Research On Pump-probe Setup And Melting Based On Mid-infrared Quantum Cascade Lasers

Melting is a thermodynamic phase transition from order to disorder,and it has important applications in the field of material science.Because of its influence factors and the complicated mechanism of internal transformation,melting has always been a focus of the scientific research.The mid-infrared quantum cascade laser is a new type of semiconductor lasers,with outstanding properties such as wide tuning,narrow linewidth,high power and polarization sensitivity.It provides a possibility for high resolution online study.A pump-probe setup based on two mid-infrared quantum cascade lasers is designed to study melting,the pump beam corresponds to a strong absorption peak to induce crystal melting by resonant heating,the probe beam corresponds to the conformation absorption peak of the sample to reflect the structure change.The pump-probe setup can achieve nanoseconds resolution,both beams can reflect the melting degree of the sample as the detection light,so as to realize online tracking structure change.Isotactic polybutylene-1(iPB-1)spherulites were used as experimental samples,according to the principle of infrared dichroism,it was proved that resonance heating and melting engraving are feasible on the spherocrystal scale.This method provides a new research method for on-line study of the rapid melting process,and provides ideas for the regulation of crystal transformation and crystal morphology in the fixed state.Using 4-cyano-4-n-heptylbiphenyl as an experimental sample,according to the different infrared absorption frequencies of each group of molecules,using the characteristics of the narrow line width of the quantum cascade laser and the time-resolved characteristics of the optical path,the fixed-point resonance heating of the radical on the molecular scale is realized.It provides new experimental means for material modification and the microscopic study of melting.The experimental light path provides a new means and method for the study of the melting process.It also greatly improves the time resolution of the infrared spectrum and extends the application of quantum cascade lasers.