​@AsafPe 

If one groove is one line (reasonable?), then 1 200 / 1 000 = 1.2 lines/um?

Take care,

David

Thank you  David, that’s what I thought but it doesn’t fit with the diffraction orders angle. It looks like there is a factor of 0.5 missing (0.6 lines/um) like one groove which is also the grooves pitch, is half a “line” ???

​@AsafPe 

I would ask your manufacturer to clarify what a groove is.

OpticStudio uses this definition:

Which seem to agree with this Wikipedia figure from the Diffraction Grating article:

The refractive indices in the Wikipedia formula were omitted:

The sign difference is due to the different case treated: reflection in Wikipedia and (probably) transmission in OpticStudio Help File.

I hope this helps.

Take care,

David