Optical Nonlinear Frequency Conversion Based On External Cavity Enhancement And Efficient Narrow Linewidth Terahertz Wave Generation

THz-wave,which locates in the transition region of the spectrum,is not only used in basic subject as physics,chemistry and biology,but also used in medical science,military field,communications and so on.The THz radiation source based on external cavity enhancement via difference frequency generation technique which can produce high power,tunable coherent THz wave has obvious advantages of compactness,simplicity for tuning,operation at room temperature and so on.Supported by NSFC project 2?m fiber laser pumped narrow linewidth m W-level CW THz source,we research each technical part of the external cavity enhancement DFG-THz source,including 2?m fiber laser MOPA system,structure study of external cavity enhancement,and THz wave-guide research.The main contents of this dissertation are as follows:1.Introduce THz wave,concluding the generation method,characteristics and applications of THz wave,summarize the research progress of cavity enhanced DFG THz source,introduce the phase matching technique;2.Derivate the wave-equation of nonlinear optical interactions.Simulate the LBO crystal I class SHG process,and work out the best effective nonlinear coefficient is 2.64×10-12m/V when the ? is 90° and ? is 11°.The walk-off angle of slow light and fast light are 0 and 0.38°,respectively,and the interaction angle between the energy flux density is 0.27°.3.Explore the structure stable condition of external cavity enhancement,derivate the pattern matching and impedance matching condition,calculate the enhancement factor under CW or pulse pump.According to the fineness of cavity,we can get dozens of even hundreds of times enhancement.4.Text the high performance dual-wavelength 2?m DFG THz pumps,the power is 7.5W after the second pre-amplification,with a linewidth of 75.1k Hz and RIN of-110 d B/Hz.5.Introduce a THz crystal fiber converter.This axisymmetric structure consists of periodically inversed Ga As core cladded with index-matched chalcogenide glass.The output power,spectral power density,and brightness are analyzed.