Fresnel diffraction is derived from the Huygens-Fresnel principle, where the complex amplitude at a point (P) on the observation screen is given by the Fresnel-Kirchhoff integral: [ U(P) = \frac{e^{ikr}}{i \lambda r} \iint_{\text{aperture}} U_0(x',y') e^{i k \frac{(x-x')^2 + (y-y')^2}{2r}} dx' dy' ] Here, (U_0(x',y')) is the amplitude at the aperture, (r) is the distance from the aperture point ((x',y')) to the observation point ((x,y)), (k = 2\pi/\lambda) is the wave number, and (\lambda) is the wavelength. The quadratic phase term (\exp\big[i k \frac{(x-x')^2 + (y-y')^2}{2r}\big]) accounts for the curvature of the wavefront. In Fresnel diffraction, the wavefront curvature cannot be neglected, so the quadratic term is retained. This occurs when the distance between the aperture and screen is finite and comparable to the aperture size. A