96 research outputs found
Cryogenically cooled 2.8 μm Er:YAP laser with watt-level output power
No full text0000-0001-6930-0843We report the first watt-level, cryogenically cooled Er:YAP laser operating in the 3 μm spectral region. The spectroscopic properties of a 5 at% Er:YAP crystal were studied at cooling temperatures ranging from 77–290 K. The fluorescence lifetime of the 4I11/2 level associated with the 3 μm laser transition decreased with an increase in temperature; whereas, the lifetime of the 4I13/2 level increased with an increase in temperature. Moreover, over 1 W of output power at 2798 nm was achieved from the liquid-nitrogen-cooled Er:YAP laser with a slope efficiency of 20%, and the limitations to higher output power were discussed
Efficient diode-pumped Er:YAP master-oscillator power-amplifier system for laser power improvement at 2920 nm
No full text0000-0001-6465-2786We report on the first demonstration of laser-diode-pumped master-oscillator power-amplifier (MOPA) system based on Er-doped bulk material working at 2920 nm. The relaxation oscillation at the beginning of the laser pulse from the Er:YAlO3 (YAP) oscillator was suppressed effectively when the pump frequency was increased to 140 Hz, as a result of the establishment of a three-level system. In the amplifier, the small signal gain of the Er:YAP strongly depends on pump duration and repetition frequency, and can reach the upper limit of parasitic oscillation. Further, 25.5 mJ of output pulse energy has been achieved from the amplifier at 150 Hz frequency (2.2 ms pump duration), with over 32% of optical-to-optical efficiency. Further improvement of the amplification ability of the MOPA system was discussed.journal articl
High-efficiency, continuous-wave Fe:ZnSe mid-IR laser end pumped by an Er:YAP laser
No full text0000-0001-6930-0843Fe:ZnSe lasers operating in the mid-IR spectral region have gained widespread attention due to their numerous potential applications. This study presents a high-efficiency, continuous-wave Fe:ZnSe laser end pumped by an Er:YAP laser at 2920 nm. The Er:YAP laser was home-constructed and generated an output power of 3.6 W and an average slope efficiency of 36.6% with a good beam quality (M2 ≤ 2). The Fe:ZnSe laser produced a maximum output power of 1 W at 4.06 µm for 2.1 W of absorbed pump power, corresponding to an average slope efficiency of 48%. Theoretical modeling of the continuous-wave Fe:ZnSe laser is presented to determine the prospects for further power scaling.journal articl
Gait phase detection based on non-contact capacitive sensing: Preliminary results
No full textGait phase detection is essential to the control of lower-limb exoskeletons. In this paper, we present a non-contact capacitive sensing strategy for gait phase detection to replace foot pressure sensors. The designed capacitance sensing system can record signals of human muscle contraction from the leg. The electrodes are non-contact with the skin, which are fixed on the particularly designed cuffs. To evaluate the performance of the capacitance sensing on gait phase detection, two experiments are conducted on healthy subjects. With selected features and sliding window classification method, the proposed method obtains 98.3% average accuracy with the sensing cuff on the shank and 96.5% accuracy with the sensing cuff on the thigh for level walking tasks. The system also accurately recognizes the gait events (largest error rate smaller than 0.6%) when walking speed changes. The preliminary results indicate that the proposed sensing strategy is a promising solution to provide useful gait information for exoskeleton control
3-Dimensional hollow graphene balls for voltammetric sensing of levodopa in the presence of uric acid
No full textThe development of novel nanomaterials brings new opportunity and challenge for high sensing detection of biomolecules. The authors describe the preparation of 3-dimentional hollow graphene balls (3D HGBs) using nickel nanoparticles (Ni-NPs) as the template. The Ni-NPs were synthesized by chemical reduction of nickel chloride and then graphene was coated onto their surface via carburization and carbonization. After etching Ni-NPs, 3D HGBs with few layers and a typical size of 100 nm were obtained. They were sprayed onto indium tin oxide glass to obtain a working electrode for electrochemical determination of levodopa in the presence of uric acid. Due to the unique hollow porous structure of the 3D HGBs, the electrode exhibits a sensitivity of 0.69 mu A.mu M-1.cm(-2) and a 1 mu M limit of detection. It is selective, reproducible and stable. It was applied to the determination of levodopa in spiked human plasma samples and it is of potential use in clinical research.
Fabrication of tungsten-based optical diffuser using fiberform nanostructure via efficient plasma route
No full text0000-0001-8616-6041Optical diffusion is an essential process used to manage photons in a wide range of photoelectric systems. This work proposes an approach to fabricate novel optical diffusers by a plasma-processing technique, using fiberform nanostructures formed by helium plasma irradiation and subsequent annealing. After an annealing procedure in the air for oxidation, the optical properties and the light-diffusing abilities of these nanostructured thin films were studied. In addition to the morphology analysis and total transmittance measurement, the diffusion efficiency of the optical diffusers was analyzed using a transmitted scatter distribution function (TDF). It was revealed that the diffusion efficiency of a device with an irradiation time of 30 minutes could reach 97%. The results demonstrate the potential of these nanostructured optical diffusers for various photoelectric applications.journal articl
Development of high-performance mid-infrared laser sources for isotope detection applications
No full text総合研究大学院大学博士（学術）application/pdf総研大甲第2444号doctoral thesi
Electro-optically Q-switched operation of a high-peak-power Tb:LiYF4 green laser
No full textWe report on an electro-optically Q-switched Tb:LiYF4 green laser pumped by a frequency-doubled optically pumped semiconductor blue laser. The electro-optically Q-switched characteristics were studied under a wide range of repetition rates from 200 Hz to 50 kHz using a KD2PO4 Q-switch. Up to 198 µJ of pulse energy was obtained with a pulse width of 248 ns at a repetition rate of 200 Hz, corresponding to a peak power of 797 W at 544 nm.journal articl
A Locomotion Intent Prediction System Based on Multi-Sensor Fusion
No full textLocomotion intent prediction is essential for the control of powered lower-limb prostheses to realize smooth locomotion transitions. In this research, we develop a multi-sensor fusion based locomotion intent prediction system, which can recognize current locomotion mode and detect locomotion transitions in advance. Seven able-bodied subjects were recruited for this research. Signals from two foot pressure insoles and three inertial measurement units (one on the thigh, one on the shank and the other on the foot) are measured. A two-level recognition strategy is used for the recognition with linear discriminate classifier. Six kinds of locomotion modes and ten kinds of locomotion transitions are tested in this study. Recognition accuracy during steady locomotion periods (i.e., no locomotion transitions) is 99.71% ± 0.05% for seven able-bodied subjects. During locomotion transition periods, all the transitions are correctly detected and most of them can be detected before transiting to new locomotion modes. No significant deterioration in recognition performance is observed in the following five hours after the system is trained, and small number of experiment trials are required to train reliable classifiers
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