The Research Of The Best Resolution To The Medium Under A Near-field Optical Microscope

Compared with the traditional optical microscope, scanning near-field optical microscope(SNOM) can break through the Rayleigh diffraction limit , providing us a resolution on nm level. Further , compared with the scanning tunnel electronic microscope that has a higher resolution, SNOM has a excellence of non-touched and non-destroyed , and has a practical value on the detection of organic creature.Because of its widespread applications, the researches and experiments on SNOM have been developed greatly during the past ten years. Based on the simple introduction of near-field optical theory, this paper illustrates the principle of high resolution of SNOM , establishes the probe-sample interaction equations by the Maxwell's equation in the medium, then, researches the resolution of the medium which is under a near-field optical microscope. Further ,the work above analyzes the influence factors on resolution of SNOM, provides the theoretical foundation of reasonable design of SNOM.The first chapter describes the birth , applications , work mode and image principle of SNOM. The second chapter illustratessome kinds of method after we give the condition of breaking through the Rayleigh diffraction limit. Based on the fore chapters, the third chapter analyzes the radiation problem of medium sphere and establishes the probe-sample interaction equations based on Maxwell's electromagnetic theory. Dipole approximate method is used to educe the constant between the optical field and the medium sphere field. Then we calculate the resolution of the particle sphere at the different positions by solving the linear equations and iterative process respectively. The results show that the contrast intensity does not monotonously increase with the increasing of the distance 1 between two samples, but reach a maximum at about 1=60nm. That is to say, at the position it has an optimum resolution effect. It is also showed from the theory that the position is just the offset place of far-field to neat-field. At last it summarizes the image factors which influence the resolution, which are composed of the shape of the probe, the wavelength and polarization of illuminating light source.