International Summer Research Program in Gravitational-Wave Physics:
Research Experiences for Undergraduates around the world

Virgo group at University of Padova, INFN Padova and Legnaro National Labs
  • Characterization of high-performance optical coatings for GW interferometers:
    Optical coatings are one of the most critical systems in GW detectors. In particular the noise floor of the interferometer in its most sensitive band is nowadays defined by the coatings of the mirror test masses. This noise arises due to the random fluctuations of the coating surface stimulated by thermally activated rearrangements of the molecular structure of the amorphous layer. An international effort is nowadays being put forward to research new ultra-high performance materials combining an improved thermal noise figure with the extreme optical quality required by gravitational wave interferometry.
    In our group we are studying how the post-deposition thermal processes that are normally performed on those coatings affect their structure. The issue here is to detect the formation of crystalline regions in the bulk of the amorphous optical layers. To this scope, we will carry out in-situ X-ray diffraction experiments on TiO -doped Tantala, which is the material of choice for present GW interferometers. The participant will be trained to use our X-ray diffraction machine in remote configuration and collect some data. The data will then be analyzed to obtain thermodynamic and structural parameters such as the crystallization kinetics, the activation energy for crystallite formation, the average size and microstrain of the crystalline grains.
    Mentor: Marco Bazzan
    Related Project 2021: "Nanocrystallite formation in amorphous titania coatings"

  • Stray light from dust contamination in GW interferometers:
    Stray light is increasingly recognized as one of the possible sources of excess noise in modern gravitational wave interferometers. Stray light leaves the laser beam for a variety of reasons and later recombines with the main optical path carrying with it extra phase noise acquired because of reflection off of vibrating surfaces. Mechanisms that can cause the light to leave the beam and/or recombine with it later include: residual reflection from anti-reflection surfaces; scattering due to surface roughness of optical and mechanical elements; and scattering due to the presence of dust contamination on optical surfaces. The latter mechanism is particularly critical, both because it has the potential to dominate all the other contributions, and because predicting the level of dust contamination on optics in a realistic setting is difficult.
    The aim of this project is that of obtaining credible estimates for the amount of stray light produced by dust contamination in different environments, both in air and in vacuum, as a function of the exposure time. Using image analysis software, the student will analyze pictures of a number of samples that have been exposed to representative environments, set up a reliable procedure to extract the distribution of dust particles in an semi-automated and uniform way, and use the data to make prediction on the amount and distribution of scattered light produced by this particular source in various cases. If time allows, this information will be used to perform ray-tracing simulations of optical setups relevant to Virgo.
    Mentor: Livia Conti
    Related Project 2021: "Characterizing dust contributions in Virgo cleanrooms"

  • Development of sensors and actuators for laser mode matching:
    Correct spatial matching of the laser modes supported by the various resonant optical cavities present in gravitational wave interferometric detectors has recently become a research priority. In the past, mismatches of 10% or more could be easily tolerated without an significant negative impact on detector performance, and relatively little effort has been put in developing sophisticated mode matching techniques. However, successful implementation of squeezing technologies in modern instruments demands the overall losses, including those due to mode-mismatch, to be at the level of 1%. This requires the development of sensors and actuators able to precisely measure and correct such a level of mismatch without negatively affecting other properties of the laser beam. We have an ongoing line of research on the topic, with the aim of developing innovative sensors and actuators and testing them on an integrated experiment before direct application in the squeezed vacuum injection line of the Virgo detector. In particular we are developing a radio-frequency sensing technique bases on a weak but very fast electro-optical actuator, and various innovative designs for quiet, high-range actuators. The student will help characterize the devices, fine-tune the sensing technique and perform tests to demonstrate closed-loop operation of a feedback system for mode matching sensing and correction on a table-top dedicated optical setup.
    Mentor: Giacomo Ciani
    Related Project 2018: "Higher Order Mode Matching in Optical Resonators"

  • Thermal noise of solids in non-equilibrium steady states:
    Thermal noise of various origins limits the sensitivity of modern Gravitational wave experiments in several frequency bands. For the purpose of estimating thermal noise contributions, the instruments are usually modeled as equilibrium systems, but it is not clear to what extent this description is adequate. For instance, various parts of an interferometric detector are kept in a out-of-equilibrium steady state by the thermal gradients due to the thermal loads from absorbed laser light. The situations that drive the GW detectors out of equilibrium will be even more obvious in future generations, due to higher laser power and cryogenic operation. Currently, there is no valid theory to describe thermal noise in these conditions. However we have already observed, both experimentally and numerically, that there are instances where thermal noise of solids in non-equilibrium departs significantly from a trivial extension of the equilibrium results (L.Conti et al., J. Stat. Mech. (2013) P12003). Building on these results we are running an experiment to further extend our past research on the thermal noise of mechanical oscillators in states out of equilibrium (i.e. subject to stable thermal gradients). The readout is based on interferometric techniques. The student will take part in this experiment, focusing on a particular thermodynamic state and studying the effect of heat fluxes on the thermal noise.
    Mentor: Livia Conti
    Related Project 2018: "Thermal Noise in Non-Equilibrium"

  • Photothermal measurement of ultra-low absorbing nonlinear crystals by a novel intra-cavity method:
    Non-linear optical materials, and potassium tytanil phosphate (KTP) in particular, are nowadays used in a variety of diverse applications, including second harmonic laser light generation; this technique is crucial for the development of squeezed light states to be used in modern gravitational-wave interferometers. However a critical requirement is to keep as low as possible the level of absorption phenomena which may spoil the overall degree of squeezing. The student will be involved in the development of a new method for measuring the absorption coefficient of (KTP) crystals. The work will be divided into two blocks: as a first step, the proposed method will be modeled by means of finite-element numerical simulations. Secondly, the student will collaborate to the experimental realization of a prototype setup.
    Mentors: Marco Bazzan and Jean-Pierre Zendri

Past IREU Projects
Other Prior Projects