A new idea of electronic framing camera is proposed aiming at exposure time less than 100ps and framing rate more than 109 frames/s. The great advantage is that the dynamic operation of the camera is very simplified by using newly devised framing image tube, that is, the only dynamic operation in this camera is to apply a ramp voltage to a pair of deflection plates, resulting in extreme high speed response.
A high-speed 16-mm cineradiographic system previously developed at the University of Michigan Transportation Research Institute for use in biomechanics research has been undergoing a continuous upgrading in capability. In addition to changes in the structural aspect of the cineradiography, improvements have been made in the procedures used to obtain better image quality as well as methods for interpretation of the digitized results. The current improvements in the system include: 1) filtering the X-ray source before penetration of the subject to increase image contrast as well as to protect the image tube; 2) pre-processing of the film to increase its effective speed; 3) development of a neutral density radio-contrast media for outlining anatomical structure without using the vascular system; and 4) development of procedures for obtaining analytical information about motion of non-rigid anatomical structures from digitized film. This system now consists of either a 35-mm Photosonics 4B, a 16-mm Photosonics 1B, or a 16-mm Milliken which views a 50-mm (2-inch) diameter output of a P-11 phosphor of a high gain, four-stage magnetically focused image intensifier tube, gated on and off synchronously with the motion picture camera shutter. A lens optically couples the input photocathode of the image tube to an X-ray fluorescent (rare earth) screen image produced by a smoothed DC X-ray generator of a conventional type. The system is capable of looking at a large spectrum of anatomical structures under a wide range of dynamic loading conditions.
A portable system that utilizes solid state electronic timing circuits and a pulsed semiconductor laser for characterizing the optical gate sequence of high-speed image shutters, including microchannel-plate intensifier tubes (MCPTs), and silicon-intensified target vidicons (SITVs), is described and compared to earlier methods of characterization. Gate sequences obtained using the system and streak camera data of the semiconductor laser pulse are presented, with a brief discussion of the electronic delay timing and avalanche circuits used in the system.
The application of high speed moire' photography to the measurement of the dynamic strains of the points in a surface is presented. This method has been used to measure the dynamic strain distribution along the axis of different bars, and the process of stress concentration of an aluminium bar with two circular holes at the high rates of the loading.
A mechanical-electrical film digitizing apparatus was developed to enable highly accurate film analysis at low cost. The design incorporated the use of X and Y axis cursors, overlaid on a rear projection screen material, with cursor positioning controlled by reversable motors through a handheld controller. Three separate schemes were investigated to provide a digitizing accuracy of 10,000 by 10,000 points on a 1 meter by 1 meter screen. Additionally, an option was incorporated to provide a 1000 by 1000 point field, with an off-set capability of up to 9000 data points, for use in digitization of film where an initial point of reference moves out of the camera field of view. Features to enable display, storage, and computer manipulation of data were incorporated, using digital circuits available at the retail level. Total system cost fOr the digitizer was less than 800 dollars.
We have designed, built and tested a fast framing camera that works in the visible and short infrared region of the spectrum, from 300 nm to 850 nm. The camera has four separate channels. Each framing channel has its own individual trigger input and individually adjustable framing gate width. Each channel is spatially separate from the other channels as well, thus allowing for complete independence among the four channels. The output from the four channels in the camera is recorded on one piece of 4" by 5" sheet of film. Each channel has a circular recording format with a useful diameter of 18 mm. The channels are positioned on the corners of a square with a center to center spacing of 4.45 cm (1.75"). The camera utilizes commercially available gated intensified microchannel-plate tubes. The camera contains its own power supply and gating circuits. It required four gating inputs (12 volts). The electronics occupy a volume of 27 cm X 33 cm X 14 cm. The framing part occupies a volume of 21 cm X 25 cm X 5 cm. Characteristics of the camera, such as: framing times, spatial modulation transfer functions, gate delay, and uniformity were studied utilizing a 35 picosecond long blue light pulse, generated by a nitrogen-pumped dye-laser system. A pulsed semiconductor laser at 820 nm was used as well for the setup.
Design Considerations For A High Speed CMOS Micro-Computer Controlled Data Recording System For Intermittent Movement Instrumentation Cameras. This New Technology Has Created Design Possibilities Never Before Possible. Other Logic Families Such As IIL And Conventional Micro-Computers Do Not Allow Operating From A Single Internal Battery For Extended Periods Without Recharging.
A comparison of gated optical shuttering responses for commercially available micro-channel plate image intensifier tubes (MCPTs) with the performance of a new design for improved optical shuttering is presented. Measurements of opacity, photocathode quantum efficiency, and shutter pulse propagation characteristics are discussed.
A laser interferometer technique is being applied to the characterization of boundary-layer conditions on models in supersonic and hypersonic wind tunnels in the von Kaman Facility at Arnold Engineering Development Center (AEDC). The Boundary-Layer Transition Detector (BLTD), based on lateral interferometry, is applicable for determining the turbulence frequency spectrum of boundary layers in compressible flow. The turbulence, in terms of air density fluctuations, is detected by monitoring interferometric fringe phase shifts (in real time) formed by one beam which passes through the boundary layer and a reference beam which is outside the boundary layer. This technique is nonintrusive to the flow field unlike other commonly used methods such as pitot tube probing and hot-wire anemometry. Model boundary-layer data are presented at Mach 8 and compared with data recorded using other methods during boundary-layer transition from laminar to turbulent flow. Spectra from the BLTD reveal the presence of a high-frequency peak during transition, which is characteristic of spectra obtained with hot wires. The BLTD is described along with operational requirements and limitations.
A high sensitivity differential interferometer has been developed to locate the region where the boundary layer flow changes from laminar to turbulent. Two experimental configurations have been used to evaluate the performance of the interferometer, open shear layer configuration and wind tunnel turbulent spot configuration. In each experiment small temperature fluctuations were introduced as the signal source. Simultaneous cold wire measurements have been compared with the interferometer data. The comparison shows that the interferometer is sensitive to very weak phase variations in the order of 10-3 the laser wavelength.
The microphysics of clouds have been studied for many years using airborne particle measuring instruments. The calibration of these instruments has presented a major measurement uncertainty because of the complexity of the probes and the lack of an absolute calibration technique. The use of holographic imaging is being explored as a means of establishing the absolute size and concentration of cloud particles. Preliminary studies which use holography for determining size calibrations for these instruments are discussed.
Practical aspects of using laser holographic interferometry in some NASA Ames wind tunnels are presented. These aspects include the development of techniques for dual-plate interferometry, optics alignment, and laser alignment. In addition, methods to alleviate problems associated with vibration, photographic processing, photographic drying, and photographic reconstruction are discussed.
A write/readout system is described for double pulsed holograms. The write subsystem utilizes rapidly addressable, angularly resolved reference beams. The readout subsystem is based on heterodyne interferometry. Several readout configurations are discussed, each with advantages for various holograms. Finally,a system is discussed to provide rapid writing and readout of wavefronts stored on the hologram.
A versatile system for collecting and analyzing multispectral images is described. This innovative system uses state-of-the-art video and microprocessor technology to collect and digitize image data in real time; an IBM-PC compatible unit is used as the host computer. The solid-state video camera is designed to automatically collect sequential multispectral images, at the rate of 60 images per second, in six user-defined spectral bands. Data can be recorded and displayed using standard video equipment. The system is small, rugged, light-weight, and suitable for collecting field data for diagnostic or surveillance purposes, from ground level or from aircraft. An automatic, focal plane, shuttering system permits collection of blur-free images of rapidly changing scenes. The microprocessor-based digitizer has programmable resolution and digitizes complete spectral sequences in real time. Software is provided for collection and display of images and to facilitate histogram, ratio, and spectral time series analysis. Other software tools are provided for various image processing tasks including the construction of color composite spectral images. The elements of this system and their performance are described in this paper, and issues of resolution and calibration are discussed.
This paper describes the techniques and concepts used in the development and construction of a gated, intensified, solid state video camera. This state-of-the-art camera provides submicrosecond image capture with excellent resolution and minimal blooming. The paper addresses the technical and practical considerations which drove the camera design and which affect the value of this instrument for both observation and measurement applications. The sensor is based on a gated, custom-designed, microchannel plate intensification of a C.I.D. (Charge Injection Device), self-scanning imaging array. The sensor operates in the visible and near-infrared (IR) spectrum, and is capable of full bandwidth image capture at sub-microsecond speeds. It can be operated in a truly asynchronous random event mode, while maintaining a standard NTSC output format. The camera is described in terms of its architecture, physical structure, application, performance and design characteristics.
The General Electric Charge Injection Device (CID) can be configured to obtain X and Y profiles, an image profile defined as the summation of photocharge along a column (X) or row (Y) in the array. X and Y profiles are directly obtainable from a CID imager as the profile read operation takes advantage of unique non-destructive readout capability of the CID sensor. Profiles contain information which can be used to determine centroid, area, or other image features and represent a considerable reduction of data (i.e., a 512 x 512 array contains 262,144 pixels but only 512 X and 512 Y profile data points). Both profiles can be acquired in less than one (1) millisecond from a 512 x 512 array compared to conventional readout times of 30 milliseconds. This capability facilitates high speed videography, measurement and inspection applications.
A recently developed prototype streak tube designed to produce high gain and resolution by incorporating the streak and readout functions in one envelope thereby minimizing photon-to-charge transformations and eliminating external coupling losses is presented. The tube is based upon a grid-gated Silicon-Intensified-Target Vidicon (SITV) with integral Focus Projection Scan (FPS) TV readout. Demagnifying electron optics (m=0.63) in the image section map the 40-mm-diameter photocathode image unto a 25-mm-diameter silicon target where gains ≥ 103 are achieved with only 10 KV accelerating voltage. This is compared with much lower gains (~ 50) at much higher voltages (~ 30 KV) reported for streak tubes using phosphor screens. Because SIT technology is well established means for electron imaging in vacuum, such fundamental problems as "backside thinning" required for electron imaging unto CCDs do not exist. The high spatial resolution (~ 30 1p/mm), variable scan formats, and high speed electrostatic deflection (250 mm2 areas are routinely rastered with 256 scan lines in 1.6 ms) available from FPS readout add versatility not available in CCD devices. Theoretical gain and spatial resolution for this design (developed jointly by Los Alamos National Laboratory and General Electric Co.) are compared with similar calculations and measured data obtained for RCA 73435 streaks fiber optically coupled to (1) 25-mm-diameter SIT FPS vidicons and (2) 40-mm-diameter MCPTs (proximity-focused microchannel plate image intensifier tubes) fiber optically coupled to 18-mm-diameter Sb2S3 FPS vidicons. Sweep sensitivity, shutter ratio, and record lengths for nanosecond duration (20 to 200 ns) streak applications are discussed.
Recent studies show that effective shuttering of photoemissive tubes, such as Silicon-Intensified-Target Vidicons (SITVs) and Microchannel-plate Image Intensifier Tubes (MCPTs), can vary widely depending upon the extent of their opacity to an input flux of photons. Optical feedthrough signals from photon transmission through the photocathode to the target or phosphor ranging from 10-4 to 10-9 (when compared with gated signals) were measured for a large sampling of commerically available units. Effective shutter ratios of 105 to 108 measured for units operated in quiescently dark environments can be substantially reduced by optical feedthrough. Furthermore, ineffective suppression of photoemission can cause further reductions in shutter ratio. Reductions are roughly correlated with the ratio of optical gate duration to light pulse duration. Experimentation with various thicknesses of aluminum depositions on MCPT phosphors and chromium layering on SITV silicon targets indicate substantial reductions (2x to 15x) in transmission with minimal increases in threshold voltages required for gain. These results, together with exploratory studies of external coating of output fiber optics with transmission filters spectrally matched to minimize feedthrough to P-20 phosphors are reported.
A summary paper proposing standardization of definitions and parameter measurements related to photonic streak cameras was generated at the 16th International Congress of High Speed Photography and Photonics at Strasborg, France (August 1984). An international committee appointed by the general Workshop on Picosecond Streak Cameras met and discussed the areas appropriate for standardization and proposed specific definitions, measurements and complementary parameter sets to be used in characterizing photonic streak cameras. These proposals were compiled into a summary paper by the committee co-chairmen, Noel Fleurot (CEA-Limeil) and Gary L. Stradling (Los Alamos National Laboratory), with the intent that it be distributed to interested streak camera users and manufacturers and that appropriate improvements and additions be solicited.
The success of laser fusion research depends upon the efficient, uniform implosion of a spherical target filled with DT fuel. In experimental investigations of these implosions, diagnostics are required which will verify the symmetry of the implosion, and measure accurately the trajectories of the shell components. This data can then be compared to the predictions of one- and two-dimensional hydrocodes to assess the performance of specific target designs. Determining the progress of specific thin shells (< 1 μm) or media-interfaces in the high velocity (> 107 cm sec-1) implosion of a laser fusion target typically of initial diameter - 500 μm, places stringent demands on time-resolving x-ray imaging instrumentation. For direct drive laser fusion studies at LLE, we have developed a time-resolved x-ray imaging system having high time (< 20 ps) and space (> 10 μm) resolving capabilities. This streak pinhole camera system has been used to study the trajectory of the coronal ablative plasma surrounding the imploding target. With the aid of a secondary source of x-ray emission provided by laser irradiation of a separate target, time-resolved x-ray streak radiography of the inward motion of cold material interfaces can be diagnosed. In order to make accurate comparisons with the predictions of one- and two-dimensional hydrocode calculations, it is important to have absolute temporal registration of the x-ray emission to the incident laser light. We will describe approaches being followed to address these requirements and illustrate with experimental data the current technical capabilities of our time-resolved x-ray photographic system.
Recent advances in the development of high resolution time-resolving x-ray spectroscopic instrumentation have considerably improved the capabilities of diagnosing details of electron and radiation transport, implosion dynamics and final compressed core conditions of laser fusion targets. In addition, the current interest in x-ray laser schemes utilizing laser-produced plasmas places even more stringent demands on time- and space-resolved x-ray and XUV diagnostics. In this paper we will summarize some of the recent technical developments made at LLE to meet these needs, and give illustrations of the capabilities of new x-ray spectroscopic instrumentation activated on recent laser fusion and x-ray laser experiments. Technical details, performance criteria and typical experimental results will be presented on several time resolving spectrographic systems. A soft x-ray, transmission grating, streak spectrograph (resolution ~ 1.5 Å) time-resolves spectra in the 3-200 Å range. A streak elliptical crystal spectrograph permits the resolution of x-rays in a number of spectral regions in the 2-100 Å range. We will also present details of (a) a streak planar crystal spectrograph having high spectral resolution and sensitivity, and (b) a novel, high resolving power (λ/Δλ ~ 103) streak spectrograph incorporating a unique crystal geometry permitting high dispersion, and having good collection efficiency. The impact these developments will have on current investigations of high temperature, dense plasmas in laser fusion and x-ray laser research will be discussed.
We present details of an absolutely calibrated twin channel x-ray spectrometer employing elliptically curved x-ray analyzer crystals. The spectrometer utilizes high-energy cut-off grazing incidence mirrors, low-energy cut-off K-edge filters and a stable of analyzer crystals including naturally occurring crystals and molecular multilayers, allowing coverage of the spectral region from 100 to 10,000 eV with a resolution of - 3 eV. One channel of the spectrometer is recorded on photographic film; the second is coupled to an x-ray streak camera of novel design which incorporates a large aperture (40 mm) photo-cathode and has a time resolution of less than 10 ps. All of the components of the spectrometer have been absolutely calibrated using a monochromatic D.C. x-ray source and proportional counter system. By cross-calibrating the time-resolving channel with the time integrating channel we obtain absolutely calibrated time-resolved spectra. This instrument has been used extensively to diagnose laser-produced plasmas at the University of Rochester's Laboratory for Laser Energetics. In this paper we will present some typical time-resolved spectra to illustrate the capabilities of the spectrometer, its sensitivity and wide application. In addition, we discuss the performance characteristics of the x-ray streak camera design.
Approx. 360fs (femtosecond) of limiting temporal resolution has been obtained with a femtosecond streak camera incorporating a femtosecond streak tube. At the same time, the dynamic range defined by 20% broadening sequence has been observed to be 2.4 at the limiting temporal resolution. In this experiment, a CPM (Colliding-Pulse Mode-locked) ring dye laser which can generate shorter than 100fs pulses at repetition rate of 100MHz has been used. In this paper, performance of the femtosecond streak camera will be discussed in detail.
A. large photocathode streak tube has been developed. The useful photocathode length is 25 mm and the useful output screen size is 32.5 mm(spatial direction) x 40 mm(temporal direction). The tube has time resolution of about 8 ps and good deflection sensitivity of 60 mm/KV. As for dynamic spatial resolution, amplitude response better than 12% at 20 1p/mm referred to the photocathode has been obtained to input square-wave test pattern over the area of 80% of useful output screen at light wavelength of 800 nm. Also the geometric distortion less than 1% and the shading of output signal less than 15% have been obtained.
An infrared sensitive synchroscan streak camera for use in the wavelength region of 1.0 to 1.6 μm is described, including system configuration, absolute photocathode sensitivity, system dynamic range, and its application. Linear (y=1) dynamic ranges of more than 103 at 1.3 and 1.5 μm wavelength have been demonstrated to confirm a single photon reaction in the photocathode at the practical power density level, using ultrashort light pulses from laser diodes. Applications of the system for direct and linear measurement such as picosecond time-resolved spectroscopy of diode laser pulses at 1.3 and 1.5 μm wavelength are also discussed. The system works in single-shot mode as well as synchroscan, by changing a plug-in. This new technique can be widely utilized for direct, linear, real-time and multichannel measurement of ultrafast optical phenomena in the wavelength range of 1.0 to 1.6 μm.
A new streak camera readout system has been developed at Lawrence Livermore National Laboratory. Streak cameras are used on the Nova laser at Livermore to monitor laser beam performance and measure experimental phenomena during target irradiation experiments. In this new system, the streak camera's optical output image is lens coupled to a thermoelectrically cooled CCD camera where the streaked image is captured. The captured image is then digitized to 14 bits and transferred to Q-bus video image buffers via a DMA (direct memory access) transfer. The captured image can then be analyzed and manipulated while resident in the image buffers or saved on disk for future reference. Basic image analysis software has been written that include background subtraction, both horizontal and vertical lineouts with and without pixel averaging, pseudo coloring, and image histograms. This new system has improved dynamic range, spatial resolution, and lower noise than any of our previous readout systems. All major system components are available commercially providing a lower cost for multiple systems and simplifying future maintenance.
Recently, streak cameras reached considerable resolution and stability to warrant their application to a highly demanding experiment in basic physics. This is the direct laboratory test of the isotropy of light propagation. This application takes advantage of another recent development, namely, the femtosecond pulse generation by colliding beam ring lasers.
A new short pulse x-ray calibration facility has been brought on line at Los Alamos. This facility is being used for the development, testing and calibration of fast x-ray diagnostic systems. The x-ray source consists of a moderate size, sub-nanosecond laser focused at high intensity on an appropriate target material to generate short pulses of x-ray emission from the resulting plasma. Dynamic performance parameters of fast x-ray diagnostic instruments, such as x-ray streak cameras, can be conveniently measured using this facility.
The performance of a streak camera recording system is strongly linked to the technique used to amplify, detect and quantify the streaked image. At the Lawrence Livermore National Laboratory (LLNL) streak camera images have been recorded both on film and by fiber-optically coupling to charge-coupled devices (CCD's). During the development of a new process for recording these images (lens coupling the image onto a cooled CCD) the definitions of important performance characteristics such as resolution and dynamic range were re-examined. As a result of this development, these performance characteristics are now presented to the streak camera user in a more useful format than in the past. This paper describes how these techniques are used within the Laser Fusion Program at LLNL. The system resolution is presented as a modulation transfer function, including the seldom reported effects that flare and light scattering have at low spatial frequencies. Data are presented such that a user can adjust image intensifier gain and pixel averaging to optimize the useful dynamic range in any particular application.
The performance response of an electronic subnanosecond streak camera to a spatially distributed optical signal varies significantly with the image location on output screen. The variations are due mainly to the combined effects of: (i) electron-optics aberrations, (ii) camera sweep ramps and gating waveform imperfections, (iii) photocathode and phosphor quantum efficiency nonuniformities, and (iv) excessive incident intensity or power. Consequently, a dynamic full-scale characterization of the streak camera is necessary for achieving a better measurement accuracy, relative or absolute. To meet this need, we are developing a simple yet versatile technique for characterizing the large-format image-converter-tube based streak cameras that are routinely used as the prime diagnostic instruments at the nuclear test site in Nevada. A mode-locked pulsed dye laser routing through beam splitters and mirrors provides the repetitive light source of multiple pulses with known intensities and inter-pulse timing for illumination along the streak sweep axis. Meanwhile, a bar-chart test pattern at the input slit intercepting an expanded form of the light source, or a bundle of equal-length fibers fanning out into a linear line array replacing the slit, distributes the illumination along the axis perpendicular to the sweep. In one single shot, this technique enables an accurate and detailed mapping of the key performance parameters of a large-format streak camera. The obtainable parameters include quantitative temporal and spatial resolutions, descriptive dynamic range, two-dimensional sweep nonlinearity, and intensity or power dependent distortions. Experimental setup is described. Sample test data, digitization plots, and computer analysis results are presented.