Refractive Index Of Specimen Research Articles

Integrated digital holographic microscopy based on surface plasmon resonance.

We propose a novel digital holographic microscopy (DHM) by integrating surface plasmon holographic microscopy (SPHM) with reflection DHM based on the angular and polarization multiplexing techniques. Taking advantages of the high sensitivity of surface plasmon resonance (SPR) and the high reflectivity of gold film, the tiny variations of specimen's refractive index (RI) can be measured by using SPHM, and meanwhile, the thickness changes of the specimen can be determined by means of reflection DHM. We experimentally monitor the volatilization process of an alcohol-water mixture droplet to verify the validity of the integrated DHM. The proposed microscopy is very promising in the objective-coupling SPR microscopy for multi-information measurements of diverse specimens with low-contrast RI distributions (biomolecules, nanofluids, etc.) in a dynamic and nondestructive way.

3D deconvolution of spherically aberrated images using commercial software

Refractive index mismatch between the specimen and the objective immersion oil results in spherical aberration, which causes distortion and spreading of the point spread function, as well as incorrect readings of the axial coordinates. These effects have to be taken into account when performing three-dimensional restoration of wide-field fluorescence images. By using objects with well-defined geometry (fluorescently stained Escherichia coli or actin filaments) separated from a cover slip by a layer of oil with known refractive index, we investigated the accuracy of three-dimensional shape restoration by the commercial programs Huygens and Autoquant. Aberration correction available in the software dramatically reduced the axial blur compared to deconvolution that ignored the refractive index mismatch. At the same time, it failed to completely recover the cylindrical symmetry of bacteria or of actin fibres, which showed up to a three to five times larger width along the optical axis compared to the lateral plane. The quality of restoration was only moderately sensitive to the exact values of the specimen refractive index but in some cases improved significantly by assuming a reduced NA of the objective. Because image restoration depends on the knowledge of the vertical scale, we also performed detailed measurements of the axial scaling factor and concluded (in agreement with some previous authors) that scaling is adequately described by the simple paraxial formula, even when high-NA oil-immersion objectives are used.

Characterization of Silica Nanowires for Optical Sensing

In this paper, the optical properties of silica nanowires in a Mach-Zehnder-based optical sensor for detecting biomaterial specimens have been studied using the full vectorial H-field formulation of the finite element method. The variation of the propagation constant, the power fraction in the composite nanowires with the variation of the nanowire size and the specimen refractive index, temperature, and wavelength are also presented.

The axial response of confocal microscopes with high numerical aperture objective lenses

We consider the axial resolution of confocal optical systems employing high numerical aperture objective lenses for the cases when the specimen refractive index is both higher and lower than that of the immersion medium. In the latter case a spherical aberration-like phase shift is introduced when the objective lens numerical aperture is greater than the refractive index of the specimen which leads, inter alia, to an asymmetrical axial response with higher side lobe levels. Theoretical and experimental results are presented.

Effect of the specimen refractive index on the imaging of a confocal fluorescence microscope employing high aperture oil immersion lenses

Effect of the specimen refractive index on the imaging of a confocal fluorescence microscope employing high aperture oil immersion lenses

Effect of the specimen refractive index on the imaging of a confocal fluorescence microscope employing high aperture oil immersion lenses

The effect of the specimen refractive index on the resolution, image brightness and axial scaling in confocal fluorescence microscopy is theoretically investigated for ten of the most popular fluorophores. The calculations are based on a vectorial theory based on Fermat's principle. We show that the axial scaling of the image does not depend on the fluorophore used. Axial scaling factors are derived for objects embedded in glycerol and water. For each fluorophore, the maximum intensity and the full-width-half-maxima of the confocal point spread function are given as a function of the focusing depth. The full-width-half-maxima allow for an assessment of the axial and lateral resolution when deeper regions of the specimen are to be investigated.

Three-dimensional specimen recording and interactive display using confocal laser microscopy and digital image processing

In this paper we first give a brief overview of three-dimensional specimen recording and display using confocal microscopy and digital image processing. We then concentrate on some practical aspects of using this technique: We investigate how the specimen refractive index and detector integration time will influence image resolution and describe an interactive user interface to the computer environment.

The influence of specimen refractive index, detector signal integration, and non‐uniform scan speed on the imaging properties in confocal microscopy

SUMMARYRefraction of light in a specimen volume may cause aberrations that influence the imaging properties in confocal microscopy. In this paper the influence on three‐dimensional resolution and geometry is experimentally investigated for a uniform specimen volume. It is found that the depth resolution is more severely affected than the lateral resolution. This is unfortunate, because even under ideal conditions the depth resolution is lower than the lateral resolution. Lateral image geometry is little affected by the specimen refractive index, whereas the depth scale can be considerably elongated or compressed.The influence of a finite detector integration time is also considered. This can give a noticeable, but not particularly severe effect on the image resolution in the line‐scan direction. Because the integration time can be accurately controlled, a shorter integration time can be used when maximum resolution is essential, albeit at the price of a higher noise level.In scanning fluorescence microscopy a non‐uniform scan speed may give large variations in bleaching over the specimen surface. Experiments illustrate how serious such non‐uniform bleaching effects can be when a specimen area is repeatedly scanned, for example when recording optical serial sections.

The determination of the refractive index of a photoelastic specimen by immersion technique

Conventional methods for determining the refractive index demand specimens of optical quality, the preparation of which is often very difficult. An indirect determination by matching the refractive indices of specimen and immersion liquid is a practical alternative for photoelastic specimen of nonoptical quality. An experimental arrangement used for this technique and observations made while matching the refractive indices of three different specimens are presented.

The Butyro and immersion refractometers

With a view to a general confirmation of the consistency, inter se, of the Immersion and the Butter Refractometer conversion tables, the relations subsisting between n, the refractive index of specimen, and N, the scale reading, are determined. The departures from strict conformity to these relations are then determined and found to be generally within the respective tolerances of the instruments. The necessity for a small zero correction in the former case is indicated as probable.