Investigations on Subwavelength-scale Variation by Far-field Characteristics: Deconvolution and Detection Sensitivity Enhancement
|關鍵字:||次波長;未知訊號分離;遠場測量法;Subwavelength;Blind singnal separation;far-field measurement|
The advance of the nanotechnology and bio-measurement highlight the importance of the measurement within the scale of subwavelength. Thus, several scanning probe microscope methods or near-field measurements have been developed to achieve high spatial resolution. In the past, the extraction of subwavelength information from far-field measurement was generally believed to be very difficult or perhaps impossible. However, the recently experimental result of Selci and Righini demonstrated that to detect subwavelength information in the far-field is possible and fully consistent with the prediction of the standard scalar diffraction theory. The result highlighted the possibility of measuring optical signals in the far field with sufficient sensitivity to show variations of diffraction structure in subwavelength scale. We believe that the far-field optical measurement was provided as a potential approach to have high-precision measure of subwavelength-scale dynamical variation of structure, accompanying the advantages of less damage on sample and facility in realization. Thus in this thesis, we investigate the possibility and approaches to retrieve subwavelength-scale dynamical variation from the measurement of far-field optical characteristics. The thesis provides some preliminary discussions on retrieving subwavelength-scale variation by far-field characteristics. (1) An approach to retrieve 1-D subwavelength feature variation from far-field irradiance measurement was proposed and was numerically verified which could have precision better than 1 nm. (2) A tunable asymmetrical embedded-aperture interferometer configuration was proposed, which could enhance detection sensitivity of 1-D subwavelength variation measurement at arbitrary aperture width. (3) A multi-detector, embedded-aperture interferometer configuration accompanies blind signal separation method was proposed could recover coupled 2-D subwavelength variation information of a rectangular aperture with far-field irradiance measurement with error ratio below 1%. (4) By using the approach to retrieve 1-D subwavelength variation from far-field irradiance measurement, a constructed-aperture measurement system behaving as an optical ruler was proposed, which could measure the marginal roughness of the test sample with error ratio below 3%. From the discussions in this thesis, we demonstrated that the far-field optical measurement was provided as a potential approach to have high-precision measure of subwavelength-scale dynamical variation of structure. To explore to test sample with realistic structures and to do more engineering applications are important issues which should be investigated in the future.
|Appears in Collections:||Thesis|
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