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Under the social background of the rapid development of big data, human beings have gradually moved towards a comprehensive digital era, and people have begun to apply digital technology in various fields. Therefore, it is necessary to study methods that can efficiently process big data and solve problems such as data intelligence. Intelligent products and applications that we use everywhere in our lives are changing people’s lives. Among them, location service is one of the important technical supports. No matter which software is opened on the mobile phone, it will prompt us to open location service. Location prediction is an important part of location-based services and plays an indispensable role in the recommendation system and urban resource planning. At present, GPS-based trajectory data is widely concerned in position prediction task. GPS trajectory data belongs to spatiotemporal series data, which not only contains time and position information but also contains abundant context information in trajectory sequence. Most of the traditional position prediction methods focus on the position sequence in GPS trajectory but do not fully mine the context information in the trajectory, which leads to poor prediction results. The intelligent optimization algorithm greatly enriches the optimization technology and provides a feasible solution for those combinatorial optimization problems which are difficult to deal with by traditional optimization technology. GPS trajectory data has the advantages of wide coverage, quick update, easy collection, and low cost, and it also implies abundant road network information. As a result, GPS trajectory data of users has gradually become a new data source for automatic construction of urban road network and has also become a research hotspot of many scholars. In this paper, the idea of swarm intelligence algorithm and swarm intelligence algorithm are used to design and implement a data analysis and behavior prediction system for calculating GPS user trajectory, aiming at solving the shortcomings of existing GPS tracking and positioning.

We show how the ultrafast laser inscription of nanodimple arrays enables near-field local enhancement in high refractive-index crystals. We first demonstrate both experimentally and numerically how, when two nanodimples are separated by intermediate distances (700–1000 nm), near-field interference can take place resulting in a near-field enhancement between nanodimples. Based on this effect, near-field enhancements close to 60% are then demonstrated at the center of nanodimple arrays, and strong optical contrasts in excess of 100% are produced. The integration of these arrays into crystal substrates provides a versatile tool for new optical trapping and evanescent-field nanosensing devices.

A novel pyridinium salt, 2,4-bis[p-(N,N-dimethylamino)styryl]-N-methyl pyridinium iodide (BMSPI) was synthesized and characterized by TG, 1H NMR spectroscopy and elemental analysis. and the reaction process was studied by Using ES-MS. When BMSPI was pumped by a pulsed 1064 nm, 50 ps laser him. it manifests highly efficient TPA (Two-Photon Absorption) and up-conversion superradiance. The up-conversion efficiency was 6.0% at the pump energy of 4–6 mJ and the Lifetime of two-photon fluorescence was measured as 59 ps.

Although majorexperimental breakthroughs have already been achieved, thefundamental limiting challenge still inheres in the achievementof experimental methods capable of 3D-sculpting any desiredmedium with nanometric resolution. This technical limitationhas caused many of the anticipated optical quantum devices tocontinuebeingpracticallyunattainable.

Understanding the inhibitionand enhancement of spontaneous emission from active mate-rials embedded in a three-dimensional (3D) PC is fundamen-tally important in the field of quantum optics, and could alsolead to technology breakthroughs in next generation photonicdevices such as highly efficient solar cells and low-thresholdlasers.

Composites with enhanced refractive index have been synthesised through a sol–gel process. A refractive index of approximately 1.70 has been achieved at a concentration of 75 wt% TiO2. The refractive index increases with the concentration of TiO2. The influence of the concentration of TiO2 on the mechanical properties has been studied. The potential application of these materials in photonics area has been demonstrated by fabricating multi-layer spherical voids in them through a femtosecond laser-driven micro-explosion method.

The reason why there is a 90 nm red-shift for the highest upconversion wavelength compared with the strongest nonlinear absorption wavelength is given. A three-level energy model is proposed for an organic dye, trans -4-[ p -(pyrrolidinyl)styryl]- N -methylpyridinium iodide (abbreviated as PSPI). It is the excited state absorption (ESA) that leads to the reduction of the upconversion efficient at wavelength shorter than 950 nm. The three-level energy model is proved to be right by using the femtosecond pumped two-photon excited spectrum. The TPA cross-sections and the ESA coefficients at various wavelengths are calculated using the measured nonlinear transmittance and upconverison efficiencies. The largest TPA cross-section σ 2 ′ is 14.1 × 10 −48 cm 4 s/photon at 960 nm. The experimental results show that the electrons are excited to the same excited states for both the TPA and one-photon absorption processes.

Two-photon-absorption (TPA)-induced upconverted amplified spontaneous emission (ASE) and cavity lasing of a styrylpyridinium dye: trans-4-[p-(N-hydroxyethyl-N-ethylamino)styryl]-N-methylpyridinium p-toluene sulfonate (abbreviated as HEASPS) in poly(2-hydroxyethyl methacrylate) (abbreviated as PHEMA) polymer were observed under a picosecond pump condition. The spectral and temporal behaviors of TPA-induced fluorescence, ASE and cavity lasing were studied. The cavity lasing with a total oscillation time of more than 200 ps was achieved when pumped with 1064-nm, 50-ps laser irradiation. The population inversion could persist for three times longer than the duration of the pump pulse. The gain coefficients of the dye-doped polymer at various wavelengths were calculated based on cavity lasing spectra and one-photon fluorescence spectra.

The fluorescence properties of a new two-photon absorption chromophore in dimethyl formamide, methanol, acetone, benzyl alcohol, methylene chloride and chloroform are reported. The lifetime, intensity and central wavelength of the fluorescence signal vary significantly in different solvents. The fluorescence properties are explained by using the twisted intra-molecular charge-transfer model, the viscosity of the solvents and the formation of the hydrogen bond. For the dye in all solvents, the longer the fluorescence lifetime, the higher the fluorescence intensity. Generally, the higher the dipole moments, the longer the central wavelengths of the dye.

The luminescence behaviors of a series of symmetrically and asymmetrically substituted stilbene or its analogues on one-photon excitation (OPE) and two-photons excitation (TPE) have been investigated and compared. To understand the influence of intramolecular charge transfer upon the fluorescence properties, steady-state and time-resolved fluorescence spectra on one-photon-/two-photons-excitation, the solvent effect and the linear absorption spectra as well as the relative fluorescence quantum yields were examined. Based on the quantum chemical calculations of the charge density and the twisted intramolecular charge transfer (TICT) model, the luminescence properties have been interpreted. The results obtained have shown that the OPE and the TPE fluorescence behaviors are both strongly influenced by the intramolecular charge transfer process and by the planarity of effective fluorophore under the excited state. On the other hand, for a given dye, its luminescence behaviors on one-photon- and two-photons-ex...

Pumped by picosecond pulses from a Nd:YAG laser, a new lasing dye, trans-4-[4′-(N,N-diethylamino)styryl]-N-methyl pyridinium methyl sulfate (abbreviated to DEASPS), shows both intense superradiance and strong lasing properties in benzyl alcohol solution. By using streak camera systems, the superradiance and lasing can be distinguished both spectrally and temporally. It has been found that the peak wavelength of lasing is at 620 nm with a red-shift of about 12 nm to the superradiance wavelength. The lasing pulse shows an oscillatory effect that it is not found in the superradiance pulse. The fluorescence lifetime is 529 ± 40 ps and the effective molecular two-photon absorption is (1.25 ± 0.1) × 10−48 cm4 ·s·photon −1, measured using a nonlinear transmittance method. This dye shows effective optical limiting of the pumping wavelength.

Linear and nonlinear optical properties of a new organic dye, trans-4-[p-(N-n-butyl-N-n-butylamino)-styryl]-N-methyl-pyridinium tetraphenylborate solution in dimethyl formamide (DMF) have been studied systematically. When excited with mode-locked picosecond 1 064 nm laser beam, intense upconversion fluorescence and superradiance can be obtained. The temporal behaviors of one-photon absorption and two-photon absorption (TPA) fluorescence and superradiance have been studied. The highest upconversion efficiency was found to be 4.1% at a pump energy of 4 mJ. By using an optical parameter amplifier (OPA) as the pump laser, the nonlinear transmittance and upconversion efficiencies of the dye solution at different wavelengths were measured. The strongest linear absorption was found at a wavelength of 930 nm whereas the highest upconversion efficiency was at 1 030 nm. The 100 nm red-shift for the highest upconversion efficiency wavelength compared with the strongest nonlinear absorption are caused by excited state absorption.

Two-photon absorption (TPA) cross sections of an organic dye, trans-4-[p-(N-hydroxyethyl-N-methylamino)tyryl]-N-methylpyridinium iodide (abbreviated as ASPI), from 720 to 1100 nm have been measured by using nonlinear transmittance method, which reflect the TPA degrees of the dye at different wavelengths. The maximum TPA wavelength is located at 930 nm . The upconversion efficiencies of ASPI in dimethyl formamide and benzyl alcohol at different pump wavelengths have also been measured. There is 90 nm red shift for the highest upconversion wavelength as comparing with the strongest TPA wavelength. The influences of the solvents on the TPA-induced emission spectrum and the conversion efficiencies have also been given.

The properties of picosecond two-photon-absorption induced amplified spontaneous emission (ASE) and cavity lasing of a newly synthesized organic dye, trans-4-(4′-pyrrolidinyl styryl)- N -methyl pyridinium methyl sulfate (abbreviated as PSPS), has been reported in this letter. There is 5 nm red-shift for the central wavelength of two-photon-absorption (TPA) induced lasing compared to that of ASE. The temporal behavior of TPA induced fluorescence, ASE and lasing has been studied. An obvious oscillation can be obtained due to the feedback of the external surface of the cuvette. The oscillation time is more than 200 ps, which is much longer that the pump laser duration (50 ps). The reason why the oscillation time is longer that the pump laser duration has also been given.

Two-photon pumped cavity lasing is firstly operated based on an organic dye, trans-4-[p-(pyrrolidinyl)styryl]-N-methylpyridium iodide, using mode-locked picosecond laser beam at 1064 nm as pump source. There is an obvious blue shift for the central wavelength of cavity lasing compared with that of the two-photon absorption (TPA) induced fluorescence. This phenomenon is explained by using the difference of the re-absorption coefficient at different condition. The lifetime of the fluorescence is measured to be 89 ps. The temporal properties of TPA induced cavity lasing are measured and obvious oscillations can be obtained.

The first operation of cavity lasing of a two-photon absorption (TPA) organic dye, trans-4-[p-(N-ethyl-N-hydroxyethylamino) styryl]-N-methylpyridinium iodide (HEASPI), by using picosecond infrared laser as pump source is reported in this paper. Temporal profile of cavity lasing shows obvious oscillations, and magnification of the feedback light can be obtained. By using the difference of re-absorption coefficient at different conditions, we explained the blue shift for cavity lasing and superradiance compared with TPA-induced fluorescence. The lifetime of TPA-induced fluorescence is measured to be 134 ps .

A new dye trans-4-[p-(N-hydroxyethyl-N-ethylamino)styryl]-N-methylpyridinium p-toluene sulfonate (HEASPS) has been synthesized. The two-photon absorption (TPA), TPA-induced frequency up-conversion emission, and two-photon pumped (TPP) frequency up-converted lasing properties of this new dye were experimentally studied. This new dye has a TPA cross-section of σ2 = 4.7 × 10-48 cm4 · s/photon at 1064 nm, but exhibits a high lasing efficiency. The net conversion efficiency from the absorbed 1064 nm pump pulse energy to the 625 nm up-converted lasing energy is 3.6% at the pump energy level of 4 mJ.

Two-photon absorption (TPA) and frequencyupconversion properties of a new upconversion laser dyetrans-4-[p-(N-hydroxyethyl-N-methyl-amino)styryl]-N-methylpyridinium toluene-p-sulfonate (abbreviated to HMASPS) were reported in this note. The linear absorption, TPA, single-photon induced fluorescence, TPA induced fluorescence and TPA induced upconverted lasing spectra of HMASPS solution in dimethyl formamide (abbreviated to DMF) were measured at room temperature. The red shift for the central wavelength of TPA induced fluorescence peak, which was compared with that of the single-photon induced fluorescence peak, and the blue shift for that of TPA induced upconverted lasing compared with that of TPA induced fluorescence, were explained by using re-absorption effect. TPA peak was at 930 nm. There is an 11 nm blue shift for two-photon energy of TPA peak compared with the linear absorption peak. The molecular TPA cross-section σ2 9′ at 1064 nm was measured to be 6.0×10−48 cm4 · s/photon by using the open aperture Z-scanning system. The highest upconversion efficiency was measured to be 8.4% at 1064 nm.

A new dye, trans -4-[ p -( N -ethyl- N -hydroxyethylamino)styryl]- N -methylpyridinium iodide has been synthesized, and the two-photon absorption (TPA), TPA-induced frequency up-conversion emission, and two-photon pumped frequency up-converted lasing properties of this new dye were experimentally studied. This new dye has a TPA cross-section of σ 2 =7.0×10 −48 cm 4 s/photon at 1064 nm, and exhibits a high lasing efficiency. The net conversion efficiency from the absorbed 1064 nm pump pulse energy to the 632 nm up-converted lasing energy is 4.3% at the pump power of 4 mJ.

Trans-4-[p-(N-hydroxyethyl-N-ethylamino)styryl]-N-methylpyridinium p-toluene sulfonate (abbreviated as HEASPS) is a two-photon-absorption (TPA) dye newly synthesized by our research group. It possesses a much larger TPA cross-section and much stronger upconversion fluorescence emission than those of common organic dyes (such as rhodamine) when excited with near-infrared (IR) radiation. TPA spectrum and upconversion efficiency spectrum of HEASPS solution at different wavelengths have been measured. The largest molecular TPA cross-section σ2′ is measured to be 2.06×10-47 cm4 s/photon at 930 nm. At 1064 nm, σ2′ is 2.71×10-48 cm4 s/photon, which is only one-ninth of that at 930 nm. The upconverted lasing efficiency spectrum has been measured at different wavelengths. The highest efficiency is 5.1% at 1020 nm, whereas it is 3.5% at 1064 nm. Its optical-power-limiting properties at 930 nm have also been illustrated.

A new dye trans-4-[p-(N-hydroxyethyl-N-methylamino)styryl]-N-methylpyridinium p-toluene sulphonate (abbreviated as HMASPS) was synthesized, the two-photon absorption (TPA), TPA-induced frequency up-conversion emission, and two-photon pumped (TPP) frequency up-converted lasing properties of HMASPS were experimentally studied. This new dye has a moderate TPA cross-section of σ2 = 6.0 × 10−48 cm4 s photon−1, but exhibits a high lasing efficiency. The net conversion efficiency from the absorbed 1064 nm pump pulse energy to the 630 nm up-converted lasing energy is 4% at a pump energy level of 4mJ.

Trans -4-[ p -(pyrrolidinyl)styryl]- N -methylpyridinium iodide (abbreviated as PSPI thereafter) is a two-photon absorption (TPA) dye newly synthesized by our research group. It possesses much larger TPA cross-section and much stronger upconversion fluorescence emission than those of common organic dye (such as rhodamine) when excited with near infrared (IR) radiation. TPA spectrum and upconversion efficiency spectrum of HEASPI solution at various wavelengths were measured. There is 34 nm blue shift for the central wavelength of the TPA induced absorption peak compared with two times of the linear absorption peak. The biggest molecular TPA cross-section σ 2 ′ is 2.85×10 −47 cm 4 s/photon at 930 nm. At 1064 nm, σ 2 ′ is 3.12×10 −48 cm 4 s/photon. The highest efficiency is 3.9% at 1010 nm, whereas 2.9% at 1064 nm. Its optical power limiting properties at 930 nm have also been illustrated.

Two-photon absorption properties of a series of symmetrically substituted stilbenes and asymmetrically substituted stilbene-type derivatives with the same conjugated length have been investigated. The effective two-photon absorption cross sections, δTPA, as large as 62.0 × 10−48 cm4 s photon−1 for D-π-D molecules and 48.5 × 10−48 cm4 s photon−1 for D-π-A counterparts have been observed. The effect of these two types of chromophores on the peak position of the linear absorption, one-photon fluorescence as well as two-photon absorptivity is reported. Dipole moment change between the ground and the first excited states (Δµge), and the transition dipole moment between the first and second excited states (Mee′) have also been calculated. It was found that the asymmetrically substituted derivatives possess relatively large Δµge, whereas the symmetrical counterparts show an increase in Mee′. Although a large two-photon absorption resonance is due to the simultaneously high values of Mee′ and Δµge, correlated to intramolecular charge transfer, the former function is larger. These results obtained have demonstrated that the magnitude and the peak position of two-photon absorption depend not only on the amount but also on the direction of the intramolecular charge transfer.

The methods to grow a novel upconversion crystal Ba2ErCl7 are reported in this note. Ba2ErCl7 material was synthesized with Er2O3, BaCl2·2H2O and NH4Cl by using a so-called “direct synthesis method”. High quality Ba2ErCl7 single crystals with size up to 4 mm×8 mm×15 mm were grown by using the Czochralski and the Bridgman methods. Intense yellow-green luminescence was detected when the crystal was pumped by an 803 laser diode (LD). Transmittance spectrum was measured by using HITACH U-3500 spectrophotometer at room temperature for the first time, in which one can see that the transmittance is high in the range from 350 to 1 600 nm and the cut-off wavelength of the crystal was 230 nm. The upconversion mechanisms were discussed.

A modified synthesis method for the preparation of Ba 2 ErCl 7 , a new laser up-conversion material using Er 2 O 3 , BaCl 2 ·2H 2 O and NH 4 Cl, is reported for the first time. Single crystals 5–8 mm in diameter and 10–20 mm in length were grown by both the Czochralski and Bridgman methods. The transmittance spectra for a Ba 2 ErCl 7 single crystal was first measured using a HITACHI U-3500 spectrophotometer. There were three intense absorption peaks 4 I 9/2 , 4 I 11/2 and 4 I 13/2 in the infrared range which can be excited by 803 and 980 nm and 1.5 μm laser diode (LD), respectively. The cut-off wavelength of the crystal was 230 nm. Intense green luminescence was observed when the crystals were pumped by an 803 nm LD. Up-conversion mechanisms are discussed.

A modified method to synthesize the new laser upconversion material Ba2ErCl7 using Er2O3, BaCl2 ⊎2H2O and NH4CI is reported for the first time in this paper. Single crystals up to 5–8mm in diameter and 10–20 mm in length have been grown by Czochralski method. The transmittance spectra of Ba2ErCl7 single crystal has first been measured by using an HITACHI U-3500 spectrophotometer. There are three intense absorption peaks 4I924I112 and 4I132 in the infrared range which can be excited by 803nm, 980nm and 1.5μm laser diodes (LDs), respectively. The cut-off wavelength of the crystal is 230mn. Intense green luminescence can be observed when the crystal is pumped by a ED at 803nm. The formation of the defects is also discussed.

Optical quality Nd:GdCa 4 O(BO 3 ) 3 (Nd:GdCOB) crystal and chromium sensitized crystal of Cr:Nd:GdCa 4 O(BO 3 ) 3 (Cr:Nd:GdCOB) were grown by the Czochralski (CZ) method. The transmittance spectra was measured at room temperature on 7at%Nd:GdCOB and lat%Cr:7at%Nd:GdCOB samples. The absorption in the blue-UV region of Cr:Nd:GdCOB was larger than that of Nd:GdCOB, which matched the xenon flash lamp very well. A 3×3×10mm 3 Nd:GdCOB sample without any antireflective coating was sidepumped using a pulsed dye-laser tuned to 595.4nm. The green-light output energy was 1.35mJ at a pump energy of 17.5mJ. The conversion efficiency was 7.7%, and the threshold energy was less than 1.2mJ which are the best results up to now to our knowledge. 3×3×7mm 3 Nd:GdCOB and Cr:Nd:GdCOB samples without antireflective coatings were pumped using a flash pump source. The threshold for Cr:Nd:GdCOB was 0.9J while for Nd:GdCOB it was I.O.J. The output green light energy was 2.46mJ for Cr:Nd:GdCOB at a 10J flash pump energy and was 1.96mJ for Nd:GdCOB at the same pump energy, which clearly shows that Cr 3+ ions have the sensitizing effect on the Nd 3+ ions in Nd:GdCOB crystal.

High purity polycrystalline PbWO4 (PWO) has been synthesized by a chemical method. Pure and doped PWO crystals were grown by using a Czochralski technique. Transmittance spectra, light yield and decay constants of the crystal were measured. The effect of PWO crystal quality and doped ions on its scintillating properties is discussed in this paper.

High quality magnesium-doped potassium lithium niobate (designated as KLN:Mg) single crystal was grown for the first time. The tetragonal tungsten bronze structure of the Mg:KLN crystal was determined by X-ray powder diffraction, in which the lattice parameters were a=1.262nm and c=0.398nm. High temperature X-ray diffraction patterns showed that the expansion of the lattice with increasing temperature was less than that of the undoped crystal. The transmittance of the as-grown crystal was measured. It increased by 80% from the cutoff wavelength 380nm to 450nm. The transmittance for 404nm was 50%, which is larger than that of the undoped crystals. The frequency-doubling property of KLN crystal was analyzed. Preliminary frequency doubling experiments showed that the crystal could generate blue light of 404nm through noncritical phase matching (NCPM) second harmonic generation (SHG) using a 808nm diode laser at room temperature.

In GdCa 4 O(BO 3 ) 3 (GdCOB) crystal, the Gd 3+ ions can be substituted by Nd 3+ ions within the concentration of 0–100 at%. Combined laser action of the Nd 3+ ions and nonlinear optical (NLO) properties of GdCOB crystal host in the mixed Nd x Gd 1− x COB causes the crystal to become self-frequency-doubling (SFD) material. The synthesis and crystal growth of Nd x Gd 1− x COB are reported in this paper. The polarized transmittance spectra and fluorescence spectra were measured at room temperature. The strong emission peaks in the range of 850–950 nm are reported for the first time for the Nd x Gd 1− x COB crystal. The ( θ =66.8°, φ =132.6°) phase-matching direction was reported for the first time as the optimum phase-matching direction at 1060 nm by calculation and experiments whose d eff was measured and found to be 2.1 pm/v. The SFD experiments were carried out on 3×3×7 mm 3 sample with (66.8°, 132.6°) direction. The green output power at 530.5 nm was 192 mW when pumped by 1600 mW Ti : sapphire tuned to 811 nm. The threshold was 16 mW. The optical–optical conversion efficiency was 12%.

The in-plane and out-of-plane band-gap properties of two-dimensional triangular void channel photonic crystals fabricated by femtosecond laser drilling in a solid polymer material were characterized for transverse electric (TE) and transverse magnetic (TM) polarization illumination. For a 24 layer structure stacked in the Γ–M direction, the fundamental stop gap resulted in the suppression of infrared transmission of as much as 96% for TE- and 85% for TM-polarized incident light. The midgap wavelength for the TM polarization was longer by 2.5% than that for the TE polarization. Increasing the angle of incidence for both the in-plane and out-of-plane cases shifted the stop gap to short wavelengths for both TE and TM polarizations. The experimental results allowed for the estimation of the cross section of void channels and the effective refractive index of the polymer after the fabrication.

By using a catalytic amount of a lanthanide bis(trifluoromethylsulfonyl)amide, Ln(NFf2)3, the Friedel–Crafts acylation of substituted benzene proceeds smoothly under mild conditions and the catalysts are easily recovered from the reaction mixture.

We report on the experimental observation of “focus splitting” when light is tightly focused into a uniaxial lithium niobate crystal along its optical axis. This effect consists in the focal spot being split into two major sub-peaks along the axial direction. For the microfabrication applications such as three-dimensional photonic crystal fabrication and waveguide writing, this effect is highly undesired since it can lead to the generation of multiple distinct voxels in the vicinity of the focus. The splitting is caused by different birefringence induced aberrations for the ordinary and extraordinary polarization eigenmodes. We present numerical simulations which support our observations and suggest methods to avoid this effect.

We report on the fabrication and characterization of void-based body-centered-cubic (bcc) photonic crystals in a solidified transparent polymer by the use of a femtosecond laser-driven microexplosion method. The change in the refractive index in the region surrounding the void dots that form the bcc structures is verified by presenting confocal microscope images, and the bandgap properties are characterized by using a Fourier transform infrared spectrometer. The effect of the angle of incidence on the photonic bandgaps is also studied. We observe multiple stop gaps with a suppression rate of the main gap of 47% for a bcc structure with a lattice constant of 2.77 microm, where the first and second stop gaps are located at 3.7 microm and 2.2 microm, respectively. We also present a theoretical approach to characterize the refractive index of the material for calculating the bandgap spectra, and confirm that the wavelengths of the observed bandgaps are in good correlation with the analytical predictions.

Tetragonal tungsten bronze-type magnesium-doped potassium lithium niobate single crystal with a dimension of 10×10×40 mm 3 was grown for the first time by slow pulling method from high-temperature solution. The as-grown crystal has a perfect square shape without cracks. Annealing experiment showed that the crystal does not crack when heating and cooling through paraelectric/ferroelectric phase transition temperature. X-ray powder diffraction experiment showed that the unit cell parameters of KLN : Mg is slightly changed by the dopant. Blue–violet laser light at wavelength 404 nm has been achieved by noncritical phase matching second harmonic generation (NCPM SHG) of 808 nm laser diodes at room temperature.

A new dye, trans-4-[p-(pyrrolidinyl)styryl]-N-methylpyridinium iodide, has been synthesized, and the two-photon-absorption (TPA), TPA-induced frequency upconversion emission, and two-photon-pumped (TPP) frequency upconverted lasing properties of this new dye were experimentally studied. This new dye has a moderate TPA cross section of varsigma(2) = 5.7 x 10(-48) (cm(4) s(-1))/photon at 1064 nm but exhibits high lasing efficiency. The slope efficiency of the TPP cavity laser with this new dye as the laser medium is 1.6%.

We report on the study of the emission property of PbSe QDs embedded in 3D woodpile polymer PCs fabricated by the two-photon polymerization (2PP) method. Photonic band gaps (PBGs) of PCs were tuned towards longer wavelengths by infiltrating the QDs. A spectral redistribution in spontaneous emission from QDs inside a 3D PC has been measured for both low and high concentrations of infiltration.

Submicron-sized voids and void channels can be generated in a solid transparent polymer by using a tightly focused femtosecond laser induced micro-explosion method. By stacking the voids and void channels layer by layer and periodically, we can fabricate various three-dimensional (3D) photonic crystals of woodpile, face-centred-cubic, body-centred-cubic, and diamond lattice structures. The photonic bandgap effects and the defect generation in the photonic crystals have been revealed.

Direct optical fabrication of 3D photonic crystals in a high refractive index LiNbO3 crystal by using the femtosecond laser-induced microexplosion method is investigated. The focal distortion, caused by the refractive index mismatch-induced spherical aberration, can be significantly reduced by using a so-called threshold fabrication method. As a result, 3D fcc photonic crystals are fabricated by stacking quasi-spherical voids layer by layer. Photonic stopgaps with suppression rates of up to 30% in the transmission spectra are observed. The angle dependence of the stopgaps is also revealed.

Fabrication of three-dimensional photonic crystals by the microexplosion techniques has recently been demonstrated by a number of groups. However, simple models which are currently used for characterizing the void-based photonic structures do not produce adequate results. Here, we suggest a new theoretical approach for analyzing the properties of the three-dimensional photonic crystals which allow to improve the results of the theoretical modeling of the photonic crystals created by the microexplosion method. In particular, we study the bandgap spectrum of the three-dimensional photonic crystals introducing a shell of a high-index material surrounding an air void in the face-centered-cubic lattice. This allows us to suggest an effective theoretical model which correlates very well with the properties of the microexplosion polymer photonic crystals produced experimentally. We also discuss some interesting effects observed in the fabricated photonic crystals which until now have not been understood due to the inadequacies of simple models.

Ultrafast laser induced micro-explosion is observed in a high refractive index Fe:LiNbO3 crystal by use of a femtosecond oscillator as a laser source. Due to the strong spherical aberration effect caused by the large refractive index mismatch between the crystal and immersion oil, the void dots take the shape of tadpoles, dumbbells or excalmatory marks. By using a threshold fabrication method, semi-spherical voids are fabricated. The potential applications in three-dimensional (3D) read-only optical data storage and 3D photonic crystal fabrication have been demonstrated.Ultrafast laser induced micro-explosion is observed in a high refractive index Fe:LiNbO3 crystal by use of a femtosecond oscillator as a laser source. Due to the strong spherical aberration effect caused by the large refractive index mismatch between the crystal and immersion oil, the void dots take the shape of tadpoles, dumbbells or excalmatory marks. By using a threshold fabrication method, semi-spherical voids are fabricated. The potential applications in three-dimensional (3D) read-only optical data storage and 3D photonic crystal fabrication have been demonstrated.

We report the fabrication of photonic crystals in lithium niobate crystal by using femtosecond laser-induced microexplosion method. Photonic stop gaps with ~30% suppression rate for a 16-layer FCC structure have been observed.

We report the fabrication of three-dimensional photonic crystals in a high refractive index lithium niobate by using a femtosecond laser-induced microexplosion method. Photonic bandgaps with ~30% suppression rate for an FCC structure have been observed.

Micron-sized void dots have been generated in a solidified resin by using ultrafast-laser driven micro-explosion method. Side view confocal images of the void dots show that the void dots are almost spherical. The diameter of the void dots can be controlled by adjusting the laser power and exposure time. Three-dimensional (3D) structures, stacked in the [100] lattice direction, of diamond, FCC and BCC lattices have been fabricated, respectively. Multi-order stop gaps are observed for all three different types of structures. The suppression rate of the first order gap can be up to 70% for diamond and FCC structures. The angle dependence of the bandgap properties of a diamond structure reveals that the observed first order gap shifts to the longer wavelength whereas the second gap shifts to the shorter wavelength as the angle of incidence increases. Such a sensitive angular dependence of the bandgap structure may find applications in photonic crystal superprisms.

Micro-sized void spheres are successfully generated in a solid polymer by use of a tightly focused femtosecond laser beam from a high-repetition-rate laser oscillator. Confocal reflection images show that the void spheres are longitudinal rotational symmetric ellipsoids with a ratio of long to short axes of approximately 1.5. Layers of void spheres are then stacked to create three-dimensional diamond-lattice photonic crystals. Three gaps are observed in the [100] direction with a suppression rate of the second gap of up to approximately 75% for a 32-layer structure. The observed first- and second-order gaps shift to longer and shorter wavelengths, respectively, as the angle of incidence increases.

Photonic stop gaps of two-dimensional triangular photonic crystals fabricated by laser scanning of void channels in solid resin are examined in two different directions. Fundamental and higher-order gaps are observed in infrared transmission and infrared reflection.

5. Summary Previous work on the generation of voids inside transparent material by ultrashort pulsed light has solely been from a data storage point of view, where only single void bits were generated. Here we have presented void channels inside a bulk polymer material and have used them in the application of two and three-dimensional photonic crystal structures. This work involved the characterisation of the response of a specific polymer material, NOA63 optical adhesive to a scanned femtosecond pulsed high repetition rate light beam. The size of individual void channels as well as the overall structure of woodpile type photonic crystals was controlled accurately. The high degree of perfection of these photonic crystals allowed for the observation of the fundamental as well as higher-order stop gaps. The benefits of fabricating photonic crystals based on void channels are numerous. Unlike other techniques the time to fabricate a structure is on the order of minutes. Polymer shrinkage has no effect and wash out or other chemical post etching is not required, unless higher dielectric contrasts for complete bandgaps are desired. In conclusion, this method is a fast, one step, and highly accurate technique suitable to fabricate a large variety of photonic crystals and micro-devices in polymers.