Precision Backscattering Coefficient Measurement Of Mirrors Based On Ring Cavity Femtosecond Ti:sapphire Laser

Laser gyro is a kind of ring-cavity laser based on Sagnac effect measurement principle,which is the core device of inertial navigation system.It has several advantages such as strong anti-interference ability,large dynamic range,fast start-up and high precision.However,the lock-in effect introduced by the backscattering of the mirrors in the ring laser gyro seriously affects the measuring precision of the laser gyro.Therefore,it is necessary to precisely measure the backscattering coefficient of mirrors to improve the performance of the laser gyro.Due to the non-uniformity of reflectance of the mirror surface and the difficulty of technical of detecting the weak scattering light,a great challenge is brought to the measurement of the backscattering of the laser gyro mirror.The traditional method for measuring the backscattering coefficient of mirrors is the bidirectional reflection distribution function(BRDF).The main feature of this method is to obtain the backscattering coefficient by directly collecting the light intensity of backscattering,but its measurement accuracy is limited by the solid angle and the precision of backscattering acquisition instrument.In this paper,a scheme of measuring the backscattering coefficient of the mirrors using a ring-cavity femtosecond Ti:sapphire laser is proposed,and the backscattering coefficient is obtained by measuring the beat note by introducing the lock-in effect of the mirror under testing.This method is not limited by the scattering detection technique and can greatly improve the measurement accuracy of the backscattering coefficient of the mirrors.The ring-cavity Ti:sapphire laser and the backscattering measurement technique of mirrors is studied in this paper revolved on precise measurement of the backscattering of mirrors in a laser gyro.The main study is shown as follows:1.The principle and the physical mechanism of the ring laser gyro are introduced.The lock-in effect in laser gyro is expounded and the source of lock-in effect both with its solution are analyzed.Based on the principle of laser gyro,the influence of the backscattering intensity of the mirror on the size of the lock-in region of the laser gyro is derived from the coupling theory and the scattering theory.A method of measuring the backscattering coefficient of the mirror with mode-locked ring-cavity Ti:sapphire laser is proposed with a detailed measurement scheme.2.The stability condition of the resonator cavity is derived,and the Kerr-lens mode-locked ring-cavity Ti:sapphire laser is designed and constructed.The 400 mW and 49 fs bidirectional Kerr lens-mode-locked pulses are obtained.The operation and the condition of unidirectional/bidirectional mode-locked are analyzed.The laser gyro effect is realized in the ring resonator cavity,which can effectively overcome the lock-in effect and greatly reduce the lock-in region of the laser gyro.3.The liquid dye passively mode-locked ring-cavity Ti:sapphire laser is constructed to avoid the production of the error as lock-in effect introduced by Ti:sapphire crystal in Kerr-lens mode-locked ring-cavity laser,to achieve a more precise backscattering coefficient measurement by using liquid dye as a saturable absorber,eliminates the phase coupling between the pulses propagating in the opposite direction.500 mw,11 ps bidirectional passively mode-locking pulses are obtained,and the feasibility of laser gyro of zero lock-in region is confirmed by experiment.4.An experimental system for measuring the backscattering coefficient of the mirror is designed,and general framework of the experimental apparatus to measure backscattering of the mirrors is completed.At the same time,the frequency shift technology of ring-cavity Ti:sapphire laser is studied theoretically,and the source and the generation of laser gyroscope initial beat note are introduced.At last,a detailed research scheme is given for how to measure the backscattering coefficient of the mirror,and the stability of the experimental system is improved by optimizing the dye circulation system and slowing down the air flow,which can further improve the measurement accuracy of the backscattering coefficient of the mirrors.