Aspheric Research Articles

Strategies for formula constant optimisation for intraocular lens power calculation

BackgroundTo investigate modern nonlinear iterative strategies for formula constant optimisation and show the application and results from a large dataset using a set of disclosed theoretical-optical lens power calculation concepts.MethodsNonlinear iterative optimisation algorithms were implemented for optimising the root mean squared (SoSPE), the mean absolute (SoAPE), the mean (MPE), the standard deviation (SDPE), the median (MEDPE), as well as the 90% confidence interval (CLPE) of the prediction error (PE), defined as the difference between postoperative achieved and formula predicted spherical equivalent power of refraction. Optimisation was performed using the Levenberg-Marquardt algorithm (SoSPE and SoAPE) or the interior point method (MPE, SDPE, MEDPE, CLPE) for the SRKT, Hoffer Q, Holladay 1, Haigis, and Castrop formulae. The results were based on a dataset of measurements made on 888 eyes after implantation of an aspherical hydrophobic monofocal intraocular lens (Vivinex, Hoya).ResultsFor all formulae and all optimisation metrics, the iterative algorithms showed a fast and stable convergence after a couple of iterations. The results prove that with optimisation for SoSPE, SoAPE, MPE, SDPE, MEDPE, and CLPE the root mean squared PE, mean absolute PE, mean PE, standard deviation of PE, median PE, and confidence interval of PE could be minimised in all situations. The results in terms of cumulative distribution function are quite coherent with optimisation for SoSPE, SoAPE, MPE and MEDPE, whereas with optimisation for SDPE and CLPE the standard deviation and confidence interval of the PE distribution could only be minimised at the cost of a systematic offset in mean and median PE.ConclusionNonlinear iterative techniques are capable of minimising any statistical metrics (e.g. root mean squared or mean absolute error) of any target parameter (e.g. PE). These optimisation strategies are an important step towards optimising for the target parameters which are used for evaluating the performance of lens power calculation formulae.

Mapping distortion correction in off-axis aspheric mirror testing with a null compensator.

Mapping distortion can be introduced in null testing for off-axis aspheric surfaces, from which the testing results with coordinate deviation cannot be used to guide deterministic optical manufacturing. We propose a correction method for mapping distortion in this study based on the imaging distortion analysis of a null lens and iteration algorithm. We use imaging distortion data to fit the distortion polynomial function by the least-squares method, and we design an iteration algorithm to determine the rotation angle and the position of the null distortion point of the testing results. Finally, the mapping distortion can be accomplished without any markers on the mirror under test. The 280mm×180mm primary mirror and 234mm×176mm tertiary mirror of the hyperspectral camera were tested with a null compensator, and the distortion correction results were obtained using the proposed method. After magnetorheological finishing based on the correction results, the rms of the primary mirror and tertiary mirror reduced from 0.263λ to 0.013λ and 0.059λ to 0.018λ (λ=632.8nm), respectively.

Effect of decentration on the quality of vision: comparison between aspheric balance curve design and posterior aspheric design intraocular lenses.

To study the effect of decentration on the quality of vision in 2 aspheric intraocular lenses (IOLs): aspheric balance curve (ABC) design Vivinex iSert XY1 (Hoya Surgical Opticals, Inc.) and posterior aspheric design AcrySof IQ SN60WF (Alcon Laboratories, Inc.). Advanced Eye Centre, PGIMER, Chandigarh, India. Randomized prospective trial using a random number table. 85 eyes were randomized to group 1 (Vivinex XY1) and group 2 (AcrySof IQ) with 40 and 45 eyes, respectively. The higher-order aberration (HOA) profile, Strehl ratio, decentration of the IOL from the visual axis (decentration from the visual axis [DVA]) and the geometric axis (decentration from the geometric axis [DGA]), angle α, and κ were recorded on the iTrace aberrometer, and contrast sensitivity was measured using the Functional Acuity Contrast Test at 12 weeks postsurgery. A total of 85 eyes in 60 patients were evaluated in this study. The mean values of the Strehl ratio (P = .48) and the HOAs (P = .12) of both IOLs were comparable. The HOAs gradually increased with increasing DVA for both lenses at 3.0 mm, 4.0 mm, and 5.0 mm pupil sizes. On comparing the HOAs with the DGA, a statistically insignificant positive correlation was observed. The Strehl ratio did not deteriorate with an increasing angle α in the Vivinex XY1 group; however, it worsened in the AcrySof IQ group. Contrast sensitivity was comparable in both the IOLs except at 1.5 cycles per degree under photopic conditions where the AcrySof IQ was better. Decentration of the lens was best measured with respect to the visual axis. In eyes with a large α, the ABC design induced lesser HOAs and maintained a better Strehl ratio.

Exploring Vision-Related Quality of Life: A Qualitative Study Comparing Patients' Experience of Cataract Surgery with a Standard Monofocal IOL and an Enhanced Monofocal IOL.

PurposeTo explore quality of life related with intermediate vision of patients before and after cataract surgery, and to make patients’ experience available for the design of future scales that assess visual function related with intermediate distance.Patients and MethodsA qualitative research methodology based on thematic content analysis was used to explore vision-related quality of life based on the experiences of patients with cataract. Patients were recruited at the Service of Ophthalmology of the Hospital de Sant Pau (Barcelona, Spain). Data were collected through nineteen semi-structured interviews conducted with patients diagnosed with cataract and implanted with a standard aspheric monofocal intraocular lens (IOL) (Tecnis® ZA9003) (n = 6), an enhanced monofocal IOL (Tecnis® Eyhance ICB000) (n = 6), and patients from the waiting list (n = 7). The data analysis consisted in coding, aggregation, and theme development of the transcribed audios.ResultsPatients on waiting lists reported difficulty and insecurity in performing daily and meaningful tasks related to near visual ranges (eg: threading a needle, reading price tags), intermediate (eg: using a computer or dialling numbers on a smartphone), and distant (eg: recognizing faces, walking on uneven surfaces). Patients after surgery with the standard IOL reported improvement in performing activities mainly in the distant visual range, but also the need for a better communication with clinical staff to adjust their own expectations on the results of the surgery. Finally, patients implanted with the enhanced IOL reported satisfaction and improved visual function in performing daily activities, especially those related to the intermediate visual range.ConclusionOur exploratory study found that patients after cataract surgery with the enhanced IOL reported a better performance in activities that require the intermediate vision. These results will inform the development of scales to assess vision-related quality of life in the intermediate visual range prioritizing outcomes according to patients’ daily and meaningful activities.

Collimation of an anastigmat objective with three off-axis aspherical mirrors

Subject of study. Objectives for a wide variety of wavelengths from the visible to the mid-infrared are currently under development for use in small spacecraft. Because of advantages such as the ability to operate over a broad spectral range, the use of low-weight mirror fabrication technologies, and their smaller size, reflective objectives are preferred for space-based applications. This paper discusses the collimation of reflective objectives with off-axis aspheric mirrors (objectives with an off-axis field of view). Collimation of reflective objectives has traditionally been performed using interferometers operating in autocollimation mode, with collimation being verified using compensatory designs. In the case of compact multimirror objectives, it is not always possible to find space for the collimation equipment (either an interferometer with an auxiliary mirror or a holographic compensator). Method. An alternative technique was developed for sequential element-by-element collimation of a prototype multimirror objective, based on monitoring focal-spot shapes and comparing them against a calculated focal-spot shape. We discuss collimation of a four-mirror anastigmat objective, in which the first mirror is an off-axis concave ellipsoid, the second mirror is an off-axis convex hyperboloid, the third mirror is a flat, and the fourth mirror is an off-axis concave ellipsoid. The objective was collimated using a He-Ne laser (wavelength 0.63 µm), with the distribution of light in the focal spot being recorded with a television camera; collimation was verified using a continuously tunable CO laser (emission wavelength of 5.415 µm) and an HF laser (emission wavelength of 2.8–3.2 µm), and the distribution of light in the focal spots was measured with an InSb photodetector array. The focal spots were inspected using a microscope whose object plane coincided with the focal plane of the element being collimated. The entrance aperture of the objective was illuminated by a collimated laser beam parallel to the collimation axis. The quality of collimation was determined by comparing the shapes of the observed focal spots against those theoretically calculated for an ideally collimated objective. Main results. Our research revealed that a test collimation technique based on the shape of the focal spots is insufficiently sensitive to miscollimation of individual mirrors and scattering within a multiple-mirror system. In addition, the technique fails to provide the required collimation accuracy. Practical significance. The proposed technique will be used to develop specialized optoelectronic instrumentation for continuous, step-by-step verification of all optical elements in a four-mirror anastigmat to sufficient accuracy for collimation.

A concentrated sunlight energy wireless transmission system for space solar energy harvest

Advancements in spacecraft formation and space solar power plant technologies promote wireless energy transmission among satellites and the Earth. Although microwave-based, laser-based, and sunlight-based wireless energy transmission technologies have been reported previously, none of them have been practically deployed because of major limitations. In this paper, a concentrated sunlight energy wireless transmission system (CSEWTS) using single plano-convex lenses to harvest space sunlight and a single corresponding optical fibre bundle (OFB) to realize flexible energy transmission is schematically developed and its prototype is established experimentally. This system utilizes sunlight as the transmission media to avoid intermediate energy conversion and where energy efficiency can be enhanced compared to microwave-based or laser-based energy wireless transmission. Furthermore, the OFB-based CSEWTS can lighten the mirror-based system, which was developed previously. Various effects of optical coupling, condenser outline in the energy receiver, smog, distance, and bending were experimentally or theoretically investigated. An optimized coupling incident angle into OFB of 18° was attained theoretically and validated experimentally where an improvement of 19.9% in system efficiency was acquired from a wrong angle to an optimal one. Besides, aspheric lenses were experimentally proved to be more appropriate to condense sunlight where a 16.5% − 19.5% enhancement was obtained. In addition, lens coating, condenser outline in the energy receiver, smog, and distance effects were also analyzed. Smog harms energy transmission which casts shadows on its space-Earth application. Energy transmission to a no-cloud area is the only probable option. The developed technologies can also be used in solar sail spacecraft, contributing to global carbon neutrality and clean aerospace flight.

Release characteristics of a high-hardness DLC coating on an aspherical glass lens mold

In this paper, we investigated the changes in the shape precision of a diamond-like carbon (DLC)-coated surface of an aspherical glass lens mold. The press molding process of the experiment involved placing a bulk material made of glass in an ultra-precision mold and applying cylinder pressure at a high temperature. Thermally stable tungsten carbide was used as the mold material. DTM grinding with a resolution of 0.1 [Formula: see text]m was performed to precisely process the tungsten carbide aspherical lens mold. HiPIMS–DLC and ta-C DLC coatings having excellent anti-stiction and hardness were applied on the polished mold. The hardness of the thin film was measured using nanoindentation. For the composition of the DLC, the [Formula: see text]/[Formula: see text] peak values were detected through Raman spectroscopy. Furthermore, the friction coefficient of the DLC thin film was measured using a tribology tester, and the friction coefficients of HiPIMS–DLC and ta-C were 0.018 and 0.014. Using FTS measurements, we confirmed that the precision of the aspherical lens shape (Peak to Valley) of the aspherical lens was 1.5 [Formula: see text]m and 0.5 [Formula: see text]m, respectively.

Polarization Aberrations in High-Numerical-Aperture Lens Systems and Their Effects on Vectorial-Information Sensing

The importance of polarization aberrations has been recognized and studied in numerous optical systems and related applications. It is known that polarization aberrations are particularly crucial in certain photogrammetry and microscopy techniques that are related to vectorial information—such as polarization imaging, stimulated emission depletion microscopy, and structured illumination microscopy. Hence, a reduction in polarization aberrations would be beneficial to different types of optical imaging/sensing techniques with enhanced vectorial information. In this work, we first analyzed the intrinsic polarization aberrations induced by a high-NA lens theoretically and experimentally. The aberrations of depolarization, diattenuation, and linear retardance were studied in detail using the Mueller matrix polar-decomposition method. Based on an analysis of the results, we proposed strategies to compensate the polarization aberrations induced by high-NA lenses for hardware-based solutions. The preliminary imaging results obtained using a Mueller matrix polarimeter equipped with multiple coated aspheric lenses for polarization-aberration reduction confirmed that the conclusions and strategies proposed in this study had the potential to provide more precise polarization information of the targets for applications spanning across classical optics, remote sensing, biomedical imaging, photogrammetry, and vectorial optical-information extraction.

A portable brightfield and fluorescence microscope toward automated malarial parasitemia quantification in thin blood smears.

Malaria is often most endemic in remote regions where diagnostic microscopy services are unavailable. In such regions, the use of rapid diagnostic tests fails to quantify parasitemia measurements which reflect the concentration of Plasmodium parasites in the bloodstream. Thus, novel diagnostic and monitoring technologies capable of providing such information could improve the quality of treatment, monitoring, and eradication efforts. A low-cost, portable microscope for gathering quantitative parasitemia data from fluorescently stained thin blood smears is presented. The system employs bimodal imaging using components optimized for cost savings, system robustness, and optical performance. The microscope is novel for its use of monochromatic visible illumination paired with a long working distance singlet aspheric objective lens that can image both traditionally mounted and cartridge-based blood smears. Eight dilutions of red blood cells containing laboratory cultured wild-type P. falciparum were used to create thin smears which were stained with SYBR Green-1 fluorescent dye. Two subsequent images are captured for each field-of-view, with brightfield images providing cell counts and fluorescence images providing parasite localization data. Results indicate the successful resolution of sub-micron sized parasites, and parasitemia measurements from the prototype microscope display linear correlation with measurements from a benchtop microscope with a limit of detection of 0.18 parasites per 100 red blood cells.

Aspheric lens processing of chalcogenide glass via combined PGM-SPDT process

Aspheric lens processing of chalcogenide glass via combined PGM-SPDT process

Thermal optics of a collimator radiatively cooled under vacuum

Infrared optoelectronic equipment with cooled optics operating in a background limited mode is tested in a vacuum and a low radiation background. The latter is ensured by cooling the optical elements of the collimator and preventing direct illumination of the entrance pupil of the equipment by warm elements of the vacuum chamber. Subject of study. The thermal optics of a two-mirror collimator are investigated in this study. The mirrors of this collimator are cooled by heat transfer through infrared emission to the cooled cylindrical shields of the thermostat, which was specifically designed for collimator cooling. Method. The collimator cooling modes are calculated considering both thermophysical material properties and structural features of the elements comprised in the thermostat and collimator. The thermophysical model of thermal equilibrium in an isolated system of solid bodies is used in the calculations. The issue of selecting a particular material for the collimator mirrors is considered provisionally. The thermal stability of the mirror material calculated as a ratio of the coefficient of thermal expansion β to its heat conduction coefficient λ is used as a parameter determining the choice. Sitall, silicon, and silicon carbide were considered in this study as materials for infrared mirrors. Main results. The magnitude of thermal deformations is determined by not only the occurring temperature gradients in a plane mirror but also the variation in the curvature of the mirror surface under general cooling of the nonplanar mirrors. The maximum temperature gradient over the surface is observed for the mirrors composed of sitall. The temperature gradient in the mirror composed of silicon carbide is significantly smaller. This is related to the heat conduction coefficient of silicon carbide being 2 orders of magnitude higher than that of sitall. Consequently, the thermal deformations of the mirror surface are also smaller in the plane mirror composed of silicon carbide. These results correspond to the criterial parameter of thermal stability β/λ for each of the discussed materials. However, in the case of cooling of the nonplanar (spherical or aspherical) mirrors, the calculations show that their thermal deformations result from not only the nonuniformity of heat flow distribution over the mirror surface but also the general reduction in mirror temperature. Practical significance. When cooled infrared mirrors are used in optical systems, the appearance of thermal deformation of their mirror surface should be considered. This thermal deformation is determined by not only the occurring temperature gradients in the volume of the mirror material, but also the change in the curvature of the mirror surface. In this regard, the mirrors composed of sitall are preferable for use under thermal vacuum conditions over mirrors composed of silicon carbide.

Photoacoustic LED imaging apparatus using a low-cost system

The use of compact and cost-effective visible light emitting diodes (LEDs) as an alternative to Q-switched lasers, the conventional photoacoustic excitation source, has been explored for vascular imaging applications [T. J. Allen and P. C. Beard, “Light emitting diodes as an excitation source for biomedical photo-acoustics,” Proc. SPIE 8581, 85811F (2013)]. This research motivated our work. Experiments used a 619 nm LED (Luminus SST-90-R-F11-HH100) pulsed for 450 ns with period 34 ms utilizing a pulse generator, MOSFET driver and power MOSFET switch, discharging a bank of capacitors (990 μF) with 36 A peak current. A pair of 2.5 cm diameter aspherical acrylic lens focused the LED—with an emitting area of 3mm × 3 mm—onto the surface of a vertical capillary tube (1.19 mm ID, 1.75 mm OD) filled with 5% McCormick Green food coloring or 5% Higgins India Ink and placed in the 10 cc acrylic water tank. An Olympus emersion transducer (1.27 cm diameter circular plane array, 1 MHz with 0.4MHz bandwidth) was amplified using four home-made low noise amplifiers (87 dB overall gain, 0.5–30 MHz bandwidth). An Agilent DSO 7014 B oscilloscope recorded the photoacoustic signal pulse averaging 8196 trials.

Aspherical liquid crystal lenses based on a variable transmission electrode.

In this work, a technique to generate aspherical liquid crystal lenses with positive and negative optical power is experimentally demonstrated. The main enabling element is a micro-metric electrode with variable spatial size. This produces a decreasing resistance towards the lens centre that generates the desired voltage/phase profiles. Then, the voltage is homogeneously distributed across the active area of the lens by micro-metric concentric electrodes. As it is demonstrated, the phase shift can be controlled with voltages from 0 to 4.5 VRMS. As a result, parabolic profiles are obtained both for negative and positive optical powers. Furthermore, this approach avoids some disadvantages of previous techniques; parabolic profiles can be obtained with only one lithographic step and one or two voltage sources. Other complex aspherical profiles could be fabricated using the same technique, such as elliptical or hyperbolic ones.

The Optimization of a Convex Aspheric Lightweight SiC Mirror and Its Optical Metrology

Space telescopes with large diameters or with wide fields require convex secondary mirrors which are mounted at the front of telescope. In this paper, a convex aspheric lightweight SiC mirror and Hindle detection method are presented. A parameter optimization method is utilized in the mirror design process in which the mirror surface accuracy is taken as the objective. As the mirror has a relative high diameter-to-thickness ratio, an S-type flexure support is proposed to maintain the surface figure under gravity, thermal change and assembly error. To minimize the surface figure under these loads, the design principle is studied separately. The optical metrology is performed by the Hindle ball supported by a gravity offloading system. The tested surface had an accuracy of λ/100 root mean square (λ = 632.8 nm). In addition, the mechanical design was validated by dynamic testing.

CONTEMPORARY PRACTICES IN CATARACT SURGERY - SUBJECTIVE PREFERENCES OF CZECH CATARACT SURGEONS.

The aim of the work was to find out the current subjective preferences of Czech cataract surgeons in terms of individual procedures, techniques and materials used during cataract surgery. This study was conducted in the form of a questionnaire (online, a total of 44 questions). The survey respondents were members of the Czech Society of Refractive and Cataract Surgery. Questions 1-10 concerned the characteristics of the respondent (age, number of operations performed, type of workplace, etc.). Questions 11-20 focused on the surgical procedure used by the specific surgeon (anaesthesia, viscomaterial, position of the main incision, use of antibiotics at the end of the operation, etc.). Questions 21-34 concerned the type of intraocular lens used. Lastly, in questions 35-44, respondents were asked about their individual preferences if cataract surgery were to be performed on them. The questionnaire was fully or partially completed by 72 surgeons (26% of the originally approached subjects). Most of the respondents were experienced surgeons, 74.5% of them have been performing surgeries for more than 10 years, out of which 55.5% perform more than 500 operations per year. The average age of the respondents was 50 years. 65.3% of surgeons use hydroxypropylmethylcellulose during surgery, 74% do not use a femtosecond laser for surgery, 50% never perform posterior circular capsulorhexia, and 98% apply antibiotics to the anterior chamber at the end of surgery. Surgeons predominantly use hydrophobic (80.8%), aspherical (72.3%), clear (54.3%), single-focal (97.9%) and non-preloaded (78.3%) lenses. However, if they were not limited or restricted in any way in their choice, they would prefer aspherical lenses (94.6%), multifocal or extended-focus lenses (78%) and preloaded lenses (96.8%). The subjective preferences of Czech cataract surgeons are relatively variable regarding the individual steps. Often the procedures used do not always correspond with the actual preferences of the surgeon. On the contrary, there is almost complete unity in the steps recommended by professional societies (intracameral antibiotics at the end of the operation).

Experimental investigation in nodal aberration theory (NAT): separation of astigmatic figure error from misalignments in a Cassegrain telescope.

We present simulations and experimental validations for separating astigmatic figure error from misalignments in Nodal Aberration Theory (NAT) with a high-precision Cassegrain telescope. Both the primary mirror figure error and the secondary mirror misalignments induce binodal astigmatism for the telescope systems. The separation of these two aberration factors plays a crucial role in the telescope alignment process. In this study, the figure error of the aspheric primary mirror of the Cassegrain telescope induced by the mirror mounts was measured interferometrically utilizing a computer-generated hologram (CGH). According to the primary mirror figure error, the astigmatic node locations in the image plane were simulated using real raytracing. The center of the nodes was located on the field center, and the nodes were placed symmetrically with respect to the field center in the image plane. The telescope's alignment was performed using the simulation results, and the node locations were measured on a grid of field points interferometrically. Thereafter, secondary mirror misalignments around the coma-free pivot point were introduced into the optical system, and the node's center was shifted from the field center in the image plane as predicted by NAT. The simulations and interferometric field measurements were performed and compared on a grid of field points for the misaligned state in the presence of primary mirror figure error. The experimental results confirm the predictions from NAT. Statistical analysis was also performed to confirm the accuracy and stability of the measurements.

High-performance imaging with an advanced non-imaging lens based on full-path optical diffraction calculation in two-dimensional space.

High-performance image-forming systems often require high system complexity due to the overdetermined nature of optical aberration correction. What we present here is a novel computational imaging modality which can achieve high-performance imaging using a simple non-image-forming optical system. The presented optical system contains an aspherical non-imaging lens which is designed with the optimal transfer of light radiation between an object and a detector. All spatial frequencies of the object collected by the non-imaging lens are delivered to the detector. No image is formed on the detector, and a full-path optical diffraction calculation method is developed to recover a high-quality image of the object from multiple intensity measurements. The effectiveness and high performance of the proposed imaging modality is verified by the examples.

The effect of concentric and aspheric multifocal soft contact lenses on binocular vision in young adult myopes

PurposeMultifocal soft contact lenses (MFCLs) are prescribed to inhibit myopia progression; these include aspheric and concentric designs. The effects of MFCLs on visual quality, accommodation and vergence in young-adult myopes were evaluated. MethodsParticipants were twenty-six myopes (19–25 years, spherical equivalent −0.50 to −5.75D), with normal binocular vision and no past myopia control. Pupil sizes were 4.4 ± 0.9 mm during distance viewing and 3.7 ± 0.8 mm at near. In random order, participants wore four MFCLs: Proclear single vision distance, MiSight concentric dual focus (+2.00D), distance center aspheric (Biofinity, +2.50D) (CooperVision lenses), and NaturalVue aspheric (Visioneering Technologies). Testing included visual acuity, contrast sensitivity (Pelli-Robson), stereoacuity, accommodation response, negative and positive relative accommodation, horizontal phorias, horizontal fusional vergence and AC/A ratio, and a visual quality questionnaire. ResultsThe four lenses differed in distance (p = 0.001) and near visual acuity (p = 0.011), and contrast sensitivity (p = 0.001). Compared with the single vision lens, the Biofinity aspheric had the greatest visual impact: 0.19 ± 0.14 logMAR distance acuity reduction, 0.22 ± 0.15 log contrast sensitivity reduction. Near acuity was affected less than distance acuity; the reduction was greatest with the NaturalVue (0.05 ± 0.07 logMAR reduction). The MFCLs altered the autorefraction measure at distance and near (p = 0.001); the accommodation response was less with aspheric lenses. Negative relative accommodation reduced with the aspheric lenses (p = 0.001): by 0.9 ± 0.5D with Biofinity and 0.5 ± 0.7D with NaturalVue. Exophoric shifts were greater with aspheric lenses (1.8 ± 2.4Δ Biofinity, 1.7 ± 1.7Δ NaturalVue) than with the concentric MiSight (0.5 ± 1.3Δ). ConclusionsMFCLs alter visual performance, refraction and vergence; two aspheric lenses had greater effect than a concentric lens.

Design and fabrication of lightweight additively manufactured mirrors for aviation.

This paper proposes a design process for additively manufactured mirrors. A central support aspheric mirror and tripod support structure were manufactured via selective laser melting. To achieve substantial weight reduction, an additively manufactured body-centered cubic lattice structure was used in the mirror design. Simulation analysis showed that the mirror had good rigidity. Single-point diamond turning was applied to obtain an optical quality mirror. After assembly, the rms surface shape accuracy of the mirror was 0.069λ (λ=632.8nm). The surface roughness (Ra) of the additively manufactured metal mirror was 8.125 nm. These findings provide a strong theoretical basis and technical support for the preparation and application of lightweight metal mirrors.

Experimental study of Terahertz superfocusing with super-oscillation phenomenon

We experimentally study the superfocusing performance of the Terahertz super-oscillation lens (TSOL). The TSOL which generates Terahertz super-oscillation light field in the focal plane is composed of a Terahertz aspheric lens and an optimized binary 0-π phase device. For a proofed TSOL (numerical aperture NA = 0.4614) @ working wavelength of λ=119μm, the FWHM of the super-oscillation spot ∼0.80λ is about 0.70 times of the Airy spot. Theoretical simulation is performed to validate the confocal scanning imaging resolution enhancement of the TSOL and the imaging resolution of the TSOL is about 0.85 times of the Rayleigh criterion. This study has potential applications in the terahertz super-resolution imaging.