Research On Absolute Length Measurement Towards Multilateration Based On The Temporal Cross-correlation Using Femtosecond Pulses

Multilateration based on the high-precision,traceable,flexible and effective spatial length measurement has become the trend for spatial positioning network with the advantages of self-calibration,self-adaptation,and self-compensation.In general,in a semi-open industrial environment with a scale of a few meters to several tens of meters,the random environmental disturbances are caused by the flow of personnel and staff during the measurement process.There is an urgent need for novel absolute length measurement with high dynamic measurement performance,strong adaptability,and multi-length monitoring abilities.The temporal cross-correlation method with the femtosecond pulse laser combines the advantages of the time-of-flight method and the fringe interferometric method.The large-scale,high-resolution,and high-precision absolute distance measurement could be achieved by utilizing the pulse repetition intervals as a traceable space ruler.Focusing on the demands of large-scale multilateration and absolute length measurement with temporal cross-correlation method using a femtosecond pulse laser,the establishment of a mathematical model for temporal coherence,the optimization method for pulse-to-pulse alignment,the elimination of measurement dead-zone,the compensation of refractive index of air,and the multi-target absolute length measurement are studied and verified by experiments.The main research content of the dissertation is introduced as follows:1.A temporal cross-correlation model of chirp broadening pulses in an unbalanced dispersive interferometer was established and simulated.An optimized pulse-to-pulse alignment method is proposed for practical application,the fringe analysis,envelope extraction and measurement efficiency are discussed in detail by theoretical experiments.Furthermore,experimental verification was performed in a femtosecond pulse interferometer with a length difference of about 12 m,and a measurement experiment with an absolute length of about 9 m was designed and completed.2.The reasons that lead to the dead zones in measurement are analyzed in detail and the conventional strategies for eliminating dead zones were summarized.Combining with the temporal cross-correlation method,two novel methods for eliminating dead zones were proposed and studied: a dynamic cavity tuning method that introduces a long-fiber delay line stabilized by a high-frequency optoelectronic oscillator,and a frequency-modulated continuous-wave method that combines precision calibration of an auxiliary interferometer.3.By comparing the sensor network for conventional compensation of refractive index of air and the two-color interferometry for online compensation of refractive index of air,the bottlenecks hindering the application of two-color interferometry were further analyzed.To solve the influence of geometric errors,the fiber components for combination harmonic laser beams were proposed,and the coupling efficiency,polarization characteristic,wave-front characteristic and coherence characteristic of the two-color emitting beams are demonstrated experimentally.Finally,the general length measurement with spatial targets was summarized.Multiple targets length measurement using the temporal cross-correlation method with a diffractive optical element were designed and presented.Meanwhile,the beam detection process is analyzed,and the repeatability and linear accuracy of the absolute distance measurement is evaluated.The application potential of this method is verified by constructing a simple multilateral positioning network and locating the initial point of beam splitting.