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.