Investigations on beam profiles and beam propagation of astigmatic laser diodes with an optical near-field microscope

For industrial applications of high power laser diodes it is of interest to know the focal region of the laser beam for efficient fiber coupling and material processing. Similar questions also occur with laser diodes for the optical communication industry. For efficient fiber coupling the beam shall be round and its waist situated at the fiber entrance. With an optical near field microscope we investigated the near field at the facettes of the laser diode and documented the change when leaving the laser diode in micrometer steps. It is a non paraxial laser beam. The beam radii can be evaluated from the intensity profiles and so the caustic curve of the laser beam in x- and y- direction, which in the ideal case yields a hyperbolic propagation law.