Study On CN Radical Spectra Based On LIBS

Laser induced breakdown spectroscopy(LIBS)is an established analytical atomic emission spectroscopic technique.In LIBS,a high-power pulsed laser is focused on the surface of a sample,then melts,vaporizes,excites,and ionizes a small amount on the surface of the sample to form a plasma.The atoms and molecules in the plasma are in excited states,consequently the particles will jump down and radiate radiation of a specific wavelength.The emission spectrum of the sample is collected,photo-electrically converted and dispersed through a spectrometer.According to the finger-print lines of different atoms or/and molecules and corresponding intensities,the ingredients and their concentrations contained in the sample are determined.In this thesis,the spectra of CN radicals are recorded and analyzed based on LIBS technology.The main contents are listed as follows:(1)Based on the principle of LIBS,a LIBS system for CN radicals was established for deriving the emission spectra of plasma.The high-power laser beam interacts with the sample to generate the plasma that expands,diffuses outward,and then radiates the spectrum outward.Radiation spectrum includes continuous spectrum,separate spectrum and energy band spectrum.The continuous spectrum,at first,appears and gradually weakens,while the separate spectrum and the band spectrum appear simultaneously and gradually increase.In order to improve the signal-to-noise ratio of the spectral signal,continuous spectra should be avoided during acquiring spectra.The LIBS detection system detecting CN radical consists of a laser light source system,a timing control system and a signal acquisition system.The laser light source system includes a Q-switched pulse laser,an aperture,and a focusing lens.The timing control system includes a time delayer and a personal computer.The signal acquisition system includes an acquisition lens,optical fiber,spectrometer and CCD.(2)The CN radicals was produced by ablating graphite.Firstly,the influence of laser energy on the plasma spectrum was discussed.Under the condition that other experimental parameters remain unchanged,the laser energy value was adjusted solely from 30 mJ to 50 mJ,and the increase was 5mJ each time.Then,the influence of the focal distance under the sample surface on the spectral signal intensity and signal-to-noise ratio was studied.The results show that the optimal distance between the optimal laser focus and the sample surface is 8 mm.Finally,the vibration temperature and rotation temperature at different distances were calculated by LIFBASE software at experiment condition that delay time,laser energy and distance between the optimal laser focus and the sample surface are 1 us,50 mJ and 8 mm respectively.