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Fast simulation of ToF spectrometers
Oral, Martin
A fast simulation method was developed for analysis of time-of-flight spectrometers and it has been successfully used to optimize parameters of a real instrument. In the general case, the function of a time-of-flight spectrometer is best modeled using the Monte Carlo method, That involves calculation of a high number of ion trajectories, which is time consuming. We have found a way to reduce the calculation time greatly by introducing a simplification and using pre-computed data independent on the ion mass and charge. The procedure makes it computationally feasible to run iterative optimizations. By comparing the results with those of a realistic simulation on a selected case, we have verified that there is no noticeable influence on the results.
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Ray tracing, aberration coefficients and intensity distribution
Oral, Martin
In particle optics paraxial ray tracing (solution of the paraxial trajectory equation) provides the basic imaging properties of an optical system and real ray tracing (solution of the equation of motion with time as the parameter) gives the complete particle paths including all aberrations. While there are methods of computing the aberration coefficients directly, for example by evaluating the aberration integrals, ray tracing can also be used for this purpose.
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Programy pro elektronově optický návrh
Lencová, Bohumila ; Oral, Martin
The paper gives a brief overview of computational method used in the Institute of Scientific Instruments of AS CR for the design of electron optical devices. New possibilities of the software are then illustrated on the computations of spot profile in a scanning electron microscope with low energy and Wien filter.
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Determination of exact charged-particle trajectories and aberrations of systems in particle optics
Oral, Martin
The paper describes a method of calculation of aberration coefficients by regression (fitting). A prerequisite for the calculation is knowledge of an analytical expression of optical aberrations, which is used not only for fitting, but also for a fast computation of particle positions behind an optical system, e. g. for evaluation of a beam profile. The method is illustrated on computation of current density profiles in a deflected ion beam.
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The assessment of accurate trajectories of charged particles and errors of systems in particle optics
Oral, Martin
The work is supposed to deal with the design of a sufficiently effective method of computation of trajectories in particle-optical systems in general cases of non-adjusted optical systems (i.e. with errors in adjustment). Contemporarily, a method of computation in systems without these errors in adjustment by geometrical aberration theory of the 3rd order and chromatic theory of the 1st is developed, while it is principally possible to use aberration theories of higher orders (for achieving of higher exactness). It is necessary to include 'non-adjustment' of the optical system in the calculations. The neighbouring project is the computation of profiles of particles beams after processing by the optical system, in which the results of the main topic of the work have been exploited.
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Calculation of the beam profile
Oral, Martin
The beam profile provides local current density distribution of a particle beam. From the known distribution we can optimize the axial position of the specimen in a SEM, understand image aberrations or find optimum function of electron or ion analyzers. Graphical plot of the profile as a function of the z coordinate shows what is happening with the beam when it passes through the optical system. The first attempts of graphical presentationof the beam aberrations and profiles based on aberration theory are discussed in the recent diploma thesis.
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Dimension measurement in a cathode lens equipped low-energy SEM
Hutař, Otakar ; Oral, Martin ; Müllerová, Ilona ; Frank, Luděk
The paper deals with calibration of magnification in a cathode lens equipped SEM, which provides a high resolution in the energy range below 2000 eV, where both the charging-up and edge effect phenomena, complicating the measurement of dimensions, are suppressed. An analytical expression for the image magnification, in the dependence on the electron impact energy and the working distance, is derived and verified with respect to the measured values. Finally, a procedure suitable for the routine calibration is proposed.
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Výpočet proudové hustoty svazků nabitých částic
Oral, Martin
A method and a program for calculation of current density profiles was developed. It simulates the propagation of a charged-particle beam in an optical system. Since it requires data of positions of a high number (billions - 109) of particles on a given target, analytical expressions for paraxial position and aberrations are used for calculation, that are very fast to evaluate (millions of particles per second). Ray tracing is slow for this purpose (up to 100 particles per second). The accuracy of the analytical expressions is comparable with ray tracing in a certain space near the optical axis
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