Precision Measurement of Complex Optics Using a Scanning-Point Multiwavelength Interferometer Operating in the Visible Domain

Abstract

The growing demands of optical systems have led to increasingly complex aspheres and freeforms. In this paper, an established measurement system in asphere production, which is also a promising approach in high-precision freeform metrology, is presented. It is based on a scanning-point multiwavelength interferometer approach. The scanning principle enables great flexibility, reduces setup time and costs, and has almost no limitations in spherical departure. Due to the absolute measurement capability, the utilized multiwavelength approach is beneficial for segmented, annular, and discrete surfaces, which are common designs of modern applications’ optical elements. The metrology system enables measurements on a nanometer scale on a great variety of apertures—from 1 to 1000 mm. Recently, a new short-coherence multiwavelength interferometer operating in the visible domain has been developed. It enables the high-precision measurement on silicon-coated surfaces, which can be found in space applications and are also commonly used for extreme-ultraviolet (EUV) lithographic setups, which will be used as an example throughout this work. Owing to the large absolute measurement capability, applied grating structures for suppressing infrared light in the EUV process can easily be measured. This paper summarizes the basic working principles of the proposed metrology system, explains the special requirements for different fields of application, highlights the capabilities of the visible multiwavelength approach, and shows the measurement results.

A Hybrid Strategy for Profile Measurement of Micro Gear Teeth

“…With the rapid development of harmonic drive technology, a variety of tooth profile measuring methods have been reported, including contact and noncontact methods: the three-coordinate method, stylus profiler methods, laser interferometer method, chromatic confocal method, structure light method, visual image method, and so [ 5 , 6 , 7 , 8 , 9 , 10 , 11 ]. Among these methods, the laser interferometer method, structure light method, and visual image method can only provide the maximum section profile with limited visual field, lateral resolution, and systematic imaging aberration.…”