Second Harmonic Generation In Glasses Research Articles

Tunable angular-dependent second-harmonic generation in glass by controlling femtosecond laser polarization

Mastering second-harmonic generation (SHG) in glasses is essential for achieving second-order nonlinear devices. Three-dimensional SHG patterns with controllable angular dependence were achieved in Li2O-Nb2O5-SiO2 glass by femtosecond laser irradiation. Electron backscatter diffraction indicated that the angular dependence was associated with preferential nanocrystal orientation: crystal polar axes are distributed within a plane perpendicular to the incident laser polarization direction. An orientation mechanism based on the application of laser-induced torques on the nanocrystal electric dipole was proposed. This work may pave the way to design devices such as frequency agile lasers based on electro-optical waveguides.

Limitation of optical poling in germanium-silicate glasses

The giant increase of the absorption of the radiation with the doubled frequency in a region of high values of the optically-induced electric fields (about 10 5–10 6 V/cm) has been observed during the investigation of the optical poling process in germanium-silicate glass. The absorption suppresses the writing of the second-order susceptibility grating and leads to the restriction of the maximum efficiency of the photoinduced second harmonic generation in glass. We demonstrate that the observed effect is not anisotropic and may be considered as a consequence of a competition between the charge separation by the local trapping levels due to electrostricted photoinduced phonons and recombination diffusion of carriers.

Polar light and symmetry of electro-optical effects

General regularities of the interaction of a polar light wave synthesized from the Fourier harmonics of a fundamental frequency with a transparent centrosymmetric optically nonlinear medium are considered. The notion of light polarity is introduced and transverse electro-optical effects specific for the problem of interaction between polar light and isotropic nonlinear media (optical rectification and the linear electro-optical effect) are analyzed. Estimates of values of the effects in combination with published experimental data on optically encoded second harmonic generation in glasses indicate promising opportunities for practical application of the effects of the interaction of polar light and matter in optical systems of information recording and processing.

Tunable room temperature second harmonic generation in glasses doped with CuCl nanocrystalline quantum dots

Two-photon excited emission centered at 379–426 nm in photodarkening borosilicate glass doped with CuCl nanocrystalline quantum dots at room temperature has been observed. The emission is detected in the direction of the fundamental near-infrared beam. Time- and frequency-resolved measurements at room temperature and 77 K indicate that the emission is largely coherent light characteristic of second harmonic generation (SHG). An average conversion efficiency of ∼10 −10 is obtained for a 2 mm thick sample. The observed SHG can originate in the individual noncentrosymmetric nanocrystals, leading to a bulk-like contribution, and at the nanocrystal-glass interface, leading to a surface contribution. The bulk-like conversion efficiency is estimated using previously reported values of coherence length ( 5 μm ) and bulk nonlinear susceptibility. This bulk-like conversion efficiency estimate is found to be smaller than the measured value, suggesting a more prominent surface contribution.

Thermal poling of transparent TeO2-based nanocrystallized glasses and enhanced second harmonic generation

A transparent TeO2-based nanocrystallized (crystalline particle size: ∼40 nm) glass (composition: 15K2O·15Nb2O5·68TeO2·2MoO3) showing a second harmonic generation (SHG) has been prepared, and a thermal poling has been applied to examine whether a poling technique is effective in enhancing the SH intensity of nanocrystallized glass. In the poling condition of 2.0 kV (DC voltage), 210 °C and 40 min, the SH intensity of nanocrystallized glass is enhanced, demonstrating that a combination of nanocrystallization and thermal poling is an useful technique to induce a SHG in glass. As similar to the case of glass, a prominent SHG is observed at the anode side in the thermal poling, suggesting the increase in polarization in nanocrystals.

IR-poled second-harmonic generation in glass

Infrared (IR)-induced second-harmonic generation in the chalcogenide glasses is observed. A phenomenological approach of IR picosecond non-linear optical (NLO) response in glass is developed for the middle IR spectral range (5– 15 μm ). The observed effect is explained within the framework of fifth-order NLO susceptibilities. A model that reproduces the basic characteristics of the experimental data, in which the optical non-linearities caused by photoinduced electron–phonon anharmonic interactions, is proposed. The role of the IR-induced phase matching conditions in the observed phenomenon is discussed.

All optical poling and second harmonic generation in glasses: theory and experiment

Theoretical and experimental evidence of light driven electron–hole self-organization resulting in amplification of seed static electric field is presented. The amplification allowed us to perform all optical poling of conventional commercial “heavy flint” silica glass. The χ (2)-grating is optically recorded in the initially centrosymmetric glass and the second harmonic generation (SHG) is observed in poled noncentrosymmetric material. The fundamental and frequency doubled output of a YAG:Nd 3+ laser starts the poling process creating rectified DC-electric field. Then single wavelength radiation (either fundamental or frequency doubled output) proceeds with optical recording of nonlinear grating amplifying this initial DC-electric field.

Electrically Stimulated Light-Induced Second-Harmonic Generation in Glass: Evidence of Coherent Photoconductivity

A strong electrostatic field applied to glass is spatially modulated by intense light at frequencies $\ensuremath{\omega}$ and $2\ensuremath{\omega}$. The phenomenon is explained in terms of photoconductivity being dependent on the relative phase of the light fields at different frequencies.

Direct measurement of photoinduced charge distribution responsible for second-harmonic generation in glasses

We have found that borosilicate glasses that produce second-harmonic generation after simultaneous irradiation by fields at omega and 2omega exhibit postexposure selective etching. We use the charge specificity of the selective etching process to spatially map the photoexcited electron distributions responsible for second-harmonic generation. The results show that nearly symmetric nondipolar charge distributions exist for some regimes of encoding and that, at higher intensities, a nearly dipolar distribution is produced.

Photoinduced Second-Harmonic Generation in Glasses and Glass Optical Fibers

The effect of photoinduced second-harmonic generation in glasses and glass optical fibers is discussed. A brief review of the main results of the investigations is presented. Models, suggested for the effect explanation, are considered. Principles of experimental separation of different models and the results of recent experimental studies of the models are reported. The phenomenology of the photogalvanic mechanism, which has been experimentally confirmed, is considered in detail.

A time-dependent beam-propagation method to model photoinduced effects in glass

A numerical model for photoinduced second-harmonic generation in glass is presented. We use the beam-propagation method (BPM) to model the effects of focusing a laser beam and its second harmonic into a bulk sample of glass. The two-color optical field produces asymmetric photoionization, and hence charge separation within the glass. We follow the evolution of the optical fields with the BPM, and compute the distribution of trapped charges in the glass using a directional photoionization source term. The model can predict the shape of the dc electric fields, the underlying charge distributions, and the modal patterns of the generated second-harmonic light. We also include the time dependence of photoinduced nonlinear effects in glass. The mode patterns and dc field shapes agree with published experimental data, confirming the results of this simulation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Light-induced second-harmonic generation in glass via multiphoton ionization.

Irradiating glass by intense light at frequencies \ensuremath{\omega} and 2\ensuremath{\omega} generates a semipermanent dc electric field in the glass that transforms the glass into a phase-method optical-frequency doubler. We map out this dc electric field over a wide variety of experimental conditions. We show that its symmetries are predicted by a theory based on the interference of competing multiphoton ionization channels.

Helicity dependence of optically encoded second-harmonic generation in glasses

Homogeneous silica-based and heterogeneous semiconductor-doped glasses were optically encoded with circularly polarized beams for efficient second-harmonic generation (SHG) at 532 nm. SHG growth rates for circularly polarized writing beams with both the same and opposite helicity show that ${\mathrm{\ensuremath{\chi}}}^{(3)}$(0;\ensuremath{\omega},\ensuremath{\omega},-2\ensuremath{\omega}) mixing symmetries are well obeyed in semiconductor microcrystallite-doped glass but not in homogeneous silicate glasses. The radiated second-harmonic free-space mode and ${\mathrm{\ensuremath{\chi}}}^{(2)}$ tensor symmetries for cohelically encoded gratings in SK5 glass determined an electric field which possessed a radial component as well as a component which had a constant direction across the readout beam axis. The results are discussed in light of present theories.

Growth rate of second-harmonic generation in glass

We study the growth rate of the light-induced second-order nonlinearity in germanium-doped optical fiber preforms. We seed the glass with both infrared light and green light (Nd:YAG and doubled Nd:YAG) to create the second-order nonlinearity and measure its formation rate while varying the intensity of either the fundamental or the second-harmonic seeding beams. We find that the formation rate varies as a power law of the intensities, but with an exponent larger than predicted by recent models.

Test of directional photoionisation models of second harmonic generation in optical fibres

We present a set of experiments in which optical fibres are prepared with three optical fields of different frequencies to produce second harmonic generation. The results obtained are shown to be inconsistent with directional photoionisation models for second harmonic generation in glasses.

Electric field induced second harmonic generation in glass

The electric field induced second harmonic coefficient has been measured in glass. We have concluded that the nuclear contribution is significantly smaller than the electronic contribution, and that this third order effect in glass cannot be neglected when measuring the molecular hyperpolarizabilities of most organic liquids.