Title: Professor
Tel: 13520398457
Department: Optical Physics
E-mail: liusir@bit.edu.cn
Address: 747 Central Teaching Building, No.5 Zhongguancun South Street, Beijing Zip Code 100081

Laser substance identification, interaction between laser and energetic materials, New detection photoelectric technology

1995-1999, Changchun Institute of Optics and Machinery, Laser, Bachelor Degree
2000-2003, Changchun Institute of Optics and Machinery, Nonlinear Optics, Master
2002-2003 National Astronomical Observatories LAMOST Project Team Project Research
2003-2007, Ph.D., Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences

2009-present, Professor and doctoral supervisor, School of Physics, Beijing Institute of Technology;
2013-2013 Visit by Michael Farle Group, University of Duisburg, Germany;
2008-2009 Visiting Scholar and co-supervisor Ning Cunzheng, Department of Electronic Engineering, Arizona State University, USA;
2007-2008, National NanoCenter Short-term Research

In recent years, in the applied physics research, we have focused on the industrialization application and national defense application research based on laser spectroscopy and photoelectric sensing technology, and successively realized the industrialization application and national defense application of the high-precision all-element detection spectrum system. The laser spectrum system for rapid detection of coal quality has been applied in batches in the coal power field. The small dose performance diagnostic spectroscopy technique for rapid evaluation of macro parameters of energetic materials has been used for rapid quantitative analysis of parameters and sensitivity of various traditional and new energetic materials. He has presided over more than 10 projects such as the National Natural Science Foundation, the key research and development program of the Ministry of Science and Technology, and national defense projects. In Nature Comm., Adv. Opt. Mater., Photonics Research, J. Anal. At. Spectrom., Optics Express, Nature Comm., adv. Opt. Mater., Photonics Research, J. Anal. At. Spectrom., Optics Express, He has published more than 120 articles in top optical and spectroscopy journals such as Optics Letter, with a total of more than 3100 citations, and applied for nearly 20 authorized invention patents, H-factor 31.
Masterpiece
[1] Ruibin Liu* et al. Sensitivities determination of energetic materials based on entire laser-induced plasma spectra. J. Anal. At. Spectrom., 2021,36 (12): 2603-2611
[2]Ruibin Liu* et al. Determination of detonation characteristics by laser induced plasma spectra and micro-explosion dynamics. Optics Express, 2022, 30(4): 4718-4736.
[3] Ruibin Liu*et al.Fast explosive performance prediction via small-dose energetic materials based on time-resolved imaging combined with machine learning,J. Materials Chemistry A 2022, 10, 13114
[4]Ruibin Liu*et al. Accuracy enhancement of laser induced breakdown spectroscopy by safely low-power discharge. Opt. Express 2018, 26(11): 13973-139784.
[5] Ruibin Liu* et al. Accuracy enhancement of laser induced breakdown spectra using permittivity and size optimized plasma confinement rings. Opt. Express 2017, 25:27559-27569.
Highlights Work
Energetic materials are important supporting materials for national economic development and national security, and the accurate measurement of explosive performance and safety performance is the basis of its application, and has very important significance for the rational application, formulation design, storage and transportation of energetic materials. The traditional energetic material performance test relies on the national military standard method, which requires the consumption of 100-kilogram energetic materials to carry out macro real explosion measurement, which is high risk and destructive, affected by the quality of the charge, test conditions, low diagnostic accuracy, repetition is difficult, and some new energetic materials are limited by the output can not complete the test. Rapid and high-precision detection technology based on small amount of drug has always been an important technology in this field. Therefore, for the detonation performance diagnosis, safety performance evaluation and detonation reaction process research of energetic materials, it is important to provide a rapid analysis principle and method with high safety, small sample consumption, simple operation, low cost and high reliability.
In response to the above technical requirements, the research group of Precision Spectroscopy and Optoelectronics Technology, based on more than 10 years of research experience in the direction of laser substance identification and quantitative analysis, took the lead in putting forward the new concept of "a new physical idea of simulating macroscopic detonation with pulsed laser acting on the plasma microdetonation process of micrograms of energetic materials" and "microdetonation simulator" in 2017. On the basis of exploring the physical theory of the interaction between laser and energetic materials, the research group has created a new principle and a new method for predicting the key performance parameters and sensitivity parameters of energetic materials based on the statistical spectroscopy model of laser microburst technology and physical parameter modification. It includes the following four aspects:
Test system construction: The physical system for testing the properties of energetic materials with small dosage was independently built, and the micro-ultrafast time-resolved spectrum and high-speed dynamic flow field microscopic imaging system were integrated. The comprehensive detection of the laser induced cross-scale microdetonation process covering nanosecond to millisecond ultrafast time scale, micrometer to centimeter micromesoscopic scale of the laser induced reaction region was carried out, and multi-dimensional optical information such as time-resolved characteristic atomic, molecular and ion spectra, laser loading dynamic images, and micro-dedetonation process were effectively obtained.
Physical mechanism exploration: The microphysical mechanism of the interaction between laser and energetic materials, as well as the related evolutionary mechanism of ultrafine plasma process and microdetonation dynamic physico-chemical process were clarified, and the strong correlation physical characteristics of laser microdetonation process and macroscopic detonation were proved, and the dynamic physical model of microdetonation was proposed, as shown in Figure 1. Therefore, through the precise physical measurement and analysis of the microdetonation process, the quantitative analysis of the detonation velocity, detonation pressure, enthalpy of formation and the prediction of detonation temperature of energetic materials can be completed. The results are published in the top optical journal Optics Express (Opt.Express, 2022, 30(4): 4718-4736.)

FIG. 1. Schematic diagram of the dynamic process of microexplosion
Rapid detection of five-burst parameters: In the study of the evolution process of high-speed flow field of micro-explosion, the research group found that there are great differences in the flow mechanical evolution form of micro-explosive plume and the space-time distribution of radiation particles in different kinds of energetic materials, as shown in Figure 2. The plasma lifetime of high-energy energetic materials is shorter and the shock wave velocity is faster, while the plasma lifetime of low-energy energetic materials is longer and the shock wave velocity is slower. The difference of plume radiation between high energy and low energy materials is mainly due to C2 molecular fragments.
At the same time, it is found in the study that during the plume expansion and plasma cooling process, the temperature corresponding to the vibrational Boltzmann distribution does not decrease all the time, but is briefly constant under a specific time delay, as shown in Figure 3. This is due to the additional heat released by the exothermic physico-chemical reaction of the energetic material compensating for the continuous decay of the plasma temperature. Therefore, taking high-speed dynamic images acquired under a specific delay as input data, combined with feature extraction and linear SVR algorithm, a machine learning model based on time-resolved images and spectra was established for quantitative analysis of five detonation parameters (detonation velocity, detonation heat, detonation capacity, detonation pressure, detonation temperature) of energetic materials, and then a high-precision prediction of detonation performance of 27 energetic materials was completed. The average prediction error of the prediction model is less than 5%, as shown in Figure 4. This work provides a new principle, new method and new idea for the rapid testing of detonation properties of energetic materials with low cost, high precision, high safety and high throughput. Compared with the traditional macroscopic testing methods with high cost, high risk and low repetition accuracy, it has significant advantages. The results were published in the international journal J Materials Chemistry A (2022, 10, 13114-13123).

Figure 2. Evolution image of high-speed flow field: (b) Evolution image of laser-induced shock wave; (c) Image of laser-induced plasma evolution
Figure 3. Time-resolved spectral results: (a) The spectral intensity of traditional high-energy energetic materials evolves with time; (b) Evolution of the spectral intensity of energetic azole materials with time; (c) Comparison of molecular peak test and simulation diagram; d) Boltzmann plan; (e) Evolution of vibration temperature of traditional high-energy energetic materials with time; (f) Evolution of vibration temperature of energetic azole materials with time
Figure 4. (left) Model prediction diagram: (a) detonation velocity; (b) explosive heat; (c) Explosive capacity; (d) detonation pressure; (e) Burst temperature (right) Random blind test results
Four sensitivity tests: The sensitivity of an energetic material is determined by the inherent properties of its molecules and crystals, such as molecular geometry, electronic structure, elemental composition, reactivity (reaction activation energy, molecular decomposition rate constant, reaction reversibility), molecular packing mode, band structure, crystal structure, lattice size and defect, and crystal equality. It is very important to study and establish the quantitative relationship between sensitivity and the above parameters on micromesoscopic scale. However, until now, the quantitative relationship between sensitivity and molecular and crystal structure has been unclear. All the key information about the molecular and crystalline properties mentioned above can be well reflected in the time-resolved laser-loaded plasma spectra.
The pulsed laser is focused to the micrometer range of the sample surface, and the laser plasma is generated at the focal point, which provides a local high temperature and high pressure environment for the decomposition of energetic materials. In high temperature plasma sparks, accompanied by strong exothermic chemical reactions, atoms, ions, electrons, molecular fragments and some free radicals collide with each other, as shown in Figure 2 (a). The release of energy in chemical reactions requires the participation of electrons, which greatly affects the cooling and recombination process of electrons. The dissociation degree and dissociation rate of energetic materials of different molecular and crystal types are related to the sensitivity. Plasma temperature and electron density can be given by the spectral line intensity. Studies show that electron density is correlated with impact sensitivity, plasma temperature and friction sensitivity to a certain extent (FIG. 5 (b-c)). Therefore, the sensitivity of energetic materials can be evaluated by the effective total radiation spectrum of laser-induced plasma. Combined with the characteristic spectrum of plasma and statistical algorithm, the sensitivity prediction model of impact, friction, static electricity and laser can be well established, and the average relative error of the prediction model is less than 10%. The results were published as a back cover article in the Journal of Analytical Atomic Spectrometry (2021, 36, 2603), the highest level academic journal in the field of atomic spectrometry.
Figure 5. Correlation analysis of laser plasma and sensitivity: (a) Sensitivity prediction mechanism based on laser plasma spectrum; (b) Correlation graph between electron density and impact sensitivity; (c) Correlation diagram of plasma temperature and friction sensitivity;
Figure 6. Prediction model based on PCA-PLS: (a) shock sensitivity, (b) friction sensitivity, (c) static inductance and (d) laser sensitivity
In short, the breakthrough of the rapid detection technology for the performance of small energetic materials has realized the rapid detection method with fast trace safety and low cost, and expanded the performance evaluation of energetic materials from the traditional macro scope to the micro scope, providing key technologies for the research and development of energetic materials, quality control and process safety. The method will also be applied to civil fields such as coal, metallurgy and electric power.