Numerical Aperture (NA) is a dimensionless number that characterizes the range of angles over which a system can accept or emit light. It is a critical parameter in optical systems such as microscopes and lithography tools used in nanotechnology. The formula for NA is given by: NA = n * sin(θ) where n is the refractive index of the medium between the lens and the object, and θ is the half-angle of the maximum cone of light that can enter or exit the lens.
