Will Raman photon counts/Spectral resolution increase if laser beam becomes parallel?
Spectral resolution is not dependent on the laser intensity. It is determined by the state of the sample ( gas, liquid or solid) and more importantly by the components of the instrument itself. For example, what is the slit width anf the number of lines on the grating? What type of detector is there? If it is charged coupled device (CCD) then the spectral resolution will also be dependent on it.