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Wei Chu

Publications and source records attributed to Wei Chu.

At least 109 records · Page 6Linked to original sources
arXiv2018

AliMe Assist: An Intelligent Assistant for Creating an Innovative E-commerce Experience

We present AliMe Assist, an intelligent assistant designed for creating an innovative online shopping experience in E-commerce. Based on question answering (QA), AliMe Assist offers assistance service, customer service, and chatting service. It is able to take voice and text input, incorporate context to QA, and support multi-round interaction. Currently, it serves millions of customer questions per day and is able to address 85% of them. In this paper, we demonstrate the system, present the underlying techniques, and share our experience in dealing with real-world QA in the E-commerce field.

cs.CL↗
arXiv2017

Centimeter-scale superfine three-dimensional printing with femtosecond laser two-photon polymerization

Nowadays three-dimensional (3D) printing has been widely used for producing geometrically complex 3D structures from a broad range of materials such as ceramics, metals, polymers, semiconductors, etc. Although it has been demonstrated that a fabrication resolution as high as ~100 nm can be achieved in 3D printing based on two photon polymerization (TPP), the end product size of TPP is typically on millimeter scale limited by the short working distance of high-numerical-aperture focal lens. Here we present a method based on simultaneous spatiotemporal focusing (SSTF) of the femtosecond laser pulses that enables to fabricate centimeter-scale 3D structures of fine features with TPP. We also demonstrate an isotropic spatial resolution which can be continuously tuned in the range of ~10 um and ~40 um by only varying the power of femtosecond laser, making this technique extremely flexible and easy to implement. We fabricate several Chinese guardian lions of a maximum height of 0.6 cm and a Terra Cotta Warrior of a height of 1.3 cm using this method.

physics.app-ph↗
arXiv2017

Modelling Domain Relationships for Transfer Learning on Retrieval-based Question Answering Systems in E-commerce

In this paper, we study transfer learning for the PI and NLI problems, aiming to propose a general framework, which can effectively and efficiently adapt the shared knowledge learned from a resource-rich source domain to a resource- poor target domain. Specifically, since most existing transfer learning methods only focus on learning a shared feature space across domains while ignoring the relationship between the source and target domains, we propose to simultaneously learn shared representations and domain relationships in a unified framework. Furthermore, we propose an efficient and effective hybrid model by combining a sentence encoding- based method and a sentence interaction-based method as our base model. Extensive experiments on both paraphrase identification and natural language inference demonstrate that our base model is efficient and has promising performance compared to the competing models, and our transfer learning method can help to significantly boost the performance. Further analysis shows that the inter-domain and intra-domain relationship captured by our model are insightful. Last but not least, we deploy our transfer learning model for PI into our online chatbot system, which can bring in significant improvements over our existing system. Finally, we launch our new system on the chatbot platform Eva in our E-commerce site AliExpress.

cs.CL↗
arXiv2017

Near-resonant Raman amplification in the rotational quantum wavepackets of nitrogen molecular ions generated by strong field ionization

Generation of laser-like narrow bandwidth emissions from nitrogen molecular ions generated in intense near- and mid-infrared femtosecond laser fields has aroused much interest because of the mysterious physics underlying such a phenomenon as well as the potential application of such an effect in atmospheric spectroscopic sensing. Here, we perform a pump-probe measurement on the nonlinear interaction of rotational quantum wavepackets of nitrogen molecular ions generated in mid-infrared (e.g., at a wavelength centered at 1580 nm) femtosecond laser fields with an ultrashort probe pulse whose broad spectrum overlaps both P- and R-branch rotational transition lines between the upper and lower electronic states. The results show that in the near-resonant conditions, stimulated Raman amplification can efficiently occur which converts the broad bandwidth ultrashort probe pulse into the narrow bandwidth laser-like beam. Our finding provides an insight into the physical mechanism of strong field induced lasing actions in atmospheric environment.

physics.optics↗
arXiv2017

PS-DBSCAN: An Efficient Parallel DBSCAN Algorithm Based on Platform Of AI (PAI)

We present PS-DBSCAN, a communication efficient parallel DBSCAN algorithm that combines the disjoint-set data structure and Parameter Server framework in Platform of AI (PAI). Since data points within the same cluster may be distributed over different workers which result in several disjoint-sets, merging them incurs large communication costs. In our algorithm, we employ a fast global union approach to union the disjoint-sets to alleviate the communication burden. Experiments over the datasets of different scales demonstrate that PS-DBSCAN outperforms the PDSDBSCAN with 2-10 times speedup on communication efficiency. We have released our PS-DBSCAN in an algorithm platform called Platform of AI (PAI - https://pai.base.shuju.aliyun.com/) in Alibaba Cloud. We have also demonstrated how to use the method in PAI.

cs.DB↗
arXiv2017

Generation of bright laser-like coherent emissions from nitrogen molecular ions in intense infrared laser fields: A unique quantum system for extreme nonlinear optics

We report on an investigation of simultaneous generation of several narrow-bandwidth laser-like coherent emissions from nitrogen molecular ions ( ) produced in intense mid-infrared laser fields. With systematic examinations on the dependences of coherent emissions on gas pressure as well as several laser parameters including laser intensity, polarization and wavelength of the pump laser pulses, we reveal that the multiple coherent emission lines generated in originate from a series of nonlinear processes beginning with four-wave mixing, followed with stimulated Raman scattering. Our analyses further show that the observed nonlinear processes are greatly enhanced at the resonant wavelengths, giving rise to high conversion efficiencies from the infrared pump laser pulses to the coherent emission lines near the transition wavelengths between the different vibrational energy levels of ground X and that of the excited B states.

physics.optics↗
arXiv2017

Metal surface structuring with spatiotemporally focused femtosecond laser pulses

Femtosecond laser micromachining provides high precision and less thermal diffusion in surface structuring as a result of the ultrashort temporal duration and ultrahigh peak intensity of the femtosecond laser pulses. To increase the throughput of surface patterning, the focal spot size can be expanded with loose focusing, which, however, could lead to nonlinear self-focusing of the pulses when the pulses propagate in air. We solve the problem by use of spatiotemporally focused femtosecond laser pulses for ablation of metal surfaces, which gives rise to improved surface quality as compared with that obtained with the conventional focusing scheme.

physics.optics↗
arXiv2016

Fabrication of polarization-independent waveguides deeply buried in crystal using aberration-corrected femtosecond laser direct writing

Writing optical waveguides with femtosecond laser pulses provides the capability of forming three-dimensional photonic circuits for manipulating light fields in both linear and nonlinear manners. To fully explore this potential, large depths of the buried waveguides in transparent substrates are often desirable to facilitate achieving vertical integration of waveguides in a multi-layer configuration, which, however, is hampered by rapidly degraded axial resolution caused by optical aberration. Here, we show that with the correction of the spherical aberration, polarization-independent waveguides can be inscribed in a nonlinear optical crystal lithium niobate (LN) at depths up to 1.4 mm, which is more than one order of magnitude deeper than the waveguides written with aberration uncorrected femtosecond laser pulses. Our technique is beneficial for applications ranging from miniaturized nonlinear light sources to quantum information processing.

physics.ins-det↗
arXiv2016

High-throughput in-volume processing in glass with isotropic spatial resolutions in three dimensions

We report on fabrication of three dimensional (3D) microstructures in glass with isotropic spatial resolutions. To achieve high throughput fabrication, we expand the focal spot size with a low-numerical-aperture lens, which naturally results in a degraded axial resolution. We solve the problem with simultaneous spatial temporal focusing which leads to an isotropic laser-affected volume with a spatial resolution of ~100 micron.

physics.optics↗
arXiv2016

Harmonic-seeded resonant Raman amplification in strong-field ionized nitrogen molecules

Generation of free-space laser-like emissions of high spatiotemporal coherence and narrow bandwidth in atmosphere opens promising opportunities for remote spectroscopic sensing. Here, we report on generation of such laser-like emissions, which results from the combined contributions of perturbative and non-perturbative nonlinear optical effects in nitrogen molecules exposed to intense mid-infrared laser fields. We systematically investigate the dependence of the generated free-space laser spectrum on wavelength and power of the driver laser. It is revealed that the free-space laser is produced by resonant Raman amplification of the fifth harmonic of the driver pulses in rotational wavepacket of the molecular nitrogen ions.

physics.optics↗
arXiv2016

Fabrication of polarization-independent single-mode waveguides in lithium niobate crystal with femtosecond laser pulses

We report on fabrication of depressed cladding optical waveguides buried in lithium niobate crystal with shaped femtosecond laser pulses. Depressed cladding waveguides of variable mode-field sizes are fabricated by forming the four sides of the cladding using a slit-beam shaping technique. We show that the waveguides fabricated by our technique allows single-mode propagation of the light polarized in both vertical and horizontal directions.

physics.optics↗
arXiv2016

Transverse writing of three-dimensional tubular optical waveguides in glass with slit-shaped femtosecond laser beams

We report on fabrication of tubular optical waveguides buried in ZBLAN glass based on transverse femtosecond laser direct writing. Irradiation in ZBLAN with focused femtosecond laser pulses leads to decrease of refractive index in the modified region. Tubular optical waveguides of variable mode areas are fabricated by forming the four sides of the cladding with slit-shaped femtosecond laser pulses, ensuring single mode waveguiding with a mode field dimension as small as ~ 4 μm.

physics.optics↗
arXiv2016

Speaker Cluster-Based Speaker Adaptive Training for Deep Neural Network Acoustic Modeling

A speaker cluster-based speaker adaptive training (SAT) method under deep neural network-hidden Markov model (DNN-HMM) framework is presented in this paper. During training, speakers that are acoustically adjacent to each other are hierarchically clustered using an i-vector based distance metric. DNNs with speaker dependent layers are then adaptively trained for each cluster of speakers. Before decoding starts, an unseen speaker in test set is matched to the closest speaker cluster through comparing i-vector based distances. The previously trained DNN of the matched speaker cluster is used for decoding utterances of the test speaker. The performance of the proposed method on a large vocabulary spontaneous speech recognition task is evaluated on a training set of with 1500 hours of speech, and a test set of 24 speakers with 1774 utterances. Comparing to a speaker independent DNN with a baseline word error rate of 11.6%, a relative 6.8% reduction in word error rate is observed from the proposed method.

cs.CL↗
arXiv2015

Generation of elliptically polarized nitrogen-ion laser fields using two-color femtosecond laser pulses

We experimentally investigate generation of molecular nitrogen-ion lasers with two femtosecond laser pulses at different wavelengths. The first pulse serves as the pump which ionizes the nitrogen molecules and excites the molecular ions to excited electronic states. The second pulse serves as the probe which leads to stimulated emission from the excited molecular ions. We observe that changing the angle between the polarization directions of the two pulses gives rise to elliptically polarized molecular nitrogen-ion laser fields, which is interpreted as a result of strong birefringence of the gain medium near the wavelengths of the molecular nitrogen-ion laser.

physics.optics↗
arXiv2015

Time-resolved shadowgraphs of transient plasma induced by spatiotemporally focused femtosecond laser pulses in fused silica glass

We report on experimental observations of formation and evolution of transient plasma produced in fused silica glass with spatiotemporally focused (STF) femtosecond laser pulses using a pump-probe shadow imaging technique. Surprisingly, the observation shows that the track of the plasma is significantly curved, which is attributed to an asymmetric density distribution of the transient plasma produced in the focal volume caused by the pulse front tilt of the STF laser field.

physics.optics↗
arXiv2015

Population Redistribution among Multiple Electronic States of Molecular Nitrogen Ions in Strong Laser Fields

We carry out a combined theoretical and experimental investigation on the population distributions in the ground and excited states of tunnel ionized N2 molecules at various driver wavelengths in the near- and mid-infrared range. Our results reveal that efficient couplings (i.e., population exchanges) between the ground state and the excited states occur in strong laser fields. The couplings result in the population inversion between the ground and the excited states at the wavelengths near 800 nm, which is verified by our experiment by observing the amplification of a seed at ~391 nm. The result provides insight into the mechanism of free-space nitrogen ion lasers generated in remote air with strong femtosecond laser pulses.

physics.optics↗
arXiv2015

Spatiotemporal focusing does not always improve axial intensity localization

We report on an experimental comparison on critical intensities of nonlinear self-focusing in air with conventional focusing and spatiotemporal focusing schemes. Our results show that the conventional focusing with the focal lens completely filled with the incident beam allows for the strongest axial intensity confinement against the self-focusing effect. This is because that in the high-numerical-aperture condition, the focal spot will have a compact size which results in a high focal intensity. Meanwhile, the Rayleigh length of the focused beam will be substantially shortened which efficiently postpones the onset of self-focusing.

physics.optics↗