Fabrication technologies for large optical components at Carl Zeiss Jena GmbH

The metrology of mirrors with an off-axis aspheric or freeform shape can be based on optical testing using a Computer Generated Hologram as wavefront matching element in an interferometric setup. Since the setup can be understood as optical system consisting of multiple elements with six degrees of freedom each, the accuracy strongly depends on the alignment of the surface under test with respect to the transmission element of the interferometer and the micro optics of the CGH. A novel alignment approach for the relative positioning of the mirror and CGH in six degrees of freedom is reported. In the presented work, a proper alignment is achieved by illuminating alignment elements outside the Clear Aperture (CA) of the optical surface with the help of auxiliary holograms next to the test CGH on the substrate. The peripheral holograms on the CGH substrate are used to generate additional phase maps in the interferogram, that indicate positioning errors. Since the reference spheres represent the coordinate system of the mirror and are measured in the same precision as the optical surface, the registration and shape has to be appropriate to embody the mirrors coordinate system. The alignment elements on the mirror body are diamond machined using freeform turning or micro milling processes in the same machine setup used for the mirror manufacturing. The differences between the turning and milling of alignment lenses is discussed. The novel approach is applied to correct the shape error of a freeform mirror using ultra precision machining. The absolute measurement of the quality of freeform mirror shapes including tilt and optical power is possible using the presented alignment concept. For a better understanding, different metrology methods for aspheres and freeforms are reviewed. To verify the novel method of alignment and the measurement results, the freeform surface is also characterized using ultra high accuracy 2½D profilometry. The results of the different techniques for the absolute measurement of freeforms are compared

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“…The technical advancements allow an accurate freeform manufacturing process. [19][20][21] Another enabler is the…”

Section: Freeform Designmentioning

confidence: 99%

Freeform mirror fabrication and metrology using a high performance test CGH and advanced alignment features

et al. 2013

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Fabricating and testing complex optical elements with high precision

Wang¹,

Giggel²,

Derst³

et al. 2011

SPIE Proceedings

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Research on the technique of large-aperture off-axis parabolic surface processing using tri-station machine and its applicability

Luo

Zhang

2015

Appl. Opt.

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In order to process large-aperture aspherical mirrors, we designed and constructed a tri-station machine processing center with a three station device, which bears vectored feed motion of up to 10 axes. Based on this processing center, an aspherical mirror-processing model is proposed, in which each station implements traversal processing of large-aperture aspherical mirrors using only two axes, while the stations are switchable, thus lowering cost and enhancing processing efficiency. The applicability of the tri-station machine is also analyzed. At the same time, a simple and efficient zero-calibration method for processing is proposed. To validate the processing model, using our processing center, we processed an off-axis parabolic SiC mirror with an aperture diameter of 1450 mm. The experimental results indicate that, with a one-step iterative process, the peak to valley (PV) and root mean square (RMS) of the mirror converged from 3.441 and 0.5203 μm to 2.637 and 0.2962 μm, respectively, where the RMS reduced by 43%. The validity and high accuracy of the model are thereby demonstrated.

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Fabrication technologies for large optical components at Carl Zeiss Jena GmbH

Cited by 5 publications

References 2 publications

Freeform mirror fabrication and metrology using a high performance test CGH and advanced alignment features

Freeform mirror fabrication and metrology using a high performance test CGH and advanced alignment features

Fabricating and testing complex optical elements with high precision

Research on the technique of large-aperture off-axis parabolic surface processing using tri-station machine and its applicability

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