Laser control electron beam focusing

Femtosecond laser excitation makes it possible to produce in a synchronous manner accurate to within a few femtoseconds an ensemble of molecules in an excited state and observe thereafter the evolution of this ensemble in the subsequent processes of decay, relaxation, and so on, by means of other femtosecond pulses. Another femtosecond pulse is usually used as a probe pulse [1]. However, one can directly observe changes in the geometry of molecules, specifically in molecular vibrations, by the method of electron diffraction using ultrashort electron pulses. This was successfully demonstrated in Ref. 2. Whereas the production of synchronous probe laser pulses is a standard technique, the situation with femtosecond electron pulses is more complicated. I would like to call attention to the possibility of using intense femtosecond laser pulses to control electron beams, specifically to obtain femtosecond electron pulses and to focus and reflect them, and so on [3, 4]. 

Lasers and electron beams. These can be used to provide local heating or to heat small quantities. The temperature control is not great, but these techniques are very versatile. Electron beams are used to vaporize silicon for thin-film deposition using molecular-beam epitaxy. A focused laser beam is the basis of the pulsed-laser deposition (PLD) thin-film growth technique (Chapter 28). 

The purpose of this chapter is to focus on controlled surface modifications of polymers, with emphasis on the advances achieved during the past decade or so. The commonly used techniques generally mentioned include corona discharge, plasma, UV, laser, and electron beam treatments. Lateral patterning techniques utiUzing soft hthography, which is the collective name for a number of techniques where a patterned elastomer is used as mold, stamp or mask to generate or transfer patterns with sub-micrometer resolution, will not be covered in this chapter, since several comprehensive reviews focused on these techniques have been recently pubhshed [46,47]. 

S. Mukai, M. Watanabe, H. Itoh, H. Yajima, Integration of a diode laser and an electronic lens for controlling the beam focus position. Appl. Phys. Lett. 54, 315 (1989)... 

Prior to extrusion the fused silica preform is usually treated with dilute hydrofluoric acid to remove any imperfections and deformations present on the inner and outer surfaces and then rinsed with distilled water and followed by annealing (55). In a cleanroom atmosphere, the preform is vertically drawn through a furnace maintained at approximately 2000°C. Guidance and careful control of the drawing process is achieved by focusing an infrared laser beam down the middle of the capillary in conjunction with feedback control electronic circuitry in order to maintain nniformity in the specifications of the inner and outer diameters in the final prodnct. 

Leaving aside the important problem of interaction between ultrahigh-intensity femtosecond laser pulses and relativistic electrons, we shall consider below only the effects involved in the control of non relativistic electrons, such as coherent diffraction, deflection, focusing, and reflection. The diffraction of an electron beam by a standing light wave (the Kapitza-Dirac effect, Kapitza and Dirac 1933) is essentially the earliest proposal for the control of matter by light. 

Laser ionization mass spectrometry or laser microprobing (LIMS) is a microanalyt-ical technique used to rapidly characterize the elemental and, sometimes, molecular composition of materials. It is based on the ability of short high-power laser pulses (-10 ns) to produce ions from solids. The ions formed in these brief pulses are analyzed using a time-of-flight mass spectrometer. The quasi-simultaneous collection of all ion masses allows the survey analysis of unknown materials. The main applications of LIMS are in failure analysis, where chemical differences between a contaminated sample and a control need to be rapidly assessed. The ability to focus the laser beam to a diameter of approximately 1 mm permits the application of this technique to the characterization of small features, for example, in integrated circuits. The LIMS detection limits for many elements are close to 10 at/cm, which makes this technique considerably more sensitive than other survey microan-alytical techniques, such as Auger Electron Spectroscopy (AES) or Electron Probe Microanalysis (EPMA). Additionally, LIMS can be used to analyze insulating sam-... 

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