Design And Implementation Of Digital Pulse Delay System For LIBS Detector

LIBS detection technology has the advantages of convenience,simplicity and real-time performance,and is widely used in the field of material analysis and detection.The pulsed laser is used to ablate the material to generate a plasma signal.The spectrometer collects the plasma signal generated after ablation and performs spectral analysis to analyze the elemental characteristics of the material.When the LIBS detector works at different acquisition delay times,it has a great influence on the collection of plasma signals.Different acquisition delay times will affect the intensity of the spectrum and the signal-to-noise ratio.In view of the above factors,this paper designs a digital pulse delay system applied to LIBS detector,which delays the acquisition of laser-induced plasma to the spectral acquisition period.The research content is mainly divided into the following aspects :Firstly,the working principle of LIBS is analyzed,the formation process and influencing factors of plasma signal are described in detail,and the composition and intensity of plasma signal under different acquisition delay time are analyzed.The principle,advantages and disadvantages of the existing pulse delay technology are analyzed and compared.The pulse delay scheme adopted in this design is confirmed.CARRY4 is used to construct the carry chain,and the pulse output scheme of coarse delay combined with fine delay is adopted.Secondly,the overall scheme of the system is designed,including hardware circuit part and software logic part.Using ZYNQ as the core processor of the system,the hardware part of the plasma photoelectric detection amplifier circuit,waveform shaping circuit,pulse width measurement circuit,LCD human-computer interaction module;the software part includes the construction of CARRY4 carry chain,IODELAY cascade,TDC-GPX2 register configuration,LCD logic function typing and communication with PS terminal,which realizes serial port transmission and USB communication.Finally,the performance of each part of the circuit in the hardware is tested.The oscilloscope is used to observe the waveform output of each part of the circuit,and the delay experiment is carried out on the overall debugging of the pulse delay system.The analysis is applied in the LIBS detector to analyze the influence of acquisition delay on spectral line intensity and signal-to-noise ratio.The experimental results show that the digital pulse delay system designed in this paper can be used in LIBS detector,and can meet the delay range of 0～ 4.294 seconds,and can achieve accurate delay of any ns level.