• 커뮤니티
  • 세미나/콜로퀴움
세미나/콜로퀴움

PHYSICS/BK21 SEMINAR[09.06.10]pm4:00~

본문

"            
              “Coherent reflection and focusing of
              He atom beams from rough surfaces
                   at near-grazing incidence”
  
♦Speaker :  Dr. Bum Suk Zhao (Max-Planck-Institute, Germany)
♦Place : Physics Seminar Room (Science Bldg, 3-201)
♦Date & Time : June, 10(Wed)  4:00  ~  5:00 pm

Abstract
  
  
We observe coherent reflection  of  thermal  He atom beams from various microscopically-rough
surfaces at  grazing  incidence.  For  a  sufficiently  small  normal component kz of the incident
wave-vector of  the atom the reflection  probability is found to be a  function  of  kz  only.  This
behavior is explained by  quantum-reflection  at  the attractive branch  of  the  Casimir-van  der
Waals  interaction  potential [1].  For  larger  values  of  kz   the  reflection probability is found to
increase with parallel  component  kx  for  a  given kz.  The material specific  kx  dependence  is
discussed in terms of an  effective  averaging-out of the surface roughness and the atom-surface
Casimir-van der Waals potential under  grazing incidence conditions. The coherent reflection at
grazing incidence is exploited to focus  He atom beams in one dimension down to 2 ㎛ with  a
Concave cylindrical mirror. The  mirror is made out of quartz and has a curvature radius of 78 m.
The focal length can be adjusted by varying the incidence angle. With a relatively large focal length,
the spot size gets larger with increasing source size and increasing deBroglie-wavelength. On the
other hand, when the focal length is adjusted to a small value by decreasing the incidence angle,
the focal spot size is mainly determined by spherical aberration of the mirror.

  
            Contact Person : Prof. Nam Ki Lee (054-279-2097, nklee@postech.ac.kr)
"
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