基于频域辐射传输模型的光学成像研究

Optical Imaging Based on Frequency-Domain Radiative Transfer Model

本文以超短脉冲激光照射参与性介质的光学成像为研究背景,分别构建了短脉冲激光在参与性介质内的频域辐射传输正问题模型和根据边界探测所得频域信号重建介质内部光学参数的逆问题模型。在瞬态辐射传输方程的基础上,利用傅里叶变换得到频域辐射传输方程,采用有限体积法求解频域传输方程,模拟超短脉冲激光在二维参与性介质内传输的过程,得到介质边界的出射频域辐射信号。选取共轭梯度法作为反演算法,采用伴随差分模型求解目标函数梯度,重建了二维非均匀参与性介质内不同位置内含物的光学参数分布。结果表明,基于频域辐射传输方程的伴随差分模型能够较为准确地反演多维参与性介质内的光学参数。

This study focuses on the optical imaging of the participating media exposed to ultrashort pulse laser.The forward model of simulating the radiative transfer in the media exposed to frequency-modulated pulse laser and the inverse model of retrieving the internal optical parameters of the media based on the detected boundary frequency information are developed,respectively.Based on the transient radiative transfer equation(RTE),the RTE in frequency domain was deduced by the Fourier Transform.The finite volume method was used to solve the frequency domain RTE.The transmission process of ultrashort pulse laser in the participating media was simulated.The transmitted radiation signals on the edge of the media were obtained.The conjugate gradient method was selected as the inversion algorithm,and the adjoint differentiation method was applied to solve the gradient of the objective function.The optical parameters of the two-dimensional inhomogeneous media with non-uniform distributed inclusions were reconstructed.The retrieval results show that the adjoint differentiation models based on RTE in frequency domain can reconstruct the optical parameters of the multi-dimensional participating media accurately.