UCO/Lick Coatings Project: Phillips' News and Progress

Interim Report on Protected Ag Coatings for DEIMOS (PDF)

  • 48" Coating Chamber (30 Jan 04)
  • First e-Gun Firing (30 Jan 04)
  • Reference Literature (07 Aug 06)
  • Environmental Testing (24 Feb 05)
  • New Ion Source! (21 Apr 05)
  • Stripping Tests (22 Apr 05)
  • Varian-Cary 5000i (26 Sep 06)

    Click on pictures for larger versions.

    48" Coating Chamber

    48" Since the Fall of 2003, a 48" coatings chamber has been under development in the Lick Optics Shop, under the direction of Bill Brown and Vern Wallace. So far, we have coated slide-glass samples with aluminum and MgF2.

    (Here, Ken Dietsch is doing some electronics testing on the e-gun.)

    More information and photos to follow!

    First e-Gun Firing

    e-Gun with Al in crucible Photo of the e-gun heating an aluminum source. This was during a testing phase so the Al was left rather cool. The bright purplish glow is the electron beam sweeping over the aluminum (glowing dully) in the circular crucible; the bright light at top is from the glow of the electron source underneath the e-gun assembly. This is a four-pocket e-gun; the other 3 crucibles are hidden but can be rotated into position under the electron beam.

    Uniformity of Deposition

    Uniformity Test Each column of 4 slides represents a single arm (out of four) spanning a radial range from about 4" (top) to 21?" (bottom). Shown are slides from Arms 1 and 3. The uniformity is measured by the transmission through a thin layer -- about 40 A -- of Al deposited via resistive filament. Two calibrating neutral density filters appear top center and bottom center. The uniformity achieved is better than +/- 3% peak-to-peak.

    H2S Testing

    Uniformity Test Test set-up. Samples are placed in dessicator jar, which is then evacuated by the line to bottom with brass fitting (going to pump). The jar is then closed, and the line switched to connect jar and test-tube. Ammonium disulfate (?) solution is placed in test tube, and HCl acid in dropper inserted through stopper at top. As HCl is added to solution, valve in dessicator jar lid is opened, drawing H2S into the jar. After the acid and solution are mixed, the jar is sealed off again.

    New Ion Source!

    On April 21, a Kaufman & Robinson EH-2000 ion source was succesfully started in the 48-inch chamber. This will enable us to perform Ion Assisted Deposition (IAD) which has become the modern standard for optical coatings.
    EH-2000 at K&R The ion source in the K&R Test Chamber (Ft. Collins, CO) on April 1.
    First ignition Ion source producing 60 eV oxygen ions in the 48-inch chamber, April 21.

    Varian Cary 5000 Spectrophometer

    The following figure is intended to help debug problems with our unit, which have plagued us for the past 1-2 years (click on image for PDF):

    click for PDF

    These data were collected over the space of about 55 minutes. The unit had been on for about 5 hours, so it should have been stable. One bare quartz slide was placed in each of the sample and reference beams, in transmission, a baseline taken, and then a regular transmission trace. The heavy black line shows the result, at 100% transmission as expected (a second thin solid black line shows a repetition, hard to see as it falls under the heavy line). The sample compartment was opened and the slide in the sample beam reversed. The colored lines show the progression from 4:06 to 4:50 pm. Then the sample compartment was opened and the sample slide reversed again, ie, restored to its original orientation. The resulting trace is shown as the black dotted line. Except for reversing the sample slide twice, the unit was not touched or changed in any way. Three zones are present in the traces:

  • IR detector/IR grating: This zone (redward of 860nm) is relatively stable. There is a slight drift with time, at a reasonable level for PbS detectors.

  • Vis detector/IR grating: 800-860 nm. The only difference from the previous zone is a detector change. Reversing the slide produced a significant step; returning it to the original position removed the step. This means that the UV-Vis detector is incredibly sensitive to alignment, as a small change in the optics in the path produces a large change in measured intensity. Note that this optical change does not affect the PbS detector, which is small and therefore highly sensitive to alignment, so the introduced optical change must be very small.

  • Vis detector/Vis grating: 800 nm blueward. The only difference from the previous zone is a grating change. The obvious pattern here is a monotonic drift with time. This must be related to the UV-Vis grating, as it is the only difference. We speculate that the alignment is changing, and because the UV_Vis detector is so sensitive to alignment, the small grating alignment drift results in a significant drift in measured intensity level.

    UPDATE (sort of): The Varian Sales Rep presponded to this data by making a visit, the first input from Varian since we notified them directly (rather than through Service) in June 2006. During the visit, he observed the drift. He stated this was clearly wrong. That was Oct.4. It is now Nov. 20. There has been absolute silence from Varian in the interim. Has the problem gone away? Check out this baseline drift over 30 minutes. The blue curve was taken immediately after a baseline, and the drift was monotonic. The scan has the same parameters as the one above. Interestingly, in this case both the IR and Vis are drifting, unlike the last figure.

    A couple of days ago, we did some reflectance measurements, followed by a straight-through base-line configuration. The step in the "100%" line was 1.5% at 800 nm. Since we are trying to measure reflectance at the 0.1% level, we're clearly being hobbled by this instrument. Varian has been told this repeatedly. And, yes, we are under service contract with them.

    UPDATE (Jan. 07): The unit was serviced in early Decemeber, and it was found to be out of alignment. The step in transmission was reduced to <= 0.1% in transmission. In reflectance, we are still seeing some apparent drift, now on the IR side, leading to steps up to 0.3%. This has not been well-characterized, though, and may be the standard "noise" in the reflectance mode. In general, the unit appears usuable again.

    Last modified: 20jan2007

    Andrew C. Phillips / Lick Observatory