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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 19 — Sep. 12, 2011
  • pp: 18199–18206
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Novel dye-doped cholesteric liquid crystal cone lasers with various birefringences and associated tunabilities of lasing feature and performance

Shih-Hung Lin and Chia-Rong Lee  »View Author Affiliations


Optics Express, Vol. 19, Issue 19, pp. 18199-18206 (2011)
http://dx.doi.org/10.1364/OE.19.018199


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Abstract

This study is the first to investigate novel cone lasers and the tunabilities of their lasing feature and performance based on dye-doped cholesteric liquid crystal (DDCLC) films with various LC birefringences (Δn). A unique conically-symmetric lasing ring with a low energy threshold occurs at a specific nonzero oblique angle (θring). The low energy threshold is comparable to those for common lasing signals occurring simultaneously at the short- and long-wavelength edges (SWE and LWE) of the CLC reflection band (CLCRB) for 0°. The lasing ring is induced by the enhancement in the density of photonic state for the fluorescence with a wavelength of λring based on an edge-overlapping effect, in which λring is just located at an edge-overlapping spectral position of the SWE of the CLCRB for 0° and the LWE of the CLCRB for θring. The lasing feature (i.e., the lasing wavelengths of the three lasing signals and the emitted angle of the lasing ring) are tuned by varying Δn. The simulated relationship of an oblique angle with Δn, in which the SWE of the CLCRB for that oblique angle just overlaps the LWE of the CLCRB for 0°, can be obtained by calculating the dispersion relation of a planar CLC structure with various values of Δn based on Berreman’s 4 × 4 matrix approach. The result of the calculation is highly consistent with the experimental data for the dependence of θring on Δn. Furthermore, the dependence of lasing performance (energy threshold and relative slope efficiency) on Δn for the three lasing signals is also measured, which findings can be used to qualitatively identify positive interaction or competition among the three lasing signals.

© 2011 OSA

1. Introduction

Planar cholesteric liquid crystals (CLCs) possess a one-dimensional (1D) photonic bandgap structure because of the periodic distribution of its refractive index in 1D space, wherein the rod-like LC molecules can self-organize by interacting with the chiral dopants to rotate continuously along the helical axis. If the planar CLC is doped by a fluorescence dye and is optically excited, the spontaneously emitted fluorescence from the dyes are suppressed within the stop band and enhanced at the band edges. Fluorescence photons with wavelengths at the long- and short-wavelength edges (LWE and SWE) of the CLC reflection band (CLCRB) can propagate via multi-reflection, yielding a very small group velocity and a very large density of photonic states (DOS) for the fluorescence. On the basis of the distributed feedback (DFB) effect of the fluorescence photons in the multi-reflection process of the active multilayer in the dye-doped CLC (DDCLC) cell, the rates of spontaneous and stimulated emissions at the band edges can both be amplified, so that a high gain can exceed the loss to induce low-threshold lasing emission [1

1. V. I. Kopp, B. Fan, H. K. M. Vithana, and A. Z. Genack, “Low-threshold lasing at the edge of a photonic stop band in cholesteric liquid crystals,” Opt. Lett. 23(21), 1707–1709 (1998). [CrossRef] [PubMed]

,2

2. V. I. Kopp, Z.-Q. Zhang, and A. Z. Genack, “Lasing in chiral photonic structures,” Prog. Quantum Electron. 27(6), 369–416 (2003). [CrossRef]

].

In the past decade, DDCLC lasers have been widely investigated because of the significance of their edge lasing mechanism [1

1. V. I. Kopp, B. Fan, H. K. M. Vithana, and A. Z. Genack, “Low-threshold lasing at the edge of a photonic stop band in cholesteric liquid crystals,” Opt. Lett. 23(21), 1707–1709 (1998). [CrossRef] [PubMed]

,2

2. V. I. Kopp, Z.-Q. Zhang, and A. Z. Genack, “Lasing in chiral photonic structures,” Prog. Quantum Electron. 27(6), 369–416 (2003). [CrossRef]

] and their potential applications [3

3. A. Chanishvili, G. Chilaya, G. Petriashvili, R. Barberi, R. Bartolino, G. Cipparrone, A. Mazzulla, and L. Oriol, “Phototunable lasing in dye-doped cholesteric liquid crystals,” Appl. Phys. Lett. 83(26), 5353–5355 (2003). [CrossRef]

16

16. M. Humar and I. Musevic, “3D microlasers from self-assembled cholesteric liquid-crystal microdroplets,” Opt. Express 18(26), 26995–27003 (2010). [CrossRef] [PubMed]

]. Particularly, in our recent work we observed a novel lasing phenomenon, a color cone lasing emission (CCLE), based on a single-pitched DDCLC cell [11

11. C.-R. Lee, S.-H. Lin, H.-C. Yeh, T.-D. Ji, K.-L. Lin, T.-S. Mo, C.-T. Kuo, K.-Y. Lo, S.-H. Chang, A. Y. Fuh, and S.-Y. Huang, “Color cone lasing emission in a dye-doped cholesteric liquid crystal with a single pitch,” Opt. Express 17(15), 12910–12921 (2009). [CrossRef] [PubMed]

]. The lasing wavelength in the CCLE is distributed continuously within a wide-band, as measured at a continuously increasing cone angle relative to the helical axis along the cell normal. Further applications of band-tunable color cone lasers, in which the CLC pitch is varied and the LC birefringence (Δn) is fixed, were also developed [12

12. C.-R. Lee, S.-H. Lin, H.-C. Yeh, and T.-D. Ji, “Band-tunable color cone lasing emission based on dye-doped cholesteric liquid crystals with various pitches and a pitch gradient,” Opt. Express 17(25), 22616–22623 (2009). [CrossRef] [PubMed]

14

14. C.-R. Lee, S.-H. Lin, H.-S. Ku, J.-H. Liu, P.-C. Yang, C.-Y. Huang, H.-C. Yeh, T.-D. Ji, and C.-H. Lin, “Spatially band-tunable color-cone lasing emission in a dye-doped cholesteric liquid crystal with a photoisomerizable chiral dopant,” Opt. Lett. 35(9), 1398–1400 (2010). [CrossRef] [PubMed]

]. The current work is the first to report a novel DDCLC cone lasers with various Δn and associated lasing feature and performance tunabilities. Experimental results reveal that a novel conically-symmetric lasing ring (seen on the screen) with a low energy threshold can be obtained at a specific nonzero oblique angle (θring) based on a DDCLC cell. The threshold is comparable to those for common normal lasing signals emitted simultaneously at the SWE and LWE for 0°. Such a lasing ring is attributable to the DOS enhancement of the fluorescence with a wavelength of λring based on an edge-overlapping effect, in which λring coincides with the edge-overlapping spectral position of the LWE of the CLCRB measured at θring and the SWE of the CLCRB measured at 0°. The wavelengths of the lasing ring and lasing signals at the SWE and LWE for 0° and the emitted oblique angle of the lasing ring are tuned by changing the Δn of LCs. The simulated relationship of an oblique angle (θoverlap) with Δn, in which the SWE of the CLCRB for that oblique angle just overlaps the LWE of the CLCRB for 0°, can be obtained by calculating the dispersion relation for planar CLC structures using Berreman’s 4 × 4 matrix method. The simulation result agrees well with the experimental result for the dependence of θring on Δn. In addition, the relationship between the lasing performance (i. e., energy threshold and relative slope efficiency) and Δn for the three lasing signals are also obtained, which findings can used accordingly to qualitatively identify positive interaction or competition among the three lasing signals.

2. Sample preparation and experimental setups

The DDCLC materials used include four different nematic LCs (NLCs), LCT-06-99 (ne = 1.5485 and no = 1.4693 at 20 °C), MDA-03-3970 (ne = 1.6309 and no = 1.4987 at 20 °C), MDA-04-606 (ne = 1.7153 and no = 1.5086 at 20 °C), and MDA-98-1602 (ne = 1.7779 and no = 1.5113 at 20 °C) (all from Merck), a left-handed chiral dopant, S811 (from Merck), and a laser dye, Pyrromethene 597 (P597) (from Exciton). Each empty cell is pre-fabricated with the same standard by combining two indium-tin-oxide-coated glass slides separated by two 23 μm-thick plastic spacers. Both glass slides in each empty cell are pre-coated with polyvinyl alcohol film and pre-rubbed in anti-parallel direction. Eight DDCLC mixtures with different prescriptions (Table 1

Table 1. Two groups for the eight DDCLC cells with different prescriptions and optical parameters [e. g., birefringence of LCs (Δn), pitch and wavelengths at LWE and SWE of CLCRB for 0°, λLWE(0°), and λSWE(0°), respectively]

table-icon
View This Table
) are prepared and injected into eight identical empty cells to form eight different DDCLC cells marked cells 1–8. These cells are then placed together in a clean and opaque specimen box at room temperature for about one week to enable the CLC in each cell to have sufficient time to gradually self-organize into a perfect planar structure. In addition to the DDCLC prescription, other optical information on these cells is also provided in Table 1. Examples include the value of the birefringence of LCs, helical pitch, and wavelengths at the LWE and SWE of CLCRB at 0° [λLWE(0°) and λSWE(0°), respectively]. All the DDCLC cells are divided into two groups for cells 1–4 and 5–8 with increasing birefringence of Δn1–Δn4. The λLWE(0°) for each cell in group I and the λSWE(0°) for each cell in group II are pre-designed to be located at the wavelengths of 639.9 and 575.0 nm, respectively.

In the experiment, two setups are utilized for measuring the lasing and transmission spectra (complementary to the reflection spectra) of the DDCLC cells. Associate setups and methods for measurement can be found in our recent published work [11

11. C.-R. Lee, S.-H. Lin, H.-C. Yeh, T.-D. Ji, K.-L. Lin, T.-S. Mo, C.-T. Kuo, K.-Y. Lo, S.-H. Chang, A. Y. Fuh, and S.-Y. Huang, “Color cone lasing emission in a dye-doped cholesteric liquid crystal with a single pitch,” Opt. Express 17(15), 12910–12921 (2009). [CrossRef] [PubMed]

]. In brief, the DDCLC cell is excited by a single incident pumped pulses beam originating from a Q-switched Nd:YAG SHG pulse laser with a wavelength of 532 nm, a pulse duration of 8 ns, a repetition rate of 10 Hz, and a pumped energy of E, at an incident angle of roughly 15° from the cell normal (N). The lasing signals can then be generated and measured behind the cell at a distance of ~4 cm from the pumped spot on the cell. To analyze the lasing signals emitted from one of the DDCLC cells with different Δn at a specific oblique angle from N, the transmission spectrum of that cell, which reveals the band structure of the corresponding CLC structure, is measured at the same angle. Both the lasing and transmission spectra of each cell are measured using the same system of the fiber-based spectrometer (Jaz-combo-2, optical resolution ~0.9 nm, Ocean Optics).

3. Results and discussion

Figure 1
Fig. 1 Measured absorption and fluorescence emission spectra of 0.5 wt.% P567 solved in four kinds of LCs with different birefringences of Δn1–Δn4 (LCT-06-99, MDA-03-3970, MDA-04-606, and MDA-98-1602, respectively), indicated by the red, green, blue, and violet curves, respectively.
shows the measured absorption and spontaneously emitted fluorescence spectra of 0.5 wt.% P597 solved in the four kinds of LCs with Δn1–Δn4 (represented by the red, green, blue, and violet curves, respectively). The experimental result in this figure shows that the four spectral curves of the laser dye for absorption or fluorescence emission are almost identical. The peaks for any one of the absorption and fluorescence emission spectra are located at nearly the wavelength positions of 526 and 575 nm, respectively. The absorption and fluorescence emission for the laser dye almost vanish and can be neglected if the wavelength position is higher than 578 and 700 nm, respectively.

4. Conclusion

In summary, this investigation is the first to report novel DDCLC cone lasers with different Δn, as well as their lasing characteristics and performance tunabilities. In addition to the common lasing signals generated simultaneously at the SWE and LWE for 0°, one particular lasing ring is generated at a specific nonzero oblique angle (θring) because of DOS enhancement of the fluorescence with a wavelength of λring based on an edge-overlapping effect. In this effect, λring just coincides with an edge-overlapping spectral position of the SWE of the CLCRB for 0° and the LWE of the CLCRB for θring. The lasing wavelength and emitted angle for the lasing ring are changeable with the variations in Δn. In the simulated relationship of an oblique angle with the Δn, in which the SWE of the CLCRB for that oblique angle superimposes the LWE of the CLCRB for 0°, can be obtained by calculating the dispersion relation for a planar CLC structure with different values of Δn based on Berreman’s 4 × 4 matrix approach. The results of the calculation are in good agreement with the experimental findings on the dependence of θring on Δn. Moreover, the dependence of the energy threshold and relative slope efficiency on Δn for the lasing signals are also measured and discussed. Work devoted to the development of a spatially tunable cone laser based on a DDCLC cell with a gradient of birefringence is currently underway.

Acknowledgments

The authors would like to thank the National Science Council of the Republic of China, Taiwan (Contract No. NSC 100-2112-M-006-012-MY3) and the Advanced Optoelectronic Technology Center, National Cheng Kung University, under projects from the Ministry of Education for the financial support. We greatly appreciate the editorial assistance extended by KGSupport.

References and links

1.

V. I. Kopp, B. Fan, H. K. M. Vithana, and A. Z. Genack, “Low-threshold lasing at the edge of a photonic stop band in cholesteric liquid crystals,” Opt. Lett. 23(21), 1707–1709 (1998). [CrossRef] [PubMed]

2.

V. I. Kopp, Z.-Q. Zhang, and A. Z. Genack, “Lasing in chiral photonic structures,” Prog. Quantum Electron. 27(6), 369–416 (2003). [CrossRef]

3.

A. Chanishvili, G. Chilaya, G. Petriashvili, R. Barberi, R. Bartolino, G. Cipparrone, A. Mazzulla, and L. Oriol, “Phototunable lasing in dye-doped cholesteric liquid crystals,” Appl. Phys. Lett. 83(26), 5353–5355 (2003). [CrossRef]

4.

A. Y.-G. Fuh, T.-H. Lin, J.-H. Liu, and F.-C. Wu, “Lasing in chiral photonic liquid crystals and associated frequency tuning,” Opt. Express 12(9), 1857–1863 (2004). [CrossRef] [PubMed]

5.

A. Chanishvili, G. Chilaya, G. Petriashvili, R. Barberi, R. Bartolino, G. Cipparrone, A. Mazzulla, R. Gimenez, L. Oriol, and M. Pinol, “Widely tunable ultraviolet-visible liquid crystal laser,” Appl. Phys. Lett. 86(5), 051107 (2005). [CrossRef]

6.

Y. Huang, Y. Zhou, and S.-T. Wu, “Spatially tunable laser emission in dye-doped photonic liquid crystals,” Appl. Phys. Lett. 88(1), 011107 (2006). [CrossRef]

7.

Y. Matsuhisa, Y. Huang, Y. Zhou, S.-T. Wu, Y. Takao, A. Fujii, and M. Ozaki, “Cholesteric liquid crystal laser in a dielectric mirror cavity upon band-edge excitation,” Opt. Express 15(2), 616–622 (2007). [CrossRef] [PubMed]

8.

K. Sonoyama, Y. Takanishi, K. Ishikawa, and H. Takezoe, “Position-sensitive cholesteric liquid crystal dye laser covering a full visible range,” Jpn. J. Appl. Phys. 46(36), L874–L876 (2007). [CrossRef]

9.

C.-T. Wang and T.-H. Lin, “Multi-wavelength laser emission in dye-doped photonic liquid crystals,” Opt. Express 16(22), 18334–18339 (2008). [CrossRef] [PubMed]

10.

M.-Y. Jeong, H. Choi, and J. W. Wu, “Spatial tuning of laser emission in a dye-doped cholesteric liquid crystal wedge cell,” Appl. Phys. Lett. 92(5), 051108 (2008). [CrossRef]

11.

C.-R. Lee, S.-H. Lin, H.-C. Yeh, T.-D. Ji, K.-L. Lin, T.-S. Mo, C.-T. Kuo, K.-Y. Lo, S.-H. Chang, A. Y. Fuh, and S.-Y. Huang, “Color cone lasing emission in a dye-doped cholesteric liquid crystal with a single pitch,” Opt. Express 17(15), 12910–12921 (2009). [CrossRef] [PubMed]

12.

C.-R. Lee, S.-H. Lin, H.-C. Yeh, and T.-D. Ji, “Band-tunable color cone lasing emission based on dye-doped cholesteric liquid crystals with various pitches and a pitch gradient,” Opt. Express 17(25), 22616–22623 (2009). [CrossRef] [PubMed]

13.

C.-R. Lee, S.-H. Lin, H.-S. Ku, J.-H. Liu, P.-C. Yang, C.-Y. Huang, H.-C. Yeh, and T.-D. Ji, “Optically band-tunable color cone lasing emission in a dye-doped cholesteric liquid crystal with a photoisomerizable chiral dopant,” Appl. Phys. Lett. 96(11), 111105 (2010). [CrossRef]

14.

C.-R. Lee, S.-H. Lin, H.-S. Ku, J.-H. Liu, P.-C. Yang, C.-Y. Huang, H.-C. Yeh, T.-D. Ji, and C.-H. Lin, “Spatially band-tunable color-cone lasing emission in a dye-doped cholesteric liquid crystal with a photoisomerizable chiral dopant,” Opt. Lett. 35(9), 1398–1400 (2010). [CrossRef] [PubMed]

15.

S.-H. Lin, C.-Y. Shyu, J.-H. Liu, P.-C. Yang, T.-S. Mo, S.-Y. Huang, and C.-R. Lee, “Photoerasable and photorewritable spatially-tunable laser based on a dye-doped cholesteric liquid crystal with a photoisomerizable chiral dopant,” Opt. Express 18(9), 9496–9503 (2010). [CrossRef] [PubMed]

16.

M. Humar and I. Musevic, “3D microlasers from self-assembled cholesteric liquid-crystal microdroplets,” Opt. Express 18(26), 26995–27003 (2010). [CrossRef] [PubMed]

17.

A. Sugita, H. Takezoe, Y. Ouchi, A. Fukuda, E. Kuze, and N. Goto, “Numerical calculation of optical eigenmodes in cholesteric liquid crystals by 4×4 matrix method,” Jpn. J. Appl. Phys. 21(Part 1, No. 11), 1543–1546 (1982). [CrossRef]

OCIS Codes
(140.3490) Lasers and laser optics : Lasers, distributed-feedback
(140.3600) Lasers and laser optics : Lasers, tunable
(160.3710) Materials : Liquid crystals
(230.3720) Optical devices : Liquid-crystal devices

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: July 1, 2011
Revised Manuscript: August 10, 2011
Manuscript Accepted: August 22, 2011
Published: September 1, 2011

Citation
Shih-Hung Lin and Chia-Rong Lee, "Novel dye-doped cholesteric liquid crystal cone lasers with various birefringences and associated tunabilities of lasing feature and performance," Opt. Express 19, 18199-18206 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-19-18199


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References

  1. V. I. Kopp, B. Fan, H. K. M. Vithana, and A. Z. Genack, “Low-threshold lasing at the edge of a photonic stop band in cholesteric liquid crystals,” Opt. Lett.23(21), 1707–1709 (1998). [CrossRef] [PubMed]
  2. V. I. Kopp, Z.-Q. Zhang, and A. Z. Genack, “Lasing in chiral photonic structures,” Prog. Quantum Electron.27(6), 369–416 (2003). [CrossRef]
  3. A. Chanishvili, G. Chilaya, G. Petriashvili, R. Barberi, R. Bartolino, G. Cipparrone, A. Mazzulla, and L. Oriol, “Phototunable lasing in dye-doped cholesteric liquid crystals,” Appl. Phys. Lett.83(26), 5353–5355 (2003). [CrossRef]
  4. A. Y.-G. Fuh, T.-H. Lin, J.-H. Liu, and F.-C. Wu, “Lasing in chiral photonic liquid crystals and associated frequency tuning,” Opt. Express12(9), 1857–1863 (2004). [CrossRef] [PubMed]
  5. A. Chanishvili, G. Chilaya, G. Petriashvili, R. Barberi, R. Bartolino, G. Cipparrone, A. Mazzulla, R. Gimenez, L. Oriol, and M. Pinol, “Widely tunable ultraviolet-visible liquid crystal laser,” Appl. Phys. Lett.86(5), 051107 (2005). [CrossRef]
  6. Y. Huang, Y. Zhou, and S.-T. Wu, “Spatially tunable laser emission in dye-doped photonic liquid crystals,” Appl. Phys. Lett.88(1), 011107 (2006). [CrossRef]
  7. Y. Matsuhisa, Y. Huang, Y. Zhou, S.-T. Wu, Y. Takao, A. Fujii, and M. Ozaki, “Cholesteric liquid crystal laser in a dielectric mirror cavity upon band-edge excitation,” Opt. Express15(2), 616–622 (2007). [CrossRef] [PubMed]
  8. K. Sonoyama, Y. Takanishi, K. Ishikawa, and H. Takezoe, “Position-sensitive cholesteric liquid crystal dye laser covering a full visible range,” Jpn. J. Appl. Phys.46(36), L874–L876 (2007). [CrossRef]
  9. C.-T. Wang and T.-H. Lin, “Multi-wavelength laser emission in dye-doped photonic liquid crystals,” Opt. Express16(22), 18334–18339 (2008). [CrossRef] [PubMed]
  10. M.-Y. Jeong, H. Choi, and J. W. Wu, “Spatial tuning of laser emission in a dye-doped cholesteric liquid crystal wedge cell,” Appl. Phys. Lett.92(5), 051108 (2008). [CrossRef]
  11. C.-R. Lee, S.-H. Lin, H.-C. Yeh, T.-D. Ji, K.-L. Lin, T.-S. Mo, C.-T. Kuo, K.-Y. Lo, S.-H. Chang, A. Y. Fuh, and S.-Y. Huang, “Color cone lasing emission in a dye-doped cholesteric liquid crystal with a single pitch,” Opt. Express17(15), 12910–12921 (2009). [CrossRef] [PubMed]
  12. C.-R. Lee, S.-H. Lin, H.-C. Yeh, and T.-D. Ji, “Band-tunable color cone lasing emission based on dye-doped cholesteric liquid crystals with various pitches and a pitch gradient,” Opt. Express17(25), 22616–22623 (2009). [CrossRef] [PubMed]
  13. C.-R. Lee, S.-H. Lin, H.-S. Ku, J.-H. Liu, P.-C. Yang, C.-Y. Huang, H.-C. Yeh, and T.-D. Ji, “Optically band-tunable color cone lasing emission in a dye-doped cholesteric liquid crystal with a photoisomerizable chiral dopant,” Appl. Phys. Lett.96(11), 111105 (2010). [CrossRef]
  14. C.-R. Lee, S.-H. Lin, H.-S. Ku, J.-H. Liu, P.-C. Yang, C.-Y. Huang, H.-C. Yeh, T.-D. Ji, and C.-H. Lin, “Spatially band-tunable color-cone lasing emission in a dye-doped cholesteric liquid crystal with a photoisomerizable chiral dopant,” Opt. Lett.35(9), 1398–1400 (2010). [CrossRef] [PubMed]
  15. S.-H. Lin, C.-Y. Shyu, J.-H. Liu, P.-C. Yang, T.-S. Mo, S.-Y. Huang, and C.-R. Lee, “Photoerasable and photorewritable spatially-tunable laser based on a dye-doped cholesteric liquid crystal with a photoisomerizable chiral dopant,” Opt. Express18(9), 9496–9503 (2010). [CrossRef] [PubMed]
  16. M. Humar and I. Musevic, “3D microlasers from self-assembled cholesteric liquid-crystal microdroplets,” Opt. Express18(26), 26995–27003 (2010). [CrossRef] [PubMed]
  17. A. Sugita, H. Takezoe, Y. Ouchi, A. Fukuda, E. Kuze, and N. Goto, “Numerical calculation of optical eigenmodes in cholesteric liquid crystals by 4×4 matrix method,” Jpn. J. Appl. Phys.21(Part 1, No. 11), 1543–1546 (1982). [CrossRef]

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