Optical Design And Image Quality Evaluation Of Small Echelle Spectrograph In LIBS

Laser induced breakdown spectroscopy(LIBS)is widely used in the detection ofsoil heavy metal as a new kind of atomic spectroscopy,it has many advantages,such as rapid and multi-element simultaneous measurement and in situ detection.As the core element of the LIBS system,the performance of the echelle spectrometer determines the detection limit and detection precision of LIBS.In this paper,with the application of LIBS in soil heavy metal detection,a small,wide-band range,high-resolution echelle spectrometer was designed.The optical design of the spectrometer was realized with zemax software,the image quality of the spectrometer was evaluated,and the prototype of the echelle spectrometer was completed.The main contents of this paper are as follows:1.Based on the basic theory of the echelle spectrometer,the principle and characteristics of the echelle are analyzed.The system composition of the echelle spectrometer is introduced.The characteristics of the echelle spectrometer which are different from the grating spectrometer are analyzed.2.In this paper,the optical design method of the echelle spectrometer is mainly studied,which is studied from the design of the optical path and the relation of the component parameters.The optical path design which combines the Littrow optical path and the Czerny-Turener optical path is proposed.A relationship model between the optical element parameters and the spectral range and spectral resolution of the spectrometer is established,and a relationship of optical components size is defined.On the basis of these relationship and optical path design,an example of echelle spectrometer is designed.3.In order to have a great spectral resolution in the wide spectral range,the aberration of the echelle spectrometer is studied,and the correction methods of spherical aberration,coma and astigmatism are proposed respectively.An optimized design of echelle spectrometer is proposed to eliminate the aberration influence.The method of image quality evaluation is used to evaluate the imaging quality of the echelle spectrometer from three aspects: wavelength plot,aberration characteristic curve and energy distribution curve.4.Through the design of the optical element holder and the overall design of the echelle spectrometer,the prototype of the echelle spectrometer was developed.The Hg standard light source was used as the test light source to carry on the experiment,the image of spectrum was analyzed and the performance of the prototype was evaluated.The experimental results showed that the spectral resolution of the echelle spectrometer is 0.1 nm in the spectral range of 200 ~ 600 nm,which meets the design requirements.