Optical resonators simultaneously resonating at different wavelengths are of interest in passive as well as active optical cavities. Dual-wavelength lasers, optical parametric amplifiers and spectrometers, e.g., in high spectral resolution lidar (HSRL) are effectively improved by employing multiply resonant cavities. In particular, HSRL allows us to measure aerosol optical properties without a priori hypotheses. Here we analyze optical dispersion in a HSRL prototype, based on a confocal Fabry-Perot interferometer (CFPI), developed to work at 532 nm (the lidar excitation wavelength). The presence of dispersion should be accounted for when realizing an effective HSRL because a second beam is required to obtain sufficient locking stability. We have performed an experiment in order to measure the dispersion contributions coming from cavity mirror coating and air and evaluate the stability of the transmission peaks in order to optimize the performances of HSRL.