XUV ALS Measurements, July 2002


David Allred, Shannon Lunt, and Steve Turley travelled to Lawrence Berkeley Laboratory to make measurements using the ALS (Advanced Light Source) on July 12 and 13, 2002. There thumbnail pictures and explanations of the trip below. To see larger pictures, click on the thumbnail.

Shannon and Steve arrived at the ALS on July 11 and received their orientation and safety training. Because of the high energy electrons used at the ALS (1.9 GeV), ionizing radiation is possible from areas near the storage ring. After the orientation, Shannon and Steve checked into an exceptionally nice hotel they managed to get for a great price using www.priceline.com. Here are two shots from the lawn just outside their rooms:
Hotel and Marina
Marina

Shannon and Steve picked up David, arriving from an SPIE conference, later that evening. The next morning, all three drove to the ALS at the Lawrence Berkeley Laboratory which is housed in Building 6 . While David received his orientation and safety training, Shannon and Steve entered this door to beamline 6.3.2 where they waited for Eric Gullickson to show them how to set up the measurements.

After Eric and David showed up, we attached our targets to the target stage. We then placed the targets in the target chamber on the target staged which would be rotated and translated by computer control. In this photograph, the beam enters from the left, reflects off the targets and is detected on the right. This photograph shows the inside of the entire reflectometer chamber with the small port in the center on the left where the beam enters, the sample stage in the center, and the detector assembly on the right. The screen on the right side at the bottom of the picture covers the gate valve in front of the cryopump.

The detectors and sample were on separate goniometers that could rotate independently under program control. The detector holder actually contained four detectors:


Here is a side view of the reflectometer chamber. The access port where we loaded the samples is behind the plastic shield on the center left of the picture.

Our photons were generated in the synchrotron shown in this view looking down from the gallery. The 1.9 GeV electrons passed through undulators in straight sections between the bending magnets which kept them circulating in the ring. This produced a narrow beam of somewhat monochromatic photons in the XUV and soft x-ray range at each of the several experimental beamlines in the facility. This is a view of the 6.3.2 beamline looking upstream towards the synchrotron storage ring. The chambers in the picture include optics used to focus the beam and a diffraction grating and slits to select a particular wavelength. The largest visible chamber in the center of the picture has the focussing mirror M3. By monitoring the current in this mirror (as well as the synchrotron current), we were able to normalize the intensity of the incident light was it varied from measurement to measurement.

The wavelength selection process by means of a diffraction grating selects light princox at the wavelength of the first-order diffraction peak. However, light from higher-order peaks (with integral multiples of the energy of the photons in the first-order peak) can also get through the grating. We filtered these out using films of silicon, aluminum, boron, or beryllium and a selectable three mirror multilayer reflector. The housing for this order selector is shown here looking upstream in the beamline towards the reflectometer chamber (behind the plastic shield).

The chamber and beamline were pumped down using this mouse-driven computer display. The red line in the display shows the path of the XUV beam. When the beam is off or blocked, the section where there is no beam turns pink.

We positioned the beam on the target by taking advantage of the small visible component in the beam. A television monitor allowed us to use the computer to position the beam spot to the desired location on the target.

Here is Shannon at the control console taking data from the reflectometer. The Labview program running on a Sun workstation allowed us to:

Most of our data was either a theta-2theta angle scan or an energy scan at fixed angle. We also took normalization runs with the detector out of the beam so we could take a ratio of the initial intensity and reflected intensity.

This last picture is a display of the beam status monitor on Saturday, our last day of measurements. On a good day, the synchrotron is down for about 15 minutes every 7-8 hours while it is refilled. This is scheduled to happen when the current drops from about 400 mA to 200 mA. Unfortunately, as you'll note in the beam current trace, we had several long stretches when electronic glitches shut down the beam for hours while they were being diagnosed and repaired. On the positive side, it sure was a nice luxury having someone else worry about getting this sophisticated equipment working rather than having to do it ourselves!


Last Updated July 14, 2002 by Steve Turley