一、引 言 介质吸收光子时,部分激发能由无辐射跃迁产生热.周期性变化的单色激励光束由光学加热区表面吸收使之变热,引起周期性的温度变化,并使介质折射率相应地改变,在邻近介质表面的区域形成折射率逐点变化的梯度场,这种现象称为“幻影”效应[1].当用另一光束探测时,变化的折 I. INTRODUCTION When a medium absorbs photons, part of the excitation energy can generate heat from the non-radiative transition. The periodically changing monochromatic excitation light beam is absorbed by the surface of the optical heating zone to make it become hot, causing periodic temperature changes and corresponding to the refractive index of the medium Change, forming a gradient field with a point-by-point index of refraction in the area adjacent to the surface of the medium, a phenomenon known as the “ghost effect.” 1 When the probe is detected with another beam, the changing fold