Polarization properties of coherent VUV light at 125 nm generated by sum-frequency four-wave mixing in mercury

The polarization of the VUV light generated by four-wave sum-frequency mixing process ω₄=2ω₁+ω₂ in mercury vapor at room temperature is analyzed in detail. Due to the specific two-photon transition used to enhance the nonlinear process, the polarization of the VUV wave is shown to be identical to the polarization of the wave at the frequency ω₂. In particular, circularly polarized VUV is observed with degree of circular polarization exceeding 0.99. Received: 11 July 1999 / Revised version: 8 October 1999 / Published online: 8 March 2000     

UV and IR coherent radiation generated simultaneously by two-photon and hybrid excitations in sodium vapor

UV coherent radiation at 330.2 nm and IR stimulated radiations at 2.34μm,2.21μm and 1.64μm were generated via processes of unequal-frequency two-photon(3S-6S)resonantly enhanced excitation and equal frequency hybrid resonant excitation with particularexcited wavelength in Na_2-Na system.The competition of the two processes is obviously.     

Collinear and non-collinear sum-frequency mixing inβ-BBO for a tunable 195–198 nm all-solid-state laser system

We attained tunable UV laser radiation between 195 and 198 nm by sum-frequency mixing two synchronized flashlamp-pumped solid-state Q-switch lasers, a Nd:YAG laser frequency quadrupled to 266 nm and a tunable (730–770 nm) alexandrite laser. UV pulse energies of 0.12 mJ with repetition rates of 10 Hz were attained in collinear, as well as non-collinear sum-frequency interaction in a-Barium Borate (BBO) crystal with a conversion efficiency of 2.5%. Theoretical models for the non-collinear phase-matching interaction were investigated at UV wavelengths below 200 nm.     

Continuously tunable VUV radiation (129–210 nm) by anti-Stokes Raman scattering in cooled H2

The generation of tunable vacuum ultraviolet radiation by anti-Stokes Raman scattering of tunable ultraviolet dye-laser radiation in cold hydrogen has been investigated. The scattering efficiency of XeCl laser and Nd:YAG laser pumped commercial dye lasers and the influence of different beam profiles has been studied. Up to 12 anti-Stokes orders down to 129 nm were observed with output powers between about 20 kW at =191 nm and somewhat less than 100 W at =129 nm. The efficiency of transversely pumped lasers with an intensity peaked in the center of the beam profile was found to be higher than doughnut shaped intensity distributions. The cooling of the active gas to liquid nitrogen temperatures improved the output pulse energies 3 to 5 times on average. It was found that this intensity increase was caused mainly by the narrowing of the Raman linewidth upon cooling.     

Photolysis of NO2 at multiple wavelengths in the spectral region 200–205 nm

A study of the photodissociation dynamics of NO₂ in the 200–205 nm region using resonance enhanced multiphoton ionization (REMPI) in conjunction with the velocity map imaging technique is presented. We chose this region because it allowed the use of a single laser to photodissociate the NO₂ molecule and probe both the O(¹D₂) fragment using (2+1) REMPI via the 3p'¹P₁ state at 2 ×205.47 nm and the 3p'¹F₃ state at 2 ×203.5 nm, and the O(³P_J) fragments using (2+1) REMPI via the P_J states around 2 ×∼200 nm. Translational energy and angular distributions are extracted from the O(¹D) and O(³P) product images. A growth in the population of highly excited vibrational levels of the NO X(²Π) co-fragment is found as the dissociation wavelength decreases. These are compared with similar trends observed previously for other triatomic O-atom containing molecules. Detailed information on the electronic angular momentum alignment of the ¹D₂ state is obtained from analysis of the polarization sensitivity of the O(¹D) images using the two resonant intermediate states. The angular dependence of the potential energy in the exit channels is examined using long-range quadrupole-dipole and quadrupole-quadrupole interaction terms, from which molecular-frame multipole moments of the total angular momentum of the recoiling O atoms have been calculated. Comparison with the experimentally derived multipole moments is used to help provide insight into the dissociation mechanism.     

Conduction mechanism of lithium bis(oxalato)borate–cellulose acetate polymer gel electrolytes

Polymer gel electrolytes (PGE) belonging to salt–solvent–polymer hybrid systems are prepared using a mixture of lithium bis(oxalato)borate (LiBOB), γ-butyrolactone (γ-BL), and cellulose acetate (CA). The increase in ionic conductivity of PGE is due to the dissociation of ion aggregates, as confirmed by Fourier transform infrared analysis. The highest conductivity attained by the PGE is 7.05 mS cm^?1 at 2.4 wt.% CA. The plots of conductivity–temperature show a classical Arrhenius relationship. The electrical properties of the sample with the highest conductivity are analyzed using electrical permittivity and electric modulus formalism studies. Meanwhile, the frequency-dependent conductivity of the polymer gel electrolyte adheres to Jonscher’s power law. Conduction mechanism study also shows that the 2.4 wt.% CA PGE is in agreement with the small polaron hopping model.     

Attaining the wavelength range 189–197 nm by frequency mixing inβ-BaB2O4

Wavelengths in the range from 188.9 to 197 nm have been obtained by type-I sum frequency generation (SFG) in -BaB₂O₄. The fundamental beams were supplied by pulsed dye lasers one of which tuned between 780 and 950 nm and the other frequency-doubled at 497 nm. The possibility of shifting the excimer wavelength 248.5 nm to the excimer wavelength 193 nm has been demonstrated, replacing the frequency-doubled dye laser by KrF excimer lasers of different beam properties.     

Simultaneous generation of ultrashort pulses at 158 and 198?nm in a single filamentation cell by cascaded four-wave mixing in Ar

Ultrashort 198- and 158-nm pulses are generated simultaneously by cascaded four-wave mixing of the second and third harmonics of a 80-fs Ti:Sapphire laser in filamentation propagation through a single Ar gas cell. The energies of the 198- and 158-nm pulses are 7.6?μJ and 600?nJ, respectively. The duration of 198-nm pulse is determined to be ca. 45?fs by transient-grating frequency-resolved optical grating, which indicates that the pulse is intrinsically transform limited and chirped by the rear window of the gas cell. The spectral bandwidths of 198- and 158?nm support the transform limited pulse durations of 40 and 28?fs, respectively.     

Upconversion in Highly Doped Er~(3 )-Yb~( 3 ) Fiber Pumped by Ti∶Sapphire Laser at 800 nm

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Ultrabroadband continuum generated in air (down to 230 nm) using ultrashort and intense laser pulses

We present results on supercontinuum generation extended up to 230 nm in air during the propagation of a powerful femtosecond laser pulse. The broad supercontinuum generated in air is contributed by self-phase modulation and self-steepening of the fundamental laser pulse, the third-harmonic pulse and their interaction. In particular, the strong interaction between the fundamental and the third-harmonic pulses leads to broad and efficient continuum generation of the third-harmonic pulse itself. The spectrum of the third-harmonic generated in air extends over several tens of nm and overlaps with the shorter wavelength extent of the fundamental continuum. PACS 42.65.Ky; 42.65.Jx; 52.35.Mw     

Improved gain on the Cl2(D′3 П g −A′3 П u ) transition at 258 nm by halogen donor mixing

The temporal development of the small-signal gain on the Cl₂(D–A) transition at 258 nm has been investigated by means of an amplified spontaneous emission (ASE) technique. For electron beam pumped He/Cl₂ mixtures, the gain appears only at the end of the pumping pulse, whereas for He/Cl₂/CCl₄ mixtures the temporal gain profile coincides with the fluorescence pulse, and the maximum gain coefficient increases by about a factor of two. The observed effects are due to the mixing of both halogen donors and can be explained by considering the quenching of theD-state by electrons.     

Er<Superscript>3+</Superscript> excited-state absorption in an erbium-doped silica fiber at the wavelengths 1490–1580 and 978 nm

The spectral features of Er³⁺ excited-state absorption (ESA) in an erbium-doped silica fiber (EF) at the telecom wavelengths 1490–1580 nm and at the wavelength 978 nm are reported. The measurement of the EF nonlinear transmission coefficient upon pumping the fiber in these spectral ranges, supplied with a theoretical background, allows one to obtain the spectrally dependent ESA parameter for the EF, which is defined as the ratio of the ESA to the ground-state absorption cross section.     

Instability of lithium bis(fluorosulfonyl)imide(LiFSI)–potassium bis(fluorosulfonyl)imide(KFSI) system with LiCoO_2 at high voltage

The cycling performance, impedance variation, and cathode surface evolution of the Li/LiCoO2 cell using Li FSI–KFSI molten salt electrolyte are reported. It is found that this battery shows poor cycling performance, with capacity retention of only about 67% after 20 cycles. It is essential to understand the origin of the instability. It is noticed that the polarization voltage and the impedance of the cell both increase slowly upon cycling. The structure and the properties of the pristine and the cycled LiCoO2 cathodes are investigated by x-ray diffraction(XRD), scanning electron microscopy(SEM), Raman spectroscopy, x-ray photoelectron spectroscopy(XPS), and transmission electron microscopy(TEM). It is found that the LiCoO2 particles are corroded by this molten salt electrolyte, and the decomposition by-product covers the surface of the LiCoO2 cathode after 20 cycles. Therefore, the surface side reaction explains the instability of the molten salt electrolyte with LiCoO2.     

Quadratic electro-optic effect in the nonconjugated conductive polymer iodine-doped poly(β-pinene) measured at longer wavelengths including 1.55μm

The quadratic electro-optic effect in the nonconjugated conductive polymer iodine-doped poly($\beta$-pinene), measured at longer wavelengths including 1.55 μm, is reported. The field-induced birefringence technique was used. A modulation depth of 0.1% was observed in a 1 μm thick sample for an applied field of 1 V/μm at 1.55 μm. The corresponding Kerr coefficient obtained is 1.6×10^?10 m/V ². The Kerr coefficients measured at 790–810 nm are also very large. This exceptionally large (largest known) optical nonlinearity has been attributed to the subnanometer size metallic quantum dots formed in this polymer upon doping with iodine and the optimized film quality recently achieved.     

Physical properties of magnetic alloy (Nd–Fe–B–C) nanoparticles generated in distilled water using Nd:YAG LASER

In this work, (Nd?CFe?CB?CC) magnetic nanoparticles are generated by pulses of Nd:YAG laser irradiation on the (Nd?CFe?CB?CC) magnetic target in distilled water. Exposure times were 1, 5, and 10 min. Percentages of elements in a bulk sample and nanoparticles are investigated by energy-dispersive X rays (EDX). Mean particle sizes of the nanosamples are analyzed by a transmission electron microscope (TEM). The average size of the nanoparticles is 6.23 nm. A typical selected-area electron-diffraction (SAED) ring pattern from the nanocrystals shows a tetragonal structure in (Nd?CFe?CB?CC) nanoparticles similar to the bulk sample. In order to investigate the nanoparticle stability, in two weeks after nanoparticle generation, the size distribution of nanoparticles is measured using dynamic light scattering (DLS). Using an atomic force microscope (AFM) and a magnetic force microscope (MFM), we show different aspects of generated nanoparticles.     

Creation of electronic excitations and defects by vuv radiation (6-40 eV) in wide-gap solids

The processes of multiplication of electronic excitations (MEE), connected with the creation of secondary excitons or electron-hole (e-h) pairs by hot conduction electrons, are realized in wide-gap metal halides and oxides. In oxides, secondary e-h pairs can be also formed by 27-40 v eV photons due to L 1 VV Auger transitions (with the participation of 2s oxygen holes). The excitation spectra of luminescence and the creation spectra of electron F centres or hole V centres have been measured for Na 6 Al 6 Si 6 O 24 (NaI) 2x sodalites and MgO:Be, respectively, at 8-80 v K. A high local density of excitations has been revealed under MEE conditions in KBr and Br sodalites with self-trapping excitons and holes.     

Identification of Structure and Position of Cu(II) Ion in Aquomethylmelonatozinc(II) Host by Powder XRD, EPR, FT-IR and UV–Vis Spectroscopy

Single-crystal electron paramagnetic resonance studies of Cu(II)-doped aquomethylmelonatozinc(II) are carried out at 300 K. Angular variation of copper hyperfine lines in the three orthogonal planes shows the presence of a single site in substitutional position, with spin Hamiltonian parameters: g ₁₁ = 2.076, g ₂₂ = 2.100, g ₃₃ = 2.379; A ₁₁ = 2.40 mT, A ₂₂ = 3.22 mT and A ₃₃ = 13.47 mT. The low value for the hyperfine structure parameter value for A ₃₃ has been explained by taking into account a considerable admixture between d_{x² - y²} d_{{x^{2} - y^{2} }} ground state and d_z² d_{{z^{2} }} excited state, with admixture coefficients being a = 0.291, b = 0.951, c = 0.054, d = 0.031 and e = −0.031, where coefficients a and b correspond to coefficients for d_z² d_{{z^{2} }} and d_{x² - y²} , d_{{x^{2} - y^{2} }} , respectively. Few other calculated parameters such as κ = 0.35, P = 303 × 10⁻⁴ cm⁻¹; α = 0.88 and α′ = 0.47 indicate considerable covalency. Powder X-ray diffraction, Fourier transform infrared and ultraviolet-visible data confirm the structure of host complex and presence of the dopant.     

Frequency-mixing scheme for the production of tunable narrowband XUV radiation (91–95 nm): application to precision spectroscopy and predissociation in diatomic molecules

Tunable narrowband extreme ultraviolet radiation in the range 91–95 nm is produced by sum-frequency mixing of the outputs of a visible pulsed dye amplifier (seeded by a ring dye laser) and of a seeded second-harmonic Nd:YAG laser and subsequent frequency tripling in a gas jet of xenon. The capability of this scheme to provide tunable narrowband extreme ultraviolet radiation is demonstrated in several spectroscopic studies. The bandwidth of this system (0.01 cm^-1) is deduced from a recording of absorption spectra of the 4p⁵(²P_1/2)6d, J=1 line in krypton. The applicability of the system for gas-phase molecular spectroscopic studies is demonstrated in recordings of the Werner bands (4,0) in H₂ and (5,0) in D₂ at unprecedented absolute accuracy. Line-broadening studies are performed on the b¹_u⁺,v=5 valence state in N₂, yielding a lifetime of 210±25 ps. A singlet–triplet perturbation, giving rise to an accidental predissociation in an excited ¹ Rydberg state in carbon monoxide at an excitation energy of 107680 cm^-1, is analyzed in high resolution. PACS 42.65.Ky; 32.80.Rm; 33.20.Ni; 33.80.Gj; 42.60.By     

Comparison of soy protein isolate-(–)-epigallocatechin gallate complexes prepared by mixing,chemical polymerization,and ultrasound treatment

The effects of the preparation method (mixing, chemical polymerization, or ultrasound treatment) on the structure and functional properties of soy protein isolate-(–)-epigallocatechin-3-gallate (SPI-EGCG) complexes were examined. The mixing treated SPI-EGCG samples (M−SE) were non-covalently linked, while the chemical polymerization and ultrasound treated SPI-EGCG samples (C-SE and U-SE, respectively) were bound covalently. The covalent binding of EGCG with protein improved the molecular weight and changed the structures of the SPI by decreasing the α-helix content. Moreover, U-SE samples had the lowest particle size (188.70 ± 33.40 nm), the highest zeta potential (−27.82 ± 0.53 mV), and the highest polyphenol binding rate (59.84 ± 2.34 %) compared with mixing and chemical polymerization-treated samples. Furthermore, adding EGCG enhanced the antioxidant activity of SPI and U-SE revealed the highest DPPH (84.84 ± 1.34 %) and ABTS (88.89 ± 1.23 %) values. In conclusion, the SPI-EGCG complexes prepared by ultrasound formed a more stable composite system with stronger antioxidant capacity, indicating that ultrasound technology may have potential applications in the preparation of protein-polyphenol complexes.