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

Abstract

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 2×10(8) W/cm(2) 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.

Spin polarization of Doppler-broadened atoms by the broadband nanosecond and transform-limited picosecond laser pulses: case study for the muonium

“…γ sp and γ L are the spontaneous decay Note that the numbering of the states is not sequential, to be consistent with the numbering of states in our previous work [15], where a set of density matrix equations have been derived. rate, which is 1.6 ns for the 2p state and laser bandwidth, respectively, with γ ≡ γ sp γ L .…”

“…Using Eqs. (1)-(34) in the recent paper [15] together with the additional laser bandwidth terms, −γ ∕ 2σ ji , to be added to the equations for the off-diagonal terms, σ ji , connecting the states jii and jji (i 0, 6, 10; j 7, 8, 9, and 11), we carry out the calculations for muoniums under the Doppler broadening of 230 GHz (FWHM) with a Gaussian distribution function. To test the validity of rate equation description, we have also shown the results by solving the rate equations given by Eqs.…”

“…1 of our previous paper [15], where the uncoupled basis states have been employed to describe the spin-polarization dynamics induced by a sequence of ps laser pulses. Note that we had to use the uncoupled basis states in the recent paper [15] due to the slow hyperfine coupling time (several ns) of the muonium 2p hyperfine states, and the same is true for the broadband ns laser pulses. Since the ns laser pulses we assume in this paper have a broad bandwidth, one may naively think that the use of ordinary rate equations may be valid.…”

“…We have recently shown that the use of a sequence of ps Lyman-α pulses can solve all these problems [15]. Because the spectral width of ps pulses is comparable to the Doppler width of ultraslow muoniums, we can efficiently excite/polarize ultraslow muoniums by the sequence of ps Lyman-α pulses.…”

“…Because the spectral width of ps pulses is comparable to the Doppler width of ultraslow muoniums, we can efficiently excite/polarize ultraslow muoniums by the sequence of ps Lyman-α pulses. In response to our proposal [15], there is a question addressed by the muon community that the use of ns Lyman-α pulses with the same (∼230 GHz) bandwidth may do the similar job. If this is indeed the case, it is a very good news for experimentalists, since one can use either broadband ns or transform-limited ps pulses, depending on the available laser system.…”