Beam quality degradation of a higher order transverse mode beam due to spherical aberration of a lens

An analysis of the increase in the beam-propagation factor, M2, of a higher order transverse mode beam caused by quartic phase aberration after transmission through a spherically aberrated lens is reported. The analysis shows that for a given beam size, the increase in the M2 parameter is less for a higher order transverse mode beam as compared to that for a diffraction limited beam. Experimental results using a multimode laser diode beam show good agreement with the theoretical results.