses
1 3
n
205 nm
3
2
3 15- 30
1700 1600 nm
1
good
better
3 ns lifetime for n2 (and the overall path
requires mores energy) 11 ns lifetime for n3
n
Two simultaneous laser pulses 1
3
Duration of pulses will be 5 ns and since
The excitations will be incoherent
5
Laser system
205 nm
3w
2w
2w
200 mJ gtgt 16 µJ
NdYAG (1064nm) 200 mJ, 4 ns
Dye- prisms
Dl gt 0.05 nm
180 mJ
1700 1600 nm
20 mJ
OPG OPA
1 mJ gtgt 174 mJ
Dl 3 nm
Down-conversion generated and amplified
20 mJ
OPG
PPLN 4cm
Generated Saturation
OPA
10 mJ
LiNb03
6
The 1
Doppler linewidth
Motional Stark effect
Width of the transition dominated by Doppler
broadening.
Laser linewidth of the first transition designed
to be 0.05 nm.
Saturation fluence calculated with rate equation
model and taking into account 30 ns of free
expansion of the Positronium cloud
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The 3
Doppler broadening negligible
Motional Stark effect mixes (n,m,l) levels
starting from n 16
Ionization effects set in at n 27
Ionization limit for lowest lying sublevel
Energy distance between unperturbed n states

• Final n should be between 15 to 30
• Energy levels will overlap

Stark broadening
Doppler broadening
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Using a laser bandwidth
?
?ES
We have predicted the incoherent excitation
probability as
The degenerate high-n levels become n2 manifolds
with a complete mixing of their l,m substates.
laser power spectrum
sublevel density n5
Interleaving of states with different n will occur
absorption coefficient 1/n5
Saturation Fluence 174 µJ
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n1--gt n3 n3--gtn25
Time length 4 ns 2 ns
Fluence 200 µJ/cm2 2 mJ/cm2
Spectral width ?? 0.045 nm 0.72 nm
Simulation of the level population as a function
of time during a single realization of incoherent
excitation.
The phase is being randomized to account for the
incoherence of the pulse
Global efficiency around 30
10
Laser system
205 nm
3w
2w
2w
200 mJ gtgt 16 µJ
NdYAG (1064nm) 200 mJ, 4 ns
Dye- prisms
Dl gt 0.05 nm
180 mJ
1700 1600 nm
20 mJ
OPG OPA
1 mJ gtgt 174 mJ
Dl 3 nm
Down-conversion generated and amplified
20 mJ
OPG
PPLN 4cm
Generated Saturation
OPA
10 mJ
LiNb03
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LASER
OPA
Filtro Spaziale
OPG
13
Experimentally........

• The first excitation can be performed with a
  commercial laser.
• We have focused our attention on the second one,
  the OPG/OPA system.
• The OPG part has been succesfully tested. The
  expected energy has been obtained (with the
  required safety factor) and the expected
  frequency bandwidth
• Now we are testing the OPA system (and this is
  the CONCLUSION)