> \Gamma, \kappa$ [@thompson_observation_1992; @agarwal_spectroscopy_1998]. Here $g_0/2\pi = 201$ kHz is maximum single atom coupling strength, $\Gamma/2\pi =  6.06$ MHz is atomic exited state decay rate, $2\kappa/2\pi =   9.5\pm0.1$ MHz is cavity full width at half maximum (FWHM) and $N_c$ is an effective number of atoms coupled to the cavity. Using an annular piezoelectric transducer (PZT) attached to one cavity mirror, the length of the cavity and hence its resonance frequency ($\omega_c$) can be tuned. On scanning $\omega_c$ around the atomic transition, with frequency $\omega_a$ (3-4$'$ transition of D2 line [@steck_rubidium_2013], which is also the cooling transition for the MOT), two peaks are observed in cavity emission. The cavity emission is monitored using a Photo Multiplier Tube (PMT) and a CCD camera. One peak is red detuned side, and another peak is formed blue detuned to the atomic transition at $\omega_a$ as shown in Fig. \[atnogrid\](a). Both these peaks show TEM$_{00}$ spatial mode structure imaged in the camera, i.e., the cavity output has Gaussian intensity profile. Other spatial modes also show similar two peaked behaviour. The peak heights and frequencies of both the peaks depend on $N_c$ and power in the MOT beams. The red detuned peak is only visible 