Hi Zemax users,

I am trying to build a transmission grating system.

The layout is as follows:
ray source → 1st transmission grating → 2nd transmission grating.

The diffracted angle from the first grating is used as the incident angle for the second grating.

My understanding is that if both gratings use the same diffraction order (here, m = −1), the dispersions should be additive.

However, in the LDE, using −1 for both gratings does not seem to work. Instead, using −1 for the first grating and +1 for the second grating works, but the total dispersion is cancelled.

I am not sure whether this is due to an incorrect setting, or if my understanding is fundamentally wrong.

I also tried another configuration: I rotated the second grating by 90° with respect to the first grating and used the same diffraction order (m = −1).

In this case, the result matches what I originally expected for the original configuration.

Could you please help explain how to achieve the expected behavior in the original layout, and point out where my understanding or settings may be incorrect?

Best Regards

Yang