Large-scale Absolute Distance Measurement Based On Fiber Femtosecond Comb-excited Two-photon Absorption

As one of the research hotspots in the field of optical precision measurement,length measurement is of great significance to the development of many scientific research experiments and advanced manufacturing industries,such as distance measurement between large aircraft parts,calibration of precision machine tools,precision measurement of microelectronic plate production,etc.The technology based on femtosecond optical frequency comb is a new optical detection technology and the measurement of absolute distance can be realized by obtaining the phase,frequency,spectrum and other parameters of femtosecond laser.Femtosecond optical frequency comb has the advantages of high reliability,high measurement accuracy and noncontact.With the rapid development of measurement field in China,real-time absolute distance measurement with large size,high precision and high stability has become the main direction of scientific research in measurement field.The advantages of ultra-fast femtosecond laser and realize real-time range measurement can be fully exploited by optical autocorrelation method.Therefore,it is of great application value to study the autocorrelation absolute technology based on optical frequency comb of optical fiber femtosecond.This article will focus on the above research work,as follows:Firstly,the characteristics of femtosecond optical comb and its development and research status are described.systematically.This paper analyzes the characteristics of silicon biphoton absorption,construct mathematical model stimulating silicon biphoton absorption,establish theoretical model of absolute distance measurements based on optical autocorrelations,and show that the optical autocorrelation function generated by two photon absorption can be used for absolute distance measurements.Secondly,this paper propose an optical autocorrelation waveform generation based on two-photon absorption by femtosecond laser excitation.The silicon photodetector is introduced to the autocorrelation measurement system and uses the nonlinear effect of the silicon photodetector.The measurement system based on the Michelson interferometer structure is built,and the experimental results show that the autocorrelation wave form of the pulse can be effectively obtained by scanning the reference arm in the interferometer and accurately measuring the femtosecond laser pulse width..In addition,Furthermore,this paper designs an absolute distance measurement system based on optical autocorrelation methods,detects the change of nonequilibrium Michaelson interference pulse time delay using two-way structures,and produces autocorrelation signals based on the two-photon absorption properties of silicon photodetectors.The modified edlen formula for refractive index is modified to analyze the system uncertainty.The experimental results show that the silicon two-photon absorption characteristics can replace the nonlinear crystals in the conventional femtosecond laser ranging system,simplify the experimental measurement structure,and measure the absolute distance in real time,and obtain the measurement accuracy of sub-micrometers,and the system has good stability.