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Ultrabroadband generation of white-light continuum spanning from ultraviolet to near-infrared (375–920 nm) is demonstrated by using induced-phase modulation between two-color femtosecond pulses in multiple thin plates. The fundamental wave and its second-harmonic wave from one Ti:sapphire chirped-pulse amplifier are injected into nine 100 μm-thick fused silica plates. When the two pulses are temporally and spatially optimized in the plates, an intense supercontinuum is efficiently achieved by utilizing self-phase modulation and self-steepening together with induced-phase modulation. As a result, using 1 kHz, 1 mJ, and 35 fs pulses at 800 nm as the pump, we demonstrate the generation of 0.6 mJ white-light pulses with an ultra-broad bandwidth supporting 1.6 fs transform-limited pulses corresponding to 0.6-optical-cycle at a central wavelength of 750 nm. Analysis of the calculated spectrum fits the experimental results well, and the pulse is quasi-linearly chirped and compressible. The resulting intense robust supercontinuum could be a promising light source for an ever greater degree of tailored optical waveform coherent control in new parameter spaces.

We present an f-to-2f interferometry method to simultaneously measure and control the relative timing (RT) and carrier-envelope phase (CEP) of an arbitrarily tailored optical-field waveform. Long-term stabilization of the phase-locking system results in a CEP stability of 280 mrad and a RT stability of 110 attosecond over 8 h at a repetition rate of 1 kHz. The synthesized optical field characterized by a transient-grating frequency-resolved optical gating delivers 3.8-fs near single-cycle waveforms. This technique constitutes a versatile tool for coherent pulse synthesis, which can be applied in experiments using a dual-color light field for high-harmonic generation and attosecond timing precision pump-probe spectroscopy.

The effects of vacuum annealing on the structural and transport properties of the La0.67Ca0.33MnO3−δ films grown on SrTiO3 (LCMO/STO) and NdGaO3 (LCMO/NGO) substrates have been studied. A lattice expansion due to oxygen release during the annealing is observed. Under the same condition, the change of the out-of-plane lattice parameter in LCMO/STO is two to three times larger than that in LCMO/NGO, indicating a strong tendency for the oxygen in the former to escape. Correspondingly, the metal-to-semiconductor transition shifts to lower temperatures, linearly with lattice constant until a critical value, Δd=0.03 A for LCMO/STO and Δd=0.05 A for LCMO/NGO, after which a sudden drop of the transition temperature to zero occurs. The different lattice strains in both films are presumably responsible for the different critical oxygen contents for the occurrence of the resistive transition.

Many unexpected properties have been found in the LaAlO3/SrTiO3 heterostructure, but the interaction of the many ground states at its interface remains unclear. Here, we demonstrate an optical property of this n-type heterostructure where the mid-infrared spectral responsivity at the interface is enhanced by an external magnetic field. The field intensity ranged from 0.8 to 6 kOe at a low temperature (19 K) as measured with our spectral response measurement system. Two spectral peaks related to the spin-orbit coupling effect were also observed at wavelengths 2400 nm and 3700 nm. The intriguing phenomena relate to changes in the crystallographic structure and subband structure at the interface.

Ultrahigh piezoelectric constant (d33 = 683 pC/N) and converse piezoelectric coefficient (dS/dE = 1257 pm/V) were observed in CuO-doped lead-free (Ba,Ca)(Ti,Sn)O3 ceramics at an optimal composition fabricated by a conventional sintering method at a low temperature 1250 °C. Since all samples showed a pure perovskite structure with coexisting multiphases including cubic, tetragonal, orthorhombic, and rhombohedral phases around two converged triple points, a good compositional stability of high piezoelectricity along with a high d33 and dS/dE over 600 pC/N and 1000 pm/V was achieved within a wide compositional region (1.0 ≤ x ≤ 3.0) regardless of the CuO content (x).

The phase structure in the (Ba,Ca)(Ti1−xSnx)O3 lead-free ceramics was evolved from inceptive orthorhombic (O) at 0 ≤ x ≤ 0.04 to a two-phase coexistence of pseudocubic-orthorhombic (PC-O) at 0.06 ≤ x ≤ 0.10 and further to a multiphase coexistence of rhombohedral-pseudocubic-orthorhombic (R-PC-O) at x = 0.11. Due to the multiphase coexistence of R-PC-O at room temperature proved by X-ray diffraction, dielectric constant er and differential scanning calorimetry, an ultrahigh piezoelectric coefficient d33 = 670 pC/N and electrostrain 0.061% were achieved. The high d33 over 520 pC/N was stabilized in a wide compositional range of 0.07 ≤ x ≤ 0.11, suggesting that (Ba,Ca)(Ti,Sn)O3 ceramics are a promising candidate for the lead-free piezoelectric ceramics.

We report a laser system that delivers 15 fs pulses with 200 mJ energy at a 10 Hz repetition rate. The broadband spectrum extending from 700 nm to 900 nm was obtained by seeding a two-stage Ti:sapphire chirped-pulse power amplifier with sub-mJ white-light pulses from a gas-filled hollow-core fiber. With this laser, an extreme ultraviolet (XUV) super-continuum supporting 230 as isolated attosecond pulses at 35 eV was generated using the generalized double optical gating technique. The XUV pulse energy was ∼100 nJ at the exit of the argon gas target.

We studied the dependence of high harmonic generation efficiency on the ellipticity of 400 nm driving laser pulses at 7.7 × 1014 W/cm2 and compared it with the 800 nm driving laser under the same conditions. The measured decrease of high harmonic yield with the ellipticity of the 400 nm laser is ∼1.5 times slower that of the 800 nm, which agrees well with theoretical predictions based on a semi-classical model. The results indicate that it is feasible to use the generalized double optical gating with 400 nm lasers for extracting single attosecond pulses with high efficiency.

We report the voltage tunable photodetecting properties of a La0.4Ca0.6MnO3 film grown on miscut LaSrAlO4 (001) substrates under ultraviolet pulsed laser irradiation at ambient temperature. The photovoltage and photocurrent peak sensitivities can be tuned in the range of 0.295–0.786 V/mJ and 0.172–0.314 A/mJ, respectively, when the applied bias is changed from −20 to +20 V, indicating that the vicinal manganite film can be used as an electric tunable ultraviolet photodetector. A possible mechanism based on the high resolution transmission electron microscopy is introduced to explain the experiment results.

The electrical modulation of the magnetoresistance (MR) from −70% to 80% under a small magnetic field of 200Oe near room temperature is found in multi-p-n heterostructures of SrTiO3−δ∕La0.9Sr0.1MnO3∕SrTiO3−δ∕La0.9Sr0.1MnO3∕Si we fabricated. The mechanism causing the modulation of MR by applied bias is proposed as the interface competition effect in the multilayer heterojunctions. Our results of the present structure are expected to meet the high desire for the application of large electronic modulation of MR near room temperature.

Micrometer-thick perovskite-type multilayer heterostructures with ten thousands of unit cells, [SrNb(0.05)Ti(0.95)O(3)/La(0.9)Sr(0.1)MnO(3)](3), have been fabricated on Si substrates. The structure exhibited nonlinear and rectifying current-voltage characteristics. Stable and temporal photovoltaic effects in the multilayer have been experimentally studied by using different wavelength light sources from ultraviolet to infrared, respectively. The photovoltage and photocurrent responsivities as a function of wavelength displayed that two cutoff wavelengths occurred corresponding to the band gaps of SrNb(0.05)Ti(0.95)O(3) and Si and La(0.9)Sr(0.1)MnO(3). Under the pulsed laser illumination the nanosecond response characterization of the present multilayer structure was obtained. Based on the band structure of the multilayers, a possible mechanism of photovoltaic process was proposed. c 2008 American Institute of Physics. [DOI: 10.1063/1.3010373]

Perovskite-type superlattices consisting of La0.9Sr0.1MnO3, LaAlO3, and SrTiO3 were fabricated on (001) SrNb0.01Ti0.99O3 substrates by laser molecular beam epitaxy. The three-component superlattice exhibited desirable low-field magnetoresistance effects. At a given current bias of 10 mu A, positive magnetoresistance ratio was enhanced from 2% to 15% and 22% with increasing temperatures from 15 to 300 and 325 K at 300 Oe, at which a maximum value occurred from the external magnetic field dependence of magnetoresistance. The nature of the enhanced magnetoresistance is discussed in connection to the interfacial effect. (C) 2007 American Institute of Physics.

An unusual and rather large transient lateral photovoltage (LPV) has been observed in La0.9Sr0.1MnO3∕SrNb0.01Ti0.99O3 and La0.7Sr0.3MnO3∕Si heterojunctions under the nonuniform irradiation of pulsed laser. The irreversible LPVs on both sides of a p-n junction challenge the well established model for LPV in conventional semiconductor p-n junctions, which can be well explained by the Dember effect. Much larger LPV is observed in La0.7Sr0.3MnO3∕Si than that in La0.9Sr0.1MnO3∕SrNb0.01Ti0.99O3. Similar results measured from both substrates of SrNb0.01Ti0.99O3 and Si also support such a Dember effect. Much larger LPVs in heterojunctions than those in simple samples (SrNb0.01Ti0.99O3 or Si) suggest a potential application of Dember effect in heterostructures.

Based on the phase separation scenario, by simulating the resistivity of La0.33Pr0.34Ca0.33MnO3 film with the known coexisting-phase sizes, the authors have obtained the theoretical ferromagnetic (FM) cluster sizes of La2∕3Ca1∕3MnO3 film, showing around 0.6μm near Tc. Subsequently the insulator-metal transition occurs when the cluster grows up to 0.7μm, and the abrupt drop in resistivity occurs when the size is around 0.9μm. Furthermore, the FM cluster sizes grow with the magnetic field. The obtained results indicate that the model and method can be used to predict the critical size of the clusters at the phase transition for the mixed-phase materials.

Ultraviolet photoelectricity based on the vicinal cut as-supplied SrTiO3 single crystals has been experimentally studied in the absence of an applied bias at room temperature. An open-circuit photovoltage of 130 ps rise time and 230 ps full width at half maximum was observed under the irradiation of a 355 nm pulsed laser of 25 ps in duration. The dependence of the photoelectric effect on the tilting angles was studied, and the optimum angle is 20.9 degrees. Seebeck effect is proposed to elucidate the tilting angle dependence of laser-induced photovoltage. This work demonstrates the potential of SrTiO3 single crystals in ultraviolet detection. (c) 2006 American Institute of Physics.

A transient lateral photovoltaic effect (LPVE) has been observed in p-La0.7Sr0.3MnO3∕n-Si heterojunctions. Under the nonuniform irradiation of a pulsed laser, the LPVE shows high sensitivity to the spot position on the La0.7Sr0.3MnO3 surface. A mechanism based on the well established model for the LPVE in conventional semiconductors has been applied to explain the LPVE in the heteroepitaxial junctions of perovskite-type metal oxides. The large LPVE in the heteroepitaxial junctions is expected to make the perovskite-type metal oxide a new and faster candidate for position-sensitive photodetectors.

BaNb0.3Ti0.7O3∕Si p-n junction combining the functional properties of oxide and Si electronics was fabricated by laser molecular-beam epitaxy, and the multifunctional properties of rectification, ferroelectricity and photoelectricity were experimentally studied. The good rectifying I-V characteristics, nanosecond ultrafast photoelectric effect, and ferroelectric property due to the interface enhancement were observed experimentally. The mechanisms of ferroelectric behavior and photoelectric process are discussed briefly.

Fe3O4 thin films have been fabricated on glass substrate by the facing-target sputtering technique and their field-modulated voltage-current behavior was investigated. The nonlinear dependence of voltage on current density displays a switching from high-resistivity to low-resistivity states above a threshold current density. The low-resistivity state is very sensitive to the applied magnetic field, and a large negative magnetoresistance of similar to-27% is observed at 300 Oe under a high current density of 100 A cm(-2) at room temperature. Furthermore, the dependence of the magnetoresistance on the magnetic field reveals a good linear relationship. The observed results seem to favor a picture of spin-polarized intergrain tunneling through the grain boundaries. (c) 2006 American Institute of Physics.

The theoretical simulation and experimental study are reported on the metal-to-insulator transition, thermal hysteresis behavior, magnetic-field-induced reduction, and anisotropic characteristics of resistivity for La2∕3Ca1∕3MnO3 thin films deposited on SrTiO3 (001)-oriented substrates tilted by 10° towards the [010] direction. The simulated results obtained by using a random network model based on phase separation scenario are in quantitative agreement with our experimental data and indicate that tilting (applying magnetic field) can increase (decrease) the scatterings and the activation energy, resulting in enhancement (reduction) of resistivity. All those results suggest that the intrinsic inhomogeneity and the lattice structure play the significant roles in the electrical conductivity and anisotropic transport properties.

Ultrafast photoelectric effects have been observed in La0.7Sr0.3MnO3∕Si p-n junctions fabricated by laser molecular-beam epitaxy. The rise time was ∼210ps and the full width at half-maximum was ∼650ps for the photovoltaic pulse when the junction was irradiated by a 1064nm laser pulse of 25ps duration. The photovoltaic sensitivity was as large as 435mV∕mJ for a 1064nm laser pulse. No such photovoltaic signal was observed with irradiation from a 10.6μm CO2 laser pulse. The results reveal that this phenomenon is an ultrafast photoelectric effect.

A photovoltaic effect is observed in the heterostructure of p-Si∕n-SrTiO3−δ (p: hole carrier type, n: electron carrier type). The current–voltage curve exhibits a good rectifying characteristic similar to that of the traditional diode. The junction shows the open circuit voltage of 126mV∕mJ, the short circuit current of 1.78mA∕mJ, and the response time faster than 10ns for ultraviolet pulsed laser of 25ns in duration at room temperature, suggesting the promising potential of this junction as a new type of ultrafast ultraviolet detectors with high sensitivity for application.