非线性自聚焦介质中光束的非傍轴传输

在标量近似下,将非傍轴项近似等效为四阶空间色散和五阶非线性效应,利用变分法研究了高斯光束的传输特性。结果表明,在非傍轴情形下,高斯光束不会崩塌,而是经历聚焦 -散焦的周期性传输过程;光束初始功率越高,则周期越小。此外,高斯光束的自聚焦过程可以通过改变啁啾参数来控制,正负啁啾分别使光束第一次聚焦的距离缩短和延长,但两者都使光束的聚焦 -散焦的周期增大,而且啁啾值越大,周期也越大

Non-paraxial Propagation of Optical Beams in Nonlinear Self-focusing Media

A non-paraxial equation for nonlinear optical propagation in the scalar approximation is derived. As a first-order correction, it is shown that the nonparaxiality can be expressed with a fourth-order spatial dispersion and fifth-order nonlinearity. By using variational approach to the modified nonlinear equation the propagation properties of Gaussian beams are obtained. It is found that the beam propagates stably with a focusing-defocusing cycle, and the beam with a higher power has a smaller cycle. It is also shown that the self-focusing process can be controlled by changing the chirp parameters. The positive (negative) chirp reduces (increases) the initial self-focusing length and both chirps increase the focusing-defocusing cycle.