Circular Aperture Fresnel Number Calculator

Square the characteristic aperture radius and divide by propagation distance times in-medium wavelength. Geometry conventions differ for slits and other characteristic sizes, so preserve the stated circular-radius definition. It evaluates only the displayed equation and entered SI values; it does not infer material data or experimental conditions. Confirm the convention and inputs against the physical setup before using the result.

The number is a regime indicator; large and small values suggest near- and far-field tendencies rather than a universal sharp boundary. Changing distance or wavelength inversely changes the dimensionless result. Display precision is not measurement accuracy. Check dimensions, scale, limiting cases, and input uncertainty against an independent source before using the value in laboratory, engineering, or safety-sensitive work.

The aperture is represented by one circular radius and scalar monochromatic paraxial diffraction is the intended model. It does not calculate the diffraction pattern, aperture transmission, coherence, polarization, aberration, or exact propagation field. This educational result is not a simulation, calibration, design approval, or safety determination. Real systems may require measured properties, geometry, boundary conditions, uncertainty propagation, and numerical models beyond these inputs.