LPC Briefs

October 1999

Hello, LPC Members!

All the news is good; the very best of it is that we are actually doing quite a bit of laser processing and Congress has appropriated funds for the upgrade. Be sure to put the next consortium meeting on your calendar and in your plans: January 13 & 14, 2000.

The summer run was our first time doing everything in the way that we expect will become business as usual. Not surprisingly, we had some yearnings and learnings about the FEL, the user lab equipment and our procedures. Pleasantly, none of them was major or painful and most of the needed adjustments have been made. All the experiments were able to operate and get at least preliminary results. We set the 1.7 kW power record that you've already heard about. We operated at primary wavelengths across the design range from 3 to 6 microns and got the predicted performance or a little better. We even had usable 5th harmonic radiation offering the FEL a means to reach into the visible before installing upgrade hardware. And we made coherent, ps-pulse x-rays.

The fall run is scheduled for 10/24 - 11/24, two shifts a day, Monday through Friday. Experimenters from nearby will do micromachining, pulsed laser deposition, materials surface processing and Navy applications. Experimenters from Rensselaer will be back to do more terahertz radiation tests. The group from Vanderbilt will make their first visit, using the FEL to study hydrogen-related mode lifetimes in silicon. Even if you're not doing experiments, we invite you to visit and see the FEL in action! The following run will probably be next March, though final schedule details are still being worked out.

The FEL upgrade is expected to begin with the arrival of funds in March and extend over almost three years. At completion, the FEL will be able to deliver at least 10 kW from 1 to 10 microns in the IR and at least 1 kW down to near 250 nm in the UV. Of course we will try to do better. Fortunately, virtually all the FEL upgrade activity will be able to proceed without impact on the present mode of operation.

A "beam conversion" upgrade is attracting attention at the FEL and we'd like your thoughts. Briefly, the FEL's 18.75 MHz minimum repetition rate (55 ns max between pulses) and 25 mJ micropulse energy are quite high and low respectively for laser ablation applications such as pulsed laser deposition and micromachining. The FEL upgrade won't change these numbers to any extent that matters. Further, the optical pulse length is relatively fixed near a picosecond. Very preliminary analysis indicates that we can construct a chirped-pulse stretcher/compressor to vary pulse length much more widely, followed by a pulse stacker to accumulate the original FEL pulses and deliver the summed pulses at 10 kHz or more. Other FEL labs have demonstrated both technologies, though not at high average power nor have they combined them. If we could deliver 0.1 - 10 ps pulses, more than a millijoule per pulse, and more than 10 kHz rep rate, would new research opportunities or applications open for you? Please tell us. It will help us write the proposal...

The June LPC/FEL Workshop Proceedings offer more details about the FEL upgrade and many other interesting things. The copies went out in the mail recently to the June 1999 Workshop attendees. If yours doesn't come, contact Linda Williams (williams@jlab.org). Also, have a look at our website: www.jlab.org/FEL for the workshop summary.

The Jan. 13 & 14 LPC/FEL Workshop will feature results from the two FEL user runs and more details about the FEL upgrade. We also want your contributions. As you know, anything related to processing with light or the science that is possible with this unique light source is fair game. The people who have run tests already know that we will appoint them as volunteers to give presentations. See you in January.