Transmission spectrum of the cavity when the cloud of atoms in the ODT is split into two parts. A near resonant intense pulse laser for 12.5 ms is used to split the atomic cloud into two parts with a separation of about 40 μ m . The red dots denote normalized transmission spectrum counted by a SPCM for 10 μ s for each point. The blue curve is a sinusoidal fitting of the data. A frequency of 73.5 ± 0.6 Hz that corresponds to twice the trap frequency in the axial direction is extracted from the transmission spectrum. An exponential increase of the spectrum indicates a decay of atomic number.