Levitating the noise performance of ultra-stable laser cavities assisted by a deep neural network: The non-intuitive role of the mirrors

The most precise measurand available to science is the frequency of ultra-stable lasers. With a relative deviation of 4 × 10−17 over a wide range of measuring times between one second and 100 seconds, the smallest effects in nature can thus be made measurable. To enable cutting-edge precision, the laser frequency is stabilized to an external optical cavity. This complex optical device must be manufactured to the highest standards and shielded from environmental influences. Given this assumption, the smallest internal sources of perturbation become dominant, namely the internal noise of the optical components. In this work, we present the optimization of all relevant noise sources from all components of the frequency-stabilized laser. We discuss the correlation between each individual noise source and the different parameters of the system and discover the significance of the mirrors. The optimized laser offers a design stability of 8 × 10−18 for an operation at room temperature for measuring times between one second and 100 seconds

Key signal contributions in photothermal deflection spectroscopy

We report on key signal contributions in photothermal deflection spectroscopy (PDS) of semiconductors at photon energies below the bandgap energy and show how to extract the actual absorption properties from the measurement data. To this end, we establish a rigorous computation scheme for the deflection signal including semi-analytic raytracing to analyze the underlying physical effects. The computation takes into account linear and nonlinear absorption processes affecting the refractive index and thus leading to a deflection of the probe beam. We find that beside the linear mirage effect, nonlinear absorption mechanisms make a substantial contribution to the signal for strongly focussed pump beams and sample materials with high two-photon absorption coefficients. For example, the measured quadratic absorption contribution exceeds 5% at a pump beam intensity of about ${1.3}\times{10^{5}}\;{W}/{cm^{2}}$ in Si and at ${5}\times{10^{4}}\;{W}/{cm^{2}}$ in GaAs. In addition, our method also includes thermal expansion effects as well as spatial gradients of the attenuation properties. We demonstrate that these effects result in an additional deflection contribution which substantially depends on the distance of the photodetector from the readout point. This distance dependent contribution enhances the surface related PDS signal up to two orders of magnitude and may be misinterpreted as surface absorption if not corrected in the analysis of the measurement data. We verify these findings by PDS measurements on crystalline silicon at a wavelength of 1550 nm and provide guidelines how to extract the actual attenuation coefficient from the PDS signal.Comment: 10 pages, 16 figures, submitted to Journal of Applied Physiv

¿Qué leían los cruzados argentinos? : Las lecturas del nacionalismo católico a través de 'Cabildo' (1973-1976)

En el siguiente artículo se aborda la revista nacionalista católica Cabildo desde una perspectiva sensible a la historia intelectual. El objetivo es ampliar y completar, a partir de las lecturas promocionadas en las publicidades y de los libros reseñados, el universo de representaciones políticas y religiosas. Luego de presentar la revista, largamente estudiada por la historiografía, se analizan las publicidades identificando redes intelectuales locales, pero también transnacionales. En forma posterior se examinan tres reseñas dedicadas a la lectura de la historia, la ciencia ficción y la guerra contrarrevolucionaria. Se concluye que el nacionalismo católico, lejos de impugnar la modernidad en un nivel ontológico, trazó un diálogo práctico bajo la condición de corregir sus peligrosas derivas.En el següent article s'aborda la revista nacionalista catòlica Cabildo des d'una perspectiva sensible a la història intel·lectual. L'objectiu és ampliar i completar, a partir de les lectures promocionades en les publicitats i dels llibres ressenyats, l'univers de representacions polítiques i religioses. Després de presentar la revista, llargament estudiada per la historiografia, s'analitzen les publicitats tot identificant xarxes intel·lectuals locals, però també transnacionals. Més endavant s'examinen tres ressenyes dedicades a la lectura de la història, la ciència-ficció i la guerra contrarevolucionària. Es conclou que el nacionalisme catòlic, lluny d'impugnar la modernitat en un nivell ontològic, va traçar un diàleg pràctic sota la condició de corregir les seves perilloses derives.The following paper focuses on the Catholic nationalist magazine Cabildo from an Intellectual History standpoint. The aim is to expand and complete, from the reading matter promoted in its advertisements and the books reviewed, the universe of its political and religious representations. After a brief introduction to the magazine, long studied in the literature, the advertisements are analyzed and transnational as well as local intellectual networks are identified. Later, three book reviews, focusing on the interpretation of Argentine history, science fiction, and the counterrevolutionary war, are examined. It is concluded that, far from challenging modernity on an ontological level, Cabildo entered into a practical dialogue with it without accepting its dangerous deviations

Investigation of mechanical losses of thin silicon flexures at low temperatures

The investigation of the mechanical loss of different silicon flexures in a temperature region from 5 to 300 K is presented. The flexures have been prepared by different fabrication techniques. A lowest mechanical loss of $3\times10^{-8}$ was observed for a 130 $\mu$m thick flexure at around 10 K. While the mechanical loss follows the thermoelastic predictions down to 50 K a difference can be observed at lower temperatures for different surface treatments. This surface loss will be limiting for all applications using silicon based oscillators at low temperatures. The extraction of a surface loss parameter using different results from our measurements and other references is presented. We focused on structures that are relevant for gravitational wave detectors. The surface loss parameter $\alpha_s$ = 0.5 pm was obtained. This reveals that the surface loss of silicon is significantly lower than the surface loss of fused silica.Comment: 16 pages, 7 figure

Eco-aesthetic dimensions: Herbert Marcuse, ecollogy and art

In his last book, The Aesthetic Dimension (1978), Marcuse argued that a concern for aesthetics is justified when political change is unlikely. But the relation between aesthetics and politics is oblique: “Art cannot change the world, but it can contribute to changing the consciousness … of the men and women who could change the world.” (p. 33). Marcuse also linked his critique of capitalism to environmentalism in the early 1970s: “the violation of the Earth is a vital aspect of the counterrevolution.” (Ecology and Revolution, in The New Left and the 1960s, Collected Papers 3, 2005, p. 173). This article revisits Marcuse’s ideas on aesthetics and ecology, and reviews two recent art projects which engage their audiences in ecological issues: The Jetty Project (2014) by Wolfgang Weileder—which used recycled material and community participation to construct a temporary monument within a wider conservation project on the Tyne, N-E England—and Fracking Futures by HeHe (Helen Evans and Heiko Hansen)—which turned the interior of the gallery at FACT, Liverpool, into what appeared to be a fracking site. The aim is not to evaluate the projects, nor to test the efficacy of Marcuse’s ideas, more to ask again whether art has a role in a shift of attitude which might contribute to dealing with the political and economic causes of climate change

Scientific Opinion on the safety and efficacy of Urea for ruminants

Urea supplementation to feed for ruminants provides non-protein nitrogen for microbial protein synthesis in the rumen and thus in part replaces other dietary protein sources. Urea supplementation of feed for ruminants at doses up to 1 % of complete feed DM (corresponding to 0.3 g/kg bw/day) is considered safe when given to animals with a well adapted ruminal microbiota and fed diets rich in easily digestible carbohydrates. Based on the metabolic fate of urea in ruminants, the use of urea in ruminant nutrition does not raise any concern for consumers\u2019 safety. Urea is considered to be non irritant to skin and eyes and its topical use suggests that it is not a dermal sensitiser. The risk of exposure by inhalation would be low. The substitution of protein by urea in well balanced feed for ruminants would not result in an increased environmental nitrogen load. Urea is an effective source of non-protein nitrogen substituting for dietary protein in ruminants

Pound-Drever-Hall error signals for the length control of three-port grating coupled cavities

Gratings enable light coupling into an optical cavity without transmission through any substrate. This concept reduces light absorption and substrate heating and was suggested for light coupling into the arm cavities of future gravitational wave detectors. One particularly interesting approach is based on all-reflective gratings with low diffraction efficiencies and three diffraction orders (three ports). However, it was discovered that, generally, three-port grating coupled cavities show an asymmetric resonance profile that results in asymmetric and low quality Pound–Drever–Hall error signals for cavity length control. We experimentally demonstrate that this problem is solved by the detection of light at both reflection ports of the cavity and the postprocessing of the two demodulated electronic signals

Scientific Objectives of Einstein Telescope

The advanced interferometer network will herald a new era in observational astronomy. There is a very strong science case to go beyond the advanced detector network and build detectors that operate in a frequency range from 1 Hz-10 kHz, with sensitivity a factor ten better in amplitude. Such detectors will be able to probe a range of topics in nuclear physics, astronomy, cosmology and fundamental physics, providing insights into many unsolved problems in these areas.Comment: 18 pages, 4 figures, Plenary talk given at Amaldi Meeting, July 201