Probing thick uniaxial birefringent medium in confined geometry: A polarised confocal micro-Raman approach

Blach, Jean‐François; Warenghem, M.; Bormann, D.

doi:10.1016/j.vibspec.2005.12.009

Cited by 11 publications

(8 citation statements)

References 19 publications

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“…3-D imaging of molecular orientations can be enabled by combining the complementary capabilities of PM and fluorescence confocal microscopy [20]; this approach, however, requires doping the LC with a specially-selected dye that has little or no influence on n ˆ. The labeling-free confocal Raman microscopy with polarized excitation/detection [21,22], that utilizes the spontaneous Raman signal dependence on orientations of molecular bonds, has also been recently applied to 3-D LC imaging; however, this technique requires long integration times of Raman signals and high excitation powers.…”

Section: Introductionmentioning

confidence: 99%

Realignment-enhanced coherent anti-Stokes Raman scattering and three-dimensional imaging in anisotropic fluids

Kachynski¹,

Kuzmin²,

Prasad³

et al. 2008

Opt. Express

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We apply coherent anti-Stokes Raman Scattering (CARS) microscopy to characterize director structures in liquid crystals. We demonstrate that the polarized CARS signal in these anisotropic fluids strongly depends on alignment of chemical bonds/molecules with respect to the collinear polarizations of Stokes and pump/probe excitation beams. This dependence allows for the visualization of the bond/molecular orientations via polarized detection of the CARS signal and thus for CARS polarization microscopy of liquid crystal director fields, as we demonstrate using structures in different phases. On the other hand, laser-induced director realignment at powers above a well-defined threshold provides the capability for all-optical CARS signal enhancement in liquid crystals. Since liquid crystalline alignment can be controlled by electric and magnetic fields, this demonstrates the feasibility of CARS signal modulation by applying external fields.

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Section: Introductionmentioning

confidence: 99%

Realignment-enhanced coherent anti-Stokes Raman scattering and three-dimensional imaging in anisotropic fluids

Kachynski¹,

Kuzmin²,

Prasad³

et al. 2008

Opt. Express

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“…For example, Ofuji et al [10] used Raman microscopy to image solid films of orientationally ordered fibrils in polyacetylene films with contrast based on the C=C bond stretching frequency, while Buyuktanir et al [11] used the cyano (CN) group stretching frequency to image defects in liquid crystal samples. Blach et al [12] developed a theory of polarized Raman microscopy in a birefringent medium and probed the director by using the vibrational mode at 2226 cm -1 . Camorani and Fontana used polarization sensitive confocal Raman microscopy to characterize liquid crystal alignment at a micropatterned substrate.…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional imaging of chemical bond orientation in liquid crystals by coherent anti- Stokes Raman scattering microscopy

Saar¹,

Park²,

Xie³

et al. 2007

Opt. Express

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Liquid crystals are a class of industrially important materials whose optical properties make them useful particularly in display technology. Optical imaging of these materials provides information about their structure and physical properties. Coherent anti-Stokes Raman scattering (CARS) microscopy is used to provide three-dimensional chemical maps of liquid crystalline samples without the use of external labels. CARS is an optical imaging technique that derives contrast from Raman-active molecular vibrations in the sample. Compared to many other three-dimensional imaging techniques, CARS offers more rapid chemical characterization without the use of external dyes or contrast agents. The use of CARS to image chemical and orientational order in liquid crystals is demonstrated using several examples, and the limitations and benefits are discussed.

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“…2-4, which is ~100,000 times faster than in confocal Raman microscopy [3,4]. The laser powers could be as low as 17mW for the pump wave and 5mW for the Stokes wave.…”

mentioning

confidence: 97%

“…However, this approach requires doping a specially selected dye that at small concentrations would provide strong contrast without affecting the LC properties. The labeling-free technique of interest is confocal Raman microscopy [3,4], which utilizes a Raman vibration and the signal dependence on orientations of molecular bonds. To study 3-D molecular orientation patterns, several techniques employ nonlinear processes, such as second harmonic generation (SHG) [5], third harmonic generation (THG) [6], and two-photon fluorescence (TPF) [7].…”

mentioning

confidence: 99%

“…Coherent anti-Stokes Raman scattering (CARS) microscopy has been used for visualizing chemical composition in biological and lyotropic systems [8,9]. We report 3-D imaging of LC director structures using CARS polarized microscopy (CARSPM), which does not require doping the LC with dyes and offers chemical selectivity and bond-orientation specificity superior to that of other techniques [2][3][4][5][6][7]; it also provides 5 10 times faster imaging (stronger signal) than confocal Raman microscopy [3,4]. We demonstrate that CARSPM is a viable technique for mapping of 3-D patterns of molecular orientations and LC director dynamics.…”

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confidence: 99%

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Coherent anti-Stokes Raman scattering polarized microscopy of three-dimensional director structures in liquid crystals

Kachynski

Kuzmin

Prasad

et al. 2007

Applied Physics Letters

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We demonstrate three-dimensional vibrational imaging of director structures in liquid crystals using coherent anti-Stokes Raman scattering (CARS) polarized microscopy. Spatial mapping of the structures is based on sensitivity of a polarized CARS signal to orientation of anisotropic molecules in liquid crystals. As an example, we study structures in a smectic material and demonstrate that single-scan CARS and two-photon fluorescence images of molecular orientation patterns are consistent with each other and with the structure model. Long-range orientational order is an important property of liquid crystals (LCs) [1]. Local average molecular orientations are described by the director n n− ≡ , which is an optical axis in the uniaxial LC materials. Non-invasive imaging of the three-dimensional (3-D) spatial patterns of ) ( r n r is important for fundamental LC research and for a broad range of technological applications. Fluorescence Confocal Polarizing Microscopy (FCPM) [2] visualizes 3-D director fields by taking advantage of (a) doping anisometric dyes that homogeneously distribute and align in the LC and (b) polarized excitation and fluorescence detection. In this approach, the absorption/emission transition dipoles of elongated dye molecules follow ) ( r n r and the polarized confocal imaging visualizes the 3-D director patterns [2]. However, this approach requires doping a specially selected dye that at small concentrations would provide strong contrast without affecting the LC properties. The labeling-free technique of interest is confocal Raman microscopy [3,4], which utilizes a Raman vibration and the signal dependence on orientations of molecular bonds. To study 3-D molecular orientation patterns, several techniques employ nonlinear processes, such as second harmonic generation (SHG) [5], third harmonic generation (THG) [6], and two-photon fluorescence (TPF) [7]. Coherent anti-Stokes Raman scattering (CARS) microscopy has been used for visualizing chemical composition in biological and lyotropic systems [8,9]. We report 3-D imaging of LC director structures using CARS polarized microscopy (CARSPM), which does not require doping the LC with dyes and offers chemical selectivity and bond-orientation specificity superior to that of other techniques [2][3][4][5][6][7]; it also provides 5 10 times faster imaging (stronger signal) than confocal Raman microscopy [3,4]. We demonstrate that CARSPM is a viable technique for mapping of 3-D patterns of molecular orientations and LC director dynamics.In CARS microscopy, a pump wave is used as a probe and the signal is derived by the 3-rd order nonlinear polarization

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Probing thick uniaxial birefringent medium in confined geometry: A polarised confocal micro-Raman approach

Cited by 11 publications

References 19 publications

Realignment-enhanced coherent anti-Stokes Raman scattering and three-dimensional imaging in anisotropic fluids

Realignment-enhanced coherent anti-Stokes Raman scattering and three-dimensional imaging in anisotropic fluids

Three-dimensional imaging of chemical bond orientation in liquid crystals by coherent anti- Stokes Raman scattering microscopy

Coherent anti-Stokes Raman scattering polarized microscopy of three-dimensional director structures in liquid crystals

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