Abstract. We present two search algorithms that implement logarithmic tiling of the time-frequency plane in order to efficiently detect astrophysically unmodeled bursts of gravitational radiation. The first is a straightforward application of the dyadic wavelet transform. The second is a modification of the windowed Fourier transform which tiles the time-frequency plane for a specific Q. In addition, we also demonstrate adaptive whitening by linear prediction, which greatly simplifies our statistical analysis. This is a methodology paper that aims to describe the techniques for identifying significant events as well as the necessary pre-processing that is required in order to improve their performance. For this reason we use simulated LIGO noise in order to illustrate the methods and to present their preliminary performance.

We report the fabrication of single mode buried channel waveguides for the whole mid-infrared transparency range of chalcogenide sulphide glasses (λ ≤ 11 µm), by means of direct laser writing. We have explored the potential of this technology by fabricating a prototype three-dimensional three-beam combiner for future application in stellar interferometry, which delivers a monochromatic interference visibility of 99.89% at 10.6 µm, and an ultrahigh bandwidth (3-11 µm) interference visibility of 21.3%. These results demonstrate that it is possible to harness the whole transparency range offered by chalcogenide glasses on a single on-chip instrument by means of direct laser writing, a finding that may be of key significance in future technologies such as astrophotonics and biochemical sensing. . An essential step in order to unleash all of this potential science is to develop integrated optical platforms capable of addressing the technological requirements that each field demands. In this sense, the development of on-chip instruments such as optical sensors, high resolution spectrometers, or sophisticated beam combiners, is currently of high interest for the previous mentioned applications [1,2,5,6,7].Although several MIR two-dimensional (2D) planar schemes have been recently developed [8,9], these are all based on multiple-step surface deposition and processing techniques, which place inherent limits to the device design and capabilities. In this Letter, we report the single-step fabrication of three-dimensional (3D) MIR photonic circuits inside chalcogenide glass, by means of ultrashort-pulse direct laser writing (DLW) [10][11][12][13][14]. We show that the MIR waveguide cores can be tailored in both size and refractive index, and can also be spatially positioned at will inside the material, making the chip extremely robust against mechanical stress, vibrations, humidity, and temperature changes [11]. Moreover, we also evidence that the useful range of these DLW waveguides is, as suspected [12], ultimately limited by the transparency range of the material used, and not by the fabrication technique.In this work, high quality research and commercial chalcogenide sulphide glasses were used, both of which are free of highly toxic arsenic compounds. These glasses were commercial GaLaS (here after GLS) [14] and the research composition 75GeS2-15Ga2S3-4CsI-2Sb2S3-4SnS (here after GCIS) [15]. The MIR transmission upper limit of commercial GLS is known to be ~10 µm [14], while for GCIS we measured a slightly higher transmission upper limit of ~11 µm, as it is shown in Figure 1(a).

Second order nonlinear optical properties of a series of trinitrosubphthalocyanine (SubPc) isomers were studied experimentally by electric field induced second harmonic (EFISH) generation and hyper Rayleigh scattering (HRS). These experimental values were compared to the ones obtained theoretically employing both sum over states (SOS) and finite field (FF) methods. From these studies, it was shown that the dipolar contributions to the beta tensor are very much dependent on the substitution pattern at the periphery of the subphthalocyanine macrocycle, whereas the octupolar contributions remain mostly unchanged. Consequently, it was deduced that SubPc is extremely well suited for the decoupling of octupolar and dipolar contribution to the NLO response.

The second-harmonic generation (SHG) response of unsubstituted subnaphthalocyanines (SubNcs) has been measured for the first time by electric field-induced second-harmonic generation (EFISH) (1.064 and 1.90 µm) and hyper-Rayleigh scattering (HRS) (1.064 µm) experiments. The quadratic hyperpolarizability derived from the experiments is significant (β HRS (0) ) 34.7 × 10 -30 esu) and similar to that also measured under the same conditions for the related unsubstituted subphthalocyanine (SubPc) molecule (β HRS (0) ) 38.3 × 10 -30 esu). To meaningfully discuss the nonlinear optical (NLO) data, semiempirical INDO/S calculations of the permanent dipole moments of the ground and excited states (Q band) have been performed. Moreover, the dipolar transition moments connecting the ground and degenerate excited states and the two excited states have been also determined. The calculations suggest that for those low-energy excited states responsible for the Q optical absorption band, the two molecules (SubPc and SubNc) behave very approximately as planar π-conjugated octupoles with D 3h symmetry but having a permanent dipole moment along the perpendicular halogen-boron axis. The charge distribution along this axis is not appreciably influenced by the optical excitation, that is, light-induced charge motion only occurs inside the macrocycle without significant contribution of the apical Cl atom. The β HRS and γ EFISH data have been quantitatively analyzed with a three-level model, taking into account that only electronic terms contribute to the EFISH hyperpolarizability. As a consequence of this analysis, a sound rationale to describe the NLO behavior of these Pc-related compounds (SubPcs and SubNcs) has now emerged.

The development of high-contrast capabilities has long been recognized as one of the top priorities for the VLTI. As of today, the VLTI routinely achieves contrasts of a few 10 −3 in the near-infrared with PIONIER (H band) and GRAVITY (K band). Nulling interferometers in the northern hemisphere and non-redundant aperture masking experiments have, however, demonstrated that contrasts of at least a few 10 −4 are within reach using specific beam combination and data acquisition techniques. In this paper, we explore the possibility to reach similar or higher contrasts on the VLTI. After reviewing the state-of-the-art in high-contrast infrared interferometry, we discuss key features that made the success of other high-contrast interferometric instruments (e.g., integrated optics, nulling, closure phase, and statistical data reduction) and address possible avenues to improve the contrast of the VLTI by at least one order of magnitude. In particular, we discuss the possibility to use integrated optics, proven in the near-infrared, in the thermal near-infrared (L and M bands, 3-5 µm), a sweet spot to image and characterize young extra-solar planetary systems. Finally, we address the science cases of a high-contrast VLTI imaging instrument and focus particularly on exoplanet science (young exoplanets, planet formation, and exozodiacal disks), stellar physics (fundamental parameters and multiplicity), and extragalactic astrophysics (active galactic nuclei and fundamental constants). Synergies and scientific preparation for other potential future instruments such as the Planet Formation Imager are also briefly discussed.

The second harmonic generation (SHG) hyperpolarizabilities of a family of peripherally substituted pushpull phthalocyanines 1, 2, and 3, having an ethynediyl subunit in the linking bridge between the acceptor and donor moieties, have been measured. Electric field induced second harmonic (EFISH) generation experiments at 1.064 and 1.900 µm and hyper-Rayleigh scattering (HRS) experiments at 1.064 µm have been carried out.The quadratic hyperpolarizabilities values derived from these experiments are quite significant and superior to those found for similar push-pull compounds lacking of a triple C-bond in the donor-acceptor path. The main electronic parameters of the three compounds (electric dipole moments, orbital electronic distributions, and optical transition moments) have been calculated using the ZINDO/S method for molecular geometries that have been optimized through the PM3 method. Excellent agreement with spectroscopic data has been achieved. The SHG results have been analyzed through a 3-level model associated to the ground level and two split levels responsible for the Q-band, assuming either strict (for compound 2) or approximate (for compounds 1 and 3) C 2V planar symmetry. The parameters used in the model were those obtained from the electronic calculations. For molecule 2, both the theoretical diagonal and off-diagonal elements of the beta tensor, as well as β EFISH and β HRS , have been determined. Good agreement with the experimental HRS values is obtained, whereas EFISH values considerably differ from those obtained from the simple expression for γ EFISH ignoring the electronic contributions.

The quest for other habitable worlds and the search for life among them are major goals of modern astronomy. One way to make progress towards these goals is to obtain high-quality spectra of a large number of exoplanets over a broad range of wavelengths. While concepts currently investigated in the United States are focused on visible/NIR wavelengths, where the planets are probed in reflected light, a compelling alternative to characterize planetary atmospheres is the mid-infrared waveband (5-20 µm). Indeed, mid-infrared observations provide key information on the presence of an atmosphere, the surface conditions (e.g., temperature, pressure, habitability), and the atmospheric composition in important species such as H 2 O, CO 2 , O 3 , CH 4 , and N 2 O. This information is essential to investigate the potential habitability of exoplanets and to make progress towards the search for life in the Universe. Obtaining high-quality mid-infrared spectra of exoplanets from the ground is however extremely challenging due to the overwhelming brightness and turbulence of the Earth's atmosphere. In this paper, we present a concept of space-based midinfrared interferometer that can tackle this observing challenge and discuss the main technological developments required to launch such a sophisticated instrument.

A novel modulator design incorporating an E-O polymer into a resonant grating waveguide structure is presented. Using purely polymeric material we developed a resonant grating waveguide structure having low loss and high finesse, with approximately 2nm spectral line width at 1.55 mum. An externally applied voltage modulates the refractive index of the E-O waveguide, thereby shifting the resonance wavelength and modulating the incident light at MHz rates. Such modulator operates in free space and does not involve waveguide patterning nor the need for facet conditioning and coupling common to operation in the Mach-Zehnder type configuration.