A novel method for determining the optical component of the paper substrate point spread function

Knowledge of the actual shape of the point spread function (PSF) is of the utmost importance for paper and print quality assessment, since the PSF represents the degree of lateral scattering of light which is closely associated with the size of the optical dot gain. Importance of the correct shape of the PSF prompted us to propose a new experimental method for determining optical component of PSF of a paper substrate by studying the interaction of collimated light and paper and at the same time demonstrate superiority of the Lorentzian shaped PSF compared to the Gaussian, which is commonly used in the description of the PSF. Additionally, measured profile of the scattered light was compared with the profile obtained from Monte Carlo simulation for identical wavelength of incident light. Once the shape of the optical PSF was determined, FTIR spectra of samples were recorded and analysed, aiming to determine how the ratio of chemical and mechanical pulp influences the shape of the optical PSF. All results indicate better approximation of Lorentzian PSF compared to Gaussian, and imply correlation between the share of mechanical and chemical pulp in paper and characteristics of PSF.