1. X-Sender: arem@lyomail LIGO-C040532-00-D X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Tue, 28 Sep 2004 17:52:25 +0200 To: Armandula Helena From: Alban REMILLIEUX Subject: Absorption maps of formula 5 on silica and sapphire Cc: Mackowski Jean-Marie X-Virus-Scanned: by amavisd-new at ipnl.in2p3.fr X-Spam-Score: undef - Message too big X-Scanned-By: CanIt (www. canit. ca) Dear Helena, Here are the absorption maps. Slide 1 presents an absorption map I made on a 1 inch diameter HR mirror (HB)19HBB we coated recently in the large coater. It is not doped. It is a simple SiO2/Ta2O5 mirror on a micropolished silica substrate. I made this map in order to tell what could be the best sensitivity of the absorption bench. The power of the YAG laser is set to 20W. After each displacement of the stages, the motors are switched off in order to reduce the noise level, and we wait about 18 s so the signal has enough time to stabilize; then we record the absorption of the pixel. The result is rather interesting: Almost all the pixels have an absorption comprised between 0.30 and 0.34 ppm. The variations of absorption within this gap of 0.04 ppm are obviously due to the noise of the bench rather than to the absorption variations of the mirror. Anyway, this map shows how uniform the absorption of our coatings is. Among the 5000 points of the map, only about 10 have an absorption higher than 0.5 ppm. The maximum of absorption is1.5 ppm. Slide 2 shows an absorption map of the 3 inch diameter HR mirroir (HmB)15 coated in the large coater. The coating is the formula 5 (Hm is Ta2O5 doped with a concentration comprised between formula 2 and formula 3). The substrate is out of fused silica. It has not been possible to use a 20W pump laser for the measurement of this mirror, because a few pixels (about 10 among the 5000 measured) have an absorption higher than 6 ppm (but less than 12 ppm). The laser may burn the coating at those points. Unfortunately, this is what happened at the top of the mirror (red line). I am sorry about that, I didn't expect it to occure! We used a 6W pump, and therefore, the sensitivity is about 3 times worst than in slide 1 : Almost all the measurements are comprised in a gap of 0.13 ppm, between 0.82 ppm and 0.95 ppm. The mean value is 0.88 ppm. Nevertheless, the sensitivity is sufficient to show a little variation of absorption between the bottom left of the mirror and the top right, which is probably due to a non uniform coating thickness, with the mount we used. Slide 3 shows an absorption map of the same coating, during the same run, but on a 3 inch sapphire substrate. Of course, the pump laser is also 6W. With sapphire, the photothermal deflection is lower than with silica and the sensitivity of the measurement is in our case about 3 times worst than with silica: Almost all the measurements are comprised in a gap of 0.40 ppm, between 0.7 and 1.1 ppm. The mean value is still about 0.88 ppm. With my best regards, Alban.

2. (HB)19HBB on silica (1 inch diameter) YAG Power = 20W

3. (H doped B)15 on silica (3 inch diameter) YAG Power = 6W (20W was not possible because of a few points absorbing up to about 10 ppm)

4. (H doped B)15 on sapphire (3 inch diameter) YAG Power = 6W Absorption measurement sensitivity is about 3 times worst on sapphire substrate than on silica substrate.