Image Converter Streak Camera Research Articles

Compressed ultrafast tomographic imaging by passive spatiotemporal projections.

Existing streak-camera-based two-dimensional (2D) ultrafast imaging techniques are limited by long acquisition time, the trade-off between spatial and temporal resolutions, and a reduced field of view. They also require additional components, customization, or active illumination. Here we develop compressed ultrafast tomographic imaging (CUTI), which passively records 2D transient events with a standard streak camera. By grafting the concept of computed tomography to the spatiotemporal domain, the operations of temporal shearing and spatiotemporal integration in a streak camera's data acquisition can be equivalently expressed as the spatiotemporal projection of an (x,y,t) datacube from a certain angle. Aided by a new, to the best of our knowledge, compressed-sensing reconstruction algorithm, the 2D transient event can be accurately recovered in a few measurements. CUTI is exhibited as a new imaging mode universally adaptable to most streak cameras. Implemented in an image-converter streak camera, CUTI captures the sequential arrival of two spatially modulated ultrashort ultraviolet laser pulses at 0.5 trillion frames per second. Applied to a rotating-mirror streak camera, CUTI records an amination of fast-bouncing balls at 5,000 frames per second.

Miniature image converter streak cameras for measurement of temporal characteristics of optical pulses in nanoand picosecond ranges

Miniature image converter streak cameras for measurement of temporal characteristics of optical pulses in nanoand picosecond ranges

An Apparatus for Measuring the Characteristics of the High-Speed Image Converter Cameras Operating in the Range of Soft X-Rays and Vacuum UV

A pumped vacuum apparatus is described that contains an electron gun with an adjustable high-voltage voltage source, interchangeable metal targets, and flanges to which the object under study is connected. The apparatus is especially designed to measure the spatial and temporal characteristics of high-speed image converter streak cameras that operate in the soft X-ray range. It can be used for research and measurements in the design of soft X-ray photodetectors and their main parts, for example, microprobe detectors, imaging devices, solid-state linear and matrix photodetectors, photoemitters operating in vacuum, etc.

Jitter measurement technique for image converter streak cameras

The phenomenon of jitter is considered for image converter streak cameras used in fast process research. Jitter measurement technique is proposed for image converter streak cameras working in linear sweep mode of the pulsed optical signal in study. The experimental setup implementing this measurement technique is described. This setup is used in VNIIOFI for jitter checking of manufactured image converter streak cameras for compliance with specification or customer requirements.

Application of Vacuum Photoelectric Detection Technology in Super-Resolution System

Due to the wave characteristics of light, diffraction occurs when the light passes through the optical system, so that the resolution of the ordinary far-field optical system is limited by the size of the Airy disk diameter. There are various factors that cause image quality degradation during system detection and imaging, such as optical system aberrations, atmospheric inter-ference, defocusing, system noise and so on. Super-resolution optical imaging technology is the most innovative breakthrough in the optical imaging and detection field in this century. It goes beyond the resolution limit of ordinary optical systems or detectors, and can get more details and information of the structure, providing unprecedented tools for various fields. Compared with ordinary optical systems, super-resolution systems have very high requirements on the signals to be detected, which cannot be met by ordinary detection techniques. Vacuum photoelectric detection and imaging technology is equipped with the characteristics of high sensitivity and fast response. It is widely used in super-resolution systems and has played a great role in super-resolution systems. In this paper, the principles and structure of the image-converter streak camera super-resolution system, scanning electron microscopy super-resolution system and laser scanning confocal super-resolution system will be sorted out separately, and the essential role of the vacuum photoelectric detection technology in the ultra-microscopic sys-tem will be analyzed.

Analysis of short optical signals by the Gabor transformation

An expression is obtained for the reconstruction of a complex optical signal from the modulus of the Gabor transform of the signal spectrum. It is shown that the temporal resolution of systems with an image-converter streak camera can be improved by spectral expansion of the signal and by mathematical processing of the results obtained.

Time characteristics of a traveling-wave laser subjected to two-photon picosecond optical pumping

An image-converter streak camera with picosecond time resolution was used in a study of the kinetics of formation of pulses in a traveling-wave laser in which molecular dye solutions were subjected to two-photon optical pumping. An analytic expression was obtained for the lasing threshold of a nonresonator traveling-wave laser in the case of pulsed (τp τe) and quasicontinuous (τp > τe) pumping. Satisfactory agreement was obtained between the calculated and experimental lasing threshold. The kinetics of the compression of output pulses, determined as a function of the pump radiation intensity, was described by rate equations. At pumping rates up to 10 times the threshold a qualitative agreement between the experimental and calculated results was obtained employing a two-band energy model of the dye with a short (compared with the duration of the pump pulses τp) vibrational relaxation time τe. At rates of excitation well above the threshold the kinetics of compression and delay changed, and the output pulses were split into two components, which was interpreted (in the specific case of rhodamine 6G) using a four-band energy scheme. A practical conclusion of this investigation was in the form of recommendations on the use of the proposed approach as a simple method for generating high-intensity single picosecond superradiance pulses of duration τsr with frequency up-con version and a compression coefficient τp/τsr ~ 10.

Use of an optical multichannel analyzer for recording absorption spectra of short-lived transients

Characteristics of an adapted commercial optical multichannel analyzer system for recording of transient absorption spectra in single-shot pulse radiolysis and flash photolysis are described. The features discussed include temporal (2 μs) and spectral (1 nm) resolution, signal-to-noise ratio and its improvement, linearity of response, and wavelength coverage (300–650 nm). The system is intermediate in both cost and capabilities compared to two other methods: (1) recording transient spectra by repetitive pulsing and (2) using an image converter streak camera. This system is convenient for discrimination of small differences in fine structured absorption of spectra short-lived species.

Measurement of the frequency shift of a picosecond pulse from a mode-locked injection laser

The frequency shift (chirp) of a picosecond pulse emitted by an actively mode-locked cw injection laser with an external dispersive resonator was observed and measured. The chirp was ?? = 0.5?1012sec?1(?? = 0.2nm at the 880 nm wavelength) for a 30 psec pulse and the frequency decreased during a pulse (down chirp). The measurements were made using dynamic spectrograms obtained using an image-converter streak camera operated in the linear horizontal scanning mode. Frequency sweeping within the pulse is attributed to the influence of changes in the injected carrier density on the refractive index of the active region and on the optical length of the laser resonator.

A study of the erosion rate of vacuum arcs in a transverse magnetic field

The cathode mass loss due to the action of low-current vacuum arcs under the influence of a high transverse magnetic field has been measured for titanium, stainless steel and graphite. The effects of magnetic field, arc current and cathode temperature on the erosion rate are investigated. The measured erosion rate decreases marginally with the magnetic field, the total variation being less than 20% and the rate of decrease is much lower at higher fields. Within the experimental accuracy only very small or no increase of erosion rate is observed with the arc current for currents up to 70 A. For measurements made at higher cathode temperatures (upto 500°C) there is a considerable increase in erosion rate for the stainless steel cathode and the results are discussed for titanium and graphite. The importance of clean cathode surfaces in the erosion studies is demonstrated by observing the cathode spot motion using an Image Converter Streak Camera. This method has proved to be an effective diagnostic tool in judging the surface condition before any measurements are made. Prolonged glow discharge cleaning in hydrogen is found to provide an acceptably clean surface. The earlier reported cathode spot velocity measurements are extended to higher magnetic fields.

Investigation of the temporal and amplitude characteristics of the stimulated Raman scattering Stokes components in fiber-optic waveguides using a high-speed camera

A study was made of the temporal structure and of the amplitude characteristics of pulses of stimulated- Raman-scattering (STRS) Stokes and anti-Stokes components appearing in fiber-optic waveguides with quartz and liquid light-transmitting cores and propagating in the forward and backward directions relative to the pump wave. An analysis was made of the influence of the mode structure, dispersion, and losses in the waveguide on the intensity distributions in the STRS components, and also on the duration of the light pulses in the waveguide. It was found that, by using an image-converter streak camera with a time resolution of 2 psec to investigate the STRS process in a fiber-optic waveguide, one could directly observe the dispersion curves of the light-transmitting core and the temporal structure of an STRS pulse during a single laser excitation pulse.

Gaseous breakdown studies using a modified image converter streak camera

The temporal and spatial information of gaseous breakdowns occurring from the nanosecond to millisecond time scales are important to the basic understanding and applications of gaseous discharges. A streak camera is an ideal tool for acquiring both time- and space-dependent data simultaneously. However, there are several problems associated with using a conventional streak camera for gaseous breakdown studies. Modifications have been made specifically to solve these problems, while the features of the original streak camera are preserved. A signal overlapping problem has been eliminated by extending the dead time to 70 ms. Streak camera response times have been minimized by adjusting the bias voltages. One streak range has been extended to 7 ms to cover the entire event of a gaseous discharge. The modifications and experimental evaluation of the modified streak camera will be presented.

Modes on a Short Spear Bunch as Observed with a Streak Camera

The longitudinal structure of electron bunches in the storage ring SPEAR on a single pass was studied with time resolution approx. 10 ps. The measuring instrument used is an image-converter streak camera, a specialized device heretofore used mostly by laser workers. Unexpectedly, under some conditions the charge in a single RF bucket breaks up into two short sub-bunches which seem to rotate about a common center in energy-phase space. No evidence is seen for other, higher-frequency structure on the bunches.

Sweep devices for picosecond image-converter streak cameras

Four different sweep devices based on microwave tubes, avalanche transistors, krytrons, and laser-triggered spark gaps are treated in detail. These control circuits are developed for picosecond image-converter cameras and generate sweep pulses providing streak speeds in the range of 107 to 5×1010 cm/s with maximum time resolution better than 10−12 s. Special low-jitter triggering schemes reduce the jitter to less than 5×10−11 s. Some problems arising in the construction and matching of the sweep devices and image-streak tube are discussed. Comparative parameters of nanosecond switching elements are presented. The results described can be used by other authors involved in streak camera development.

An economic and compact image-converter camera

An image-converter streak camera is described which utilises an English Electric P856/20 electrostatically focused shutter tube operated in a normally cut-off mode. Streak record-time ranges of 50 ns to 10 mu s are obtained by sequentially pulsing two of the tube electrodes, using avalanche pulse generators to give the shutter action. The sweep deflection voltages, obtained from hard valves, type EL822, are gated from transistor switches. The use of these circuits has enabled a start delay time of 10 ns to be achieved. The camera has been used to investigate spark-channel formation in hydrogen using parallel gap structures. A typical result is presented.

Image Converter Camera Optical Measurements In Laser Fusion Research

High speed optical measurements in the picosecond regime play a crucial role in any laser .fusion program. At KMS Fusion,image converter streak cameras have been used to study a high power neodymium glass laser system and to observe target response to the laser pulse. Experimental techniques and results ©I several studies will be discussed. A stacker produced the desired pulse shape in 30 psec steps. These stacked trains were monitored at various points along the laser system. Perturbations of the pulse train as it propagates through the laser are most evident at the final output where examples of pulse splitting and breakup, which occur in extreme situations, will be shown. Target diagnostic studies include incident and nonabsorbed laser energy pulse shape and blast-wave photographs to determine absorbed energy.

The characteristics of a medium current relativistic electron-beam diode

In a previous paper we reported observation of ion flow in the Nereus diode. We report here more detailed observations of the diode, employing a Thomson parabola analyzer to measure ion species and energies, a four-pulse holographic interferometer to observe plasma blowoff from the electrodes, and an image-converter streak camera to record total optical radiation and time-resolved emission spectra. The large current on axis (the ’’pinch’’ current) of this diode appears to be caused by rapid local gap closure on axis. A model describing the behavior of this diode is discussed and compared with experimental data.

Picosecond resolution, real-time linear detection system for 10-μm radiation

A 10-μm detection system based on up-conversion in proustite has been developed for the measurement of subnanosecond pulses of CO2 laser radiation. This has involved the development of a ’’stretched-pulse’’ Q-switched Nd:YAG oscillator which can be synchronized with the output of a transverse discharge CO2 laser. The 1.06-μm radiation generated by this oscillator and the incoming 10-μm radiation pass collinearly through a 0.6-cm-long proustite crystal which is oriented for type II phase matching. An investigation of the bandwidth of the up-conversion process has shown that it should be possible to resolve 10-μm pulses with durations of ∼5 psec. Using an image converter streak camera to record the 0.96-μm sum frequency, the overall performance of the system has been investigated with the aid of a mode-locked CO2 laser operating at a pressure of 12 atm. The results have demonstrated that mode-locked CO2 pulses as short as ∼75 psec can be generated and that the temporal resolution of the complete detection system corresponds to that of the streak camera.

Spatial, temporal, and spectral characteristics of radiation emitted by aQ-switched YAG:Nd laser

An investigation was made of the fine structure of the intensity and spectrum of giant pulses emitted by a YAG:Nd laser. These ultrashort pulses were recorded using an image-converter streak camera with a resolution of at least 25 psec. In general, a domain spatial-temporal structure was observed in the radiation and it corresponded to a partial locking of the longitudinal and transverse modes. Special cases of the transverse or longitudinal mode selection were investigated. A fine structure of this kind should be allowed for in estimating the optical strength of the resonator elements and in nonlinear conversion processes.

Broadening of the emission spectrum of a self-mode-locked laser

The emission spectrum of a self-mode-locked ruby laser was broadened by a plane-parallel glass plate to widths exceeding 6 cm–1. The pulse duration was measured by the two-photon luminescence method and with an image-converter streak camera. It was established that the pulse duration was not affected by the broadening of the spectrum. This was explained by the finite relaxation time of the nonlinear absorber and was in agreement with the results of earlier investigation of the present authors.