Wavefront aberrations of rotationally symmetric CGHs fabricated by a polar coordinate laser plotter

Abstract

Computer-generated holograms (CGHs) were fabricated by a polar coordinate laser plotter. The wavefront aberrations of these CGHs caused by fabrication inaccuracies were measured interferometrically. We tested Fresnel zone plates as typical examples of CGHs with focal ratios of f =10 and f=5 with a Fizeau interferometer. The tests comprised both binary phase holograms and binary amplitude holograms. The wavefront aberrations of the CGHs had an rms variation of about ¶=50. Two types of aberrations were identi®ed and could be referred to certain writing errors. Their size was deduced from the interferograms. IntroductionIn interferometric measurement technology, computer-generated holograms (CGHs) are used in an increased manner for wavefront shaping [1±3]. One reason for this is the relatively simple generation of wavefronts speci®cally adapted to the surface under test by means of the CGH. It is possible to design the CGH to be more¯exible than spherical lenses or mirrors, because the place of de¯ection and the angle of de¯ection of a beam are independent of each other. Furthermore, the dispersion inherent to any CGH does not pose any di culty, because laser interferometry uses quasi-monochromatic light. However, the wavefront aberrations introduced due to errors in the CGH pattern in¯uence the result of the measurement and, therefore, the CGH must be calibrated ®rst. At our institute we have the technology to produce both binary amplitude holograms and binary phase holograms.The purpose of this work was to control and to improve the quality of the CGHs produced with a polar coordinate plotter.

Tolerancing of single point diamond turned diffractive optical elements and optical surfaces

“…With diamond turning, deformations of the generated surface may arise, which are very typical of the production process [4]. Similar errors occur with polar coordinate laser plot-ting, but the substrate is mostly plane here [6]. The following sources of error are definitely present, but there may be some others:…”

“…Vibrations of the spindle perpendicular to the workpiece can result in azimuthal ripples on the surface. In the interferogram of the surface a star is seen, the "spindles star" [4]- [6]. However, a "spindle star" is more indicative of a machine defect than of a reasonably tolerable size.…”

“…Typical surface figure errors of the SPDT process will be modelled here. In addition to SPDT, polar coordinate laser plotting [6], which produces some similar phase errors to SPDT, will be examined. Polar coordinate laser plotting allows the manufacture of diffractive structures in the form of circular rings on flat surfaces.…”

“…On the other hand, errors in the groove shape of diffractive optical elements are described by Freimann [5] for laser plotting, but the effect on the aberrations is only examined by approximation and the carrier of the diffractive element is neglected or it is a flat surface. Reichelt et al [6] examine manufacturing errors which occur on computer-generated holograms on plane surfaces written with a polar coordinate laser plotter.…”

Ultraviolet laser writing system based on polar scanning strategy to produce subwavelength metal gratings for surface plasmon resonance

“…In laser writing, which is the subject of the present study, a beam can be scanned in the x − y format [5][6][7] or in the r − θ format. [8][9][10] The most suitable format depends on the symmetries of the structures that need to be produced. The x − y format is typically preferred when square symmetries are sought in the x and y directions; it can be applied to most one-and two-dimensional (2-D) patterns.…”