Fast imaging of hard x rays with a laboratory microscope

An improved x-ray microscope with a fully electronic CCD detector system has been constructed that allows improved laboratory-based microstructural investigations of materials with hard x rays. It uses the Kirkpatrick-Baez multilayer mirror design to form an image that has a demonstrated resolution of 4 mum at 8 keV (Cu K(alpha) radiation). This microscope performs well with standard sealed-tube laboratory x-ray sources, producing digital images with 20-s exposure times for a 5-mum Au grid (a thickness of two absorption lengths).     

Hard X-Ray Microscope With Submicrometer Spatial Resolution

A high-resolution hard x-ray microscope is described. This system is capable of detecting line features as small as 0.6 µm in width, and resolving line pairs 1.2-µm wide and 1.2-µm apart. Three types of two-dimensional image detectors are discussed and compared for use with hard x rays in high resolution. Principles of x-ray image magnification are discussed based on x-ray optics and diffraction physics. Examples of applications are shown in microradiography with fiber reinforced composite materials (SiC in Ti₃Al Nb) and in diffraction imaging (topography) with device patterns on a silicon single crystal. High-resolution tomography has now become a reality.     

High-efficiency production of propagation-invariant spot arrays

Tailoring of the transverse intensity profiles of propagation-invariant optical fields is considered. The design of diffractive elements capable of realizing such fields by Fourier synthesis is discussed. High-efficiency realization of finite-aperture approximations of the constructed fields is demonstrated in a system consisting of two multilevel diffractive elements. The first element is a diffractive toroidal lens, which focuses the incident field into a ring pattern. The second diffractive element, located at the focal plane of the first element, introduces the phase modulation necessary to realize the desired transverse intensity profile behind a separate collimating lens. The influence of the fabrication errors of the diffractive elements on the fidelity of the propagation-invariant spot array is simulated, and system-integration aspects based on substrate-mode planar-integrated optics are considered.     

Theoretical foundations for joint digital-optical analysis of electro-optical imaging systems

We describe the mathematical and conceptual foundations for a novel methodology for jointly optimizing the design and analysis of the optics, detector, and digital image processing for imaging systems. Our methodology is based on the end-to-end merit function of predicted average pixel sum-squared error to find the optical and image processing parameters that minimize this merit function. Our approach offers several advantages over the traditional principles of optical design, such as improved imaging performance, expanded operating capabilities, and improved as-built performance.     

Wolter type I x-ray focusing mirror using multilayer coatings

A multilayer coating is a useful addition to a mirror in the x-ray region and has been applied to normal incidence mirrors used with soft x rays. When a multilayer coating is used on grazing incidence optics, higher performance can be achieved than without it. Cr/Sc multilayers coated on a Wolter type I mirror substrate for a soft x-ray microscope are considered. The reflectivity and effective solid angle are calculated for Wolter type I mirrors with uniform and laterally graded multilayer coatings. The laterally graded multilayer mirror showed superior x-ray performance, and the multilayer tolerances were relaxed. This multilayer mirror could be especially useful in the soft x-ray microscope intended for biological applications.     

Relationship between microscanned image quality and fill factor of detectors

Microscanning is an important technique in high-resolution electro-optical imaging. It can increase the resolution and improve the performance of imaging systems. For optimum design of a staring imaging system with microscanning modes it is necessary to choose the optimum microscanning mode according to the fill factor of the detector. Hence it is important to study the effect of the fill factor on the microscanning image quality. With some assumptions, we introduce the sampling-averaging modulation transfer function of a detector array at the spatial Nyquist frequency with which to study quantitatively the improvement in image quality of various microscanning modes for selected fill factors (1, 2/3, and 1/2). Analytical results show that the amount of improvement is closely associated with the fill factor. Finally, typical sampling imaging of focal plane arrays with these fill factors are simulated. Experimental results qualitatively describe the effect of the fill factor on the microscanning image and show good agreement with theoretical analysis.     

A diffusive light collection system for hard X-ray astronomical scintillation detectors

A novel design of a detector system for hard X-ray astronomy is described which permits large sensitive areas to be constructed on a modular basis. The system also incorporates high quality active shielding without the use of the phoswich system. The development and performance of the diffusive light collection optics are discussed.     

Compact infrared cryogenic wafer-level camera: design and experimental validation

We present a compact infrared cryogenic multichannel camera with a wide field of view equal to 120°. By merging the optics with the detector, the concept is compatible with both cryogenic constraints and wafer-level fabrication. The design strategy of such a camera is described, as well as its fabrication and integration process. Its characterization has been carried out in terms of the modulation transfer function and the noise equivalent temperature difference (NETD). The optical system is limited by the diffraction. By cooling the optics, we achieve a very low NETD equal to 15 mK compared with traditional infrared cameras. A postprocessing algorithm that aims at reconstructing a well-sampled image from the set of undersampled raw subimages produced by the camera is proposed and validated on experimental images.     

Quantitative characterization of the x-ray imaging capability of rotating modulation collimators with laser light

We developed a method for making quantitative characterizations of bi-grid rotating modulation collimators (RMC's) that are used in a Fourier transform x-ray imager. With appropriate choices of the collimator spacings, this technique can be implemented with a beam-expanded He-Ne laser to simulate the plane wave produced by a point source at infinity even though the RMC's are diffraction limited at the He-Ne wavelength of 632.8 nm. The expanded beam passes through the grid pairs at a small angle with respect to their axis of rotation, and the modulated transmission through the grids as the RMC's rotate is detected with a photomultiplier tube. In addition to providing a quantitative characterization of the RMC's, the method also produces a measured point response function and provides an end-to-end check of the imaging system. We applied our method to the RMC's on the high-energy imaging device (HEIDI) balloon payload in its preflight configuration. We computed the harmonic ratios of the modulation time profile from the laser measurements and compared them with theoretical calculations, including the diffraction effects on irregular grids. Our results indicate the 25-in. (64-cm) x-ray imaging optics on HEIDI are capable of achieving images near the theoretical limit and are not seriously compromised by imperfections in the grids.     

Design, assembly, and optical bench testing of a high-numerical-aperture miniature injection-molded objective for fiber-optic confocal reflectance microscopy

The design, analysis, assembly methods, and optical-bench test results for a miniature injection-molded plastic objective lens used in a fiber-optic confocal reflectance microscope are presented. The five-lens plastic objective was tested as a stand-alone optical system before its integration into a confocal microscope for in vivo imaging of cells and tissue. Changing the spacing and rotation of the individual optical elements can compensate for fabrication inaccuracies and improve performance. The system performance of the miniature objective lens is measured by use of an industry-accepted slanted-edge modulation transfer function (MTF) metric. An estimated Strehl ratio of 0.61 and a MTF value of 0.66 at the fiber-optic bundle Nyquist frequency have been obtained. The optical bench testing system is configured to permit interactive optical alignment during testing to optimize performance. These results are part of an effort to demonstrate the manufacturability of low-cost, high-performance biomedical optics for high-resolution in vivo imaging. Disposable endoscopic microscope objectives could help in vivo confocal microscopy technology mature to permit wide-scale clinical screening and detection of early cancers and precancerous lesions.     

High-spatial resolution mass spectrometric imaging of peptide and protein distributions on a surface

For the first time macromolecular ion microscope images have been recorded using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Single-shot, mass-resolved images of the spatial distributions of intact peptide and protein ions over an area of 200 microm in diameter were obtained in less than 1 ms at a repetition rate of 12 Hz. The magnifying ion optics of the ion microscope allowed ion images to be obtained with a lateral resolution of 4 microm. These results prove the concept of high-resolution MALDI-MS imaging in microscope mode without the need for a tight laser focus and the accompanying sensitivity losses. The ion microscopy approach offers an improvement of several orders of magnitude in speed of acquisition compared to the conventional (microprobe) approach to MALDI-MS imaging.     

Computer-generated optical multiwavelet filters for hybrid image-classification systems

Optical coherent Fourier correlators are applicable in real-time image analysis such as image classification. The functionality of Fourier correlators can be increased by use of multifunctional filters, which have many spatially multiplexed impulse responses. The concept of multiresolution analysis on the basis of wavelet theory offers profitable methods to design multifunctional filters for image analysis. The applicability of such filters is demonstrated by an example in which different characteristic textures of medical images are extracted. The physical implementation of multiwavelet filters is restricted by modulation-domain constraints imposed by the use of spatial-light-modulator or of diffractive-element fabrication technology. Coding methods of diffractive optics are shown to be helpful to transform the original complex-valued distributions of multiwavelet filters into light-efficient quantized phase-only distributions by preservation of the original filter functionality. The quality of the designed diffractive phase filters is documented by computer experiments.     

Chemical imaging with variable angles of incidence using a diamond attenuated total reflection accessory

A new development in Fourier transform infrared (FT-IR) imaging using a diamond attenuated total reflection (ATR) imaging accessory in a novel manner that allows the angle of incidence to be varied in order to obtain images from subsurface layers of different thickness is introduced. Chemical images of samples from the same area but with different depths of penetration are obtained by changing the angle of incidence as well as using different spectral bands at different wavenumbers. Changes in the angle of incidence with this accessory were made possible by taking advantage of the relatively large numerical aperture employed by the original imaging optics. This arrangement allowed us to introduce an additional movable aperture in the optical design to restrict the angle of incidence to certain values. Two samples have been studied, one for the calibration of the angle of incidence while the other demonstrates the capability of obtaining three-dimensional (3D) information using this approach. Advantages of this new approach include the relatively high spatial resolution (it can spatially resolve features as small as 12 mum without a microscope) and no change in the imaging area and sampling area during manipulation of the angle of incidence.     

Time-resolved step-scan infrared imaging system utilizing a linear array detector

A time-resolved infrared (IR) imaging system combined with a multichannel IR microscope, which utilizes a 16 channel linear array (LA) detector, and step-scan Fourier transform infrared (FT-IR) microscope was developed. The LA detector integrates a readout circuit on each detector element, so the detected signals can be read simultaneously. Thus, this system can perform high speed imaging using the step-scan method, similar to a single channel detector. To verify the capabilities of this system, a reflective sample was examined whose position was altered using a piezo actuator activated by an alternating voltage. In addition, the localization of relaxation dynamics for the liquid crystal (LC) molecules in an LC cell under oscillating electric field conditions was detected by this system.     

Figure tolerance of a Wolter type I mirror for a soft-x-ray microscope

The demand for an x-ray microscope has received much attention because of the desire to study living cells at a high resolution and in a hydrated environment. A Wolter type I mirror used for soft-x-ray microscope optics has many advantages. From the mirror fabrication point of view, it is necessary to perform tolerance analysis, particularly with respect to figure errors that considerably degrade the image quality. The figure tolerance of a Wolter type I mirror for a biological application in terms of the image quality and the state-of-the-art fabrication technology is discussed. The figure errors rapidly destroyed the image quality, and the required slope error depended on the detector used in the soft-x-ray microscope.     

Reciprocal-space analysis of compositional modulation in short-period superlattices using position-sensitive x-ray detection

Epitaxial growth of AlAs-InAs short-period superlattices on (0 0 1) InP can lead to heterostructures exhibiting strong, quasi-periodic, lateral modulation of the alloy composition; transverse satellites arise in reciprocal space as a signature of the compositional modulation. Using an x-ray diffractometer equipped with a position-sensitive x-ray detector, we demonstrate reciprocal-space mapping of these satellites as an efficient, non-destructive means for detecting and characterizing the occurrence of compositional modulation. Systematic variations in the compositional modulation due to the structural design and the growth conditions of the short-period superlattice are characterized by routine mapping of the lateral satellites.     

Shack-Hartmann sensor improvement using optical binning

We present a design improvement for a recently proposed type of Shack-Hartmann wavefront sensor that uses a cylindrical (lenticular) lenslet array. The improved sensor design uses optical binning and requires significantly fewer detector pixels than the corresponding conventional or cylindrical Shack-Hartmann sensor, and so detector readout noise causes less signal degradation. Additionally, detector readout time is significantly reduced, which reduces the latency for closed loop systems and data processing requirements. We provide simple analytical noise considerations and Monte Carlo simulations, we show that the optically binned Shack-Hartmann sensor can offer better performance than the conventional counterpart in most practical situations, and our design is particularly suited for use with astronomical adaptive optics systems.     

Joint digital-optical design of superresolution multiframe imaging systems

Typical electro-optic imaging systems produce image aliasing artifacts. Superresolution algorithms process multiple aliased images to yield a single high-resolution image. We design imaging systems by jointly optimizing the optics and postprocessing to maximize such multiframe imaging performance. We describe efficient software methods that can be used to perform joint design by use of commercially available lens design software.     

Phase Identification in a Scanning Electron Microscope Using Backscattered Electron Kikuchi Patterns

Backscattered electron Kikuchi patterns (BEKP) suitable for crystallographic phase analysis can be collected in the scanning electron microscope (SEM) with a newly developed charge coupled device (CCD) based detector. Crystallographic phase identification using BEKP in the SEM is unique in that it permits high magnification images and BEKPs to be collected from a bulk specimen. The combination of scanning electron microscope (SEM) imaging, BEKP, and energy dispersive x-ray spectrometry holds the promise of a powerful new tool for materials science.     

Consideration on the Condenser for an Imaging Type Schwarzschild Soft X-ray Microscope

Abstract

Proposed is an imaging type Schwarzschild soft X-ray microscope including a condenser optimized for better imaging properties on the basis of Hopkins's theory. The condenser using grazing incidence reflective optics is found most suitable for a Schwarzschild objective. The modulation transfer function (MTF) for the microscope is calculated and it is shown that the MTF is improved with the light intensity distribution on the condenser pupil.