Research On Laser Parameter Measurement Technology Based On Beam Reduced Array Fibers

Evaluating and quantifying the characteristics and quality of laser beams is a fundamental research topic in the fields of laser measurement and control,laser transmission,laser communication,laser processing and laser lighting.The method to achieve quantification is measuring laser parameters,and various measurement technologies have a long history of development.At present,relevant research mainly focuses on the high-resolution and wide incidence angle measurement of high-power beams with large cross-section.This project aims to design a laser parameter measurement system based on reduced beam array fibers for this application requirement.This project uses array fibers to sample and reduce the entire beam spot,and the reduced beam spot is detected with high resolution by a charge coupled device(CCD)camera.Compared with traditional CCD imaging methods,the technology breaks through measurable beam cross-sectional area and measurable power through technologies such as beam reduction detection and sampling attenuation.Compared with the array photoelectric detection method,the technology improves the resolution of spot distribution measurement through high-resolution fiber sampling and camera imaging.In addition,the technology relies on fiber optic low loss total reflection transmission,providing a wide allowable range of incident angles for the measurement system.The innovation of this technology is mainly reflected in the design of spot sampling and detection systems with performance advantages,the analysis of technical issues such as optical fiber numerical aperture(NA)mismatch,and the development of spot restoration algorithms such as crosstalk correction and Smear effect denoising.The main research contents of this paper are followed:(1)To improve the performance of laser parameter measurement,a sampling and detection system of the spot composed by beam reduced array fibers,diffuse transmissive material and CCD camera is designed.The technical problems such as allowable bending,NA mismatch and divergence angle difference when using bent array fibers are mainly analyzed.And the diffuse transmissive material is used to eliminate the measurement error caused by divergence angle difference.Also,the CCD camera is used to photograph the face of the diffuse transmissive material with a lens to obtain a high-resolution image.This integrated system has 900 sampling units totally(30 X 30)and achieves a sampling resolution of 4 mm.The size of the receiving surface is 116 mm;the measurable peak power density is greater than 1000 W/cm2;the allowable incidence angle range is-20°～20°;and the measurable wavelength range is 380～1100 nm.(2)According to the original image taken by the system,this paper designs a series of targeted restoration algorithms,which achieve the spot location and extraction,correct the crosstalk caused by diffuse transmission material,and improve the resolution of spot visualization by interpolation.The restored spot has 639 pixel × 639 pixel,and the pixel size is 180 μm.The diameter measurement error caused by restoration technology is not more than 5%.In addition,in the shooting application of low quantum efficiency(QE)and low exposure time,the smear effect often occurs,resulting in the failure of providing effective M2 factor and other laser parameter from the captured image.Based on this,the paper proposes a innovative pre-calibration fitting method,and finally realizes the effective measurement of M2 factor with an error of less than 3%.(3)To verify the accuracy of the laser parameter measurement technology,the calibration experiment and performance test have been carried out after the system integration.For the laser beams of 532 nm,670 nm and 1064 nm,the unit response difference of the system is less than 1%after calibration;the fitting goodness of the power coefficient is higher than 0.9900;the maximum error of diameter measurement is about 6%,and the maximum error of M2 factor measurement is about 9%.When the incident angle changes from-20° to 20°,the error of total power measurement is less than 15%,and the error of diameter measurement is less than 6%.Compared with other measurement methods,this technology has comprehensive improvement in many performance indicators such as measurable wavelength,power,section size,resolution and allowable incidence angle.The measurement results have been verified to be reliable and effective.This technology is expected to take effect in the laser atmospheric transmission measurement and the design analysis of laser resource.And the relevant research and analysis are expected to provide reference value for the fields of fiber coupling,CCD camera detection and spot denoising.