Ettore and I tested one of the beamsplitters currently being used by IONIC on the scanning platforms. There has been some controversy regarding the characteristics of the particular optical pieces being used. The following is our report. ------------------------------------------------------------------------- 2002Oct13 IOTA The test was simple: light was injected into one of the fibers of IONIC, thus illuminating 4 pixels on the PICNIC detector. The transmission was measured by placing the 60mm x 60mm x 10mm beamsplitters in-between the two lenses of the IONIC re-imaging optics (in a parallel beam at near normal incidence); the reflecting (coated) surface was directed towards the incoming (IR) rays. Its worth noting that both of the beamsplitters tested were remarkable flat, causing no image motion on the detector. The results of the tests follow: H-band Optic Under Test Transmission Comment --------------------------------------------------------- None 100% Transmission normalized to this Janos Infrasil ** This one currently is in use P/N 904098-01, SN8 59% ** by IONIC Janos BK7 ** Currently not in use and P/N R904172-1, SN1 0.8% ** virtually opaque at H. A figure showing the transmission test results is attached. Discussion ---------- An inventory of the Janos boxes at the site revealed: 10 boxes labeled Infrasil P/N 904098-01, of which 9 were empty. Six of these have handwritten on them "Class. BC 9/21/01", presumably indicating their destination: the classical ("CfA") beam combiner. One of the boxes still has an optical piece in it (spare?). 1 box also labeled Infrasil P/N 904098-01 UNCOATED (also hand-labeled "Infrasil Compensator"), and this one does contain an optic. 3 boxes labeled CSM BK-7 SqBs 60x60x10mm, (Ref: RMA#01102). These 3 boxes each still contain an optic (I measured one of these in the test above). I also inventoried the square optical pieces currently deployed on the two tables and can identify a total of nine (9): the 3 ionic pieces on the scanning platform, and six (6) in the CfA Combiner. In conclusion, there are 9 empty boxes (all labeled Infrasil P/N 904098-01) and 9 pieces in use. Assuming the pieces in the "CSM BK-7 SqBs 60x60x10mm" are not misplaced, then it seems plausible that the 3 ionic beamsplitters are indeed 50/50 beamsplitters and not dichroics. Further, the piece I tested from the IONIC platform was handlabeled SN#8, also consistent with the fact it came from the batch of 10 Infrasil P/N904098-01. Also, this inventory analysis is consistent with the measurements of 59% transmission at H band for the IONIC piece under test -- that, indeed, we have been using more-or-less 50/50 broadband beamsplitters during the last year, instead of dichroics. Action Items ------------ Could somebody check the purchase orders that the Janos Bk7 R904172-1 set (3 pieces,RMA#01102)) are indeed the dichroics that were ordered (if not, what are these for?). This would be consistent with the 0.8% H-band transmission (Note: 10-mm of BK7 does not absorb a significant fraction of the H-band light). If these part #s check out, I would strongly urge we deploy the Jano BK7 R904172-1 beamsplitters in the IONIC scanning platform, and attempt to confirm the expected 1 magnitude increase in sensitivity. [Watch out YSOs!! Here we come!] -John & Ettore ps. Cloudy nights do serve some purpose.