Non-contact control of two-photon absorption

In this experimental work, we address the issue of the control of two-photon absorption in a Doppler broadened medium of ⁸⁵Rb atoms under the ladder level coupling 5S_1/2 → 5P_3/2 → 5D_3/2. Here, suppression and enhancement of two-photon absorption are executed by applying an auxiliary laser beam, which is not physically propagating in the same line of the pump-probe combination. Instead, the auxiliary beam, which is in resonance with the ⁸⁵Rb D₂ transition, is at a finite distance from the line of propagation of the pump-probe combination. The resonant auxiliary beam produces an atomic beam in the vapor cell, and when it reaches the pump-probe path, it creates an asymmetry in the population of ground state hyperfine components. This asymmetry is responsible for controlling two-photon absorption. We present here results obtained by us along with a qualitative explanation of the physical principles behind the control mechanism.