# [RCWA Stochastic mode] Discussion of Start Order・Stop Order / Max Order / Only These Orders

• 59 views

Userlevel 2 +1
• Zemax Staff
• 51 replies

Simulating diffraction efficiency of surface-relief grating using the RCWA method - From the OnlyTheseOrders description in the Knowledgebase, if we have the below 2 case,

Case A Start Order: 2, Stop Order: 2, Max Order: 10, Only These Orders: 0

Case B Start Order: 2, Stop Order: 2, Max Order: 10, Only These Orders: 63

Is it correct to say that when Stochastic mode is off, the results are not the same (A is -2~+2 orders, B is -1~+1 orders)?

In the case of Stochastic mode on, what are the results of A and B?

Also, I would like to know the best order setting when using Stochastic mode.

Userlevel 2 +1

When Stochastic mode is on, the settings for Start Order and Stop Order are practically meaningless.
It is recommended to set Start Order=Stop Order when Stochastic mode is on . (e.g. Start Order=Stop Order=0 or Start Order=Stop Order=1)

For example, if Max Order: 10 and Start Order=Stop Order=0
The first ray trace calculates the probability from the -10th order to the 10th order.
Based on the probability information, “Only These Orders” can limit the order that you want to trace.

For example, if Max Order: 10, Start Order=-1, Stop Order=1
, the system will trace the -1, 0, and 1 orders ray, so there will be a total of three times ray tracing.
The first ray tracing computes the probability from the -10th order to the 10th order.
The second ray tracing computes the probability from the -10th order to the 10th order again.
The third ray tracing computes the probability from the -10th to the 10th order again.
Since the three calculations have the same result, from the efficiency point of view, it is recommended to set Start Order=Stop Order.

• If Stochastic mode is off, the results will not be the same (A will be -2~+2 orders, B will be -1~+1 orders), is my understanding correct?

Yes, that is correct.

• In the case of Stochastic mode on, what are the results of A and B?

In the case A, -10~10 order will be traced.

In the case B, -1~+1 order will be traced.

If the number of ray tracing is sufficient, the results will not be the same.
When Stochastic mode is on, Only These Orders is the only way to select (or limit) the order.

•  Also, I would like to know the best order setting when using Stochastic mode.

We recommend to use Start Order=Stop Order when using Stochastic mode.
Please use Only These Orders to further limit the orders.