Diffractive optics and achromaticism

[Beer-monster]

Hi

I've been resarching interference lithography and have read on wikipedia, and some more reputable sources, that if diffractive optics are used to split the beam and/or focus the beam onto the screen (surface) the temperal coherence of the light source is no longer an issue. i.e. the output light is achromatic.

However, I'm not sure I understand why?

Does it have something to do with the diffraction grating acting almost like a prism, dispersing the light so that waves along a specific angle and path are of one frequency and phase?

 

[Andy Resnick]

Can you provide some reference material? I am barely familiar with "grating prisms" (grisms) in spectroscopy and the use of diffractive optical elements to counteract chromatic aberration in imaging systems, but I don't understand the application you are describing.

 

[Beer-monster]

Try this .pdf from a company that researches EUV lithography.

http://lmn.web.psi.ch/xil/xil_pres.pdf

On page 9, they mention that using diffraction optics removes the need for strict temporal coherence from the formation of the interference pattern.

I'm just not sure why the should be so?

 

[Andy Resnick]

Thanks- that helps.

I wonder if it's just a poor choice of words; the diagram shows something similar to a Young's double slit interferometer: the diffraction gratings could be used to select out a particular wavelength by using high orders, but that means the temporal coherence of the etching light is high. Of course, the original source (synchotron) has a low temporal coherence, but from what I gather on the diagram that doesn't matter since the gratings act to spectrally filter the light.

Maybe I am not understanding the brochure... I'll keep reading.

 

[sardar]

I can provide some insight into the concept of diffractive optics and achromaticism. Diffractive optics refers to the use of diffraction gratings, which are structures with closely spaced lines or grooves, to manipulate light. These gratings can be used to split a beam of light into multiple beams or to focus the beam onto a surface.

Achromaticism, on the other hand, refers to the ability to produce light that is free from color or chromatic aberrations. This means that the light does not have any specific wavelength or color, but rather appears as white light.

Now, to address your question, the reason why diffractive optics can produce achromatic light is due to the principle of diffraction. When light passes through a diffraction grating, it is dispersed into its component wavelengths. However, as you mentioned, the grating also acts as a prism, dispersing the different wavelengths at different angles. This means that when the light is focused onto a surface, the different wavelengths are brought to the same focal point, producing a white light.

In contrast, traditional lenses or mirrors can only focus a specific wavelength of light, leading to chromatic aberrations. But with diffractive optics, the light is dispersed and then brought back together, effectively canceling out any chromatic aberrations and producing an achromatic output.

I hope this explanation helps clarify the concept of diffractive optics and achromaticism. Let me know if you have any further questions.