Ann: SILEX Uranium Enrichment Project Update, page-13

I think it's not clear what the Beam Control System (BCS) says about the laser Silex is using. Zog may be right that they've decide to stick with the TEA CO₂ laser, but a solid state laser (likely some quantum cascade laser) might still require some control system for the entire laser module to become reliable.

First, on the CO₂ laser, you wouldn't necessarily need a rotating mirror to combine the beams. I don't see anywhere in Snyder's paper where he mentioned a rotating mirror. What Snyder showed in his paper it that with that laser you could interleave the beams if you had enough lasers that performed well enough (obviously the correct wavelength and a high enough repetition rate), then you could use mirror bounces to increase the effective repetition rate and irradiate all of the UF₆ moving through the separation unit. But he didn't go into much detail about how you would interleave the laser beams so that the pulses were spaced apart. The way you do that is by just adding a bit of extra path length on an optics table so that one beam would have to travel a multiple of a half wavelength further (or some fraction of a wavelength if you wanted to add more beams). You could then see on an oscilloscope that the path length added correctly interleaved the beam. There are beam splitters that allow laser beams to be combined once you've got the pulses adequately spaced apart. I don't think any rotating mirror is necessary.

My guess is that if they stuck with the CO₂ laser, either the Raman shifter or something internal to the laser itself needed to become more reliable. If I had to guess, getting the correct wavelength out of a TEA CO₂ laser is at one end of the range of a CO₂ molecule for which the 10.2 micron light is quite a challenge. They need this wavelength to downshift through the Raman shifter to ~16 micron light. They may have needed to do development here to stabilize this. That's just a guess.

On the other hand, if the power output of a 16 micron quantum cascade laser is only in mW, there may have been development needed to use a lot of mirrors to multiply this power or combing low power beams in reliable ways to get up to around ~380 Watts, which is about the minimum power needed to excite all of the ²³⁵UF₆ (see Snyder's main paper for this argument). So, the BCS may just be for the new quantum cascade laser system, it's hard to tell.

What I do know is that Snyder regretted not focusing more on the quantum cascade laser because he now feels that this will likely be the future of this technology. The TEX CO₂ seems quite cumbersome, but Silex may have still stuck with it as Zog suggests. I don't think you can make any determination, however.

I know that Argentina is doing research on this laser enrichment technology, and they are using the 16 micron solid state laser (yes, to enrich uranium), so I doubt Silex can afford any kind of edge technologically by planning on the CO₂ laser over the long term. It seems that eventually they will have to switch. There is likely to be too much competition with a better laser, but it appears too hard to say from here.

I still owe Zog a longer post to his thoughtful reply to my questions, but I just wanted to weigh in with what I know about this topic.