When it comes to diffractive optics, rest assured they are not magic. They are just another tool to be used in designing an optical system. They would do various kinds of things that refractive optics cannot. They would be relatively lightweight and smaller than the equivalent refractive optic.
It would be imperative to remember that several benefits have been associated with a diffractive optical element or DOE. Rest assured that the benefits would not come free of charge. The DOEs would come with limitations as well. It would be difficult to produce the desired results under specific conditions. If you were looking forward to producing a circular laser beam having a uniform intensity profile, you would be required to undergo the below-mentioned options.
- A majority of laser sources would produce a roughly Gaussian beam. It would help you expand the beam heavily with a refractive expander. You would mask everything, but the center of the beam. It would help you provide a uniform beam, but it wastes a lot of light.
- You could make the most complicated refractive design inclusive of the micro-lens array. It would be relatively difficult to engineer. Moreover, it would not offer you perfect results. However, it could do a decently good job under numerous conditions. The beam intensity could be made uniform over a large distance. The input beam would not be required to be parallel with the microlens array. It would also work across a broad range of wavelengths.
- You could also design the DOE beam shaper by giving any intensity profile. However, it would cost a fortune. It could entail a few flaws of DOEs. Despite it being a highly sensitive error in the input beam wavelength, it would only be producing the desired intensity profile over a short distance.
Similar to any tool made available to a lens designer, the DOEs would have their uses. They would offer a strong negative dispersion useful for correct chromatic aberration. It could be designed for producing arbitrary illumination patterns that would be highly difficult to produce with purely refractive optics.
When you come across a Fresnel lens with smaller features, it would be important for you to understand that a Fresnel lens would be a diffractive optic. When the diffraction is deep, it would appear that all lenses have been deemed as diffractive optics. While the phase profile of the DOE could be engineered for producing complicated optical fields, you could design the one for producing a simple focal point. It would be pertinent to mention here that the resulting design would be a simple lens.