Circular Pinhole Research Articles

Scanning X-ray Apparatus for Crystal Texture Mapping and Micro-Fluorescence Analysis

Scanning x-ray mapping based on energy dispersive x-ray diffraction is a powerful technique for imaging the spatial distributions of crystal texture and elements [1, 2]. Odd-shaped samples can be studied in air at ambient pressure and without special preparation. A schematic drawing of the scanning x-ray apparatus is shown in Figure 1. A “white” radiation x-ray source (PHILIPS generator PW 1830/25 equipped with a fine-focus tungsten tube) rather than characteristic radiation is used. The high density target material gives rise to an intense continuous Bremsstrahlung background. A collimator, consisting of two circular pinhole diaphragms, is attached to the tube and produces an aperture of 0.3° and an effective beam diameter of 50 μm on the sample. The apertures, Δθ, of the primary and secondary beams are not critical, since crystal texture is scarcely sharper than several degrees, and x-ray fluorescence lines are not affected at all by the aperture settings.

Location of pinholes in a pipeline

This paper describes a new acoustic method to detect and locate very small leaks, i.e. pinholes in a closed gas pipe or a closed empty liquid pipe. A decrease or increase in the pressure of the gas in the closed pipe leads to gas blowing in or out of the pinhole, if it exists, and the gas flowing through the pinhole generates acoustic noise with a broadband spectrum. The acoustic noise induces standing waves in the pipe just as in a flute. The length of the closed pipe and the pinhole site determine the modes and frequencies of the standing waves. We built a mathematical model that describes the above acoustic phenomena, and present here a method to locate a pinhole in a pipe by using the model. The method requires only one microphone set at a terminal in the closed pipeline. The autocorrelation of the acoustic noise picked up by the microphone shows pulses if leaks exist, and the pulse occurrence times can be used to uniquely calculate the length of the closed pipe and the leak site. Laboratory experiments we carried out have validated the proposed pinhole location method. The method located a circular pinhole of 0.3 mm in diameter at various sites, a crack, a loosened joint, and two pinholes in the pipe which had a length of 10.24 m and a diameter of 53.4 mm. The calculated results proved to be unique, clear-cut and accurate.

Three-dimensional Imaging in Confocal Fluorescent Microscopy with Annular Lenses

Abstract Three-dimensional imaging properties in confocal fluorescent microscope systems with annular lenses are investigated in terms of the three-dimensional optical transfer function (OTF). Starting from the OTF, we also consider the optical sectioning property. The dependence of the OTF and the optical sectioning strength on the radius of the central obstruction of the lens is revealed. For the case of a finite-sized circular pinhole in front of the detector, both the OTF and the optical sectioning strength, together with the signal level, are calculated as a function of the radius of the pinhole. Investigations show that for a given finite size of the pinhole, the optical sectioning strength can be increased by altering the radius of the central obstruction of the lens to an optimum value, and that a higher signal level may be maintained by using an annular objective only.

Signal strength and noise in confocal microscopy: Factors influencing selection of an optimum detector aperture

AbstractIn confocal microscopy, several factors influence the selection of an optimum size and geometry of detector aperture. These include (1) strength of signal from the specimen, (2) noise level in the system, (3) optical configuration of the microscope (e.g., reflection or fluorescence), (4) time available for signal accumulation, (5) specimen thickness, and (6) amount of reduction in axial and transverse resolution (from the theoretical maximum) that can be tolerated. It is shown both theoretically and experimentally that the size of the detector aperture critically influences the type and amount of system noise that is detected along with the specimen signal. It is also demonstrated that increasing the size of the detector pinhole does not appreciably increase the signal strength from any single thin plane, but only increases the sampling depth, enhancing brightness at the cost of a reduction in axial resolution. As a result, it is shown that there is no advantage, from the standpoint of signal strength, to using a slit aperture rather than a circular detector pinhole. Finally, it is concluded that all confocal microscopes should be designed to allow the user the capability of selecting ah optimum compromise detector aperture setting based on the particular specimen properties, type of microscopy (e.g., fluorescence or reflection) and resolution required.

X-ray computed tomography system: 39356 Kabushiki Kaisha Toshiba U.S. Patent No. 4,754,468 (28 Jun. 1988)

Pinhole single-photon emission computed tomography (SPECT) with high spatial-resolution is suitable for small-animal imaging, but has limitations associated with spatial-resolution inhomogeneity or axial blurring. We have hypothesized that this blurring is due to incompleteness of projection data acquired by a single circular pinhole orbit. And we have developed a pinhole SPECT system with two circular orbits which satisfy Tuy's condition so as to provide complete data for 3D pinhole SPECT reconstruction within the whole field-of-view (FOV); a dedicated 3D ordered subsets expectation maximization (3D-OSEM) reconstruction method for two-orbit data. This study is aimed at evaluating accuracy and impact of this system. In this system, not the camera but the object rotates and the two orbits are 90° and 45° relative to object's axis. Experiments using a multiple-disk phantom filled with 99mTc solution and a mouse bone scan using 99mTc-labeled HMDP agent were carried out. The Feldkamp's filtered back-projection (FBP) method and the 3D-OSEM method were applied to these data sets. The axial blurring was apparent on images reconstructed by FBP for single-orbit data, while the 3D-OSEM using two-orbit data dramatically improved the resolution homogeneity and statistical noise property, and also demonstrated considerably better image quality in the mouse scan.

Imaging with oriented photographic diffusers

We analyse the imaging property of an oriented photographic diffuser which is the record of an elongated speckle pattern. It is found that the contrast transfer, when gratings are imaged through the slits in the diffuser, is considerably higher compared to imaging through a circular pinhole of comparable dimensions. We use the diffuser to produce high frequency gratings through multiple imaging a low frequency grating. The grating is used to demonstrate optical image subtraction.

The NSLS VUV undulator: Spectral characteristics and operating experience

The design and operating characteristics of the VUV undulator installed on the NSLS VUV ring are presented. Specifically, the spectral output through three circular on-axis pinholes of different diameters has been measured. Near the minimum magnetic gap (40 mm), the flux into a 0.25 mrad circular aperture at the peak of the fundamental ( hv = 57 eV) is ≈ 1 × 10 14 photons/(s·0.1 A·1% bandwidth). We find good agreement in spectral shape between these measured spectra and spectra calculated by integrating the theoretical undulator emission over the relevant spatial variables and including electron beam emittance. We also show calculated zero-emittance and on-axis flux spectra for comparison. A description is given of the beam line and monochromator currently installed on this undulator for the purpose of performing spin-resolved photoemission.

Multiple scattering of light in near-critical methanol-cyclohexane

We have experimentally and theoretically investigated the polarized and depolarized double-scattered intensity in the critical system methanol-cyclohexane in the temperature range $0.003<T\ensuremath{-}{T}_{c}<1$\ifmmode^\circ\else\textdegree\fi{}C. We have used a scattering geometry typical of spectroscopic studies, in which the single-scattering volume is illuminated by a narrow, cylindrically symmetric beam, viewed through small circular pinholes by a detector at a 90\ifmmode^\circ\else\textdegree\fi{} scattering angle. We have investigated the multiple-scattering effects for aperture sizes ranging from 5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ to 5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ rad, where coherence effects become important. Our results for the total polarized and depolarized intensity are well described by double-scattering theory with $\ensuremath{\gamma}=1.26$, ${\ensuremath{\xi}}_{0}=2.6$ \AA{}, and $\ensuremath{\nu}=0.60$. At our closest approach to ${T}_{c}$, we find that the contribution of polarized double scattering to the total scattered intensity is \ensuremath{\cong}40%. At this temperature the effects of attenuation on the incident and scattered light become important. We have observed the effects of triple- and higher-order scattering events as an additional attenuation of the singly and doubly scattered light, and we have employed this observation to estimate the intensity of these higher-order scattering events.

Graphic design of pinhole cameras

The paper describes a graphic technique for the analysis and optimization of pinhole size and focal length. The technique is based on the use of the transfer function of optical elements described by Scott (1959) to construct the transfer function of a circular pinhole camera. This transfer function is the response of a component or system to a pattern of lines having a sinusoidally varying radiance at varying spatial frequencies. Some specific examples of graphic design are presented.