光學非線性特性可應用於許多領域，如多光子螢光、倍頻等已廣泛應用於生醫顯微術，除能 透過訊號的性質來分析生物組織的組成及結構外，又因非線性訊號需極高光強度來激發，在 顯微術上具有極佳的光學切片能力，能應用於厚組織中。為能進一步提升解析度，受激輻射 耗乏顯微術已被應用於雙光子顯微術，藉由受激輻射耗乏來抑制螢光的放光，等效減小被激 發的螢光點擴散函數以提升解析度至高於繞射極限，然而因倍頻的產生不牽涉電子能階躍 遷，無法藉由受激輻射耗乏來抑制倍頻訊號，必須尋求其他途徑。雖然倍頻訊號的產生不牽 涉電子能階躍遷，但過去文獻中已證實，當材料具有符合激發光單光子或多光子能量之吸收 能階時，所產生的倍頻訊號可被增強，利用吸收與倍頻訊號強度正相關之特性，若能抑制材 料的吸收即能達成倍頻訊號的抑制。本計畫擬進行以基態耗乏進行倍頻訊號抑制之研究，藉 由選擇適當的激發光波長及非線性材料，該材料可產生吸收增強的三倍頻訊號，此外，若該 材料同時具有暗能階或三重態能階，則可藉由基態耗乏來抑制材料的吸收，從而達到三倍頻 訊號的抑制，本計畫將透過模擬及實驗兩方面來證實此想法之可行性，並將之應用於顯微影 像系統以達成三倍頻顯微影像解析度之提升。 ;Optical nonlinearity can be applied to various fields. Nonlinearity such as multiphoton fluorescence and harmonic generation has been widely used for biomedical microscopy. Through the properties of the excited signals, the structures and molecular composition of bio-tissues can be revealed. Due to the extremely high intensity required for nonlinear signal excitation, nonlinear microscopy can provide optical sectioning power so that it is suitable for thick-tissue applications. To further improve the resolution, stimulated emission depletion microscopy (STED microscopy) has been applied to two-photon fluorescence microscopy. By suppressing the fluorescence through stimulated emission, the excited fluorescence point spread function (PSF) can be effectively reduced so that the resolution can be increased to higher than diffraction limit. However, because no real state transition is involved in production of harmonic generation signals, the harmonic generation signals cannot be suppressed through stimulated emission. Other ways has to be discovered to achieve the signal suppression. Although the production of harmonic generation signals has no real-state involved, in the previous researches, the harmonic generation signals have been proved to be enhanced through absorption when the materials contain real levels which match the signal-photon or multiphoton absorption. Making use of the positive correlation between absorption and harmonic generation intensity, suppression of the harmonic generation can be achieved by absorption suppression. In this project, research of suppressing harmonic generation signals through ground-state depletion will be carried out. By choosing proper excitation wavelength and nonlinear material, absorption-enhancement third harmonic generation signals should be observed from the materials. In addition, if the material contains dart-state or triplet-state, the absorption of the material can be suppressed through ground-state depletion and the suppression of third harmonic generation can thus be achieved. From simulations and experiments, this project aims to demonstrate this idea and apply this concept to third harmonic generation microscopy to improve the spatial resolution.
