The origin of self-focusing effect in terahertz quantum cascade lasers

3rd International Conference on Mathematical Modeling in Physical Sciences

物理学;数学

Wang, Jian^1 ; Li, Yanfang^2 ; Yang, Ning^2

Department of Physics, Beijing Jiaotong University, Beijing

100044, China^1

Institute of Applied Physics and Computational Mathematics, PO Box 8009(28), Beijing

100088, China^2

关键词: Far field divergence;    Intersubband transitions;    Kerr lensing;    Refractive index changes;    Self focusing effect;    Self-focusing;    Terahertz quantum-cascade lasers;    Third-order non-linearity;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/574/1/012053/pdf
DOI  :  10.1088/1742-6596/574/1/012053

来源: IOP

【 摘 要 】

The terahertz quantum cascade lasers (THz-QCLs) are the compact and coherent terahertz light sources based on the inter-subband transition and resonant tunneling of carriers in semiconductor superlattice. In recent studies on tapered THz-QCLs, it was found that the self-focusing effect in the active region of the devices may cause the abnormal increase of the far-field divergence of the laser beam. By simulating the propagation of optical mode in QCL waveguide and considering both the nonlinearity effect and thermal accumulation in the active region, we propose that the refractive index change caused by the third-order nonlinearity of multi-quantum-wells in active region may be the key reason for the self-focusing in THz-QCLs. This result indicates that the nonlinear effect may have great impact on the beam quality of QCLs which must be carefully considered in applications of THz-QCLs, such as the TH- imaging systems.