the modulated illumination module is configured to obtain vortex light with different fractional orders through modulation using vortex phase patterns with different fractional orders, so as to scan the to-be-measured sample, wherein the vortex light with different fractional orders irradiates the to-be-measured sample and is reflected out; the to-be-measured sample is fixed on the XYZ translation stage, and the XYZ translation stage is configured to drive the to-be-measured sample to move within a field of view of the modulated illumination module; and

the signal collection and demodulation module is configured to: collect reflected light after the vortex light with different fractional orders irradiates the to-be-measured sample, and generate dark-field images, wherein the signal collection and demodulation module generates one dark-field image for the vortex light with any fractional order; and perform cross-correlation processing on the dark-field images generated under the vortex light with different fractional orders, to obtain high-signal-to-noise ratio (SNR) data;

wherein the modulated illumination module comprises: a laser, a two-dimensional (2D) optical diffraction element, a turntable, and a beam expander; the 2D optical diffraction element is etched with a plurality of vortex phase patterns with different fractional orders in a circular arrangement; the laser is configured to emit laser light; the 2D optical diffraction element is configured to modulate the laser light using the vortex phase pattern with any fractional order, to produce vortex light of a corresponding fractional order; the turntable is configured to rotate the 2D optical diffraction element, to enable the 2D optical diffraction element to modulate the laser light using the vortex phase patterns with different fractional orders; and the beam expander is configured to expand and output the vortex light.