Beam Behaviors In Near-field Enhancement Configurations And Its Applications

People's cognitive abilities have extended to the scope of microcosmic in nowadays 21st century with the rapid advances in science and technology.With the development of micro-machining and integrated optics,the dimension of the optical devices has approached and even reached micro-nanometre scale.The research of the novel effects in this field is the forerunner and basis for modern high and latest technology.This Ph.D.dissertation focuses on the investigation of the properties of finite-sized beam propagation in microstructures and the resonance phenomena associated.The main contents involved in this dissertation are as follows:In the first introductory chapter,firstly,the history and current researches on light beam transmitting through microstructures and the phenomena of resonance are briefly reviewed.The emphases are placed on the resonant enhancement of the Goos-H(?)nchen(GH) and Goos-H(?)nchen-like(GHL) displacement of light beam.It is indicated that large GH displacement of the transmitted evanescent beam generated by total internal refletion(TIR) should be considered in near-field imaging and evanescent wave mirror in atom optics.Secondly,the main approach employed to discuss the GH displacement is introduced as the stationary phase method.Lastly, the primary problelns discussed in this dissertation are stressed and the corresponding results are presented.The second chapter is about the general representation of a 2-dimension Gaussian beam.It is reported that the equation of beam axis should be taken as the restriction condition when performing coordinate rotation transformation on the conventional expressions of beam characteristics parameters to obtain the general expressions of the Gaussian beam with it's axis inclined to the strnctural coordinate. The problems discussed here form the basis for the discussion of a 2D inclined beam impinges on planar optical configurations.The third chapter concentrates on the non-geometrical effects on Gaussian beams transmitting through a thin dielectric slab optical microstructure.We will show that apart from the GHL displacement,the transmitted beam undergoes other effects that are also different from the prediction by geometrical optics.In much the same way as the non-specular effects for the reflected beam,those effects include angular deflection,width modification,and longitudinal focal shift.Due.to the waist-width dependent term,the non-geometrical effects of transmitted beam are not equal to the non-specular effects of reflected beam.Necessary conditions for the transmitted and reflected beam to maintain well the shape of the incident beam are advanced.The experimental observations of the backward displacement considering angular deflection in the microwave region are reported for the first time.In the fourth chapter large GH displacement of evanescent light beam in nearfield enhanced configuration is reported.At first,it is shown that the GH displacement of both TE and TM light beams totally reflected from a dielectric interface can be greatly enhanced by a dielectric thin fihn coated onto the dielectric surface. Secondly,it is found that the profile of the transmitted evanescent beam maintains well the shape of the incident beam if the restriction on the thickness of the thin fihn is satisfied.The transmitted evanescent light beam under TIR will experience a displacement silnilarly to that of the reflected beam.More importantly,the GH displacelnent of the transmitted evanescent beam can be greatly enhanced at transmission resonance.It is proved by numerical simulations that the stationary-phase approach also can be used to the case of evanescent beam and the magnitude of the Gtt displacement of transnfitted beam is just half as that of the reflected beain.At last,scheme for the probe of the enhanced GH displacement of the reflected beam is given by the analysis of the symmetric double-prism configuration with a dielectric thin fihn coated onto the surface of the first prism,where the role of the second prism is to probe the evanescent beam in the vacuum gap,and the total internal reflection becomes frustrated.The fifth chapter indicates that large GH displacement of transmitted evanescent beam may have effects on near-field microscope imaging and atom mirrors. Evanescent waves have great importance in optics of nanotechnology particularly in areas of near-field microscope and atom optics thanks to the intriguing fcatures. For applications,it is desirable that the evanescent field intensity be as large as possible.A promising approach to enhance the evanescent field is to coat the dielectric thin films in order to form a passive resonant structure.The novel properties of the evanescent field claimed in present thesis pose new challenges to near-field scanning imaging.Among the family of the near-field scanning optical microscope (NSOM),the Photon Scanning Tunneling Microscope(PSTM) uses the evanescent field frustrated by a probe in FTIR geometry,providing images with a resolution below the Rayleigh limit.Theoretical and experimental results have shown that the formation of images in PSTM depends not only on the interaction between the probes and near-field of the sample but also on the characteristics of the illuminating evanescent wave.The resulting images are very sensitive to illumination conditions, such as angle of incidence,polarization and the orientation of the sample relative to the illumination.It has been observed that the images of a single-step object differ significantly when the direction of the laser beam is reversed.The GH displacement discussed in the dissertation may be helpful to give interpretations of the problem.Also,it is conceivable that large displacement of the evanescent beam will have effects on the mechanism of evanescent wave mirrors,which demands detailed theoretical analysis.In the last chapter,I conclude the whole dissertation with briefly discussions on further work.