Influence of approximation range of the hologram transmission spectrum on the inverse problem solution

Transmission spectra of holographic sensors based on the Denisyuk holograms with silver nanograins embedded in the polymer matrix are investigated. It is necessary for the determination of the operation mode and of optical parameters of the sensors. The spectra have a narrow Bragg dip against a background decreasing with decreasing the wavelength. Three parameters of this dip determine the operating mode of the sensor. To calculate them, it is necessary to know 3 background parameters. All the parameters are calculated from fitting curves based on the formula proposed earlier which approximates the experimental spectrum quite well. It turns out that the spectral interval chosen for fitting is important and a solution exists not over any interval. When it exists, the parameters of the dip (the main goal of our work) are determined with a good accuracy. As for the optical parameters of the background, those associated with light scattering and with absorption seem to be strongly related. Changing the fitting interval leads to a correlated change of the values of parameters, sometimes considerably. Nevertheless, the fitting function approximates the experimental spectrum quite well and the accuracy of determining the Bragg dip is high.