A common aberration with water-immersion objective lenses

We describe here an aberration that is frequently encountered with water‐immersion but not oil‐immersion objectives. The aberration is shown to be induced by tilt of the coverslip out of the plane normal to the optical axis. Model calculations taking into account the path‐length distortions introduced by a tilted coverslip satisfactorily reproduce the observed effect on the images of small subresolution fluorescent beads.     

Measuring and correcting aberrations of a cathode objective lens

In this paper I discuss several theoretical and practical aspects related to measuring and correcting the chromatic and spherical aberrations of a cathode objective lens as used in Low Energy Electron Microscopy (LEEM) and Photo Electron Emission Microscopy (PEEM) experiments. Special attention is paid to the various components of the cathode objective lens as they contribute to chromatic and spherical aberrations, and affect practical methods for aberration correction. This analysis has enabled us to correct a LEEM instrument for the spherical and chromatic aberrations of the objective lens.     

Improved correction of axial geometrical distortion in index-mismatched fluorescent confocal microscopic images using high-aperture objective lenses

Extracting quantitative data from microscopic volume images is straightforward when the refractive indices of the immersion medium and the mounting medium are equal. The readings of the position of the specimen stage can be directly used to measure depth and width. Imperfectly matched immersion and mounting media result in axial geometrical distortion. Linear correction of the axial distortion using the paraxial estimate of the axial scaling factor yields results that may differ as much as 4% from the actual values. From calculations based on a theoretical expression of the 3‐D point‐spread function in the focal region of a high‐aperture microscope focussing into a mismatched mounting medium, we derived axial scaling factors that result in quantitative results accurate to better than 1%. From a non‐linear correction procedure, an improved formula for the paraxial estimate of the axial scaling factor is derived.     

Characterization of microscope objective lenses from 1,400 to 1,650 nm to evaluate performance for long-wavelength nonlinear microscopy applications

We have demonstrated a simple method for characterization of objective lens performance at longer wavelengths for 3PLSM and THG imaging. We investigated a range of air and oil-immersion objective lenses across a wavelength range of 1,400-1,650 nm using a synchronously pumped optical parametric oscillator laser source. In the first instance, we investigated the percentage light transmission across this spectral range. Second, we used a simple second harmonic autocorrelation pulse measurement technique to study the dispersion properties of these lenses at the range of input wavelengths. For the objective lenses investigated, we observed pulse broadening on the order of around 4%-7% for air immersion lenses and 9%-12% for oil immersion lenses. Even for the greater dispersion incurred by the application of the oil immersion lenses, these objectives are suitable for longer wavelength application in conjunction with a suitable light source. The same techniques could easily be applied for a larger range of objective lenses and adapted for alternative spectral windows and pulse durations.     

Diffractive-refractive intraocular lenses

Optical characteristics and properties of AcrySof ReSTOR® bifocal intraocular lenses (Alcon, USA) and elastic polymer MIOL-Akkord lenses (Russia) are compared. The lenses differ by the form of refractive component, the type of diffractive microstructure, and their fabrication technology. Investigations showed that the lenses have similar optical characteristics in resolution, but the bifocal properties of the MIOL-Akkord are much less dependent on the pupil diameter.     

Image acquisition with immersion objective lenses using electrons emitted with several tenths of an electron volt energies: towards high spatial resolution ESCA analysis

This study aims to evaluate the spatial resolution achievable with photoelectrons in order to perform localised UPS or XPS analyses on various heterogeneous samples. This investigation is intentionally restricted to direct image acquisition by immersion objective lenses, involving electrons ejected with initial energies of several tenths of an electron-volt. In order to characterise the contribution of all optical elements, analytical investigations were associated to numerical simulations based on SIMION 7 software. The acquisition of high-quality images implies a simultaneous reduction in spherical and chromatic aberrations by a narrow aperture stop placed at the output pupil of the objective. With such limitations in useful emission angles, it is shown that monochromatic electron beams build images with a resolution of about 1 nm, especially for the acceleration bias mode where the focussing electrode is biased at a positive high voltage. Even energy dispersed electron beams, limited by a 4 eV band pass spectrometer, can produce images convenient for highly localised ESCA analyses (resolution 3 nm), where the objective lens is associated with an aperture stop of 30 microm in diameter without using acceleration voltages above 5000 V.     

Studies on condenser-objective lenses

Scaling down the dimensions of a conventional magnetic objective lens to reduce aberrations is studied in detail. The values of other aberration coefficients for optimum lens size corresponding to desired minimum aberration are estimated. The possibility of using iron-free condenser–objective lenses at high voltage is examined.     

A study of cathode aging and the threshold of autoemission from cathode wires in drift chambers

Radiation aging of wire chambers and the effect exerted on it by various contaminants on the surface of a cathode wire are investigated. The threshold electric field strength that gives rise to autoelectronic emission has been measured for several cathode wire samples.     

Colour thresholding and objective quantification in bioimaging

Computer imaging is rapidly becoming an indispensable tool for the quantification of variables in research and medicine. Whilst its use in medicine has largely been limited to qualitative observations, imaging in applied basic sciences, medical research and biotechnology demands objective quantification of the variables in question. In black and white densitometry (0–256 levels of intensity) the separation of subtle differences between closely related hues from stains is sometimes very difficult. True-colour and real-time video microscopy analysis offer choices not previously available with monochrome systems. In this paper we demonstrate the usefulness of colour thresholding, which has so far proven indispensable for proper objective quantification of the products of histochemical reactions and/or subtle differences in tissue and cells. In addition, we provide interested, but untrained readers with basic information that may assist decisions regarding the most suitable set-up for a project under consideration. Data from projects in progress at Tulane are shown to illustrate the advantage of colour thresholding over monochrome densitometry and for objective quantification of subtle colour differences between experimental and control samples.     

Vision correction by intraocular lenses

The advantages of correcting the refractive errors of the eye (nearsightedness and farsightedness) by introocular phakic (i.e., without removing the crystalline lens) lenses over the other types of correction are considered. A relation between the optical power of spectacle glasses and contact and phakic lenses is obtained and analyzed. New, more accurate approximate formulas for calculating the optical power of intraocular artificial lenses and phakic lenses are derived. It is shown that the deviation of calculations by the proposed formulas from the calculations by the formulas based on geometrical optics are much less than the deviation of calculations by the regressive formulas used in ophthalmic practice.     

渐进多焦点镜片的评价

为了更准确地评价渐进多焦点镜片(PAL)的设计结果,采用Zemax对渐进多焦点镜片进行评价。结合一个光焦度增量为2.5m-1的渐进镜片实例,辅以MatLab软件,计算出镜片表面参数,以及球面度和柱面度的理论分布图。然后将镜片参数导入Zemax,获得球面度和柱面度的仿真结果,与理论分布图比较,得出更准确的评价结果,说明Zemax能更准确、全面地评价渐进镜片。     

A compact three-mirror astronomical objective

A procedure for synthesizing a mirror astronomical objective with small axial dimensions is proposed. The objective contains two reflecting surfaces one of which is aspheric. Radiation is reflected from it twice with the result that the optical arrangement of the objective becomes three-mirror. An example of the calculation according to the proposed procedure of the long-focus mirror objective with a focal distance of 2000 mm and a relative aperture of 1: 8 is presented.     

Subdivision of a graded-density cathode

The behaviour of a subdivided graded-density cathode is briefly discussed and supporting experimental measurements are presented. With two-channel readout, the capacitive loading on each channel pre-amplifier has been reduced by a factor 2.7 by subdivision of the GD cathode into two sections. It has also been shown that a specific non-linear grading may be used to compensate a predicted non-linear response.     

A study of cathode agitation in ultrasonic-aided microelectroforming

In this study, a composite processing technique that combines ultrasonic vibration and electroforming process was utilised to investigate the machining performance of copper electroforming. Supersonic agitation mechanisms were mounted on a cathode and electrolyte separately to evaluate the processing performance of electroforming. Results revealed that a copper deposit speed can be raised by cathode agitation of ultrasonic-aided electroforming. Processed copper surface of cathode agitation is better than no agitation. An array multi-mould microstructure is fabricated by cathode agitation of ultrasonic-aided copper electroforming .     

Testing aspheric lenses: New approaches

Optical metrology provides a unique approach to measuring surfaces, both technical and optical, over a wide measurement range from macro to nano. We present two new approaches to measuring aspheric lenses with increased flexibility. The first is based on a modified Twyman-Green interferometer where multiple sources for the illumination of the aspheric surface with different angles are adopted to achieve a local compensation of the gradient and consequently a reduction of interference fringes. The second is based on a chromatic Fizeau interferometer with a diffractive element as null-optic for the measurement of extreme ultraviolet aspheres.     

渐进多焦点眼用镜片的个性化设计

介绍了渐进多焦点眼用镜片的渐变通道和视近区位置的个性化设计方法。推导出与眼用镜片佩戴者瞳距,镜片到眼球旋转中心的距离,镜片球光度分布以及与镜片的棱镜效应相关的镜片矢高偏移公式,并将该公式引入渐进多焦点眼用镜片设计中。在给出的设计实例中,镜片视远区中心点偏移了0.5mm,视近区中心点偏移了3mm。与对称设计相比,偏移后视远区和阅读区的屈光度变化在0.03m-1以内。视远区散光度分布没有因为镜片通道和视近区的位置偏移而改变,保持了视远区屈光度和散光度分布的对称性。该个性化设计方法使老视眼患者在视近物时,视线自然地通过渐进多焦点眼用镜片的渐变通道或视近区,且该处的屈光度也与视物所需屈光度相符,提高了渐进多焦点眼用镜片佩戴者的佩戴舒适度和适应这种镜片的能力。