We experimentally investigate the spectral broadening in fused silica in the multiphoton absorption regime. Under standard conditions of laser irradiation, linear polarization of laser pulses is more advantageous for supercontinuum generation. However, with high non-linear absorption, we observe more efficient spectral broadening for circular polarizations for both Gaussian and doughnut-shaped beams. The multiphoton absorption in fused silica is studied by measuring the total transmission of laser pulses and by the intensity dependence of the self-trapped exciton luminescence observation. The strong polarization dependence of multiphoton transitions fundamentally affects the broadening of the spectrum in solids.