The metrology of freeform wavefront can be performed by the use of a noninterferometric method, such as a Shack–Hartmann sensor (SHS). Detailed experimental investigations employing an SHS as metrology head are presented. The scheme is of nonnull nature where small subapertures are measured using an SHS and stitched to give the full wavefront. For the assessment of complex misalignment errors during the spiral scanning, a library of residual slope errors has been created, which makes the alignment process fast converging for minimizing the scanning errors. A detailed analysis of the effects of slope and positioning error on reproducibility is presented. It is validated by null test where a null diffractive optical element has been used in a Mach–Zehnder configuration for compensating the freeform shape. A freeform optics is measured by both measurement schemes, and the results are in good agreement. Further, the nonnull-based scanning subaperture stitching scheme is also validated by performing measurements on an aspheric surface and compared with the measurements from the interferometric method (Zygo Verifire).

Micro-optical elements and complex optical microsystems require ultraprecise manufacturing processes. The maximum tolerable roughness is defined by fractions of the used wavelength $\lambda$, e.g., $\frac{\lambda }{100}$ or better, whereas the overall size and shape of the elements can easily reach the millimeter or centimeter range. Next to the industrially established ion beam polishing approaches for optical surfaces with ultra low surface roughness, reactive ion etching (RIE) has been demonstrated for the efficient realization of highly precise microstructured optical surfaces for beam-shaping^1,2 and beam-splitting,³ as well as for imaging⁴ and illumination^5,6 applications. During RIE, material transport is achieved by a combination of physical and chemical (reactive) interaction of ions and reactive gases with the surface in a plasma reactor. The chemical fraction of the process is naturally highly dependent on the substrate/precursor gas composition. Thus, the process has been developed for the semiconductor industry and is well-established and successfully applied for microstructuring of pure materials (e.g., semiconducting alloys such as GaAs, GaN, and others or Si)⁷ as well as pure fused silica (FS) substrates for optical purposes.⁸ Also polymers can be etched in a reactive plasma based on oxygen and in combination with other gases (if required).⁹ Significant advantages are provided as plasma etching does not necessarily require high process temperatures, while the energy of the individual etching species can be very high. This decoupling of temperature and energy is a significant advantage of plasma enhanced etching processes against purely chemical etching in which the activation energy is applied by temperature only. On the other hand, numerous effects influence the local material removal rate, so defined etching profiles require a detailed knowledge of the etching process.

We present a compact optical decryption system using the generalized phase contrast (GPC) method implemented in a planar integrated micro-optical (PO) device. An encrypted phase pattern is deciphered by the application of a decrypting phase key and visualized using a miniaturized implementation of the GPC method. The current proof-of-principle demonstration makes use of a PO device composed of diffractive micro-optical elements to form a $4-f$ lens imaging setup with a spatial phase-only filter at the Fourier plane. Successful decryption of a $17×9-pixel$ encrypted phase mask is achieved with high-contrast visualization of the original pattern. © 2004 Society of Photo-Optical Instrumentation Engineers.

Deep etching of glass and glass ceramics is far more challenging than silicon etching. For thermally insensitive microelectromechanical and microoptical systems, zero‐expansion materials such as Zerodur or ultralow expansion (ULE) glass are intriguing. In contrast to Zerodur that exhibits a complex glass network composition, ULE glass consists of only two components, namely, TiO₂ and SiO₂. This fact is highly beneficial for plasma etching. Herein, a deep fluorine‐based etching process for ULE 7972 glass is shown for the first time that yields an etch rate of up to 425 nm min⁻¹ while still achieving vertical sidewall angles of 87°. The process offers a selectivity of almost 20 with respect to a nickel hard mask and is overall comparable with fused silica. The chemical surface composition is additionally investigated to elucidate the etching process and the impact of the tool configuration in comparison with previously published etching results achieved in Zerodur. Therefore, deep and narrow trenches can be etched in ULE glass with high anisotropy, which supports a prospective implementation of ULE glass microstructures, for instance, in metrology and miniaturized precision applications.

An innovative optical system for trapping particles in air is presented. We demonstrate an optical system specifically optimized for high precision positioning of objects with a size of several micrometers within a nanopositioning and nanomeasuring machine (NPMM). Based on a specification sheet, an initial system design was calculated and optimized in an iterative design process. By combining optical design software with optical force simulation tools, a highly efficient optical system was developed. Both components of the system, which include a refractive double axicon and a parabolic ring mirror, were fabricated by ultra-precision turning. The characterization of the optical elements and the whole system, especially the force simulations based on caustic measurements, represent an important interim result for the subsequently performed trapping experiments. The caustic of the trapping beam produced by the system was visualized with the help of image processing techniques. Finally, we demonstrated the unique efficiency of the configuration by reproducibly trapping fused silica spheres with a diameter of 10 μm at a distance of 2.05 mm from the final optical surface.

We present tunable lenses based on aluminum nitride membranes. The achievable tuning range in the refractive power is 0 to 25 dpt with an external pressure load of $≤20kPa$. The lenses are manufactured using MOEMS technology. For 500-nm-thick membranes with a diameter of 3 mm, a spherical deflection profile is found. The system provides good long-term stability showing no creep or hysteresis. A model for the refractive power versus applied pressure is derived and validated experimentally. Based on this model, design guidelines are discussed. One essential parameter is the residual stress of the aluminum nitride layer that can be controlled during deposition.