Phase Diversity (PD) is a kind of wavefront sensing technology based on image collecting and restoration. Two images
with different defocus are collected, and the Zernike coefficients of the system wavefront can be solved. In order to expand the traditional PD method from monochromatic light illumination to broadband light illumination condition, this
paper focuses on the improvement of PD method. When there is broadband light illumination, the strategy of wavelength
sampling is applied. Furthermore, when the width of spectrum is small, the monochromatic light assumption is proposed. The Structural Similarity (SSIM) is also selected to evaluate the quality of restored images. Results show that when the interval of wavelength sampling is less than 50nm, the residual errors of calculation are less than 0.02λ (RMS), and the
images similarities are better than 0.96. Also, when the width of spectrum is less than 30nm, the monochromatic light
assumption is carried out well. The residual errors of calculation are also less than 0.02λ (RMS), and the images
similarities are better than 0.9.