Einstein Telescope (ET) is the pioneer project aiming to the realisation of a 3rd generation Gravitational Wave Observatory in Europe. Benefiting of the momentum given by the scientific successes of the LIGO and Virgo detectors, the ET project had, in the last few years, an important boost toward its realisation, entering in many of the national and international roadmaps. ET will be simultaneously a new discovery and a precision measurement observatory; it has a rich variety of scientific and multidisciplinary targets in astrophysics, nuclear physics, fundamental physics and cosmology. ET will be also a technological challenge: in order to achieve the expected sensitivity a new underground research infrastructure will be realised, a multi-interferometer per detector design will be implemented hosting new or updated technologies studied to reduce the noises limiting the current detectors. An overview of the science targets, of the observatory design, of the needed technologies and of the ET project organisation will be presented.

We demonstrate a novel, fully-integrated approach to spectral sensing in the near-infrared range suitable for analyzing the chemical composition of organic materials. The sensor consists of 16 detector pixels, each forming a resonant-cavity enhanced photodetector consisting of an InGaAs/InP photodiode and a tuning layer enclosed in a planar cavity formed by two metal mirrors. For wavelengths meeting the resonance condition of the optical cavity, the absorption in the photodiode is enhanced, which leads to a wavelength-specific response of the photodetector. As the thickness of the tuning layer is varied throughout the pixels, each of the 16 photodetectors features an individual complex spectral response with several peaks of about 50 nm linewidth and responsivity above 0.1 A/W. All pixels together cover the whole wavelength range from 900 nm to 1700 nm, allowing for the analysis of broad spectral features typical for diffuse reflectance spectra of organic materials in the near-infrared range. The photocurrents read-out from the spectral sensors can be combined with chemometric analysis methods to determine the material composition. We demonstrate the performance of the spectral sensor for the determinate of moisture in rice grains, leading to a coefficient of determination of R² = 0.97. Other demonstrated applications include the quantification of the sugar content in tomatoes, fat and protein content in raw cow milk and the classification of different types of plastic. With a size of 1.5 mm by 1.5mm and a fabrication scheme based on optical lithography, this on-chip spectral sensor yields potential for large-scale production. Together with the mechanical stability of the sensor, this approach is an important step towards portable, low-cost spectral sensing solutions.

Recent advances in integration technologies enable constructing novel, highly complex and miniaturized photonic systems for a large variety of applications. A constantly increasing interest can be observed in implementing application specific photonic integrated circuits (ASPICs) in a new generation of optical sensing systems. The InP platform allows to realize complete interrogators of sensing systems, comprising the light sources and photodetectors. An InP PIC can also be used as a sensing element itself. In this work we discuss the sensing systems addressing two different application fields, which can benefit from the recent developments of InP platforms - optical gyroscopes and interrogators of fiber Bragg gratings. The principle of work of optical gyroscope is based on the Sagnac effect. Two typical configurations can be identified – interferometric fiber-optic gyroscope (IFOG) and ring laser gyroscope (RLG). An integrated interrogator unit of an IFOG system presented here was realized using a DBR laser, passive couplers and PIN photodiodes. Characterization results have proven the possibility of detection of the Sagnac signal for the length of the fiber loop of 1 km. We also discuss monolithic single-frequency lasers, which were realized in the framework of the development of an integrated optical gyro. Also, the integrated interrogators of fiber Bragg gratings are presented and discussed. The investigated solutions are based on the interrogation scheme in which a broadband signal is coupled to a network of FBGs, and the reflected signals are analyzed using a spectrometer based on an arrayed waveguide grating. Several realized circuits are discussed with respect to their design, characterization results and potential for application in sensing systems. Studies were funded by FOTECH-1 project granted by Warsaw University of Technology under the program Excellence Initiative: Research University (ID-UB). This work was partially supported by National Centre for Research and Development (PBS3/B9/41/2015).

Optical fibers are widely used for temperature sensing due to their intrinsic temperature sensitivity. However, such sensitivity is an issue when one wants to sense other parameters, as for example, the refractive index of a sample. Thus, somehow it is necessary to compensate the effect of temperature. For this reason, different dual-parameter fiber optic sensing schemes have been reported in the literature. To the best of our knowledge, the majority of such schemes need two sensors (one for reference) or two platforms to monitor two parameters. In this work, we demonstrate that a single optical fiber interferometer is capable of monitoring two parameters (refractive index and temperature) simultaneously. Said interferometer is built with a short segment of coupled-core multicore fiber fusion spliced at the end of a conventional single mode fiber. In the multicore fiber, two supermodes are excited with similar intensities. As a result, the interference pattern is truly sinusoidal with high visibility. Temperature induces a shift to the interference pattern and refractive index alters the amplitude of such a pattern. We have investigated analytically and experimentally the performance of our dual-parameter sensor under different fabrication conditions and its multiple practical applications. For example, it can be used to measure the thermo-optic coefficient of gels, polymers or liquids. Such results will be presented at the conference.

In this work, we show a gas detection system based on fiber enhanced Raman spectroscopy intended to be used in rapid detection of gas mixtures. Here, a photonic crystal fibre (HCPCF) is used for Raman enhancement. The HCPCF acts as a multi-pass cavity, increases the energy density and Raman scattering efficiency in the core. The band gap of the HCPCF used is centred around 800 nm. Furthermore, a solid state diode laser with an emission wavelength at 785 nm is used. Measurements are made on atmospheric gases as well as CH4 and NH3 with varying fibre length, integration time and analyte concentration.

Near-IR (~1.5 µm) and mid-IR (~8 µm) laser heterodyne radiometers have been recently developed for ground-based remote sensing greenhouse gases in the atmospheric column. Field campaigns have been performed. The developed LHR instruments as well as the preliminary results of their applications to the measurements of CH4, N2O, CO2 (including 13CO2/12CO2), H2O vapor (and its isotopologue HDO) in the atmospheric column will be presented and discussed.

Zinc oxide (ZnO) is one of the most studied materials in nanoscience and chemical sensing research area. Monitoring the variations of electrical conductance of different ZnO nanostructure has enabled the detection of different gases and volatile organic compounds (VOCs). Another interesting perspective emerges from the development of optical sensors and experiments based on the photoluminescence of the semiconductor, has shown excellent sensing properties towards different chemical substances, ranging from oxygen, NO2, CO and volatile compounds (ethanol, H2S), to biomolecules, such as glucose, in aqueous solutions. In the present study ZnO has been investigated as optical sensing material towards ozone (O3) detection, by monitoring its laser induced room temperature photoluminescence (PL) emission. The optical material consists of ZnO/polymer nanohybrids (ZnO/poly(poly(ethylene glycol) methyl ether methacrylate) (ZnO/PPEGMA) and ZnO/polydimethylsiloxane (ZnΟ)/PDMS)) which are excited with a UV pulsed laser source (λex= 248 nm, τex= 15 ns). The performance of these sensing systems has been investigated with respect to response, reversibility, and dynamic characteristics (response/recovery time) as a function of ozone concentration in synthetic air (1600 down to 50 ppb).

Fiber optic spectroscopy label-free composition analysis makes it the best tool for reaction monitoring in Process Analytical Technologies (PAT) and chemical analysis of bio tissues for medical diagnostics in-citu and in-vivo. Biological samples and modern chemicals are complex substances, which composition analysis requires combining several spectroscopic techniques. Fiber optics probes provide compact, flexible, robust, and cost-effective solutions to merge different optical modalities in one tool for sample analysis at the same point. This spatial synchronization of the analysis is critical for heterogeneous samples. Recent advances in optical fiber manufacturing significantly expand the wavelength range of the analysis from 0,3-2µm range with Silica fibers towards middle IR (with chalcogenide, AgCl:AgBr Polycrystalline PIR fibers, and Ag/AgI hollow glass waveguides covering together 1-20 µm range). We were able to fuse all 4 key spectroscopic methods (Fluorescence, NIR, MIR, and Raman) in compact fiber probes. In preliminary studies of tissue samples we showed that a combination of fluorescence with NIR or ATR-IR spectroscopy results in much better accuracy of the tumor margin detection than each of the individual methods separately. This synergy is explained by the capability of different light modalities to deliver complementary chemical information. We are using information from fluorescence background subtracted from Raman spectra to enhance the accuracy of the analysis. This concept, combined with advanced chemometrics data analysis, enables the development of customized spectral fiber sensors based only on several wavelengths or wavelength regions. Our recent experiments have shown the possibility of combining mid-IR ATR absorption and Raman spectroscopy in one compact fiber-optic probe. Thus it is possible to obtain an extended optical spectrum of molecular vibrations from the same point of a complex sample. These advances turn fiber-optic multispectral probes into the universal tool for applications that require in vivo analysis or real-time process monitoring.

Time resolved infrared spectroscopic measurement techniques during CW-laser matter interaction of Fiber-Reinforced-Polymers (FRP) Hartmut Borchert, Robert Paetzold, Vadim Allheily French-German Research Institute of Saint-Louis, 5 rue du Général Cassagnou, BP 70034, 68301 Saint-Louis, France corresponding author: hartmut.borchert@isl.eu Composite materials have shown a marked increase in their use in aerospace and military applications in recent years. The matrix phase of many common aerospace composite materials are made of polymeric materials and a fiber material. Future laser-based weapons with solid-state high energy laser sources are considered to neutralize that kind of threat. The thermodynamics as well as the thermo-mechanical behavior of such heterogeneous materials submitted to a typical laser weapon irradiation need therefore to be further explored to understand the deterioration process induced by the illumination process. One common measurement technique to visualize the heating and decomposition process is the use of time resolved emission spectroscopy in the visible (λ = 400 nm - 850 nm) [1,2,3] and infrared (λ = 1µm - 5.5µm) wavelength regime to retrieve the onset and time distribution of decomposition products as well as the temperature distribution from typical line and molecular emission involved. In the current work, we introduce the potential of time resolved emission and absorption spectroscopy in the infrared wavelength band from λ = 1µm up to λ = 5.5µm for monitoring thermal decomposition and combustion in the gas and fire plumes generated by laser irradiation of surfaces containing carbon, glass and polymer materials. The effectiveness of high-energy lasers to render a target nonfunctional depends on the propagation of the laser light through these evolving gas- and fire-plumes. First results on time- and wavelength-resolved infrared emission signals of decomposition gases and their influence on temperature determination are presented. 1. C.Th.Alkemade, Fundamentals of analytical flame spectroscopy, Hilger Bristol, 1972 2. V.Allheily, L.Merlat, F.Lacroix, A.Eichhorn, G.L’Hostos, Physics Procedia, 83 (2016) 1044-1054 3. H.Borchert, Time resolved spectroscopic temperature measurement techniques during CW-laser matter interaction of glass-fiber-reinforced-polymers (GFRP), Proc.SPIE 11162, doi: 10.1117/12.2532324, 7.October 2019