High quality ultrafast transmission electron microscopy using resonant microwave cavities

Ultrashort, low-emittance electron pulses can be created at a high repetition rate by using a TM$_{110}$ deflection cavity to sweep a continuous beam across an aperture. These pulses can be used for time-resolved electron microscopy with atomic spatial and temporal resolution at relatively large average currents. In order to demonstrate this, a cavity has been inserted in a transmission electron microscope, and picosecond pulses have been created. No significant increase of either emittance or energy spread has been measured for these pulses. At a peak current of $814\pm2$ pA, the root-mean-square transverse normalized emittance of the electron pulses is $\varepsilon_{n,x}=(2.7\pm0.1)\cdot 10^{-12}$ m rad in the direction parallel to the streak of the cavity, and $\varepsilon_{n,y}=(2.5\pm0.1)\cdot 10^{-12}$ m rad in the perpendicular direction for pulses with a pulse length of 1.1-1.3 ps. Under the same conditions, the emittance of the continuous beam is $\varepsilon_{n,x}=\varepsilon_{n,y}=(2.5\pm0.1)\cdot 10^{-12}$ m rad. Furthermore, for both the pulsed and the continuous beam a full width at half maximum energy spread of $0.95\pm0.05$ eV has been measured

Theory and particle tracking simulations of a resonant radiofrequency deflection cavity in TM110_{110} mode for ultrafast electron microscopy

We present a theoretical description of resonant radiofrequency (RF) deflecting cavities in TM$_{110}$ mode as dynamic optical elements for ultrafast electron microscopy. We first derive the optical transfer matrix of an ideal pillbox cavity and use a Courant-Snyder formalism to calculate the 6D phase space propagation of a Gaussian electron distribution through the cavity. We derive closed, analytic expressions for the increase in transverse emittance and energy spread of the electron distribution. We demonstrate that for the special case of a beam focused in the center of the cavity, the low emittance and low energy spread of a high quality beam can be maintained, which allows high-repetition rate, ultrafast electron microscopy with 100 fs temporal resolution combined with the atomic resolution of a high-end TEM. This is confirmed by charged particle tracking simulations using a realistic cavity geometry, including fringe fields at the cavity entrance and exit apertures

Materials science experiments in space

The criteria for the selection of the experimental areas and individual experiments were that the experiment or area must make a meaningful contribution to the field of material science and that the space environment was either an absolute requirement for the successful execution of the experiment or that the experiment can be more economically or more conveniently performed in space. A number of experimental areas and individual experiments were recommended for further consideration as space experiments. Areas not considered to be fruitful and others needing additional analysis in order to determine their suitability for conduct in space are also listed. Recommendations were made concerning the manner in which these materials science experiments are carried out and the related studies that should be pursued

Construction of Special Solutions for Nonintegrable Systems

The Painleve test is very useful to construct not only the Laurent series solutions of systems of nonlinear ordinary differential equations but also the elliptic and trigonometric ones. The standard methods for constructing the elliptic solutions consist of two independent steps: transformation of a nonlinear polynomial differential equation into a nonlinear algebraic system and a search for solutions of the obtained system. It has been demonstrated by the example of the generalized Henon-Heiles system that the use of the Laurent series solutions of the initial differential equation assists to solve the obtained algebraic system. This procedure has been automatized and generalized on some type of multivalued solutions. To find solutions of the initial differential equation in the form of the Laurent or Puiseux series we use the Painleve test. This test can also assist to solve the inverse problem: to find the form of a polynomial potential, which corresponds to the required type of solutions. We consider the five-dimensional gravitational model with a scalar field to demonstrate this.Comment: LaTeX, 14 pages, the paper has been published in the Journal of Nonlinear Mathematical Physics (http://www.sm.luth.se/math/JNMP/

Design and characterization of dielectric filled TM110_{110} microwave cavities for ultrafast electron microscopy

Microwave cavities oscillating in the TM$_{110}$ mode can be used as dynamic electron-optical elements inside an electron microscope. By filling the cavity with a dielectric material it becomes more compact and power efficient, facilitating the implementation in an electron microscope. However, the incorporation of the dielectric material makes the manufacturing process more difficult. Presented here are the steps taken to characterize the dielectric material, and to reproducibly fabricate dielectric filled cavities. Also presented are two versions with improved capabilities. The first, called a dual-mode cavity, is designed to support two modes simultaneously. The second has been optimized for low power consumption. With this optimized cavity a magnetic field strength of 2.84 $\pm$ 0.07 mT was generated at an input power of 14.2 $\pm$ 0.2 W. Due to the low input powers and small dimensions, these dielectric cavities are ideal as electron-optical elements for electron microscopy setups

Angular and energy dependence of ion bombardment of Mo/Si multilayers

The process of ion bombardment is investigated for the fabrication of Mo/Si multilayer x-ray mirrors using e-beam evaporation. The ion treatment is applied immediately after deposition of each of the Si layers to smoothen the layers by removing an additional thickness of the Si layer. In this study the parameters of Kr+ ion bombardment have been optimized within the energy range 300 eV-2 keV and an angular range between 20 degrees and 50 degrees. The optical performance of the Mo/Si multilayers is determined by absolute measurements of the near-normal-incidence reflectivity at 14.4 nm wavelength. The multilayer structures are analyzed further with small-angle reflectivity measurements using both specular reflectivity and diffuse x-ray scattering. The optimal smoothening parameters are obtained by determining the effect of ion bombardment on the interface roughness of the Si layer. The optimal conditions are found to be 2 keV at 50 degrees angle of incidence with respect to the surface. These settings result in 47% reflectivity at 85 degrees (lambda = 14.4 nm) for a 16-period Mo/Si multilayer mirror, corresponding to an interface roughness of 0.21 nm rms. Analysis shows that the interface roughness is determined by ion induced viscous flow, an effect which increases with ion energy as well as angle of incidence. In order to determine the effect of intermixing of the Si and Mo atoms, the penetration depth of the Kr+ ions is calculated as a function of ion energy and angle of incidence. Furthermore, the angular dependence of the etch yield, obtained from the in situ reflectivity measurements, is investigated in order o determine the optimal ion beam parameters for the production of multilayer mirrors on curved substrates. (C) 1997 American Institute of Physics

Dual mode microwave deflection cavities for ultrafast electron microscopy

This paper presents the experimental realization of an ultrafast electron microscope operating at a repetition rate of 75 MHz based on a single compact resonant microwave cavity operating in dual mode. This elliptical cavity supports two orthogonal TM$_{110}$ modes with different resonance frequencies that are driven independently. The microwave signals used to drive the two cavity modes are generated from higher harmonics of the same Ti:Sapphire laser oscillator. Therefore the modes are accurately phase-locked, resulting in periodic transverse deflection of electrons described by a Lissajous pattern. By sending the periodically deflected beam through an aperture, ultrashort electron pulses are created at a repetition rate of 75 MHz. Electron pulses with $\tau=(750\pm10)$ fs pulse duration are created with only $(2.4\pm0.1)$ W of microwave input power; with normalized rms emittances of $\epsilon_{n,x}=(2.1\pm0.2)$ pm rad and $\epsilon_{n,y}=(1.3\pm0.2)$ pm rad for a peak current of $I_p=(0.4\pm0.1)$ nA. This corresponds to an rms normalized peak brightness of $B_{np,\textrm{rms}}=(7\pm1)\times10^6$ A/m$^2$ sr V, equal to previous measurements for the continuous beam. In addition, the FWHM energy spread of $\Delta U = (0.90\pm0.05)$ eV is also unaffected by the dual mode cavity. This allows for ultrafast pump-probe experiments at the same spatial resolution of the original TEM in which a 75 MHz Ti:Sapphire oscillator can be used for exciting the sample. Moreover, the dual mode cavity can be used as a streak camera or time-of-flight EELS detector with a dynamic range $>10^4$

Guideline versus non-guideline based management of rectal cancer in octogenarians

The number of octogenarians with rectal adenocarcinoma is growing. Current guidelines seem difficult to apply on octogenarians which may result in non-adherence. The aim of this retrospective cohort study is to give insight in occurrence of treatment-related complications, hospitalisations and survival among octogenarians treated according to guidelines versus octogenarians treated otherwise. 108 octogenarians with rectal adenocarcinoma were identified by screening of medical records. 22 patients were excluded for treatment process analysis because of stage IV disease or unknown stage. Baseline characteristics, diagnostic process, received treatment, motivation for deviation from guidelines, complications, hospitalisations and date of death were documented. Patients were divided in two groups depending on adherence to treatment guidelines. Differences in baseline characteristics, treatment-related complications and survival between both groups were evaluated. Diagnosis and treatment according to guidelines occurred in 95 and 54% of the patients, respectively. When documented, patient's preference and comorbidities were major reasons to deviate from guidelines. 66% of patients who were treated according to guidelines experienced complications versus 34% of those treated otherwise (p = 0.02). After adjustment for differences in age and polypharmacy, this association was not significant. Patients treated according to the guideline had better survival 18 months after diagnosis (80 versus 56%, p = 0.02). Treating octogenarians with rectal cancer according to guidelines seem to lead to better overall survival, but may lead to a high risk of complications. This may jeopardise quality of life. More and prospective studies in octogenarians with rectal cancer are needed to customize guidelines for these patients