Abstract

Radially-polarized beams can be strongly amplified without significant birefringence-induced aberrations. However, further improvement of the beam-quality and brightness is desirable. We present two new methods for efficient conversion of a radially-polarized LG(0,1)^* mode to a linearly-polarized nearly-Gaussian beam. In both methods, we use Mach-Zehnder-like interferometric arrangements. In the first method [1], we separate the radially- polarized mode into two degenerate modes with orthogonal polarizations, rotate one one mode’s polarization, flatten the phases of the two degenerate modes, and combine them coherently on a non-polarizing beam splitter (NPBS), to obtain a nearly-doughnut-shaped beam with flat phase and uniform polarization in the output (Fig. 1). As a result, a bright central peak surrounded by a slight ring, appears in the far-field. The slight ring can be spatially filtered. We calculated that the beam quality factor M² of the output nearly-Gaussian beam, obtained with optimal spatial-filter diameter, is M²=1.034, which is much smaller than the input (theoretical) value of 2. The calculated efficiency of our method is 76.59%. So, the theoretical improvement of the ratio of the power to (M²)² (proportional to brightness), is by factor of 2.876.

© 2007 IEEE