Second-harmonic generation in Ge(20)As(25)S(55) glass irradiated by an electron beam

Second-harmonic generation was observed in Ge(20)As(25)S(55) chalcogenide glass irradiated by an electron beam. The second-harmonic intensity increased with increasing electron-beam current and accelerating voltage. The second-harmonic generation in Ge(20)As(25)S(55) glass was caused by the space-charge electrostatic field that was generated by irradiation of an electron beam. Second-order nonlinearity X((2)) as great as 0.8 pm/V was obtained. The results of measurements of thermally stimulated depolarization current indicated that the glass was poled in the thin layers of its surface (several micrometers) and that the nonlinearity was stable.     

Large optical second-order nonlinearity of poled WO3-TeO2 glass

Second-harmonic generation, one of the second-order nonlinear optical properties of thermally and electrically poled WO>(3)-TeO>(2) glasses, has been examined. We poled glass samples with two thicknesses (0.60 and 0.86 mm) at various temperatures to explore the effects of external electric field strength and poling temperature on second-order nonlinearity. The dependence of second-harmonic intensity on the poling temperature is maximum at a specific poling temperature. A second-order nonlinear susceptibility of 2.1 pm/V was attained for the 0.60-mm-thick glass poled at 250 degrees C. This value is fairly large compared with those for poled silica and tellurite glasses reported thus far. We speculate that the large third-order nonlinear susceptibility of WO>(3)- TeO>(2) glasses gives rise to the large second-order nonlinearity by means of a X((2)) = 3X((3)) E(dc) process.     

Second-harmonic generation in thermally poled chalcohalide glass

Second-harmonic generation in 60GeS(2)-20Ga(2)S(3)-20KBr chalcohalide glass was investigated by the thermal poling method. A large second-order nonlinear susceptibility, as high as 7.0 pm/V, was obtained in a poled sample by Maker fringe analysis. We believe this to be the first time that a clear second-harmonic wave was observed in chalcohalide glasses containing large amount of alkali ions (6.25 at. %). Such observation is of great potential use in all optical waveguide devices.     

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.     

Real-time monitoring of all-optical poling of azo-dye polymer thin film

Simultaneous writing and probing of photoinduced second-order susceptibility chi((2)) in an azo-dye polymer thin film is demonstrated. The method is based on the fact that tensor properties of chi((2)) provide different planes of polarization for seeding and signal second harmonics. Our technique allows the chi((2)) value to be monitored in real time, completely eliminating the distortion of optical poling that can occur in traditional probing configurations. The possibility of attaining high values of chi((2)) in a DR1-PMMA guest?host system under low seeding intensities is shown.     

Origin of thermally induced second harmonic generation in PbO-B2O3 glasses

Optical second harmonic generation (SHG) with second-order nonlinearity χ((2)) as high as 2.1 pm/V has been achieved in water quenched PbO-B(2)O(3) glasses. No nonlinear depletion layer or microcrystals were observed in these glasses and the mechanism for nonlinearity has been explored in this Letter. Our results show that the possible mechanism for SHG in these glasses can be attributed to their low thermal conductivity that led to a large surface stress gradient, which broke the inversion symmetry of the glasses and subsequently induced the nonlinear effect. These findings suggest that low thermal conductivity induced high stress gradients to lead to large SHG.     

Conical second harmonic generation in a two-dimensional chi(2) photonic crystal: a hexagonally poled LiTaO3 crystal

A new type of conical second-harmonic generation was discovered in a 2D chi((2)) photonic crystal-a hexagonally poled LiTaO3 crystal. It reveals the presence of another type of nonlinear interaction-a scattering involved optical parametric generation in a nonlinear medium. Such a nonlinear interaction can be significantly enlarged in a modulated chi((2)) structure by a quasi-phase-matching process. The conical beam records the spatial distribution of the scattering signal and discloses the structure information and symmetry of the 2D chi((2)) photonic crystal.     

Optical polarization driven giant relief modulation in amorphous chalcogenide glasses

We report on the observation of giant relief modulation in amorphous chalcogenide As2S3 glass under polarization modulated near band gap light illumination. We show that these periodic modulations are created as a result of the photoinduced mass transport despite the very low and uniform intensity light illumination. A phenomenological model, based on a photoinduced alignment of anisotropic microvolumes within the glass, is proposed to explain the phenomenon.     

Measuring the electric charge in cloud droplets by use of second-harmonic generation

We report on the observation of second-harmonic generation (SHG) from electrically charged microdroplets while they are excited with femtosecond laser pulses. The intense SHG emission results from chi(3) coupling between two photons of the incident laser pulse and the electrostatic field induced by the surface charges. For Iinc= 2 x 10(12) W/cm2, we estimate the second-harmonic emission to be ISHG= 2.5 x 10(3) photons per droplet and per pulse. The possibility of using SHG to measure remotely the electric charge of water droplets in thunderclouds is discussed.     

ESR in GeS glasses

In GeS glasses ESR signals were observed at g ? 2.00. The signal in GeS₂ was a single Gaussian line with linewidth of ca. 15 G. The signal in the glass containing more sulfer than GeS₂ changed into multi-lined spectra. The signal disappeared by addition of 5 molar % arsenic. Discussion is given in the concept of ‘defects’ in the chalcogenide glass.     

Femtosecond Kerr-lens mode locking with negative nonlinear phase shifts

We report a Kerr-lens mode-locked Cr:forsterite laser operated with negative nonlinear phase shift. The nonlinear phase shift is induced by the cascade chi((2;)):chi((2)) process in a lithium triborate crystal. Employing the cascade process at large phase mismatch produces a nearly linear frequency chirp. Transform-limited pulses as short as 60 fs are generated with positive cavity dispersion.     

Control of the polarization dependence of optically poled nonlinear polymer films

We demonstrate the possibility of controlling the symmetry properties of photoinduced chi((2)) macroscopic susceptibility in polymer films. Ellipsometric adjustment of the write beams allows one to monitor the macroscopic chi((2)) symmetry from a dipolar to an octupolar configuration. Experimental results are in agreement with an irreducible spherical tensor-based model jointly applied to the molecular beta hyperpolarizability and field tensors. We found a purely octupolar polarization-independent photoinduced second-harmonic-generation response in a Dispersed Red 1-methyl methacrylate thin film. Such a configuration, as generated by an octupolar tensor write field tensor made up of counterclockwise circularly polarized omega and 2omega beams, is not within the reach of the classical electric-field poling technique.     

Second-harmonic generation in resonant waveguide gratings incorporating ionic self-assembled monolayer polymer films

Experimental results on resonantly excited second-harmonic generation (SHG) in a periodic ionically self-assembled monolayer (ISAM) film are reported. A double-layer guided-mode resonance filter (GMRF) structure is coated with 40 bilayers of pyrlium-based chi(2) ISAM thin film and excited with the fundamental of a Nd:YAG laser. Enhanced second-harmonic conversion in the ISAM film is achieved because of the local field enhancement associated with the fundamental resonating leaky mode. This method of SHG is particularly promising, as the ISAM films under investigation exhibit anomalous dispersion that may be applied for phase matching to improve nonlinear conversion efficiency.     

Second-harmonic generation from a first-order quasi-phase-matched GaAs/AlGaAs waveguide crystal

We demonstrate, for the first time to our knowledge, the generation of second-harmonic pulses by use of a novel methodology for achieving first-order quasi-phase matching in a semiconductor waveguide crystal. This methodology is based on a periodic modulation of the susceptibility coefficient along the direction of light-beam propagation in which advantage is taken of the fact that chi((2))(GaAs)>chi((2))(Al(x)Ga(1-x)As) . Efficient second-harmonic generation at 975 nm of a pump wavelength of 1950 nm has been demonstrated for a crystal with a nonuniform domain dimension (duty cycle, ~39/61).     

Freely adjusted properties in Ge–S based chalcogenide glasses with iodine incorporation

In this study, we examined the function of halogen iodine acting as a glass network modifier in green chalcogenide glasses based on the Ge–S system. We obtained a series of Ge–S–I glasses and determined their glass-forming region. We then recorded the physical, thermal, and optical properties and studied the effect of halogen iodine on Ge–S–I glasses. Results show that these glasses have relatively wide optical transmission window for infrared (IR) applications. The softening temperature of Ge–S–I glasses varies from 210.54 °C to 321.63 °C, this temperature fits well with some kinds of high-temperature polymers, such as PES and PEI, the polymers serve as protective layers with high strength and flexibility, thus simplifying the fabrication processes of IR chalcogenide glass fiber. Finally, we performed a purification process to eliminate impurities and to improve optical spectra.     

Spatial versus temporal deterministic wave breakup of nonlinearly coupled light waves

We investigate experimentally the competition between spatial and temporal breakup due to modulational instability in chi((2)) nonlinear mixing. The modulation of the wave packets caused by the energy exchange between fundamental and second-harmonic components is found to be the prevailing trigger mechanism which, according to the relative weight of diffraction and dispersion, leads to the appearance of a multisoliton pattern in the low-dimensional spatial or temporal domain.     

2μm波段硫系玻璃微球激光器的制备和表征

工作在2μm波段附近的中红外微球激光器在生物医学传感、激光雷达、窄带光学滤波和空气污染监控等领域具有重要的应用价值.本文以自制的Tm~(3+)-Ho~(3+)共掺的Ge-Ga-Sb-S (2S2G)硫系玻璃为基质材料,采用玻璃粉末高温漂浮熔融法批量制备了高品质(典型品质因数大于10~5)硫系玻璃微球.优选一颗直径为205.82μm的微球为实验对象,利用光纤锥耦合法对其进行光学近场耦合实验.在808 nm抽运光的作用下,在1.8—2.1μm波段处可观测到明显的荧光回廊模现象.当抽运功率达到0.848 mW的阈值时,可在2080 nm附近观测到明显的激光输出.上述实验结果表明本文采用的2S2G硫系玻璃具有用于制备工作在中远红外波段的有源光学/光电子学器件的潜力.     

Second-harmonic microscopy of unstained living cardiac myocytes: measurements of sarcomere length with 20-nm accuracy

We extend second-harmonic generation (SHG) microscopy to the measurement of sarcomere length in unstained living cardiac myocytes with 20-nm accuracy. We quantify individual sarcomere shortening in the presence of saxitoxin and find that it is in agreement with mechanical measurements of atrial tissue contracture. This functional application of SHG microscopy is generally applicable to quantify the physiological effects of drugs on contractile tissue. Our data also suggest that packed myosin heads in sarcomere thick filaments are responsible for the large second-harmonic endogenous signal in muscle tissue.     

Effect of replacement of Se by S on structural and physical properties of Ge–Sb–As–Se–S chalcogenide glasses

In the present study, the structural and opto-mechanical properties of Ge–Sb–As–Se–S chalcogenide glasses have been investigated. For this purpose, different bulk glasses of Ge₂₀Sb₅As₁₅Se_60?xS_x (0 ≤ x≤50) were prepared by conventional melt quenching technique in quartz ampoule and different characteristics of prepared glasses such as glass transition temperature, density, hardness, transmittance, optical band gap energy and refractive index were determined. The value of hardness and glass transition temperature of prepared glasses were found to increase with increasing the sulfur content as a result of formation of GeS₄ tetrahedral units and increasing the network connectivity and average bonding energy. The optical energy gap (according to Tauc’s relation), transmittance and refractive index of prepared glasses are in direct relation with sulfur content. In this study, the highest value of transmittance (about 70%) and lowest value of refractive index (2–2.3) was achieved in Ge₂₀Sb₅As₁₅Se₄₀S₂₀ and Ge₂₀Sb₅As₁₅Se₁₀S₅₀ glasses, respectively.