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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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Photographs and juxtapositions of five pieces of polarized microscope images at different spatial positions of the WL-cell (a and b), the WM-cell (c and d), and WS-cell (e and f), respectively.
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f2-ijms-12-02007: Photographs and juxtapositions of five pieces of polarized microscope images at different spatial positions of the WL-cell (a and b), the WM-cell (c and d), and WS-cell (e and f), respectively.

Mentions: Figures 2 and 3 show the photographic images and juxtapositions of five pieces of polarized microscope images at different spatial positions within the CLC-cells, respectively. When the photographic images are compared, the wedge cells with positive slope (WL-, WM-, WS-, and WL2-cell), parallel cell (P-cell), and the wedge cell with negative slope (WL3-cell) appear to be similar, with the exception of the WM-cell and WL2-cell, where some signature of dye aggregation due to a high dye concentration should be noted, Figures 2c,d and Figure 3a. When examined with a polarization microscope, in Figure 2b,d,f and Figure 3b, the wedge cells with positive slope show a continuous color change, stemming from a continuous pitch change. However, the parallel cell (P-cell) and wedge cell with negative slope (WL3-cell), in Figure 3d,f, show discontinuous color change when crossing Cano lines (or dislocation lines) in each of the polarized microscope images. Cano lines originate from a mismatch between the CLC pitch and the helical pitch determined by the cell thickness. This discontinuous color change is related to the discontinuous pitch change of the CLC (Figure 1b,c); discontinuous pitch jumping leads to discontinuous laser tuning (Figure 7b,c). However, when the concentration of pitch gradient fits with the helical pitch determined by the cell thickness with positive slope, Cano lines disappear, which is similar to the wedge cell with positive slope, (Figure 2b,d,f).


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

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

Photographs and juxtapositions of five pieces of polarized microscope images at different spatial positions of the WL-cell (a and b), the WM-cell (c and d), and WS-cell (e and f), respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2-ijms-12-02007: Photographs and juxtapositions of five pieces of polarized microscope images at different spatial positions of the WL-cell (a and b), the WM-cell (c and d), and WS-cell (e and f), respectively.
Mentions: Figures 2 and 3 show the photographic images and juxtapositions of five pieces of polarized microscope images at different spatial positions within the CLC-cells, respectively. When the photographic images are compared, the wedge cells with positive slope (WL-, WM-, WS-, and WL2-cell), parallel cell (P-cell), and the wedge cell with negative slope (WL3-cell) appear to be similar, with the exception of the WM-cell and WL2-cell, where some signature of dye aggregation due to a high dye concentration should be noted, Figures 2c,d and Figure 3a. When examined with a polarization microscope, in Figure 2b,d,f and Figure 3b, the wedge cells with positive slope show a continuous color change, stemming from a continuous pitch change. However, the parallel cell (P-cell) and wedge cell with negative slope (WL3-cell), in Figure 3d,f, show discontinuous color change when crossing Cano lines (or dislocation lines) in each of the polarized microscope images. Cano lines originate from a mismatch between the CLC pitch and the helical pitch determined by the cell thickness. This discontinuous color change is related to the discontinuous pitch change of the CLC (Figure 1b,c); discontinuous pitch jumping leads to discontinuous laser tuning (Figure 7b,c). However, when the concentration of pitch gradient fits with the helical pitch determined by the cell thickness with positive slope, Cano lines disappear, which is similar to the wedge cell with positive slope, (Figure 2b,d,f).

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