A scheme to polarize nuclear-spin of atoms by a sequence of short laser pulses: application to the muonium

摘要

We theoretically show that a sequence of short laser pulses can efficiently polarize nuclear-spin of atoms/ions. This is a variant of optical pumping with an important difference that a sequence of short laser pulses is used instead of a continuous-wave laser. Such a replacement is particularly useful if the pumping wavelength is in the ultraviolet or vacuum-ultraviolet region where obtaining a continuous-wave light source with a sufficient intensity is very difficult. Because of the use of short laser pulses neither hyperfine transitions nor fine structure transitions are spectrally resolved, which is quite in contrast to the standard optical pumping scheme by a continuous-wave laser. As an example we apply the scheme to polarize the muonium (μ+e−, lifetime 2.2 μs), for which the pumping wavelength is 122 nm. From numerical solutions of a set of density matrix equations, we find that the use of only a single, two, and five pulses with a ps duration at the peak intensity of 2×108 W/cm2 and a 5 ns time interval results in the degrees of spin-polarization of 33, 50, and 80 %, respectively, within the time scale of a few tens of ns.