Signal Processing Method For Nanometer Displacement Measurement Based On Circularly Polairzed Laser Interferometry

Nano-measurements are an important branch of nanometer science, and is the basis ofdiscovering new phenomena and creating new technology in nanometer scale. With the rapiddevelopment of microelectronic technology and ultra-precision machining technology, therequirements of greater range and higher precision are put forward for the correspondingnano-measurement equipments.In this thesis, the principle of laser circularly polarized light interference is described,nanometer displacement measurement system based on circularly polarized laser interference isdesigned, laser circularly polarized light interference nanometer displacement measuring methodbased on FPGA+DSP architecture is proposed, meanwhile, a kind of processing method of sineand cosine interference signal switching fractional interference fringe. The pretreatment circuit isdesigned specific; the influence of temperature drifting on the measurement accuracy is reduced;the programmable logic device FPGA is adopt to realize data acquisition and number counting ofthe measurement signal and communication with PC; DSP microprocessor was used to realizethe decimal calculation; the measuring software based Visual Basic language is designed; asystem of laser circular polarization interference of nanometer displacement measurement isfinally designed and constructed.In order to verify the feasibility of laser circularly polarized interference nanometerdisplacement measurement system and nanometer displacement measurement method proposedby this thesis, in the thesis, the experiment on the nanometer displacement measurement andmicron displacement measurement can be carried on by adopt the data processing way combineddual integral count with two different fractional counts, and the measured results are comparedwith the data provided by PI flexure-hinge stage-P-752.1CD. In the experiment of nanometerdisplacement measurement, including the displacement step is30nm,100nm and350nmrespectively, meanwhile, the displacement step is1μm in the experiment of micron displacementmeasurement. The results are obtained by the data processing way combined dual integral countwith tangent fractional count: the average error is-0.5489nm,-1.2555nm,-0.3584nm,-0.7927nmrespectively; the standard deviation is3.2522nm,3.3656nm,4.9000nm,5.3344nm respectively.The results are obtainedby the data processing way combined dual integral count with sine and cosine switching fractional count: the average error is-0.2537nm，-1.5454nm，-1.9908nm，-0.5912nm respectively; the standard deviation is1.8778nm，1.8806nm，1.4486nm，2.9610nmrespectively. The verification results show that two kinds of different calculation methods bothcan carry out higher precision nanometer displacement measurement, however, the resultsobtained by sine andcosine switching fractional count are relatively more accurate and morestable.