Abstract: The invention relates to a laser utilizing a negative branch unstable cavity resonator, comprising two opposed and aligned reflecting mirrors and a baffle aligned with the optic axis of the cavity and located in close proximity to the effective focal point of at least one of the mirrors as determined by the influence of the cavity's remaining optical components. The baffle is provided with an aperture of size such as to stop down the focal spot at its first minimum level of luminous intensity from center. The laser beam, which is out-coupled by conventional techniques, possesses optimum intensity-distribution spatial characteristics in space, and can be focused almost to the diffraction limits.