Ultrafast spectroscopy of exciton and exciton dynamics in mono to few layers of WS$_{2}$

2D materials, beyond Graphene, having a direct band gap in visible spectrum are monolayer of group 6 transitional metal dichalcogenides (MX$_{2})$ that have possibile application in optoelectronic devices, photovoltaics and photodetection, molecular sensing, 'valleytronics', and flexible transparent electronics. Tungsten Disulphide (WS$_{2})$, one of the MX$_{2\, }$, has direct band gap of 2.2 eV and a large valley splitting of about 0.4 eV. This leads to the existence of two distinct and direct excitons A and B. Here, we present a detailed study of exciton states and their decay mechanisms in mono and few layer WS$_{2}$ using femto-second transient absorption spectroscopy. Originally, this set up was designed for the study of macroscopic samples, so we modified it to perform microscopic FTAS on CVD grown flakes of WS$_{2}$. Here, we report a new peak at 3.01 $+$/- 0.1 eV whose origin in k space is under further investigation. The tri-exponential fitting of decay curve of the exciton A reveals three time components as 1.7$+$/-0.3 ps, 33.5$+$/-10 ps and 670$+$/-15 ps, most likely corresponding to carrier-carrier scattering, carrier-phonon scattering, and radiative relaxation respectively.