Mikhail Ya. Schelev

500-fs photoelectron gun for time-resolved electron diffraction experiments

A photoelectron gun as a source of a photoinduced, monoen- ergetic (energy spread ,0.5 eV), well-collimated (divergence ,0.5 deg), sharp (diameter ,0.7 mm at the 1/e level), and ultrashort (<500 fs) bunch of electrons to be used for time-resolved electron diffraction (TRED) experiments is computer designed, assembled, and tested. In single-shot mode, it generates up to 10 3 of 30 keV electrons, and the electron pulse can be either measured in streak mode or focused onto a solid state target chosen from a set of interchangeable targets. High temporal resolution enables measurement with femtosecond precision of the diffraction pattern perturbation after the exiting laser radiation drops onto a target. Demonstration experiments with a 300-A A1 target in transmission-type mode result in diffraction images of reasonable quality under accumulation of up to 4310 4 500-fs photoelectron pulses.

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 modeling of a subfemtosecond photoelectron gun with time-dependent electric field for TRED experiments

In the paper, theoretical and numerical studies on temporal focusing of photoelectron bunch in time-dependent fields are continued. Presented are the results of computer modeling on electron-optical system with combined time-dependent electric and static magnetic fields to ensure both spatial focusing and temporal compressing of photoelectron bunch down to sub-femtosecond level. The peculiarity of space charge effect contribution to the bunch broadening in the case of time-dependent electric field is discussed.

Theoretical and computer study on the possibility of sub- femtosecond (attosecond) temporal focusing of photoelectron probing bunches with quasi-stationary electromagnetic fields

The problem of ideal first-order temporal focusing of photoelectron bunches with quasi-stationary electromagnetic fields is discussed on the basis of theoretical electron optics and computer modelling.

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.

Circular streak camera application for satellite laser ranging

The application of the streak camera with the circular sweep for satellite laser ranging is described. The Modular Streak Camera system employing the circular sweep option was integrated into the conventional Satellite Laser System. The experimental satellite tracking and ranging has been performed. The first satellite laser echo streak camera records are presented.

Recent research and development in electron image tubes/cameras/systems

Recent results in development of the principal components of picosecond image converter recording systems are reviewed focusing on image tubes, streak and framing cameras, and CCD readout devices. Attention is also given to new laser sources capable of generating very stable femtosecond and picosecond optical pulses for dynamic calibration of image tubes and cameras and application of the designed instruments in laser research.

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.