laser rod or slab and then ducted along the length of the rod or slab by total internal reflection these reflections occur at the polished sides of the rod or slab when the pump light strikes them as the pump light is ducted down the rod or the slab it is gradually absorbed however the use of polished side surfaces to reflect the pump light may potentially make lasers of this type susceptible to parasitic oscillations and amplified spontaneous emission zig zag slab laser geometry relies on low loss reflections of the laser beam many systems confine diode pump light by total internal reflection off of polished faces of the laser rod or slab parasitic oscillations or amplified spontaneous emission can also reflect off of these faces it is generally necessary to avoid geometries where rays can be reflected with low loss and path lengths long enough to result in substantial amplification and depletion of the stored energy in cases where these undesirable rays fill the entire gain volume the entire stored energy could be depleted before useful extraction in particular some of these undesirable rays could be trapped in the laser volume via total internal reflections suffering little or no loss this could prevent any useful gain from being developed and stored in the laser lasers to date have solved this problem by.