Abstract

This experimental work is aimed to investigate the thermal behavior of random laser action in dye doped nematic liquid crystals. The study evidenced an important temperature dependence of the random lasing characteristics in the nematic phase and in close proximity of the nematic -isotropic (N-I) phase transition. A lowering of the laser emission intensity as the temperature increases is strictly related to the shift of the lasing threshold as function of the temperature even though the pump energy is kept fixed. The optical losses increasing owing to the thermal fluctuation enhanced scattering drive the input-output smoother behavior until the system stops to lase, because below threshold. The unexpected reoccurrence of random lasing at higher temperature, in proximity of N-I transition is found to be related to a different scattering mechanism, the micro-droplets nucleation and critical opalescence.

© 2009 Optical Society of America

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  1. D. S. Wiersma, R. Sapienza, S. Mujumdar, M. Colocci, M. Ghulinyan, and L. Pavesi, "Optics of nanostructured dielectrics," J. Opt. A: Pure Appl. Opt. 7,S190-S197(2005).
    [CrossRef]
  2. X. H. Wu, A. Yamilov, H. Noh, H. Cao, E. W. Seelig, and R. P. H. Chang, "Random lasing in closely packed resonant scatterers," J. Opt. Soc. Am. B,  21, 159-167 (2004).
    [CrossRef]
  3. R. C. Polson and Z. V. Vardeny, "Random lasing in human tissues" Appl. Phys. Lett. 85, 1289-1291 (2004).
    [CrossRef]
  4. M. A. Noginov, Solid-State Random Lasers (Springer, Berlin, 2005).
  5. M. P. Van Albada and A. Lagendijk, "Observation of Weak Localization of Light in a Random Medium," Phys. Rev. Lett.,  55, 2692- 2695 (1985).
    [CrossRef] [PubMed]
  6. P.W. Anderson, "Absence of Diffusion in Certain Random Lattices" Phys. Rev. 109, 1492-1505 (1958).
    [CrossRef]
  7. V. S. Letokhov, "Quantum statistics of multiple- mode emission of an atomic ensemble," Sov. Phys. JETP 26, 1246-1251 (1968).
  8. N. M. Lawandy, R. M. Balachandran, A. S. L. Gomes, and E. Sauvin, "Laser action in strongly scattering media," Nature (London) 368, 436-438 (1994).
    [CrossRef]
  9. H. Cao, J. Y. Xu, Y. Ling, A. L. Burin, E. W. Seeling, X. Liu, and R. P. Chang, "Random Laser With Coherent Feedback," IEEE J. S. Top. Quantum Electron. 9, 111-119, (2003).
    [CrossRef]
  10. G. Strangi, S. Ferjani, V. Barna, A. De Luca, C. Versace, N. Scaramuzza, and R. Bartolino, "Random lasing and weak localization of light in dye-doped nematic liquid crystals," Opt. Express 14, 7737-7744 (2006).
    [CrossRef] [PubMed]
  11. S. Ferjani, V. Barna, A. De Luca, C. Versace, and G. Strangi, "Random lasing in freely suspended dye doped complex fluids," Opt. Lett. 33, 557-559 (2008).
    [CrossRef] [PubMed]
  12. P. G de Gennes and J. Prost, The physics of liquid crystals 2nd Ed. (Oxford, New York, 1993).
  13. H. Stark and T. C. Lubensky, "Multiple Light Scattering in Nematic Liquid Crystals," Phys. Rev. Lett. 77, 2229-2232 (1996).
    [CrossRef] [PubMed]
  14. M. H. Kao, K. A. Jester, A. G. Yodh, and P. J. Colling, "Observation of Light Diffusion and Correlation Transport in Nematic Liquid Crystals," Phys. Rev. Lett. 77, 2233-2236 (1996).
    [CrossRef] [PubMed]
  15. D. S. Wiersma, A. Muzzi, M. Colocci, and R. Righini, "Time-Resolved Anisotropic Multiple Light Scattering in Nematic Liquid Crystals," Phys. Rev. Lett. 83, 4321-4324 (1999).
    [CrossRef]
  16. G. V. Soest and Ad Lagendijk, "β factor in a random laser," Phys. Rev. E, 65, 047601.1-047601.4 (2002).
  17. S. Ferjani, V. Barna, A. De Luca, N. Scaramuzza, C. Versace, C. Umeton, R. Bartolino, and G. Strangi "Thermal Behaviour of Random Lasing in Dye Doped Nematic Liquid Crystals," App. Phy. Lett. 89, 121109.1-121109.3 (2006).
    [CrossRef]
  18. B. J. Berne and R. Pecora, Dynamic Light Scattering (Wiley, New York, 1976).
  19. R. R. Garcia, I. L. Martinez, I. G. Iturbide, A. Sanchez-Castillo, M. Boffety, and P. Rück "Colossal Nonlinear Optical Effect in Dye-Doped Liquid Crystals," Mol. Cryst. Liq. Cryst 454, 179, 581 (2006).
  20. P. Barthelemy, J. Bertolotti, and D. S. Wiersma " A levy flight for light" Nature 453, 495-498 (2008).
    [CrossRef] [PubMed]

2008

2006

2005

D. S. Wiersma, R. Sapienza, S. Mujumdar, M. Colocci, M. Ghulinyan, and L. Pavesi, "Optics of nanostructured dielectrics," J. Opt. A: Pure Appl. Opt. 7,S190-S197(2005).
[CrossRef]

2004

2003

H. Cao, J. Y. Xu, Y. Ling, A. L. Burin, E. W. Seeling, X. Liu, and R. P. Chang, "Random Laser With Coherent Feedback," IEEE J. S. Top. Quantum Electron. 9, 111-119, (2003).
[CrossRef]

1999

D. S. Wiersma, A. Muzzi, M. Colocci, and R. Righini, "Time-Resolved Anisotropic Multiple Light Scattering in Nematic Liquid Crystals," Phys. Rev. Lett. 83, 4321-4324 (1999).
[CrossRef]

1996

H. Stark and T. C. Lubensky, "Multiple Light Scattering in Nematic Liquid Crystals," Phys. Rev. Lett. 77, 2229-2232 (1996).
[CrossRef] [PubMed]

M. H. Kao, K. A. Jester, A. G. Yodh, and P. J. Colling, "Observation of Light Diffusion and Correlation Transport in Nematic Liquid Crystals," Phys. Rev. Lett. 77, 2233-2236 (1996).
[CrossRef] [PubMed]

1994

N. M. Lawandy, R. M. Balachandran, A. S. L. Gomes, and E. Sauvin, "Laser action in strongly scattering media," Nature (London) 368, 436-438 (1994).
[CrossRef]

1985

M. P. Van Albada and A. Lagendijk, "Observation of Weak Localization of Light in a Random Medium," Phys. Rev. Lett.,  55, 2692- 2695 (1985).
[CrossRef] [PubMed]

1968

V. S. Letokhov, "Quantum statistics of multiple- mode emission of an atomic ensemble," Sov. Phys. JETP 26, 1246-1251 (1968).

1958

P.W. Anderson, "Absence of Diffusion in Certain Random Lattices" Phys. Rev. 109, 1492-1505 (1958).
[CrossRef]

Anderson, P.W.

P.W. Anderson, "Absence of Diffusion in Certain Random Lattices" Phys. Rev. 109, 1492-1505 (1958).
[CrossRef]

Balachandran, R. M.

N. M. Lawandy, R. M. Balachandran, A. S. L. Gomes, and E. Sauvin, "Laser action in strongly scattering media," Nature (London) 368, 436-438 (1994).
[CrossRef]

Barna, V.

Barthelemy, P.

P. Barthelemy, J. Bertolotti, and D. S. Wiersma " A levy flight for light" Nature 453, 495-498 (2008).
[CrossRef] [PubMed]

Bartolino, R.

G. Strangi, S. Ferjani, V. Barna, A. De Luca, C. Versace, N. Scaramuzza, and R. Bartolino, "Random lasing and weak localization of light in dye-doped nematic liquid crystals," Opt. Express 14, 7737-7744 (2006).
[CrossRef] [PubMed]

S. Ferjani, V. Barna, A. De Luca, N. Scaramuzza, C. Versace, C. Umeton, R. Bartolino, and G. Strangi "Thermal Behaviour of Random Lasing in Dye Doped Nematic Liquid Crystals," App. Phy. Lett. 89, 121109.1-121109.3 (2006).
[CrossRef]

Bertolotti, J.

P. Barthelemy, J. Bertolotti, and D. S. Wiersma " A levy flight for light" Nature 453, 495-498 (2008).
[CrossRef] [PubMed]

Boffety, M.

R. R. Garcia, I. L. Martinez, I. G. Iturbide, A. Sanchez-Castillo, M. Boffety, and P. Rück "Colossal Nonlinear Optical Effect in Dye-Doped Liquid Crystals," Mol. Cryst. Liq. Cryst 454, 179, 581 (2006).

Burin, A. L.

H. Cao, J. Y. Xu, Y. Ling, A. L. Burin, E. W. Seeling, X. Liu, and R. P. Chang, "Random Laser With Coherent Feedback," IEEE J. S. Top. Quantum Electron. 9, 111-119, (2003).
[CrossRef]

Cao, H.

X. H. Wu, A. Yamilov, H. Noh, H. Cao, E. W. Seelig, and R. P. H. Chang, "Random lasing in closely packed resonant scatterers," J. Opt. Soc. Am. B,  21, 159-167 (2004).
[CrossRef]

H. Cao, J. Y. Xu, Y. Ling, A. L. Burin, E. W. Seeling, X. Liu, and R. P. Chang, "Random Laser With Coherent Feedback," IEEE J. S. Top. Quantum Electron. 9, 111-119, (2003).
[CrossRef]

Chang, R. P.

H. Cao, J. Y. Xu, Y. Ling, A. L. Burin, E. W. Seeling, X. Liu, and R. P. Chang, "Random Laser With Coherent Feedback," IEEE J. S. Top. Quantum Electron. 9, 111-119, (2003).
[CrossRef]

Chang, R. P. H.

Colling, P. J.

M. H. Kao, K. A. Jester, A. G. Yodh, and P. J. Colling, "Observation of Light Diffusion and Correlation Transport in Nematic Liquid Crystals," Phys. Rev. Lett. 77, 2233-2236 (1996).
[CrossRef] [PubMed]

Colocci, M.

D. S. Wiersma, R. Sapienza, S. Mujumdar, M. Colocci, M. Ghulinyan, and L. Pavesi, "Optics of nanostructured dielectrics," J. Opt. A: Pure Appl. Opt. 7,S190-S197(2005).
[CrossRef]

D. S. Wiersma, A. Muzzi, M. Colocci, and R. Righini, "Time-Resolved Anisotropic Multiple Light Scattering in Nematic Liquid Crystals," Phys. Rev. Lett. 83, 4321-4324 (1999).
[CrossRef]

De Luca, A.

Ferjani, S.

Garcia, R. R.

R. R. Garcia, I. L. Martinez, I. G. Iturbide, A. Sanchez-Castillo, M. Boffety, and P. Rück "Colossal Nonlinear Optical Effect in Dye-Doped Liquid Crystals," Mol. Cryst. Liq. Cryst 454, 179, 581 (2006).

Ghulinyan, M.

D. S. Wiersma, R. Sapienza, S. Mujumdar, M. Colocci, M. Ghulinyan, and L. Pavesi, "Optics of nanostructured dielectrics," J. Opt. A: Pure Appl. Opt. 7,S190-S197(2005).
[CrossRef]

Gomes, A. S. L.

N. M. Lawandy, R. M. Balachandran, A. S. L. Gomes, and E. Sauvin, "Laser action in strongly scattering media," Nature (London) 368, 436-438 (1994).
[CrossRef]

Iturbide, I. G.

R. R. Garcia, I. L. Martinez, I. G. Iturbide, A. Sanchez-Castillo, M. Boffety, and P. Rück "Colossal Nonlinear Optical Effect in Dye-Doped Liquid Crystals," Mol. Cryst. Liq. Cryst 454, 179, 581 (2006).

Jester, K. A.

M. H. Kao, K. A. Jester, A. G. Yodh, and P. J. Colling, "Observation of Light Diffusion and Correlation Transport in Nematic Liquid Crystals," Phys. Rev. Lett. 77, 2233-2236 (1996).
[CrossRef] [PubMed]

Kao, M. H.

M. H. Kao, K. A. Jester, A. G. Yodh, and P. J. Colling, "Observation of Light Diffusion and Correlation Transport in Nematic Liquid Crystals," Phys. Rev. Lett. 77, 2233-2236 (1996).
[CrossRef] [PubMed]

Lagendijk, A.

M. P. Van Albada and A. Lagendijk, "Observation of Weak Localization of Light in a Random Medium," Phys. Rev. Lett.,  55, 2692- 2695 (1985).
[CrossRef] [PubMed]

Lawandy, N. M.

N. M. Lawandy, R. M. Balachandran, A. S. L. Gomes, and E. Sauvin, "Laser action in strongly scattering media," Nature (London) 368, 436-438 (1994).
[CrossRef]

Letokhov, V. S.

V. S. Letokhov, "Quantum statistics of multiple- mode emission of an atomic ensemble," Sov. Phys. JETP 26, 1246-1251 (1968).

Ling, Y.

H. Cao, J. Y. Xu, Y. Ling, A. L. Burin, E. W. Seeling, X. Liu, and R. P. Chang, "Random Laser With Coherent Feedback," IEEE J. S. Top. Quantum Electron. 9, 111-119, (2003).
[CrossRef]

Liu, X.

H. Cao, J. Y. Xu, Y. Ling, A. L. Burin, E. W. Seeling, X. Liu, and R. P. Chang, "Random Laser With Coherent Feedback," IEEE J. S. Top. Quantum Electron. 9, 111-119, (2003).
[CrossRef]

Lubensky, T. C.

H. Stark and T. C. Lubensky, "Multiple Light Scattering in Nematic Liquid Crystals," Phys. Rev. Lett. 77, 2229-2232 (1996).
[CrossRef] [PubMed]

Martinez, I. L.

R. R. Garcia, I. L. Martinez, I. G. Iturbide, A. Sanchez-Castillo, M. Boffety, and P. Rück "Colossal Nonlinear Optical Effect in Dye-Doped Liquid Crystals," Mol. Cryst. Liq. Cryst 454, 179, 581 (2006).

Mujumdar, S.

D. S. Wiersma, R. Sapienza, S. Mujumdar, M. Colocci, M. Ghulinyan, and L. Pavesi, "Optics of nanostructured dielectrics," J. Opt. A: Pure Appl. Opt. 7,S190-S197(2005).
[CrossRef]

Muzzi, A.

D. S. Wiersma, A. Muzzi, M. Colocci, and R. Righini, "Time-Resolved Anisotropic Multiple Light Scattering in Nematic Liquid Crystals," Phys. Rev. Lett. 83, 4321-4324 (1999).
[CrossRef]

Noh, H.

Pavesi, L.

D. S. Wiersma, R. Sapienza, S. Mujumdar, M. Colocci, M. Ghulinyan, and L. Pavesi, "Optics of nanostructured dielectrics," J. Opt. A: Pure Appl. Opt. 7,S190-S197(2005).
[CrossRef]

Polson, R. C.

R. C. Polson and Z. V. Vardeny, "Random lasing in human tissues" Appl. Phys. Lett. 85, 1289-1291 (2004).
[CrossRef]

Righini, R.

D. S. Wiersma, A. Muzzi, M. Colocci, and R. Righini, "Time-Resolved Anisotropic Multiple Light Scattering in Nematic Liquid Crystals," Phys. Rev. Lett. 83, 4321-4324 (1999).
[CrossRef]

Rück, P.

R. R. Garcia, I. L. Martinez, I. G. Iturbide, A. Sanchez-Castillo, M. Boffety, and P. Rück "Colossal Nonlinear Optical Effect in Dye-Doped Liquid Crystals," Mol. Cryst. Liq. Cryst 454, 179, 581 (2006).

Sanchez-Castillo, A.

R. R. Garcia, I. L. Martinez, I. G. Iturbide, A. Sanchez-Castillo, M. Boffety, and P. Rück "Colossal Nonlinear Optical Effect in Dye-Doped Liquid Crystals," Mol. Cryst. Liq. Cryst 454, 179, 581 (2006).

Sapienza, R.

D. S. Wiersma, R. Sapienza, S. Mujumdar, M. Colocci, M. Ghulinyan, and L. Pavesi, "Optics of nanostructured dielectrics," J. Opt. A: Pure Appl. Opt. 7,S190-S197(2005).
[CrossRef]

Sauvin, E.

N. M. Lawandy, R. M. Balachandran, A. S. L. Gomes, and E. Sauvin, "Laser action in strongly scattering media," Nature (London) 368, 436-438 (1994).
[CrossRef]

Scaramuzza, N.

G. Strangi, S. Ferjani, V. Barna, A. De Luca, C. Versace, N. Scaramuzza, and R. Bartolino, "Random lasing and weak localization of light in dye-doped nematic liquid crystals," Opt. Express 14, 7737-7744 (2006).
[CrossRef] [PubMed]

S. Ferjani, V. Barna, A. De Luca, N. Scaramuzza, C. Versace, C. Umeton, R. Bartolino, and G. Strangi "Thermal Behaviour of Random Lasing in Dye Doped Nematic Liquid Crystals," App. Phy. Lett. 89, 121109.1-121109.3 (2006).
[CrossRef]

Seelig, E. W.

Seeling, E. W.

H. Cao, J. Y. Xu, Y. Ling, A. L. Burin, E. W. Seeling, X. Liu, and R. P. Chang, "Random Laser With Coherent Feedback," IEEE J. S. Top. Quantum Electron. 9, 111-119, (2003).
[CrossRef]

Soest, G. V.

G. V. Soest and Ad Lagendijk, "β factor in a random laser," Phys. Rev. E, 65, 047601.1-047601.4 (2002).

Stark, H.

H. Stark and T. C. Lubensky, "Multiple Light Scattering in Nematic Liquid Crystals," Phys. Rev. Lett. 77, 2229-2232 (1996).
[CrossRef] [PubMed]

Strangi, G.

Umeton, C.

S. Ferjani, V. Barna, A. De Luca, N. Scaramuzza, C. Versace, C. Umeton, R. Bartolino, and G. Strangi "Thermal Behaviour of Random Lasing in Dye Doped Nematic Liquid Crystals," App. Phy. Lett. 89, 121109.1-121109.3 (2006).
[CrossRef]

Van Albada, M. P.

M. P. Van Albada and A. Lagendijk, "Observation of Weak Localization of Light in a Random Medium," Phys. Rev. Lett.,  55, 2692- 2695 (1985).
[CrossRef] [PubMed]

Vardeny, Z. V.

R. C. Polson and Z. V. Vardeny, "Random lasing in human tissues" Appl. Phys. Lett. 85, 1289-1291 (2004).
[CrossRef]

Versace, C.

Wiersma, D. S.

P. Barthelemy, J. Bertolotti, and D. S. Wiersma " A levy flight for light" Nature 453, 495-498 (2008).
[CrossRef] [PubMed]

D. S. Wiersma, R. Sapienza, S. Mujumdar, M. Colocci, M. Ghulinyan, and L. Pavesi, "Optics of nanostructured dielectrics," J. Opt. A: Pure Appl. Opt. 7,S190-S197(2005).
[CrossRef]

D. S. Wiersma, A. Muzzi, M. Colocci, and R. Righini, "Time-Resolved Anisotropic Multiple Light Scattering in Nematic Liquid Crystals," Phys. Rev. Lett. 83, 4321-4324 (1999).
[CrossRef]

Wu, X. H.

Xu, J. Y.

H. Cao, J. Y. Xu, Y. Ling, A. L. Burin, E. W. Seeling, X. Liu, and R. P. Chang, "Random Laser With Coherent Feedback," IEEE J. S. Top. Quantum Electron. 9, 111-119, (2003).
[CrossRef]

Yamilov, A.

Yodh, A. G.

M. H. Kao, K. A. Jester, A. G. Yodh, and P. J. Colling, "Observation of Light Diffusion and Correlation Transport in Nematic Liquid Crystals," Phys. Rev. Lett. 77, 2233-2236 (1996).
[CrossRef] [PubMed]

Appl. Phys. Lett.

R. C. Polson and Z. V. Vardeny, "Random lasing in human tissues" Appl. Phys. Lett. 85, 1289-1291 (2004).
[CrossRef]

IEEE J. S. Top. Quantum Electron.

H. Cao, J. Y. Xu, Y. Ling, A. L. Burin, E. W. Seeling, X. Liu, and R. P. Chang, "Random Laser With Coherent Feedback," IEEE J. S. Top. Quantum Electron. 9, 111-119, (2003).
[CrossRef]

J. Opt. A: Pure Appl. Opt.

D. S. Wiersma, R. Sapienza, S. Mujumdar, M. Colocci, M. Ghulinyan, and L. Pavesi, "Optics of nanostructured dielectrics," J. Opt. A: Pure Appl. Opt. 7,S190-S197(2005).
[CrossRef]

J. Opt. Soc. Am. B

Nature

P. Barthelemy, J. Bertolotti, and D. S. Wiersma " A levy flight for light" Nature 453, 495-498 (2008).
[CrossRef] [PubMed]

Nature (London)

N. M. Lawandy, R. M. Balachandran, A. S. L. Gomes, and E. Sauvin, "Laser action in strongly scattering media," Nature (London) 368, 436-438 (1994).
[CrossRef]

Opt. Express

Opt. Lett.

Phys. Rev.

P.W. Anderson, "Absence of Diffusion in Certain Random Lattices" Phys. Rev. 109, 1492-1505 (1958).
[CrossRef]

Phys. Rev. Lett.

M. P. Van Albada and A. Lagendijk, "Observation of Weak Localization of Light in a Random Medium," Phys. Rev. Lett.,  55, 2692- 2695 (1985).
[CrossRef] [PubMed]

H. Stark and T. C. Lubensky, "Multiple Light Scattering in Nematic Liquid Crystals," Phys. Rev. Lett. 77, 2229-2232 (1996).
[CrossRef] [PubMed]

M. H. Kao, K. A. Jester, A. G. Yodh, and P. J. Colling, "Observation of Light Diffusion and Correlation Transport in Nematic Liquid Crystals," Phys. Rev. Lett. 77, 2233-2236 (1996).
[CrossRef] [PubMed]

D. S. Wiersma, A. Muzzi, M. Colocci, and R. Righini, "Time-Resolved Anisotropic Multiple Light Scattering in Nematic Liquid Crystals," Phys. Rev. Lett. 83, 4321-4324 (1999).
[CrossRef]

Sov. Phys. JETP

V. S. Letokhov, "Quantum statistics of multiple- mode emission of an atomic ensemble," Sov. Phys. JETP 26, 1246-1251 (1968).

Other

M. A. Noginov, Solid-State Random Lasers (Springer, Berlin, 2005).

P. G de Gennes and J. Prost, The physics of liquid crystals 2nd Ed. (Oxford, New York, 1993).

G. V. Soest and Ad Lagendijk, "β factor in a random laser," Phys. Rev. E, 65, 047601.1-047601.4 (2002).

S. Ferjani, V. Barna, A. De Luca, N. Scaramuzza, C. Versace, C. Umeton, R. Bartolino, and G. Strangi "Thermal Behaviour of Random Lasing in Dye Doped Nematic Liquid Crystals," App. Phy. Lett. 89, 121109.1-121109.3 (2006).
[CrossRef]

B. J. Berne and R. Pecora, Dynamic Light Scattering (Wiley, New York, 1976).

R. R. Garcia, I. L. Martinez, I. G. Iturbide, A. Sanchez-Castillo, M. Boffety, and P. Rück "Colossal Nonlinear Optical Effect in Dye-Doped Liquid Crystals," Mol. Cryst. Liq. Cryst 454, 179, 581 (2006).

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Figures (4)

Fig. 1.
Fig. 1.

Schematic diagram of the experimental set-up. A=Attenuator, P=Polarizer, S=Sample, SC=Screen and FI=Fiber. Inset (a) represents the lasing spectrum for a wedge cell maintained at fixed temperature. (b) The intensity spatial distribution is acquired by a high resolution CCD camera, demonstrating a speckle like behavior.

Fig. 2.
Fig. 2.

(a) Time resolved emission intensity behavior in a wedge cell at different temperatures (T = 28 °C, 36 °C, 46 °C). (b) Emission intensity from a wedge cell versus pump energy. With increasing temperature, a smoother lasing threshold behavior is obtained, as shown by the black lines used as guide to the eye.

Fig. 3.
Fig. 3.

(a) Emission intensity dependence on temperature for a wedge cell. (b) Emission intensity dependence on temperature for a capillary with a transverse section of about 200 μm.

Fig. 4.
Fig. 4.

Crossed polarizers optical microscopy images of a wedge cell filled by our mixture, taken for temperatures below the isotropic/nematic transition. (a) 62.5 °C; (b) 61 °C; (c) 60 °C; (d) 59 °C; (e) 58 °C; (f) 57.5 °C; (g) 57 °C; (h) 56.5 °C. Size bar in (a) is 300 μm.

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