V denotes the 'vertical', and H denotes the 'Horizontal', the VV denotes that the polarization of the laser is vertical to the table and you collected the Raman scattering light of which the polarization is also vertical to the table. the VH denotes that you collected the scattering light of which the polarization is horizontal to the table. you could see my paper about the reorientation motion of alcohol in liquid water.