Research On The Generation Of The Stokes Wavelength For All-fiber CARS Laser Source

CARS microscopy is a label-free optical nonlinearity technology. There are many advantages in CARS microscopy including its non-invasive imaging, strong signal strength and three dimensional chromatographic capability, so it has a very good development in the field of life sciences. However, now the most CARS systems made from Ti: Sapphire mode-locking pulse lasers are based on many space optical path. These systems are very versatile and have poor stability. Apart from these, they are very expensive, large and require technical staffs devoted to their constant alignment and maintenance. For this reason the application of CARS microscopy is still limited to a few specialized laboratories world-wide. To overcome these problems, we make a research on the all-fiber CARS laser source. From the picosecond mode-locking pulse seed source, fiber amplification techniques and the non-linear optical interaction in photonic crystal fiber, the major work of the thesis are as follow:(1) A picosecond mode-locking pulse fiber laser is presented with narrow bandwidth and low repetition rates theoretically. There is no dispersion management device in it. The intra-cavity pulse evolution is analyzed through numerical simulations. The influence of the cavity length and the FBG's bandwidth to the mode-locking stability and pulse duration are obtained.(2) Experiments with different cavity length and pump power are carried out. When the cavity is 24.1 meters long, the pulse duration and bandwidth is 86 ps and 0.04 nm. The repetition rate is 4.3MHz and the output power is 3mW.(3) Using high Yb-doped single mode fibers and double-clad Yb-doped fibers, we finish the pre-amplification stage and the main amplification stage. The final output power is 2.34 W and the peak power of the pulse is up to 6kW. The amplified spontaneous emission(ASE) in the gain progress is studied, we can effectively reduce the ASE noise by the forward pumping.(4) we study the four-wave mixing and stimulated Raman interaction phenomena in three photonic crystal fibers. Through the non-linear optical interaction in photonic crystal fiber, we generate the Stokes light for CARS detection. The spectral bandwidth is 3nm. It is able to detect the 400 ~ 800cm-1 molecular vibration theoretically.