利用遠場特徵回溯次波長尺度變化及提升其量測靈敏度之探討

Abstract

由於奈米科技、生醫檢測諸多領域的蓬勃發展，次波長尺度的量測也愈見其重要性。有鑑於此，許多高空間解析度的探針掃描或近場的量測方法陸續被開發出來。以往，在遠場量測次波長尺度的資訊被視作困難或不可行。然而在Selci等前人的工作中，實驗發現在遠場仍可觀測到物體在次波長尺度變化下相應的光學特徵變化，並滿足純量光學理論的預測。其結果隱含著在遠場利用光學方式去量測物體的次波長尺度動態變化的潛力。基於遠場的光學量測方式具有易於觀測，且不易傷害待測物的優點，因此本論文探討了利用遠場的光學特徵去回溯出待測物的次波長尺度動態變化的可行性及其測量方式。

本論文對利用遠場的光學特徵去回溯出待測物的次波長尺度變化作了下列的初步探討：（一）提出利用遠場輻照度的變化，去回推物體作一維次波長尺度變化的算則，其精準度可到一個奈米的等級。（二）提出一外加孔徑干涉儀的架構，可對任意待測孔徑寬度優化其遠場量測到的輻照度變化量值，而可提高其一維次波長尺度動態變化的測量靈敏度。（三）提出利用未知訊號分離的手法，利用多光偵測器及外加孔徑干涉儀的架構，去回推孔徑兩個維度的次波長尺度動態變化，其精準度可到1%。（四）利用量測遠場輻照度回推孔徑一維次波長尺度動態變化的手法，提出了一個可量測待測物的邊緣平整度誤差低於3%的量測架構。

由本論文的探討，展現了利用遠場光學特徵去回溯物體次波長尺度動態變化的應用潛力。對於利用遠場光學特徵去量測真實的待測結構及其工程上的量測應用將是未來值得被探討的重點課題。

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.