Chung W. See

Scanning optical microellipsometer for pure surface profiling

We describe a scanning optical interferometer that can simultaneously perform ellipsometry measurements and thus provides a true surface profile. This is accomplished by projecting the back focal plane of the objective lens onto a CCD array. The measured phase differences between the p- and s-polarization components are converted, by using a specially developed algorithm, to optical phase changes caused by material variations. The compensation process is then applied to extract the true profile of the object surface. Experimental results obtained with the system are shown.

High-resolution scanning surface-plasmon microscopy

Surface plasmons (SPs) are electromagnetic surface waves that propagate along the interface between conductors and dielectrics. The k vector of these waves is larger than the free-space wave vector. The importance of SPs lies in the fact that they are extremely sensitive to small changes in the dielectric properties of substances that are in contact with the conductors. This property means that SPs have many sensor applications; however, when they are used in microscopic applications the lateral resolution is limited to several micrometers. We discuss how this limit can be overcome by use of defocused high-numerical-aperture liquid-immersion objectives. We also present SP images that demonstrate a resolution comparable with that expected from high-numerical-aperture optical microscopes. Finally, we discuss how ultrahigh-numerical-aperture objectives with numerical apertures greater than 1.5 can be expected to have considerable influence on biological imaging.

High-resolution wide-field surface plasmon microscopy

This paper describes the application of a Köhler illuminated high‐resolution wide‐field microscope using surface plasmons to provide the image contrast. The response of the microscope to a grating structure in both the Fourier and the image planes is presented to demonstrate image formation by surface waves. The effect of spatial filtering in the back focal (Fourier) plane to enhance image constrast is described. We also discuss how the surface wave contrast mechanism affects the imaging performance of the microscope and discuss factors that can be expected to lead to even greater improvements in lateral resolution and sensitivity.

Optical V(z) for high-resolution 2π surface plasmon microscopy

Surface plasmons are electromagnetic surface waves whose k vectors are greater than that of free-space radiation. We excite surface plasmons by using an oil-immersion lens, which forms one arm of an interferometer. We demonstrate the way in which the characteristic output variation with defocus is determined by the propagation properties of the surface plasmons, which leads to diffraction-limited surface plasmon microscopy in the far field.

Wide field amplitude and phase confocal microscope with speckle illumination

This communication describes a wide field phase sensitive confocal optical microscope based on correlation between speckles. We show both experimentally and theoretically that the system operates as a wide field amplitude and phase confocal system; and demonstrate unique modes of operation such as extended focus phase measurement, which have, hitherto, only been demonstrated on scanning systems. Some potential applications of the system are discussed.

Common path interferometric microellipsometry

Common path interferometric microellipsometry based on the Youngs interference principle is presented. Interference of the pure p and s reflections at the back focal plane of a microscopic objective takes place by means of Youngs interferometry. Therefore, the amplitude ratio, tan (psi) , and the phase different, (Delta) , of the two polarization components are represented as the contrast and the phase shift of the Youngs fringe pattern. Hence, the complex refractive index of the sample can be calculated using well- known equations. This technique is particularly applicable in pure topography where the measured optical phase is actually a contribution of both the surface height change and material change as well.

Imaging of the cell surface interface using objective coupled widefield surface plasmon microscopy

We report on the development and on the first use of the widefield surface plasmon (WSPR) microscope in the examination of the cell surface interface at submicron lateral resolutions. The microscope is Kohler illuminated and uses either a 1.45 numerical aperture (NA) oil immersion lens, or a 1.65 NA oil immersion lens to excite surface plasmons at the interface between a thin gold layer and a glass or sapphire cover slip. Like all surface plasmon microscope systems the WSPR has been proven in previous studies to also be capable of nanometric z-scale resolutions. In this study we used the system to image the interface between HaCaT cells and the gold layer. Imaging was performed in air using fixed samples and the 1.45 NA objective based system and also using live cells in culture media using the 1.65 NA based system. Imaging in air enabled the visualisation of high resolution and high-contrast submicron features identified by vinculin immunostaining as component of focal contacts and focal adhesions. In comparison, imaging in fluid enabled cell surface interfacial interactions to be tracked by time-lapse video WSPR microscopy. Our results indicate that the cell surface interface and thus cell signalling mechanisms may be readily interrogated in live cells without the use of labelling techniques.

Quantitative optical microscope with enhanced resolution using a pixelated liquid crystal spatial light modulator

This paper presents a brief account of a novel optical microscope, which combines the advantages of two well‐known techniques, namely phase contrast and phase stepping, to provide high contrast imaging and precision measurements. The inclusion of a programmable liquid crystal spatial light modulator provides for the phase stepping required, while also allowing flexibility for future improvements. The results shown reveal an important aspect of the system to facilitate quantitative sample measurements, with an enhancement of optical resolution compared with conventional optical imaging systems.

Full-field heterodyne interference microscope with spatially incoherent illumination

A heterodyne interference microscope arrangement for full-field imaging is described. The reference and object beams are formed with highly correlated, time-varying laser speckle patterns. The speckle illumination confers a confocal transfer function to the system, and by temporal averaging, the coherence noise that often degrades coherent full-field microscope images is suppressed. The microscope described is similar to a Linnik-type microscope and allows the use of high-numerical-aperture objective lenses, but the temporal coherence of the illumination permits the use of a low-power achromatic doublet in the reference arm. The use of a doublet simplifies alignment of the microscope and can reduce the cost. Preliminary results are presented that demonstrate full-field surface height precision of 1 nm rms.

Wide-field surface plasmon microscopy with solid immersion excitation

This letter shows how an aplanatic solid immersion lens system may be used for high-resolution wide-field surface plasmon microscopy. The lens configuration means that no fluid couplant is required; it has the additional advantage that very high refractive indices may be used to reduce the incident angle at which surface plasmons are excited. A transmission spatial light modulator is incorporated conjugate with the back focal plane; this allows the image contrast to be controlled in a precise and flexible manner. Its use also provides definitive demonstration that the image contrast arises from surface plasmon excitation.