X-Sender: arem@lyomailLIGO-C040532-00-D X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Tue, 28 Sep 2004 17:52:25 0200 To: Armandula Helena <[e-mail]> From: Alban REMILLIEUX <[e-mail]> Subject: Absorption maps of

1

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  Helena ltahelena_at_ligo.caltech.edugtFrom Alban
  REMILLIEUX lta.remillieux_at_lma.in2p3.frgtSubject
  Absorption maps of formula 5 on silica and
  sapphireCc Mackowski Jean-Marie
  ltmackowski_at_lma.in2p3.frgtX-Virus-Scanned by
  amavisd-new at ipnl.in2p3.frX-Spam-Score undef
  - Message too bigX-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
(HdopedB)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
(HdopedB)15 on sapphire (3 inch diameter) YAG
Power 6W Absorption measurement sensitivity is
about 3 times worst on sapphire substrate than on
silica substrate.