|
|
1.INTRODUCTIONThe course Laser Principles and Technology is an integrated curriculum for undergraduates, related with multiple basic subjects such as quantum mechanics, statistical physics, electromagnetic field theory, physical optics and applied optics. The purpose of this course is basically to answer the following questions: how does the laser generate; why laser has high brightness, small divergence angle and high coherence; how to increase the laser intensity, compress the pulse width, change the frequency, et al.. The main contents of this course include the interaction of light with materials, the emission line width and broadening, the laser cavities modes, the propagation of the Gaussian beams, the Q-switching and mode locking techniques, etc.. In order to help the students understand the abstract physical concepts and to integrate the theory with the engineering practice, we developed a virtual simulation experiment platform/software, namely Laser V-Lab 1.0, to provide virtual simulation experiments about the key knowledge in this course. The main GUI and the module structure of the software Laser V-Lab 1.0 are shown in Fig. 1. The software contains three main modules (laser generating, laser propagation and laser controlling), which can be subdivided into the following eight secondary modules:
Each of the above mentioned modules has its own interface where the user can specify and modify the input and output parameters. 2.SIMULATION EXAMPLEThe figure 2 shows the interface of the Laser Output Characteristics Module. We take Nd3+: YAG as an example to illustrate its transient output characteristics and to explain the relaxation oscillation process. The rate equations[12, 13] is given in the top left corner of the interface (Fig.2) and also in Eqs.1. The physical meaning of the parameters are as following[12, 13]:
The calculation result can also be saved as JPG files as Fig.3 and Fig.4, which illustrated the evolution of the photon density in the laser cavity and the population inversion density of the gain medium on time scale, respectively. We can see from Fig.3 that the photon density oscillated intensively in the beginning 0.2ms and then turned to be stable in the next 0.1ms. This reveals the transition from the relaxation oscillation to stable state under the continuous pumping. The population inversion density of the gain medium oscillated around its threshold and trended to be stable at its threshold after 0.2ms. In most teaching material about the course laser principles, the output characteristics of the laser is analyzed based on analytical calculation under the following two conditions: a) short pulse pumping, i.e. the pumping pulse width tp << the lifetime of the upper laser level of the gain medium tg; and b) long pulse pumping or continuous pumping, i.e. tp ≫ tg. As for the relaxation oscillation state, the time dependent perturbation theory is often used to give approximation solutions of the rate equations. These calculation results have the limitations that they cannot be very accurate compared with the real laser system. The calculation accuracy can be obviously improved with numerical method. The parameters such as the pumping rate, the cavity loss, the population inversion density of different laser medium, can be specified or modified by the user to see their influences on the output behavior of the laser. These simulations in this module of our software can help students better understand the free oscillation laser in the actual engineering application. 3.CONCLUSIONSBy using this virtual simulation experiment software Laser V-Lab, students can have more intuitive understanding of the structures and the functions of the laser device, as well as better comprehension about the concepts and the variables in the physical formulas of the course. The virtual experiment can be a necessary complement to curricular study and can play an important role to encourage the students’ creativity. At present, the simulation modules in this software are aimed at the curriculum of Laser Principles and Techniques. The upgraded software will further increase its interactivity with the user, improve the animation effect, and add some new functional modules such as to analyze the thermal effect in the gain medium, to analyze the beam quality, to add more types of laser medium, etc.. ACKNOWLEDGEMENTSThis work was supported by the teaching reform projects for undergraduates of the University of Electronic Science and Technology of China (Project Number: 2017XJYJ-ZD12). REFERENCESGhani B. A., Abbas B., Sheikh-Khalil M.,
“Mathematical modeling of the intracavity Q-switched Nd-glass laser,”
Optics and Laser Technology, 37
(2), 117
–124
(2005). https://doi.org/10.1016/j.optlastec.2004.02.021 Google Scholar
Song F., Yao J. Q., Zhou D. W.,
“Rate-equation theory and experimental research on dual-wavelength operation of a Ti: sapphire laser,”
Applied Physics B-Lasers and Optics, 72
(5), 605
–610
(2001). https://doi.org/10.1007/s003400100541 Google Scholar
Soukieh M., Ghani B. A., Hammadi M.,
“Numerical calculations of intracavity dye Q-switched ruby laser,”
Optics and Lasers in Engineering, 41
(1), 177
–187
(2004). https://doi.org/10.1016/S0143-8166(02)00149-5 Google Scholar
Zou H., Zhou L. F., Yang Z.,
“Simulation study on transverse mode of laser resonator,”
in Proc. SPIE,
(2015). Google Scholar
Morin M., Belanger P. A.,
“Diffractive analysis of annular resonators,”
Applied Optics, 31
(12), 1942
–1947
(1992). https://doi.org/10.1364/AO.31.001942 Google Scholar
Asoubar D., Zhang S., Kuhn M.,
“Laser resonator modeling by field tracing: a flexible approach for fully vectorial transversal eigenmode calculation,”
Journal of the Optical Society of America B-Optical Physics, 33
(11), 2565
–2573
(2014). https://doi.org/10.1364/JOSAB.31.002565 Google Scholar
Su Binghua, Xue Junwen, Sun Lu,
“Generalised ABCD matrix treatment for laser resonators and beam propagation,”
Optics and Laser Technology, 43
(7), 1318
–1320
(2011). https://doi.org/10.1016/j.optlastec.2011.03.031 Google Scholar
Shao Jing, Liang Xiaojun, Kumar Shiva,
“Comparison of split-step Fourier schemes for simulating fiber optic communication systems,”
IEEE Photonics Journal, 6
(4), 7200515
(2014). Google Scholar
Cambronero-Lopez F., Gomez-Varela A. I., Bao-Varela C.,
“Designing an ultrafast laser virtual laboratory using MATLAB GUIDE,”
European Journal of Physics, 38
(3), 034006
(2017). https://doi.org/10.1088/1361-6404/aa5a93 Google Scholar
Li Q., Feng B., Zhang D.,
“Numerical solution and experiment of a self-Q-switched 946 nm Cr, Nd:YAG laser,”
Applied Physics B-Laser and Optics”, 93
(2-3), 421
–427
(2008). https://doi.org/10.1007/s00340-008-3226-9 Google Scholar
Li Kun, Zhang Bin,
“Analysis of broadband third harmonic generation with non-collinear angular dispersion in KDP crystals,”
Optics Communications, 281
(8), 2271
–2278
(2008). https://doi.org/10.1016/j.optcom.2007.12.014 Google Scholar
Zhao Jia, Zhao Shengzhi, Li Kang,
“Optimization of passively Q-switched and mode-locked laser with Cr4+:YAG saturable absorber,”
Optics Communications, 284
(6), 1648
–1651
(2011). https://doi.org/10.1016/j.optcom.2010.11.054 Google Scholar
Dong J., Deng P. Z.,
“Laser performance of monolithic Cr, Nd: YAG self-Q-switched laser,”
Optics Communications, 220 425
–431
(2003). https://doi.org/10.1016/S0030-4018(03)01450-0 Google Scholar
|
