High-power Ti:sapphire lasers for spectroscopy of antiprotonic atoms and radioactive ions
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High-power Ti:sapphire lasers for spectroscopy of antiprotonic atoms and radioactive ions M. Hori · A. Dax · A. Soter
Published online: 6 September 2012 © Springer Science+Business Media B.V. 2012
Abstract The ASACUSA collaboration has developed injection-seeded Ti:sapphire lasers of linewidth pl ∼ 6 MHz, pulse energy 50–100 mJ, and output wavelength λ = 726–941 nm. They are being used in two-photon spectroscopy experiments of antiprotonic helium atoms at the Antiproton Decelerator (AD) of CERN. Ti:sapphire lasers of larger linewidth pl ∼ 100 MHz but more robust design will also be used in collinear resonance ionization spectroscopy (CRIS) experiments of neutron-deficient francium ions at the ISOLDE facility. Keywords Antiprotonic helium · CPT symmetry · Laser spectroscopy
1 Introduction The ASACUSA collaboration has carried out high-precision laser spectroscopy [1–4] experiments on antiprotonic helium atoms ( pHe+ ≡ p + He2+ + e− ) for many years. By comparing the measured optical frequencies of pHe+ with the results of threebody QED [5] calculations, the antiproton-to-electron mass ratio was determined as M p /me = 1836.152674(5) [4]. This is in good agreement with the known protonto-electron mass ratio [6–10]. These experiments probe the consistency of the CPT symmetry of particle physics, and complement laser spectroscopy and recombination experiments on antihydrogen proposed by other collaborations [11–13] using the Antiproton Decelerator. The latest pHe+ experiments involve inducing two-photon transitions of the antiproton by irradiating the atom with two counter-propagating laser pulses as
M. Hori (B) · A. Soter Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, 85748 Garching, Germany e-mail: [email protected] M. Hori · A. Dax Department of Physics, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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M. Hori et al. Microstructure optical fiber
Frequency comb
Femtosecond laser 0.7 W, 200 MHz
CW Nd:YVO4 laser 532 nm, 10 W (A)
Stabilization
νCW
ν
CW dye laser 574−673 nm, 1 W CW Ti:S laser 723−941 nm, 1 W
AOM
CW Nd:YVO4 laser 532 nm, 10 W (B)
Heterodyne chirp measurement
νCW +400 MHz
Seed beam
νCW
EOM chirp compensation
Pulsed Nd:YAG laser 532 nm, 200 mJ (C)
To target
CW pulse amplifier
νpl
BBO + LBO crystals
t2
Pulse stretcher
Fig. 1 Dye laser system used for previous single-photon spectroscopy experiments of pHe+ . The seed beam was generated by single-line-mode cw dye and Ti:sapphire lasers locked to a femtosecond frequency comb. This beam was amplified to a pulse energy of E = 5–20 mJ using three dye cells pumped by a Nd:YAG laser. The frequency chirp induced in the dye cells were measured by a heterodyne spectrometer, and corrected using an electro-optic modulator (EOM)
theoretically described in ref. [14]. This effectively reduces the first-order Doppler broadening of the pHe+ resonance line [15], allowing us to measure the transition frequencies at higher precisions than before. To excite these non-linear transitions, however, nanosecond laser
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