Abstract

Cationic-induced two-photon photo-polymerization is demonstrated at 710 nm, using an isopropylthioxanthone/diarylidonium salt initiating system for the cationic polymerization of an epoxide. In-situ monitoring of the polymer conversion using interferometry allows for determination of the polymerization threshold J2th, polymerization rate R and its dependence of initiator’s concentration z. Best J2th achieved is 1 GW/cm2, with a dynamic range of > 100, i.e. the material can be fully polymerized at intensities > 100 times the threshold level without damage. The R is found to be proportional to the m=1.7 power of the intensity, or R=[C (J-J2th)]m=[C (J-J2th)]1.7, which implies a significantly stronger localization of the photochemical response than that of free radical photoinitiators. Both R and J2th significantly improve when the concentration z of the initiator (onium salt) increases, reduction of J2th exhibiting z-m trend.

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  1. B.H. Cumpston, S.P. Ananthavel, S. Barlow, D.L. Dyer, J.E. Ehrlich, L.L. Erskine, A.A. Heikal, S.M. Kuebler, I-Y.S. Lee, D. McCord-Maughon, Jinqui Qin, H. Rockel, M. Rumi, Xiang-Li Wu, S.R. Marder, J.W. Perry, "Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication," Nature, 398 (6722), 51-54 (1999).
    [CrossRef]
  2. Cokgor, R. Piyaket, S.C. Esener, A.S. Dvornikov, P.M. Rentzepis, "Two-photon absorption induced photochromic reactions in spirobenzopyran-doped PMMA waveguides," Proc. SPIE 3623, 92-103 (1999).
    [CrossRef]
  3. W.Y. Liu, D.P. Steenson, M.B. Steer, "Technique of microfabrication suitable for machining submillimeter-wave components," Proc. SPIE 4088, 144-147 (2000).
    [CrossRef]
  4. H. Misawa, S. Juodkazis, H. Sun, S. Matsuo, J. Nishii, "Formation of photonic crystals by femtosecond laser microfabrication," Proc. SPIE 4088, 29-32 (2000).
    [CrossRef]
  5. Jing Yong Ye; M. Ishikawa, Y. Yamane, N. Tsurumachi, H. Nakatsuka, "Enhancement of two-photon excited fluorescence using one-dimensional photonic crystals," Appl. Phys. Lett. 75, 3605-3607 (1999).
    [CrossRef]
  6. Y. Kawata, "Three-dimensional memory," Proc. SPIE 4081, 76-85 (2000).
    [CrossRef]
  7. R. Sivaraman, S.J. Clarson, B.K. Lee, A.J. Steckl, B.A. Reinhardt, "Photoluminescence studies and read/write process of a strong two-photon absorbing chromophore," Appl. Phys. Lett. 77, 328-330 (2000).
    [CrossRef]
  8. K. Yamasaki, S. Juodkazis, M. Watanabe, H.B. Sun, S. Matsuo, H. Misawa, "Recording by microexplosion and two-photon reading of three-dimensional optical memory in polymethylmethacrylate films," Appl. Phys. Lett. 76, 1000-1002 (2000).
    [CrossRef]
  9. D. Day, Gu Min, A. Smallridge, "Use of two-photon excitation for erasable-rewritable three-dimensional bit optical data storage in a photorefractive polymer," Opt. Lett. 24, 948-950 (1999).
    [CrossRef]
  10. H.E. Pudavar, M.P. Joshi, P.N. Prasad, B.A. Reinhardt, "High-density three-dimensional optical data storage in a stacked compact disk format with two-photon writing and single photon readout," Appl. Phys. Lett. 74, 1338-1340 (1999).
    [CrossRef]
  11. S. M. Kirkpatrick, J. W. Baur, C. M. Clark, L. R. Denny, D. W. Tomlin, B. A. Reinhardt, R. Kannan and M. O. Stone, "Holographic Recording Using Two-Photon Induced Photopolymerization," Appl. Phys. A 69, 461-464 (1999).
    [CrossRef]
  12. C. Diamond, Y. Boiko and S. Esener, "Two-photon holography in a 3D photopolymer host-guest matrix," Opt. Express 6, 64-68 (2000); http://www.opticsexpress.org/oearchive/source/18896.htm Errata: Opt. Express 6, 109-110 (2000); http://www.opticsexpress.org/oearchive/source/19560.htm
    [CrossRef] [PubMed]
  13. S.M. Kuebler, B.H. Cumpston, S. Ananthavel, S. Barlow, J.E. Ehrlich, L.L. Erskine, A.A. Heikal, D. McCord-Maughon, J. Qin, H. Rockel, M. Rumi, S.R. Marder, J.W. Perry, "Three-dimensional microfabrication using two-photon activated chemistry," Micro- and Nano-photonic Materials and Devices, Proc. SPIE 3937, 97-105 (2000).
  14. Y. Boiko, M. Bowen, M. Wang, J. Costa and S. Esener, 'Threshold enhancement in two-photon photo-polymerization," Complex Mediums, Proc. SPIE 4097, 254-263 (2000).
  15. M. Shirai and M. Tsunooka, "Photoacid and photobase generators: chemistry and applications to polymeric materials," Prog. Polym. Sci. 21, 1-45 (1996).
    [CrossRef]
  16. Y. Boiko, E. Tikhonov, V. Shilov, "Photopolymerization studies by Michelson interferometer," stored in and available from Ukr. Sci.-Research Inst. of Sci. and Technical Information (UkrNIINTI), Dep. No. 2155, 17p., 15.09.1986 (in Russian).
  17. Y. Boiko, "Volume holographic optics recording in photopolymerizable layers," Holographic Optics III - Principles and Applications, Proc. SPIE 1507, 318-327 (1991).
  18. G. Manivannan and J. Fouassier, "Primary process in the photosensitized polymerization of cationic monomers," J. Polym. Sci. A: Polym. Chem. 29, 1113-1124 (1991).
    [CrossRef]

Other (18)

B.H. Cumpston, S.P. Ananthavel, S. Barlow, D.L. Dyer, J.E. Ehrlich, L.L. Erskine, A.A. Heikal, S.M. Kuebler, I-Y.S. Lee, D. McCord-Maughon, Jinqui Qin, H. Rockel, M. Rumi, Xiang-Li Wu, S.R. Marder, J.W. Perry, "Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication," Nature, 398 (6722), 51-54 (1999).
[CrossRef]

Cokgor, R. Piyaket, S.C. Esener, A.S. Dvornikov, P.M. Rentzepis, "Two-photon absorption induced photochromic reactions in spirobenzopyran-doped PMMA waveguides," Proc. SPIE 3623, 92-103 (1999).
[CrossRef]

W.Y. Liu, D.P. Steenson, M.B. Steer, "Technique of microfabrication suitable for machining submillimeter-wave components," Proc. SPIE 4088, 144-147 (2000).
[CrossRef]

H. Misawa, S. Juodkazis, H. Sun, S. Matsuo, J. Nishii, "Formation of photonic crystals by femtosecond laser microfabrication," Proc. SPIE 4088, 29-32 (2000).
[CrossRef]

Jing Yong Ye; M. Ishikawa, Y. Yamane, N. Tsurumachi, H. Nakatsuka, "Enhancement of two-photon excited fluorescence using one-dimensional photonic crystals," Appl. Phys. Lett. 75, 3605-3607 (1999).
[CrossRef]

Y. Kawata, "Three-dimensional memory," Proc. SPIE 4081, 76-85 (2000).
[CrossRef]

R. Sivaraman, S.J. Clarson, B.K. Lee, A.J. Steckl, B.A. Reinhardt, "Photoluminescence studies and read/write process of a strong two-photon absorbing chromophore," Appl. Phys. Lett. 77, 328-330 (2000).
[CrossRef]

K. Yamasaki, S. Juodkazis, M. Watanabe, H.B. Sun, S. Matsuo, H. Misawa, "Recording by microexplosion and two-photon reading of three-dimensional optical memory in polymethylmethacrylate films," Appl. Phys. Lett. 76, 1000-1002 (2000).
[CrossRef]

D. Day, Gu Min, A. Smallridge, "Use of two-photon excitation for erasable-rewritable three-dimensional bit optical data storage in a photorefractive polymer," Opt. Lett. 24, 948-950 (1999).
[CrossRef]

H.E. Pudavar, M.P. Joshi, P.N. Prasad, B.A. Reinhardt, "High-density three-dimensional optical data storage in a stacked compact disk format with two-photon writing and single photon readout," Appl. Phys. Lett. 74, 1338-1340 (1999).
[CrossRef]

S. M. Kirkpatrick, J. W. Baur, C. M. Clark, L. R. Denny, D. W. Tomlin, B. A. Reinhardt, R. Kannan and M. O. Stone, "Holographic Recording Using Two-Photon Induced Photopolymerization," Appl. Phys. A 69, 461-464 (1999).
[CrossRef]

C. Diamond, Y. Boiko and S. Esener, "Two-photon holography in a 3D photopolymer host-guest matrix," Opt. Express 6, 64-68 (2000); http://www.opticsexpress.org/oearchive/source/18896.htm Errata: Opt. Express 6, 109-110 (2000); http://www.opticsexpress.org/oearchive/source/19560.htm
[CrossRef] [PubMed]

S.M. Kuebler, B.H. Cumpston, S. Ananthavel, S. Barlow, J.E. Ehrlich, L.L. Erskine, A.A. Heikal, D. McCord-Maughon, J. Qin, H. Rockel, M. Rumi, S.R. Marder, J.W. Perry, "Three-dimensional microfabrication using two-photon activated chemistry," Micro- and Nano-photonic Materials and Devices, Proc. SPIE 3937, 97-105 (2000).

Y. Boiko, M. Bowen, M. Wang, J. Costa and S. Esener, 'Threshold enhancement in two-photon photo-polymerization," Complex Mediums, Proc. SPIE 4097, 254-263 (2000).

M. Shirai and M. Tsunooka, "Photoacid and photobase generators: chemistry and applications to polymeric materials," Prog. Polym. Sci. 21, 1-45 (1996).
[CrossRef]

Y. Boiko, E. Tikhonov, V. Shilov, "Photopolymerization studies by Michelson interferometer," stored in and available from Ukr. Sci.-Research Inst. of Sci. and Technical Information (UkrNIINTI), Dep. No. 2155, 17p., 15.09.1986 (in Russian).

Y. Boiko, "Volume holographic optics recording in photopolymerizable layers," Holographic Optics III - Principles and Applications, Proc. SPIE 1507, 318-327 (1991).

G. Manivannan and J. Fouassier, "Primary process in the photosensitized polymerization of cationic monomers," J. Polym. Sci. A: Polym. Chem. 29, 1113-1124 (1991).
[CrossRef]

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Figures (9)

Fig. 1.
Fig. 1.

Chemical structure of cationic sensitizer Isopropylthioxanthone (ITX; 2&4 isomer mixture; C16H14OS)

Fig. 2.
Fig. 2.

Schematic for in-situ interferometric monitoring of two-photon photopolymerization. Only the two-photon induced contribution to the local change of the refractive index, Δntotal, is contributing to the signal on the detector. This technique is “blind” to the single photon induced contribution to Δn. The dominant contribution is due to Δnpol=n(Npol) - nmon, i.e. Δnpol≫Δnthermal, Δnbleaching, Δnothers if any.

Fig. 3.
Fig. 3.

Change of two-photon initiated cationic photopolymerization rate (which is proportional to the slope of the curve as indicated by Eq. (12)) at different peak intensities J of the laser beam - (a) J=10 GW/cm2; (b) J=20 GW/cm2 - for low concentrations (z=0.5%) of the cationic initiator DAI (formulation K126:ITX:DAI=97:2.5:0.5). Vertical axis is in arbitrary units of I using Eq. (8). Horizontal axis is exposure time in seconds. The polymerization rate Rlin is proportional to the slope of the beginning stages of exposure. Initial zero shift is due to background contribution after the beam is turned on. . Differences in appearance are not essential here, which is commented on in the text of the article.

Fig. 4.
Fig. 4.

Change of two-photon initiated cationic photopolymerization rate (which is proportional to the slope of the curve as indicated by Eq. (12)) at different peak intensities J of the laser beam - (a) J=10 GW/cm2; (b) J=20 GW/cm2 - for high concentrations (z=1.5%) of the cationic initiator DAI (formulation K126:ITX:DAI=96:2.5:1.5). Vertical axis is in arbitrary units of I using Eq. (8). Horizontal axis is exposure time in seconds. The polymerization rate Rlin is proportional to the slope of the beginning stages of exposure. Initial zero shift is due to background contribution after the beam is turned on.

Fig. 5.
Fig. 5.

Saturation of two-photon initiated cationic photopolymerization rate at near-threshold laser intensity. Formulation is K126:ITX:DAI=96:2.5:1.5. Vertical axis is in arbitrary units of I from using Eq. (8). Horizontal axis is exposure time in seconds. The polymerization rate Rlin is proportional to the slope of the beginning stages of exposure. Initial zero shift is due to background contribution after the beam is turned on.

Fig. 6.
Fig. 6.

Dynamic range of two-photon cationic photopolymerizable formulation K126:ITX:DAI=x:y:z, where x:y:z=96:2.5:1.5 for Series1 and x:y:z=97:2.5:0.5 for Series2. Points A and B are near-threshold conditions for each respective Series; upper plot is on a linear scale (a); lower plot is on a power m=1.7 scale (b), Jmax=300 GW/cm2.

Fig. 7.
Fig. 7.

Polymerization rate increase with the increase of the light intensity i for single-photon initiated polymerization reactions: (a) cationic photo-polymerization of the formulation K126:ITX:DAI=96:2.5:1.5 ; (b) free radical photo-polymerization of the formulation DPEPA:BDMK=95:5. UV light of 365 nm wavelength is from UVP lamp (Blak-Ray). Exposure time intervals are 2 min for (a) and 30 sec for (b).

Fig. 8.
Fig. 8.

Increase of initiator’s concentration z allows the reduction of the threshold peak intensity J2th of cationically induced two-photon photopolymerization of the formulation K126:ITX:DAI=x:2.5:z, where x+2.5+z=100%, 0.5%<z<1.5%.

Fig. 9.
Fig. 9.

Threshold peak intensity J2th of two-photon free radical polymerization reduces as the concentration z of the initiator increases in the formulation DPEPA:BDMK=x:z, where x+z=100%, 1%<z<5%.

Equations (20)

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R = dN dt
N = n 0 n ( N ) n 0 n sat = Δ n ( N ) Δ n sat
R ( N ) = k d [ Δ n ( N ) ] dt = k d [ n ( N ) ] dt ,
ϕ 1 = ( L λ ) ( n 0 + Δ n )
ϕ 2 = ( L λ ) n 0
Φ = Δ ϕ = ϕ 1 ϕ 2 = ( L λ ) Δ n
d ( Δ ϕ ) dt = ( L λ ) d ( Δ n ) dt .
I = 2 I 1 ( 1 + cos Δ ϕ ) = 2 I 1 ( 1 + cos Φ ) .
dI dt = 2 I 1 d dt ( cos Δ ϕ ) = 2 I 1 sin Φ d Φ dt .
dI dt = 2 I 1 d Φ dt ; ( Φ = π 2 ) ,
dI dt = 2 I 1 ( L λ ) d ( Δ n ) dt = 0.5 I max ( L λ ) ( R k ) ; ( Φ = π 2 )
R ( N ) K = ( dI dt ) I max ; ( Φ = π 2 )
R = C J 1 2
R = C ( J J 2 th )
R = ( C J ) m 2
R = [ C ( J J 2 th ) ] m
R ( 1 ) = [ C ( J ( 1 ) J 2 th ) ] m
R ( 2 ) = [ C ( J ( 2 ) J 2 th ) ] m
m = [ ln ( R ( 1 ) ) ln ( R ( 2 ) ) ] [ ln ( J ( 1 ) J 2 th ) ln ( J ( 2 ) J 2 th ) ] =
= Δ 12 [ ln ( R ) ] Δ 12 [ ln ( J J 2 th ) ]

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