High-precision Measurement Of Terahertz Frequency Based On Terahertz Frequency Comb

Along with recent progress in THz technology,the requirements of THz metrology have increased in various applications.Frequency is one of the most important quantities to be measured because it is a fundamental physical quantity of electromagnetic wave.Frequency comb refers to a spectrum which insists of a series of uniform and coherent frequency components in frequency domain.It is a useful tool in frequency metrology.In the optical band,femtosecond optical frequency comb has been applied to optical frequency measurement,and it has high accuracy and stability.Then the Japanese researchers promoted the concept of frequency comb to the terahertz frequency domain.The study found that this method had high measurement accuracy,so frequency comb would play an important role in the field of terahertz frequency metrology.In this paper,we introduce the basic principles of optical frequency comb in the optical band frequency measurement in the second chapter.The femtosecond optical frequency comb based on mode-locker laser is a laser source which can emit trains of pulses with stable repetition rate,and the spectrum of the pulse consists of a comb optical frequency with equal spacing.But when we try to produce terahertz comb,the carrier envelope frequency has been already offset.In the third chapter,the system of locking terahertz frequency comb system is introduced in the article,and based on LabVIEW we program a VI which is prepared for the frequency counter Agilent53132A to collect frequency data.In the fourth chapter,we use the stable terahertz comb system to measure a THz source.In the end,we obtain the result with accuracy in the order of 4.7×10^-13.Then we find the main factors which affect the signal to noise ratio of beat frequency.In the fifth chapter,a method for terahertz frequency measurement by using an unstabilized femtosecond laser is introduced.Terahertz frequency can be calculated from the data with accuracy in the order of 10^-10.Compared to the method by using a stabilized femtosecond laser,the system is greatly simplified.