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Enhanced sensitivity of the LIGO gravitational wave detector by using squeezed states of light
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)Nearly a century after Einstein first predicted the existence of gravitational waves, a global network of Earth-based gravitational wave observatories1, 2, 3, 4 is seeking to directly detect this faint radiation using precision laser interferometry. Photon shot noise, due to the quantum nature of light, imposes a fundamental limit on the attometre-level sensitivity of the kilometre-scale Michelson interferometers deployed for this task. Here, we inject squeezed states to improve the performance of one of the detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO) beyond the quantum noise limit, most notably in the frequency region down to 150 Hz, critically important for several astrophysical sources, with no deterioration of performance observed at any frequency. With the injection of squeezed states, this LIGO detector demonstrated the best broadband sensitivity to gravitational waves ever achieved, with important implications for observing the gravitational-wave Universe with unprecedented sensitivit
Polar columnar and lamellar mesophases in homologous bent-core compounds derived from methyl 3,5-dihydroxybenzoate
No full textRestricted Access.The synthesis and mesomorphic properties of the first three homologous series of symmetrical seven-ring bent-core compounds derived from methyl 3,5-dihydroxybenzoate have been described. In all the three series the lower homologues show an intercalated smectic (B6) phase. The middle homologues exhibit a polar columnar phase that shows antiferroelectric characteristics, while the higher homologues exhibit a switchable smectic phase with chiral conglomerates (SmCPAF). More interestingly, in one of the homologues, coexistence of a switchable columnar phase and a switchable lamellar phase has been observed. The mesophases were characterised using classical techniques of polarised light optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical studies
Synthesis of Banana-Shaped liquid crystals for photoswitching properties.
No full textRestricted Access.Three banana-shaped monomers containing naphthalene as central units and azobenzene in side arms with terminal alkenes were synthesized and characterized. DSC, polarizing optical microscopy, and X-ray diffraction measurements prove that all compounds exhibit B6 phase. The trans-azobenzene showed high-intensity π–π* transition at about 365 nm and low-intensity n–π* transition at about 450 nm. The strong photoisomerization behavior in solutions of the molecules displayed that trans to cis isomerization takes 45 sec whereas reverse process takes about 28 h and 30 min. This long thermal back relaxation is useful for creation of optical image storage
Conditions for supernovae-driven galactic winds.
No full textRestricted AccessWe point out that the commonly assumed condition for galactic outflows, that supernovae (SNe) heating is efficient in the central regions of starburst galaxies, suffers from invalid assumptions. We show that a large filling factor of hot (?106?K) gas is difficult to achieve through SNe heating, irrespective of the SN's initial gas temperature and density, its uniformity, or its clumpiness. We instead suggest that correlated supernovae from OB associations in molecular clouds in the central region can drive powerful outflows if the molecular surface density is >103 M. pc-
Book review of Beyond the Stars. Our Origins and the Search for Life in the Universe. Paolo Saraceno
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Galactic winds driven by cosmic ray streaming
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)Galactic winds are observed in many spiral galaxies with sizes from dwarfs up to the Milky Way, and they sometimes carry a mass in excess of that of newly formed stars by up to a factor of ten. Multiple driving processes of such winds have been proposed, including thermal pressure due to supernova-heating, UV radiation pressure on dust grains, or cosmic ray (CR) pressure. We here study wind formation due to CR physics using a numerical model that accounts for CR acceleration by supernovae, CR thermalization, and advective CR transport. In addition, we introduce a novel implementation of CR streaming relative to the rest frame of the gas. We find that CR streaming drives powerful and sustained winds in galaxies with virial masses M_200 < 10^{11} Msun. In dwarf galaxies (M_200 ~ 10^9 Msun) the winds reach a mass loading factor of ~5, expel ~60 per cent of the initial baryonic mass contained inside the halo's virial radius and suppress the star formation rate by a factor of ~5. In dwarfs, the winds are spherically symmetric while in larger galaxies the outflows transition to bi-conical morphologies that are aligned with the disc's angular momentum axis. We show that damping of Alfven waves excited by streaming CRs provides a means of heating the outflows to temperatures that scale with the square of the escape speed. In larger haloes (M_200 > 10^{11} Msun), CR streaming is able to drive fountain flows that excite turbulence. For halo masses M_200 > 10^{10} Msun, we predict an observable level of H-alpha and X-ray emission from the heated halo gas. We conclude that CR-driven winds should be crucial in suppressing and regulating the first epoch of galaxy formation, expelling a large fraction of baryons, and - by extension - aid in shaping the faint end of the galaxy luminosity function. They should then also be responsible for much of the metal enrichment of the intergalactic medium
Enhanced optical limiting in nanosized mixed zinc ferrites
No full textOpen AccessOptical limiting performance of zinc ferrite, nickel zinc ferrite, and copper zinc ferrite nanoparticles is investigated at 532 nm using 5 nanosecond laser pulses. Enhanced optical limiting is observed in the mixed zinc ferrites, which is attributed to the relative longevity of self-trapped charge transfer states. Samples exhibit absorption saturation followed by a rapid onset of optical limiting as the input fluence is increased. This is advantageous in applications where detector sensitivity should be retained at the maximum value until the input fluence approaches the detector damage regime. The Z-scan results are compared to those measured in C60
