Single-Slit Diffraction Pattern of a Thermal Atomic Potassium Beam

Abstract

The diffraction of a full thermal neutral atomic potassium beam by a single slit has been observed. Four experimental diffraction patterns of a 23.0(±0.4)μ diffracting slit were obtained with an atomic-beam apparatus which had a 2.5(±1)μ source slit, a 3.0(±0.1)μ detector wire, a source-to-slit distance of 96 cm, a slit-to-detector distance of 100 cm, and an oven temperature of 533° K. The experimental pattern was reproducible and is in good general agreement with the prediction of de Broglie's hypothesis and simple scalar Fresnel diffraction theory. The effect of diffraction is clearly evident; two prominent diffraction fringes are present on the top corners of the beam profiles. The theoretical prediction, calculated with the aid of a computer, included the effects of finite source and detector widths and the Maxwellian speed distribution of the K beam. Additional theoretical calculations showed that no major improvement in the clarity of the diffraction fringes could be obtained by using a velocity-selected beam, a Li7 beam, or a narrower diffracting slit.