To deal with the case of 2 dimension spatial self - focusing , it predicts the catastrophic collapse of a self - focusing beam in a kerr medium . this un - physical collapse is due to the invalidity of the paraxial wave equation in the neighborhood of a self - focus 在該理論應(yīng)用于空間二維的自聚焦時(shí),出現(xiàn)了光束將無限聚焦的結(jié)果,這在物理上是不可想像的,原因是在自聚焦點(diǎn)附近傍軸方程已經(jīng)失效了。