| The electromagnetic spectrum of terahertz(THz)wave is located between millimeter wave and infrared wave,with a frequency range of 0.1 THz to 10THz.Compared with them,THz wave has many unique properties and has broad application prospects in the fields of safety inspection and substance detection,However,for a long time,the development of terahertz application technology has been restricted due to the low output power,large size,and high cost of the terahertz source.In recent years,with the development of semiconductor energy band engineering and nanostructure processing technology,terahertz quantum cascade laser(THz-QCL)came into being.Compared with other lasers in the terahertz band,THz-QCL has high power,small size,and stable operation,which lays the foundation for the wide application of the terahertz band.The detection of terahertz wave in the application of the existing terahertz band mainly relies on various types of detectors.The accuracy and sensitivity of the detector are greatly affected by conditions such as temperature and humidity,which not only increases the error of signal detection,but also increased the application cost.In the optical path of self-mixing interference effect,the laser is both a radiation source and a detector,which reduces the error caused by the detector,the experimental cost and optical path complexity are also greatly reduced.Compared with other lasers,THz-QCL has picosecond carrier relaxation time and smaller linewidth enhancement factor,which makes its dynamic characteristics more stable under optical feedback,so it is more suitable for laser self-mixing interference effects.Based on the self-mixing interference effect,this paper carried out the related research of THz-QCL in detection.The main work is as follows:(1)The spectrum of THz-QCL under different driving currents was measured using the self-mixing interference effect.The experimental results show that as the current increases,the frequency of THz-QCL decreases,which is consistent with the theory.When the drive current is increased to 0.7A,the working mode of the laser is changed from single mode to multimode,and the mode spacing is 2GHz,which is consistent with the calculation results.In order to verify the accuracy of the measurement results,an error analysis of the experimental data was performed using a self-built simulation model.The analysis results show that the laser frequency error measured by this method is at the MHz level,compared with the 1.5 GHz spectral resolution of the experimental system,which has less impact on the results.(2)A speed measurement experiment based on THz-QCL self-mixing interference effect is designed.In this experiment,the movement speeds of single target and multi-target were measured respectively,the experimental results show that the method has less error in speed measurement,and the faster the object movement speed,the higher the accuracy,when the moving speed of the object is 30mm/s,the error is only 0.008%.For multi-target movement,not only can accurately measure its speed of movement,but also can determine the relative movement direction between objects from the signal.(3)A two-dimensional imaging system was designed using THz-QCL self-mixing technology.Using this system,a dime coin was partially scanned and imaged point by point,and a clear image with pixels of 100pix × 100pix and pixel pitch of 100 was obtained.Experimental results show that the imaging technology based on the THz-QCL self-mixing interference effect can achieve high-resolution imaging of objects.Compared with the previous terahertz imaging system,the imaging system has lower optical path complexity and higher collimation.Finally,this paper summarizes the problems that need to be further solved in the application of THz-QCL self-mixing interference. |
PDF Full Text Request