Guilin Sun
Ansys Employee

I did not see any abnormal response. Do you have theoretical base that this resonance at 633 should not appear?

When the period, or distance change, we are simulating different arrays. So different response is expected. I suspect that there are higher diffraction orders. You can use the farfield of the monitors using visualizer to check with log sclae. you may use more number of PML if the diffraction angle is found.