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Intriguing anisotropic electrical and optoelectrical properties in two-dimensional (2D) materials are currently gaining increasing interest both for fundamental research and emerging optoelectronic devices. Identifying promising new 2D materials with low-symmetry structures will be rewarding in the development of polarization-integrated nanodevices. In this work, the anisotropic electron transport and optoelectrical properties of multilayer 2D ternary Ta2NiSe5 were systematically researched. The polarization-sensitive Ta2NiSe5 photodetector shows a linearly anisotropy ratio of ≈3.24 with 1064 nm illumination. The multilayer Ta2NiSe5-based field-effective transistors exhibit an excellent field-effective mobility of 161.25 cm2·V-1·s-1 along the a axis (armchair direction) as well as a great current saturation characteristic at room temperature. These results will promote a better understanding of the optoelectrical properties and applications in new categories of the in-plane anisotropic 2D materials.

Anisotropic borophene surface plasmons with extraordinary features have triggered considerable research interest since its discovery. However, due to the atomically thin thickness of monolayer borophene, it is difficult to achieve borophene surface plasmons with high absorption, especially for high-order plasmonic resonant modes. In this paper, we theoretically proposed a hybrid plasmonic system consisting of a borophene monolayer and a periodic metallic grating separated by a dielectric spacer, where multi-order anisotropic borophene surface plasmons and magnetic polaritons can be simultaneously excited. Benefitting from the high electric field enhancement and localization of the magnetic polaritons, the intrinsic absorption of the multi-order borophene surface plasmons can be improved by at least 3 times when the resonant wavelengths of borophene plasmons and magnetic polaritons are tailored to match each other, either by passively tuning the height of grating slits or by actively adjusting the borophene electron density. By further designing compound grating with multiple slits in one period, the overall absorption of the system can be significantly improved within a wide infrared region. Such hybrid system with may find applications in the design of boron-based optoelectronics devices in the infrared region.

We report a theoretical investigation of a surface plasmon resonance (SPR)-based acoustic sensor for optical detection of ultrasound. The structure being studied is arranged in the Krestchmann configuration and the detection is performed by observing the change of refractive index of water next to the SPR metal. The acoustic pressure is simulated using COMSOL. The simulation results illustrate an insight into mechanism of pressure variation on the surface of SPR sensor due to a constructive interference of the ultrasound. This leads to a local refractive index change of water. The local refractive index change is calculated by converting the incident pressure to water density using IAPWS-95 formulation. Then, the water density is converted to the refractive index using Lorentz-Lorenz formulation. Here we report the change in the refractive index of the water to pressure, dn/dp, which is calculated to be 1.4 x 10-10 Pa-1, which is very close to the dn/dp reported by M. W. Sigrist 1986. We also investigated the effect of temperature and wavelength on the dn/dp and found that the variation in temperature and wavelength does not show any significant effect on the dn/dp relationship. We also discuss the effect of quality factor (Q) and possible improvements to enhance the sensitivity of SPR-based acoustic sensor.

Confocal microscopy is a high resolution microscope technique, which operates by scanning a diffraction limited focal spot over a sample. This focal point on the sample is then imaged through an objective lens and a pinhole to ensure that only the information coming from the focal plane is captured and the information from the other planes are blocked by the pinhole. Although this gives better lateral resolution, this method is inefficient in terms of the amount of light required and the scanning time. In this paper, we discuss an alternative solution using digital micromirror device (DMD) to perform multiple focal points scanning simultaneously. This is done by projecting a series of orthogonal codes onto the DMD. The corresponding images obtained from the orthogonal codes are then saved and processed offline in a computer to calculate a confocal image. We use incoherent illumination rather than a laser source as used previously. We also discuss a key issue in this confocal system, which is a suitable separation between each focal spots and a crosstalk between them. We demonstrate that the proposed confocal configuration with the DMD device improves the light efficiency, the scanning time through the parallel confocal spots and a laser source is not required.

In this paper, we present a direct method to measure surface wave attenuation arising from both ohmic and coupling losses using our recently developed phase spatial light modulator (phase-SLM) based confocal surface plasmon microscope. The measurement is carried out in the far-field using a phase-SLM to impose an artificial surface wave phase profile in the back focal plane (BFP) of a microscope objective. In other words, we effectively provide an artificially engineered backward surface wave by modulating the Goos Hänchen (GH) phase shift of the surface wave. Such waves with opposing phase and group velocities are well known in acoustics and electromagnetic metamaterials but usually require structured or layered surfaces, here the effective wave is produced externally in the microscope illumination path. Key features of the technique developed here are that it (i) is self-calibrating and (ii) can distinguish between attenuation arising from ohmic loss (k″ Ω ) and coupling (reradiation) loss (k″ c ). This latter feature has not been achieved with existing methods. In addition to providing a unique measurement the measurement occurs of over a localized region of a few microns. The results were then validated against the surface plasmons (SP) dip measurement in the BFP and a theoretical model based on a simplified Green’s function.

Spatially resolved acoustic spectroscopy (SRAS) is a laser ultrasound technique used to determine the crystallographic orientation (i.e., microstructure) of materials through the generation and measurement of surface acoustic wave velocity on a sample. Previous implementations have used a grating pattern imaged onto the surface to control the frequency of the generated wave in a single direction—grain orientation can be computed by acquiring wave velocities in different directions on the surface (gathered by physically rotating the grating pattern). This paper reports an advance to this methodology, inspired by single pixel cameras, using a coded grating pattern, created using a spatial light modulator, to excite surface acoustic waves in multiple directions simultaneously. This change to the optical arrangement can simplify the overall system alignment, remove mechanical complexities, and is well suited for point-by-point full orientation imaging, potentially allowing for faster orientation imaging using SRAS microscopy. Improvements to the robustness of measurement may be expected to extend the applicability of SRAS in the materials science field. To demonstrate this methodology, experiments were conducted on isotropic and anisotropic samples.

Phase sensitive Surface Plasmon Resonance (SPR) techniques are a popular means of characterizing biomolecular interactions. However, limitations due to the narrow dynamic range and difficulty in adapting the method for multi-point sensing have restricted its range of applications. This paper presents a compact phase sensitive SPR technology using a custom CMOS camera. The system is exceptionally versatile enabling one to trade dynamic range for sensitivity without altering the optical system. We present results showing sensitivity over the array of better than 10−6 Refractive Index Units (RIU) over a refractive index range of 2×10−2 RIU, with peak sensitivity of 3×10−7 RIU at the center of this range. We also explain how simply altering the settings of polarization components can give sensitivity on the order of 10−8 RIU albeit at the cost of lower dynamic range. The consistent response of the custom CMOS camera in the system also allowed us to demonstrate precise quantitative detection of two Fibrinogen antibody–protein binding sites. Moreover, we use the system to determine reaction kinetics and argue how the multipoint detection gives useful insight into the molecular binding mechanisms., Highlights • We introduced a SPR sensor with an optimal sensitivity of 3×10−7 RIU. • Sensitivity better than 10−6 RIU was achieved for refractive index 1.33 ~1.35 RIU. • Relation between responsivity and dynamic range was illustrated. • Potential performance (sensitivity of 4.7×10−8 RIU) was estimated. • New AC detector enabling multi-point sensing was introduced.

The third-order elastic constants of a material are believed to be sensitive to residual stress, fatigue, and creep damage. The acoustoelastic coefficient is directly related to these third-order elastic constants. Several techniques have been developed to monitor the acoustoelastic coefficient using ultrasound. In this article, two techniques to impose stress on a sample are compared, one using the classical method of applying a static strain using a bending jig and the other applying a dynamic stress due to the presence of an acoustic wave. Results on aluminum samples are compared. Both techniques are found to produce similar values for the acoustoelastic coefficient. The dynamic strain technique however has the advantages that it can be applied to large, real world components, in situ, while ensuring the measurement takes place in the nondestructive, elastic regime.

We present the design and numerical characterization of a hybrid photonic-plasmonic nanoresonator comprised of a 2D photonic crystal (PhC) cavity, a gold bowtie nanoantenna (BNA) and a silicon dioxide, SiO2, spacer. This device is designed to serve as the building block of a multicomponent platform capable of running multiple single-molecule experiments such as optical trapping and sample interrogation simultaneously. The thickness and structure of the spacer layer are adjusted to maximize the energy in the externally accessible hot-spot in the BNA gap. Suitability of the device for photonic integration is demonstrated by exciting it through a PhC waveguide.

Gold film (∼50 nm) serves as the working electrode to allow the electrochemical process to be monitored using surface plasmon resonance (SPR) technology. The extracted precise value of time resolved SPR signal perturbed by the non-faradic potential was investigated to study the response time of gold film under potential application. A qualitative model of the reflection and transmission spectra of gold film working as the electrochemical interface is presented. The correlation between three parameters, including thickness of gold film, incident angle and wavelength of beam, were analyzed to generate an optimized configuration for gold film to detect potential. These results emphasis the efficiency of SPR technique used as a diagnostic tool for the electrochemical process.

The uniqueness of the acoustic microscope lies in its ability to image the way in which acoustic waves interact with the elastic properties of a specimen with microscopic resolution. A dominant role in the contrast achieved is played by Rayleigh waves that are excited in the surface of the specimen. They enable very fine surface cracks to be imaged, because they can strike them from the side and be strongly scattered. To account for this theoretically, the imaging theory of the acoustic microscope must be extended to account for non-specular scattering due to the crack. Experiments have been conducted using a cylindrical line-focus lens to measure the signal from a crack in glass, and the results can be compared directly with two-dimensional calculations from the theory. Applications of the ability of the microscope to image microscopic surface cracks include the analysis of metal fatigue and inspection of engineering ceramics, and the theoretical analysis may provide the basis for eventually characterizing surface microcracks quantitatively.

We describe the theory and practical implementation of an iterative computer algorithm (an extension of the Gerchberg Saxton algorithm, originally developed for electron microscopy) for enabling an estimate of the complex reflectance function of a material to be reconstructed from measured values of only the magnitude of the response of an acoustic microscope (i.e. without the phase of the transducer voltage). Results are presented for eight materials measured with a spherical lens (at 320 MHz) and five with a cylindrical line-focus lens (at 210 and 228 MHz).

Conventional ultrasonic imaging uses frequencies up to 10 MHz or perhaps a little higher. Scanning acoustic microscopy extends the frequencies used to the GHz region, with a corresponding improvement in resolution. The technique is now beginning to be applied to problems in the study of materials. The advantages over other kinds of microscopy lie in the unique ways that ultrasonic waves interact with elastic solids. The development of diffusion bonds and plastic deformation at a stressed notch have been studied using transmission. In reflection, the contrast must be understood in terms of its variation with defocus. This enables images of grain structure in polycrystalline materials to be accounted for. The depth sampled corresponds to a Rayleigh wave profile. Damping mechanisms in the material, due, for example, to dislocations, can affect the contrast. Enhanced contrast is found from surface-breaking discontinuities, such as fine microcracks.

In previous work we demonstrated how a confocal microscope with a spatial light modulator in the back focal plane could perform accurate measurement of the k-vector of a propagating surface plasmon. This involved forming an embedded interferometer between light incident close to normal incidence (reference beam) and light incident at the angle to excite surface plasmons (sample beam). The signal from the interferometer was extracted by stepping the phase of the reference beam relative to the sample beam using a spatial light modulator; this requires at least 3 phase steps, which limits the speed of operation. To overcome this and extract the same information with a single measurement, we project an azimuthal varying phase between 0 and 2π in the central region of the back focal plane; corresponding to small angles of incidence. This projects a vortex beam as the reference, so that the phase of the reference beam varies with azimuthal angle. By extracting the interference signal from different portions of the reference beam, different phase steps between the reference and the sample are obtained, so all the values required for phase reconstruction can be extracted simultaneously. It is thus possible to obtain the same information with a single shot measurement, at each defocus position, without additional changes to the back focal plane illumination. Results are presented to show that the vortex illuminated sample provides similar results to the phase stepped version, whose values are, in turn, validated with ellipsometry and surface profilometry.

The principal strength of the confocal microscope for biological imaging lies its ability to detect only light that emerges at close to the focal plane, eliminating light originating from different focal planes. We discuss how this confocal property has considerable advantage in the detection of surface plasmons, since it defines the path of the detected radiation, thus greatly improving the lateral resolution and also the measurement precision. In this paper we show how a spatial light modulator in the back focal plane allows one to generate a whole range of new imaging properties that confer great flexibility on the system. The technique allows one to measure surface wave velocity, surface wave attenuation and perform rapid single shot measurement and effect common path operation.

We investigate the use of a hybrid nanoresonator comprising a photonic crystal (PhC) cavity coupled to a plasmonic bowtie nanoantenna (BNA) for the optical trapping of nanoparticles in water. Using finite-difference time-domain simulations, we show that this structure can confine light to an extremely small volume of $${\sim } 30,000\, \hbox {nm} ^3 ({\sim } 30$$ zl) in the BNA gap whilst maintaining a high quality factor (5400–7700). The optical intensity inside the BNA gap is enhanced by a factor larger than 40 compared to when the BNA is not present above the PhC cavity. Such a device has potential applications in optical manipulation, creating high precision optical traps with an intensity gradient over a distance much smaller than the diffraction limit, potentially allowing objects to be confined to much smaller volumes and making it ideal for optical trapping of Rayleigh particles (particles much smaller than the wavelength of light).

We describe the construction of a prismless widefield surface plasmon microscope; this has been applied to imaging of the interactions of protein and antibodies in aqueous media. The illumination angle of spatially incoherent diffuse laser illumination was controlled with an amplitude spatial light modulator placed in a conjugate back focal plane to allow dynamic control of the illumination angle. Quantitative surface plasmon microscopy images with high spatial resolution were acquired by post-processing a series of images obtained as a function of illumination angle. Experimental results are presented showing spatially and temporally resolved binding of a protein to a ligand. We also show theoretical results calculated by vector diffraction theory that accurately predict the response of the microscope on a spatially varying sample thus allowing proper quantification and interpretation of the experimental results.

A previously described laser ultrasonic technique known as spatially resolved acoustic spectroscopy (SRAS) can be used to image surface microstructure, using the local surface acoustic wave (SAW) velocity as a contrast mechanism. It is shown here that measuring the SAW velocity in multiple directions can be used to determine the crystallographic orientation of grains. The orientations are determined by fitting experimentally measured velocities to theoretical velocities. Using this technique the orientations of 12 nickel and 3 aluminum single crystal samples have been measured, and these are compared with x-ray Laue backreflection (LBR) measurements with good agreement. The root mean square difference between SRAS and LBR measurements in terms of an R-value is less than 4.1°. The influence of systematic errors in the SAW velocity determination due to instrument miscalibration, which affects the accurate determination of the planes, is discussed. SRAS has great potential for complementary measurements or even for replacing established orientation determination and imaging techniques.

Summary This paper develops the theoretical framework to understand the capability of the interferometric surface plasmon microscope to quantify sample properties in a confined region. We use rigorous diffraction theory to quantify the ability of the system to measure local properties and eliminate crosstalk from adjacent regions. We argue that the interferometric system in the defocused condition defines the measured point of excitation and reradiation of the surface plasmons; which greatly improves localisation. We also present results for the noninterferometric microscope, which confirm that the interferometric based system can perform quantitative measurements over smaller regions.

Much interest has arisen in nonlinear acoustic techniques because of their reported sensitivity to variations in residual stress, fatigue life, and creep damage when compared to traditional linear ultrasonic techniques. However, there is also evidence that the nonlinear acoustic properties are also sensitive to material microstructure. As many industrially relevant materials have a polycrystalline structure, this could potentially complicate the monitoring of material processes when using nonlinear acoustics. Variations in the nonlinear acoustoelastic coefficient on the same length scale as the microstructure of a polycrystalline sample of aluminum are investigated in this paper. This is achieved by the development of a measurement protocol that allows imaging of the acoustoelastic response of a material across a samples surface at the same time as imaging the microstructure. The development, validation, and limitations of this technique are discussed. The nonlinear acoustic response is found to vary spatially by a large factor (>20) between different grains. A relationship is observed when the spatial variation of the acoustoelastic coefficient is compared to the variation in material microstructure.

Gold nanostructures of various morphologies, including nanospheres, nanorods, nanoprisms, and thin films, were immobilized on ITO-coated coverslips in order to investigate the response of their scattering to potential. Shifts in the plasmon band obtained by potential-modulated spectroscopic imaging indicated that the voltage sensitivity of the gold nanostructure is dependent on its morphology, with nanospheres exhibiting the lowest sensitivity and ultrathin gold films exhibiting the highest. The effects of potential on gold nanoparticles are in qualitative agreement with Mie and Gans' theories in which the shift of the gold plasma frequency is due to the charging-discharging of the nanoparticles.

Laser ultrasonics conventionally use direct absorption in the sample to generate ultrasound and monitor the sample to detect the ultrasound. However, in some circumstances there are significant advantages to using an optical transducer – a device to facilitate the conversion of optical energy into acoustic energy or to facilitate the modulation of light by an acoustic wave. These devices are known as ‘cheap optical transducers’ (CHOTs). For some applications, they offer considerable advantages over conventional laser ultrasonics or conventional contact ultrasonics. In this paper, the design, operation and applications of CHOTs are discussed, and the concept is extended to the use of superCHOTs that can achieve amplitudes and sensitivities above the usual laser ultrasound limits, nano-scale devices capable of the generation and the detection of ultrasound with wavelengths smaller than that of visible light and devices capable of generating modes not normally accessible to laser ultrasound.

A nonlinear ultrasonic technique for evaluating material elastic nonlinearity has been developed. It measures the phase modulation of a high frequency (82 MHz) surface acoustic wave interacting with a low frequency (1 MHz) high amplitude stress inducing surface acoustic wave. A new breed of optical transducers has been developed and used for the generation and detection of the high frequency wave. The CHeap Optical Transducer (CHOT) is an ultrasonic transducer system, optically activated and read by a laser. We show that CHOTs offer advantages over alternative transducers. CHOTs and nonlinear ultrasonics have great potential for aerospace applications. Results measuring changes in ultrasonic velocity corresponding to different stress states of the sample are presented on fused silica and aluminium.

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.

The study of protein interactions is an area of much interest, particularly towards obtaining more detailed information about biological processes. Current methods involve the use of complicated, specialised techniques which are beyond the scope of most laboratories. Here, we show how information about the binding of proteins to conjugated gold nanospheres can be obtained using straightforward experimental techniques. A Perkin Elmer LS 55 luminescence spectrometer was used to observe the changes in light scattering caused by the binding of complementary proteins to conjugated nanoparticles, measured by the intensity change over time. Mie theory simulations have been used to predict the expected observations and to quantify the changes in intensity as a function of surface coverage. Further kinetic studies have been carried out at 530 nm to obtain more detailed information about the processes involved in the binding reaction. Thus, we have demonstrated that the interaction of proteins can be studied using a straightforward method which provides information about surface coverage and reaction kinetics.

Surface plasmon microscopes are mostly built around the prism based Kretschmann configuration. In these systems, an image of a sample can be obtained in terms of an intensity map, where the intensity of the image is dependent on the coupling of the light into the surface plasmons. Unfortunately the lateral resolution of these systems relies on the ability of plasmons to propagate along the metallised layer and is usually limited to a few microns unless special measures are taken. The widefield surface plasmon microscope (WSPR), used here enables surface plasmon imaging at significantly higher lateral resolutions than prism based systems. In this study we demonstrate the functionality of the WSPR by imaging a sequence of binding events between micro-patterned extracellular matrix proteins and their specific antibodies. Using the WSPR system a change in contrast was observed with each binding event. Images produced via the WSPR system were analyzed and compared qualitatively and quantitatively. Consequently, we confirm that the WSPR microscope described here can be used to study sequential monomolecular layer binding events on a micron scale. These results have significant implications in the development of new micron scale bioassays.

Summary In this paper, we demonstrate how the confinement and enhancement of optical fields by surface plasmon resonance can allow non-linear microscopy to be performed in a simple, cost-effective widefield configuration, rather than the more usual laser-scanning arrangement. We present second harmonic and two-photon luminescence widefield images of dielectric and gold samples obtained with both prism-based and high numerical aperture objective (‘prismless’) microscope arrangements.

Materials that consist of a random microstructure can affect ultrasonic measurements--reducing signal strength, increasing noise, and reducing measurement accuracy--through scattering and aberration of the acoustic field. To account for these adverse effects a phase screen model, alongside the stochastic wave equation, has been developed. This approach allows the field and study aberrations to be modeled from a statistical point of view. Experimental evidence of aberration and statistical properties of the measured acoustic field are shown. A measured correlation function of the acoustic field is interlinked to mean crystallite size by using a theoretical coherence function that can be mainly described by the correlation length and wave velocity variation of microstructure. The estimation of the mean crystallite size using this technique would provide some insight into material characterization.

© The Institution of Engineering and Technology 2015. A wide-field pseudo-heterodyne interference contrast microscope is described, which employs a complementary metal-oxide semiconductor (CMOS) phase-sensitive camera. The use of multiple wells in the camera enables extremely rapid measurement of a full phase field at high resolution and the modulation frequency is not limited by the camera frame rate. The high data acquisition frequency allows the effects of microphonics to be frozen to mitigate the effect of lowfrequency disturbance.

Structured illumination microscopy (SIM) has been widely used in life science imaging applications. The maximum resolution improvement of SIM, compared to conventional bright field system is a factor of 2. Here we present an approach to structured illumination microscopy using the proximity projection grating scheme (PPGS), which has the ability to further enhance the SIM resolution without invoking any nonlinearity response from the sample. With the PPGS-based SIM, sub-100 nm resolution has been obtained experimentally and results corresponding to 2.4 times resolution improvement are presented. Furthermore, it will be shown that an improvement of greater than 3 times can be achieved.

© 2015 Acoustical Society of America. In order to work at higher ultrasonic frequencies, for instance, to increase the resolution, it is necessary to fabricate smaller and higher frequency transducers. This paper presents an ultrasonic transducer capable of being made at a very small size and operated at GHz frequencies. The transducers are activated and read optically using pulsed lasers and without physical contact between the instrumentation and the transducer. This removes some of the practical impediments of traditional piezoelectric architectures (such as wiring) and allows the devices to be placed immediately on or within samples, reducing the significant effect of attenuation which is very strong at frequencies above 1 GHz. The transducers presented in this paper exploit simultaneous optical and mechanical resonances to couple the optical input into ultrasonic waves and vice versa. This paper discusses the mechanical and optical design of the devices at a modest scale (a few μm) and explores the scaling of the transducers toward the sub-micron scale. Results are presented that show how the transducers response changes depending on its local environment and how the resonant frequency shifts when the transducer is loaded by a printed protein sample.

We have developed surface plasmon interferometric microscope and demonstrated that by integrating a phase spatial light modulator (SLM) on conjugate back focal plane of confocal microscope objective lens, this enables us to perform surface plasmon phase imaging and phase sensing using phase stepping interferometry over well confined region [1-6]. In this paper, we address one of the key limitations of the system, which is data acquisition time. Since phase stepping algorithm requires 3 (for 120 degrees step) to 4 (for 90 degrees step) phases in order to obtain a relative phase value between the reference beam and the signal beam the phase pattern on the SLM needs to be frequently updated and the liquid crystal takes time to respond. This slows down the data acquisition process. Moreover, acquiring the phase steps at different times increases microphonic noise and introduces artefacts into real time experiments, such as protein binding. In this paper, we show that a simple and innovative method to overcome these issues is to employ a vortex reference beam provided by 0 to 2π rad topological phase pattern on the SLM; this enables us to obtain multiple phase information in one single shot measurement without updating the SLM pattern.

This paper describes a fast-scanning Kerr microscope which produces quantitative and repeatable images with a scan rate of one frame/s. The rapid scan facility results in a practical system for routine examination of magnetic samples, whereas presently available scanning and full-field systems are relatively slow.

This paper discusses the feasibility of using artificial neural networks (ANNs), together with a high precision scanning optical profiler, to measure very fine track widths that are considerably below the conventional diffraction limit of a conventional optical microscope. The ANN is trained using optical profiles obtained from tracks of known widths, the network is then assessed by applying it to test profiles. The optical profiler is an ultra-stable common path scanning interferometer, which provides extremely precise surface measurements. Preliminary results, obtained with a 0.3 NA objective lens and a laser wavelength of 633 nm, show that the system is capable of measuring a 50 nm track width, with a standard deviation less than 4 nm.

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.

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 contrast 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.

Sub-pixel image correlation has been applied to the measurement of surface deformation, in particular to the measurement of thermally induced strain in microchips. A Fourier shift technique coupled with successive approximation is used to determine the sub-pixel component of the deformation. This reduces the effects of systematic errors on data associated with interpolation or curve-fitting present in other sub-pixel techniques. For all image correlation techniques, defocus errors can have serious effects on the accuracy of the technique. These errors are eliminated in this case through use of a set of images at different axial positions, where only the in focus information is used. This allows determination of the out-of-plane component of the displacement to within roughly 1/40 of the depth of focus (250 nm at ×10 magnification). An in-plane deformation/displacement uncertainty of roughly 2% of a pixel (

A phase-sensitive wide field transmission microscope, combining the advantages of both interferometric and confocal techniques, has been developed and applied to analysis of particulates, both in dry powder form and in suspensions. The microscope has also been used in detecting defects in crystals. Confocal operation is achieved by superimposing speckle illumination of a reference beam in a Mach-Zehnder interferometer with a matched speckle pattern of the object beam. It is shown that the phase measurement enables particle size to be determined even when the particle is smaller than the focal spot size. The data acquisition time is below 1ms, making the system suitable for dynamic process measurement. The experimental results are in good agreement with modelled results giving rise to the possibility of simultaneous determination of both the size and refractive index of small particles.

A high-speed, high-resolution interferometer was constructed on the basis of four-channel phase-shift acquisition, real-time phase detection, unwrapping and profile-fitting image processing. This instrument was applied for visualisation of the mixing process between supercritical carbon dioxide and ethanol solvent above mixture critical pressure, at high Reynolds numbers. The instantaneous phase distribution and time-averaged concentration profiles in the jet have been obtained. The high sensitivity of this system also allowed measurements of the temperature profiles and determination of the excess enthalpy of ethanol–CO2 mixing.

The amplitude and phase response of a high numerical aperture interferometric microscope to subwavelength grooves are investigated both experimentally and theoretically. It is well known that for narrow and deep structures scalar diffraction theory is no longer valid and a rigorous vector diffraction model is required. Conical diffraction results presented demonstrate significant differences in measurements taken in different polarisation states. Significant light coupling occurs when the polarisation state of light at the back focal plane of the microscope is aligned perpendicular to the groove (TE) whereas relatively poor coupling occurs when the polarisation is aligned along the groove (TM). The stronger coupling of TE incident light in the groove means that there is much greater contrast compared to TM. Under certain circumstances an inversion of the phase occurs in TE, which is intuitively explained in terms of interference between the top and bottom of the groove. The greater coupling that occurs in TE enables the depth of narrow grooves to be measured more accurately and over a wider range of depths than in TM.

We demonstrate a fast all-optical surface acoustic wave (SAW) microscope. This acoustic microscope may be thought of as a non-contact (hence non-perturbing) surface acoustic microscope. The key to producing a sufficiently high SAW amplitude for imaging without producing surface damage is to tailor the generating optical distribution. This can be used to spread the optical power on the sample surface (preventing damage) and to focus the acoustic waves (increasing the amplitude). This paper discusses the general and specific design features of our microscope and important new developments in the general design of such instruments. Our microscope based on this technology is capable of producing high quality, quantitative images of SAW amplitude and phase (velocity) on many materials; this and new, unique, forms of acoustic contrast are demonstrated and discussed.

In a laser based surface acoustic wave (SAW) system the initial wavefront of the SAW is determined by the distribution of generating light on the sample surface. In our usual system the generating light is focussed into an arc or concentric arcs which spatially focus and temporally filter the SAWs. We have developed acoustic diffractive elements (DAEs) which, like diffractive optical elements, can shape the SAW distribution by diffraction. These DAEs are, like their optical analogues, highly dispersive and special consideration has to be made at the design stage in order to accommodate and utilize this dispersion. We demonstrate DAEs that produce well controlled multiple focii, frequency suppression and frequency selection. We also show that these complex acoustic elements can be accurately modelled using a simple angular spectrum technique. The DAEs are produced by computer generated holograms which control the generating distribution of light. These DAEs have applications in multi-frequency acoustic, harmonic acoustic imaging, SAW wavefront control and imaging on curved surfaces.

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.

A fast, non-contact Rayleigh wave scanning microscope is demonstrated, which is capable of scan rates of up to a maximum of 1000 measurements/s with typical speeds of up to 250 measurements/s on real samples. The system uses a mode-locked, Q-switched Nd:YAG laser operating at a mode-locked frequency of 82 MHz and a Q-switch frequency of 1 kHz. The Q-switch frequency determines the upper limit of the scanning rate. The generating laser illumination is delivered and controlled by a computer-generated hologram (CGH). The generating laser produces around 30 pulses at 82 MHz and additional harmonics at 164 and 246 MHz and above. The microscope can operate at these harmonics provided the spatial bandwidth of the optics and the temporal bandwidth of the electronics are suitable. The ultrasound is detected with a specialized knife-edge detector. The microscope has been developed for imaging on isotropic materials. Despite this, the system can be used on anisotropic materials, but imaging and interpreting images can be difficult. The anisotropy and grain structure of the material can distort the Rayleigh wavefront, leading to signal loss. A model has been developed to simulate polycrystalline-anisotropic materials; this is discussed along with possible solutions that would overcome the problems associated with anisotropy. Rayleigh wave amplitude images are demonstrated on silicon nitride at 82 and 164 MHz and on polycrystalline aluminium at 82 MHz.

In this paper we show how a tightly focused pump beam can be used to alter the local refractive index of the sample. This local variation acts as a scattering site, which enables resolution exceeding that of a conventional scanning microscope to be obtained in the far field. The improvement in resolution depends on a number of factors which are discussed in the paper, including the optical configuration (confocal or non-confocal), the thermal properties of the sample, the ‘strength’ of the object and the duration of the heating pulse. Experimental results confirming the theoretical predictions are presented; these demonstrate more than 25% improvement in edge response compared with a conventional scanning system.

This paper discusses the approach we have taken to developing laser ultrasonics so that it can fufil many of the functions normaly associated with the scanning acoustic microscope. In particular, we discuss applications involving accurate measurement of surface acoustic wave velocity and imaging applications involving the scattering of surface acoustic waves (SAWs). We present some novel techniques for detection ofSAWs and show how computer-generated holography should be a valuable solution to improve the laser generation efficiency of SAWs.