Comparison of superresolution effects with annular phase and amplitude filters

The characteristics of annular amplitude and phase filters are compared. The behavior of two-zone phase and amplitude filters as the inner zone is increased is studied in detail. Numerical simulations show that a phase filter can achieve a superresolution effect, a circular Dammann effect, and flat-topped intensity for different applications, whereas a two-zone amplitude filter can generate only a superresolution effect. The experimental results show that both amplitude and phase filters can achieve superresolution. Generally, a phase superresolution filter is recommended for its higher efficiency and its special diffraction patterns that are impossible to achieve with an amplitude filter.     

Transcranial ultrasound focus reconstruction with phase and amplitude correction

Therapeutic and diagnostic ultrasound procedures performed noninvasively through the skull require a reliable method for maintaining acoustic focus integrity after transmission through layered bone structures. This study used a multiple-element, phased-array transducer to reconstruct ultrasound foci through the human skull by amplitude and phase correction. It was previously demonstrated that adaptive phase correction using a multiple-element, focused transducer array yields a significant correction to an acoustic field that has been distorted by the heterogeneities of the skull bone. The introduction of amplitude correction, in a regime in which acoustic pressures from individual transducer array elements are adjusted to be normalized at the focus, has demonstrated a 6% (-0.27 dB) average decrease in acoustic sidelobe acoustic intensity relative to the focal intensity and a 2% (-0.09 dB) average decrease in the full-width-at-half-maximum (FWHM) of the acoustic intensity profile at the focus. These improvements come at the expense of significant ultrasound intensity loss--as much as 30% lower (-1.55 dB)--at the focus because the amplitude correction method requires that, at constant power, a larger proportion of energy is absorbed or reflected by regions of the skull that transmit less energy. In contrast, a second correction method that distributes pressure amplitudes such that the sections of the skull which transmit more ultrasound energy are exposed with higher ultrasound intensities has demonstrated an average sidelobe intensity decrease of 3% (-0.13 dB) with no change in the FWHM at the focus. On average, there was a 2% (0.09 dB) increase in the acoustic intensity at the focus for this inverse amplitude correction method. These results indicate that amplitude correction according to the transmission properties of various segments of the skull have a clear effect on ultrasound energy throughput into a target site within the brain parenchyma.     

Interferometric measurement of near-cylindrical surfaces with high amplitude resolution

Subaperture interferometric measurements of highly curved surfaces with a shape close to a cylinder have been performed in a normal-incident setup that consists of a Fizeau interferometer in combination with a plano-concave cylindrical lens. Since the field of view in the circumferential direction is limited by spherical aberration, the optical components were designed to minimize spherical aberration. For reference measurements a second plano-convex cylindrical lens was used. The subaperture setup leads to three-dimensional surface maps of the objects under test. To eliminate the influence of residual geometric aberrations, rectangular polynomials have been fitted and subtracted from the raw data. For deformations with spatial wavelengths below 30 mm, a rms amplitude resolution of 1 nm and a rms amplitude accuracy of 3 nm were achieved. Measurements on Wolter-type-I mirror shells are discussed in detail.     

Superresolution along extended depth of focus with binary-phase filters for the Gaussian beam

In the paraxial Debye regime, simple and power-efficient pupil filters are designed to break the diffraction limit along a large depth of focus (DOF) for the Gaussian beam. Dependences of the superresolution factor, DOF gain, Strehl ratio, sidelobe strength, and axial intensity nonuniformity on the Gaussian profile in the pupil plane are characterized using the numerical method. Optimal filter designs are proposed for either high-resolution or ultra-large-DOF applications followed by experimental verifications.     

Scanning holographic microscopy with transverse resolution exceeding the Rayleigh limit and extended depth of focus

We demonstrate experimentally that the method of scanning holographic microscopy is capable of producing images reconstructed numerically from holograms recorded digitally in the time domain by scanning, with transverse and axial resolutions comparable to those of wide-field or scanning microscopy with the same objective. Furthermore, we show that it is possible to synthesize the point-spread function of scanning holographic microscopy to obtain, with the same objective, holographic reconstructions with a transverse resolution exceeding the Rayleigh limit of the objective up to a factor of 2 in the limit of low numerical aperture. These holographic reconstructions also exhibit an extended depth of focus, the extent of which is adjustable without compromising the transverse resolution.     

Development of a high spectral resolution lidar based on confocal Fabry-Perot spectral filters

The high spectral resolution lidar (HSRL) instrument described in this paper utilizes the fundamental and second-harmonic output from an injection seeded Nd:YAG laser as the laser transmitter. The light scattered in the atmosphere is collected using a commercial Schmidt-Cassegrain telescope with the optical receiver train first splitting the fundamental and second-harmonic return signal with the fundament light monitored using an avalanche photodiode. The second-harmonic return signal is mode matched into a tunable confocal Fabry-Perot (CFP) interferometer with a free spectral range of 7.5?GHz and a finesse of 50.7 (312) at 532?nm (1064?nm) placed in the optical receiver for spectrally filtering the molecular and aerosol return signals. The light transmitted through the CFP is used to monitor the aerosol return signal while the light reflected from the CFP is used to monitor the molecular return signal. Data collected with the HSRL are presented and inversion results are compared to a co-located solar radiometer, demonstrating the successful operation of the instrument. The CFP-based filtering technique successfully employed by this HSRL instrument is easily portable to other arbitrary wavelengths, thus allowing for the future development of multiwavelength HSRL instruments.     

Temperature imaging in a supersonic free jet of combustion gases with two-line OH fluorescence

Temperature measurements were performed in a shock-tunnel-generated free jet of hydrogen/oxygen reaction products diluted in argon with a nonsimultaneous, two-excitation-line planar laser-induced fluorescence technique with the hydroxyl radical (OH) as a tracer. Single-shot images were obtained with broadband excitation of isolated transitions in the A(2)Σ(+) ? X(2)Π(1, 0) band of OH near 282 nm, with broadband, temporally integrated detection of the resulting nonresonant emission. A measurement of the fluorescence lifetime in the free jet showed no variation with excited rotational level, allowing the rotational temperature to be obtained from the ratio of single-shot images with laser excitation of different rovibronic transitions.     

Variation of magnification with focus

Applications of optical systems, including depth by focus and three-dimensional metrology, have been developed recently in which the image is characterized over a range of object depths simultaneously and in which the focus of the systems is also varied. Important to such applications is the variation of image magnification with focus. A general understanding of this phenomenon is developed, and two new and useful concepts associated with the variation of the magnification of an image are introduced. Errors and oversights in the existing literature are explained and corrected, and the requirements for an optical system to exhibit the magnification properties desired in such applications are identified. It is shown that not all telecentric systems have these properties and that there exist practical and attractive nontelecentric systems that do exhibit them.     

Millimeter-wave filters with laser control in waveguides

A detailed analysis of a microwave reflection pattern that is due to periodically photoexcited layers of semiconductor material in a waveguide is presented. Different photoconductivity profiles that are due to different excitation conditions with different materials are tested. The diffusion of carriers in the direction of propagation can strongly affect the passband-filtering responses, especially the efficiency and the bandwidth. These configurations can be used as light-induced tunable filters and as a variable matching section between different levels of impedances.     

Finite amplitude transverse waves in materials with memory

We consider the propagation of finite amplitude plane transverse waves in a class of homogeneous isotropic incompressible viscoelastic solids with memory. It is assumed that the Cauchy stress may be written as the sum of an elastic part and a dissipative viscoelastic part. The elastic part is of the form of the stress corresponding to a Mooney–Rivlin material, whereas the dissipative part depends not only on current but also on previous deformations. The body is first subjected to a homogeneous static deformation. It is seen that two finite amplitude transverse plane waves may propagate in every direction in the deformed body. It is also seen that finite amplitude circularly polarized waves may propagate along either n⁺ or n⁻, where n⁺, n⁻ are the normals to the planes of the central circular section of the ellipsoid x · B⁻¹x = 1. Here B is the left Cauchy–Green strain tensor corresponding to the finite static homogeneous deformation.     

Properties of seawater with ice slurry use in focus

Seawater is the most common fluid on earth and ice generating machines are increasingly used on fishing vessels to produce ice slurry from seawater with up to 60% ice to be poured over the catch. In this study, a literature search has been made to establish physical property data of seawater as function of salinity and temperature. Ice slurry properties of seawater have been generated and are presented by means of an enthalpy-phase diagram and related tables with ice concentration, enthalpy change and density. This material confirms that an initial salt content of 2–3 % is optimal and it can help determine the potential for long preservation of catch on board and during transport, improving seafood quality. As seawater is known to be corrosive, a brief discussion on corrosion factors and problems, the use of corrosion inhibitors and choice of materials is included in this paper.     

Evaluation of spatial resolution of spherical-planar-pair lensesfor elasticity measurement with microscopic resolution

The spatial resolution of spherical-planar-pair (SPP) lenses used in an ultrasonic microspectrometer (UMSM) was evaluated by scanning the lenses over a sharp edge of a specimen. The variation of the output observed in experiments was in good agreement with the theory. In the direction perpendicular to the propagation of a leaky surface acoustic wave (SAW), the best spatial resolution was obtained. The distance a_90-10 over which the magnitude decreased from 90% to 10% was 5 μm at the frequency of 260 MHz. In the direction parallel to the leaky SAW propagation, the spatial resolution was severely affected by the excitation of the leaky SAW     

Design of polarizing color filters with double-liquid-crystal cells

A method of designing polarization rotators with double-liquid-crystal (LC) cells is presented. When placed between a polarizer and an analyzer, the polarization rotator becomes a polarizing color filter. Any required color can be generated by optimization of the parameters of the double-LC layers. One specific example of a green filter is given. This filter is analyzed in terms of the optical performance, including transmission spectrum, color coordinates, and viewing angle. A sample green polarizing color filter was made and compared with the theoretical results.     

Realizations of focus invariance in optical-digital systems with wave-front coding

We report experimental verification of an extended depth of focus (EDF) system with near-diffraction-limited performance capabilities. Dowski and Cathey [Appl. Opt. 34, 1859-1866 (1995)] described the theory of this system in detail. We can create an EDF system by modifying a standard incoherent optical system with a special cubic phase plate placed at the aperture stop. We briefly review the theory and present the first optical experimental verification of this EDF system. The phase plate codes the wave front, producing a modified optical transfer function. Once the image is transformed into digital form, a signal-processing step decodes the image and produces the final in-focus image. We have produced a number of images from various optical systems using the phase plate, thus demonstrating the success of this EDF system.     

SAW ring filters with insertion loss of 1 dB

This paper presents low loss ring SAW filters on 49°YX, 64°YX, 128°YX LiNbO₃ with reflective multistrip couplers (RMSCs). Using the RMSCs with 3 electrodes per λ (λ is the SAW wavelength at the center frequency) and the self-matching approach, when the static capacitance of the IDT is compensated by the acoustic radiation susceptance, the ring filters have shown very low insertion loss of 0.8-1 dB, 3-dB fractional bandwidth of 2-5% with very low ripple of 0.1 dB, stopband attenuation over 50 dB at 10-33% offset from the center frequency of 45 MHz. In a 50 ohm system, 148, 164, 172 MHz ring filters on 128°YX for low power transceivers have provided an insertion loss of 1 dB, 1 dB bandwidth of 1.8-2 MHz, stopband attenuation over 55 dB at ±25 MHz offset from the center frequency. Two cascaded filters at 164.5 MHz have shown insertion losses below 3 dB and stopband attenuation over 90 dB at ±25 MHz, offset from the center frequency. The chip size is 5×4×0.7 mm     

Localization of an object in tissue with phase modulation spectroscopy: Reduction of the effects of the relative amplitude and phase on amplitude cancellation

Abstract

In this paper, we discuss the effects of various factors on the localization of an object with amplitude cancellation phase modulation spectroscopy (PMS) by an analytical method. The factors include the relative modulation phase and the amplitude between two sources, the absorption coefficient and the size of the localized absorber. A localization method that can reduce the effects of the relative modulation amplitude and phase between two sources on measurement is presented. In the new method, two measurements are carried out, where modulation signals of two sources in the second measurement are exchanged relative to those in the first measurement. The principle and the feasibility of the method are shown theoretically. Primary experimental results are presented.