Meniscus Lens Research Articles

Laser cutting stainless steel with dual focus lenses

In this article the performance of a new type of lens is compared with traditional meniscus lenses for CO2 laser cutting of medium (>5 mm) section stainless steel. Dual Focus™ lenses produce two focus spots, one above the other. This type of optic was found to be capable of higher cutting speeds and better quality cuts. A phenomenological model is presented which explains the superior performance of Dual Focus lenses. The model concentrates upon the fact that during high speed cutting of medium section metals, the laser does not irradiate the lower portion of the cut zone. This lower part of the cut is heated by the melt flowing over it, which has been previously heated by the laser. This melt preheating involves narrower kerfs and higher cut speeds if a dual focus lens is used.

Gradient-index meniscus lens free of spherical aberration

The gradient-index aberration-free meniscus lens for focusing of a beam parallel to the optical axis is considered in this paper.

An optical flatness measurement system for medium-sized surface plates

This paper describes the work to develop a parallel beam scanning system (PBSS) for the noncontact measurement of surface flatness of such medium-sized surface plates, as sheet metals, sheet-moulding compound (SMC) plates, and glass plates, which are difficult to measure by traditional methods. The PBSS consists of a HeNe laser source with good pointing stability, a scanner to create divergent scanning beams, a large aplanatic meniscus lens to convert the divergent beams to parallel beams, a linear stage to drive the testpiece to each sampling position, a screen for the projection of reflected beams from the tested surface, and an image-processing unit to analyze the projected image. Because of the out-of-flatness of the surface, the straight line formed by the incident parallel beams will be distorted and magnified on the screen as it is reflected from the surface. A charge-coupled-device (CCD) camera is employed to capture the image of the distorted line each time, and proceeds in line-by-line sequence. With the proposed mathematical model, the three dimensional (3-D) flatness data of the testpiece can be converted from the input image data and analyzed by the least-squares method. Experimental results by the use of this system have shown good agreement with the results obtained from a coordinate measuring machine (CMM). Because of the limit of the meniscus lens, the workpiece size is within 200 mm in width.

Efficient First Stokes Generation Using a Brillouin Resonator Coupled with a Raman Half Resonator

We report an efficient Raman laser system which utilizes stimulated Brillouin scattering as a dual-cavity resonator mirror for fundamental and Raman waves. A Raman laser at the eye-safe wavelength of 1.54 µ m is generated in high pressure CH4 gas from a passively Q-switched Nd:YAG laser. Employing a meniscus lens with an optimized reflectance of 10% at the fundamental wavelength, a maximum Raman energy of 33 mJ with a residual fundamental energy of 20 mJ has been obtained, where the pressure of CH4 gas is 800 psi.

Alternative Design for Improved FT-IR/VCD Capabilities

A Bomem MB100-based vibrational circular dichroism (VCD) spectrometer suitable for chiroptical studies in the infrared region is described. The optical layout utilizes the spectrometer's external collimated beam. Standard VCD optics consisting of a KRS-5 polarizer and a ZnSe photoelastic modulator are mounted on an optical breadboard. A ZnSe meniscus lens focuses the beam on a small-area MCT detector. Several optical designs were examined to find the optimal positions of the optical elements. The experiments aimed to improve the energy throughput, minimize polarization artifacts, and increase signal-to-noise ratio to such an extent that single-enantiomer VCD spectra could be recorded routinely and dependably. Examples are presented illustrating the high-performance characteristics of the instrument.

New focusing optics for second-harmonic waves radiated from crystal-cored fibers

The optical second-harmonic (SH) wave generated from a crystal-cored fiber under Cerenkov-radiation-type phase matching can be collimated by an axicon and then can be focused by a spherical lens to a diffraction-limited spot. The deviation of the radiation angle of the SH wave or the angle mismatch between the radiation angle and apex angle of the axicon causes spherical aberration. However, because the focusing system using the axicon is sensitive, such a system is not practical enough. A new optical system is proposed that consists of three spherical lenses: biconvex, biconcave, and meniscus lenses. The system can collimate the SH light radiated from the fiber. The new lens system is overcorrected for spherical aberration in certain zones. When the radiation angle of the SH wave deviates from the desired angle, the aberration can be compensated by adjusting the spacing between the biconcave lens and the meniscus lens.

A new form of atmospheric dispersion corrector

Earlier proposals for atmospheric dispersion correctors (ADC) are briefly reviewed and a new form described consisting of a doublet meniscus lens whose outer surfaces are concentric. The two glasses of the doublet have different dispersions, and the corrector can be tuned for different zenith distance by tipping the meniscus about the common centre of its outer surfaces. This new form is simpler than earlier proposals and, in addition, in some applications it can enhance the optical performance by giving better aberration correction and reduced defect of telecentricity. Numerical data and performance figures are provided for one possible embodiment of this device

Optical performance of decentered monofocal intraocular lenses

A model eye water cell was used to evaluate the optical performance of biconvex, meniscus, and piano-convex (spheric and aspheric) monofocal poly(methyl methacrylate) intraocular lenses when the lenses were centered and when they were decentered 1 mm and 2 mm. Resolution, induced astigmatism, and modulation transfer function measurements were performed for all lenses with the more convex surface of the lens oriented toward the incident light. The same measurements were performed for the piano-convex and meniscus lenses in the reverse orientation. The lens shapes least affected by decentration were the biconvex and spheric piano-convex with the convex surface oriented toward the incident light. When centered, the aspheric piano-convex lenses had the best overall contrast performance based on the modulation transfer function measurements. However, once decentered the performance of the aspheric lenses approached that of the meniscus lenses in the reverse orientation, the lens shape which had the worst performance.

Vaulted posterior chamber lenses and the posterior capsule

Sixty-eight patients who had extracapsular cataract surgery with intraocular lens implantation in the bag received one of two types of lenses that had been designed to create a gap between the posterior surface of the optic and the posterior capsule. Two to four months after surgery, we found that the central spacing between the posterior lens surface and the posterior capsule measured by optical pachymetry averaged 0.25 mm. The mean of the spacing for the Pharmacia LSP laser ridge was 0.25 mm (range 0.1 to 0.6) and that of the 3M LE meniscus lens was 0.24 mm (range 0 to 0.8). The amount of adherence of the posterior capsule to the posterior lens surface was less with the laser ridge design than with the meniscus lens.

Accuracy of Lens Power Calculations with the Biconvex and Meniscus Intraocular Lenses

In a prospective study, intraocular lens power calculations were within +/- 0.50 diopter of the final refraction in 77 of 88 eyes (87.5%) with a biconvex lens and in 41 of 90 eyes (45.5%) with a meniscus lens. The more precise power calculations with the biconvex intraocular lens seemed to be related to the superior optical design of the lens, with its close configuration to a normal crystalline lens.

Posterior capsule fibrosis and intraocular lens design

Four different posterior chamber lens designs were used in 1,845 consecutive, unselected extracapsular cataract extractions performed over a 31-month period in Vejle, Denmark. Ninety-seven eyes (5.3%) required a posterior capsulotomy during a postoperative observation period ranging from two to 32 months. At 16 months postoperatively, the cumulative capsulotomy rate was 7.1% with plano-convex anterior lenses, but only 1.7% with meniscus lenses and 1.8% with continuous ridged lenses. These results suggest that close contact between the posterior capsule and the optic could induce early posterior capsule opacification.

Comparison of the keratometer and the lens bench in measuring intraocular lens power

Intraocular lenses (IOLs) from six manufacturers were measured on a Terry keratometer and on a calibrated lens bench for lens power. Differences between the two methods appeared when the IOLs were (1) a different refractive index than polymethylmethac:rylate (PMMA) and (2) a shape other than planoconvex. These differences were consistent for ultraviolet absorbing PMMA and for meniscus lenses.

Aberration-corrected catadioptric magnifiers useful for simple microfiche readers

The present paper considers the magnifying power and aberration properties of three different catadioptric magnifying systems useful for application as simple hand-held microfiche readers. These are in the form of a plano-convex lens, a meniscus lens and an achromatic doublet lens and all their outer surfaces have been coated with a semi-reflecting film so that they behave like catadioptric elements. These can be designed to give magnification in the range of 15 × to 25 × with sufficient eye relief. Using such magnifiers, it is possible to read microfiche having frame sizes of 16 × 12 mm and 12 × 9 mm. The cemented achromatic doublet coated on the outer surfaces seems to give a very good image for use in microfiche reader.

Meniscus-lens-corrected corrugated horn: a compact feed for a Cassegrain antenna

The physical size of a corrugated conical horn feed having narrow beamwidth can be reduced considerably by correcting the spherical phase front in the aperture using a meniscus lens. Measured and calculated radiation characteristics of such lens-corrected scalar horns are presented. It is shown that the horns can provide efficient aperture illuminations when used as feeds for conventional Cassegrain antennas, for example radiotelescopes. Further, it is shown that the high crosspolarisation, which is normally present in lens horn designs, can be reduced to that of the horn itself by corrugating the lens surfaces with holes. Improved design formulas for such holes are given.

Thick meniscus field correctors

Thick meniscus lenses with almost equal curvatures are routinely used for the correction of spherical aberration in optical systems. The use of such quasi-concentric menisci (QCM) for correction of field curvature and astigmatism is less well known. Three limiting forms of QCM can be identified, namely, equal curvatures, true concentric, and zero deviation, and each exhibits radically different field aberrations. A doublet lens has field curvature and astigmatism; the former can be removed by adding a strong negative lens at the image plane, but the latter is uncorrected. Use of a QCM, however, corrects both aberrations, moreover, without causing the chief rays to diverge as the conventional field flattener does. Indeed the chief rays may be made to converge so that the QCM can be used as a field-correcting field lens, and we illustrate its use in a periscopic vehicle sight comprising an objective lens, relay stage, and eyepiece. Even in cases in which a measure of field curvature and astigmatism correction is possible, for example, when a double Gauss-type relay lens is used, the QCM results in smaller high-order aberrations and lower ray heights through the system.

Low Profile Optical System for an Aircraft Beacon

An optical system producing an annular cone of radiation from a point source using a low profile front lens is shown to have application as a beacon for high speed vehicles. The system comprises a high pressure short are light source with axial electrodes and integral collector, a conical reflector, and a divergent meniscus lens that has low protrusion over the surface of the vehicle. The system has minimal drag, and the radiation is distributed in directions close to the plane perpendicular to the optical axis. The influences of various parameters such as lens camber, lens aperture, source size, collector shape, collection efficiency, and beam divergence are discussed. A prototype was built at Eimae Division of Varian using a xenon short arc lamp with metal ceramic structure and integral collector.

Radiation pattern of a lens-corrected conical scalar horn

An expression for the radiation pattern of a lens-corrected conical scalar horn is derived. Computed radiation patterns are presented for scalar-horns feeds containing planoconvex and meniscus lenses in their apertures. The patterns and beamwidths are compared with those of an uncorrected wide-angle scalar horn and an open-ended corrugated waveguide.

Optimization of Information-Processing Optical Systems by Transcorrelation-Function Maximization*

A method for optimizing optical systems which process information-carrying signals is presented. The method consists of deriving the transcorrelation function for a general optical system and then maximizing it with respect to the variable parameters of the system. The transcorrelation function is a space- and time-averaged statistic relating the desired object, or “signal” field, and the system output, or image field. The suggested procedure not only minimizes aberrations in the system itself, but also discriminates against noise in both the object and image regions. It can be shown that the maximization of the transcorrelation coefficient also maximizes the useful information content at the output relative to the desired input. For this reason, the criterion is particularly appropriate to optical systems which are used for transmitting and processing information.An example of the application of transcorrelation theory to lens design is carried out at the end of the paper. A meniscus lens is chosen for optimization, where the variable parameters are the radii of curvature of the lens surfaces, which are constrained to be circular in cross section. The transcorrelation function for this lens is determined, and the optimum radii are found by maximizing this function.

Microscope Objectives with Plano-Correction

Twenty-six years ago, Boegehold of Jena was the first to suggest the use of thick meniscus lenses in microscope objectives to attain flatness of the field of view in microscopic images. These menisci had the shape of a negative lens but actually were positive lenses. In the following, a report is given which covers the last two decades of developments in which this suggestion was taken up. The result has been a number of different types of so-called plano-objectives for microscopes, ranging from very low-power systems to systems of the highest power.

Power of the lacrimal layer in the corneal contact lens.

The corneal contact lens is a new type of lens consisting of a small shell. 11 to 12 mm. in diameter, which is applied directly to the cornea. The lens was developed, in part, by the department of ophthalmology of the College of Medical Evangelists, Los Angeles. The lens is applied to the eye without any solution, and there is only a capillary layer of tears between the lens and the cornea. The inner surface of the lens is made on a slightly longer radius than the radius of the outer surface of the cornea, so that the tears which fill the space between lens and cornea form a concave meniscus lens. The power of this lacrimal lens is given by the makers of the contact lens as about — 1.50 D. This does not seem correct, as can be seen by a simple calculation. (The discussion here presented has