"            
              “Coherent reflection and focusing of
              He atom beams from rough surfaces
                   at near-grazing incidence”
  
♦Speaker :피망 바카라Dr. Bum Suk Zhao (Max-Planck-Institute, Germany)
♦Place : Physics Seminar Room (Science Bldg, 3-201)
♦Date & Time : June, 10(Wed)피망 바카라4:00피망 바카라~피망 바카라5:00 pm

Abstract
  
  
We observe coherent reflection피망 바카라of피망 바카라thermal피망 바카라He atom beams from various microscopically-rough
surfaces at피망 바카라grazing피망 바카라incidence.피망 바카라For피망 바카라a피망 바카라sufficiently피망 바카라small피망 바카라normal component kz of the incident
wave-vector of피망 바카라the atom the reflection피망 바카라probability is found to be a피망 바카라function피망 바카라of피망 바카라kz피망 바카라only.피망 바카라This
behavior is explained by피망 바카라quantum-reflection피망 바카라at피망 바카라the attractive branch피망 바카라of피망 바카라the피망 바카라Casimir-van피망 바카라der
Waals피망 바카라interaction피망 바카라potential [1].피망 바카라For피망 바카라larger피망 바카라values피망 바카라of피망 바카라kz피망 바카라 the피망 바카라reflection probability is found to
increase with parallel피망 바카라component피망 바카라kx피망 바카라for피망 바카라a피망 바카라given kz.피망 바카라The material specific피망 바카라kx피망 바카라dependence피망 바카라is
discussed in terms of an피망 바카라effective피망 바카라averaging-out of the surface roughness and the atom-surface
Casimir-van der Waals potential under피망 바카라grazing incidence conditions. The coherent reflection at
grazing incidence is exploited to focus피망 바카라He atom beams in one dimension down to 2 ㎛ with피망 바카라a
Concave cylindrical mirror. The피망 바카라mirror 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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