Beam Transformation by Defocused Imaging Lens.

The effects of spherical aberration and beam truncation have been clarified in the beam transformation of laser radiation by a defocused imaging lens. Excellent agreement was obtained between calculated and measured patterns. The beamwidths are largely determined by geometrical optics. Amplitude ripples of about 1 dB are primarily caused by interference between geometrical optic rays and edge diffraction rays, and will occur even in the absence of spherical aberration and lens surface reflections. Moderate spherical aberration only produces minor modification in beamwidth and amplitude taper within the beam, whereas very large spherical aberration with opposite phase curvature to that of defocusing can lead to pattern break- up.