近場光學顯微術及其應用之研究

Abstract

本論文中,將以如何建立近場光學顯微鏡系統及其應用為主要的研究重點,對於近場光學顯微鏡系統部份,將注重於探針的製造,探針與樣品相對距離之控制,系統校正,及系統操作o 關於探針的製造,我們提出二種新的製作探針方法,這二種方法皆用標準的通訊光纖為材料,做成的探針有二個斜角的形狀(two tapered shape),因此探針具有高光穿透率(約為10-4),而其空間解析能力約為250奈米o 關於探針與樣品相對距離之控制,本實驗室提出一種新穎的非光電式技術 我們將探針膠封在音叉的一支腳上,以切斷的弦波訊號(gated sinusoidal signal)驅動此音叉,配合分時多工技巧(time multiplexing technique),使得探針-樣品相對距離能夠控制o 我們自製的近場光學顯微鏡系統,具有50微米的橫向掃描範圍,及10微米縱向位移量,三軸皆用光干涉儀校正之,系統的操作程式建立於DOS作業系統上,以拉下視窗方式做為人機介面o 關於應用的部分,我們用上述系統研究: (1) 2微米多苯乙烯球(polystyrene sphere)的光學特性,(2)光從單模光纖輸出時,由進近場到遠場傳播的行為,以及(3)垂直面射型半導體雷射的橫模分佈o

Two chemical etching techniques have been developed for fabricating scanning near-field optical microscopy (SNOM) probes. These probes have two tapered regions that can be reproducibly constructed with a wide range of cone angles. Our methods can be applied to commercial silica glass fibers. The demonstrated in-plane resolution was estimated to be about 250 nm which is mainly limited by the diameter of the metal-coated tip. The transmission efficiency is better than 10-4. We propose and demonstrate a novel non-optical technique for regulation of tip-sample distance in a near-field scanning optical microscope (NSOM). The fiber tip for the NSOM is attached to one prong of a quartz tuning fork. The fork is dithered with a gated sinusoidal signal. The vibration of the freely oscillating fiber tip, which manifests as the induced piezoelectric voltage on the fork electrodes, is monitored during the half-period of the gated sinusoid for which the fork is not driven. The time-multiplexing scheme thus allows the tuning fork to serve as a dither and a sensor with high Q-factor simultaneously. The gating technique could also potentially allow the SNOM be used for the investigation of surface relaxation dynamics with high spatial resolution and sub-millisecond time resolution. We design and calibrate the tube scanner of our home-made NSOM with the lateral deflection about 50mm (in x, y direction), and the longitudinal displacement (in z direction ) is about 10mm. The control program of our NSOM system was developed successfully. This program is based on DOS system. In order to characterize the image-taking capability of our NSOM, we acquire near-field optical images of a compact mono-layer of polystyrene spheres with a diameter of 2 mm as example. We have also investigated the characteristics of some optical components by using NSOM, such as single-mode optical fiber, and vertical-cavity surface-emitting laser diode (VCSEL).