Optical properties of germania and titania at 1064 nm and at 1550 nm

One of the main noise sources in current gravitational wave detectors is the thermal noise of the high-reflectivity coatings on the main interferometer optics.
Coating thermal noise is dominated by the mechanical loss of the high-refractive index material within the coating stacks, Ta2O5 mixed with TiO2. For upgrades to room-temperature detectors, a mixture of GeO2 and TiO2 is an interesting alternative candidate coating material. While the rather low refractive index of GeO2 increases with increasing TiO2 content, a higher TiO2 content results in a lower threshold temperature before heat treatment leads to crystallisation, and potentially to a degradation of optical properties. For future cryogenic detectors, on the other hand, a higher TiO2 content is beneficial as the TiO2 suppresses the low-temperature mechanical loss peak of GeO2. In this paper, we present the optical properties of coatings -- produced by plasma-assisted ion-beam evaporation -- with high TiO2 content at 1550nm, a laser wavelength considered for cryogenic gravitational-wave detectors, as a function of heat-treatment temperature. For comparison, the absorption was also measured of pure GeO2. Furthermore, results at the currently-used wavelength of 1064nm are presented

Environmental impact of producing and operating server infrastructure : A systematic literature review

Technologies that use cloud computing have increased considerably in the last decades. Computer services that we had in local devices have evolved to cloud services, resulting in applications such as online shopping stores, streaming platforms, or databases of large companies. In order to store and manage all the information that these types of services create, data centers were built and have been increasing in number and size in the last years. A big part of these databases is formed by server infrastructures, which are the devices that are responsible for storing and managing the data. Considerable research has been carried out to analyze the quantity of energy that servers consume and reduce it. What has been less considered is the environmental impact that servers have, not when they are operational but in the production phase (material gathering, transportation, assembly, etc.). A Systematic Literature Review (SLR) has been carried out to answer the research question that has been defined. The environmental impact of different stages is presented confirming the idea that other life cycle phases also have a big importance in the total environmental impact. Methods to reduce that impact are also explained