Digital Image Analysis Assisted Microradiography—Measurement of Mineral Content of Caries Lesions in Teeth

This study investigated the feasibility of using a digital image analysis system to process the information contained in microradiographs of tooth sections that included dental caries lesions. The results show that by using an aluminum step wedge to provide a range of thickness standards and a sound area of the sample as an internal reference, data on tooth mineral content as a function of the location can be obtained with an estimated error of less than 5% relative to the mineral content of sound area. This microradiographic technique allows the response of tooth samples to a remineralization treatment to be quantitatively measured and statistically analyzed.     

Single-shot full resolution region-of-interest (ROI) reconstruction in image plane digital holographic microscopy

We describe a numerical processing technique that allows single-shot region-of-interest (ROI) reconstruction in image plane digital holographic microscopy with full pixel resolution. The ROI reconstruction is modelled as an optimization problem where the cost function to be minimized consists of an L2-norm squared data fitting term and a modified Huber penalty term that are minimized alternately in an adaptive fashion. The technique can provide full pixel resolution complex-valued images of the selected ROI which is not possible to achieve with the commonly used Fourier transform method. The technique can facilitate holographic reconstruction of individual cells of interest from a large field-of-view digital holographic microscopy data. The complementary phase information in addition to the usual absorption information already available in the form of bright field microscopy can make the methodology attractive to the biomedical user community.     

Investigation on sol–gel boehmite-AlOOH films on Kapton and their erosion resistance to atomic oxygen

To improve the atomic oxygen (AO) erosion resistance of Kapton, boehmite-AlOOH films were deposited on it by sol–gel method and AO exposure experiments were performed in a ground-based AO simulator. The results indicate that the AlOOH-coated samples show an improved AO resistance and their erosion yield is one order of magnitude less than that of pristine Kapton. Furthermore, the AlOOH-coated Kapton remained optically stable under AO exposure. The AlOOH film structure before and after AO exposure was analyzed by scanning electronic microscope, atomic force microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. It was found that after AO exposure, the film structure tends to transfer from an octahedral coordination for AlOOH to an octahedral and tetrahedral mixed-coordination for γ-Al₂O₃. This implies that a more stable γ-Al₂O₃ structure could be formed in AlOOH film during AO exposure. The AO erosion mechanism of the coated Kapton was discussed.     

用感光仪绿色施照光测定感绿医用X线胶片时感光度的计算

本文阐明了用特定光谱可见光对感绿医用X线胶片进行感光测定时 ,以能量纯物理绝对单位焦耳 /平方米为单位计量曝光量的计算方法和依据 ,以求取感光度。     

Thick dye-doped poly(methyl methacrylate) films for real-time holography

Molding and direct-polymerization techniques are used for the fabrication of holographic materials based on dye-doped poly(methyl methacrylate). The thickness of the samples obtained ranges from several micrometers to several millimeters. Pump-signal cross modulation is studied experimentally, and photophysical mechanisms responsible for refractive-index and absorption changes are discussed. Self-developing intensity and polarization holographic recording capability, strong anisotropy of diffraction, and high angular selectivity are demonstrated in thick samples.     

Resolution improvement in microscopic imaging through turbid media based on differential polarization gating

We report a new method for microscopic imaging of an object embedded in a turbid medium, based on the differential polarization-gating mechanism. It is demonstrated that with this method, image resolution through optically thick milk suspensions can be improved by as much as 30% compared with no-gating methods. An image resolution of tens of micrometers is achieved in an optically thick turbid medium, which is approximately 10 times better than that achieved in transillumination imaging in a similar medium.     

pH-sensitive holographic sensors

Holographic sensors for monitoring H+ (pH) have been fabricated from ionizable monomers incorporated into thin, polymeric, hydrogel films which were transformed into volume holograms using a diffusion method coupled with holographic recording, using a frequency doubled Nd:YAG laser (532 nm). Unlike other optical pH sensors, it is possible to tailor the operational replay wavelength of the holographic sensor by careful control of the exposure conditions. The holographic diffraction wavelength (color) of the holograms was used to characterize their shrinkage and swelling behavior as a function of pH in various media. The effects of hydrogel composition, ionic strength, temperature, and factors influencing reversibility and response time are evaluated. Optimized holographic pH sensors show milli-pH resolution. The pH-sensing range of the holograms can be controlled through variation of the nature of the ionizable co-monomer used in polymer film construction; a series of holographic sensors displaying visually perceptible, fully reversible color changes over different pH ranges are demonstrated. A poly(hydroxyethyl methacrylate-co-methacrylic acid) holographic sensor was shown to be able to quantify the change in H+ concentrations in real time in a sample of milk undergoing homolactic fermentation in the presence of Lactobacillus casei.     

Sub-20 nm laser ablation for lithographic dry development

Pattern collapse of small or high aspect ratio lines during traditional wet development is a major challenge for miniaturization in nanolithography. Here we report on a new dry process which combines high resolution resist exposure with selective laser ablation to achieve high resolution with high aspect ratios. Using a low power 532?nm laser, we dry develop a normally negative tone methyl acetoxy calix(6)arene in positive tone to reveal sub-20?nm half-pitch features in a ～100?nm film at aspect ratios unattainable with conventional development with ablation time of 1-2?s per laser pixel (～600?nm diameter spot). We also demonstrate superior negative tone wet development by combining electron beam exposure with subsequent laser exposure at a non-ablative threshold that requires far less electron beam exposure doses than traditional wet development.     

A pixel detector-based single photon-counting system as fast spectrometer for diagnostic X-ray beams

Recent advances in semiconductor pixel detectors and read-out electronics allowed to build the first prototypes of single photon-counting imaging systems that represent the last frontier of digital radiography. Among the advantages with respect to commercially available digital imaging systems, there are direct conversion of photon energy into electrical charge and the effective rejection of electronic noise by means of a thresholding process. These features allow the photon-counting systems to achieve high imaging performances in terms of spatial and contrast resolution. Moreover, the now available deep integration techniques allow the reduction of the pixel size and the improvement of the functionality of the single cell and the read-out speed so as to cope with the high fluxes found in diagnostic radiology. In particular, the single photon-counting system presented in this paper is based on a 300-microm thick silicon pixel detector bump-bonded to the Medipix2 read-out chip to form an assembly of 256 x 256 square pixels at a pitch of 55 microm. Each cell comprises a low-noise preamplifier, two pulse height discriminators and a 14-bit counter. The maximum counting rate per pixel is 1 MHz. The chip can operate in two modalities: it records the events with energy above a threshold (single mode) or between two energy thresholds (window mode). Exploiting this latter feature, a possible application of such a system as a fast spectrometer is presented to study the energy spectrum of diagnostic beams produced by X-ray tubes.     

Holographic scattering in SiO2 nanoparticle-dispersed photopolymer films

We describe an experimental study of holographic (coherent) scattering due to parasitic noise gratings recorded in SiO2 nanoparticle-dispersed photopolymer films. Dependences of film thickness and nanoparticle concentration on holographic scattering losses are evaluated. It is shown that the geometric feature of the holographic scattering pattern in the two-beam recording setup can be explained by the Ewald sphere construction. It is found that holographic scattering becomes noticeable when a film with nanoparticle concentrations higher than 10 vol.% is thicker than 100 microm. The significance of holographic scattering in the characterization of a volume grating recorded in a thick (>100 microm) nanoparticle-dispersed photopolymer film is also discussed.     

Growth and hydrogenation of epitaxial yttrium switchable mirrors on CaF2

Rutherford backscattering (RBS) ion channeling measurements and X-ray diffraction experiments are performed to study the epitaxial nature of as-deposited yttrium on CaF₂〈111〉 substrates and the effect of hydrogenation on the crystalline quality. The RBS and X-ray results clearly demonstrate the unique epitaxial relation between as-deposited films and the substrate, which is preserved upon loading with hydrogen. X-Ray diffraction reveals: (i) a remarkably large lattice expansion in the direction normal to the substrate, which decreases with increasing film thickness; and (ii) an in-plane compression of the lattice. This peculiar result is related to the difference in thermal expansion coefficients of film and substrate. RBS ion channeling measurements reveal a thickness dependence of the mismatch-induced stresses. As expected, the stresses relax with increasing distance from the film/substrate interface, but surprisingly, even with films as thick as 400 nm considerable dechanneling is still observed at the film surface. Film quality, i.e. the film/substrate mismatch as well as the induced stresses and their relaxation, are discussed in relation to atomic force microscopy (AFM) results on these epitaxial films.     

Digital holography of particle fields: reconstruction by use of complex amplitude

Digital holography appears to be a strong contender as the next-generation technology for holographic diagnostics of particle fields and holographic particle image velocimetry for flow field measurement. With the digital holographic approach, holograms are directly recorded by a digital camera and reconstructed numerically. This not only eliminates wet chemical processing and mechanical scanning, but also enables the use of complex amplitude information inaccessible by optical reconstruction, thereby allowing flexible reconstruction algorithms to achieve optimization of specific information. However, owing to the inherently low pixel resolution of solid-state imaging sensors, digital holography gives poor depth resolution for images, a problem that severely impairs the usefulness of digital holography especially in densely populated particle fields. This paper describes a technique that significantly improves particle axial-location accuracy by exploring the reconstructed complex amplitude information, compared with other numerical reconstruction schemes that merely mimic traditional optical reconstruction. This novel method allows accurate extraction of particle locations from forward-scattering particle holograms even at high particle loadings.     

Lötbarkeitsuntersuchungen in der Dickschicht-Hybridmikroelektronik

Thick Film Hybrid Microelectronics – Aspects of Solderability The interconnection techniques for microelectric circuits requires a high level of reliability. Soft solder applications are widely used because of their economy. The quality of bonds made in this technology is determined by the solderability of the materials used. Starting with a definition of the solderability this paper describes a method to determine the solderability of thick film metallizations.     

The deposition of selenium coatings on beryllium foils

A technique for preparing selenium films on 50.8μm thick beryllium foils is described. The selenium was deposited in vacuum from a resistance heated evaporation source. A water-cooled enclosure was used to minimize contamination of the vacuum system and to reduce the exposure of personnel to toxic and noxious materials. Profilometry measurements of the coatings indicated selenium thicknesses of 5.5, 12.9, 37.5, 49.8 and 74.5 μm. The control of deposition rate and of coating thickness was facilitated using a commercially available closed-loop programmable deposition controller. The X-ray transmission of the coated substrates was measured using a tritiated zirconium source. The transmissivities of the film/substrate combination are presented for the range of energies from 4 to 20 keV.     

X-Ray Detection Using a Two-Transistor Active Pixel Sensor Array Coupled to an a-Se X-Ray Photoconductor

A direct-conversion X-ray sensor array using amorphous silicon (a-Si) thin-film transistor (TFT) based active pixel sensor (APS) readout circuit coupled with a stabilized amorphous selenium (a-Se) photoconductor for large-area digital imaging applications is presented. The pixel readout circuit employs a novel two-transistor (2T) active/passive pixel architecture that enables a compact pixel circuit for high-resolution sensor arrays with high large-area fabrication reliability. The X-ray detector consists of an in-house fabricated 150 $mu$m pixel pitch 2-TFT pixel coated with an 80 $mu$m thick a-Se photoconductor. A detector dark current of 110 pA/cm$^{2}$ at 10 V/$mu$ m electric field, and a controllable pixel conversion gain up to 8.4 nA/mR with a quantum efficiency of 60% was measured. Capabilities such as voltage programmable gain and dynamic range control, as well as nondestructive readout during X-ray exposure are demonstrated. The detector in this work represents a highly promising technology for high-resolution X-ray digital imaging, adaptable to a wide range of applications owing to its gain and dynamic range programmability.      

Optimization of a thick polyvinyl alcohol-acrylamide photopolymer for data storage using a combination of angular and peristrophic holographic multiplexing

The capability of polyvinyl alcohol-acrylamide photopolymer materials to obtain angularly multiplexed holographic gratings has been demonstrated [Appl. Phys. B 76, 851 (2003)]. A combination of two multiplexing methods--peristrophic and angular multiplexing--is used to record 60 holograms. An exposure schedule method is used to optimize the capability of the photopolymerizable holographic material and obtain holograms with a higher, more uniform diffraction efficiency. In addition, because of this exposure schedule method, the entire dynamic range (M#) of the material will be exploited, obtaining values of approximately M# approximately 9 in layers approximately 800 microm thick.     

Small pixel CZT detector for hard X-ray spectroscopy

A new small pixel cadmium zinc telluride (CZT) detector has been developed for hard X-ray spectroscopy. The X-ray performance of four detectors is presented and the detectors are analysed in terms of the energy resolution of each pixel. The detectors were made from CZT crystals grown by the travelling heater method (THM) bonded to a 20×20 application specific integrated circuit (ASIC) and data acquisition (DAQ) system. The detectors had an array of 20×20 pixels on a 250 μm pitch, with each pixel gold-stud bonded to an energy resolving circuit in the ASIC. The DAQ system digitised the ASIC output with 14 bit resolution, performing offset corrections and data storage to disc in real time at up to 40,000 frames per second. The detector geometry and ASIC design was optimised for X-ray spectroscopy up to 150 keV and made use of the small pixel effect to preferentially measure the electron signal. A ²⁴¹Am source was used to measure the spectroscopic performance and uniformity of the detectors. The average energy resolution (FWHM at 59.54 keV) of each pixel ranged from 1.09±0.46 to 1.50±0.57 keV across the four detectors. The detectors showed good spectral performance and uniform response over almost all pixels in the 20×20 array. A large area 80×80 pixel detector will be built that will utilise the scalable design of the ASIC and the large areas of monolithic spectroscopic grade THM grown CZT that are now available. The large area detector will have the same performance as that demonstrated here.     

A simplified broadband coupling approach applied to chemically robust sol-gel, planar integrated optical waveguides

A new generation waveguide spectrometer with broadband coupling capabilities has been developed. As opposed to previous devices, this attenuated total reflection (ATR) spectrometer is much simpler in design, is more chemically robust, and transmits light down to at least 400 nm. The attenuated total reflection element consists of a single-mode, planar integrated optical waveguide fabricated by dip-coating a approximately 300 nm thick, sol-gel composite layer on a glass substrate. A commercially available prism is used as the incoupler with an integral holographic diffraction grating acting as the dispersive outcoupling element. The transmission of narrow band-pass filters was used to compare the response of the waveguide spectrometer to that of a conventional transmission instrument. Spectral resolution was assessed by measuring the fwhm of various laser lines, which were found to range from 0.5 to 1.3 nm. The measured limits of detection for the waveguide spectrometer from 400 to 600 nm are 8.0 and 10.1 milliabsorbance units for TE and TM polarizations, respectively. Finally, to demonstrate the application of this technology to a molecular film confined to a solid-liquid interface, visible ATR spectra of an adsorbed submonolayer of horse heart cytochrome c were acquired. A procedure to correct the waveguide spectra for the wavelength dependence in ATR path length is described.     

Optical properties and instrumental performance of thin gold films near the surface plasmon resonance

The optical properties of very thin gold films have been evaluated by Fresnel analysis, with optical boundary conditions pertaining to the surface plasmon resonance (SPR) at the gold-water interface. The experimental SPR characteristic was evaluated in the angular interrogation mode. Film morphology was characterized by high resolution transmission electron microscopy. The magnitude of the resonance, i.e., the SPR signal, sensitively depends on, and is affected by film thickness and morphology. A sharply defined thickness of 55 ± 5 nm is required, to achieve optimum SPR excitation conditions, and instrumental sensitivity. With decreasing film thickness, below 40 nm, the resonance angle starts to shift to larger values. A substantial increase of the intrinsic resonance broadening parameter is observed below 70 nm, associated with an increasingly asymmetric SPR line shape. A similar effect occurs in the presence of a very thin chromium adhesion layer. Surface roughness and film thickness modulations determine the experimentally observed line broadening parameter. Instrumental noise levels largely depend on accuracy and quality at which the resonance angle can be determined. Substantial improvement and instrumental sub-pixel resolution is achievable by optimum fitting routines, accounting for drastic noise reduction and improved instrumental sensitivity, up to two orders of magnitude over the inherent geometric sensor pixel resolution.     

Ultraviolet-induced surface modification of polyurethane films in the presence of oxygen or acrylic acid vapours

An efficient surface functionalization of polyurethane (PU) films has been obtained by ultraviolet (UV)-assisted modification in the presence of oxygen or acrylic acid (AA) vapours. Film analyses were carried out by water contact angle measurements, X-ray photoelectron spectroscopy (XPS) and Near-edge X-ray absorption fine structure (NEXAFS). Film hydrophilicity increased with photolysis time in the presence of oxygen or AA vapours. Incorporation of COO and CO functional groups at the polymer surface after the UV-assisted treatments was observed. In addition, High resolution XPS and NEXAFS results showed that a thin film of poly (acrylic acid) (PAA) is formed over the PU films during the UV irradiation with AA vapours. The obtained results are compared with previous published oxygen and AA low-power plasma treatments. Similarity between both treatment methodologies is shown. UV surface functionalization and polymerization of PAA can be used instead of a traditional plasma treatment with the advantage of set-up simplicity and lower costs.