Tunable lasing in doped liquid crystals with one-dimensional periodic structure

Ozaki, Masanori; Kasano, Masahiro; Funamoto, Kazuhiro; Ozaki, Ryotaro; Matsui, Tatsunosuke; Yoshino, Katsumi

doi:10.1117/12.509184

Cited by 4 publications

(1 citation statement)

References 8 publications

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“…1,2 In particular, electrical laser-color tuning can be achieved with CLC lasers because the helix pitch can be controlled by varying the electric field. [3][4][5] The types of CLC lasers thus far proposed have been based on a planar-aligned cell configuration with the helix axis oriented perpendicularly to the cell substrates: see Figure 1(a). Laser light is emitted perpendicularly to the cell plates.…”

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Color-tunable liquid-crystal laser

Ozaki¹

2009

SPIE Newsroom

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An in-plane configuration of the liquid-crystal helix axes enables electric-field-controlled laser tuning.Cholesteric liquid crystals (CLCs) composed of chiral molecules spontaneously form helical structures in which the refractive index changes periodically along the helix axis, and which is essentially a 1D photonic crystal. In this type of spiral periodic structure, laser action-caused by suppression of the photon-group velocity at the photonic band edge-is expected. CLCs have attracted significant interest for applications in mirrorless lasers because of these spontaneously formed periodic structures. 1, 2 In particular, electrical laser-color tuning can be achieved with CLC lasers because the helix pitch can be controlled by varying the electric field. [3][4][5] The types of CLC lasers thus far proposed have been based on a planar-aligned cell configuration with the helix axis oriented perpendicularly to the cell substrates: see Figure 1(a). Laser light is emitted perpendicularly to the cell plates. In this setup, the helix pitch does not change smoothly when the electric field is applied normal to the helix axis, because the CLC molecules on the surfaces of both substrates are strongly anchored in an initially aligned direction while the free molecular motion required for helix-pitch elongation is blocked. 6 Despite a number of attempts to use planar aligned cells, 7 continuous color tuning of CLC laser action has never been accomplished over a wide wavelength range.To achieve continuous tuning of the lasing wavelength by a varying electric field, the molecules must be released from their strong anchoring to the substrate surfaces. We propose a waveguide-cell configuration in which the helix axis is confined to a plane as shown in Figure 1(b). For in-plane helix alignment, surface anchoring does not affect the pitch change and a smooth shift of the stop band is expected. This can be used to construct a CLC laser with continuous color tunability. Figure 2 shows the resulting lasing spectra as a function of the electric field applied perpendicularly to both the helix axis and the substrates of the in-plane cell. The CLC-waveguide laser device was sandwiched between two In 2 O 3 :Sn (tin-doped Figure 1. Device configurations of cholesteric liquid-crystal (CLC) lasers. (a) Conventional planar configuration with the helix axis perpendicular to the substrates. (b) Proposed in-plane configuration with the helix axis parallel to the substrates.indium oxide, or ITO)-coated glass substrates. The laser's dye-doped cell thickness was 6µm and the CLC film was photopumped at 532nm using 20ns pulses from a frequency-doubled quality-switched neodymium-doped yttrium-aluminum-garnet laser, with a threshold lasing pump energy of 0.4mJ/cm 2 . The lasing emitted along the helix axis was collected from the cell edge.The lasing peak wavelength shifts to the red with increases of the electric field (see Figure 2, inset). Although the lasing wavelength remains almost constant for smaller fields, above 1.0V/µm it can be tuned by ch...

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confidence: 99%

Color-tunable liquid-crystal laser

Ozaki¹

2009

SPIE Newsroom

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Photonic Crystals based on Chiral Liquid Crystal

Ozaki

Matsuhisa

Yoshida

et al. 2008

Nanophotonic Materials

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Photonic crystals based on chiral liquid crystal

Ozaki

Matsuhisa

Yoshida

et al. 2007

Physica Status Solidi (a)

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Liquid crystals including chiral molecule have a self‐organized helical structure with nano‐scaled periodicity, which can be regarded as a one‐dimensional (1D) photonic crystal. We have so far investigated lasing characteristics at an edge of the 1D photonic band gap (PBG) of dye‐doped chiral liquid crystals such as cholesteric liquid crystal (CLC) and ferroelectric liquid crystal (FLC). A band‐edge excitation effect on the CLC lasing has been experimentally demonstrated by matching the excitation laser wavelength to the higher energy‐edge of the PBG of a dye‐doped CLC. The wavelength tuning of the laser action upon changing electric field strength has been achieved in FLC. We have proposed the defect modes characteristic to the helicoidal structure of the chiral liquid crystal and demonstrated the lasing from the chiral defect modes. A twist defect mode in a transmission spectrum of the composite film consisting of two photopolymerized CLC layers has been experimentally demonstrated. A new type of defect mode in a chiral liquid crystal on the basis of the local deformation of the 1D periodic helical structure has also been proposed, and the possibility of the wavelength tuning has been demonstrated in this system. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Tunable lasing in doped liquid crystals with one-dimensional periodic structure

Cited by 4 publications

References 8 publications

Color-tunable liquid-crystal laser

Color-tunable liquid-crystal laser

Photonic Crystals based on Chiral Liquid Crystal

Photonic crystals based on chiral liquid crystal

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