Proposal and theoretical investigation with optimization for nuclear spin-polarization using intense laser pulses

(1)我们认为，如果能使光电子的自旋极化，就有可能使残馀离子的电子自旋极化。基于这一假设，我们探索了在光离作用下同时产生自旋极化电子/离子的可能性。碱土原子是这种研究的理想选择，我们选择了锶原子作为目标原子。考虑了两种方案：第一种方案是单光子共振双光子电离，第二种方案是单光子共振单光子电离。经过理论研究，我们发现后者可以达到66%的自旋极化，而>可以达到90%的自旋极化，但代价是产率要小几个数量级。(2)基于(1)的理论结果，我们进行了实验研究，得到了预期的64%的自旋极化。该实验结果为构建自旋极化源奠定了重要的基础。(3)为了获得更好的自旋极化源性能，必须提高自旋极化度和良率。出于这个目的，使用自电离共振似乎是一个很有前途的方案。我们用可调谐染料激光器取代了波长固定的电离激光器（准分子激光器），并进行了实验，发现自旋极化明显改善（64%至78%），产率提高了两个数量级。此外，我们还从理论上研究了一种利用短激光脉冲极化自旋的新方案。

(1)We came to the idea that there may be a possibility to polarize electron-spin of residual ions if one can polarize spin of photoelectrons. Based on this assumption, we have pursued the possibility of the simultaneous production of spin-polarized electrons/ions upon photoionization. Alkaline-earth atoms are ideal for such investigation, and we have chosen Sr for a target atom. Two schemes are considered : The first one is one-photon resonant two-photon ionization, and the second one is one-photon resonant one-photon ionization. After the theoretical study, we have found that 66% spin-polarization is possible for the latter, while >90% spin polarization is possible for the former at the expense of more than few orders of magnitude smaller yield.(2)Based on the theoretical result in (1), we have performed experimental study, and obtained 64% spin-polarization as we expected. This experimental result is an important cornerstone toward the construction of a spin-polarized source.(3)In order to achieve a better performance as a spin-polarized source, it is essential to improve the degree of spin-polarization and yield. For that purpose, the use of autoionizing resonance seems to be a promising scheme. We have replaced a wavelength-fixed ionization laser (excimer laser) by a tunable dye-laser, and carried out experiments to find that the significant improvement of spin-polarization (64% to 78%) and two-orders of magnitude improvement in terms of yield. Furthermore, we have theoretically investigate a new scheme to polarize spin using short laser pulses.