Nearly diffraction‐free CO2 laser beam

Nearly diffraction‐free beams have been generated by a CO2 laser with a new type of cavity composed of a concave mirror and an output mirror with high reflectivity (99.4%) in the marginal part and low reflectivity (94.5%) in the central part. The beam propagation behavior is reproduced fairly well by the Fresnel–Kirchhoff integral of the Bessel–Gauss beam.