Fig. 4: Experimental broadband differential imaging results of amplitude objects.

a The first- to fourth-order differential imaging results of the U-shaped and circular objects at the wavelength of 633 nm. Scale bars: 20 μm. b The first- to fourth-order differential imaging results of the circular object at the wavelengths of 580, 532, and 490 nm, respectively. Scale bars: 20 μm.