@misk94555 I haven't looked in a long time, it's possible they only provide the information for the order that they are blazed. For most small period gratings they are usually first order. So maybe I'm wrong about that.

If the efficiency is 20% then "how much did I miss" you could just say 80% but I guess you really want it broken down into each order.

I checked quickly and I'm surprised I didn't see any questions or answers about this in Physics SE, nor in Astronomy SE. Maybe it's time to ask a question?

I think that this book comes for free if you order it, but of course you have give them your mailing address; nothing is 100% free :-) gratinglab.com/Information/Handbook/Handbook.aspx

This can be downloaded, but I'm not sure it helps researchgate.net/publication/…

OH! Section 9.5 shows the 1st, 2nd, and 3rd order absolute efficiency for some grating. I think this is the type of data you are looking for. It's only one example but at least it's a start!