利用週期性極化反轉鈮酸鋰產生1.3微米到1.8微米調頻脈衝雷射光源

Abstract

生物材料因為軟物質的混濁性及複雜結構的光學散射，共軛焦螢光顯微鏡顯微鏡，光學穿透深度難以超過100微米，使得光學影像難以看到100微米以下的組織結構。根據散射理論，光波長越長散射強度越小，降低散射強度則可以提高穿透深度。因此，雙光子螢光顯微鏡與二倍頻顯微鏡基於兩倍的激發頻率而可以超過500微米、甚至達到1釐米的深度。所以紅外光的生物影像是有必要研究的。在材料方面，須選擇特定波長才能激發各種生物材料或染劑的螢光，使得螢光顯微術難以比較出該材料中，散射效應最小的波長。另一方面，二倍頻顯微術可以選擇任意波長做為激發光源，只要入射光波長遠離材料的吸收帶。在我們的實驗中，我們希望建立紅外光波段的多組紅外光光源。因此，我們利用光參數產生的方法，可以在極化反轉鈮酸鋰中取得紅外雷射光源，其擁有可調頻率的光譜、高光強度、超短脈衝的特性。在我們的系統裡，產生出來的調頻光源功率在1315至1650奈米的波至少都有60毫瓦，最高超過1瓦，十分適合做為二倍頻顯微術的光源。結合光參數產生與二倍頻顯微術，我們可以建立出特定生物材料的光譜性影像，進而找出該材料最佳穿透深度的波長。

In bio-materials, confocal fluorescence(CF) microscopy reaching penetration depth over 100μm is difficult because of turbidity of soft-material and scattering of complex structure. Based on scattering theory, the longer wavelength, the lower scattering effect. We can increase penetration depth by using larger wavelength with less scattering. Because of double frequency of excitation, two-photon fluorescence (2PF) microscopy and second harmonic generation (SHG) microscopy can observe more deeper than 500 μm, even to reach 1 mm . Therefore, a bio-imaging system combined with an infrared (IR) source is required. However, only special wavelength can excite to fluorescence of bio-materials or stains, IR sources are not commonly applied to fluorescence microscopy. On the other hand, for imaging, SHG microscopy is free on excitation wavelength selection as far away resonance frequency. In our experiment, we expect to generate multi-frequencies laser source in IR. By optical parametric generation (OPG), we easily generate IR laser source on periodically poled lithium niobate (PPLN), which is tunable frequency, high intensity and ultrafast pulse duration. Commonly, in our system, the power of the tunable source is at least 60 mW from 1315 nm to 1650 nm, and the highest is over 1 W. The tunable IR source properly apply to SHG microscopy. Combined OPG with SHG microscopy, we can achieve spectral imaging.