Point defects in IBS coating for very low loss mirrors.

High-reflective coatings are used in many physics experiments. Despite the high quality of the optical coating, the performances of the mirrors are altered by the scattered light induced by micrometer size defects in the coating layers. The topic of this paper is the study of the point-like scatterers present in the specific coating of the mirrors used in state-of-the-art, high-sensitivity optical experiments. We studied the behavior of the materials according to different thicknesses and the resulting defects after annealing. To the best of our knowledge, this is the first insight into the formation of such defects for different materials and thickness and how this is reduced when samples are annealed.

Prior-damage dynamics in a high-finesse optical enhancement cavity.

An observation of prior-damage behavior inside a high-finesse optical resonator is reported. Intra-cavity average power drops appeared with magnitude and time scale depending on the power level. Increasing further the incident laser beam power led to irreversible damage of the cavity coupling mirror surface. The origin of this phenomenon is investigated with post mortem mirror surface imaging and analysis of the signals reflected and transmitted by the enhancement cavity. Scattering losses induced by surface deformation due to a hot-spot surface contaminant is found to be most likely the dominant physics process behind this phenomenon.

Large and extremely low loss: the unique challenges of gravitational wave mirrors.

This paper describes the making of large mirrors for laser interferometer gravitational wave detectors. These optics, working in the near infrared, are among the best optics ever created and played a crucial role in the first direct detection of gravitational waves from black holes or neutron star fusions.

Realistic loss estimation due to the mirror surfaces in a 10 meters-long high finesse Fabry-Perot filter-cavity.

In order to benefit over the entire frequency range from the injection of squeezed vacuum light at the output of laser gravitational wave detectors, a small bandwidth high finesse cavity is required. In this paper, we investigate the light losses due to the flatness and the roughness of realistic mirrors in a 10 meters-long Fabry-Perot filter cavity. Using measurements of commercial super-polished mirrors, we were able to estimate the cavity round trip losses separating the loss contribution from low and high spatial frequencies. By careful tuning of the cavity g-factor and the incident position of the light on the mirrors, round trip losses due to imperfect mirror surfaces as low as 3 ppm can be achieved in the simulations.

Cryogenic measurements of mechanical loss of high-reflectivity coating and estimation of thermal noise.

We report on low-frequency measurements of the mechanical loss of a high-quality (transmissivity T<5 ppm at λ(0)=1064 nm, absorption loss <0.5 ppm) multilayer dielectric coating of ion-beam-sputtered fused silica and titanium-doped tantala in the 10-300 K temperature range. A useful parameter for the computation of coating thermal noise on different substrates is derived as a function of temperature and frequency.

Bulk optical absorption of high resistivity silicon at 1550 nm.

We report on the measurement of the optical absorption of bulk crystalline silicon at 1550 nm. Using the photodeflection technique, absorption as low as 5 ppm/cm has been measured on a sample with a resistivity of 10 kΩ·cm. The absorption as a function of the resistivity has been derived for n-type silicon.

Direct measurement of absorption-induced wavefront distortion in high optical power systems.

Wavefront distortion due to absorption in the substrates and coatings of mirrors in advanced gravitational wave interferometers has the potential to compromise the operation and sensitivity of these interferometers [Opt. Lett.29, 2635-2637 (2004)]. We report the first direct spatially-resolved measurement, to our knowledge, of such wavefront distortion in a high optical power cavity. The measurement was made using an ultrahigh sensitivity Hartmann wavefront sensor on a dedicated test facility. The sensitivity of the sensor was lambda/730, where lambda=800 nm.