Laser wave, evanescent, electron reflection

Let us consider the possibility of reflection of electrons by an evanescent laser wave formed due to total internal reflection of femtosecond laser pulses from a dielectric-vacuum interface [4] (Fig. lb). Such a laser field was considered elsewhere [7, 8] to effect the mirror reflection of atoms (references to the latest works on the mirror reflection of atoms can be found in Refs. 9 and 10). The light intensity distribution in the evanescent wave in the vacuum may be represented in the form [11]... 

The character of reflection of electrons from the evanescent wave strongly depends on the relationship between the duration r of the laser pulse and the time of flight of an electron through the laser wave, rtr. It may be shown that when the laser pulse duration is much longer than the characteristic transit time rtr, the character of reflection of the electrons is close to the mirror. Where the relationship between these times is reversed, the mirrorlike character of reflection is disturbed. Let us make some simple estimates of the laser field and electron beam parameters with which the reflection of electrons is possible. 

The possibility of reflection of electrons by an evanescent wave formed upon the total internal reflection of femtosecond light pulses from a dielectric-vacuum interface is quite realistic. The duration of the reflected electron pulses may be as long as 100 fs. In the case of electrons reflecting from a curved evanescent wave, one can simultaneously control the duration of the reflected electron pulse and affect its focusing (Fig. lc). Of course, one can imagine many other schemes for controlling the motion of electrons, as is now the case with resonant laser radiation of moderate intensity [9, 10]. In other words, one can think of the possibility of developing femtosecond laser-induced electron optics. Such ultrashort electron pulses may possibly find application in studies into the molecular dynamics of chemical reactions [1,2]. 

Reflection of an electron beam by an evanescent laser wave... 

With the laser pulse energy W = 10 5 J, the laser spot diameter d = 10X on the dielectric surface, and the light frequency v = 5x 1014 s 1, the electron velocity variation is Au = 2x 108exp(-z/zo) centimeters per second. This means that an electron beam with an energy E - 100 eV (v = 5.9 x 108 cm/s) reflects at a substantial angle of

evanescent wave produced by a femtosecond laser pulse. 

Instead of the dielectric/dielectric interface used in evanescent wave sensors, it is possible to arrange a dielectric/metal/dielectric sandwich layer such that when monochromatic polarized light (e.g., from a laser source) impinges on a transparent medium having a metalhzed (e.g., Ag or Au) surface, light is absorbed within the plasma formed by the conduction electrons of the metal. This results in a phenomenon known as surface plasmon resonance (SPR). When SPR is induced, the effect is observed as a minimum in the intensity of the light reflected off the metal surface. 

The idea of reflecting an electron beam by an evanescent light wave is illustrated in Fig. 13.8. The internal reflection of a laser beam at a dielectric-vacuum interface produces an evanescent light wave with an intensity distribution given by... 

By using a curved evanescent wave, one can, in principle, obtain focusing of an electron beam simultaneously with reflection. Of course, all these potentialities of laser-induced reflective electron optics should be the subject matter of future studies, specifically into the damage threshold of the materials used for the formation of the high-intensity femtosecond evanescent laser light waves. 

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