Last week I finished the lapping and mirror polishing on back surface. The resulting parallelism is very good for the back target plate (within 3microns). The flyer plate and back target plate are easily been lapped while the front target plate needs more lapping time.
I did the 600 grating on the mirror surface on back target plate.
I tried the S1813 positive photoresist first and found that edges of lines are not sharp and the quality is not so good. Also, I have the secondary grating, which can not be solved. I observed the mask under OM and the lines are very narrow compared with space. Hence, I think a negative photoresist would do a better job. I used SU 08-2002 photoresist and made the grating on above graph. This time the grating quality is good and the secondary grating disappeared in some region. The left graph is S1813 grating and the right is SU 08 which is the final one.
The next task is powder compaction and I will do the shot this week or next week, as on my summer schedule.