Numerical ab initio variational calculations of the transition probabilities and ac Stark shifts in two-photon transitions of antiprotonic helium atoms driven by two counter-propagating laser beams are presented. We found that sub-Doppler spectroscopy is in principle possible by exciting transitions of the type (n,L)->(n-2,L-2) between antiprotonic states of principal and angular momentum quantum numbers n~L-1~35, first by using highly monochromatic, nanosecond laser beams of intensities 10^4-10^5 W/cm^2, and then by tuning the virtual intermediate state close (e.g., within 10-20 GHz) to the real state (n-1,L-1) to enhance the nonlinear transition probability. We expect that ac Stark shifts of a few MHz or more will become an important source of systematic error at fractional precisions of better than a few parts in 10^9. These shifts can in principle be minimized and even canceled by selecting an optimum combination of laser intensities and frequencies. We simulated the resonance profiles of some two-photon transitions in the regions n=30-40 of the \bar{p}^4He^+ and \bar{p} ^3He^+ isotopes to find the best conditions that would allow this.
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机译:提出了由两个反向传播的激光束驱动的反质子氦原子的双光子跃迁的跃迁概率和ac Stark跃迁的数值从头算变化。我们发现,通过在主质子和质子角动量量子数n〜L-1〜35的反质子态之间激发(n,L)->(n-2,L-2)类型的跃迁,原则上可以实现亚多普勒光谱,首先使用强度为10 ^ 4-10 ^ 5 W / cm ^ 2的高度单色的纳秒激光束,然后通过将虚拟中间状态接近(例如,在10-20 GHz之内)调整为真实状态(n- 1,L-1)增强非线性跃迁几率。我们预计,几分之一兆赫或更高的交流斯塔克频移将成为系统误差的重要来源,其分数精度要优于10 ^ 9的几分之一。通过选择激光强度和频率的最佳组合,原则上可以最小化甚至消除这些偏移。我们模拟了\ bar {p} ^ 4He ^ +和\ bar {p} ^ 3He ^ +同位素的n = 30-40区域中某些双光子跃迁的共振曲线,以找到最佳条件。
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