JonathanB, Patrick, RickS

After locking down H1 ETMX, we proceeded to measure the optical efficiency from the photon calibrator output to the light incident on the ETM - basically just the viewport transmission.  Measurements were made about 35 cm upstream of the ETM using the Woring Standard power sensor (integrating sphere and InGaAs PD).  We did not use the TEC controller due to cable length issues.

We used the Pcal internal power monitor (PM)as a laser power reference.  We measured the PM voltage using a Keithly 2100 VOM connected to the Blue Box PD out.  The WS voltage was measured in the usual way.  Typical measurements were two minutes long with one sample every 25 ms.

The H1ETMx pcal beams do not cross, so the Pcal refl beam impinges on the mass on the -y (east) side.

For the in-chamber measurements, the WS/PM ratios were:
Pcal refl beam: 0.2788, 0.2781; avg = 0.2785
Pcal trans beam: 0.2828, 0.2831; avg. = 0.2830

Before going into the chamber, we measured the WS/PM ratios with the WS located inside the Pcal calibration box (just upstream of the vacuum window).  Note that the TEC was used for these measurements.  The ratios were:
Pcal relf beam: 0.3239, 0.3190; avg. = 0.3215
Pcal trans beam: 0.3253, 0.3201, 0.3176; avg. = 0.3210

After the in-vacuum measurements, we repeated the external measurements, but this time without using the TEC.  The results were:
Pcal refl beam: 0.3159, 0.3145; avg. = 0.3152
Pcal trans beam: 0.3168, 0.3176; avg. = 0.3172

Using the data taken wihout the TEC (we don't expect it to make a difference, but just in case ...) we get for the optical efficiencies:
Pcal refl beam: 0.884
Pcal trans beam: 0.892

The optical efficiencies, for slightlyl different positions on the ETM, thus slightly different incidence angles were measured in Oct. 2007 (just after S5) to be 0.902 and 0.912.
Thus the optical efficiencies measured today are almost 2% lower than what we measured 3 years ago.