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

Efficient Rydberg positronium laser excitation for antihydrogen production in a magnetic field. S. Cialdi, F. Castelli, I. Boscolo, F. Villa Dept. of Physics, Milano University. Marco G. Giammarchi * Istituto Nazionale Fisica Nucleare - Milano. D. Comparat

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

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  1. Efficient Rydberg positronium laser excitation for antihydrogen production in a magnetic field S. Cialdi, F. Castelli, I. Boscolo, F. Villa Dept. of Physics, Milano University Marco G. Giammarchi* Istituto Nazionale Fisica Nucleare - Milano D. Comparat Lab. Aimé Cotton – CNRS Univ. Paris Sud, Orsay In the frame of the antimatter AEGIS experiment at CERN LEAP08 Conference Vienna, September 2008

  2. 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+ LEAP08 Conference Vienna, September 2008

  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 LEAP08 Conference Vienna, September 2008

  4. Ps excitation scheme: two laser pulses 1 3 n 205 nm 3 2 3 15- 30 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 n Two simultaneous laser pulses: 1 3 Duration of pulses will be ~ 5 ns and since The excitations will be incoherent LEAP08 Conference Vienna, September 2008

  5. Laser system 205 nm 2w 3w 2w 200 mJ >> 16 μJ Nd:YAG (1064nm) 200 mJ, 4 ns Dye- prisms Dl > 0.05 nm 180 mJ 1700 – 1600 nm 20 mJ 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 LEAP08 Conference Vienna, September 2008

  6. 3 transition 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 LEAP08 Conference Vienna, September 2008

  7. n transition 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 LEAP08 Conference Vienna, September 2008

  8. 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 LEAP08 Conference Vienna, September 2008

  9. 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% LEAP08 Conference Vienna, September 2008

  10. Laser system 205 nm 2w 3w 2w 200 mJ >> 16 μJ Nd:YAG (1064nm) 200 mJ, 4 ns Dye- prisms Dl > 0.05 nm 180 mJ 1700 – 1600 nm 20 mJ 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 LEAP08 Conference Vienna, September 2008

  11. LEAP08 Conference Vienna, September 2008

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

  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) LEAP08 Conference Vienna, September 2008

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