1. Marco G. Giammarchi* Istituto Nazionale Fisica Nucleare - Milano
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
12/10/2018
LEAP08 Conference Vienna, September 2008

2. LEAP08 Conference Vienna, September 2008
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+
12/10/2018
LEAP08 Conference Vienna, September 2008

3. LEAP08 Conference Vienna, September 2008
Ps excitation
Motivations:
Cross section
Final state distribution better defined
Ps Excitation
Laser Light n
Conditions:
1 mm Ø beam spot
100 K temperature
1 T Magnetic Field
Target
e+ Bunch
Ps* AD
12/10/2018
LEAP08 Conference Vienna, September 2008

4. Ps excitation scheme: two laser pulses
1 3 3
205 nm 2 1
1700 – 1600 nm
good
better
3 ns lifetime for n=2 (and the overall path requires mores energy)
11 ns lifetime for n=3
Two simultaneous laser pulses: 1 3 n
Duration of pulses will be ~ 5 ns and since
The excitations will be incoherent
12/10/2018
LEAP08 Conference Vienna, September 2008

5. LEAP08 Conference Vienna, September 2008
Laser system
205 nm 2w 2w 3w
200 mJ >> 16 μJ
Nd:YAG (1064nm)
200 mJ, 4 ns
Dye- prisms
Dl > 0.05 nm
180 mJ
20 mJ
1700 – 1600 nm
OPG + OPA
1 mJ >> 174 mJ
Dl = 3 nm
Down-conversion generated and amplified
20 mJ
OPG
PPLN 4cm
Generated
Saturation
OPA
10 mJ
LiNb03
12/10/2018
LEAP08 Conference Vienna, September 2008

6. LEAP08 Conference Vienna, September 2008
The 1
3 transition
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.
Sto parametro della laser linewidth della prima transizione si puo’ aumentare se si vuole?
Saturation fluence calculated with rate equation model and taking into account 30 ns of free expansion of the Positronium cloud
12/10/2018
LEAP08 Conference Vienna, September 2008

7. LEAP08 Conference Vienna, September 2008
The 3
n transition
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
12/10/2018
LEAP08 Conference Vienna, September 2008

8. LEAP08 Conference Vienna, September 2008
Using a laser bandwidth Δ
ΔES
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
12/10/2018
LEAP08 Conference Vienna, September 2008

9. LEAP08 Conference Vienna, September 2008
Time length
4 ns
2 ns
Fluence
200 μJ/cm2
2 mJ/cm2
Spectral width Δλ
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%
12/10/2018
LEAP08 Conference Vienna, September 2008

10. LEAP08 Conference Vienna, September 2008
Laser system
205 nm 2w 2w 3w
200 mJ >> 16 μJ
Nd:YAG (1064nm)
200 mJ, 4 ns
Dye- prisms
Dl > 0.05 nm
180 mJ
20 mJ
1700 – 1600 nm
OPG + OPA
1 mJ >> 174 mJ
Dl = 3 nm
Down-conversion generated and amplified
20 mJ
OPG
PPLN 4cm
Generated
Saturation
OPA
10 mJ
LiNb03
12/10/2018
LEAP08 Conference Vienna, September 2008

11. LEAP08 Conference Vienna, September 2008
12/10/2018
LEAP08 Conference Vienna, September 2008

12. LEAP08 Conference Vienna, September 2008
LASER
OPA
Filtro Spaziale
OPG
12/10/2018
LEAP08 Conference Vienna, September 2008

13. LEAP08 Conference Vienna, September 2008
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)
12/10/2018
LEAP08 Conference Vienna, September 2008