Measurement Science and Technology Volume 25 Number 5,2014.
Laura Russell1,2, Ravi Kumar1,2, Vibhuti Bhushan Tiwari1,3 and Sìle Nic Chormaic1,2,4
1 Department of Physics, University College Cork, Cork, Ireland and
2 Light-Matter Interactions Unit, OIST Graduate University, 1919-1 Tancha, Onna-son, Okinawa 904-0495, Japan and
3 Laser Physics Applications Section, Raja Ramanna Centre for Advanced Technology, Indore 452013, India and
4 School of Chemistry and Physics, University of KwaZulu-Natal, Durban 4001, South Africa.
We report here the first measurements on a dark magneto-optical trap (DMOT) of 85Rb atoms using an optical nanofibre (ONF) with a waist of ~1 um. The DMOT is created using a doughnut-shaped repump beam along with a depump beam for efficient transfer of cold atoms from the bright hyperfine ground state (F = 3) into the dark hyperfine ground state (F = 2). The fluorescence from the cold 85Rb atoms of the DMOT is detected by coupling it into the fibre-guided modes of the ONF. The measured fractional population of cold atoms in the bright hyperfine ground state (p) is as low as ~0.04. The dependence of the loading rate of the DMOT on cooling laser intensity is investigated and also compared with the loading rate of a bright MOT. This work lays the foundation for the use of an ONF for probing a small number of atoms in an optically-dense cold atomic cloud.