Optical switching in a Ξ system: A comparative study on DROP and EIT

In this experimental work we address the issue of optical switching through pump induced atomic coherence in pump-probe spectroscopy of Doppler broadened medium of Rubidium atoms. Here a cascade system 5S → 5P → 5D is chosen as the medium for optical switching. The merit of using this level scheme for current study lies in the fact that two photon spectroscopy conducted in the above-mentioned manifold results into a combination of double resonance optical pumping (DROP) and electromagnetically induced transparency (EIT) signals. Within an intensity modulation frequency range of 10 Hz → 10 MHz, DROP and EIT behave differently. This fact may be attributed to the distinctive difference in mechanisms giving rise to DROP and EIT signals. Though both DROP and EIT stem from two photon spectroscopy, unlike DROP, which arises due to population transfer between dipole forbidden 5S → 5D levels, EIT originates from destructive quantum interference mechanism. This subtle difference is well evidenced when optical switching is conducted through the coherently prepared alkali vapour sample. The EIT is found to be more agile towards faster optical switching while DROP acts as an over damped medium for the same. A simple qualitative discussion is included to explain our results on optical switching