SIOS Meβtechnik GmbH developed a universal interferometrical profilometer for 3D measurements of freeform optics topography. Due to the measurement principle using a scanning differential interferometer, no expensive and individually shaped reference optics are required. All optic shapes such as plane-,spherical-, and freeform-optics with local slopes up to 7 mrad and sizes up to 100 × 100 mm2 can be measured with sub-nanometer resolution. The capability of the setup has been proven by measurements of highly precise machined silicon mirrors (plane and spherical). A maximum of ± 3 nm peak-valley deviation between two subsequent measurements of a 30 mm × 100 mm plane mirror topography has been achieved, which proves a very good repeatability. Furthermore, measurement results show very good accordance with those from Fizeau interferometer measurements of this precision plane mirror. The maximum deviation was ± 10 nm, which is a hint to a very good accuracy of our measurements. Furthermore, form parameters such as the radii of spherical mirrors can be determined precisely due to the interferometer-based synchronous measurements of the x- and y- positions of the z- topography. A reproducibility of 1.4 × 10-4 of the radius measurements of a 29 m radius mirror was achieved, whereat the mirror was measured on different supports and in different orientations.
In 2019, the Institut für angewandte Photonik (IAP) e. V. in cooperation with Nano Optics Berlin (NOB) GmbH and SIOS Meßtechnik GmbH has made an important progress in the technology for precision soft X-ray optics – the development of three-dimensional (3-D) reflection zone plates (RZPs) with diffractive compensation of slope errors. 2-D mapping of spherical and toroidal grating substrates was used for the metrology of their individual profile. Based on these data, the inscribed grating structure, which corrects the slope error distribution, was computed. The correction algorithm has been implemented as a Python script, and first pilot samples of slope error compensated RZPs are in fabrication process. The 3-D device can replace two or three components in an optical scheme and, therefore, reduce absorption losses by several orders of magnitude. Beyond, the fabrication of customized 3-D Fresnel structures on curved substrates promises considerable improvements for efficiency, resolution and energy range in wavelength dispersive applications. As an example, we present simulations for a compact instrument within (150 – 250) eV. Further development of this approach toward commercial availability will enable the design and construction of compact soft Xray monochromators and spectrometers with unique parameters.
Laser interferometer deliver non-contact and zero mass loading measurements. They provide unique opportunities by measuring the movement of macroscopic and microscopic objects with an extraordinary high resolution and precision. Usually laser interferometer measure along the out-of-plane direction, the measurement object is moved along the measurement beam. But there is an increasing need to determine the in-plane motion or vibration characteristics of structures like MEMS or industrial surfaces.
An in-plane laserinterferometric sensor for measuring the lateral displacement of a surface was developed. The measuring principle of the sensor is based on the heterodyne detection of a moving object. Two laser beams with different frequencies are focused to a common point at the surface and the scattered light is collected by a common lens. The Doppler shift due to a lateral movement of the surface is detected. The sensitivity of the detection is a function of the incident light angle. This principle provides high sensitive measurements of the lateral velocity of the object.
The in-plane laserinterferometric sensor consists of a measuring head and a separate controller which includes the laser light sources and the demodulation electronics. The light sources are fiber coupled, so the sensor size is only defined by the size of the optical components used and the reasonable incident angle. Due to the highly integrated design, a small sensor size can be realized by using standard optics.
It can be shown that the in-plane laserinterferometric sensor is able to track surfaces with very low reflectivity as industrially rough surfaces. A short term noise with a standard deviation of 4 nm at 10 kHz bandwidth can be achieved. High precision measurements of objects displacement, speed, acceleration or frequencies are possible.