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In this study, we present a simulation and experimental investigation of binodal astigmatism in NAT with a Cassegrain telescope. The high-precision telescope system utilizes a piezo-actuated flexural mechanism to introduce secondary mirror misalignments and generate aberrations intentionally. The induced aberrations are measured interferometrically and quantified for a grid of field points on the image plane of the telescope. For this purpose, a coma-free pivot point of the secondary mirror was simulated for isolating the binodal astigmatism field response. A simulation of binodal astigmatism was generated using a real ray trace model of the Cassegrain system and analyzed to compare to the experimental results. The experimental results were consistent with the simulations, hence experimentally validating NAT for binodal astigmatism for the first time.

We present simulations and an experimental investigation of binodal astigmatism in nodal aberration theory (NAT) for a customized, high-precision Cassegrain telescope system. The telescope system utilizes a five-axis, piezo-actuated flexural mechanism to introduce secondary mirror misalignments and generate aberrations intentionally. The induced aberrations are measured interferometrically and quantified for a grid of field points on the telescope system's image plane. For this purpose, a coma-free pivot point of the secondary mirror was simulated for isolating the binodal astigmatism field response. The separation of the nodes is proportional to the introduced misalignments. A simulation of Fringe Zernike coma and binodal astigmatism was generated using a real ray trace model of the optical system and analyzed to compare to the experimental results. A statistical analysis of the measurements was performed to show the experimental results' accuracy and stability. The experimental results were consistent with the simulations, hence experimentally validating NAT for binodal astigmatism for the first time. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

We present a quantitative evaluation of abrasive grit size dependency of subsurface damages on Zerodur glassceramic substrates induced by precision grinding. The depths of subsurface damages are evaluated for the metal-bonded grinding cup tools with four different grit sizes, D126, D64, D35, and D15, for the fixed nominal grinding process parameters. The micro-crack depth is driven by the mechanism between the abrasive grit and brittle glass, which generates median or radial cracks through the bulk material. The initiation and propagation of subsurface damages beneath the brittle glass-ceramic substrate of Zerodur are explored by the cross-sectional polishing method, which takes advantage of the optical contact bonding method without any adhesive, and are imaged by scanning electron microscopy. A novel hybrid methodology, which comprises both destructive and nondestructive subsurface evaluation tools, is developed and employed for evaluating the micro-cracks quantitively. The procedure is based on a repetitive and consecutive chemical acid etching after the surface is grounded, flat substrate polishing with a conventional polishing machine, a white light interferometer, and an image analysis. The four grit sizes, D126, D64, D35, and D15, correspond to the rough cut through to the complete precision grinding's fine cut. The subsurface damages are measured to be 71 mu m, 35 mu m, 25 and 7 mu m from rough to fine grit sizes. The results are consistent with the theoretical model and previous work. (C) 2021 Optical Society of America

We describe a novel radiation pressure based cantilever excitation method for imaging in dynamic mode atomic force microscopy (AFM) for the first time. Piezo-excitation is the most common method for cantilever excitation, however it may cause spurious resonance peaks. Therefore, the direct excitation of the cantilever plays a crucial role in AFM imaging. A fiber optic interferometer with a 1310 nm laser was used both for the excitation of the cantilever at the resonance and the deflection measurement of the cantilever in a commercial low temperature atomic force microscope/magnetic force microscope (AFM/MFM) from NanoMagnetics Instruments. The laser power was modulated at the cantilever’s resonance frequency by a digital Phase Locked Loop (PLL). The laser beam is typically modulated by ∼500 μW, and ∼141.8 nmpp oscillation amplitude is obtained in moderate vacuum levels between 4 and 300 K. We have demonstrated the performance of the radiation pressure excitation in AFM/MFM by imaging atomic steps in graph...

We present the optical transfer function (OTF) analysis of a spaceborne imaging sensor. This includes the effects of detector footprint, diffusion, smear, jitter, sampling, and time delay and integration. Each effect is analyzed under various design choices one of which corresponds to our designed complementary metal-oxide semiconductor imaging sensor. Effect of each subsystem is separately demonstrated using OTF values and corresponding degradation on a test image.

We describe the design of a thermal refocusing method for spaceborne high-resolution imagers where Korsch optical design is usually implemented. The secondary mirror is made of aluminum, a high thermal expansion coefficient material, instead of conventional zero-expansion glass ceramics. In this way, the radius of the curvature can be controlled by means of temperature change of the mirror. Change in the radius of curvature also changes the effective focal length of the camera which is used for compensation of the defocus that occurred in space. We show that the 30 mu m despace of the secondary mirror in the optical system can be compensated by an similar to 10 degrees C temperature change of the mirror while the image quality is maintained. (C) 2016 Optical Society of America

We studied periodic aperture imaging with various subaperture configurations in terms of their point spread functions, optical transfer functions, and imaging quality. A circular-shaped unit cell provides the best performance compared to square- and cross-shaped unit cells when the total aperture size and collection area are kept the same. Moreover, decreasing the separation among the unit cells or the number of subapertures also improve the imaging performance. Results have potential applications in optical periodic aperture telescopes, diffraction masks, and coded aperture imaging. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)

We describe the design of a wide temperature range (300 mK-300 K) atomic force microscope/magnetic force microscope with a self-aligned fibre-cantilever mechanism. An alignment chip with alignment groves and a special mechanical design are used to eliminate tedious and time consuming fibre-cantilever alignment procedure for the entire temperature range. A low noise, Michelson fibre interferometer was integrated into the system for measuring deflection of the cantilever. The spectral noise density of the system was measured to be similar to 12 fm/root Hz at 4.2 K at 3 mW incident optical power. Abrikosov vortices in BSCCO(2212) single crystal sample and a high density hard disk sample were imaged at 10 nm resolution to demonstrate the performance of the system. (C) 2014 AIP Publishing LLC.

We describe the design of a low temperature scanning Hall probe microscope (SHPM) for a dilution refrigerator system. A detachable SHPM head with 25.4 mm OD and 200 mm length is integrated at the end of the mixing chamber base plate of the dilution refrigerator insert (Oxford Instruments, Kelvinox MX-400) by means of a dedicated docking station. It is also possible to use this detachable SHPM head with a variable temperature insert (VTI) for 2 K-300 K operations. A microfabricated 1 mu m size Hall sensor (GaAs/AlGaAs) with integrated scanning tunneling microscopy tip was used for magnetic imaging. The field sensitivity of the Hall sensor was better than 1 mG/root Hz at 1 kHz bandwidth at 4 K. Both the domain structure and topography of LiHoF4, which is a transverse-field Ising model ferromagnet which orders below T-C = 1.53 K, were imaged simultaneously below 40 mK. (C) 2014 AIP Publishing LLC.