3D mapping of intensity field about the focus of a micrometer scale parabolic mirror

We report on the fabrication and diffraction-limited characterization of parabolic focusing micromirrors. Sub - micron beam waists are measured for mirrors with 10 {\mu}m radius aperture and measured fixed focal lengths in the range from 24 {\mu}m to 36 {\mu}m. Optical characterization of the 3D intensity in the nearfield produced when the device is illuminated with collimated light is performed using a modified confocal microscope. Results are compared directly with angular spectrum simulations, yielding strong agreement between experiment and theory, and identifying the competition between diffraction and focusing in the regime probed.