High-sensitivity Q-band electron spin resonance imaging system with submicron resolution

A pulsed electron spin resonance (ESR) microimaging system operating at the Q-band frequency range is presented. The system includes a pulsed ESR spectrometer, gradient drivers, and a unique high-sensitivity imaging probe. The pulsed gradient drivers are capable of producing peak currents ranging from ～9 A for short 150 ns pulses up to more than 94 A for long 1400 ns gradient pulses. Under optimal conditions, the imaging probe provides spin sensitivity of ～1.6 × 10(8) spins∕√Hz or ～2.7 × 10(6) spins for 1 h of acquisition. This combination of high gradients and high spin sensitivity enables the acquisition of ESR images with a resolution down to ～440 nm for a high spin concentration solid sample (～10(8) spins∕μm(3)) and ～6.7 μm for a low spin concentration liquid sample (～6 × 10(5) spins/μm(3)). Potential applications of this system range from the imaging of point defects in crystals and semiconductors to measurements of oxygen concentration in biological samples.     

Wide band focusing x-ray spectrograph with spatial resolution

A new, wide spectral bandwidth x-ray spectrograph, the wide-bandwidth focusing spectrograph with spatial resolution (WB-FSSR), based on spherically bent mica crystals, is described. The wide bandwidth is achieved by combining three crystals to form a large aperture dispersive element. Since the WB-FSSR covers a wide spectral band, it is very convenient for application as a routine diagnostic tool in experiments in which the desired spectral coverage is different from one test to the next. The WB-FSSR has been tested in imploding wire-array experiments on a 1 MA pulsed power machine, and x-ray spectra were recorded in the 1-20 A spectral band using different orders of mica crystal reflection. Using a two mirror-symmetrically placed WB-FSSR configuration, it was also possible to distinguish between a real spectral shift and a shift of recorded spectral lines caused by the spatial distribution of the radiating plasma. A spectral resolution of about 2000 was demonstrated and a spatial resolution of approximately 100 microm was achieved in the spectral band of 5-10 A in second order of mica reflection. A simple method of numerical analysis of spectrograph capability is proposed.     

Characterization of one-dimensional position sensitive detectors with improved efficiency and position resolution for neutron spectrometers

Development and characterization of one-dimentional (1D) position sensitive detectors (PSDs) with improved efficiency and position resolution for neutron scattering applications are reported. The PSDs are characterized for energy resolution, count rate capability, sensitivity, efficiency, position resolution, and uniformity of response over the sensitive length. The studies are carried out to verify the dependence of position resolution on detector geometry, electronic noise, and stopping power of the fill gas. One of the PSDs is mounted on the small angle neutron scattering spectrometer and spectra from CTAB micelle sample are recorded using 5.4 A neutrons. A gain of factors 1.1 and 1.2 is obtained compared to earlier in house made 1D PSD and LND-made 1D PSD, respectively. The diffraction patterns from standard vanadium, nickel, and silicon samples are recorded on a powder diffractometer using newly designed PSDs. Gain in efficiency obtained at shorter wavelength of 0.783 A is by a factor of 1.6. All high pressure PSDs show improvement in the position resolution by 2-3 mm. It is observed that 1D PSD filled with isobutane as stopping gas improves the gamma tolerance and position resolution at lower partial pressures as compared to Kr. It is advantageous to use two or more 36C-type PSDs stacked together. It is economic and gives better efficiency due to scanning more beam height.     

Transient conductivity measurements with subnanosecond time resolution

The parameters governing the response time of a system to follow transient changes of conductivity caused by short pulses of radiation are discussed, and designs for coaxial conductivity cells with parallel-plate electrodes to obtain subnanosecond time resolution are described. The performance of the system is evaluated using ionization pulses of 30-ps width. This yields values in agreement with theory: 95 ps for the rise time and 80 ps for the fall time with virtually no signal distortion. Ways to decrease these times further are discussed.     

Laser NIR lifetime spectrometer with nanosecond time resolution

A laser lifetime spectrometer (fluorometer) for recording the luminescence kinetics in the range 950–1400 nm with a time resolution of 1 ns is described. The performance capabilities of the facility are demonstrated by an example of studying the near-IR luminescence of molecular singlet oxygen ¹O₂. The fluorometer allows measurements of quenched luminescence of ¹O₂ with a quantum yield of up to 6 × 10⁻⁹.     

Flat-response, subkiloelectronvolt x-ray detector with a subnanosecond time response

A detector that has a flat response to x rays with energies between 100 eV and 1.5 keV has been built. It has been used to measure x rays emitted from gold disks irradiated by the Argus laser at Lawrence Livermore Laboratory. Results from this detector are in good agreement with results from other techniques.     

Pressure jump relaxation setup with IR detection and millisecond time resolution

An instrument is described that allows the use of Fourier transform infrared (FTIR) spectroscopy as a detection system for kinetic processes after a pressure jump of up to 100 bars. The pressure is generated using a high performance liquid chromatography (HPLC) pump and water as a pressure transducing medium. A flexible membrane separates the liquid sample in the IR cell from the pressure transducing medium. Two electromagnetic switching valves in the setup enable pressure jumps with a decay time of 4 ms. The FTIR spectrometer is configured to measure time resolved spectra in the millisecond time regime using the rapid scan mode. All components are computer controlled. For a demonstration of the capability of the method first results on the kinetics of a phase transition between two lamellar phases of an aqueous phospholipid dispersion are presented. This combination of FTIR spectroscopy with the pressure jump relaxation technique can also be used for other systems which display cooperative transitions with concomitant volume changes.     

Compact terahertz time domain spectroscopy system with diffraction-limited spatial resolution

A compact and rigid terahertz time domain spectroscopy system is presented. The size of the device is 20 mm diameter times 61 mm length with four parabolic-shaped concave mirrors dug in it to effectively focus a terahertz beam on a sample. The device has no chromatic aberration over the whole bandwidth of the beam (0.3-2 THz), and an effective numerical aperture of about 0.45 is achieved, which has a capability to image the structure whose size is almost the same as the wavelength. Frequency resolved images clearly show this performance. We also show that quantitative retrieval of the complex refractive index of the structure as small as twice of the wavelength is possible.     

Measurement of the position and displacement of a light beam with a spiral scanner

A rotating spiral scanner interrupts an incident light beam for time intervals which are proportional to the position of the beam. This produces an electrical signal via a photodetector system which is independent of beam intensity. The device was used to measure the relative change in sarcomere spacing during the initial development of tension in a contracting frog sartorius muscle.     

Experimental facility for two- and three-dimensional ultrafast electron beam x-ray computed tomography

An experimental facility is described, which has been designed to perform ultrafast two-dimensional (2D) and three-dimensional (3D) electron beam computed tomographies. As a novelty, a specially designed transparent target enables tomography with no axial offset for 2D imaging and high axial resolution 3D imaging employing the cone-beam tomography principles. The imaging speed is 10 000 frames per second for planar scanning and more than 1000 frames per second for 3D imaging. The facility serves a broad spectrum of potential applications; primarily, the study of multiphase flows, but also in principle nondestructive testing or small animal imaging. In order to demonstrate the aptitude for these applications, static phantom experiments at a frame rate of 2000 frames per second were performed. Resulting spatial resolution was found to be 1.2 mm and better for a reduced temporal resolution.     

Quick-scanning x-ray absorption spectroscopy system with a servo-motor-driven channel-cut monochromator with a temporal resolution of 10 ms

We have developed a quick-scanning x-ray absorption fine structure (QXAFS) system and installed it at the recently constructed synchrotron radiation beamline BL33XU at the SPring-8. Rapid acquisition of high-quality QXAFS data was realized by combining a servo-motor-driven Si channel-cut monochromator with a tapered undulator. Two tandemly aligned monochromators with channel-cut Si(111) and Si(220) crystals covered energy ranges of 4.0-28.2 keV and 6.6-46.0 keV, respectively. The system allows the users to adjust instantly the energy ranges of scans, the starting angles of oscillations, and the frequencies. The channel-cut crystals are cooled with liquid nitrogen to enable them to withstand the high heat load from the undulator radiation. Deformation of the reflecting planes is reduced by clamping each crystal with two cooling blocks. Performance tests at the Cu K-edge demonstrated sufficiently high data quality for x-ray absorption near-edge structure and extended x-ray absorption fine-structure analyses with temporal resolutions of up to 10 and 25 ms, respectively.     

A phase-shift technique for high-speed e-beam testing with picosecond time resolution

Electron beam sampling of high speed digital devices requires a high time resolution. At the same time, long-range phase shifting is necessary because signals in these circuits may have very long period lengths. In this article, a new phase-shift method is described which allows sampling of low repetition rate signals without any degradation of the time resolution. This long range phase shift is realized by an additional set of blanking plates or blanking capacitor, which, acting as a gate, selects one of a large number of electron pulses produced by a first blanking capacitor. This technique also allows fast switching between different phase angles. The phase-shift method was evaluated experimentally using the picosecond e-beam tester which was developed here. The time resolution of this tester has been optimized recently to allow for stroboscopic testing with a 7 ps pulse width at 20 mV/√Hz noise voltage and 0.5 μm spot size. This allows for the measuring of rise times down to 14 ps with an error below 10%. Phase shifts of 100 ns were realized without any degradation of this time resolution. Propagation delays of 3.5 ps could be resolved. Signal rise times of 40 ps, corresponding to 0.04% of the total delay could be easily measured.     

Time-of-flight scintillation spectrometer of charged particles with a subnanosecond time resolution

A time-of-flight spectrometer based on a fast plastic scintillator was developed to study the spectral and angular distribution of charged particles emitted from laser-produced plasmas. The measured time resolution of the spectrometer was ～0.3 ns, which made it possible to observe the fine structure in the spectrum of protons originated from the back surface of the target in experiments on the SOKOL-P laser facility.     

Wavefield characterization of nearly diffraction-limited focused hard x-ray beam with size less than 10 nm

In situ wavefront compensation is a promising method to realize a focus size of only a few nanometers for x-ray beams. However, precise compensation requires evaluation of the wavefront with an accuracy much shorter than the wavelength. Here, we characterized a one-dimensionally focused beam with a width of 7 nm at 20 keV using a multilayer mirror. We demonstrate that the wavefront can be determined precisely from multiple intensity profiles measured around the beamwaist. We compare the phase profiles recovered from intensity profiles measured under the same mirror condition but with three different aperture sizes and find that the accuracy of phase retrieval is as small as λ∕12.     

高分辨X-RAY成像系统的搭建及其血管造影研究

本实验目的在于初步探讨血管造影技术在评定动物血管疾病模型中的应用与研究。方法是搭建X-RAY血管造影系统,测定体模,验证X射线焦斑分辨率。建立大鼠后肢缺血模型,利用搭建好X-RAY的血管造影系统检验动物模型。体模测定结果显示,该系统可以观察到10μm的线对板条纹,动物在体造影检查,可清楚地观察到血管的结构,发现缺血模型的血管阻塞部位,以及阻塞部位上游血管的侧支循环的建立。利用高分辨X-RAY,可以进行小动物的血管造影检查,该系统在小动物的血管研究中将发挥重要作用。     

高分辨X—RAY成像系统的搭建及其血管造影研究

本实验目的在于初步探讨血管造影技术在评定动物血管疾病模型中的应用与研究。方法是搭建X—RAY血管造影系统,测定体模,验证X射线焦斑分辨率。建立大鼠后肢缺血模型,利用搭建好X—RAY的血管造影系统检验动物模型。体模测定结果显示,该系统可以观察到10μm的线对板条纹,动物在体造影检查,可清楚地观察到血管的结构,发现缺血模型的血管阻塞部位,以及阻塞部位上游血管的侧支循环的建立。利用高分辨X—RAY,可以进行小动物的血管造影检查,该系统在小动物的血管研究中将发挥重要作用。     

A method for measuring spectral and time characteristics of mixed pulsed gamma-neutron fields with scintillation and Cherenkov detectors with nanosecond time resolution

A method for measuring spectral and time characteristics of pulsed mixed (n, γ) fields is described. The essence of this method is that a sequence of signals from individual (n, γ) particles registered by (n, γ) detectors is written in a computer with the subsequent amplitude-time analysis of the signal parameters. Fast scintillation and Cherenkov detectors with FWHM of pulses of ～1.5 and 2.5 ns, respectively, are used as (n, γ) detectors. A TDS-3054 broadband digital oscilloscope records signals and transmits them to the computer through a GPIB-USB interface. The equipment used ensures efficient detection of (n, γ) particles at detector counting rates of up to ～2 × 10⁸ pulses/s. The efficiency of this method has been tested in measurements of characteristics of (n, γ) radiation fields from an ИНГ-031 pulsed neutron generator and from a copper target irradiated with a beam of carbon nuclei with an energy of 200 MeV/amu from the TVN-ITEF acceleration-storage complex.     

Simple positioner with nanometer reproducibility of the focused light beam position on an object

A simple positioner, which allows one to ensure the position of a focused light beam on an object with nanometer precision and reproducibility, is proposed and studied. It can be used for positioning of focused beams (in particular, laser beams) on surfaces of optical fibers, biological objects, optical disks, thin film modulators, and holographic memory systems in the micrometer and nanometer ranges.     

Axial resolution of confocal Raman microscopes: Gaussian beam theory and practice

A straightforward and transparent model, based on Gaussian beam optics, for the axial r ₀ resolution of a confocal microscope is presented. A confocal Raman microscope was used to determine the axial confocality in practice. The axial response of a thin planar object was measured for three different objectives, two pinhole sizes and a slit. The results show that, in the case of a confocal configuration, the response calculated with the model provides a good prediction of the axial resolution of the confocal microscope.     

KMC-1: a high resolution and high flux soft x-ray beamline at BESSY

The crystal monochromator beamline KMC-1 at a BESSY II bending magnet covers the energy range from soft (1.7 keV) to hard x-rays (12 keV) employing the (n,-n) double crystal arrangement with constant beam offset. The monochromator is equipped with three sets of crystals, InSb, Si (111), and Si (422) which are exchangeable in situ within a few minutes. Beamline and monochromator have been optimized for high flux and high resolution. This could be achieved by (1) a windowless setup under ultrahigh-vacuum conditions up to the experiment, (2) by the use of only three optical elements to minimize reflection losses, (3) by collecting an unusually large horizontal radiation fan (6 mrad) with the toroidal premirror, and (4) the optimization of the crystal optics to the soft x-ray range necessitating quasibackscattering crystal geometry (theta(Bragg,max)=82 degrees) delivering crystal limited resolution. The multipurpose beamline is in use for a variety of user facilities such as extended x-ray absorption fine structure, ((Bio-)EXAFS) near-edge x-ray absorption fine structure (NEXAFS), absorption and fluorescence spectroscopy. Due to the windowless UHV setup the k edges of the technologically and biologically important elements such as Si, P, and S are accessible. In addition to these experiments this beamline is now extensively used for photoelectron spectroscopy at high kinetic energies. Photon flux in the 10(11)-10(12) photons/s range and beamline resolving powers of more than E/DeltaE approximately 100.000 have been measured at selected energies employing Si (nnn) high order radiation in quasibackscattering geometry, thus photoelectron spectroscopy with a total instrumental resolution of about 150 meV is possible. This article describes the design features of the beamline and reports some experimental results in the above mentioned fields.