Single-atom detection by SONRES

Abstract

The new method of atomic fluorescence detection, called saturated optical nonresonant emission spectroscopy (SONRES), has been modeled for a three-level atom, and experiments on sodium have been conducted that support the model. A rate equation analysis yielded expressions for excited-state atomic populations and saturation intensity. The detection of sodium in buffer gases that promote collisional transfer of excitation between 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> P <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</inf> → 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> p <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3/2</inf> both without quenching the fluorescence emission and with quenching was considered. Experimental results are presented for sodium in argon. At -25°C, approximately 180 atoms/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> were monitored with a S/N of ∼ 15 representing detection at the level of one part in 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> . The signal at this temperature was generated by less than a single atom in the laser beam.