the cavity mode is possible, robust and natural under reasonable experimental conditions. The gain mechanism for the lasing action is a result of multi-photon scattering [@grynberg_central_1993; @wu_observation_1977]. However, unlike previous works [@guerin_mechanisms_2008; @wu_observation_1977], we observe lasing action even when the cavity is not driven by a seed laser. Lezama *et.al* [@lezama_radiative_1990] have earlier seen lasing in an atomic beam experiment, but the atom-cavity coupling was very small for any co-operative effect to manifest.

![Experimental schematics. $^{85}$Rb atoms are cooled by the six red MOT beams and trapped with the help of magnetic gradient. The centre of MOT beams and centre of the cavity formed by the two mirrors overlap. PMT - Photo multiplier tube, CBS - Common beam splitter, CCD- Charge coupled device (camera).[]{data-label="exp"}](setup1.pdf){width="12cm"}

The experiment
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The experimental schematic is as shown in the Fig. \[exp\], $^{85}$Rb atoms are cooled and trapped in a Magnet-optical trap (MOT). The centre of the MOT and centre of the Fabry-Pérot cavity formed around it are made to overlap [@ray_thin_2014; @ray_temperature_2013]. The atomic ensemble is constantly illuminated by the six MOT light beams. There is no light incident on the cavity mirrors. The atom-cavity is in collective strong coupling regime, i.e., $g_0 \sqrt{N_c} 