All Optical Calibration-free Approach For Quantitative Analysis Of D/H Isotope Ratio

Laser Induced Breakdown Spectrometry(LIBS)and Laser Ablation Molecular Isotopic Spectrometry(LAMIS)have been proved to be powerful tools to provide real time,in-situ and analyte-preparation-free advantages to qualitative and quantitative analysis in various fields.In coordinate with Partial Least Square Regression(PLSR),LIBS and LAMIS improve the quantitative performance for determination of isotope abundance in different states of many substances.However,when they are applied to optical isotopic analysis of the deuterium to hydrogen ratio in enriched water samples in ambient air at atmospheric pressure,the problems involving the features of filament-emission,the standard sample for calibration,and the sensitivity of predicted model,deserves detailed investigation.This work introduces some background information including the research development,chemical quantitative theory,atom and molecular spectra,and the characteristic of femtosecond laser induced filament.Two aspects of this study are discussed.First,we construct PLSR calibration model to predict deuterium abundance(f_D)from H_α/D_αatom lines through LIBS.Second,a series of synthesized OH spectra withf_Dconcentrations from1%to 90%are used to establish the database for PLSR calibration matrix.Moreover,this improved PLSR is calibration free(PLSR-CF).We demonstrate that H_α/D_α atom lines induced from femtosecond laser filament can reach a pretty narrow width(50 pm)through proper detection set up.Stark broadening dominates H_α/D_αlines broadening.Four methods are provided to predictf_Dfrom 0.5%to20%:(1)spectral deconvolution algorithm(SDA);(2)partial least square regression-internal validation(PLSR-IV);(3)partial least square regression-cross validation(PLSR-CV);and(4)partial least square regression-calibration free(PLSR-CF).The result shows that the forth approach PLSR-CF with smaller REP and RSD values provides better performance in qualification.The A~2Σ~+-X~2Π system’s(0-0)belt of OH molecule involves many detailed structures(R11 R22),beneficial to distinguish isotope characteristic.The work extracts isotope component from OD/OH molecular spectra through a homemade fingerprints database constructed by simulating a series of experimental OD/OH molecular spectra withf_Dvalues of 1%-90%and a step size of 10%.The time resolution information of(0-0)belt intensity,rotational temperature and electronic density induced from the interaction between femtosecond laser filament and OH/OD molecular spectrum are take into account-which are useful to clarity molecular formation mechanisms and for explaining the reason of better quantitative performance using PLSR-CF.Molecular broadening is lower than 30 pm for all delay times.Moreover,for delay time from 0.75μs to 3μs,there is a satisfied PLSR-CF calibration curve correlating each unknownf_Dconcentration from experimental sample set to that of synthetic sample set.