"            
              “Coherent reflection and focusing of
              He atom beams from rough surfaces
                   at near-grazing incidence”
  
♦Speaker :보증 토토Dr. Bum Suk Zhao (Max-Planck-Institute, Germany)
♦Place : Physics Seminar Room (Science Bldg, 3-201)
♦Date & Time : June, 10(Wed)보증 토토4:00보증 토토~보증 토토5:00 pm

Abstract
  
  
We observe coherent reflection보증 토토of보증 토토thermal보증 토토He atom beams from various microscopically-rough
surfaces at보증 토토grazing보증 토토incidence.보증 토토For보증 토토a보증 토토sufficiently보증 토토small보증 토토normal component kz of the incident
wave-vector of보증 토토the atom the reflection보증 토토probability is found to be a보증 토토function보증 토토of보증 토토kz보증 토토only.보증 토토This
behavior is explained by보증 토토quantum-reflection보증 토토at보증 토토the attractive branch보증 토토of보증 토토the보증 토토Casimir-van보증 토토der
Waals보증 토토interaction보증 토토potential [1].보증 토토For보증 토토larger보증 토토values보증 토토of보증 토토kz보증 토토 the보증 토토reflection probability is found to
increase with parallel보증 토토component보증 토토kx보증 토토for보증 토토a보증 토토given kz.보증 토토The material specific보증 토토kx보증 토토dependence보증 토토is
discussed in terms of an보증 토토effective보증 토토averaging-out of the surface roughness and the atom-surface
Casimir-van der Waals potential under보증 토토grazing incidence conditions. The coherent reflection at
grazing incidence is exploited to focus보증 토토He atom beams in one dimension down to 2 ㎛ with보증 토토a
Concave cylindrical mirror. The보증 토토mirror 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)
"