Valentina P. Degtyareva

Dynamics of electron bunches in subpicosecond streak tubes

Abstract The dynamics of electron bunches in subpicosecond streak tubes is studied numerically taking into account space-charge effects and various initial photoelectron energy distributions. Three computing and analytical models (aberrational-Lorentz model, the model describing the limiting case of zero initial energy and simplified analytical model) are used.

A Specially Designed Femtosecond Streak Image Tube With Temporal Resolution Of 50fs

In our specially designed femtosecond streak image tube, the electron beam was focused by a cylindrical electron optical lens. In order to achieve temporal resolution of less than 50fs and large dynamic range, the electric field near the photocathode was 6-8kV/mm with a slit acceleration electrode. The temporal dispersion in our lens has been eliminated completely by optimization of the electron focusing lens. To compensate the temporal dispersion arising from photocathode to accelerating electrode, a compensation element and a half open aperture have been introduced, so that the total temporal dispersion of less than 50fs has been achieved. To overcome the influence of a strong fringe field of the deflector in dynamic mode on the total temporal dispersion and spatial resolution, a travelling wave deflector will be used. In addition, to minimize the space charge effects, the electron transit time in this specially designed electron optical lens was shortened to 840ps and the so called crossover in slit direction disappeared. The discrete space charge effects have been modeled by Monte Carlo method including photoelectron emission process and induced charge on the electrode. The calculations have shown that this tube can handle the current density of up to 20A/cm2 without deterioration of the temporal resolution.

The New Streak Image Tube PIF-01

A new, small-size image-converter tube type PIF-01 has been developed for recording of various high speed phenomena with subpicosecond time resolution. The designing goal of the new image-converter tube having four electrodes geometry (photocathode, acceleration mesh, focusing electrode, anode diaphragm) and incorporating with a modern deflection system, was to simultaneously improve temporal resolution and dynamic range.Preliminary experimental results confirm the efficiency of the software developed for picofemtosecond streak tube computation and optimization.

Computer studies on dynamics of ultrashort electron packets in streak tubes and diffractometers

Computer techniques and software are developed to study the dynamics of electron packets on a subpicosecond time scale in streak image tubes and photoelectron diffractometers. It is shown that the Coulomb spread of an electron packet substantially increases for a sufficiently narrow energy distribution of photoelectrons, due to disinte- grative space charge effects inside the packet.

Femtosecond streak tubes designing, manufacturing, and testing

New generation of streak tubes intended for single-shot and synchroscan operations with femtosecond time resolution was computer modelled, designed, manufactured, tested and adopted for further application in laser research. The developed PV-FS type tubes provide close to 100 fs-time resolution in single-shot streak mode. It is important to note that the PV-FS tubes may be equipped with Peltier cooled S1-photocathodes and their spectral sensitivity may cover the range of 115 - 1550 nm. The developed photocathodes have very low surface resistance (tens of Ohm per square unit). New tubes offer a high (more than 50 line pairs/mm) spatial resolution when recording ultrafast optical images with femtosecond time resolution. Due to keeping the PV-FS external geometry similar to the well-known PV-type tubes it becomes possible to install new devices into available streak cameras (AGAT, Imacon 500, etc.).

The results of computer and experimental studies on compressing the ultrashort photoelectron bunches with time-dependent electric fields

Some theoretical milestones, in definite sense summarizing our studies on temporal compressing of photoelectron bunch with time-depending electric fields, are elucidated. The recent experimental results on dynamic compression of photoelectron bunches of picosecond duration, gained with the use of a newly designed photoelectron gun employing the electric field ramp of about 1.5 kV/ns, are presented and compared with the results of computer simulation.

Dynamic parameters evaluation for femtosecond streak tubes

Presented are the experimental results on femtosecond streak tubes measurements in dynamic mode. Several streak tube prototypes have been manufactured, with either distributed coaxial-strip line or capacitor-type photocathode-accelerating mesh assembly. Electrical field transition time in the photocathode-accelerating mesh gap was investigated. Tubes have been tested in a variety of regimes, in order to define the most efficient ones. Dynamic parameters of the developed femtosecond streak tubes were measured inside the streak camera prototype. The following dynamic parameters were evaluated: ultimate time resolution, dynamic range, and signal/noise ratio, spectral range, input sensitivity, streak speed and its nonlinearities, etc. The developed and optimized femtosecond streak tubes represent a reliable basis for design of streak cameras being required for photographic recording of ultrafast events in laser and plasma physics, time-resolved spectroscopy, laser interaction with matter, laser fusion, etc.

Sub-100 fs streak tube: computer-aided design, manufacturing, and testing

In the present communication we describe the design of the sub-100 fs streak-tube that may be used for commercial streak cameras manufacturing. Careful attention is paid to preparing of a very smooth input photocathode substrate on which a low surface resistance (1-5 Ohm/) photocathode of S-1 type is deposited. Our estimations have shown that the photocathode surface roughness of about tens of nanometers may restrict the ultimate time resolution at the level of 100 fs. This is the reason why the photocathode substrate surface has to be smooth within the units of nanometers. The curvature of the photocathode surface is also very important to compensate the difference in the time-of-flight of electrons emitted from the central and peripheral photocathode areas. Further modernization was conducted with a photocathode-accelerating mesh assembly. The assembly may operate with 2 - 3 ns (FWHM) electrical pulses of 12 - 15 kV amplitude. In order to improve the S/N ratio in the streaked images, a shuttering system was incorporated inside the tube. As the result, a completely new femtosecond streak tube of PV-FS-M type was designed, manufactured, and tested.

Femtosecond streak image converter camera

An experimental prototype of a femtosecond streak image converter camera was built around a specially designed femtosecond streak image tube having a cylindrical type electron focusing lens. Experimentally measured temporal resolution of the camera is better than 500 fs while its spatial resolution is not worse than 40 lp/mm across the slit direction.

Simplified picosecond streak image tube for designing inexpensive commercial cameras

The current demand for inexpensive streak camera manufacturing leads to the necessity in development of a variety of relatively simple and low cost image-converter tubes. One such tube, known as PIF-C, designed and manufactured in the Photoelectronics Department of the General Physics Institute (GPI), is now commercially available. Its experimentally measured time resolution in streak mode has approached one picosecond, and 3 ps in synchroscan mode at 82 MHz operation frequency. In single frame mode at 100 ns exposure time, the spatial resolution over 6 mm input area is within 15 lp/mm. Electron optical magnification of the tube is 1.5 x. PIF-C tubes may be supplied with one of the S1/S20/S25 photocathodes, fabricated either on borosilicate glass, UV-glass, or MgF2 substrate. Its P11 phosphor screen is deposited onto the fiber optic window. EBI of the PIF-C/S1 tube is in the range of 5 (DOT) 10-10 A/cm2.