Six-degrees-of-freedom alignment technique that provides diagnostic misalignment information

We introduce a new six-degrees-of-freedom alignment technique that enables the precise alignment of two optical device planes. The method combines linear diffraction gratings and cylindrical Fresnel lenses that allow the diagnosis of misalignment in each degree of freedom independently. The technique was used to align two 20 mm x 20 mm fused-silica substrates separated by 17 mm. The worst-case alignment precision was found to be better than +/- 5 microm laterally, +/- 20 microm longitudinally, +/- 0.036 degrees rotationally, and +/- 0.007degrees in tilt.     

Design and fabrication of continuous-profile diffractive micro-optical elements as a beam splitter

An optimization algorithm that combines a rigorous electromagnetic computation model with an effective iterative method is utilized to design diffractive micro-optical elements that exhibit fast convergence and better design quality. The design example is a two-dimensional 1-to-2 beam splitter that can symmetrically generate two focal lines separated by 80 microm at the observation plane with a small angle separation of +/- 16 degrees. Experimental results are presented for an element with continuous profiles fabricated into a monocrystalline silicon substrate that has a width of 160 microm and a focal length of 140 microm at a free-space wavelength of 10.6 microm.     

Characterization of a polarization-independent transmission trap detector

A six-element polarization-independent transmission trap detector with coaxial input and output beams has been constructed and full characterized. The measured optical parameters are compared with their values, predicted by Fresnel equations. Measured transmittances are in agreement with the predicted values within 2 x 10(-5) in the wavelength region from 450 to 650nm. The spectral responsivity of the transmission trap detector is in agreement with the predicted values within 0.035% at 543.5- and 633.0-nm vacuum wavelengths. The spatial uniformity of the responsivity is +/-0.03% across the active area of approximately 5 x 6 mm(2), measured with a laser beam of 1-mm diameter. The angular uniformity of the transmission trap detector is better than +/-0.01% for +/-3 degrees rotation around two perpendicular axes.     

Fabrication of nano- and micro-scale UV imprint stamp using diamond-like carbon coating technology

Two-dimensional (2-D) and three-dimensional (3-D) diamond-like carbon (DLC) stamps for ultraviolet nanoimprint lithography were fabricated with two methods: namely, a DLC coating process, followed by focused ion beam lithography; and two-photon polymerization patterning, followed by nanoscale-thick DLC coating. We used focused ion beam lithography to fabricate 70 nm deep lines with a width of 100 nm, as well as 70 nm deep lines with a width of 150 nm, on 100 nm thick DLC layers coated on quartz substrates. We also used two-photon polymerization patterning and a DLC coating process to successfully fabricate 200 nm wide lines, as well as 3-D rings with a diameter of 1.35 microm and a height of 1.97 microm, and a 3-D cone with a bottom diameter of 2.88 microm and a height of 1.97 microm. The wafers were successfully printed on an UV-NIL using the DLC stamps without an anti-adhesive layer. The correlation between the dimensions of the stamp's features and the corresponding imprinted features was excellent.     

The PTB microbeam: a versatile instrument for radiobiological research

The PTB microbeam is routinely used for the irradiation of living cells using protons (1-20 MeV) and alpha particles (1-28 MeV). The beam diameter is approximately 2 microm (fwhm), achieved by focussing, resulting in an excellent energy resolution and practically no scattered particles. Recently, an electrostatic beam scanner was added to the facility which allows targeting of each cell within 1 ms. This and other improvements led to an increase in the experimental speed of the system to a maximum of 50,000 cells per hour including all experimental steps. To improve the versatility of the facility further, a module for automatic quantification of immunocytochemical staining was implemented. This allows the analysis of protein activation, taking into account the positional information of the irradiation run.     

An electron microbeam cell-irradiation system at KIRAMS: performance and preliminary experiments

An electron microbeam cell-irradiation (EMCI) system is now ready for routine operation in Korea. The system components include an electron gun operating at 1-100 keV, a beam transport chamber delivering a micron-sized beam, a cell image acquisition and positioning part and an automatic system control section. The present choice of source beam energy is 30 keV so that the radiation impact is conveyed to the targeted cells with a minimum spatial dispersion. The beam is available at 5 microm in diameter now, but can be changed in the range of 1-200 microm. The cellular dose is delivered with a standard deviation of 30% at 0.1 Gy, 10% at 1 Gy and 3% at 10 Gy. The cells are recognised by over 98% in a 1 mm x 1 mm area and the system is capable of irradiating up to 30,000 cells h(-1).     

Polarization properties of retroreflecting right-angle prisms

The cumulative retardance Delta(t) introduced between the p and the s orthogonal linear polarizations after two successive total internal reflections (TIRs) inside a right-angle prism at complementary angles phi and 90 degrees - phi is calculated as a function of phi and prism refractive index n. Quarter-wave retardation (QWR) is obtained on retroreflection with minimum angular sensitivity when n=(sqr rt 2+1)(1/2)=1.55377 and phi =45 degrees. A QWR prism made of N-BAK4 Schott glass (n=1.55377 at lambda=1303.5 nm) has good spectral response (<5 degrees retardance error) over the 0.5-2 microm visible and near-IR spectral range. A ZnS-coated right-angle Si prism achieves QWR with an error of < +/- 2.5 degrees in the 9-11 microm (CO(2) laser) IR spectral range. This device functions as a linear-to-circular polarization transformer and can be tuned to exact QWR at any desired wavelength (within a given range) by tilting the prism by a small angle around phi =45 degrees. A PbTe right-angle prism introduces near-half-wave retardation (near-HWR) with a < or =2% error over a broad (4< or =lambda< or =12.5 microm) IR spectral range. This device also has a wide field of view and its interesting polarization properties are discussed. A compact (aspect ratio of 2), in-line, HWR is described that uses a chevron dual Fresnel rhomb with four TIRs at the same angle phi =45 degrees. Finally, a useful algorithm is presented that transforms a three-term Sellmeier dispersion relation of a transparent optical material to an equivalent cubic equation that can be solved for the wavelengths at which the refractive index assumes any desired value.     

Micromachining of a bimorph Pb(Zr,Ti)O3 (PZT) cantilever using a micro-electromechanical systems (MEMS) process for energy harvesting application

We designed and fabricated a bimorph Pb(Zr,Ti)O3 (PZT) cantilever with an integrated Si proof mass to obtain a low resonant frequency for an energy harvesting application. The cantilevers were fabricated on the micro-electromechanical systems (MEMS) scale. A mode of piezoelectric conversions were d31 and d33 mode in cantilever vibration Therefore, we designed and fabricated a single cantilever with d31 unimorph, d31 bimorph, d33 unimorph, and d33 bimorph modes. Finally, we fabricated a device with beam dimensions of about 5,400 microm x 480 microm x 14 microm (< +/- 5%), and an integrated Si proof mass with dimensions of about 1,481 microm x 988 microm x 450 microm (< +/- 5%). In order to measure the d31 and d33 modes, we fabricated top and bottom electrodes. The distance between the top electrodes was 50 microm and the resonant frequency was 89.4 Hz. The average powers of the d31 unimorph, d31 bimorph, d33 unimorph, and d33 bimorph modes were 3.90, 9.60, 21.42, and 22.47 nW at 0.8 g (g = 9.8 m/s2) and optimal resistance, respectively.     

Innovative tissue engineering structures through advanced manufacturing technologies

Awide range of rapid prototyping (RP) techniques for the construction of three-dimensional (3-D) scaffolds for tissue engineering has been recently developed. In this study, we report and compare two methods for the fabrication of poly-(epsilon-caprolactone) and poly-(epsilon-caprolactone)-poly-(oxyethylene)-poly-(epsilon-caprolactone) copolymer scaffolds. The first technique is based on the use of a microsyringe and a computer-controlled three-axis micropositioner, which regulates motor speed and position. Polymer solutions are extruded through the needle of the microsyringe by the application of a constant pressure of 10-300 mm Hg, resulting in controlled polymer deposition of 5-600 microm lateral dimensions. The second method utilises the heating energy of a laser beam to sinter polymer microparticles according to computer-guided geometries. Materials may be fed either as dry powder or slurry of microparticles. Both powder granulometry and laser working parameters influence resolution (generally 300 microm x 700 microm), accuracy of sintering and surface and bulk properties of the final structures. The two RP methods allow the fabrication of 3-D scaffolds with a controlled architecture, providing a powerful means to study cell response to an environment similar to that found     

Ti: sapphire-based picosecond visible-infrared sum-frequency spectroscopy from 900-3100 cm-1

Visible-infrared sum-frequency spectroscopy is ideally suited to the study of surfaces and interfaces. This paper introduces new sum-frequency spectroscopy instrumentation that we have developed with two novel features: (1) stable and robust infrared generation in the 900-3100 cm(-1) (11-3.2 microm) region using an amplified Ti : sapphire oscillator with a home-built OPG/OPA, and (2) continuous tuning over either 900-2700 cm(-1) (11-3.7 microm) or 1800-3100 cm(-1) (5.5-3.2 microm) in a single experiment. All practical details of baseline correction issues due to the picosecond pulses (including variation in infrared (IR) energy, spatial and temporal overlap, Fresnel coefficients) are addressed while demonstrating signal throughout this region from an amorphous gold surface. A sum-frequency spectrum from an oriented polymer is shown as a complete example of the data treatment, which reveals the vibrational modes accessible in this wavelength region.     

Code-multiplexed optical scanner

A three-dimensional (3-D) optical-scanning technique is proposed based on spatial optical phase code activation on an input beam. This code-multiplexed optical scanner (C-MOS) relies on holographically stored 3-D beam-forming information. Proof-of-concept C-MOS experimental results by use of a photorefractive crystal as a holographic medium generates eight beams representing a basic 3-D voxel element generated via a binary-code matrix of the Hadamard type. The experiment demonstrates the C-MOS features of no moving parts, beam-forming flexibility, and large centimeter-size apertures. A novel application of the C-MOS as an optical security lock is highlighted.     

2-D motion estimation using two parallel receive beams

We describe a method for estimating 2-D target motion using ultrasound. The method is based on previous ensemble tracking techniques, which required at least four parallel receive beams and 2-D pattern matching. In contrast, the method described requires only two parallel receive beams and 1-D pattern matching. Two 1-D searches are performed, one in each lateral direction. The direction yielding the best match indicates the lateral direction of motion. Interpolation provides sub-pixel magnitude resolution. We compared the two beam method with the four beam method using a translating speckle target at three different parallel beam steering angles and transducer angles of 0, 45, and 90 degrees. The largest differences were found at 90 degrees, where the two beam method was generally more accurate and precise than the four beam method and also less prone to directional errors at small translations. We also examined the performance of both methods in a laminar flow phantom. Results indicated that the two beam method was more accurate in measuring the flow angle when the flow velocity was small. Computer simulations supported the experimental findings. The poorer performance of the four beam method was attributed to differences in correlation among the parallel beams. Specifically, center beams 2 and 3 correlated better with each other than with the outer beams. Because the four beam method used a comparison of a kernel region in beam pair 2-3 with two different beam pairs 1-2 and 3-4, the 2-to-1 and 3-to-4 components of this comparison increased the incidence of directional errors, especially at small translations. The two beam method used a comparison between only two beams and so was not subject to this source of error. Finally, the two beam method did not require amplitude normalization, as was necessary for the four beam method, when the two beams were chosen symmetric to the transmit axis. We conclude that two beam ensemble tracking can accurately estimate motion using only two parallel receive beams.     

Measurement of spatial cross sections of ultrasound pressure fields by optical scanning means

The measurement of spatial cross sections of ultrasound pressure fields is an essential element of exposimetry of ultrasonic medical equipment. An optical technique is presented that allows the two-dimensional (2-D) determination of ultrasound pressure using an optical multilayer hydrophone in which a laser beam with suitable wavelength is partially reflected from a dielectric optical multilayer system. By detecting the change in reflectivity of the multilayer coating induced by the incident ultrasound, the pressure time waveform can be determined. A 2-D data acquisition covering an area of at least 15 mm x 5 mm was realized by two complementary approaches. A serial detection scheme was set up by scanning the sensing point across the area of interest by a micromechanically engineered scanning mirror and acquiring pressure time waveforms sequentially and pointwise. This allows the measurement of repeating ultrasonic waveforms with a spatial resolution of better than 70 microm and a minimal detectable pressure of 50 kPa (bandwidth: 50 MHz) in a few seconds. In an alternative approach exploiting the parallel processing capabilities of a charge-coupled devices (CCD) camera chip, the probe was strobe-illuminated by a large-diameter collimated beam of a pulsed laser diode. The 2-D pressure distribution at a particular moment was derived from captured reflectivity distributions with a spatial resolution of 75 microm. By successive delaying of the laser pulse with respect to the ultrasound pulse, the complete 2-D pulse waveform was acquired with high spatial resolution. Measurement results on ultrasound fields from plane and focusing transducers are presented and compared to simulation results. Individual advantages and drawbacks of both approaches are discussed. A combined setup merging both detection schemes into a single device was developed and represents a milestone on the way toward constructing an optical ultrasound measuring camera.     

Focal shift in focused truncated pulsed-laser beam

The focal shift of a focused truncated pulsed-laser beam is investigated. In the case of the Fresnel approximation, the analytic expression of the time-averaged intensity distribution along the axis is derived based on the series expansion. It shows that the focal shift of the pulsed beam can be completely determined by a series of normalized spectrum moments and the central Fresnel number defined according to the central frequency of the pulse. The absolute value of the focal shift of the pulsed beam decreases monotonously and slowly with the normalized spectrum width increasing and the central Fresnel number fixed, and it increases monotonously with the central Fresnel number decreasing and the normalized spectrum width fixed. Besides the central Fresnel number and the normalized spectrum width, the shape of spectral intensity of the pulse affects the focal shift too.     

High-speed ultrasound volumetric imaging system. I. Transducer design and beam steering

Transducer design and phased array beam steering are developed for a volumetric ultrasound scanner that enables the 3-D visualization of dynamic structures in real time. The authors describe the design considerations and preliminary evaluation of a high-speed, online volumetric ultrasound imaging system that uses the principles of pulse-echo, phased array scanning with a 2-D array transducer. Several 2-D array designs are analyzed for resolution and main lobe-side lobe ratio by simulation using 2-D fast Fourier transform methods. Fabrication techniques are described for 2-D array transducer. Experimental measurements of pulse-echo point spread responses for 2-D arrays agree with the simulations. Measurements of pulse-echo sensitivity, bandwidth, and crosstalk are included     

Strain measurement in a concrete beam by use of the Brillouin-scattering-based distributed fiber sensor with single-mode fibers embedded in glass fiber reinforced polymer rods and bonded to steel reinforcing bars

The strain measurement of a 1.65-m reinforced concrete beam by use of a distributed fiber strain sensor with a 50-cm spatial resolution and 5-cm readout resolution is reported. The strain-measurement accuracy is +/-15 microepsilon (microm/m) according to the system calibration in the laboratory environment with non-uniform-distributed strain and +/-5 microepsilon with uniform strain distribution. The strain distribution has been measured for one-point and two-point loading patterns for optical fibers embedded in pultruded glass fiber reinforced polymer (GFRP) rods and those bonded to steel reinforcing bars. In the one-point loading case, the strain deviations are +/-7 and +/-15 microepsilon for fibers embedded in the GFRP rods and fibers bonded to steel reinforcing bars, respectively, whereas the strain deviation is +/-20 microepsilon for the two-point loading case.     

Elliptic Laguerre-Gaussian beams

An analytical expression for the diffraction of an elliptic Laguerre-Gaussian (LG) beam is derived and analyzed. We show that a beam with even singularity order has nonzero axial intensity for any degree of ellipticity and at any finite distance z from the initial plane, whereas at z = 0 and z = infinity the axial intensity is zero. We show that for a beam with a small degree of ellipticity and even order of singularity, two isolated intensity zeroes appear in the Fresnel zone on a straight line at an angle of 45 deg or -45 deg, depending whether the beam's spin is right or left. The theoretical conclusions are confirmed by numerical simulation and physical experiments.     

Characterization of a broadband all-optical ultrasound transducer-from optical and acoustical properties to imaging

A broadband all-optical ultrasound transducer has been designed, fabricated, and evaluated for high- frequency ultrasound imaging. The device consists of a 2-D gold nanostructure imprinted on top of a glass substrate, followed by a 3 microm PDMS layer and a 30 nm gold layer. A laser pulse at the resonance wavelength of the gold nanostructure is focused onto the surface for ultrasound generation, while the gold nanostructure, together with the 30 nm thick gold layer and the PDMS layer in between, forms an etalon for ultrasound detection, which uses a CW laser at a wavelength far from resonance as the probing beam. The center frequency of a pulse-echo signal recorded in the far field of the transducer is 40 MHz with -6 dB bandwidth of 57 MHz. The signal to noise ratio (SNR) from a 70 microm diameter transmit element combined with a 20 microm diameter receive element probing a near perfect reflector positioned 1.5 mm from the transducer surface is more than 10 dB and has the potential to be improved by at least another 40 dB. A high-frequency ultrasound array has been emulated using multiple measurements from the transducer while mechanically scanning an imaging target. Characterization of the device's optical and acoustical properties, as well as preliminary imaging results, strongly suggest that all-optical ultrasound transducers can be used to build high-frequency arrays for real-time high-resolution ultrasound imaging.     

Sub-Structural Parameter Identification Including Cracks of Beam Structure Using PZT Patch

This paper presents the numerical simulation of damage identification of beam structures using novel One Dimensional (1-D) PZT patch model with sub-structuring applied to the PZT Patch boundaries. The 1-D PZT patch model is simple and requires less computational effort than 2-D or 3-D models. A hybrid element constituted of 1-D beam element and a PZT sensor is used with reduced material properties which is very convenient for beams and is a novel application. The accuracy of 1-D hybrid element with cracked structure is first verified experimentally. The stiffness, damping and crack parameters are identified by minimizing the deviation between the predicted and measured voltage from the PZT patch using an optimization algorithm. The numerical signals are polluted with 5% Gaussian noise to simulate experimental noise. Numerical studies are performed on a beam and a nine member frame structure for sub-structural parameter and multiple crack identification. The PZT patches are attached at either ends of beam member to be identified. Sub-structuring is done to isolate the beam with patch, thus reducing the size of model to be identified. The numerical results show significant improvement in identification accuracy compared to other methods.     

Fabrication of x-ray zone plates by surface-plasma chemical vapor deposition

A new cost-efficient sputter-slice technology for hard x-ray (10-30 keV) Fresnel zone plates fabrication, imposing no limitation to aspect ratio, is proposed. By means of a plasma chemical process, SiO(2)/Si(1-x)Ge(x)O(2) glassy film multilayer structures are deposited on a lateral surface of a silica rod, outermost layers being as thin as 100 nm. It has been shown by numerical simulation that for x=0.2 germanium fraction, 100-300 microm zone plate thickness and the number of zones of about 1000, first order diffraction efficiency as high as 20%-30% at the energy of approximately 20 keV can be achieved.