The influence of converse piezoelectric effect on the electro-optic coefficient of single domain relaxor-based 0.93Pb(Zn(1/3)Nb(2/3))O(3)-0.07PbTiO(3) (PZN-0.07PT) has been quantified under ambient conditions. It was found that the large piezoelectric constants d(31) and d(33) have significant influence to the half-wave voltage of electro-optic modulators. For single domain PZN-0.07PT crystal, Vπ13T is reduced by a factor of 8 and Vπ13L can be decreased by more than an order of magnitude due to the large piezoelectric effect. Compared to commonly used electro-optic crystal LiNbO(3) and BaTiO(3), PZN-xPT single crystal is much superior for optic phase modulation applications because they have much higher linear electro-optic coefficients and much lower half-wave voltage when piezoelectric strain influence is considered.
Polycrystalline cerium activated lutetium oxyorthosilicate (LSO:Ce) is highly desirable technique to make cost effective and highly reproducible radiation detectors for medical imaging. In this article methods to improve transparency in polycrystalline LSO:Ce were explored. Two commercially available powders of different particulate sizes (average particle size 30 and 1500 nm) were evaluated for producing dense LSO:Ce by pressure assisted densification routes, such as hot pressing and hot isostatic pressing. Consolidation of the powders at optimum conditions produced three polycrystalline ceramics with average grain sizes of 500 nm, 700 and 2000 nm. Microstructural evolution studies showed that for grain sizes larger than 1 µm, anisotropy in thermal expansion coefficient and elastic constants of LSO, resulted in residual stress at grain boundaries and triple points that led to intragranular microcracking. However, reducing the grain size below 1 µm effectively avoids microcracking, leading to more favorable optical properties. The optical scattering profiles generated by a Stover scatterometer, measured by a He-Ne laser of wavelength 633 nm, showed that by reducing the grain size from 2 µm to 500 nm, the in-line transmission increased by a factor of 10(3). Although these values were encouraging and showed that small changes in grain size could increase transmission by almost 3 orders of magnitude, even smaller grain sizes need to be achieved in order to get truly transparent material with high in-line transmission.
In this paper we report on the fabrication and characterization of SrHfO(3):Ce ceramics. Powders were prepared by solid-state synthesis using metal oxides and carbonates. X-ray diffraction measurements showed that phase-pure SrHfO(3) is formed at 1200°C. Inductively coupled plasma spectroscopy confirmed the purity and composition of each batch. SrHfO(3) exhibits several phase changes in the solid, but this does not appear to be detrimental to the ceramics. Microprobe experiments showed uniform elemental grain composition, whereas aluminum added as charge compensation for trivalent cerium congregated at grain boundaries and triple points. Radioluminescence spectra revealed that the light yield decreases when the concentration of excess Sr increases. The decrease in the light yield may be related to the change of Ce(3+) into Ce(4+) ions. For stoichiometric SrHfO(3):Ce, the light yield is about four times that of bismuth germanate (BGO), the conventional benchmark, indicating great potential for many scintillator applications.
A photoluminescence (PL) study has been performed from 10 to 330 K on a 3,4:9, 10-perylenetetracarboxylic dianhydride (PTCDA) and aluminum tris (8-hydroxyquinoline) (Alq3) thin layers, grown on Si substrates by thermal evaporation. The observed anisotropy of the excitation energies, the spectral shape and the dispersion indicates the presence of two types of excitons near the excitation onset. These are associated with mixed intramolecular Frenkel and intermolecular charge-transfer excitons. In particular, the excitons exhibit a negative dispersion along the molecular stacks which has important consequences for their recombination.
0.56GeS2–0.24Ga2S3–0.2KX(X = Cl, Br, I) chalcohalide glasses were prepared and their third-order optical non-linearities χ(3) have been studied systematically using the femtosecond time-resolved Optical Kerr Effect technique at wavelength of 800 nm. In this system, 0.56GeS2–0.24Ga2S3–0.2KCl glass shows the largest χ(3) (1.82 × 10−13 esu), but 0.56GeS2–0.24Ga2S3–0.2KBr glass has the fastest optical non-linear response time in subpicosecond domain (about 340 fs), which is due to the ultrafast distortion of the electron clouds surrounding the balanced position of Ge, Ga, S, K and Br atoms. The local hyperpolarizability determining non-linear optical response are determined by the partially ionic bonds originating from Ge(Ga)–S bonds and halogen valence bonds. They show great potential applications on the glass-based optoelectronic devices like optical switching.
In this work we report the spectroscopic properties of the infrared emission at 1.5 μm and the infrared to visible upconversion processes in Er3+-doped glasses with the 0.8CaSiO3–0.2Ca3(PO4)2 eutectic composition. Intense upconversion green emissions at 529 and 550 nm have been observed under infrared excitation at 800 nm in the 4I9/2 level and attributed to a two photon upconversion process. The possible excitation mechanisms responsible for this upconversion luminescence are discussed in terms of excitation spectrum and time evolution of the upconverted luminescence. The time evolution of the green emission from the 4S3/2 level indicates that an ETU process is responsible for the upconversion luminescence.
The refractive indices of 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 under different wavelengths were measured by the minimum deviation method at room temperature, thus dispersion equations were determined. The parameters connected to the energy band structure were obtained by fitting single-oscillator dispersion equation. Similar to most oxygen-octahedra ferroelectrics, PMNT35% has the same dispersion behavior described by the refractive-index dispersion parameter.
The nonlinear absorption properties of p type 0.5 at% Sn doped GaSe crystal have been studied by using open-aperture Z-scan technique under 1064 nm wavelength and 4 ns or 65 ps pulse duration. A switching from negative nonlinear absorption (saturated absorption) to positive nonlinear absorption (two photon absorption) has been observed as the input laser irradiance increases from 0.049 GW/cm2 to 0.106 GW/cm2. The nonlinear absorption coefficient increases monotonically with the increase of pulse duration from 65 ps to 4 ns.
A new series of conjugated copolymers (P1–P3) consisting of alternate 3,4-dialkoxythiophene and (1,3,4-oxadiazolyl)pyridine moieties have been synthesized using the precursor polyhydrazide route. They have been characterized by FTIR, 1H NMR spectral and elemental analyses. These copolymers possess well defined structure and exhibit good thermal stability with the onset decomposition temperature in nitrogen at around 300 °C. Their molecular weights were determined by gel permeation chromatography (GPC). The optical and charge-transporting properties of the copolymers were investigated by UV–visible spectroscopy, fluorescence emission spectroscopy and cyclic voltammetry. Their UV–visible absorption spectra showed a λmax at around 342 nm and displayed bluish-green fluorescence in solution state. The band gaps were found to be at about 2.55 eV for all the copolymers. The third-order nonlinear optical properties (NLO) of these copolymers were studied by Z-scan technique. The measurements were performed at 532 nm with 7 ns laser pulses using a Nd:YAG laser in solution form. The real part of χ(3) were estimated to be −0.881 × 10−12, −0.901 × 10−12 and −1.030 × 10−12 esu for P1, P2 and P3 respectively. The imaginary part of χ(3) for the copolymers P1, P2 and P3 were determined to be 0.192 × 10−12, 0.253 × 10−12 and 0.272 × 10−12 esu respectively. The copolymers exhibit strong reverse saturable absorption and good optical limiting behaviour at 532 nm.
We report here a comparative study of the second-order nonlinear optical properties of 4-nitroaniline (p-NA), 1, 5-diamino-2, 4-di-nitrobenzene (DADB) and 1, 3, 5-triamino-2, 4, 6-trinitrobenzene (TATB). First hyperpolarizabilities (β) of p-NA, DADB, and TATB calculated using the Molecular Orbital Package (MOPAC) AM1 method were found to be 12.017×10-30, 6.793×10-30 and -0.196×10-30 esu, respectively. These results demonstrate that the number and location of donor-acceptor substituents on the benzene ring strongly influence the molecular hyperpolarizability. Both p-NA and DADB show no powder second-harmonic generation (SHG). On the other hand, the TATB has a SHG intensity three times that of standard urea as reported by Ledoux et al. [Chem. Phys. Lett. 172 (1990) 440]. The physical properties of these three molecules are discussed here in view of second-order nonlinear optics. In particular, the molecular engineering of DADB leads to novel two-dimensional charge transfer molecules. First hyperpolarizability of model compounds of DADB, i.e., N, N' -dimethy1-2, 4-dinitro-1, 5-diaminobenzene and N, N' -diethyl-2, 4-dinitro-1, 5-diaminobenzene were also calculated using the same quantum chemistry program. The first hyperpolarizability of 10.642×10-30 esu was estimated for N, N' -diethyl-2, 4-dinitro-1, 5-diaminobenzene which is almost the same as of p-NA molecule. The molecularly designed amphiphile N, N' -dioctadecyl-2, 4-dinitro-1, 5-diaminobenzene (DIODD) showed second-order nonlinear optical susceptibility χ(2)111 of 22×10-9 esu and χ(2)133 of 7.7×10-9 esu from the Langmuir- Blodgett monolayer. An analysis of the second-order nonlinear optical properties of two-dimensional charge transfer molecules is presented.
Chalcogenide glasses present high values for third-order non-linear optical properties, i.e., high non-linear refractive indices (800 times as high as the non-linearity of silica glass at 1.064 μm) and a high non-linear absorption coefficient, which can reach more than 5 cm/GW. We study here the optical limiting properties of several chalcogenide glasses at 1.064 μm with a picosecond pulsed Nd:YAG laser and we observed a real optical limiting behavior. In the case of GeAs2Se2, glass for example, the decrease of the transmitted intensity is around 75% compared to the theoretical linear transmission, for incident pulses of 5 GW/cm2. The comparison between the theoretical non-linear transmission induced by the two photon absorption effect and the experimental non-linear transmittance shows that the optical limiting properties are mainly due to non-linear absorption.
The optical and structural properties of a single array of emitting quantum dots (QDs) grown by LP-MOVPE are presented after different thermal treatments (between 570°C and 670°C under arsine flux during 25 min) simulating the overgrowth of the confinement layers for broad area lasers. The photoluminescence (PL) efficiency of the line is not affected by a thermal treatment below 620°C. Nevertheless, a drastic decrease of the peak intensity occurs for higher anneal temperature (670°C), together with an important blueshift of the PL spectrum (≈40 meV). The structural modifications of the QDs were studied by TEM, showing an important In/Ga intermixing during the thermal treatment. A low thermal budget (<620°C) during the growth is clearly required to avoid the PL spectrum blueshift.
Two longitudinally diode-pumped Nd:YAG/V:YAG Q-switched microchip lasers emitting radiation at wavelength 1.3 μm were realized. The first laser, designed for higher pump power, was based on the composite crystal which combines in one piece a 4 mm long cooling undoped YAG crystal, 12 mm long Nd:YAG laser active part, and 0.7 mm long V:YAG saturable absorber. The second one was designed to obtain shorter pulse length. It consists of 4 mm long Nd:YAG crystal and 0.7 mm long V:YAG crystal. The initial transmission of the V:YAG part (85%) and the output coupler reflectivity (90%) was the same in both cases. The generated pulse length was independent on pumping power for both crystals. For longer (shorter) crystal it was equal to 6.2 ns (1.7 ns FWHM). The wavelength of linearly polarized TEM00 laser mode was fixed to 1338 nm for longer crystal. In case of shorter crystal instabilities were observed for higher pump power. The average pulse energy was equal to 37 μJ for longer crystal, and 15 μJ for shorter one.
Optical transitions of Er3+ ion in two tellurite glasses of molar composition 75TeO2:12ZnO:10Na2O:2PbO:1Er2O3 and 75TeO2:12ZnO:10Na2O:2GeO2:1Er2O3 were investigated. The measured absorption and emission spectra were analysed by Judd–Ofelt and McCumber theories, in order to obtain radiative transition rates and stimulated emission cross sections. It was found that these glasses have high and broadband absorption and stimulated emission cross sections at 1.5 μm. For the metastable 4I13/2 level, by comparing the measured lifetime with the calculated radiative decay time, quantum efficiency higher than 80% was found.
For the first time, a quaternary doping system of Er3+, Yb3+, Ce3+, Na+:CaF2 single crystal was demonstrated to have high fluorescence yield in the eye-safe 1.5 μm region under 980 nm laser diode pumping, with relatively broad and flat gain curves. A simplified model was established to illustrate the effect of Ce3+ on the branching ratio for the Er3+4I11/2 → 4I13/2 transition. With 0.2-at.% Er3+ and 2.0-at.% Ce3+ in the quaternary-doped CaF2 crystal, the branching ratio was estimated to be improved more than 40 times by the deactivating effect of Ce3+ on the Er3+4I11/2 level. The quaternary-doped CaF2 system shows great potential to achieve high laser performance in the 1.5 μm region.
The spectral properties of the Er3+-doped lead halotellurite glasses, PbX2–TeO2 (X=F, Cl, Br), were measured and analyzed with Judd-Ofelt and McCumber theories. These glasses showed high refractive indices, high cross-sections for both absorption and stimulated emission, and very broad bandwidths for the 1.5 μm band. The bandwidths of the 1.5 μm band, which have substantial magnetic dipole transition component, increased significantly with the refractive index of the host materials. The halotellurite glasses have very good glass formation ability or glass stability. The halotellurite glasses will be the promising host materials for 1.5 μm broadband amplification.
By combining the sol–gel method and the spin-coating technique, silica-on-silicon Er-doped glass optical planar waveguides were fabricated. The active guiding layer consisted of SiO2–TiO2–Er2O3–Yb2O3–Al2O3 and its composition was optimized by measuring the fluorescence lifetime τ of the 4I13/2 metastable level of Er3+ ions. The Er concentration was chosen as the quenching concentration, which was found to be 1.4 × 1020 ions/cm3. The Yb concentration was found to have little influence on τ, whereas a concentration of 1.5 × 1021 ions/cm3 of AlO3/2 was found to be enough to maximize τ. The 71aluminum concentration barely influenced the flatness of the amplified spontaneous emission spectrum. Strip-loaded waveguides were designed by reactive ion etching of the cladding layer and their performance as candidates for integrated optical amplifiers was assessed. Propagation losses of 0.7 dB/cm and loss reduction of 2.7 dB (for a 5.7 cm long waveguide) were measured.
A birefringence phase-matching (BPM) scheme for second harmonic generation, difference frequency generation (DFG), and their cascading is developed in a polymer rib waveguide. Poling-induced birefringence (nTM–nTE) of PMMA:DANS side-chain polymer films showed quadratic increase upon applied DC poling fields, and was controlled for satisfying the BPM. The three conversion processes using the nonlinear coefficient of the d15 were simultaneously phase matched at the poling field around 150 V/μm when the fundamental guiding modes of a pump (DFG: 0.775 μm, cascading: 1.55 μm) and a signal (∼1.55 μm) waves were used. In addition, a numerical simulation of the DFG including the waveguide losses showed high conversion efficiencies around 0 dB on the conditions: the pump power of 100 mW, the waveguide length around 2 cm, and the waveguide losses of 2 dB/cm, demonstrating that the poling-induced BPM is an effective phase-matching method in the wavelength conversion processes.
We have investigated spectroscopic properties and energy transfer (ET) of Er3+/RE3+ (RE3+ = Ce3+, Tb3+, and Eu3+) codoped Ga2O3–PbO–Bi2O3–GeO2 (GPBG) glass. An intense 1.53-μm emission with a full width at half-maximum (FWHM) of 48 nm and a peak emission cross-section of 1.14 × 10−20 cm2 of Er3+-doped GPBG glass has been obtained upon 980 nm diode-laser excitation. Effects of rare-earths RE3+ (RE3+ = Ce3+, Tb3+, and Eu3+) co-doping on the spectroscopic properties of the GPBG glass have also been investigated. It is found that the incorporation of RE3+ into Er3+-doped GPBG glass could effectively reduce upconversion (UC) emission. Moreover, co-doping Ce3+ could also enhanced the 1.53-μm emission quite significantly, which makes Er3+-doped GPBG glass more attractive for using in 1.53-μm optical fiber amplifiers.
Two types of Si:Er light emitting devices have been processed and characterized with an aim to efficiently use hot electrons for impact excitation. One is a p+-SiGe/i-Si/n-Si:Er:O/n+-Si tunneling diode with a design favoring electron tunneling from the SiGe valence band to the Si conduction band and subsequent acceleration. Another type of Si:Er light emitters is based on a heterojunction bipolar transistor (HBT) structure containing an Er-doped active layer in the collector. In these devices, one can introduce hot electrons from the HBT emitter in a controlled way with a collector bias voltage prior to the avalanche breakdown to improve the impact excitation efficiency. Intense electroluminescence was observed at 300 K at low current and low bias (3 V). An impact cross-section value of has been estimated, which is a 100-fold increase compared with the values reported from any other type of Er-doped LEDs.
The MOVPE growth of (InGa)(NAs)/GaAs structures with room temperature photoluminescence (RTPL) in 1–1.59 μm range is presented. Infinite threshold current densities of 0.095, 1.22 and 2.3 kA/cm2 at 1.18, 1.22 and 1.24 μm emission wavelengths, for the In0.35Ga0.65NyAs1−y/GaAs quantum well (QW) laser diodes with 0%, 0.4% and 0.5% of nitrogen, respectively, were obtained. Characteristic temperature (T0) values of 82, 117 and 102 K were determined for as-cleaved lasers in the 20–80°C temperature range.
A Tm doped ZBLAN glass is investigated to obtain a laser emission near 1.8 μm instead of classical crystalline host materials. After a brief description of the basic optical properties of Tm doped ZBLAN glass, demonstration of an efficient laser emission in the bulk material is presented. The other investigations are focussed on its wavelength tunability, its tolerance versus the pump wavelength and its behaviour in terms of thermal acceptance which are the main characteristics to consider in order to scale up such laser system.
53.3BiO1.5–33.3GeO2–13.4NaO0.5 (cation%) glasses with various Tm3+ concentration were prepared by melt-quenching method. These glasses show high density, high refractive index, low phonon energy and good stability against crystallization. Absorption spectra of Tm3+-doped bismuthate glass were measured to obtain the radiative lifetimes by Judd-Ofelt theory. The absorption (4.5 × 10−21 cm2) and emission (6.7 × 10−21 cm2) cross-sections were calculated by Beer–Lambert and McCumber theory. The results show that the Tm3+ (3F4 → 3H6) in these glasses have high spontaneous radiative transition probabilities and large stimulated emission cross-section. Then the fluorescence emission spectra were measured under 808 nm excitation and the maximum emission intensity at 1.8 μm is obtained at 0.9 mol% Tm2O3 in the glasses.
This work presents the characterization of high optical quality Gd0.8La0.2VO4:Tm3+ single crystal fibers grown by the low cost laser heated pedestal growth technique. The 400 μm diameter fibers were grown completely free from inclusions, without the need of O2 atmosphere. Their structural and spectroscopic characteristics are very similar to those of GdVO4:Tm3+, with the advantageous inhomogeneous broadening that eliminates the need of temperature control of the diode pumping laser for excitation at 0.8 μm. ESA transitions do not affect the population in level 3F4 significantly, and intense emission is observed at 1.8 μm. On the other hand, the 1.45 μm emission is deeply affected by ESA, while pumped at 0.8 μm excitation. The lower cost and easier growth of compact, excellent optical quality single crystal fibers, as compared to GdVO4:Tm3+ bulk crystals, indicates the fibers are interesting candidates for the construction of miniature lasers in the eye-safe spectral region (1.5–2.0 μm).
Ce/Nd co-doped YAG transparent ceramics were fabricated by solid-state reaction and vacuum sintering method for the first time. By comparison of the samples for various Ce3+ concentrations ranging from 0.01 to 1 at%, it was shown that the 0.3 at%Ce:1.0 at%Nd:YAG ceramic exhibited the strongest near-infrared (NIR) luminescence as well as a good transparency. The intense 1064 nm emission due to the Nd3+4F3/2 → 4I11/2 was observed upon the excitation of 5d level of Ce3+. The energy transfer from Ce3+ to Nd3+consists of non-radiative and radiative parts. The efficient energy transfer from Ce3+ to Nd3+ could make the NIR luminescence in Ce/Nd co-doped YAG easily excited by GaN LED. Therefore, the Ce/Nd co-doped transparent ceramics have the potential to be a new efficient NIR luminophor or a low threshold, high efficiency laser grain medium.
