S. Benet

CsLiB6O10 crystallites embedded into olygoether photopolymer matrices as new materials for acoustically induced nonlinear optics

Abstract Acoustically induced optical second harmonic generation (SHG) in CsLiB6O10 (CLBO) nanocrystallites incorporated into the olygoether photopolymer matrices has been revealed at liquid helium temperature (4.2 K). The SHG has been measured for the source wavelength of an YAG-Nd laser (λ=1.06 μm ) . With increasing acoustical power, the SHG signal increases and achieves its maximum at acoustical intensity of about 18.1 W/cm2 and frequency of about 14 kHz. The value of the SHG χ222 tensor component was comparable with the one for the traditional nonlinear optical crystals such as KH2PO4, KTiOPO4, LiNbO3. With decreasing temperature (below 28 K) the acoustically induced SHG signal strongly increases. A correlation between the acoustically nonlinear optical response and low-frequency Raman intensities has been found. The maximal acoustically induced SHG has been observed for the nanocrystallite concentration of about 3.1% (in weight units) and the nanocrystallite sizes lying within 35–40 nm. The SHG tensor coefficients were larger than for the bulk CLBO crystals (at least 13%). Advantages and drawbacks of the presented model are discussed. The theory of the observed phenomena is explained on the grounds of the ab initio band energy calculations with taking into account anharmonic electron–phonon interactions.

Photoinduced optical second harmonic generation in Fe–Co metallic spin glasses

Abstract For the first time, second-order nonlinear optical effects have been observed in metallic spin glasses. Photoinduced second harmonic generation (PISHG) in reflected light was used as a particular nonlinear optical method. We have varied degree of long-range spin ordering. PISHG is measured immediately after the thermo-treatment using thermoannealing treatment (up to 823 K) of Fe–Co glasses. As a photoinducing beam, Q-switched nitrogen laser ( λ =337 nm) was used. YAG–Nd pulse laser ( W =30 MW, τ =30 ps, frequency repetition about 12 Hz) was applied as a probe. Only the presence of the photoexcitation stimulates an appearance of the PISHG with values up to 0.128 pm/V. Influence of surface, phase synchronism conditions, fluorescence, etc. is discussed. We have revealed almost a linear correlation between degree of spin ordering and the output PISHG signal. Molecular dynamics geometry optimization and self-consistent quantum chemical simulations have been done. The observed phenomenon can be explained by contributions of long-range ordered spins to electronic dipole moments determining second-order nonlinear optical susceptibilities. Specially performed X-ray diffractometry structural and magnetically induced nonlinear optical effects show that the observed effects are caused by contribution of collective spin interactions.

Synthesized rare-earth doped oxide glasses for nonlinear optics

Photostimulated nonlinear optical effects in synthesized PbO–Ga2O3–Bi2O3–CdO (PGBC) glasses doped by Yb3+, Er3+, and Dy3+ rare-earth (RE3+) ions were discovered. Temperature-dependent measurements of optical photoinduced second-harmonic generation (PISHG) and two-photon absorption were performed in the infrared (IR) range. CO pulse laser (λ=5.5 μm, energy power density up to 3.8 GW/cm2 per pulse) was applied as a source of IR-photoinducing and probing (fundamental) light. Absolute values of the PISHG were more than 22% higher than corresponding values obtained for other glasses: As2Te3–CaCl2–PbCl2 [1] or Sb2Se3–BaCl2–PbCl2 [2] type. The investigated PGBC system possesses a shorter time response (about 18 ps), compared with other IR nonlinear optical glasses. We have also established that all nonlinear optical susceptibilities are dependent on the type of RE3+ ion. A maximal value of the PISHG is achieved for the glasses doped by Yb3+. The PISHG values increase significantly below 25 K. We have carried out...

Non-linear optical effects and transport phenomena of magnetic semiconductors Pb1−xPrxTe near the semiconductor–metal phase transformation

Measurements of transport and non-linear optical (NLO) properties of the new, synthesized semiconductor Pb0.9835Pr0.0165Te in the vicinity of low-temperature metal–semiconductor phase transformations were performed. A correlation between the temperature behaviour of transport properties near the phase transition and NLO susceptibilities of second- and third-order was observed. FTIR spectra show the substantial role played by the Pr3+ localized levels in the observed anomalies.Among the transport properties, the resistivity, Seebeck coefficient and specific heat were measured. The presence of the minimum at about in the temperature dependence of the resistivity ρ(T) is due to the metal–semiconductor transition in Pb1−xPrxTe and the low-temperature upturn observed in the resistivity is well fitted by the Mott law. Substitution of PbTe by other rare earths shows the crucial role played by Pr in the observed dependences.Experimental temperature measurements using photo-induced NLO (pumped by a UV-laser as well as by second harmonics of the YAG–Nd lasers) and a probing YAG–Nd (at λ = 1.06 µm) laser, show the existence of two maxima in the photo-induced second harmonic generation (PISHG) at temperatures 17 and 30 K, the behaviours of which substantially depend on the wavelength of the pump beam. At the same time the third-order two-photon absorption possesses maxima near 50 K, i.e. at about . Such discrepancies in the positions of the temperature maxima are caused by the difference in contributions of the photo-induced anharmonic phonons near the surfaces PISHG and the bulk. Varying the penetration depth of the photo-inducing light one can operate with the output NLO properties.

Electron–phonon contribution to electrooptical coefficient in Ca4GdO(BO3)3 single crystals

Abstract Electrooptical r222 coefficient in new synthesized (Ca4GdO(BO3)3) (GdCOB) single crystals has been measured at room and liquid nitrogen temperature. To separate electronic and phonon contributions we carry out experimental measurements and theoretical calculations. To determine electronic contributions we have used experimental measurements for the SHG (λ=1.06 μm). We also measured electrooptics tensor coefficients at λ=0.694 μm as well for the IR spectral region within the 1.2–2.45 μm. From temperature dependencies within the 77–295 K we evaluate phonon harmonic and electron–phonon anharmonic contributions. Using ab initio norm-conserving pseudopotential calculations and Green function evaluations of electron–phonon contributions we estimate quantitatively electron–phonon contributions. A good agreement between the experimental and theoretical data is achieved. The presented approach can be proposed for another complex crystals in order to receive an information concerning the origin of the observed phenomena.

Etude numérique d'un séchoir solaire fonctionnant en convection forcée

A mathematical model for simulating the behaviour of a solar crop dryer in forced convection is presented. Then, this model is validated by comparing the obtained results with the experimental ones. Also, we present the influence of some parameters over the behaviour. Finally, we give the optimal values for the parameters to give the best possible behaviour.

Optical second harmonic generation in CsLiB6O10 nanocrystallites incorporated to the olygoether photopolymer matrices induced by acustical field

Optical second harmonic generation in CsLiB6O10 (CLBO) large-sized nanocrystallites (15–40 nm) incorporated into the olygoether photopolymer matrices has been found at liquid helium temperature (LHeT). The second harmonic generation (SHG) has been measured for the source wavelength of the YAG : Nd laser (λ = 1.06 μm). Increasing acoustical power (up to 18.1 W/cm2) and acoustical frequencies at 14 kHz give maximal values of the output SHG. The measured SHG χ222 tensor component was comparable with the one for the traditional nonlinear optical crystals such as KH2PO4, KTiOPO4, LiNbO3. With decreasing temperature below 28 K the acoustically induced SHG signal strongly increases. A correlation between the acoustically induced SHG and low-frequency Raman modes has been found. The maximal acoustically induced SHG has been observed for the nanocrystallite concentration about 3.1% (in weighting units) and the crystallite sizes lying within the 35–40 nm. The SHG tensor coefficients were higher than for the proper CLBO crystals at least on the 13%. Advantageous and drawbacks of the presented model are discussed. The theory of the observed phenomena is explained on the ground of ab initio band energy calculations with taking into account of anharmonic electron-phonon interactions.

Photoinduced optical second-harmonic generation of SiNO films deposited on Si〈111〉 substrate

Optical photoinduced second-harmonic generation (PISHG) of SiON films deposited on Si〈111〉 substrates has been studied. Nitrogen laser (λ=337 nm) was used as a source of pumping light. We have found that with an increase of photoinducing power and nitrogen-to-oxygen (N/O) ratio, the PISHG for probe YAG-Nd laser (for the doubled frequency λ=0.53 μm) signal increases and achieves its maximum value at photoinducing power about 0.96 GW/cm2. The maximal value of the PISHG was equal about 1 pm/V. With decreasing temperature, the PISHG signal strongly increases below 28 K. Femtosecond probe-pump measurements indicate the existence of the PISHG maximum at pump-probe time delay about 0.4 ps. We explain these dependencies within a framework of the quantum chemical approach and molecular dynamics interface structure optimization. Role of photoinduced anharmonic electron-phonon interaction is demonstrated. We have revealed that Si–N chemical bonds play a key role in the observed photoinduced nonlinear optics effect.

Photoinduced second harmonic generation in Bi2Se3–CaBr2–PbCl2 optical fibers

Abstract Photoinduced second harmonic generation (SHG) in Bi2Se3–CaBr2–PbCl2 optical fibers have been studied using experimental and theoretical quantum chemical and molecular-dynamics methods. Infra-red (IR) induced SHG was measured in the IR region within the 5.5–21 μm . CO laser ( λ=5.5 μm ) was used as a source of the photoinducing IR light. The glasses had diameters varied within the 5–35 μm . The lengths of the fibers varied from 0.5 cm up to the 1.4 m. We have found that with increasing photoinducing power, the SHG for the doubled frequency 5.3 μm of the CO2-laser increases and achieves its maximum value at photoinducing power 1.35 GW / cm 2 per pulse. The maximal by achieved values of the second-order nonlinear optical susceptibilities d222 was equal about 1.5 pm/V. With decreasing temperature, the SHG signal strongly increases within the 75–220 K temperature range. Picosecond probe–pump measurements indicate on the occurrence of the SHG maximum at pump–probe time delay about 25 ps. These dependencies we explain within a framework of the quantum chemical approach taken into acount photoinduced anharmonic electron–phonon interactions. We have found that Bi–Se tetrahedral bonds play a key role in the observed IR photoinduced nonlinear optical (NLO) effects. The obtained results show that the mentioned glasses may be applied as materials for IR picosecond–second quantum electronics.

Non-linear optical diagnostics of phase transitions in 1,4-cis-polybutadiene polymers

Abstract The photoinduced optical second harmonic generation (PISHG) in 1,4- cis -polybutadiene has been investigated as a function of temperature in the vicinity of the glassing and crystallisation temperatures. Both the addition of centrosymmetric tetraphene molecules as well as the trans -isomers lead to an enhancement of the local non-centrosymmetric charge density distribution determining optical second harmonic generation. Using ab initio quantum chemical calculations with the inclusion of electron–vibration anharmonic interactions and combined with experimental PISHG data we show that increasing molecular localisation favours increasing non-centrosymmetry detected by PISHG. Two maxima of the PISHG signals have been observed at temperatures of ≅52 and 153 K for the specimens doped with p -terphenyl molecules and those doped with isomer trans -polybutadiene phase. Good correlation of the experimental data is obtained with theoretical calculations. The main mechanism of the observed temperature anomalies is connected with the enhancement of electron–vibration anharmonicity during glassing and crystallisation structural rearrangements.