Velocity Transfer Spectroscopy of Rb 420 nm Transition

We propose and demonstrate the velocity transfer spectroscopy of a V-type energy structure with Rb atoms at 420 nm transition. The weak oscillator strength of a lower excited state for V-type energy structure atoms limits the high signal-to-noise ratio of atomic laser spectroscopy, which can be usually realized by optical-optical double-resonance or double-resonance optical pumping for cascade-type energy structure atoms. For ⁸⁷Rb atoms, the weak 420 nm transition spectrum between the energy level of 5²S_1/2 and 6²P_3/2 is transferred to the spectrum on lower excited states at 780 nm with strong oscillator strength, which is recorded by a 780 nm probe laser. This method, which is similar to the electron-shelving detection method, at a certain degree can indirectly measure a higher excited state transition with weak oscillator strength for any V-type energy structure of atoms by transferring the transition spectrum information of the very weak oscillator strength to the strong oscillator strength in an optical-optical double-resonance configuration.