Research On External Cavity Enhanced Laser And Waveguide Grating In Terahertz Region

THz wave,which locates in the transition region of the microwave and the far infrared spectrum,can be applied in many different areas such as military,communication,and medicine.Supported by NSFC project called “2?m fiber laser pumped narrow linewidth m W-level CW THz source”,we design and set up the external cavity enhancement.Take the double frequency I of LBO for example,we get the enhancement factor of 3.9 and achieve about 90 m W of the double frequency output power with the incident light at 3W.At the same time,we design a waveguide grating in THz range based on surface Plasmon effect,and simulate the propagation of the surface wave with the finite-difference-time-domain(FDTD)method.The main contents of the dissertation are as follows:1.Introduce the properties of the THz wave,expound electronic and optic methods which are two means of generating THz wave,and summarize the research progress of cavity enhanced DFG THz source.2.Introduce the concept of the cavity enhancement,and focus the research of four-mirror ring cavity.We analysis the stability condition,mode matching,impedance matching which must be taken into account in the design of the cavity.We import the concept of stable cavity,analysis three methods of extracting the error signal in initiative cavity stable,and describe their theory respectively.At last,we realize feedback regulation of the cavity's length by the output signal which is from the action of(PID)automatic control system and the error signal.3.Take the double frequency I of LBO at 1064 nm for example,we verify the enhancement of the four-mirror ring cavity.Mainly includes the detection and correction of incident light's polarization,choice of the cavity's length,the construction of the cavity and the stability of the cavity length by Lase Lock.4.In order to overcome the diffraction limit of the photonic device and realize the subwavelength regulation,we introduce the surface Plasmon and simulate the propagation of the THz wave with the FDTD.By designing the waveguide-grating,we can control the propagation distance of the THz wave through changing the construction and temperature of the grating.