Large second-harmonic generation of thermally poled sodium borophosphate glasses

Abstract

Second harmonic generation (SHG) has been obtained in a rich in sodium niobium orophosphate glass by a thermal poling treatment. The thermally poled glass SHG signal has been studied through an original analysis of both transmitted and reflected polarized Maker-fringe patterns. Therefore, the second order nonlinear optical (NLO) efficiency was estimated from the simulation of the Maker-fringe patterns with a stepwise decreasing profile from the anode surface. A reproducible chi(2) susceptibility value as high as 5.0 +/-0.3 pm/V was achieved at the anode side. The nonlinear layer, found to be sodium-depleted up to 5 microm deep inside the anode side, identical to the simulated nonlinear zone thickness, indicates a complex space-charge-migration/ nonlinear glass matrix response process.

Enhanced Raman scattering in thermally poled sodium-niobium borophosphate glasses

“…Figure 6 presents the integrated Raman intensity of the poled bpn40 glass from 400 to 1400 cm −1 versus distance from the anode surface that manifests a clear enhancement of the Raman signal in the NLO layer. According to the axial spatial resolution of this experiment ͑ϳ1.5 m͒, we estimate a thickness of the NLO layer in the range of 3 -4 m. This result is in very good agreement with previous findings from Maker fringes analyses 6 and depth profile determinations of sodium concentration 4 on similar poled glasses.…”

“…We recall that the NLO layer formed by thermal poling is characterized by a depletion of sodium ions. 4 Thus, the decrease in intensity of the 900 cm −1 band characteristic of NbO 6 octahedral with Nb-O¯Na + bonds is consistent with a migration of sodium ions from the anode area.…”

“…13 As we measured a ͑2͒ value ranging in 1 -3 pm/ V for this particular glass composition, 6 we estimate that the internal electric field ranges in the order of 10 9 V / m. We recall that for this kind of poled glasses, the quadratic NLO response measured by the Maker fringes technique ͓ ͑2͒ ͑−2 ; , ͔͒ were related to the ͑3͒ ͑−2 ;0, , ͒ term. 4 Similarly, concerning the enhanced Raman response we expect the third order term ͓first term of the quadratic electro-optical contribution in Eq. ͑7͔͒ to be dominant versus the second order term ͑linear electro-optic contribution͒.…”

“…4,5 In such glasses, the second order nonlinear optical ͑NLO͒ response has been correlated to a third order NLO process through interaction of a high ͑3͒ value, linked to the presence of a three-dimensional ͑3D͒ niobate network, [6][7][8] with a static internal electric field ͑E int ͒ induced by a migration of sodium ions away from the anode surface. 4,9 ͑2͒ = 3 ͑3͒ E int . ͑1͒…”

“…Notably, the extent of displacement of the positive charge ͑sodium ions͒ in the NLO layer would induce alone an internal field 10 4 times larger than that corresponding to the measured ͑2͒ value. 4 Thus, structural rearrangements should prevent the development of such a strong internal field. This work is an attempt to reveal possible reorganizations of the glass matrix by employing microRaman spectroscopy.…”