Ultramicroscope

Abstract: We have developed a scanning near-field optical microscope with an optically trapped metallic particle that has a small diameter compared to the wavelength of visible light. In this microscope we employed spot illumination to enhance the intensity of light scattered from a probe particle so we could reduce the diameter of the probe particle to 40 nm. We detected slight irregularities of the surface of the cover glass near 10-nm depth. Also, we observed gold colloidal particles on the surface of the cover glass.

Abstract: 1. Hitherto, the majority of researches into the character of turbulent fluid flow have been concerned with the motions of relatively large molar masses of fluid, and the methods used to obtain visual impressions of the flow pattern have usually involved the introduction into the fluid of particles of extraneous matter, such as aluminium particles, oil drops, etc. It is questionable whether such methods are permissible for the examination of microturbulence, especially near the boundary of the fluid where the scale of the turbulence is small, since if the particles introduced are comparable in size with the molar masses, their internal motions may not be faithfully represented. In a study of this kind of motion it is very desirable therefore to avoid any such interference with the flow, and the ultramicroscope offered a possible means of doing this provided the difficulties in applying the instrument could be surmounted. 2. The principle of the ultramicroscope depends on the fact that minute particles usually present in most fluids, but invisible in ordinary light even under the most powerful microscope, become visible when intensely illuminated provided they are seen against a dark background. Particles whose shapes are not discernible, because they are smaller than the wave-length of light, then become visible as bright points of light.