Directional edge enhancement using a liquid-crystal display

We present a method for orientation-selective enhancement of the first derivatives of an image. The proposed method is based on the polarization properties of the twisted-nematic liquid-crystal displays (LCDs). LCDs are manufactured to work between a polarizer-analyzer pair, and for a given incident polarization direction, the image contrast will depend on the analyzer orientation. In particular, two analyzer orientations of interest could be identified for the proposed experiments: one that reproduces the image displayed on the LCD, and the other one (orthogonal to the former) that gives a negative (contrast reversed) replica of the original image. By placing a beamsplitter after the LCD, two images are spatially separated, analyzed by linear polarizers in perpendicular directions, and then slightly displaced. When the original image and its displaced (contrast reverted) replica are imagined together across a plane, one obtains a resultant image with enhanced first derivatives along a specific direction. Unlike the usual Fourier (coherent) image processing, the technique proposed here works with incoherent illumination. Validation experiments are presented.     

Video-rate near-infrared optical tomography using spectrally encoded parallel light delivery

A novel parallel source implementation approach to near-infrared tomography is demonstrated through spectral encoding of the light delivery. This new technique allows many sources to be input into the tissue at the same time, and a high-resolution spectrometer is used to spatially spread out the signals from each spectrally encoded source. The parallel sampling of all sources at all detection locations renders rapid imaging. Acquisition of complete tomographic data sets at a video rate of 35 frames/s is achieved for imaging of a 6.35 mm diameter inclusion with an absorption coefficient of 0.01 mm(-1) and a reduced scattering coefficient of 1.5 mm(-1) that is moving along a circular path inside a 1% Intralipid solution.     

Electron-holographic interference microscopy

Recent developments in electron interference microscopy are introduced based on holography principles. This technique has been given a major boost due to the development of a coherent field-emission electron beam. This has facilitated the measurement of the phase distribution of an electron beam transmitted through or reflected from an object to within 1/100 of the electron wavelength. Phase distribution can be displayed as a phase contour map in an electron micrograph. There the contour fringes directly and quantitatively indicate the thickness contours of a uniform sample, magnetic lines of force of a magnetic sample and equipotential lines of an electrostatic sample. Microscopic objects or fields have made their appearance in amplified interference micrographs through the use of this technique. Specific examples are the static and even dynamic observation of magnetic fluxons penetrating a superconductor and the quantitative measurement of specimen thickness or topography in atomic dimensions.     

Determination of the standard deviation of height on a rough surface using interference microscopy

When a rough surface is viewed in an interference microscope with tilt fringes introduced, the effect of the roughness is to reduce the average visibility of the tilt fringes. The relationship between the standard deviation of surface height and the average visibility of the tilt fringes is derived, and experimental results are presented of measurements made on ground glass surfaces using a Linnik interference microscope.     

Fourier-transform spectroscopy using liquid-crystal technology

We report the use of a ferroelectric liquid-crystal (FLC) mask as an optical encoder for development of a solid-state Fourier-transform spectrometer. For this demonstration a 1x64 element array was striped and used as a 1x4 element device. The device intersected dispersed radiation and encoded each spectral component with a carrier signal by applying half-wave potential to each of the four striped (1x16) FLC elements, which varied the transmitted amplitude of the light from 0.03% to 28% of full scale. The light was spectrally recombined and imaged onto a photomultiplier and the resulting carriers (and their amplitudes) detected by Fourier transformation of the time-varying signal. Spectra of colored-glass filters were taken to demonstrate the possibilities of the instrument.     

Static and dynamic characterization of AlN-driven microcantilevers using optical interference microscopy

We have developed an optomechanical methodology, combining interferometric deflection data, the nanoindentation technique and analytical modeling to perform the characterization of piezoelectrically driven microcantilevers operating as MEMS actuators. Here, the association of standard Twyman–Green interferometry (TGI) with time averaged and stroboscopic techniques permits the evaluation of the 3-D out-of-plane deflections of microdevices and provides feedback of measurements that helps us to optimize MEMS structures and improve the reliability and stability of microcantilevers.The goal of the presented study was investigation of high-quality cantilevers composed from silicon beam and a transducer including the aluminum nitride (AlN) layer. It is a material with piezoelectric properties, which can be an alternative for PZT films in micromachining technology. After presenting the fabrication process of the testing devices, the rest of the paper will focus on non-contact measurements of cantilevers deflection by interferometry: static data (e.g., initial shape, deformation, stress) and dynamic parameters of samples (e.g., resonance frequency and amplitude distributions in vibration modes). On the basis of these experimental data, parameters such as piezoelectric coefficient d₃₁ have been calculated taking into account multiple film stacking.     

Assessment of ion exchanged channel waveguides in glass using interference microscopy

The use of an interference microscope in the assessment of channel waveguides formed by ion exchange in glass is presented. In the particular mode of operation discussed, light is passed through the guide parallel to the surface normal to yield the lateral index profile. It is shown that the surface expansion of the glass that occurs during the exchange has a significant effect on the interference data. A simple method of correcting for this effect is reported and justified. The application of the above technique to the characterisation of Cu ion exchanged channel guides is demonstrated. Some observations concerning the relationship between the index profile and surface expansion profile are made.     

非平行光干涉照明显微镜三维形貌检测研究

为实现表面微观形貌快速而较简单的检测, 一种使用非平行光干涉照明的光学显微三维形貌检测方法被提出。该方法使用空间光调制器对激光光束进行衍射, 选取光强相近的2个衍射级通过显微物镜, 双光束干涉可得到周期接近图像分辨率、相位可精确调节的照明条纹, 被测样本的三维形貌可通过拍摄4帧等相位差的条纹照明图像来计算得到。该方法不需借助干涉物镜产生条纹, 不需要轴向扫描装置记录条纹变化, 相位调节精确, 成像直观。此外, 该方法所产生干涉条纹的相位随坐标线性变化, 不需对条纹周期进行修正。因为照明条纹参数调节光路独立于显微成像光路, 系统装置具有光路简洁、易于调节的优点。为验证所提出三维检测精度, 以粗糙度100 nm的粗糙度对比模块和硅片为被测样品进行了三维轮廓重建实验, 实验结果显示, 所提出方法轴向重复性测量精度为8.6 nm(2σ)。     

Spectral-domain differential interference contrast microscopy

We present a fiber-optic low-coherence imaging technique, termed spectral-domain differential interference contrast microscopy (SD-DIC), for quantitative DIC imaging of both reflective surfaces and transparent biological specimens. SD-DIC combines the common-path nature of a Nomarski DIC interferometer with the high sensitivity of spectral-domain low-coherence interferometry to obtain high-resolution, quantitative measurements of optical pathlength gradients from a single point on the sample. Full-field imaging can be achieved by scanning the sample. A reflected-light SD-DIC system was demonstrated using a USAF resolution target as the phase object. Live cardiomyocytes were also imaged, achieving a resolution of 36 pm for pathlength gradient measurements. The dynamics of cardiomyocyte contraction were recorded with high sensitivity at selected sites on the cells.     

Wavefront formation using modal liquid-crystal correctors

Results of experiments on wavefront formation using multichannel modal correctors in an adaptive optical system with feedback are reported. Two types of correctors, one based on a glass substrate with a high-resistance layer deposited onto it and the other based on a high-permittivity ceramic substrate, are developed and investigated. The results show that it is expedient to use the correctors in applications that do not require a high speed of response.     

Femtosecond pulse shaping using a two-dimensional liquid-crystal spatial light modulator

We introduce a programmable, high-rate scanning femtosecond pulse shaper based on a two-dimensional liquid crystal on a silicon spatial light modulator (SLM). While horizontal resolution of 1920 addressable pixels provides superior fidelity for generating complex waveforms, scanning across the vertical dimension (1080 pixels) has been used to facilitate at least 3 orders of magnitude speed increase as compared with typical liquid-crystal SLM-based pulse shapers. An update rate in excess of 100 kHz is demonstrated.     

Geometric phase-shifting for low-coherence interference microscopy

A low-coherence Linnik interference microscope using high numerical aperture optics has been constructed. The system uses a tungsten halogen lamp and Köhler illumination, with separate control over field and aperture stops, so that experiments can be conducted with a range of different operating conditions. The novel feature of the system is the use of an achromatic phase-shifter operating on the principle of the geometric phase, achieved by using a polarising beam splitter, a quarter wave plate and a rotating polariser. Image information is extracted from the visibility of the fringes, the position of the visibility peak along the scanning axis yielding the height of the test surface at the corresponding point.     

Absorption panel cooling using a TFE-NMP mixture

A panel system for cooling buildings is proposed, working with an absorption-refrigeration unit, the evaporator of which is the panel itself. Trifluoroethanol (TFE) and N-methylpyrrolidinone (NMP) are proposed as refrigerant and absorbent, respectively. Use of the TFE-NMP mixture seems to offer advantages over the usual H₂OLiBr or NH₃H₂O mixtures, and suits well the modest refrigeration temperatures needed in panel cooling. Analytical expressions are presented for the properties of the TFE-NMP mixture and a calculation procedure for NH₃H₂O units is used after suitable modifications to simulate the operation of the TFE-NMP absorption-refrigeration unit. Under the conditions considered, the lowest evaporation temperature varies from 3 to 16°C, and the theoretical coefficient of performance from 60% to 68.4%, with its maximum value obtained at 9°C. Under the above conditions, for panel cooling power 50–150 W/m², a refrigerant mass flow rate through the panel from 400 g/m² h to 1600 g/m² h is needed with a driving thermal power from 80 W/m² to 220 W/m².     

Transflective liquid-crystal display using low-twisted vertically aligned mode

We present the design of a transflective and low-power LCD using a low-twist vertically aligned liquid crystal (LC) cell, achieved by blending a chiral additive with a patterned reflector in a single-domain configuration. Unlike the conventional single-domain transflective LCD, in which it is possible to optimize only one of the transmissive and reflective regions, the device suggests that it is possible to optimize both the transmission and reflection design to obtain favorable results in both reflective and transmissive light conditions by optimizing the chiral pitch and twist angle. From the parameter space diagram (PSD) method, which does not include the information on chiral pitch and the nonuniform LC director tilt angle, optimization focused on the transmissive region is performed. By analyzing the relation between the transmittance and the chiral pitch under the applied voltage, the optimized twist angle and chiral pitch are proposed. It is described that the optimized twist angle is also available for the reflective region by the dynamic PSD method by considering the average tilt angle under applied voltage.     

Video-rate optical low-coherence reflectometry based on a linear smart detector array

A low-coherence reflectometer based on a conventional Michelson interferometer and a novel silicon detector chip that allows parallel heterodyne detection is presented. Cross-sectional images of 64x256 pixels covering an area of 1.92 mm x 1.3 mm are acquired at video rate and with a sensitivity close to the shot-noise limit. Applications in surface profiling and thickness measurement are demonstrated.     

Optical sectioning in differential interference contrast microscopy

While developing a three-dimensional (3-D) measurement technique for the retardation-modulated differential interference contrast (RM-DIC) microscope, we encountered a problem. The problem was that the measurement range was restricted in λ because it applies weak phase approximation.To overcome this drawback, we propose a 3-D reconstruction method with z-axis scanning. This technique needs high optical sectioning, like confocal microscopy.We investigated the characteristic of optical sectioning in a DIC microscope, then we confirmed experimentally that a DIC microscope has high optical sectioning. We also confirmed that a RM-DIC microscope has higher optical sectioning.By combining the optical sectioning of a RM-DIC microscope and z-scanning, we developed a new 3-D reconstruction method. This novel technique overcomes the observed problem as the measurement range is increased to micron order.     

4Pi confocal microscopy with alternate interference

We introduce 4Pi confocal microscopy with destructive interference of converging waves. Linear lobe deconvolution as well as nonlinear restoration of 4Pi confocal raw data with their point-spread functions (PSF's) leads to almost-identical images, irrespective of whether the 4Pi confocal PSF relies on constructive or destructive interference. Three-dimensional imaging of microtubules of a mouse fibroblast cell yielded an axial resolution near 100-nm in both cases. Moreover, restoration of 4Pi confocal images of the same object with alternate phases is introduced as a powerful test for (nonlinear) image restoration.