In this paper, we present experimental techniques to resolve the closely spaced hyperfine levels of a weak transition by eliminating the residual or partial two-photon Doppler broadening and crossover resonances in a wavelength-mismatched double-resonance spectroscopy. The elimination of the partial Doppler broadening is based on velocity-induced population oscillation (VIPO) and velocity-selective saturation (VSS) effects followed by the subtraction of the broad background of the two-photon spectrum. Since the VIPO and VSS effects are the phenomena for near-zero-velocity group atoms, the subtraction gives rise to Doppler-free peaks and the closely spaced hyperfine levels of the $6P_{3/2}$ state in Rb are well resolved. The double-resonance experiment is conducted on the $5S_{1/2}\to 5P_{3/2}$ strong transition (at 780 nm) and $5S_{1/2}\to 6P_{3/2}$ weak transition (at 420 nm) at room temperature.

中文翻译：

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解决紧密间隔的多普勒不匹配双共振水平

在本文中，我们提出了通过消除波长不匹配的双共振光谱中的残留或部分双光子多普勒加宽和交叉共振来解决弱跃迁的近距离超精细水平的实验技术。多普勒局部展宽的消除基于速度引起的总体振荡（VIPO）和速度选择饱和（VSS）效应，然后减去双光子光谱的宽背景。由于VIPO和VSS效应是近零速度基团原子的现象，因此减法会产生无多普勒峰和原子的紧密间隔的超精细能级。$6P_{3/2}$Rb中的状态已得到很好解决。双共振实验是在$5{\mathrm{小号}}_{\mathrm{1个}/2}\to 5P_{3/2}$ 强跃迁（在780 nm处）和 $5{\mathrm{小号}}_{\mathrm{1个}/2}\to 6P_{3/2}$ 室温下的弱跃迁（在420 nm）。