利用全像光學鑷夾三維操控微粒子之研究

Abstract

全像光學鑷夾(holographic optical tweezers HOTs)是一套利用空間光調變器(spatial light modulator SLM)控制光學鑷夾中捕捉光場性質的系統。只要顯示所需的相位圖樣於SLM上，即可同時操控多個微粒子。但HOTs的操作需要用到許多不同領域的知識，如富氏光學、電腦全像片演算法、程式語言與數值方法，研究者需要同時具備這些知識才能將HOTs當成工具用於自己的研究上，因此限制了HOTs的應用。因此在本論文中我們發展了兩種方法來擴展HOTs操控微粒子能力。 一種是發展控制光場橫向動量(或散射力)的方法，讓粒子在一個固定相位圖樣所產生的光場下，自行沿著設定的路徑移動，而無需其他外力。我們利用幾何光學分析HOTs中光場的橫向動量分布，發現只要將相位圖樣顯示在SLM上的某個方位角區域中，HOTs所產生的光場橫向動量的方向是由該方位角區域的中心角度決定，而橫向動量的大小是正比於入射光的功率、光場強度分布與sin(Δt/2)，其中Δt是方位角區域的範圍大小。我們利用此方法產生的具有橫向動量分布的光場，讓微粒子自行沿著設計好的路徑移動與控制粒子局部濃度。 另一種方式是建立一套整合即時樣品影像之示、使用者輸入資訊之接收與捕捉光點之控制的圖形式使用者介面。使用者只需在樣品即時影像上，以滑鼠游標指定捕捉點位置，即可輕鬆地捕捉、搬運與旋轉粒子。讓一般不具備相關知識的人也可以輕鬆容易地使用HOTs操控粒子

Holographic optical tweezers (HOTs) use a spatial light modulator (SLM) to control properties of a light field in optical tweezers. By displaying a hologram on the SLM, many particles can be manipulated at the same time. However, the operation of HOTs requires knowledge of different fields, such as Fourier optics, algorithms of computer-generated holograms, programming languages and numerical methods. Only the people who have all the knowledge can use HOTs as a tool for their own research. This limits the application of HOTs in other fields. This thesis thus developed two different approaches to expand the ability of HOTs in manipulating particles. One is developing a method of controlling the transverse momentum (TM) by displaying a hologram only in an azimuth region that centers at t0 and has a range of Δt of a spatial light modulator in HOTs. Ray optics is utilized to analyze the TM of the resultant field, revealing that the direction of the TM is determined by the center angle of the azimuth region and that the magnitude of the TM is proportional to sin (Δt/2), without regarding the intensity. By using this method, particles can move automatically along a designed path in the field without applying any external forces or changing holograms. The other is developing a graphic user interface that integrates the functions of displaying live sample image, receiving user input and computing required holograms in one program. Users simply use a mouse to click or drag on the live sample image to manipulate particles. People who do not have any related knowledge can use HOTs to manipulate particles easily.