Microwave Plasma Assisted Chemical Vapour Deposition (MPACVD) is widely used for the production of diamond films, for which hydrogen atoms and methyl radicals have been shown to constitute the key species for growing crystal diamond [1]. The growth of very high purity and quality diamond at elevated deposition rate relies on high production of H atoms and CH3 radicals in a very clean system at very high power density. That is the reason why understanding the physical and chemical processes involved in diamond deposition and how the experimental conditions impact the growth mechanisms at high pressure / high power (> 100 hPa, > 2 kW) requires in particular the determination of H plasma concentration. Following Optical Emission Spectroscopy (OES) used previously [2], Two-Photons Absorption Induced Fluorescence (TALIF) technique has been implemented to study a H2/CH4 CVD plasma under high pressures and high microwave power densities. Indeed, this laser technique is a powerful and spatially resolved tool for chemical characterization of plasma [3].