Shaping of laser light intensities by using Diffractive Optical Elements allows the adaption of the incident light to its application. Fused silica is used where for example UV-light or high temperatures are mandatory. For high diffraction efficiency the quality of the etched surface areas is important. The investigation of different process parameters for Ion Beam and Reactive Ion Etching reveals that only Ion Beam Etching provides surfaces with optical quality. Measurements of the influence of the surface quality on the diffraction efficiencies prove that the surfaces generated by Reactive Ion Etching are not suitable.
Due to the high selectivity of the process Reactive Ion Etching is nevertheless a reasonable choice for the fabrication of Diffractive Optical Elements. To improve the quality of the etched surfaces a post processing with Ion Beam Etching is developed. Simulations in MATLAB display that the angle dependent removal of the surface during the Ion Beam Etching causes a smoothing of the surface roughness. The positive influence of a post processing on the diffraction efficiency is outlined by measurements.
The ion beam post processing leads to an increase of the etching depth. For the fabrication of high efficient Diffractive Optical Elements this has to be taken into account. The relation is investigated and transferred to the fabrication of four-level gratings. Diffraction efficiencies up to 78 % instead of the ideal 81 % underline the practicability of the developed post processing.
Laser beam shaping elements can be used e.g. for material processing. The results of these processes can be improved when the usually Gaussian profile of the laser is transformed into a top hat profile, which can be circular or rectangular in shape. Another frequently used type of beam-forming devices are beam splitters for parallel processing using only one laser. These types of beam formers can be implemented as diffractive or refractive elements. So far these optics are produced either directly by means of lithography e.g. in glass or in plastic using a hot embossing process or nanoimprint technology. Elements produced in this way have either the disadvantage of high costs or they are limited in temperature range, laser power or wavelength. A newly developed molding process for glass allows the manufacture of larger numbers of optics with reduced cost.
The production of molds for refractive top hat beam shaping devices requires very high precision of the applied grinding process. Form deviations below 100 nm are necessary to obtain a homogeneous illumination. Measurements of the surface topography of gauss to top hat beam shaping elements using white light interferometry are presented as well as results of optical measurements of the beam profile using a camera.
Continuous diffractive beam shaping elements for beam splitting applications are designed to generate several sub-beams each carrying the same energy. In order to achieve this, form deviations of less than 50 nm are required. Measurements of the surface of a 1 x 5 beam splitter are compared with ideal beam splitter profiles. The resulting beam intensity distribution of a molded element is presented.