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Continuous spatial tuning of laser emissions in a full visible spectral range.

Jeong MY, Wu JW - Int J Mol Sci (2011)

Bottom Line: The length of the cholesteric liquid crystal pitch could be elongated up to 10 nm, allowing the lasing behavior of continuous or discontinuous spatial tuning determined by the boundary conditions of the cholesteric liquid crystal cell.This continuous tuning behavior is due to the fact that the concentration of pitch gradient matches the fixed helical pitch determined by the cell thickness.The scheme of the spatial laser tuning in the wedge cell bearing a pitch gradient enabled a route to designing small-sized optical devices that allow for a wide tunability of single-mode laser emissions.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Research Institute of Natural Science, Gyeongsang National University, Jinju 660-701, Korea.

ABSTRACT
In order to achieve a continuous tuning of laser emission, the authors designed and fabricated three types of cholesteric liquid crystal cells with pitch gradient, a wedge cell with positive slope, a wedge cell with negative slope, and a parallel cell. The length of the cholesteric liquid crystal pitch could be elongated up to 10 nm, allowing the lasing behavior of continuous or discontinuous spatial tuning determined by the boundary conditions of the cholesteric liquid crystal cell. In the wedge cell with positive slope, the authors demonstrated a continuous spatial laser tuning in the near full visible spectral range, with a tuning resolution less than 1 nm by pumping with only a single 355 nm laser beam. This continuous tuning behavior is due to the fact that the concentration of pitch gradient matches the fixed helical pitch determined by the cell thickness. This characteristic continuous spatial laser tuning could be confirmed again by pumping with a 532 nm laser beam, over 90 nm in the visible spectral range. The scheme of the spatial laser tuning in the wedge cell bearing a pitch gradient enabled a route to designing small-sized optical devices that allow for a wide tunability of single-mode laser emissions.

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Spectra of the reflectance (PBG) and laser peaks of the WS-cell for area A (a); area B (b); and area C (c) in Figure 4 (a); respectively. Molecular structures of the laser dyes (d).
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f6-ijms-12-02007: Spectra of the reflectance (PBG) and laser peaks of the WS-cell for area A (a); area B (b); and area C (c) in Figure 4 (a); respectively. Molecular structures of the laser dyes (d).

Mentions: In order to study the relationship between lasing position and photonic band gap (PBG), we simultaneously measured PBG and lasing of the samples with a spectrophotometer (OOI, Ocean optics instrument: HR 2000+, USA). Near the PBG edges, since the group velocity vg, becomes near to zero and the number of the density of mode (DOM) increases remarkably, a lasing operation occurs. In the case of the WL-cell, since the linearly shaped rod-like DCM and LDS698 molecules (Figure 6d) prefer to align parallel to the nematic director, the CLC laser cavity in the longer wavelength band edge of the PBG was much more efficient in amplifying the stimulated emission of fluorescence, so the lasing operation occurred at the longer wavelength band edge of the PBG, Figure 5a. However, in the cases of the WM- and WS-cells, when the T-shaped Rhodamine590 and the plane-shaped Coumarin540A molecules (Figure 6d) aligned parallel to the nematic director, both the longer and the shorter wavelength band edges of the PBG could be efficient in amplifying the stimulated emission of fluorescence, so the lasing operation could occur at both sides of the PBG edges. Figure 6a–c shows the spectra of the PBG and lasing of areas A, B, and C of the WS-cell of Figure 4, respectively. In area A (Figure 6a), lasing is generated at the shorter wavelength PBG edge. In area C (Figure 6c), the lasing is generated at the longer wavelength PBG edge. In area B (Figure 6b), lasing is generated at both longer and shorter wavelength PBG edges. The missing lasing at the longer (or shorter) wavelength PBG edge is due to the fact that the lasing spectral range is limited by the fluorescence range of the dyes, Figure 6a (in Figure 6c).


Continuous spatial tuning of laser emissions in a full visible spectral range.

Jeong MY, Wu JW - Int J Mol Sci (2011)

Spectra of the reflectance (PBG) and laser peaks of the WS-cell for area A (a); area B (b); and area C (c) in Figure 4 (a); respectively. Molecular structures of the laser dyes (d).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3111647&req=5

f6-ijms-12-02007: Spectra of the reflectance (PBG) and laser peaks of the WS-cell for area A (a); area B (b); and area C (c) in Figure 4 (a); respectively. Molecular structures of the laser dyes (d).
Mentions: In order to study the relationship between lasing position and photonic band gap (PBG), we simultaneously measured PBG and lasing of the samples with a spectrophotometer (OOI, Ocean optics instrument: HR 2000+, USA). Near the PBG edges, since the group velocity vg, becomes near to zero and the number of the density of mode (DOM) increases remarkably, a lasing operation occurs. In the case of the WL-cell, since the linearly shaped rod-like DCM and LDS698 molecules (Figure 6d) prefer to align parallel to the nematic director, the CLC laser cavity in the longer wavelength band edge of the PBG was much more efficient in amplifying the stimulated emission of fluorescence, so the lasing operation occurred at the longer wavelength band edge of the PBG, Figure 5a. However, in the cases of the WM- and WS-cells, when the T-shaped Rhodamine590 and the plane-shaped Coumarin540A molecules (Figure 6d) aligned parallel to the nematic director, both the longer and the shorter wavelength band edges of the PBG could be efficient in amplifying the stimulated emission of fluorescence, so the lasing operation could occur at both sides of the PBG edges. Figure 6a–c shows the spectra of the PBG and lasing of areas A, B, and C of the WS-cell of Figure 4, respectively. In area A (Figure 6a), lasing is generated at the shorter wavelength PBG edge. In area C (Figure 6c), the lasing is generated at the longer wavelength PBG edge. In area B (Figure 6b), lasing is generated at both longer and shorter wavelength PBG edges. The missing lasing at the longer (or shorter) wavelength PBG edge is due to the fact that the lasing spectral range is limited by the fluorescence range of the dyes, Figure 6a (in Figure 6c).

Bottom Line: The length of the cholesteric liquid crystal pitch could be elongated up to 10 nm, allowing the lasing behavior of continuous or discontinuous spatial tuning determined by the boundary conditions of the cholesteric liquid crystal cell.This continuous tuning behavior is due to the fact that the concentration of pitch gradient matches the fixed helical pitch determined by the cell thickness.The scheme of the spatial laser tuning in the wedge cell bearing a pitch gradient enabled a route to designing small-sized optical devices that allow for a wide tunability of single-mode laser emissions.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Research Institute of Natural Science, Gyeongsang National University, Jinju 660-701, Korea.

ABSTRACT
In order to achieve a continuous tuning of laser emission, the authors designed and fabricated three types of cholesteric liquid crystal cells with pitch gradient, a wedge cell with positive slope, a wedge cell with negative slope, and a parallel cell. The length of the cholesteric liquid crystal pitch could be elongated up to 10 nm, allowing the lasing behavior of continuous or discontinuous spatial tuning determined by the boundary conditions of the cholesteric liquid crystal cell. In the wedge cell with positive slope, the authors demonstrated a continuous spatial laser tuning in the near full visible spectral range, with a tuning resolution less than 1 nm by pumping with only a single 355 nm laser beam. This continuous tuning behavior is due to the fact that the concentration of pitch gradient matches the fixed helical pitch determined by the cell thickness. This characteristic continuous spatial laser tuning could be confirmed again by pumping with a 532 nm laser beam, over 90 nm in the visible spectral range. The scheme of the spatial laser tuning in the wedge cell bearing a pitch gradient enabled a route to designing small-sized optical devices that allow for a wide tunability of single-mode laser emissions.

Show MeSH