Optical properties aperture diffraction

The choice of wavelength depends on the optical properties of the substrate material such as absorption and reflection characteristics and on the minimum structure size to be achieved. Since short wavelengths are diffracted less than longer wavelengths, optical beam delivery systems can have greater resolution that allows smaller lateral feature sizes to be machined. Theoretically, minimal feature sizes down to the minimum achievable focal spot (about twice the laser wavelength X) or the optical diffraction limit k/(2-NA) are possible (NA numerical aperture of the optical system). 

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