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High Sensitive and Spatial-Resolution Atom Sensor Using Two-Step Photoionization with Two-Color Near-Field Lights Generated at a Nano-Slit

We develop a nanoslit to detect a small number of neutral atoms in the ground state. The detection scheme of using two-step photoionization is very sensitive and the use of nanometric near-field lights leads to an ultrahigh spatial resolution. An edge-sharpened nanoslit is fabricated with FIB milling. Considering the case of detecting Rb atoms, the polarization-dependent spatial distribution of near-field light generated at the nanoslit by total-internal reflection of a 476.5-nm Ar-ion laser beam is obtained with a scanning near-field optical microscope. Based on the experimental results, the ionization efficiency is estimated for both s-polarization and p-polarization. We also discuss the discrepancy between the experimental value and the numerical one obtained from the finite difference time domain simulations in the p-polarization case.