Mikhail Monastyrskiy

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.

Space-charge effects in an electrostatic multireflection ion trap.

The multireflection ion traps with isochronous properties offer a lot of opportunities for time-of-flight mass spectrometry by elongation of the ion path, thus preserving the compact dimensions of an instrument. We have built and tested a two-mirror linear trap that provides at least 80,000 mass-resolving power. Although the mass resolution appears promising, there are substantial limitations that arise from Coulomb interactions of the trapped ions. Among these, the mutual repulsion of ions with same or close mass-to-charge ratios appears dominant, resulting in counterintuitive motion synchronization. The self-bunching and coalescence effects are also examined by numerical simulation.

New Computer Modeling and Experimental Results on Photoelectron Gun with Time-Dependent Electric Field

Presented are the recent, numerically-supported experimental results on temporal compressing of electron bunch in timedependent electric field, derived with the use of a unique photoelectron gun that has been simulated, designed, manufactured, and tested at the Photoelectronics Department of A.M. Prokhorov General Physics Institute, RAS. An original photoelectron bunch generated from the photocathode by a 7 ps laser pulse was compressed down to ~fs. The future prospects of temporal compressing of electron bunch in time-dependent fields are discussed.

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.

Some aspects of space-charge effect calculation in high-resolution mass spectrometry

A variational 3D approach to the problem of simulating stationary distributions of ions in the radiofrequency low-vacuum ion traps with regard to Coulomb interaction and collisions of ions with buffer gas molecules is proposed. The software developed in the course of this work is employed to study the structure of stationary ion ensembles in the radiofrequency ion traps of various types. The effect of high-frequency and constant voltages, space-charge density, and buffer gas temperature on the formation of stationary distributions in the radiofrequency ion traps and their limiting capacitance is investigated. It is shown that the use of electrodes with a constant voltage in the presence of high enough ion density allows pre-filtering of ions directly in a high-frequency trap-accumulator.

Simulation of the stationary distributions of ions in radiofrequency low-vacuum traps with regard to the coulomb interaction

The paper presents main peculiarities of implementation and testing of an algorithm based on the variational approach to the problem of simulating the stationary distributions of ions in the radiofrequency, low-vacuum ion traps with taking into consideration the Coulomb interaction and interaction with buffer gas. A good agreement between the results of numerical modeling and analytical results obtained earlier by other authors for simpler models is attained. The employment of the software that has been developed in the course of this work enables studying the structure of ion ensembles in the radiofrequency ion traps of different types and obtaining the results being of interest for high-resolution mass spectrometry. The algorithm allows a natural generalization to three-dimensional case.

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.

New computer modeling and experimental results on a photoelectron gun with time-dependent electric field

The paper elucidates some new computer modeling and experimental results on the design of a photoelectron gun with time-dependent electric field. The main essence of the new approach is based on the fact that the properly chosen electric field ramp ensures first-order temporal focusing of photoelectron bunch, which is principally impossible in static field previously used. This new technology allows a real breakthrough in time resolution of photoelectron guns and diffractometers intended for time-resolved electron diffraction experiments (TRED).

Chapter Four - Generation of Ultrashort Electron Bunches for Time-Resolved Electron Diffraction Experiments

Chapter 4 considers the results of the design of 500 fs photoelectron gun with electrostatic focusing to be used in time-resolved electron diffraction experiments. The photoelectron gun represents a source of photo-induced, well-collimated (divergence <0.5°), sharp (effective diameter < 0.7mm), ultrashort (duration about 500 fs) bunches of electrons. Demonstration experiments in transmission mode with an aluminum sample of 300 A thicknesses resulted in diffraction pattern of reasonable quality under accumulation of up to 4 × 104 electron bunches with about 1500 electrons per each single bunch. Theoretical and experimental aspects of temporal focusing of electron bunches in time-dependent electric fields are also considered. Main essence of this approach is based on the fact that a real temporal focusing of photoelectron bunch can be attained using a properly chosen electric ramp. This new technology allows a real breakthrough in time resolution of photoelectron guns and diffractometers designated for time-resolved electron diffraction experiments.

Chapter Three - Examples of Streak Image Tube Application

Abstract Chapter 3 acquaints the reader with various applications of streak image tubes in laser and laser physics research. Among them are light “beats” generation using phase-modulated laser radiation, formation of bimodal temporal distribution of photons ultrashort laser pulse passed through a turbid medium, temporal shaping of ultrashort laser pulses by volume Bragg gratings, high-resolution investigation of radiation from a Ti: sapphire laser, time-intensity profile measurements of stimulated radiation from GaAs, dynamics of femtosecond laser microplasma in gases, streak-camera diagnostic of femtosecond laser spark, studies on optical fiber destruction under intense laser radiation.