From jrb@aaoepp2.aao.GOV.AU Mon Dec 22 17:57 EST 1997 Date: Mon, 22 Dec 1997 17:56:37 +1100 (Sydney Daylight Time) From: "JOHN BARTON, AAO, EPPING, OZ" Subject: COATED MITLL2 CCD PERFORMANCE... To: DIRECTOR@aaoepp2.aao.GOV.AU, KT@aaoepp2.aao.GOV.AU, CGT@aaoepp2.aao.GOV.AU, JBH@aaoepp2.aao.GOV.AU Reply-to: jrb@aaoepp2.aao.GOV.AU Priority: NORMAL X-Authentication: IMSP Dear all, I briefly report on my tests performed, over the weekend, on the engineering grade MITLL2 CCD (CCID-20 W20C2) following the Lumogen coating applied by Stromlo on about the 17th Dec, 1997. In summary, the coating has been successful in that flat-field response down to 300nm appears very flat, the brick wall pattern, not exceeding 10% p-p, being the dominating feature. The uneven coating as seen by eye is apparent only in the I band at the level of 15% p-p at most. There was no attempt made to estimate the QE of the coated CCD. APPEARANCE: The coated CCD had acquired a pastel green appearance that was notably darker in the central rectanglar region of the image area extending to within a few mm of the edges. The "rectangle" appeared slightly wider towards the readout end of the CCD and narrowed slightly towards the far end of the CCD where it showed quite rounded corners. Surrounding the central rectangular region were three ring patterns, the outer one close to the edges of the image area. The CCD looked clean, the original spots and deposits on the surface were still evident and the only new features were about 8 smudgy spots where the coating appeared to be thinner. The CCD was returned to its red Oxford dewar. There were no problems getting it operating and all appears, after coating, to be unchanged. FLAT-FIELDS: The Setup. The CCD dewar was fitted with a 100mm Prontor shutter with nominal opening and closing times of about 30ms. Exposures were kept long (mostly 3 to 20 secs although three were at 1 sec) in order to minimise the difference in exposure between the centre of the chip and the corners. The CCD was illuminated by various lamps with two 35mm diameter diffusers interposed about 50 and 80mm above the lamp. In between the lamp and the diffusers various filters could be placed. The lamp and diffuser assembly was held about 300mm away from the CCD so that it was equivalent to about an f/10 beam. This eliminated the effect of dust particles and defects on the window and provided a fairly even illumination over the 60x30mm CCD image area. General Characteristics. All flats exhibited a domed structure the intensity in the centre being from 3 to 13% higher than that at the mid-edge and a few % extra above that at the corners. Profiles of a central column and row were quickly analysed for the very large scale peak-to-peak amplitude of the dome (Vdome and Hdome) expressed as a % of the flat-field intensity. In all flats except for two, the brick wall (BW) structure could be seen and in these profiles the peak-to-peak amplitude was estimated as a % of the flat-field intensity. DETAILS: Led Illumination IR LED illumination (880nm) 10% Vdome 14% Hdome 3% BW. Central rectangle and surrounding rings dominant. BW faint and in background. RED LED illumination (660nm) 7% Vdome, 6% Hdome, 5% BW. BW dominates with a slight darkening of the edges of the chip Hg Lamp Illumination: A UV curing lamp emits all the Hg lines plus many strong emission lines (unknown source) above 700nm. It was used with the following RG filters and 5 narrow-band filters (NBF) with stated passbands (PB) all in nm. UV+RG1000 30% Vdome, 30% Hdome mostly comprising 8 to 30% p-p of broad fringes with a superimposed fine circular structure (from the wafer polishing?) plus a fine straight structure angled to the row direction. UV+RG695 similar to the above but with 20% doming and 15% of fringing UV+685NBF (PB 85) 18% Vdome, 14% Hdome with up to 8% fringing similar to above UV+578 (PB 50) 6% Vdome, 6% Hdome, 6% BW, a good flat flat, BW dominates UV+502 (PB 37) 7% Vdome, 6% Hdome, 7% BW, a good flat flat, BW dominates UV+449 (PB 47) 7% Vdome, 6% Hdome, 6% BW, a good flat flat, BW dominates UV+418 (PB 30) 4% Vdome, 5% Hdome, 4% BW, a very flat flat, BW dominates UV+SL1 (350-400nm) 8% Vdome, 6% Hdome, 4% BW, a good flat flat, BW dominates UV+SL3 (300-350nm) 7% Vdome, 6% Hdome, 3% BW, a good flat flat, BW dominates Deuterium Lamp Illumination: UV+SL1 (350-400nm) 6% Vdome, 6% Hdome, 3% BW, a good flat flat, BW dominates UV+SL3 (300-350nm) 6% Vdome, 6% Hdome, 3% BW, a good flat flat, BW dominates Quartz Halogen (QH) Illumination: I band filter 13% Vdome, 14% Hdome, 3% BW, the central rectangle dominates with no sign of the fringes seen with the UV lamp, BW pattern is present. R band filter 10% Vdome, 9% Hdome, 4% BW, the BW pattern dominates with doming into the corners and only a very faint central rectangle detected. V band filter 5% Vdome, 8% Hdome, 6% BW, a good flat flat, the BW pattern dominates B band filter 3% Vdome, 6% Hdome, 6% BW, a very flat flat, the BW pattern dominates SL1 (350-400nm) looks so much like the I band that I suspect a red leak SL2 (300-350nm) was the same CONCLUSIONS: The coating had no deletarious effect on the CCD performance electronically. Curously, only the I band seems to be affected by the uneven coat with the central rectangular region being clearly more visible in the flats. The fringing above 700nm (not seen with the I band filter on QH lamps, but seen only with strong emission line sources) probably has nothing to do with the coating. The flats taken below 600nm down to about 300nm are very flat, the brick wall pattern dominating in all of these. A critical examination of the brick wall pattern in the QH + B filter flat showed that at worst the peak-to-peak pattern was about 9%. Overall, a histogram of this flat showed that 99% of all pixels fell within an intensity range that spanned the average +/- 6% and this includes the fall-off in illumination at the edges and the corners of the CCD.