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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.

Metasurfaces offer diverse wavefront control by manipulating amplitude, phase, and polarization of light which is beneficial to design subwavelength scaled integrated photonic devices. Metasurfaces based tunable circular polarization (CP) beam splitting is one functionality of interest in polarization control. Here, we propose and numerically realize metasurface based spin tunable beam splitter which splits the incoming CP beam into two different directions and tune the splitting angles by switching the handedness of incident light polarization. The proposed design approach has potential in applications such as optical communication, multiplexing, and imaging.

Metasurfaces have drawn considerable attention in manipulation of electromagnetic waves due to their exotic subwavelength footprints. Regardless of immense progress of polarization-dependent flat optics, the realization of on-device switchable complete phase multiplication is still missing from design multifunctional devices. Here, by combining geometric and propagation phases, a generalized design principle is proposed that can achieve switchable integer or fractional multiple complete phase modulation in transmitted circularly cross-polarized light by switching the handedness of incident polarization. As a proof of concept, two types of spin-dependent bifunctional wavefront manipulating devices, including switchable beam splitter/beam deflector and spin-to-orbital angular momentum converter designs are numerically realized. It is believed that the proposed single-cell spin-switchable rational-multiple complete-phase-modulation design principle based on combined propagation and geometric phases has great potential to underpin the development of meta-optics-based multifunctional operations in the field of integrated optics, imaging, and optical communication.

Phase retrieval with pre-defined optical masks can provide extra constraints and thus achieve improved performance. Recent progress in optimization theory demonstrates the superiority of random masks in enhancing the accuracy of phase retrieval algorithms. However, traditional approaches only focus on the randomness of the masks but ignore their non-bandlimited nature. When using these masks for phase retrieval, the intensity measurements contain many significant high-frequency components that the phase retrieval algorithm cannot take care of and thus leads to degraded performance. Based on the concept of digital halftoning, this paper proposes a green noise binary masking scheme that can significantly reduce the high-frequency contents of the masks while fulfilling the randomness requirement. The resulting intensity measurements will contain data concentrated in the mid-frequency band and around zero frequency areas which can be fully utilized in the phase retrieval optimization process. Our experimental results show that the proposed green noise binary masking scheme consistently outperforms the traditional ones when using in binary coded diffraction pattern phase retrieval systems.

This paper presents formulations to evaluate noise in differential and ratiometric measurements that are often performed in biosensing. These measurements are performed to improve signal to noise ratio of the sensing systems for sensitive detection of dynamic biological processes. The use of these formulations is discussed in the context of the differential intensity surface plasmon resonance (SPR) system that is widely used to characterise molecular interactions on a confined axial scale. Previous studies provide qualitative descriptions of the noise performance of such systems but lack rigorous characterisation. Here we present analytical expressions for quantitative evaluation of the noise in differential and ratiometric measurements by applying the rules of arithmetic operations on random variables. Such formulations provide the means for evaluating the signal to noise ratio of such systems. We present how correlated noise can be removed by performing differential or ratiometric processing. Applying these formulations, we also show how the sensitivity of the differential intensity SPR system changes during the experiment.

This paper illustrates how the amplitude and phase of back focal plane distribution can be recovered in a confocal microscope system from several intensity images in the image plane. These will have a wide range of uses for imaging and sensing. We believe this method is complementary to the V(z) technique where the sample is defocused. The field generated in the back focal plane may be processed by virtual propagation which averages noise in a highly efficient manner. In this paper, we demonstrate that the phase information on the back focal plane can be recovered using ptychography with no need to modify the optical configuration and employ an interferometer. This phase information plays a crucial role in sensitivity of surface plasmons resonance biosensing systems.

In this paper, we firstly explain the concept of surface plasmon resonance imaging and a main key issue in the field of localized SPR imaging, which is the trade-off between resolution and sensitivity. We will then explain how V(z) scanning confocal microscope can overcome the trade-off and enable us to make a localized detection of multiple analytes in small quantities. This paper provides a brief review on a chronological development of the confocal surface plasmon embedded interferometric microscope and highlights the key idea behind each developments. Theoretical detection limit of the confocal system is within a single molecule detection regime, where 100kD molecule can be detected with 100μJ of light in the confocal system. We also discuss some key challenges in achieving the theoretical limit, such as, microphonic vibration and slow scanning speed of the system and how to get around these challenges. Lastly, we discuss some possible future developments to improve the system.

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.

A label-free microscopy method for assessing the differentiation status of stem cells is presented with potential application for characterization of therapeutic stem cell populations. The microscopy system is capable of characterizing live cells based on the use of evanescent wave microscopy and quantitative phase contrast (QPC) microscopy. The capability of the microscopy system is demonstrated by studying the differentiation of live immortalised neonatal mouse neural stem cells over a 15 day time course. Metrics extracted from microscope images are assessed and images compared with results from endpoint immuno-staining studies to illustrate the system’s performance. Results demonstrate the potential of the microscopy system as a valuable tool for cell biologists to readily identify the differentiation status of unlabelled live cells.

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.

We investigate the performance of surface plasmon and Fabry-Perot modes formed between two closely spaced layers. The motivation for this study is twofold: first, to look for modes that may be excited at lower incident angles compared to the usual Kretschmann configuration with similar or superior refractive index responsivity and, second, to develop a simple and applicable method to study these structures over a wide range of separations without recourse to the construction of ad hoc structures. Using back focal plane observation and appropriate signal processing, we show results for the Otto configuration at visible wavelengths at a range of separations not reported hitherto. Moreover, we investigate a hybrid structure we call the Kretschmann-Otto configuration that gives modes that change continuously from a hybridized surface plasmon mode to a zero-order Fabry-Perot mode. The ability to change the separation to small gap distances enables us to examine the Fabry-Perot modes where we show that it has superior refractive index responsivity, by more than an order of magnitude, compared to the Kretschmann configuration.

Optical surface waves are guided light on surface of optical structures. There are several optical structures that support optical surface waves, such as, nanostructures, gratings, optical waveguides and metamaterials. Optical surface waves have proven themselves very promising candidates for several applications including, biosensing, optical computing and optical circuitry. The characteristics of surface wave can be characterised by the wave vector (k-vector) of the surface wave. In this paper, we will discuss how a modified confocal microscope integrated with a phase spatial light modulator allows us to measure both the real part and the imaginary part (attenuation coefficient) of the surface wave k-vector. Surface plasmon resonance (SPR) excited on a uniform gold surface through Kretschmann configuration is employed as an example in this talk. Note that the system is not limited to the SPR. It is also applicable to other types of optical surface waves. We have demonstrated in our recent publication that the modified confocal not only provides the k-vector measurement both real and imaginary, it also allows us to separate different loss mechanisms in SPR. One limitation of the system was the single point detection. Here we will discuss the current stage of our development in widefield confocal surface plasmon microscope, which allows us to measure multiple points simultaneously. This has been achieved by integrating another amplitude spatial light modulator in the image plane of the objective lens. Use of orthogonal illumination patterns allows the image plane to be sequentially amplitude modulated and post-processed to recover the confocal image.

This paper describes theoretical and experimental study of the fundamentals of using surface plasmon resonance (SPR) for label-free detection of voltage. Plasmonic voltage sensing relies on the capacitive properties of metal-electrolyte interface that are governed by electrostatic interactions between charge carriers in both phases. Externally-applied voltage leads to changes in the free electron density in the surface of the metal, shifting the SPR position. The study shows the effects of the applied voltage on the shape of the SPR curve. It also provides a comparison between the theoretical and experimental response to the applied voltage. The response is presented in a universal term that can be used to assess the voltage sensitivity of different SPR instruments. Finally, it demonstrates the capacity of the SPR system in resolving dynamic voltage signals; a detection limit of 10mV with a temporal resolution of 5ms is achievable. These findings pave the way for the use of SPR systems in the detection of electrical activity of biological cells.

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.

Femtosecond stimulated Raman microscopy (FSRM) aims at the reduction of acquisition times in Raman microscopy while preserving the spectral coverage. An improved light source for FSRM is briefly described. This light source delivers a narrow bandwidth Raman pump pulse and a broad-band Raman probe. The small spectral changes (relative magnitude 10−6 to 10−3) in the probe light due to the stimulated Raman effect are recorded simultaneously relying on array detectors. Here, estimates for the parameters of an ideal detector are derived and compared with the technical status quo of available detectors. Copyright © 2014 John Wiley & Sons, Ltd.

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.

To improve the diagnostic prediction of recurrence of otitis media with effusion after surgery, an anti-confocal system combined with spectroscopic measurements is proposed to reject unwanted signals from the eardrum and assess the blood content. The anti-confocal system was experimentally evaluated on both optical middle ear phantom and human skin. Results showed effective rejection of signals from the eardrum using a central stop replacing the confocal pinhole, while still detecting signals from the middle ear mucosa. The system is sensitive to changes in blood content, but scattering and absorption characteristics of the eardrum can distort the measurement. Confocal detection of eardrum properties was shown to be a promising approach to correct measurements.

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.

This paper discusses theoretical aspects of the V ( z ) response of the scanning acoustic microscope (s. a. m.) when used to examine specimens with lateral discontinuities. The problem is introduced in terms of a simple ray model to establish a physical picture of the processes involved. An approximate Green function is then developed which enables use of a modified form of the Fourier optical formulations to calculate V ( z ) for a cylindrical lens. These calculations explain two different types of contrast observed when imaging specimens in the reflection s. a. m., such as (i) the ability to image fine discontinuities and display them with enhanced contrast and an apparent width determined by the acoustic wavelength; and (ii) to give a quantitative account of the amplitude of periodic ripple often observed running parallel to cracks on acoustic micrographs. Both these types of contrast may be predicted by using the same model and arise naturally from variation of the reflection and transmission properties of the discontinuity, the relative value of these parameters determines which type of contrast predominates. At an interface between media with different elastic properties, the contrast is affected not only by the scattering properties of the boundary but also by the very fact that surface waves must propagate in media with different elastic properties. This effect alone can provide a powerful contrast mechanism which enables one to understand the light to dark contrast reversals often observed at grain boundaries in polycrystalline specimens at different values of defocus.

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.

Summary This paper presents a simple, high-resolution, non-fluorescent imaging technique called total internal reflection microscopy (TIRM) and demonstrates its potential application to real-time imaging of live cellular events. In addition, a novel instrument is introduced that combines the simplicity of TIRM with the specificity afforded by dual-colour total internal reflection fluorescence (TIRF) microscopy and allows sequential imaging with the two modalities. The key design considerations necessary to apply these imaging modes in a single instrument are discussed. The application of TIRM alone yielded high-resolution live images of cell adherence to a poly-l-lysine modified substrate, whereby fine cellular structures are imaged. Non-fluorescent imaging of the uptake of sub-micron–sized polymeric particles by live cells is also demonstrated. Finally, images of fluorescently labelled cells were obtained in TIRF mode, sequentially to images obtained of the same cell in TIRM mode. Visual information gained using TIRF is compared with TIRM to demonstrate that the level of cell structure information obtainable with our total internal reflection microscope is comparable with the TIRF technique.

Since the discovery of X-rays in 1895, curiosity as well as clinical need has produced huge advances in our ability to visualize structures inside the human body. X-ray radiographic imaging led the way, followed in 1957 by the use of gamma-ray cameras, and then ultrasound imaging, magnetic resonance imaging (MRI), and positron emission tomography (PET). Together, these tools, in which physics plays a key part, underpin modern clinical-imaging practice.

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.

We have developed an innovative ultrasonic transducer system (CHOT) which is optically excited by means of lasers. It can be used both for generation and detection of narrowband ultrasound and provides non-contact (or even remote), couplant-free generation and/or detection. It has also the advantage of being inexpensive to manufacture and the simplicity of its concept makes it ideal for industrial applications. In this study we present results where CHOTs have been used both for excitation and detection of surface acoustic waves. An initial theoretical model is also presented which describes the principle of operation.