Attosecond Photoelectron Bunches Generation
Generation of Sub-Femtosecond (Attosecond) Probing Photoelectron Bunches with Quasi-Stationary Electromagnetic Fields
Tech Area / Field
- PHY-OPL/Optics and Lasers/Physics
- PHY-PFA/Particles, Fields and Accelerator Physics/Physics
8 Project completed
Senior Project Manager
Malakhov Yu I
Institute of General Physics named after A.M. Prokhorov RAS, Russia, Moscow
- VNIIEF, Russia, N. Novgorod reg., Sarov
- University of Toronto / Department of Electrical & Computer Engineering, Canada, ON, Toronto\nCORDIN Co., USA, UT, Salt Lake City\nUniversity of Central Florida / Center for Research and Education in Optics and Lasers / School of Optics, USA, FL, Orlando\nUniversity of Alberta, Canada, AB, Edmonton
Project summaryThe project's purpose, the state of the art in the field and the impact of the proposed project on the progress in this field.
The Project is aimed at solving a fundamental problem connected with theoretical and experimental studies on main physical principles and peculiarities of spatial/temporal focusing of ultrashort photoelectron bunches in quasistationary electromagnetic fields. It is assumed to carry out computer modelling and practical realisation of a quasistationary electron-optical system ensuring subfemtosecond (attosecond) temporal focusing of photoelectron bunches.
The main factor determining the duration of photoelectron bunch resulted from interaction of incident ultrashort optical pulse with photocathode is the so-called first-order temporal chromatic aberration (Zavoisky-Fanchenko aberration) due to initial spread of photoelectrons in energies. As well known, that aberration is unavoidable in static fields and being inversely proportional to the field intensity at the photocathode. The substantial progress achieved during the last 30-40 years in advancing temporal resolution of streak cameras with static focusing was immensely conditioned by rising field intensity at the photocathode. Temporal resolution of about 200 fs being presently announced in the best streak cameras developed by Hamamatsu Co. (Japan) is ensured by field intensity at the photocathode not less than 10 kV/mm in the pulse mode. Nevertheless, as the last 24th ICHSPP in Sendai (Japan) has earnestly demonstrated, the huge engineering difficulties connected with electrical breakdown problem make the perspectives of somewhat essential progress on this way rather dim.
From the other hand, the problem of subfemtosecond electron bunches formation remains to be exceedingly urgent because those bunches represent an indispensable tool in time-resolved electron diffraction studies on fundamental properties of transient phenomena in solid-state and gaseous-state matter. Solid-state materials science and biological crystallography could also be the principal beneficiaries of this development.
As can be seen from the stated above, the situation about a substantial (at least, by the order of magnitude) shortening electron pulse duration seems to be rather hard if we are still trying to pursue two purposes simultaneously: the first - to gain extremely short electron pulse, and the second – to keep in that pulse temporal structure of incident optical radiation.
We may find ourselves in quite different situation if we would consider an ultrashort photoelectron bunch produced by photocathode not as a carrier of information on optical radiation having given birth to the bunch but as probing tool for interaction with matter. In this case our purpose is to gain an ultrashort electron pulse of controllable duration able of getting in some time moments (those are the points of temporal focusing) even substantially shorter than the incident light pulse. Such a look opens a possibility of using non-stationary electromagnetic fields for temporal focusing of probing electron bunches.
Principal possibility of spatial/temporal focusing of electron bunches in non-stationary (as example, periodic in time) electromagnetic fields is rather well-known and widely used in microwave devices with continuous electronic flows (such as klystrons, magnetrons, etc.) as well as in some types of time-of-flight mass-analyzers. The possibility of spatial/temporal focusing of photoelectron bunches with time-dependent field have been discussing in the world scientific press since the middle of 90s, though according to the known publications, no adequate theoretical base, software for computer experiments, and all the more, working experimental prototype have been yet developed. Therefore the problem stated in the Project should be considered as new and urgent one.
Our preliminary investigations and estimations show the time-dependent fields able to give a cardinal solution to the problem of temporal focusing and to ensure subfemtosecond dynamic compression of electron bunch during its travelling inside the vacuum tube. It is very important that approach procedure does not need extremely high field intensity to be applied to the photocathode.
The competence of the project team in the specified area.
The experts of Photoelectronics Department, GPI, have gained great experience in computer modelling and practical design of time-analysing image tubes and photoelectron guns with subpicosecond temporal resolution.
A group of experts involved in this Project have developed a unique applied program package ELIMDYNAMICS oriented to computer simulation and optimisation of photoemission static/dynamic image tubes. The sophisticated methods and algorithms used in ELIMDYNAMICS package are based on about 30-years experience of the authors’ working in the field of computer electron optics and have been well tested and verified in practice. The difference between the calculated and experimentally measured data does not normally exceeds 0.5ч2 % as to the first order parameters (position of the limiting focusing and crossover planes, electron-optical magnification, etc.), and 5ч10 % as to integral characteristics of electron image (scale distortion, MTFs, spatial and temporal resolution, etc).
The Package itself as well as the works of the Package’ authors in the area of charged particle optics and related applications are well known and highly estimated among the experts in Russia and abroad.
The experimental facilities now available in Photoelectronics Department, GPI, ensure effective development and manufacturing of time-analysing image tubes and photoelectron guns with subpicosecond temporal resolution. The closed technological chain functioning in Photoelectronics Department allows the complete cycle of image tube manufacturing comprising computer modelling, engineering design, producing photocathodes and luminescent screens, mechanical works, etc. This chain has been completed with all necessary equipment such as evaporation units, hydrogen-annealing unit, welding equipment, etc. Experimental investigations and measurements of the newly made image tube samples are carried out with unique femtosecond laser system, capable of generation powerful laser pulses as short as 120 fs duration, and 20-30 fs after upgrading.
The group of the highly experienced experts from VNIIEF has a very strong potential in the field of laser optics, which is very important for solving the problem of image focusing with femtosecond precision. The group of scientists and engineers from RIPT provides one of the most sophisticated part of the Project development: manufacturing and testing the high-speed pulsing circuitries for photoelectron bunches monitoring. This group is able to create electrical pulses of 1-3 KV in amplitude with rise time better than 100 ps on the loads with nominal resistance less than 55 Ohm.
Martin Richardson and his laboratory at CREOL are very anxious to arrange mutual experiments aimed to generate, measure, and to employ the 20-40 KeV electron bunches of subfemtosecond duration. This american group for more than thirty years fruitfully collaborates with scientists from GPI.
GPI and Cordin Company almost 15 years are working very closely within the scientific Agreement on high-speed image converter technology.
Thus, the expected results of the Project implementation are as follows:
1. A detailed theory of spatial/temporal focusing of ultrashort electron bunches in quasi-stationary electromagnetic fields with regard to collective Coulomb repulsion effects will be developed on the basis of aberration theory and tau-variation approach.
2. A software will be designed for accurate computer modelling on ultrashort electron bunches dynamics in quasi-stationary electromagnetic fields. Comprehensive computations of electrode geometry and time-dependent electrode voltages ensuring optimal modes of spatial/temporal focusing will be carried out.
3. The specialized subnanosecond high-voltage pulse generators able to produce quasistationary electromagnetic fields with previously calculated parameters will be developed and designed.
4. An upgraded femtosecond laser system together with femtosecond streak cameras will be mounted for providing test experiments.
5. An experimental prototype of the source of attosecond bunches of electrons (SABE) will be designed and manufactured.
6. A series of dynamic testing experiments on formation of 20-40 KeV photoelectron bunches of sub-femtosecond duration will be carried out with the upgraded femtosecond laser installation.
Those works, being implemented, would give to experimentalists a sophisticated tool to be applied in studies on transient phenomena in solid-state and gaseous-state matter and thus result in a resolute breakthrough in getting new knowledge on fundamental properties of the Nature.
Furthermore the femtosecond streak cameras developed within the scope of the Project will provide a starting point for their commercialization in the frame of cooperation with Cordin Company.
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