High-efficiency Optical Parametric Amplification as a Laser Source Applied to Deep-tissue Multiphoton Microscopy
Date Issued
2014
Date
2014
Author(s)
Kan, Che-Wei
Abstract
Since Hooke first used optical microscope to observe the plate cells in 1665, optical microscope has been widely applied to biomedical image. Convention optical microscope doesn’t provide optical sectioning which makes it fail to recognize signals from the depth of signals. Later in 1957, Marvin Lee Minsky displayed the confocal fluorescence microscope which has optical section. However, as we know from the theory of scattering, the shorter wavelength is, the stronger scattering will be, the penetration depth is highly related to wavelength. Generally, visible light is the source of confocal fluorescence microscopy, which restricts its penetration depth 100 μm. On the contrary, multiphoton microscopy usually uses infrared light as its source and thus has higher penetration depth because it has longer wavelength and lower scattering. Besides, the whole process is nonlinear, which means the signal power increases nonlinearly by source intensity. Only signal from focus spot is enough for detecting. Therefore, multiphoton microscopy also has optical section. From previous perspective, my core question is that whether we can get unlimited high penetration depth by lengthening the wavelength. Take biological sample into consideration, which mainly contains water. Water strongly absorb EM-wave of wavelength near 1.4 μm, which is unsuitable for biomedical imaging. In order to lengthen the wavelength as much as possible and avoid the absorption of water, light between 1.3~1.4 μm would be very suitable for deep-tissue imaging.
People often use Ti: sapphire laser with optical parametric oscillator (Ti:sa + OPO), Supercontinuum generation laser (SC) and Cr: forsterite to generate 1.3~1.4 μm laser source. Ti:sa + OPO has ultrashort pulse which is often shorter than 100 fs and its peak wavelength can be fast tuned. But its output power is limited and oscillator is complex setup. SC usually uses photonic crystal fiber to generate. Its advantage is that spectrum is very broad, which is from ultraviolet to infrared. However, because it is broadband laser, its spectral power is low, usually ___. And the dispersion of fiber causes long pulse, which is not suitable for multiphoton microscopy. Cr:forsterite can achieve high output power, but its oscillator makes setup complex and less robust. How can we achieve easily single pass and high output power laser source with 1.3~1.4 μm wavelength? The aforementioned lasers all have some defects, which don’t fit our requirement.
Our experiment succeeds in creating optical parametric generation/amplification record. We generate the pulse laser, whose output power is over 1 W, quantum efficiency (the number of the output photons/the number of the input photons) achieves 60% at high repetition rate, wavelength 1.3~1.4 μm and pulsewidth 1 ps. Besides, using 1.36 μm as source, which we generate, of multiphoton microscopy is success getting the second harmonic generation bulk image of the type 1 collagen. To compare the image with 1 μm as source obviously, 1.36 μm as source can get deeper image. It proved 1.36 μm is more suitable for deep-tissue multiphoton microscopy.
Subjects
超快雷射
可調頻率光源
光參數放大
週期性極化反轉鈮酸鋰
多光子光學顯微術
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-103-R01245008-1.pdf
Size
23.54 KB
Format
Adobe PDF
Checksum
(MD5):3cf40c95563dcad77583420d0c6895f4