Personne : Galstian, Tigran
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Galstian
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Tigran
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Département de physique, de génie physique et d'optique, Faculté des sciences et de génie, Université Laval
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0000000116613117
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ncf11857328
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- PublicationAccès libreOptical design challenges of subnivean camera trapping under extreme arctic conditions(2021-12-09) Galstian, Tigran; Gauthier, Gilles; Kalhor, Davood; Maldague, X.; Pusenkova, Anastasiia; Poirier, MathildeCamera trapping is widely used in different ecological studies and is particularly important for remote locations and extreme environments. However, the application of camera traps in Arctic regions remains very limited. One of the challenges is the formation of hoar on the lens of cameras. In this article, we propose a solution to address this problem by changing the camera parameters and its position in order to optimize the camera trap for long-term subnivean deployment in the Canadian Arctic. Preliminary field tests show that this approach allows tracking lemmings in the frozen environment without natural light or external electrical power supply, where the direct observations are impossible for the most part of the year. We obtained the first videos of lemmings under the snow during the Arctic winter. Extending the observational network of the newly designed camera traps will help to better understand lemming population dynamics. The demonstrated approach is also promising for other polar applications.
- PublicationRestreintDynamics of light induced reorientation of nematic liquid crystals in spatially confined beams(Gordon and Breach, 2010-10-18) Brasselet, Étienne.; Galstian, Tigran; Dubé, Louis J.Optically induced reorientation dynamics in a nematic liquid crystal is investigated for circularly polarized laser beams with spot sizes smaller than the sample thickness. Various dynamical regimes, such as periodic, quasi-periodic, intermittent, self-organized and possibly chaotic regimes are observed. The role finite beam size is identified and a qualitative interpretation based on the spatial walk-off of the ordinary and extraordinary beams arising from double refraction phenomenon is proposed.
- PublicationAccès libreChip-scale full-Stokes spectropolarimeter in silicon photonic circuits(Optical Society of America, 2020-05-14) Galstian, Tigran; Dadalyan, Tigran; Bélander-de Villers, Simon; Lin, Zhongjin; Shi, WeiWavelength-dependent polarization state of light carries crucial information about light–matter interactions. However, its measurement is limited to bulky, high energy-consuming devices, which prohibits many modern, portable applications. Here, we propose and demonstrate a chip-scale spectropolarimeter implemented using a complementary metal oxide semiconductor compatible silicon photonics technology. Four compact Vernier microresonator spectrometers are monolithically integrated with a broadband polarimeter consisting of a 2D nanophotonic antenna and a polarimetric circuit to achieve full-Stokes spectropolarimetric analysis. The proposed device offers a solid-state spectropolarimetry solution with a small footprint of 1 mm × 0.6 mm and low power consumption of 360 mW. Full-Stokes spectral detection across a broad spectral range of 50 nm with a resolution of 1 nm is demonstrated in characterizing a material possessing structural chirality. The proposed device may enable a broader application of spectropolarimetry in the fields ranging from biomedical diagnostics and chemical analysis to observational astronomy.
- PublicationRestreintBifurcation analysis of optically induced dynamics in nematic liquid crystals : circular polarization at normal incidence(Optical Society of America, 2005-08-01) Brasselet, Étienne.; Galstian, Tigran; Dubé, Louis J.; Dmitry, Krimer; Kramer, LorenzWe present a detailed bifurcation analysis of the nonlinear reorientation dynamics of a homeotropically aligned nematic liquid-crystal film excited by an elliptically polarized beam at normal incidence with the intensity and the polarization state of light as the control parameters. The asymmetry arising from the elliptical polarization of the excitation lightwave is shown to affect dramatically the dynamics, and various new dynamical behaviors are reported: (i) quasi-periodic rotations for almost circular polarization; (ii) a discontinuous transition, identified as a homoclinic bifurcation, to a largely reoriented state over a large range of ellipticity values; (iii) oscillations associated with large reorientation; and (iv) optical multistability between several distinct dynamical regimes.
- PublicationRestreintBifurcation analysis of optically induced dynamics in nematic liquid crystals : elliptical polarization at normal incidence(Optical Society of America, 2005-08-01) Krimer, Dmitry; Brasselet, Étienne.; Kramer, Lorenz; Galstian, Tigran; Dubé, Louis J.We present a detailed bifurcation analysis of the nonlinear reorientation dynamics of a homeotropically aligned nematic liquid-crystal film excited by an elliptically polarized beam at normal incidence with the intensity and the polarization state of light as the control parameters. The asymmetry arising from the elliptical polarization of the excitation lightwave is shown to affect dramatically the dynamics, and various new dynamical behaviors are reported: (i) quasi-periodic rotations for almost circular polarization; (ii) a discontinuous transition, identified as a homoclinic bifurcation, to a largely reoriented state over a large range of ellipticity values; (iii) oscillations associated with large reorientation; and (iv) optical multistability between several distinct dynamical regimes.
- PublicationAccès libreOptically induced dynamics in nematic liquid crystals : the role of twist deformation and asymmetry(American Physical Society, 2003-03-26) Brasselet, Étienne.; Galstian, Tigran; Dubé, Louis J.; Doyon, BernardWe present a theoretical study of optically induced dynamics in a homeotropic nematic liquid crystal excited at normal incidence. By retaining the first symmetric and antisymmetric reorientation modes, the dynamical equations are reduced to a four-dimensional problem. The main advantage of this minimal approach is to emphasize the role of twisted mode and asymmetry of the light-induced molecular reorientation in a manner suitable for a clear physical interpretation. Theoretical results are compared with experiments in the particular case of circularly polarized light beams to show the physical origin of mode competition and of the breakdown of chiral and longitudinal symmetry. The model successfully describes previous experimental studies such as time-dependent three-dimensional molecular dynamics, light-induced stabilized helical reorientation, and in-plane precession regime in achiral nematics. While a recent experiment has revealed a new spatiotemporal transition, the model succeeds to describe all the features of such a bifurcation pointing out anew the importance of asymmetry. Finally, the first quantitative description of the appearance of a giant mirrorless optical bistability when twisted reorientation modes are excited is demonstrated. A qualitative physical interpretation is suggested for all these phenomen
- PublicationRestreintNew laser induced spatio–temporal transition in nematics(Elsevier Science, 2002-05-07) Brasselet, Étienne.; Galstian, Tigran; Dubé, Louis J.; Doyon, BernardWe report the observation of a new light-induced spatio–temporal transition in homeotropically aligned nematic liquid crystals under the action of circularly polarized light. We believe that the competition of symmetric and asymmetric excitation modes is at the origin of this abrupt transition. A theoretical model explaining the main features of the observation is proposed
- PublicationAccès libreOptically induced dynamics in nematic liquid crystals : the role of finite beam size(American Physical Society, 2004-02-10) Brasselet, Étienne.; Galstian, Tigran; Dubé, Louis J.; Doyon, BernardWe report on the influence of a finite beam size on the molecular reorientation dynamics when a nematic liquid crystal film is excited by a laser beam. We present experimental evidence of a new class of nonlinear dynamics when the excitation is a Gaussian shaped, circularly polarized laser beam at normal incidence. Various nonlinear regimes, periodic, quasiperiodic, intermittent, and possibly chaotic, are observed. A physical interpretation based on walk-off effects is proposed and its implications on current research in the field are discussed