- Email: [email protected]
Laser induced third harmonic generation in δ-Bi1−xNdxB3O6 nanocomposites
Physica E 78 (2016) 31–34
Contents lists available at ScienceDirect
Physica E journal homepage: www.elsevier.com/locate/physe
Laser induced third harmonic generation in δ-Bi1 xNdxB3O6 nanocomposites By M. Chrunik a, J. Ebothé b, A.K. Aloufy c, A. Majchrowski a, L.R. Jaroszewicz a, I.V. Kityk d,n a
Institute of Applied Physics, Military University of Technology, Kaliskiego 2, 00-908 Warsaw, Poland LRN no 4682-UFR Sciences Exactes, University of Reims, 21 rue Clément Ader, 51096 REIMS Cedex 02, France c New Advanced Materials & Nanotechnology Lab, NNREL, Textile Engineering Dept. Faculty of Engineering, Alexandria University, Alexandria, Egypt d Faculty of Electrical Engineering, Czestochowa University of Technology, Armii Krajowej 17, 42-201 Czestochowa, Poland b
H I G H L I G H T S
Tunable THG effect for polymer/Nd-doped δ-BiB3O6 nanocomposites was shown. THG features are strongly dependent not only on the pumping power but also on their relative polarizations. The effective anisotropic sixth rank tensor for description of such kind of photoinduced processes was introduced.
art ic l e i nf o
a b s t r a c t
Article history: Received 5 November 2015 Received in revised form 27 November 2015 Accepted 30 November 2015 Available online 2 December 2015
A possibility of optically operated third harmonic generation (THG) in polymer nanocomposites based on orthorhombic δ-Bi1 xNdxB3O6 powders (where x ¼ 0.025C0.100) is presented. The nanoparticles were fabricated using polymeric precursor method. The particles were acoustically milled and then they were embedded into polyvinyl alcohol (PVA) photopolymer matrix. After solidification the additional photoinducing treatment was performed by two coherent 1064 nm Nd:YAG laser beams. The angle between the photoinducing beams and their polarization was varied in order to achieve the maximum of THG. THG efficiency was monitored immediately after Nd:YAG laser treatment at different temperatures. The photoinduced THG was explored versus the Nd3 þ content and temperature. Origin of the effect is discussed within a framework of phenomenological description. & 2015 Elsevier B.V. All rights reserved.
Keywords: Polymer nanocomposites Photoinduced nonlinear optical properties Rare earth doped borates
1. Introduction A search and design of optically operated materials based on nanocomposites is crucial for laser light modulation, telecommunications, triggering and recording of optical information [1–3]. Among such kind of materials particular interest present nanoparticles interacting on their borders with polymer matrices [4], zeolites [5] as well as nanoparticles with complicated morphologies [6]. All the mentioned approaches possess a principal drawbacks caused by relatively low efficiency of the output nonlinear optical response. Another restraining factors for their applications in different technological devices are requirements of low light scattering [7], high photo-thermal stability [8], as well as resistance to different external environments [9]. Among the main optical parameters defining the efficiency of light harmonic generation and rectification effects are nonlinear n
Corresponding author. E-mail address: [email protected] (I.V. Kityk).
http://dx.doi.org/10.1016/j.physe.2015.11.042 1386-9477/& 2015 Elsevier B.V. All rights reserved.
optical constants [10]. Recently an enhanced interest has been given to composite materials which can be operated by external laser light [11]. Different materials were investigated for that purpose such as surface plasmon nanoparticles [11] and efficient crystalline materials. Among the crystallites, oxides, especially borate compounds, are very perspective for such applications [12,13]. Some previous works revealed that among the borates the most promising seem to be crystallites possessing enhanced number of intrinsic defects, such as δ-BiB3O6 (δ-BIBO) [14]. In this article we study a possibility of use the nanocomposites formed by orthorhombic bismuth triborate micro- and nanocrystallites doped with Nd3 þ ions incorporated into the polymer matrices as nonlinear optical operated materials. We focus on studies of third harmonic generation (THG) which, contrary to other nonlinear optical phenomena, does not require macroscopic acentricity. We explore role of laser power, geometry and polarization of photoinducing beams as well as temperature dependences. Influence of Nd3 þ ions concentration in investigated powders on THG efficiency is established. The coexistence of high local hyperpolarizablities of borate clusters and f-localized states
32
B.M. Chrunik et al. / Physica E 78 (2016) 31–34
Fig. 1. Typical TEM view of the powders incorporated into the PVA matrix monitored in the bright field regime for different parts of the nanocrystallites (a) scale about 50 nm; (b) scale at 20 nm with enhanced contrast.
of borates are used here to form long-range macroscopic ordering. This is realized through the photopolarization by external illumination.
2. Experimental Powder samples of δ-Bi1 xNdxB3O6 (where x¼ 0.025, 0.075 and 0.100) were synthesized by means of polymeric precursor method through the citrate way exactly as described in Ref. [15]. The starting materials were bismuth oxide (Bi2O3, SIGMA ALDRICH, 99.999%), neodymium oxide (Nd2O3, ALFA, 99.999%), boric acid (H3BO3, STENMARK, 99.5%) and citric acid monohydrate (C6H8O7 H2O, POCH, 99.4%). Initially the stoichiometric quantities of Bi2O3 and Nd2O3 were dissolved in concentrated HNO3 (65% a.r.) under conditions of stirring and heating at T¼ 70 °C to form metal nitrates. A proper amount of citric acid monohydrate was charged into solution in order to chelate the metal ions. It was taken with respect to metal ions content in 4:1 molar ratio . After its complete dissolution boric acid was added with 10% molar excess (to compensate the losses of highly-volatile boron oxide at higher temperatures). Such prepared solution was stirred for 1 h at 80 °C to initialize the polyesterification, then moved to alumina crucible and put into the resistance furnace equipped with digital EUROTHERM 906S temperature controller. It was kept for 20 h at 180 °C until the brown polymeric resin appeared due to polyesterification of citric acid. Then the furnace temperature was raised to 650 °C for 25 h to get rid of the organic parts due to pyrolysis. After cooling the obtained powders were crushed and ground in agate mortar, then put back to furnace and finally calcined for 75 h at 695 °C. The presence of pure δ-BIBO phase was confirmed using the XRD phase analysis [16]. The structural parameters of the crystallites were explored earlier [16,17]. The as-prepared δ-BIBO:Nd3 þ powders were additionally milled in 20 W acoustical field and then embedded into the photopolymer liquid compositions based on polyvinyl alcohol with I-BEB photoinitiator. The photosolidification was performed by
external continuous wave UV laser at 371 nm with simultaneously applied external DC-electric field with electric strength 4 kV/cm between the quartz/ITO electrodes. Generally the approach is similar to procedure described in Ref. [18]. The whole process was carried out at about 245 K which corresponded to phase transformation of PVA [19]. External DC electric field allowed to fabricate aligned composite films with thicknesses up to 0.4 mm. The illumination was performed by Gaussian-like beam 3 mm in diameter. Its deviation from the stable power density about 45 W/cm2 was less than 0.1%. The homogeneity of the nanoparticle distribution was equal to about 4.8%.
3. Results and discussion The TEM imaging of the composites was done for the thin layer of δ-BIBO:Nd3 þ nanoparticles embedded in the PVA. A droplet of trichloromethane was deposited on the PVA layer on the glass, favouring local dissolution of polymer. For 2–3 s the 2.5 mm TEM Cu ring possessing a mesh of 400 was immersed in the liquid. The drying treatment was carried out in normal atmosphere conditions initially during 15 min, and then at enhanced temperature up to 55 °C for the next 70 min. Fabricated in such a way membrane was transparent for electron beam. As a consequence the mesh cells had only few nanoparticles. For reference, specimens of the PVA scratched from the substrate on a holey carbon film with a copper grid were explored. The JEOL 2000 microscope operating at 200 kV and with a point resolution of about 0.35 nm was used. TEM imaging was done in bright field approach. The corresponding TEM pictures are presented in Fig. 1. Orthorhombic structure of the obtained δ-Bi1 xNdxB3O6 powders was confirmed previously [16]. The third order nonlinear optical effects are described by fourth rank tensors and do not require acentric symmetry. Extending of the fourth rank tensors for the optical and DC-electric components allows introducing the sixth rank tensors of nonlinear optical susceptibility:
B.M. Chrunik et al. / Physica E 78 (2016) 31–34
Pi = χ
ijklmnEjEkElE
0
0 mEn
33
(1)
where Pi is polarization of the medium; Ei,j,k– particular (i,j,k)) components of the electric field part of the optical fields; E0 – optically formed local electric fields created due to two-beam coherent nonlinear optical interference (poling). Sixth rank tensor χijklmn plays here principal role and takes into account both components of probing optical field (j,k,l–components and optically poled local electric field strength En0). It is principal that these components do not require non-centrosymmetry, as it was mentioned above. In semi-empirical approximation the fourth rank tensor of optical hyperpolarizability may be described in a form of threelevel approach [10]: t γijkl ≅
2 2 μ 01 ⋅(μ12 + Δμ12 )
(E01 −
E02 2 ) ⋅Γ 2
(2)
where: μ 01—variation in the dipole moment i.e. the difference between first excited (1) and ground (0) states;
μ12—variation in the dipole moment i.e. the difference between
first excited (1) and higher (2) states; E01—energy of transition between ground (0) and first excited (1) states; E12—energy of transition between first (1) and higher (2) excited states; Δ μ1—dipole moment difference between ground state and the lowest charge transfer excited-state. The applied external fields do not disturb substantially the excited states and interact mainly with the ground state dipole moment magnitudes. In the first approximation one can consider only linear interaction between the ground state dipole moments and DC-electric field. These interactions may be described within a framework of linear dipole-dipole interactions of the DC-electric field components and the localized polarized dipole moments. The changes of the ground state dipole moments Δμ0 may be described by an expression
Δμ 0 = μ 0 E 0ε*
(3)
where ε*-is the local effective Lorenz field defning the screening of electrostatic potential. Dependence measurements of the photoinduced THG coefficient at 1064 nm fundamental laser pulses were conducted at incident beam angles between two photoinducing coherent beams varying within 12–37°. All the measurements were done as a function of laser energy density. Maximal efficiency was achieved at incident angle's magnitudes varying within 22–26°. All the measurements were carried out immediately after the two-beam coherent treatment at different laser polarizations. In order to achieve the necessary reproducibility of the data the measurements were done in more than 20 different points of the samples. We established that for δ-Bi1 xNdxB3O6/PVA composites with 7.5% content of Nd3 þ the THG magnitudes reached maximal values. Following Fig. 2 one can see non-monotonous increasing dependences of the THG versus the applied photoinducing energy density. For all the polarizations there is observed substantial enhancement of the THG efficiency. However this feature is very sensitive to the relative polarization orientation for the two photoinducing beams originating from the same laser. It may reflect symmetry of the sixth rank tensors (Eq. 1). The light polarizations define the indices of the particular tensor. Some role here is played by thermo-heating created by photoinducing two-beam coherent treatment. The enhancement of temperature leads to enhanced
Fig. 2. Experimental photoinduced THG effect dependences for δBi0.925Nd0.075B3O6/PVA composites at different polarization if the two coherent photoinduced beams. Arrows indicate heating of the samples during photoinducing laser treatment. The bold arrow marks occurrence of multi-photon processes.
photo-thermal effect. The thermo-heating is crucially dependent on the energy of photoinducing pulses. However, maximal magnitude of THG enhancement was reached when temperature of the samples was risen at about 4 K. The processes relaxed with time of about 2 s (see Fig. 3) after switching off the treatment. Following this figure it is also clear that samples containing 7.5% of Nd3 þ perform the maximal THG after 2–3 min. treatment. For other samples this value is substantially smaller (see Fig. 3). Very crucial is also an occurrence of many local maxima of intensity in the THG beam profile sequence (see Fig. 4). It may reflect the multi-photon phase matching conditions. The profile is substantially non-Gaussian despite the excitation of the Gaussianlike two-beam profiles. Such deformation of the profile may be a consequence of the anisotropy of the tensors described by Eq. (1). Additionally the different polarization causes anisotropy of the photoinduced ground state dipole moments [20]. All the effects are observed at RT. With decreasing temperature the photoinduced THG is quickly suppressed. The observed steplike dependences may be a consequence of competition between the light photo-polarization and the decaying processes of the
Fig. 3. Typical decay of THG efficiency for δ-Bi0.925Nd0.075B3O6/PVA composites after switching off of the photoinducing field. Arrow indicates a stabilization of the decay.
34
B.M. Chrunik et al. / Physica E 78 (2016) 31–34
earth-doped borate powders was demonstrated. Dependence measurements of the photoinduced THG coefficient at 1064 nm fundamental laser pulses were conducted. All the measurements were done as a function of laser energy density. We discovered that for the studied δ-Bi1 xNdxB3O6/PVA nanocomposites with 7.5% content of Nd3 þ the THG magnitudes are maximal. Additionally the THG features are very sensitive not only to the pumping power, but also to their relative polarizations. It is a consequence of symmetry of the sixth rank tensors. The enhancement of temperature leads to enhanced photo-thermal effect. The observed photoinduced THG processes are relaxed at time of about 2 s after switching off the treatment.
Aknowledgements This work was partially supported by the Polish Ministry of Sciences and Higher Education, Key Project POIG. 01.03.01-14-06/ 08 “New Photonic Materials and their Advanced Applications”.
References Fig. 4. Reconstructed profile field of the THG changes in the near field.
localized Nd f-states and interface levels. The latter factors lead to modification of the final tensor presentation in the following form:
χ
el, cr loc , cr )+ δ (χ ijklmn = δcr (χijklmn + χijklmn in
el, interface
ijklmn
phon, int
+ χijklmn
)
(4)
where el,cr is electronic contribution intra the crystallites; loc,cr is contribution of the localized levels; el,interface – electronic contribution of the interface; phon,int.–contribution of phonon interaction. Such formed DC-electric field long-range polarization forms renormalized oriented ground state dipole moments which change the effective susceptibilities in Eq. (4) due to variation of the ground state dipole moments screened by localized fields (Eqs. (3) and (4)). So varying of the rare earth content and interface electrostatic gradients may be a prime direction of search of the nanocomposites with desirable optically operated properties.
4. Conclusions A possibility of varying THG for the polymer embedded rare
[1] A. Radu, C.A. Duque, Phys. E 72 (2015) 165–177. [2] P. Soundarrajan, K. Sankarasubramanian, M. Sampath, T. Logu, K. Sethuraman, K. Ramamurthi, Phys. E 71 (2015) 56–63. [3] A. Aloufy, J. Ebothé, N. Dumelié, I. Chaki, M. Abd-Lefdil, N.S. Alzayed, A.M. ElNaggar, A.A. Albassam, I.V. Kityk, Phys. E 73 (2015) 96–99. [4] K.J. Plucinski, G. Lakshminarayana, Phys. E 68 (2015) 140–142. [5] J. Flores-Valenzuela, M. Cortez-Valadez, R. Ramírez-Bon, H. Arizpe-Chavez, J. F. Román-Zamorano, M. Flores-Acosta, Phys. E 72 (2015) 1–6. [6] S. Nafisah, S.K.M. Saad, A.A. Umar, K. Plucinski, M. Lis, A. Maciaga, R. Miedzinski, Opt. Appl. 45 (2015) 263–271. [7] R.N. Jana, S. Sinha, A.K. Meikap, Phys. E 77 (2016) 7–12. [8] A. Jolly, B. Chassagne, J.C. Jolly, Opt. Commun. 311 (2013) 325–331. [9] Z. Pan, Y. Li, X. Hou, J. Yan, C. Wang, Phys. E 63 (2014) 1–7. [10] S.A. Mohammadi, R. Khordad, G. Rezaei, Phys. E 76 (2016) 203–208. [11] A. Semenov, V. Puziko, S. Skorik, A. Wojciechowski, A.O. Fedorchuk, A. Maciąg, Phys. E 69 (2015) 378–383. [12] A. Majchrowski, I.V. Kityk, T. Łukasiewicz, A. Mefleh, S. Benet, Opt. Mater. 15 (2000) 51–58. [13] I.V. Kityk, A. Majchrowski, Opt. Mater. 25 (2004) 33–37. [14] A. Majchrowski, M. Chrunik, I.V. Kityk, K. Ozga, E. Michalski, P. Morawiak, L. R. Jaroszewicz, Mater. Lett. 122 (2014) 114–116. [15] R. Cong, T. Yang, Z. Lin, L. Bai, J. Ju, F. Liao, Y. Wang, J. Lin, J. Mater. Chem. 22 (2012) 17934–17941. [16] M. Chrunik, J. Ebothe, A. Majchrowski, J. Michel, L.R. Jaroszewicz, I.V. Kityk, Opt. Commun. 364 (2016) 13–17. [17] A. Majchrowski, J. Ebothe, J. Michel, M. Chrunik, L.R. Jaroszewicz, D. Kulwas, Mater. Lett. 162 (2016) 114–116. [18] I.V. Kityk, R.I. Mervinskii, J. Kasperczyk, S. Jossi, Mater. Lett. 27 (1996) 233–237. [19] I.V. Kityk, J. Kasperczyk, B. Sahraoui, M.F. Yasinskii, B. Holan, Polymers 38 (1997) 4803–4806. [20] I.V. Kityk, Sov. Phys. Solid State 33 (1991) 1026–1030.
Contents lists available at ScienceDirect
Physica E journal homepage: www.elsevier.com/locate/physe
Laser induced third harmonic generation in δ-Bi1 xNdxB3O6 nanocomposites By M. Chrunik a, J. Ebothé b, A.K. Aloufy c, A. Majchrowski a, L.R. Jaroszewicz a, I.V. Kityk d,n a
Institute of Applied Physics, Military University of Technology, Kaliskiego 2, 00-908 Warsaw, Poland LRN no 4682-UFR Sciences Exactes, University of Reims, 21 rue Clément Ader, 51096 REIMS Cedex 02, France c New Advanced Materials & Nanotechnology Lab, NNREL, Textile Engineering Dept. Faculty of Engineering, Alexandria University, Alexandria, Egypt d Faculty of Electrical Engineering, Czestochowa University of Technology, Armii Krajowej 17, 42-201 Czestochowa, Poland b
H I G H L I G H T S
Tunable THG effect for polymer/Nd-doped δ-BiB3O6 nanocomposites was shown. THG features are strongly dependent not only on the pumping power but also on their relative polarizations. The effective anisotropic sixth rank tensor for description of such kind of photoinduced processes was introduced.
art ic l e i nf o
a b s t r a c t
Article history: Received 5 November 2015 Received in revised form 27 November 2015 Accepted 30 November 2015 Available online 2 December 2015
A possibility of optically operated third harmonic generation (THG) in polymer nanocomposites based on orthorhombic δ-Bi1 xNdxB3O6 powders (where x ¼ 0.025C0.100) is presented. The nanoparticles were fabricated using polymeric precursor method. The particles were acoustically milled and then they were embedded into polyvinyl alcohol (PVA) photopolymer matrix. After solidification the additional photoinducing treatment was performed by two coherent 1064 nm Nd:YAG laser beams. The angle between the photoinducing beams and their polarization was varied in order to achieve the maximum of THG. THG efficiency was monitored immediately after Nd:YAG laser treatment at different temperatures. The photoinduced THG was explored versus the Nd3 þ content and temperature. Origin of the effect is discussed within a framework of phenomenological description. & 2015 Elsevier B.V. All rights reserved.
Keywords: Polymer nanocomposites Photoinduced nonlinear optical properties Rare earth doped borates
1. Introduction A search and design of optically operated materials based on nanocomposites is crucial for laser light modulation, telecommunications, triggering and recording of optical information [1–3]. Among such kind of materials particular interest present nanoparticles interacting on their borders with polymer matrices [4], zeolites [5] as well as nanoparticles with complicated morphologies [6]. All the mentioned approaches possess a principal drawbacks caused by relatively low efficiency of the output nonlinear optical response. Another restraining factors for their applications in different technological devices are requirements of low light scattering [7], high photo-thermal stability [8], as well as resistance to different external environments [9]. Among the main optical parameters defining the efficiency of light harmonic generation and rectification effects are nonlinear n
Corresponding author. E-mail address: [email protected] (I.V. Kityk).
http://dx.doi.org/10.1016/j.physe.2015.11.042 1386-9477/& 2015 Elsevier B.V. All rights reserved.
optical constants [10]. Recently an enhanced interest has been given to composite materials which can be operated by external laser light [11]. Different materials were investigated for that purpose such as surface plasmon nanoparticles [11] and efficient crystalline materials. Among the crystallites, oxides, especially borate compounds, are very perspective for such applications [12,13]. Some previous works revealed that among the borates the most promising seem to be crystallites possessing enhanced number of intrinsic defects, such as δ-BiB3O6 (δ-BIBO) [14]. In this article we study a possibility of use the nanocomposites formed by orthorhombic bismuth triborate micro- and nanocrystallites doped with Nd3 þ ions incorporated into the polymer matrices as nonlinear optical operated materials. We focus on studies of third harmonic generation (THG) which, contrary to other nonlinear optical phenomena, does not require macroscopic acentricity. We explore role of laser power, geometry and polarization of photoinducing beams as well as temperature dependences. Influence of Nd3 þ ions concentration in investigated powders on THG efficiency is established. The coexistence of high local hyperpolarizablities of borate clusters and f-localized states
32
B.M. Chrunik et al. / Physica E 78 (2016) 31–34
Fig. 1. Typical TEM view of the powders incorporated into the PVA matrix monitored in the bright field regime for different parts of the nanocrystallites (a) scale about 50 nm; (b) scale at 20 nm with enhanced contrast.
of borates are used here to form long-range macroscopic ordering. This is realized through the photopolarization by external illumination.
2. Experimental Powder samples of δ-Bi1 xNdxB3O6 (where x¼ 0.025, 0.075 and 0.100) were synthesized by means of polymeric precursor method through the citrate way exactly as described in Ref. [15]. The starting materials were bismuth oxide (Bi2O3, SIGMA ALDRICH, 99.999%), neodymium oxide (Nd2O3, ALFA, 99.999%), boric acid (H3BO3, STENMARK, 99.5%) and citric acid monohydrate (C6H8O7 H2O, POCH, 99.4%). Initially the stoichiometric quantities of Bi2O3 and Nd2O3 were dissolved in concentrated HNO3 (65% a.r.) under conditions of stirring and heating at T¼ 70 °C to form metal nitrates. A proper amount of citric acid monohydrate was charged into solution in order to chelate the metal ions. It was taken with respect to metal ions content in 4:1 molar ratio . After its complete dissolution boric acid was added with 10% molar excess (to compensate the losses of highly-volatile boron oxide at higher temperatures). Such prepared solution was stirred for 1 h at 80 °C to initialize the polyesterification, then moved to alumina crucible and put into the resistance furnace equipped with digital EUROTHERM 906S temperature controller. It was kept for 20 h at 180 °C until the brown polymeric resin appeared due to polyesterification of citric acid. Then the furnace temperature was raised to 650 °C for 25 h to get rid of the organic parts due to pyrolysis. After cooling the obtained powders were crushed and ground in agate mortar, then put back to furnace and finally calcined for 75 h at 695 °C. The presence of pure δ-BIBO phase was confirmed using the XRD phase analysis [16]. The structural parameters of the crystallites were explored earlier [16,17]. The as-prepared δ-BIBO:Nd3 þ powders were additionally milled in 20 W acoustical field and then embedded into the photopolymer liquid compositions based on polyvinyl alcohol with I-BEB photoinitiator. The photosolidification was performed by
external continuous wave UV laser at 371 nm with simultaneously applied external DC-electric field with electric strength 4 kV/cm between the quartz/ITO electrodes. Generally the approach is similar to procedure described in Ref. [18]. The whole process was carried out at about 245 K which corresponded to phase transformation of PVA [19]. External DC electric field allowed to fabricate aligned composite films with thicknesses up to 0.4 mm. The illumination was performed by Gaussian-like beam 3 mm in diameter. Its deviation from the stable power density about 45 W/cm2 was less than 0.1%. The homogeneity of the nanoparticle distribution was equal to about 4.8%.
3. Results and discussion The TEM imaging of the composites was done for the thin layer of δ-BIBO:Nd3 þ nanoparticles embedded in the PVA. A droplet of trichloromethane was deposited on the PVA layer on the glass, favouring local dissolution of polymer. For 2–3 s the 2.5 mm TEM Cu ring possessing a mesh of 400 was immersed in the liquid. The drying treatment was carried out in normal atmosphere conditions initially during 15 min, and then at enhanced temperature up to 55 °C for the next 70 min. Fabricated in such a way membrane was transparent for electron beam. As a consequence the mesh cells had only few nanoparticles. For reference, specimens of the PVA scratched from the substrate on a holey carbon film with a copper grid were explored. The JEOL 2000 microscope operating at 200 kV and with a point resolution of about 0.35 nm was used. TEM imaging was done in bright field approach. The corresponding TEM pictures are presented in Fig. 1. Orthorhombic structure of the obtained δ-Bi1 xNdxB3O6 powders was confirmed previously [16]. The third order nonlinear optical effects are described by fourth rank tensors and do not require acentric symmetry. Extending of the fourth rank tensors for the optical and DC-electric components allows introducing the sixth rank tensors of nonlinear optical susceptibility:
B.M. Chrunik et al. / Physica E 78 (2016) 31–34
Pi = χ
ijklmnEjEkElE
0
0 mEn
33
(1)
where Pi is polarization of the medium; Ei,j,k– particular (i,j,k)) components of the electric field part of the optical fields; E0 – optically formed local electric fields created due to two-beam coherent nonlinear optical interference (poling). Sixth rank tensor χijklmn plays here principal role and takes into account both components of probing optical field (j,k,l–components and optically poled local electric field strength En0). It is principal that these components do not require non-centrosymmetry, as it was mentioned above. In semi-empirical approximation the fourth rank tensor of optical hyperpolarizability may be described in a form of threelevel approach [10]: t γijkl ≅
2 2 μ 01 ⋅(μ12 + Δμ12 )
(E01 −
E02 2 ) ⋅Γ 2
(2)
where: μ 01—variation in the dipole moment i.e. the difference between first excited (1) and ground (0) states;
μ12—variation in the dipole moment i.e. the difference between
first excited (1) and higher (2) states; E01—energy of transition between ground (0) and first excited (1) states; E12—energy of transition between first (1) and higher (2) excited states; Δ μ1—dipole moment difference between ground state and the lowest charge transfer excited-state. The applied external fields do not disturb substantially the excited states and interact mainly with the ground state dipole moment magnitudes. In the first approximation one can consider only linear interaction between the ground state dipole moments and DC-electric field. These interactions may be described within a framework of linear dipole-dipole interactions of the DC-electric field components and the localized polarized dipole moments. The changes of the ground state dipole moments Δμ0 may be described by an expression
Δμ 0 = μ 0 E 0ε*
(3)
where ε*-is the local effective Lorenz field defning the screening of electrostatic potential. Dependence measurements of the photoinduced THG coefficient at 1064 nm fundamental laser pulses were conducted at incident beam angles between two photoinducing coherent beams varying within 12–37°. All the measurements were done as a function of laser energy density. Maximal efficiency was achieved at incident angle's magnitudes varying within 22–26°. All the measurements were carried out immediately after the two-beam coherent treatment at different laser polarizations. In order to achieve the necessary reproducibility of the data the measurements were done in more than 20 different points of the samples. We established that for δ-Bi1 xNdxB3O6/PVA composites with 7.5% content of Nd3 þ the THG magnitudes reached maximal values. Following Fig. 2 one can see non-monotonous increasing dependences of the THG versus the applied photoinducing energy density. For all the polarizations there is observed substantial enhancement of the THG efficiency. However this feature is very sensitive to the relative polarization orientation for the two photoinducing beams originating from the same laser. It may reflect symmetry of the sixth rank tensors (Eq. 1). The light polarizations define the indices of the particular tensor. Some role here is played by thermo-heating created by photoinducing two-beam coherent treatment. The enhancement of temperature leads to enhanced
Fig. 2. Experimental photoinduced THG effect dependences for δBi0.925Nd0.075B3O6/PVA composites at different polarization if the two coherent photoinduced beams. Arrows indicate heating of the samples during photoinducing laser treatment. The bold arrow marks occurrence of multi-photon processes.
photo-thermal effect. The thermo-heating is crucially dependent on the energy of photoinducing pulses. However, maximal magnitude of THG enhancement was reached when temperature of the samples was risen at about 4 K. The processes relaxed with time of about 2 s (see Fig. 3) after switching off the treatment. Following this figure it is also clear that samples containing 7.5% of Nd3 þ perform the maximal THG after 2–3 min. treatment. For other samples this value is substantially smaller (see Fig. 3). Very crucial is also an occurrence of many local maxima of intensity in the THG beam profile sequence (see Fig. 4). It may reflect the multi-photon phase matching conditions. The profile is substantially non-Gaussian despite the excitation of the Gaussianlike two-beam profiles. Such deformation of the profile may be a consequence of the anisotropy of the tensors described by Eq. (1). Additionally the different polarization causes anisotropy of the photoinduced ground state dipole moments [20]. All the effects are observed at RT. With decreasing temperature the photoinduced THG is quickly suppressed. The observed steplike dependences may be a consequence of competition between the light photo-polarization and the decaying processes of the
Fig. 3. Typical decay of THG efficiency for δ-Bi0.925Nd0.075B3O6/PVA composites after switching off of the photoinducing field. Arrow indicates a stabilization of the decay.
34
B.M. Chrunik et al. / Physica E 78 (2016) 31–34
earth-doped borate powders was demonstrated. Dependence measurements of the photoinduced THG coefficient at 1064 nm fundamental laser pulses were conducted. All the measurements were done as a function of laser energy density. We discovered that for the studied δ-Bi1 xNdxB3O6/PVA nanocomposites with 7.5% content of Nd3 þ the THG magnitudes are maximal. Additionally the THG features are very sensitive not only to the pumping power, but also to their relative polarizations. It is a consequence of symmetry of the sixth rank tensors. The enhancement of temperature leads to enhanced photo-thermal effect. The observed photoinduced THG processes are relaxed at time of about 2 s after switching off the treatment.
Aknowledgements This work was partially supported by the Polish Ministry of Sciences and Higher Education, Key Project POIG. 01.03.01-14-06/ 08 “New Photonic Materials and their Advanced Applications”.
References Fig. 4. Reconstructed profile field of the THG changes in the near field.
localized Nd f-states and interface levels. The latter factors lead to modification of the final tensor presentation in the following form:
χ
el, cr loc , cr )+ δ (χ ijklmn = δcr (χijklmn + χijklmn in
el, interface
ijklmn
phon, int
+ χijklmn
)
(4)
where el,cr is electronic contribution intra the crystallites; loc,cr is contribution of the localized levels; el,interface – electronic contribution of the interface; phon,int.–contribution of phonon interaction. Such formed DC-electric field long-range polarization forms renormalized oriented ground state dipole moments which change the effective susceptibilities in Eq. (4) due to variation of the ground state dipole moments screened by localized fields (Eqs. (3) and (4)). So varying of the rare earth content and interface electrostatic gradients may be a prime direction of search of the nanocomposites with desirable optically operated properties.
4. Conclusions A possibility of varying THG for the polymer embedded rare
[1] A. Radu, C.A. Duque, Phys. E 72 (2015) 165–177. [2] P. Soundarrajan, K. Sankarasubramanian, M. Sampath, T. Logu, K. Sethuraman, K. Ramamurthi, Phys. E 71 (2015) 56–63. [3] A. Aloufy, J. Ebothé, N. Dumelié, I. Chaki, M. Abd-Lefdil, N.S. Alzayed, A.M. ElNaggar, A.A. Albassam, I.V. Kityk, Phys. E 73 (2015) 96–99. [4] K.J. Plucinski, G. Lakshminarayana, Phys. E 68 (2015) 140–142. [5] J. Flores-Valenzuela, M. Cortez-Valadez, R. Ramírez-Bon, H. Arizpe-Chavez, J. F. Román-Zamorano, M. Flores-Acosta, Phys. E 72 (2015) 1–6. [6] S. Nafisah, S.K.M. Saad, A.A. Umar, K. Plucinski, M. Lis, A. Maciaga, R. Miedzinski, Opt. Appl. 45 (2015) 263–271. [7] R.N. Jana, S. Sinha, A.K. Meikap, Phys. E 77 (2016) 7–12. [8] A. Jolly, B. Chassagne, J.C. Jolly, Opt. Commun. 311 (2013) 325–331. [9] Z. Pan, Y. Li, X. Hou, J. Yan, C. Wang, Phys. E 63 (2014) 1–7. [10] S.A. Mohammadi, R. Khordad, G. Rezaei, Phys. E 76 (2016) 203–208. [11] A. Semenov, V. Puziko, S. Skorik, A. Wojciechowski, A.O. Fedorchuk, A. Maciąg, Phys. E 69 (2015) 378–383. [12] A. Majchrowski, I.V. Kityk, T. Łukasiewicz, A. Mefleh, S. Benet, Opt. Mater. 15 (2000) 51–58. [13] I.V. Kityk, A. Majchrowski, Opt. Mater. 25 (2004) 33–37. [14] A. Majchrowski, M. Chrunik, I.V. Kityk, K. Ozga, E. Michalski, P. Morawiak, L. R. Jaroszewicz, Mater. Lett. 122 (2014) 114–116. [15] R. Cong, T. Yang, Z. Lin, L. Bai, J. Ju, F. Liao, Y. Wang, J. Lin, J. Mater. Chem. 22 (2012) 17934–17941. [16] M. Chrunik, J. Ebothe, A. Majchrowski, J. Michel, L.R. Jaroszewicz, I.V. Kityk, Opt. Commun. 364 (2016) 13–17. [17] A. Majchrowski, J. Ebothe, J. Michel, M. Chrunik, L.R. Jaroszewicz, D. Kulwas, Mater. Lett. 162 (2016) 114–116. [18] I.V. Kityk, R.I. Mervinskii, J. Kasperczyk, S. Jossi, Mater. Lett. 27 (1996) 233–237. [19] I.V. Kityk, J. Kasperczyk, B. Sahraoui, M.F. Yasinskii, B. Holan, Polymers 38 (1997) 4803–4806. [20] I.V. Kityk, Sov. Phys. Solid State 33 (1991) 1026–1030.