Photoinduced Second Harmonic Generation Research Articles

Six-wave mixing probe of light-induced second-harmonic generation: example of dye solutions

Using a phase-conjugation configuration based on six-wave mixing interactions, we have investigated in detail the mechanism of photoinduced second-harmonic generation (SHG) in initially centrosymmetric materials. After some theoretical study of the process we discuss how different complementary tests (with the same experimental setup), such as investigations of the polarization properties or the lifetime dependence of the induced χ(2) grating on the solvent, can reveal the microscopic characteristics of the process. We present experimental studies performed in various solutions of an azo-dye molecule (Disperse Red 1) with the 532-nm harmonic light along with the 1.064-μm light from a picosecond-pulsed Nd:YAG laser. The results show good agreement with the theoretical predictions. It is shown moreover that the light-induced χ(2) grating is due to oriental hole burning of the molecules, whereas reorientation of the molecules in the solvent is one major cause of relaxation.

Two-photon-resonant photoinduced second-harmonic generation in Er^3+-doped germano-aluminosilicate optical fibers pumped at 1319 μm

The growth of a two-photon-resonant photoinduced second-harmonic signal at 660 nm in Er(3+)-doped GeO(2)-Al(2)O(3)-SiO(2) single-mode optical fibers pumped by a Nd:YAG laser at 1.319 microm is reported. Defect states in the band gap are optically excited through a resonant two-photon absorption process connecting the (4)I(15/2)-(4)F(9/2) energy levels of the erbium ions present in the fiber core. As a result a periodic X((2)) grating is formed, and efficient second-harmonic generation takes place. For erbium-free GeO(2)-doped silica test fibers no second-harmonic signal has been detected, even after hours of seeded preparation process.

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.

Efficient photoinduced second-harmonic generation in Ce-doped lead germanate glasses

Efficient photoinduced second-harmonic generation in Ce-doped bulk lead germanate glasses is observed. A linear increase of photoinduced second-order nonlinearity with Ce concentration is obtained. The reported glasses can be encoded for frequency doubling with extremely low (as little as 30 W of peak power at 1.064 microm) preparation intensities.

Photoinduced second-harmonic generation of YBa2Cu3O7- delta single crystals

Complex investigations of the photoinduced changes in YBa2Cu3O7- delta ( delta >0.5) single crystals have been carried out using the time-resolved dependences of the photocurrent, photoresistivity, photovoltage and optical second-harmonic generation (SHG). Simultaneously the spectroscopic parameters were monitored by time-resolved Raman and UV-visible reflection spectra. A time delay shift between the SHG and photocurrent dependences was found. The contributions of two different mechanisms in the formation of the superconducting behaviour were unambiguously shown. It was clearly shown that only by simultaneously taking into account the anharmonicity due to the specific electron-phonon interaction together with the traditional Anderson metal-insulator transition we can clarify the main physical mechanisms of the high-temperature superconductivity. Magnetic fields of up to 1 T suppress the SHG signal. The different delay times for the electronic and phonon spectra indicate the essential role of the electron-phonon anharmonic coupling in the high-temperature superconductivity. Some different approaches to explain the observed phenomena are discussed.

Photoinduced second-harmonic generation in fibers doped with rare-earth ions

Photoinduced second-harmonic generation in silica fibers doped with Er(3+), Sm(3+), and Tb(3+) has been investigated. Er(3+)-doped fibers have been found to tune a chi((2)) grating easily to the mode structure of the laser radiation, whereas Sm(3+)-doped fibers have been found to possess the greatest resistance to chi((2)) grating erasure by radiation at 532 nm. From the beginning of the preparation processes, the third harmonic at 355 nm is registered in all the fibers.

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>

Observation of resonant enhancement of photoinduced second-harmonic generation in Tm-doped aluminosilicate glass fibers

We report a 10(3) increase in efficiency of second-harmonic generation in Tm(3+)-doped aluminosilicate glass fibers when the wavelength of the fundamental beam is tuned to the maximum of the (3)H(6) ? (3)F(4) absorption of Tm(3+) at 785 nm. This result shows the role of resonance enhancement in the nonlinear optical process that is responsible for the formation of the X((2)) grating.

Experimental study of second-harmonic-generation saturation in fibers by phase modulation between the fundamental and second-harmonic writing beams

We study saturation of photoinduced second-harmonic generation in a Ge-doped silica fiber by modulating the relative phase between the fundamental and second-harmonic writing beams. We shift the phase by pi and present measurements that identify saturation that is due to site depletion and saturation that is due to a backfield.

Photoinduced second-harmonic generation in rare-earth-doped aluminosilicate optical fibers

The presence of defect states in the band gap is an essential ingredient of recent models of photoinduced second-harmonic generation (SHG) in fibers. We have created such states by doping aluminosilicate glass fibers that do not contain Ge with Ce or Eu and observed SHG from 1.06-microm light after preparation of the fibers with 0.532- and 1.06-microm light. In an aluminosilicate fiber doped with 0.008 wt. % Ce, the SHG conversion efficiency is as high as 1.5% at infrared (1.06-microm) peak powers of 200 W.

Photoinduced Second Harmonic Generation in Optical Fibers: Materials and Mechanisms

ABSTRACTPermanent X(2) gratings can be written in doped silica fibers by coherent irradiation with light at ω and 2ω. The X(2) gratings give rise to phase-matched second harmonic generation (SHG), i.e. subsequent irradiation of the prepared fiber with light at ω results in an output at 2ω. The efficiency with which the gratings can be written depends on the nature and concentration of defect states induced by dopants in the, glass. We present results for fibers doped with Ge and rare earth ions and discuss the implications of our results for the various mechanisms that have been proposed to explain photoinduced SHG in fibers.

Polarization study of photoinduced second-harmonic generation in glass optical fibers

By studying the polarization properties of photoinduced second-harmonic generation in a germania-doped silica glass optical fiber we show that the induced χ (2) is consistent with being due to the χ (3) of the glass acted on by an internal dc electric field. Additional arguments are provided to support the view that the observed χ (2) is not simply due to the microscopic χ (2) of ordered dipoles.

Photoinduced second-harmonic generation in gamma-ray-irradiated optical fibers

The effect of gamma-ray irradiation on photoinduced second-harmonic generation in optical fibers is investigated for the first time to our knowledge. A significant increase (by a factor of 20) in the conversion efficiency of gamma-ray-irradiated optical fibers is found. An explanation of the experimental results is suggested, which is based on the photovoltaic mechanism of the photoinduced second-harmonic generation.