Investigation on form-preserving polishing of side-wall surfaces via an active fluid jet.

In recent years, extensive research and development have been conducted on an active fluid jet (AFJ) polishing-based post-polishing process aimed at removing periodic marks from diamond-turned surfaces. This cost-effective method demonstrates its machining capability across a wide range of materials. Notably, it excels in preserving the form accuracy during the post-polishing process for traditional optics, allowing for the attainment of high-precision shape and an ultra-smooth texture. However, the challenge arises when attempting to maintain form preservation on diamond-cut surfaces located on the side-walls of structures due to non-uniform material removal. This limitation significantly restricts its application in advanced opto-mechanical systems, including monolithic multi-surface workpieces. Therefore, this paper systematically investigates the form-preserving capability of AFJ polishing for side-wall surfaces through multi-scale analysis. The micromachining characteristics of the diamond-cut surface are elaborated upon using elastic-plastic theory, and the impact of polishing parameters on form preservation is studied at the microscopic scale. Furthermore, at the macroscopic scale, a simulation model of the AFJ polishing process is established based on fluid-structure interaction (FSI) analysis and rigid dynamic analysis. To validate the proposed theory, a series of tests are conducted. Theoretical and experimental results indicate that non-uniform material removal occurs in the contact area between the tool and the workpiece due to the influence of gravity, thereby hindering the form-preservation polishing process. Building upon the simulation model, a new AFJ tool is designed and optimized to enhance the form-preserving capability of AFJ post-polishing for side-wall surfaces. Experimental results confirm that the innovative AFJ tool uniformly eliminates the periodic marks on diamond-cut surfaces. The theory and methodology presented in this work have broad applicability to various form-preservation post-polishing processes on diamond-cut surfaces.

Construction of a compact off-axis three-mirror reflective system.

Off-axis reflective optical systems have been widely used due to the nature of miniaturization and no obscuration. However, it is difficult to control the desired system structure during the designation and optimization, especially to maintain the compact system structure. In this paper, a constructing method of off-axis reflective optical systems is proposed to achieve the compact feature. The structure construction combines the constraints of the aberration and the system structure. Multiple parameters of aberration (optical performance) and the mirror coordinates (system structure) are simultaneously optimized to obtain the initial structure using the genetic algorithm. The initial structure is compact, unobscured, and remains less difficult to optimize. A compact off-axis three-mirror reflective system was designed with an entrance pupil diameter of 90 mm, a focal length of 405 mm, and a field of view of 3∘×3∘. Each mirror is expressed by an XY polynomial to achieve optimized optical performance.

A Self-Established "Machining-Measurement-Evaluation" Integrated Platform for Taper Cutting Experiments and Applications.

Taper-cutting experiments are important means of exploring the nano-cutting mechanisms of hard and brittle materials. Under current cutting conditions, the brittle-ductile transition depth (BDTD) of a material can be obtained through a taper-cutting experiment. However, taper-cutting experiments mostly rely on ultra-precision machining tools, which have a low efficiency and high cost, and it is thus difficult to realize in situ measurements. For taper-cut surfaces, three-dimensional microscopy and two-dimensional image calculation methods are generally used to obtain the BDTDs of materials, which have a great degree of subjectivity, leading to low accuracy. In this paper, an integrated system-processing platform is designed and established in order to realize the processing, measurement, and evaluation of taper-cutting experiments on hard and brittle materials. A spectral confocal sensor is introduced to assist in the assembly and adjustment of the workpiece. This system can directly perform taper-cutting experiments rather than using ultra-precision machining tools, and a small white light interference sensor is integrated for in situ measurement of the three-dimensional topography of the cutting surface. A method for the calculation of BDTD is proposed in order to accurately obtain the BDTDs of materials based on three-dimensional data that are supplemented by two-dimensional images. The results show that the cutting effects of the integrated platform on taper cutting have a strong agreement with the effects of ultra-precision machining tools, thus proving the stability and reliability of the integrated platform. The two-dimensional image measurement results show that the proposed measurement method is accurate and feasible. Finally, microstructure arrays were fabricated on the integrated platform as a typical case of a high-precision application.

Phase Compensation of the Non-Uniformity of the Liquid Crystal on Silicon Spatial Light Modulator at Pixel Level.

Phase compensation is a critical step for the optical measuring system using spatial light modulator (SLM). The wavefront distortion from SLM is mainly caused by the phase modulation non-linearity and non-uniformity of SLM's physical structure and environmental conditions. A phase modulation characteristic calibration and compensation method for liquid crystal on silicon spatial light modulator (LCoS-SLM) with a Twyman-Green interferometer is illustrated in this study. A method using two sequences of phase maps is proposed to calibrate the non-uniformity character over the whole aperture of LCoS-SLM at pixel level. A phase compensation matrix is calculated to correct the actual phase modulation of the LCoS-SLM and ensure that the designed wavefront could be achieved. Compared with previously known compensation methods, the proposed method could obtain the phase modulation characteristic curve of each pixel on the LCoS-SLM, rather than a mono look-up table (LUT) curve or multi-LUT curves corresponding to an array of blocks over the whole aperture of the LCoS-SLM. The experiment results show that the phase compensation precision could reach a peak-valley value of 0.061λ in wavefront and this method can be applied in generating freeform wave front for precise optical performance.

Tool path generation of turning optical freeform surfaces using arbitrary rake angle tools.

Slow tool servo diamond turning has widespread application in fabricating freeform optics. Previous studies are focused on the methods of the tool path generation and verification of zero-rake-angle tools. However, these methods are unsuitable for non-zero-rake tools that are used for machining hard-and-brittle materials. This paper presents a universal location-point-drive tool path generation method, which caters to arbitrary rake angle tools and the steady X movement feature, and the corresponding universal tool interference check method. Systematic analysis and ultra-precision machining experiments confirmed the feasibility of our methods and present better surface quality and form accuracy compared to the traditional method.

Uniform Polishing Method of Spherical Lens Based on Material Removal Model of High-Speed Polishing Procedure.

Although the high-speed polishing technology has been widely applied to obtain an ultra-smooth surface in the field of spherical optical manufacture, it is still mainly used in small-size or easily polished lenses. In the infrared optical system, large-size silicon lenses are often used to increase the luminous flux. As is known, the material is hard-polished, it is time-consuming to reduce the surface roughness by iterative polishing and it is difficult to avoid the form accuracy getting worse. To produce an ultra-smooth surface efficiently without destroying the figure, a scientific understanding of material removal in the high-speed polishing process is necessary, which would lead to the process being more deterministic. In this paper, a mathematical model of material removal is developed based on the classic Preston equation. The predicted results of the proposed model show good agreement with the experimental data. Further, a method to achieve uniform polishing can be addressed with a systematic analysis of the key factors affecting material removal and their contribution to spatial non-uniform removal. Finally, the experimental results indicate that the surface roughness of hard-polished spherical optics can be improved efficiently using the uniform polishing method without the surface figure being destroyed.

A Novel Surface Recovery Algorithm for Dual Wavelength White LED in Vertical Scanning Interferometry (VSI).

The two peaks characteristic of yellow and blue light in the spectrum of dual-wavelength white light emitting diodes (LEDs) introduce distinctive features to the interference signal of white light scanning interferometry (WLSI). The distinctive features are defined as discontinuities, so that the fringe contrast function cannot be modeled as a single Gaussian function, and causes the interferogram to have uneven distribution of fringes of different orders in the scanning interferometer. This phenomenon leads to the low accuracy of the zero-order fringe position in the envelope calculation, which affects the repeatability and accuracy of the interferometry. This paper proposes a new surface recovery algorithm based on the Hilbert phase envelope and adjacent reference points calculation, which can effectively overcome the influence of the discontinuous signal of dual-wavelength LED white light interference on the three-dimensional reconstruction of WLSI measurements. The reliability of the algorithm is verified by experiments, and the measurement accuracy of LED WLSI system is evaluated.

Off-spindle-axis spiral grinding of aspheric microlens array mold inserts.

A novel approach named off-spindle-axis (OSA) spiral grinding for fabricating aspheric microlens array (AMLA) mold inserts for precision glass molding (PGM) is presented. In OSA spiral grinding, three translational motions of the grinding wheel are synchronized with the rotation of the workpiece to form a local spiral wheel path for individual lens-lets. With this approach, the form accuracy of lens-lets can be compensated within sub-micrometer by means of the on-machine measurement. The determination of wheel path and form error compensation via on-machine measurement are systematically studied. A tungsten carbide mold insert with four convex aspheric lens-lets is fabricated to evaluate the grinding performance. PGM experiments are performed to produce glass AMLA using the ground insert. The experimental results indicate that both the ground and molded AMLA with homogeneous quality are achieved. The form accuracy and surface roughness of both the mold insert and the molded AMLA were less than 0.3 µm in PV and 10 nm in Sa, respectively.

Quality improvement of collimating lens produced by precision glass molding according to performance evaluation.

Precision glass molding technology is one of the most important approaches to produce optical glass lenses. However, the high fidelity and repeatability of optical performance be sometimes achieved even though the lenses meet the requirements of geometric assessments. The surface errorform errors transferred from mold surface with a complicated combination of components of different spatial-frequencies greatly influence the optical lenses performance. An optical model is built to investigate the impact of form errors with various frequencies on the optical performance of the lens. The mid-spatial frequency error is proved to be the factor that results in the most serious surrounding circle phenomenon. Based on the diffraction theory of the sinusoidal grating, numerical calculation is carried out to analyze their relationship. Experiments are conducted to validate the analysis and a mold polishing procedure is provided as a method to improve the quality of lenses according to performance evaluation.

Manufacturing-constrained optical design methodology for cylindrical freeform reflective imaging system.

Off-axis reflective imaging systems are widely used, but manufacturing issues are seldom considered in their design. This paper proposes a direct design method for cylindrical freeform imaging systems considering manufacturing constraints to facilitate ultraprecise raster milling. The initial freeform shapes of a well-restricted system configuration are constructed using feature data points and calculated based on the constant optical path length condition. An iterative process with coefficient adjustment of the surface expression is employed to optimize the freeform mirrors for both image quality and the degree of deviation from a reference surface. The method's feasibility is validated by designing an off-axis three-mirror imaging system that operates at F/2.0 with a 100 mm entrance pupil diameter and a 4° × 4° field of view. The freeform surfaces are guaranteed to be distributed along a cylinder 150 mm in radius for ultraprecise raster milling.

Integrated manufacture of a freeform off-axis multi-reflective imaging system without optical alignment.

Multi-reflective imaging systems find wide applications in optical imaging and space detection. However, it is faced with difficulties in adjusting the freeform mirrors with high accuracy to guarantee the optical function. Motivated by this, an alignment-free manufacture approach is proposed to machine the optical system. The direct optical performance-guided manufacture route is established without measuring the form error of freeform optics. An analytical model is established to investigate the effects of machine errors to serve the error identification and compensation in machining. Based on the integrated manufactured system, an ingenious self-designed testing configuration is constructed to evaluate the optical performance by directly measuring the wavefront aberration. Experiments are carried out to manufacture a three-mirror anastigmat, surface topographical details and optical performance shows agreement to the designed expectation. The final system works as an off-axis infrared imaging system. Results validate the feasibility of the proposed method to achieve excellent optical application.

Freeform-objective Chernin multipass cell: application of a freeform surface on assembly simplification.

This paper aims at decreasing the assembly difficulty and reducing the cost of optical systems using multiple components. A strategy is proposed to substitute one freeform surface for multi-separated surfaces. A freeform-objective Chernin multipass cell is implemented as a typical instance for assembly simplification. The application of a freeform surface helps in decreasing the degree of objective assembly tolerances from 24 to 4, by representing the original four objectives with a linear combination of a 2D Gaussian radial basis function, which is analytical, global C∞ smooth, and locally influencing. The simulation result verifies the feasibility and performance of the designed freeform-objective Chernin multipass cell, whose base length is 0.2 m, volume is less than 0.8 L, and adjustable optical length is 0.4-34 m. Results prove that by using a proper approach to approximate the original surfaces as an integrated freeform, one can simultaneously reduce the assembly cost and the assembly difficulty.

Highly efficient machining of non-circular freeform optics using fast tool servo assisted ultra-precision turning.

Freeform optics has been regarded as the next generation of the optical components, especially those with non-circular apertures are playing an increasingly significant role in scanning field and specialized optical system. However, there still exist challenges to machine non-circular optical freeform surface. This paper is focused on highly efficiently generating freeform surfaces with optical surface quality by ultra-precision turning using a fast tool servo (FTS). A systematic strategy of machining smooth freeform surfaces with rectangular aperture is proposed in this paper. The contour of freeform optics is decomposed and assigned to the motions of slide and FTS back-and-forth. An optimized model is established for deriving the profile of the rotational component to cater for the capacity of FTS. Tool path reconstruction is carried out to generate a smooth tool trajectory and modified the contour to cater for the stroke of FTS. Simulation is adopted to analyze the machining property of a typical rectangular freeform surface. A rectangular freeform surface is efficiently machined via the proposed method, where a micron level profile error and nanometric finish in Ra are realized. Characteristics of reflection are analyzed via experiment and simulation. Prospects of such machining approach are discussed to provide guidance to future study.

Machining approach of freeform optics on infrared materials via ultra-precision turning.

Optical freeform surfaces are of great advantage in excellent optical performance and integrated alignment features. It has wide applications in illumination, imaging and non-imaging, etc. Machining freeform surfaces on infrared (IR) materials with ultra-precision finish is difficult due to its brittle nature. Fast tool servo (FTS) assisted diamond turning is a powerful technique for the realization of freeform optics on brittle materials due to its features of high spindle speed and high cutting speed. However it has difficulties with large slope angles and large rise-and-falls in the sagittal direction. In order to overcome this defect, the balance of the machining quality on the freeform surface and the brittle nature in IR materials should be realized. This paper presents the design of a near-rotational freeform surface (NRFS) with a low non-rotational degree (NRD) to constraint the variation of traditional freeform optics to solve this issue. In NRFS, the separation of the surface results in a rotational part and a residual part denoted as a non-rotational surface (NRS). Machining NRFS on germanium is operated by FTS diamond turning. Characteristics of the surface indicate that the optical finish of the freeform surface has been achieved. The modulation transfer function (MTF) of the freeform optics shows a good agreement to the design expectation. Images of the final optical system confirm that the fabricating strategy is of high efficiency and high quality. Challenges and prospects are discussed to provide guidance of future work.

Steroids do not prevent photoreceptor degeneration in the light-exposed T4R rhodopsin mutant dog retina irrespective of AP-1 inhibition.

PURPOSE: AP-1 has been proposed as a key intermediate linking exposure to light and photoreceptor cell death in rodent light-damage models. Inhibition of AP-1 associated with steroid administration also prevents light damage. In this study the role of steroids in inhibiting AP-1 activation and/or in preventing photoreceptor degeneration was examined in the rhodopsin mutant dog model. METHODS: The dogs were dark adapted overnight, eyes dilated with mydriatics; the right eye was light occluded and the fundus of the left eye photographed ( approximately 15-17 overlapping frames) with a fundus camera. For biochemical studies, the dogs remained in the dark for 1 to 3 hours after exposure. Twenty-four hours before exposure to light, some dogs were treated with systemic dexamethasone or intravitreal/subconjunctival triamcinolone. AP-1 DNA-binding activity was determined by electrophoresis mobility shift assay (EMSA) and phosphorylation of c-Fos and activation of ERK1/2 were determined by immunoblot analyses. The eyes were collected 1 hour and 2 weeks after exposure to light, for histopathology and immunocytochemistry. RESULTS: Inhibition of AP-1 activation, and phosphorylation of ERK1/2 and c-Fos were found after dexamethasone treatment in light-exposed T4R RHO mutant dog retinas. In contrast, increased AP-1 activity and phosphorylation of c-Fos and ERK1/2 were found in triamcinolone-treated mutant retinas. Similar extensive rod degeneration was found after exposure to light with or without treatment, and areas with surviving photoreceptor nuclei consisted primarily of cones. Only with systemic dexamethasone did the RPE cell layer remain. CONCLUSIONS: Intraocular or systemic steroids fail to prevent light-induced photoreceptor degeneration in the T4R RHO dog retina. Finding that systemic dexamethasone prevents AP-1 activation, yet does not prevent retinal light damage, further supports the hypothesis that AP-1 is not the critical player in the cell-death signal that occurs in rods.

Clinical light exposure, photoreceptor degeneration, and AP-1 activation: a cell death or cell survival signal in the rhodopsin mutant retina?

PURPOSE: The T4R RHO mutant dog retina shows retinal degeneration with exposures to light comparable to those used in clinical eye examinations of patients. To define the molecular mechanisms of the degeneration, AP-1 DNA-binding activity, composition, posttranslational modification of the protein complex, and modulation of ERK/MAPK signaling pathways were examined in light-exposed mutant retinas. METHODS: Dark-adapted retinas were exposed to short-duration light flashes from a retinal camera used clinically for retinal photography and were collected at different time points after exposure. Electrophoretic mobility shift assay (EMSA), supershift EMSA, Western blot analysis, and immunocytochemistry were used to examine AP-1 signaling. RESULTS: Exposure to light of mutant retinas significantly increased AP-1 DNA-binding activity by 1 hour after exposure, and levels remained elevated for 6 hours. Shielded mutant retinas had similar AP-1 levels to shielded or exposed wild-type retinas. The parallel phosphorylation of c-Fos and activation of ERK1/2 was detected only in exposed mutant retinas. Exposure to light changed the composition of the AP-1 protein complex in the mutant retina from c-Jun/Fra-1/c-Fos to JunB/c-Fos. Immunohistochemistry showed that the components of activated AP-1 (JunB, and phosphorylated c-Fos, and phosphorylated ERK1/2 isoforms) were localized in Müller cells. CONCLUSIONS: The inner nuclear layer/Müller cell localization of the key proteins induced by light exposure raises the question of the direct involvement of AP-1 in mediating photoreceptor cell death in this model of autosomal dominant retinitis pigmentosa.

Mitch a rapidly evolving component of the Ndc80 kinetochore complex required for correct chromosome segregation in Drosophila.

We identified an essential kinetochore protein, Mitch, from a genetic screen in D. melanogaster. Mitch localizes to the kinetochore, and its targeting is independent of microtubules (MTs) and several other known kinetochore components. Animals carrying mutations in mitch die as late third-instar larvae; mitotic neuroblasts in larval brains exhibit high levels of aneuploidy. Analysis of fixed D. melanogaster brains and mitch RNAi in cultured cells, as well as video recordings of cultured mitch mutant neuroblasts, reveal that chromosome alignment in mitch mutants is compromised during spindle formation, with many chromosomes displaying persistent mono-orientation. These misalignments lead to aneuploidy during anaphase. Mutations in mitch also disrupt chromosome behavior during both meiotic divisions in spermatocytes: the entire chromosome complement often moves to only one spindle pole. Mutant mitotic cells exhibit contradictory behavior with respect to the spindle assembly checkpoint (SAC). Anaphase onset is delayed in untreated cells, probably because incorrect kinetochore attachment maintains the SAC. However, mutant brain cells and mitch RNAi cells treated with MT poisons prematurely disjoin their chromatids, and exit mitosis. These data suggest that Mitch participates in SAC signaling that responds specifically to disruptions in spindle microtubule dynamics. The mitch gene corresponds to the transcriptional unit CG7242, and encodes a protein that is a possible ortholog of the Spc24 or Spc25 subunit of the Ndc80 kinetochore complex. Despite the crucial role of Mitch in cell division, the mitch gene has evolved very rapidly among species in the genus Drosophila.

Greatwall kinase participates in the Cdc2 autoregulatory loop in Xenopus egg extracts.

Mutations in the Drosophila gene encoding the serine-threonine protein kinase Greatwall have previously been shown to disrupt mitotic progression. To investigate Greatwall's mitotic function, we examined its behavior in Xenopus egg extracts. Greatwall is activated during mitosis by phosphorylation; in vitro evidence indicates that maturation promoting factor (MPF) is an upstream kinase. Conversely, depletion of Greatwall from mitotic extracts rapidly lowers MPF activity due to the accumulation of inhibitory phosphorylations on Cdc2 kinase. Greatwall depletion similarly prevents cycling extracts from entering M phase. The effects of Greatwall depletion can be rescued by the addition of either wild-type (wt) Greatwall or a noninhibitable form of Cdc2 kinase. These results demonstrate that Greatwall participates in an autoregulatory loop that generates and maintains sufficiently high MPF activity levels to support mitosis.

Greatwall kinase: a nuclear protein required for proper chromosome condensation and mitotic progression in Drosophila.

Mutations in the Drosophila gene greatwall cause improper chromosome condensation and delay cell cycle progression in larval neuroblasts. Chromosomes are highly undercondensed, particularly in the euchromatin, but nevertheless contain phosphorylated histone H3, condensin, and topoisomerase II. Cells take much longer to transit the period of chromosome condensation from late G2 through nuclear envelope breakdown. Mutant cells are also subsequently delayed at metaphase, due to spindle checkpoint activity. These mutant phenotypes are not caused by spindle aberrations, by global defects in chromosome replication, or by activation of a caffeine-sensitive checkpoint. The Greatwall proteins in insects and vertebrates are located in the nucleus and belong to the AGC family of serine/threonine protein kinases; the kinase domain of Greatwall is interrupted by a long stretch of unrelated amino acids.

Two putative acetyltransferases, san and deco, are required for establishing sister chromatid cohesion in Drosophila.

BACKGROUND: Sister chromatid cohesion is needed for proper alignment and segregation of chromosomes during cell division. Chromatids are linked by the multiprotein cohesin complex, which binds to DNA during G(1) and then establishes cohesion during S phase DNA replication. However, many aspects of the mechanisms that establish and maintain cohesion during mitosis remain unclear. RESULTS: We found that mutations in two evolutionarily conserved Drosophila genes, san (separation anxiety) and deco (Drosophila eco1), disrupt centromeric sister chromatid cohesion very early in division. This failure of sister chromatid cohesion does not require separase and is correlated with a failure of the cohesin component Scc1 to accumulate in centromeric regions. It thus appears that these mutations interfere with the establishment of centromeric sister chromatid cohesion. Secondary consequences of these mutations include activation of the spindle checkpoint, causing metaphase delay or arrest. Some cells eventually escape the block but incur many errors in anaphase chromosome segregation. Both san and deco are predicted to encode acetyltransferases, which transfer acetyl groups either to internal lysine residues or to the N terminus of other proteins. The San protein is itself acetylated, and it associates with the Nat1 and Ard1 subunits of the NatA acetyltransferase. CONCLUSIONS: At least two diverse acetyltransferases play vital roles in regulating sister chromatid cohesion during Drosophila mitosis.