Spherical Optics Research Articles

Integration of Metrology in Grinding and Polishing Processes for Rotationally Symmetrical Aspherical Surfaces with Optimized Material Removal Functions

Aspherical surfaces, with their varying curvature, minimize aberrations and enhance clarity, making them essential in optics, aerospace, medical devices, and telecommunications. However, manufacturing these surfaces is challenging because of systematic errors in CNC equipment, tool wear, measurement inaccuracies, and environmental disturbances. These issues necessitate precise error compensation to achieve the desired surface shape. Traditional methods for spherical optics are inadequate for aspherical components, making accurate surface shape error detection and compensation crucial. This study integrates advanced metrology with optimized material removal functions in the grinding and polishing processes. By combining numerical control technology, computer technology, and data analysis, we developed CAM software (version 1) tailored for aspherical surfaces. This software uses a compensation correction algorithm to process error data and generate NC programs for machining. Our approach automates and digitizes the grinding and polishing process, improving efficiency and surface accuracy. This advancement enables high-precision mass production of rotationally symmetrical aspherical optical components, addressing existing manufacturing challenges and enhancing optical system performance.

At-focus scanning ptychography for high resolution imaging with a wide field of view.

From manufacturing to medicine, there is a demand for phase-resolved, high resolution imaging of large samples. Here we present at-focus scanning ptychography (AFSP), a novel ptychographic metrology station designed for high resolution imaging over a large field of view. AFSP builds on scanning ptychography, but samples remain stationary during the imaging process, allowing for in-situ imaging. We demonstrate a resolution of 44.19μm, present images of spherical and freeform optics with a FOV of over 4cm, and validate the fidelity of the AFSP system by comparing it to established commercial instruments. AFSP's comparable performance underscores its credibility as a valuable addition to quantitative phase imaging technologies.

Laser transverse dual differential confocal radius measurement with high efficiency and high precision.

To meet the need for rapid, high-precision, and non-contact measurement of the radius of curvature (ROC) for large quantities of spherical optics, a radius measurement method based on transverse dual differential confocal (TDDC) detection is proposed in this study. First, a template S0 with a known ROC, R0, is axially scanned on its confocal position to obtain the fitted linear function lTDDC(z) using TDDC. Second, the template S0 is replaced by Sn, which is one of the test sample in large quantities, then the single point TDDC intensity ITDDC(Δzn) is captured without scan, which will be applied to obtain the defocus Δzn according to the linear function lTDDC(z). Finally, the ROC Rn under test is calculated using Δzn and R0. Simulation and experiments show that the measurement accuracy can achieve 8.0 ppm, and the measurement efficiency is 60 times higher than that of the traditional differential confocal scanning measurement. Measurement based on TDDC only requires scanning once and replacing Sn N times to realize the fast, high-precision, non-contact ROC detection of N pieces of spherical optics, which enables the high-efficiency and high-precision measurement of large quantities of spherical optics.

Energy and economic comparison of three optical systems adopted in a point-focus CPV system

The concentrating photovoltaic (CPV) systems allow good results for generation of clean energy at competitive costs, but a careful selection of the optical system is essential to obtain energy and economic advantages. Hence, three different point-focus optics (parabolic mirror, spherical mirror and a commonly used Fresnel lens) characterized by same dimensions are compared in this paper from energy and economic point of view in order to identify the most convenient in terms of unit cost of electrical power. The optical concentration factor, the maximum values of triple-junction (TJ) cell electrical power and temperature are experimentally measured for each optical system, and successively, the unit cost of electrical power is calculated. The parabolic mirror results the least convenient because it guarantees almost the same performances of a spherical optics but with costs of about 2.7 times higher than it. The Fresnel lens presents a value of the unit cost of electrical power near to the spherical mirror, but its much lower optical efficiency implies a necessary area for the CPV plant about three times larger. Moreover, a forecast of the increase in the CPV plant power capacity in Italy and the consequent decrease in the unit cost of electrical power in two possible scenarios, optimistic and pessimistic, is realized. A reduction of the unit cost of electrical power, between 13 and 30%, is expected for the CPV systems.

Method for reducing longitudinal spherical aberration of intraocular lenses

It has been established that of all types of aberrations following the implantation of intraocular lenses, the most significant is spherical, inherent in the spherical optics in various aspects. This paper proposes a method for reducing the longitudinal spherical aberration of intraocular lenses by applying an additional optical layer onto their surface. To reduce spherical aberration, the thickness of a layer of polytetrafluoroethylene (Teflon) was simulated in the programming environment Zemax 13 (USA). Calculations that were performed included refractive indices of the environment and the material of the optics. It was established that in order to reduce the value of the longitudinal spherical aberration of an intraocular lens made of hydrophobic acrylic, the thickness of aTeflon layer should be about 100 nm. The results of spraying indicate an improvement in the optical characteristics of the lens by reducing longitudinal spherical aberration. When examining different areas of lenses with spraying, it was established that there is no spherical aberration in the lens area. In the 4 mm zone, the spherical aberration indicator decreased by 4 times compared to the original lens. In the region with a diameter of 6 mm, spherical aberration decreased by 0.2. Applying a layer of Teflon reduced Fresnel reflection by 4 times, which improves the sensitivity and contrast of vision. The hydrophobic properties of Teflon provide the anti-adhesive state of the lens, which is a counteraction to the development of secondary cataracts. The SolidWorks 19 software (France) was used to design a model of the lens "NVision Optics" whose aberrations were eliminated as much as possible

Characterization of spherical optics performance compared to other types of optical systems in a point-focus CPV system

In this paper the novelty is represented by comparison of optical and energy performances of spherical mirror, rarely used as primary optics in point-focus CPV systems, with those of refractive or parabolic reflective optics. First, concentration factor and optical efficiency are experimentally determined varying distance between Triple-Junction (TJ) cell and spherical mirror, also with secondary optics that increases acceptance angle reducing precision required to solar tracker. Successively, the TJ cell temperature and electrical power values are evaluated under maximum concentration obtaining daily electrical producibility of 98Wh at Fisciano (Italy). Producibility is evaluated for correct and incorrect solar tracking, showing after 750 s decrease of 38.0% and 50.3% respectively with and without secondary optics. Hence, equations linking optical parameters are obtained by experimental data collected for three months and are adoptable for similar point-focus configurations with same TJ cell dimensions and ranges of concentration factor and focal distance. Finally, spherical optics performances are theoretically compared with those of parabolic mirror and experimentally with those of Fresnel lens. Spherical optics is preferable to parabolic from technical-economic point of view because it is easier to produce. Moreover, spherical mirror allows concentration factor and optical efficiency values three times higher than Fresnel lens. The electric power unitary costs of both optics are near but spherical optics requires a CPV system area about three times smaller with same power output. Electrical power and temperature values reached by single TJ cell with spherical optics are respectively about 10 W and 30 °C higher than those of Fresnel lens.

Vision ray metrology for freeform optics

Vision ray techniques are known in the optical community to provide low-uncertainty image formation models. In this work, we extend this approach and propose a vision ray metrology system that estimates the geometric wavefront of a measurement sample using the sample-induced deflection in the vision rays. We show the feasibility of this approach using simulations and measurements of spherical and freeform optics. In contrast to the competitive technique deflectometry, this approach relies on differential measurements and, hence, requires no elaborated calibration procedure that uses sophisticated optimization algorithms to estimate geometric constraints. Applications of this work are the metrology and alignment of freeform optics.

Experimental Comparison between Spherical and Refractive Optics in a Concentrating Photovoltaic System

Since there are not standard configurations of the Concentrating Photovoltaic (CPV) systems, several types of optics are designed and analyzed. In this paper, the optical performances of a spherical mirror and a commonly used Fresnel lens of the same diameter are compared, highlighting their impact on the CPV system energy performance. First, the absolute and percentual variation trends of optical concentration factor and optical efficiency as function of the distance between each optical system and receiver are analyzed. The concentration levels obtained by means of the spherical mirror are much higher than the Fresnel lens, with maximum values of optical efficiency equal to 72.8% and 24.1%, respectively. The analysis of the concentration reduction due to a solar-tracking failure has also allowed the estimation of the acceptance angle, thus observing that the spherical mirror requires a less accurate solar tracker with respect to the Fresnel lens, especially if a secondary optics is adopted. As for the energy comparison, the spherical mirror allows increase of the Triple-Junction (TJ) cell temperature up to about 65 °C higher than the environmental temperature and to reach an electrical power of about 15 W in correspondence of a concentrated solar radiation of 470 kW/m2. Finally, the deviation between the cumulative electric energy produced by the TJ cell in the cases of correct and incorrect solar tracking and for the configurations with and without secondary optics has been also evaluated for both the optics. The equations experimentally obtained in this paper represent a more accurate tool to describe the physical phenomenon in comparison with the equations theoretically obtained for similar CPV systems. The results can be used to design a real CPV system that adopts a Fresnel lens or a spherical mirror. The equations experimentally obtained in this paper represent a more accurate tool to describe the physical phenomenon in comparison with the equations theoretically obtained for similar CPV systems. The results can be used to design a real CPV system that adopts a Fresnel lens or a spherical mirror.

Optical cloaking and invisibility: From fiction toward a technological reality

Optical invisibility, which started in the pages of fiction before becoming an intriguing quest of humankind for over a century, has blossomed into a remarkable scientific journey toward reality over the last two decades. Perfect optical cloaking requires the total scattering of electromagnetic waves around an object at all angles, all polarizations, over a wide frequency range, irrespective of the medium. Such a device is still far-fetched, requiring the transformation of space around a cloaked region such that the phase velocity is faster than other areas to preserve the phase relationships. However, by simplifying the invisibility requirements, pioneering work on spherical transformation cloaks, carpet cloaks, plasmonic cloaks, and mantle cloaks has been realized in narrowband microwave, infrared, and even optical wavelengths. In this Tutorial, we review the theoretical basis for invisibility cloaking, from spherical transformational optics to non-Euclidian cases, and discuss their limitations. Subsequently, we highlight the recent trends in realizing reconfigurable intelligent cloaks to overcome the traditional limitations of wideband operation and parallel efforts in unidirectional cloaking. Because the human eye is insensitive to the phase and polarization of visible light, a class of ray optics cloaking devices has been recently developed by eliminating phase preservation requirements. Notably, we focus on the recent progress achieved on invisibility cloaks that function in natural incoherent light and can be realized using standard optical components. We conclude this Tutorial with a prospective of potential applications and the practicality of optical cloaks in everyday life.

Stimulated Raman scattering in CH4 gas using single cylindrical lens focusing

In this work, single cylindrical lens, an extreme of the astigmatic case, is used to study Stimulated Raman scattering (SRS) in CH4 gas. In comparison with the conventional spherical optics case, single cylindrical lens focusing has three obvious advantages: (1) an increase of the dimension of the focus will decrease pump power density, and the laser-induced breakdown is suppressed. (2) It will efficiently disperse the heat generated in the SRS process, and benefit for the heat management for SRS. Consequently, SRS with cylindrical lens focusing configuration shows stronger resistance to thermal defocusing effect. (3) The forward high-order Stokes and backward SRS are suppressed. Therefore, the utilization of cylindrical lens has improved forward first Stokes in CH4, acquiring the maximum photon conversion efficiency of 67.1% at 188.5 mJ pump energy and 1Hz, and 44.9% at 109.4 mJ pump energy and 10 Hz, for the condition of 3 Mpa pressure. This effect has great potential for the gaseous SRS with high repetition rates and high pressure.

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.

Quasi-optical electron cyclotron emission imaging diagnostic advancements on the J-TEXT tokamak

Abstract The new quasi-optical electron cyclotron emission imaging (ECEI) diagnostic system on the J-TEXT tokamak has been developed and characterized. The quasi-optical system consists of two subsystems: the major imaging optics system for plasma imaging and the local oscillator (LO) optics system to drive the mixers in the antenna array. For the updated demands, some modifications and adaptations are accomplished on the major imaging optics. The vertical zoom ratio, focus capability, and field curvature have been measured on the J-TEXT facility, with good matching with the simulation results. For the various experimental requirements on J-TEXT, the remote control system is adopted for the major imaging optics. As for LO optics systems, spherical LO optics and hyperbolic LO optics have demonstrated high performance. Uniform power deposition has been optimized to drive all mixers and minimize insertion loss.

Fabrication of aspherical polymeric lenses using tunable ferrogel molds.

The majority of optical lenses have spherical surface profiles because they are convenient to fabricate. Replacing spherical optics with aspheric optics leads to smaller size, lighter weight, and less complicated optical systems with a superior imaging quality. However, fabrication of aspheric lenses is expensive and time-consuming. Here, we introduce a straightforward and low-cost casting method to fabricate polymeric aspheric lenses. An elastomeric ferrogel was formed into an aspherical profile by using a designed magnetic field and then was used as a mold. Different types of aspherical profiles from parabola to hyperbola can be formed with this method by tuning the magnetic field. A home-built Shack-Hartmann sensor was employed to characterize the cast polymeric lenses. The effects of magnetic field intensity, gradient of the magnetic field, and magnetic susceptibility of the ferrogel on the lens profiles were investigated. This technique can be used for rapid-forming polymeric aspherical lenses with different sizes and shapes.

Experimental study of the filamentation phenomenon and measurement of filaments parameters

The article experimentally investigated the phenomenon of filamentation in the propagation of femtosecond laser radiation in transparent solid media. The experimental scheme for measuring the parameters of filaments using spherical and cylindrical optics was developed and assembled. A series of experiments on the spatial ordering of filaments was carried out. The sample was structured in the filamentation mode with a predetermined distribution of laser radiation intensity. The spatial redistribution of laser radiation passing through the formed structures in the quartz glass sample is also investigated.

Cherenkov emission-based external radiotherapy dosimetry: I. Formalism and feasibility.

Cherenkov emission (CE)-based external beam dosimetry is envisioned to involve the detection of CE directly in water with placement of a high-resolution detector out of the field, avoiding perturbations encountered with traditional dosimeters. In this work, we lay out the groundwork for its implementation in the clinic and motivate CE-based dosimeter design efforts. To that end, we examine a formalism for broad-beam in-water CE-based dosimetry of external radiotherapy beams, design and test a Monte Carlo (MC) simulation framework for the calculation of CE-to-dose conversion factors used by the formalism, and demonstrate the experimental feasibility of this method. The formalism is conceptually analogous to ionization-based dosimetry and employs CE-to-dose conversion factors, , including only and all CE generated within polar angles θ±δθ on beam axis. The EGSnrc user code SPRRZnrc is modified to calculate , as well as CE spectral and angular distributions. The modified code is tested with monoenergetic parallel electrons on a thin water slab. Detector configurations are examined for broad 6-22MeV electron beams from a BEAMnrc TrueBeam model, with a focus on (4π detection), , and ( is the CE angle of relativistic electrons in water). We perform a relative experimental validation at with electron beams, using a simple detector design with spherical optics and geometrical optics approximation of the sensitive volume, which spans the water tank. Due to transient charged particle equilibrium, broad photon beams are generally less sensitive to beam quality, depth, and angle. For 0.1-50MeV electrons on a thin water slab, the code outputs CE photon spectral density per unit mass (calculated from dose and ) and angle in agreement with theory within ±0.03% and , respectively, corresponding to the output precision. The configuration was found impractical due to detection considerations. Detection at for small δθ exhibited beam quality dependence of the same order as well as strong superficial depth dependence. A 4π configuration ameliorates these effects. A more practical approach may employ a large numerical aperture. In comparing with literature, we find that these effects are less pronounced for broad photon beams in water, as expected. Measured relative at small δθ were within 1% of simulated factors (relative to their local average) for percent-depth CE (PDC) >50%. At other depths, deviations were in accordance with signal-to-noise, known detector limitations, and approximations. It was found that the CE spectrum is beam quality and depth invariant, while for electron beams the CE angular distribution is strongly dependent on beam quality and depth. However, the uncertainty of CE and PDC measurement at detection for small δθ due to deviations around δθ was shown to be ≤1% and <0.1% (k=1), respectively. The robustness to expected detector setup variations was found to result in ≤1% (k=1) local uncertainty contribution for PDC >50%. Based on our MC and experimental studies, we conclude that the CE-based method is promising for high-resolution, perturbation-free, three-dimensional dosimetry in water, with specific applications contingent on comprehensive detector development and characterization.

Metrology Data-Based Simulation of Freeform Optics

This paper describes the approach to use measurement data to enhance the simulation model for designing freeform optics. Design for manufacturing of freeform optics is still challenging, since the classical tolerancing procedures cannot be applied. In the case of spherical optics manufacturing, tolerances are more or less isotropic, and this relationship is lost in case of freeform surfaces. Hence, an accurate performance prediction of the manufactured optics cannot be made. To make the modeling approach as accurate as possible, integration of measured surface data of fabricated freeform optics in the modeling environment is proposed. This approach enables performance prediction of the real manufactured freeform surfaces as well as optimization of the manufacturing process. In our case study this approach is used on the design of an Alvarez-optics manufactured using a microinjection molding (µIM) process. The parameters of the µIM process are optimized on the basis of simulation analysis resulting in optics, with a performance very close to the nominal design. Measurement of the freeform surfaces is conducted using a tactile surface measurement tool.

Study of the Filamentation Phenomenon of Femtosecond Laser Radiation

The filamentation phenomenon during propagation of femtosecond laser radiation in transparent solid media is experimentally studied. An experimental scheme for measuring the filament parameters using spherical and cylindrical optics is developed and assembled. The sample is structured in the filamentation mode, which makes it possible to obtain a specified distribution of laser radiation intensity.

Quartz-based flat-crystal resonant inelastic x-ray scattering spectrometer with sub-10 meV energy resolution

Continued improvement of the energy resolution of resonant inelastic x-ray scattering (RIXS) spectrometers is crucial for fulfilling the potential of this technique in the study of electron dynamics in materials of fundamental and technological importance. In particular, RIXS is the only alternative tool to inelastic neutron scattering capable of providing fully momentum resolved information on dynamic spin structures of magnetic materials, but is limited to systems whose magnetic excitation energy scales are comparable to the energy resolution. The state-of-the-art spherical diced crystal analyzer optics provides energy resolution as good as 25 meV but has already reached its theoretical limit. Here, we demonstrate a novel sub-10 meV RIXS spectrometer based on flat-crystal optics at the Ir-L3 absorption edge (11.215 keV) that achieves an analyzer energy resolution of 3.9 meV, very close to the theoretical value of 3.7 meV. In addition, the new spectrometer allows efficient polarization analysis without loss of energy resolution. The performance of the instrument is demonstrated using longitudinal acoustical and optical phonons in diamond, and magnon in Sr3Ir2O7. The novel sub-10 meV RIXS spectrometer thus provides a window into magnetic materials with small energy scales.

Cylinder Lenses for Beam Shaping

AbstractIn the modern world, lasers are a critical part of so many new technologies. Fields like manufacturing, measurement, medical treatments and scientific research and many more all depend on lasers. The quality of the beam in all of these application areas is crucial and can often be the difference between success and failure. Cylinder lenses are commonly used to shape and manipulate a laser beam and any errors or aberrations they introduce will have a direct impact on the beam quality. Manufacturing methods for cylinder lenses differ from traditional spherical optics and because of this, there are additional specifications to be aware of and consider when using them. Without properly specifying and controlling these parameters problems such as uneven line thickness, beam deviation and image rotation can reduce system performance. This article will line out the unique specifications of cylinder lenses that need to be considered in the process of system integration and their potential effect on the performance (Fig. 1).

Extended shift-rotation method for absolute interferometric testing of a spherical surface with pixel-level spatial resolution.

An improved shift-rotation method for the absolute testing of spherical surfaces is developed to obtain pixel-level spatial resolution and a low noise propagation ratio. The absolute testing process includes multiple rotational tests and two lateral shifting tests with large shifts. A wavefront reconstruction algorithm based on subaperture division and least squares fitting is proposed to reconstruct the surface figure of the test optics. Numerical simulation results show that the method reveals high-frequency figures missed in the traditional Zernike-based shift-rotation method. The algorithm error is lower than 0.4%, and the noise propagation ratio can be reduced by 70% using large shifts. The absolute testing of spherical optics is carried out to verify this method. One spherical surface was tested with the presented absolute testing method and the method using a point diffraction interferometer. The difference of the measurement results based on the two methods showed that the testing uncertainty reached 0.19nm root mean square (RMS), which indicated that the presented method has potential subnanometer testing uncertainty.