Compact efficient high-power continuous-wave Nd:YVO4/KGW/LBO Raman lasers for selectable wavelengths within 559-603†nm.

Compact efficient high-power continuous-wave Nd:YVO4 Raman lasers for selectable wavelengths within 559-603 nm are achieved by using KGW crystal for intracavity stimulated Raman scattering (SRS) and lithium triborate (LBO) crystal for intracavity sum frequency generation (SFG) and second harmonic generation (SHG). The LBO crystal with the cut angle in the XY plane for the type-I phase matching is used to perform intracavity SHG or SFG. Experimental results reveal that the participated Stokes lines include the internal vibration mode at 901 cm-1, the external vibrational mode at 209 cm-1, and the combination mode of the 901 cm-1 and 209 cm-1 Raman shifts. By tuning LBO temperature for attaining the maximum output power, the output spectrum reveals the triple peaks of 588.7, 595.7, and 603.1 nm with the intensity ratio of 10:4:1. Under this circumstance, the output power can reach the highest value of 10.8 W at a pump power of 40 W. Furthermore, the output spectrum can be simply concentrated on the single peaks among 588.7 (orange), 565.7 (yellow), and 559.1 nm (lime) by tuning LBO temperature to fulfill the selection of the critical phase matching. The output powers at a pump power of 40 W can be up to 8.0, 6.1, and 9.8 W for the single-peak emission at 588.7, 565.7, and 559.1 nm, respectively. Finally, a dual-peak emission of 565.7 and 572.3 nm with total output power of 5.2 W can be generated by tuning LBO temperature to match the SFG for 572.3 nm.

Highly efficient continuous-wave solid-state Raman crystal lasers at 555 and 559†nm.

High-power efficient continuous-wave Nd:YVO4/KGW Raman lasers at 555 and 559 nm are achieved by using a double-sided dichroic coating output coupler to improve the resonance quality factor. The Np-cut potassium gadolinium tungstate (KGW) is used to generate the Stokes waves at 1159 and 1177 nm by placing the polarization of the1064 nm fundamental wave parallel to the Ng and Nm axes, respectively. The lithium triborate (LBO) crystal with the cut angle in the XY plane for the type-I phase matching is used to perform the intracavity sum frequency generation for yielding the green light at 555 nm and the lime light at 559 nm at the optimal phase matching temperature. Experimental results were systematically accomplished to comprehend the optimal cavity length for the conversion efficiency. Under the optimal cavity length, the output powers can reach 6.6 and 6.3 W at a pump power of 22 W for the wavelengths of 555 and 559 nm, respectively. The conversion efficiencies can be up to 30% and 28.6% for 555 and 559 nm, respectively.

Compact continuous-wave solid-state Raman lasers at 707 and 714†nm for laser trapping and cooling of atomic strontium and radium.

Two compact laser sources at 707 and 714 nm are realized efficiently by using a diode-pumped a-cut Nd:YVO4 laser with intracavity stimulated Raman scattering and sum-frequency generation (SFG). The fundamental wave at 1342 nm is generated by the 4F3/2 → 4I13/2 transition in Nd:YVO4 crystal. The Raman Stokes waves at 1496 and 1526 nm were obtained by placing the c-axis of the Nd:YVO4 crystal along the Ng and Nm axes of an Np-cut KGW crystal, respectively. LBO crystals with critical phase matching are used to perform the intracavity SFG of fundamental and Stokes waves. At a pump power of 36 W, the maximum output powers at 707 and 714 nm can reach 2.72 and 3.14 W, corresponding to light-to-light conversion efficiencies of 7.5% and 8.7%, respectively. The developed 707 and 714 nm laser sources are practically useful in laser trapping and cooling related to atomic strontium and radium.

Highly efficient diode-pumped passively Q-switched Nd:YVO4/KGW Raman lasers at yellow and orange wavelengths.

Efficient diode-pumped passively Q-switched Nd:YVO4 yellow and orange lasers are developed with the pulse pumping scheme and the intracavity stimulated Raman scattering (SRS) and second harmonic generation (SHG). A Np-cut KGW is exploited in the SRS process to generate the yellow 579 nm laser or the orange 589 nm laser in a selectable way. The high efficiency is achieved by designing a compact resonator to include a coupled cavity for intracavity SRS and SHG and to provide a focused beam waist on the saturable absorber for reaching an excellent passive Q-switching. The output pulse energy and peak power can reach 0.08 mJ and 50 kW for the orange laser at 589 nm. On the other hand, the output pulse energy and peak power can be up to 0.10 mJ and 80 kW for the yellow laser at 579 nm.

Selectable two-wavelength Nd:YVO4 Raman laser at 671 and 714†nm.

A compact efficient continuous wave (CW) laser with selectable two wavelengths at 671 and 714 nm is developed. The laser cavity comprises an Nd-doped and an undoped YVO4 crystal to generate the fundamental wave at 1342 nm and the first-Stokes Raman wave at 1525 nm, respectively. A single LBO crystal with the cut angle in the XZ plane is designed to achieve the selectable phase-matching via the thermal tuning for the second harmonic generation (SHG) of 1342 nm and the sum frequency generation (SFG) of 1342 and 1525 nm. At a pump power of 40 W, the optimal output powers at 671 and 714 nm can reach 4.5 and 1.8 W, respectively. The present compact CW laser source at 671 and 714 nm has practical usefulness for laser spectroscopy and numerous applications.

Left ventricular hypertrophy detection using electrocardiographic signal.

Left ventricular hypertrophy (LVH) indicates subclinical organ damage, associating with the incidence of cardiovascular diseases. From the medical perspective, electrocardiogram (ECG) is a low-cost, non-invasive, and easily reproducible tool that is often used as a preliminary diagnosis for the detection of heart disease. Nowadays, there are many criteria for assessing LVH by ECG. These criteria usually include that voltage combination of RS peaks in multi-lead ECG must be greater than one or more thresholds for diagnosis. We developed a system for detecting LVH using ECG signals by two steps: firstly, the R-peak and S-valley amplitudes of the 12-lead ECG were extracted to automatically obtain a total of 24 features and ECG beats of each case (LVH or non-LVH) were segmented; secondly, a back propagation neural network (BPN) was trained using a dataset with these features. Echocardiography (ECHO) was used as the gold standard for diagnosing LVH. The number of LVH cases (of a Taiwanese population) identified was 173. As each ECG sequence generally included 8 to 13 cycles (heartbeats) due to differences in heart rate, etc., we identified 1466 ECG cycles of LVH patients after beat segmentation. Results showed that our BPN model for detecting LVH reached the testing accuracy, precision, sensitivity, and specificity of 0.961, 0.958, 0.966 and 0.956, respectively. Detection performances of our BPN model, on the whole, outperform 7 methods using ECG criteria and many ECG-based artificial intelligence (AI) models reported previously for detecting LVH.

Passivated Interfacial Traps of Monolayer MoS2 with Bipolar Electrical Pulse.

Heterogeneous integration of monolayers is an emergent route of spatially combining materials with available platforms for unprecedented properties. A long-standing challenge along this route is to manipulate interfacial configurations of each unit in stacking architecture. A monolayer of transition metal dichalcogenides (TMDs) offers an embodiment of studying interface engineering of integrated systems because optoelectronic performances generally trade off with each other due to interfacial trap states. While ultrahigh photoresponsivity of TMDs phototransistors has been realized, a long response time commonly appears and hinders applications. Here, fundamental processes in excitation and relaxation of the photoresponse are studied and correlated with interfacial traps of the monolayer MoS2. A mechanism for the onset of saturation photocurrent and the reset behavior in the monolayer photodetector is illustrated based on device performances. Electrostatic passivation of interfacial traps is achieved with the bipolar gate pulse and significantly reduces the response time for photocurrent to reach saturated states. This work paves the way toward fast-speed and ultrahigh-gain devices of stacked two-dimensional monolayers.

Taiwan axion search experiment with haloscope: Designs and operations.

We report on a holoscope axion search experiment near 19.6 µeV from the Taiwan Axion Search Experiment with Haloscope collaboration. This experiment is carried out via a frequency-tunable cavity detector with a volume V = 0.234 liter in a magnetic field B0 = 8 T. With a signal receiver that has a system noise temperature Tsys ≅ 2.2 K and an experiment time of about one month, the search excludes values of the axion-photon coupling constant gaγγ ≳ 8.1 × 10-14 GeV-1, a factor of 11 above the Kim-Shifman-Vainshtein-Zakharov benchmark model, at the 95% confidence level in the mass range of 19.4687-19.8436 µeV. We present the experimental setup and procedures to accomplish this search.

First Results from the Taiwan Axion Search Experiment with a Haloscope at 19.6 µeV.

This Letter reports on the first results from the Taiwan Axion Search Experiment with a Haloscope, a search for axions using a microwave cavity at frequencies between 4.707 50 and 4.798 15 GHz. Apart from the nonaxion signals, no candidates with a significance of more than 3.355 were found. The experiment excludes models with the axion-two-photon coupling |g_{aγγ}|≳8.1×10^{-14} GeV^{-1}, a factor of eleven above the benchmark Kim-Shifman-Vainshtein-Zakharov model, in the mass range 19.4687

Exploring the Origin of Maximum Entropy States Relevant to Resonant Modes in Modern Chladni Plates.

The resonant modes generated from the modern Chladni experiment are systematically confirmed to intimately correspond to the maximum entropy states obtained from the inhomogeneous Helmholtz equation for the square and equilateral triangle plates. To investigate the origin of maximum entropy states, the inhomogeneous Helmholtz equation is modified to consider the point interaction coming from the driving oscillator. The coupling strength associated with the point interaction is characterized by a dimensionless factor α. The δ potential of the point interaction is numerically modelled by a truncated basis with an upper index N. The asymptotic behavior for the upper index N is thoroughly explored to verify that the coupling strength of α = 1.0 can make the theoretical resonant modes agree excellently with the maximum entropy states as N→∞. It is further authenticated that nearly the same resonant modes can be obtained by using a larger coupling strength α when a smaller upper index N is exploited in the calculation.

Generation of virtual potentials by controlled feedback in electric circuit systems.

Electric circuits influenced by thermal noise are analogous to confined Brownian particles and can be an alternative and convenient scheme for studying stochastic thermodynamics. Here we experimentally demonstrate an effective technique of generating tunable potentials for Brownian dynamics in an electric circuit, realized by external controlled feedback. We present two illustrative examples of one-dimensional virtual potentials: static harmonic potential and time-varying double-well potential. The thermal noises of both cases undergo equivalent Brownian dynamics as if they were in the authentic potentials as long as the feedback is fast enough to respond to the designed potentials. The results show that the electric circuit provides a simple, effective, and programmable scheme to study the feedback-controlled virtual potential.

Autonomous Brownian gyrators: A study on gyrating characteristics.

We study the nonequilibrium steady-state (NESS) dynamics of two-dimensional Brownian gyrators under harmonic and nonharmonic potentials via computer simulations and analyses based on the Fokker-Planck equation, while our nonharmonic cases feature a double-well potential and an isotropic quartic potential. In particular, we report two simple methods that can help understand gyrating patterns. For harmonic potentials, we use the Fokker-Planck equation to survey the NESS dynamical characteristics; i.e., the NESS currents gyrate along the equiprobability contours and the stationary point of flow coincides with the potential minimum. As a contrast, the NESS results in our nonharmonic potentials show that these properties are largely absent, as the gyrating patterns are very distinct from those of corresponding probability distributions. Furthermore, we observe a critical case of the double-well potential, where the harmonic contribution to the gyrating pattern becomes absent, and the NESS currents do not circulate about the equiprobability contours near the potential minima even at low temperatures.

Selective Growth of WSe2 with Graphene Contacts.

Nanoelectronics of two-dimensional (2D) materials and related applications are hindered with critical contact issues with the semiconducting monolayers. To solve these issues, a fundamental challenge is selective and controllable fabrication of p-type or ambipolar transistors with a low Schottky barrier. Most p-type transistors are demonstrated with tungsten selenides (WSe2) but a high growth temperature is required. Here, we utilize seeding promoter and low pressure CVD process to enhance sequential WSe2 growth with a reduced growth temperature of 800 °C for reduced compositional fluctuations and high hetero-interface quality. Growth behavior of the sequential WSe2 growth at the edge of patterned graphene is discussed. With optimized growth conditions, high-quality interface of the laterally stitched WSe2-graphene is achieved and characterized with transmission electron microscopy (TEM). Device fabrication and electronic performances of the laterally stitched WSe2-graphene are presented.

Energy scale-up and mode-quality enhancement of the LED-pumped Nd:YAG Q-switched laser achieving a millijoule green pulse.

An efficient LED pumping module is explored for the demonstration of energy scaling of passively Q-switched output to millijoule high-pulse-energy level. For the free-running operation at fundamental wavelength, the highest optical conversion efficiency of 23.7% is reached. By using a Cr4+:YAG crystal as the saturable absorber, the passively Q-switched output energy is up to 14.5 mJ in a compact setup. The laser resonator is further optimized to shorten the output pulse width and to obtain better mode quality. The pulse width of the Q-switched emission is as short as 25 ns, and the peak power is up to 0.7 MW. With such a highly efficient configuration, the extracavity second-harmonic generation at 532 nm can be achieved with 4.5 mJ pulse energy.

Employing graphene acoustoelectric switch by dual surface acoustic wave transducers.

We implement a logic switch by using a graphene acoustoelectric transducer at room temperature. We operate two pairs of inter-digital transducers (IDTs) to launch surface acoustic waves (SAWs) on a LiNbO3 substrate and utilize graphene as a channel material to sustain acoustoelectric current Iae induced by SAWs. By cooperatively tuning the input power on the IDTs, we can manipulate the propagation direction of Iae such that the measured Iae can be deliberately controlled to be positive, negative, or even zero. We define the zero-crossing Iae as [Formula: see text], and then demonstrate that Iae can be switched with a ratio [Formula: see text] at a rate up to few tens kHz. Our device with an accessible operation scheme provides a means to convert incoming acoustic waves modulated by digitized data sequence onto electric signals with frequency band suitable for digital audio modulation. Consequently, it could potentially open a route for developing graphene-based logic devices in large-scale integration electronics.

Direct generation of red and orange optical vortex beams from an off-axis diode-pumped Pr3+:YLF laser.

We demonstrate the direct generation of visible vortex beams at 640 nm and 607 nm by employing an off-axis pumping scheme in a diode end-pumped Pr3+:YLF laser. A detailed numerical analysis, based on the coherent superposition of Hermite-Gaussian modes with different amplitudes and phases, is perfectly consistent with the experimentally observed lasing modes. The maximum vortex output powers have been measured to be 808 mW and 211 mW at a pump power of 3.16 W, for the wavelengths of 640 nm and 607 nm, respectively. We also demonstrate the handedness control of the generated vortex beam. Such a visible vortex laser can potentially be applied in super-resolution fluorescent microscopes and micro-fabrication research.

Exploring the DBR superlattice effect on the thermal performance of a VECSEL with the finite element method.

The design criterion of thermal conductivity for the GaAs/AlAs distributed Bragg reflector (DBR) superlattice structure was thoroughly investigated to precisely analyze the thermal behaviors of the optically pumped vertically external cavity surface-emitting laser (VECSEL). A finite element model with detailed configuration of a VECSEL gain chip was constructed to fulfill the analysis. A 1060 nm VECSEL with different pump conditions was further demonstrated to verify the finite element analysis. At the VECSEL thermal rollover point, the analysis results show that the model with the superlattice property predicts more precise temperature values than that using a bulk composite property. It reveals that the accurate determination of the thermal conductivity of the DBR superlattice is significantly important for the VECSEL thermal analysis.

Design of a Clinical Decision Support System for Predicting Erectile Dysfunction in Men Using NHIRD Dataset.

Erectile dysfunction (ED) affects millions of men worldwide. Men with ED generally complain failure to attain or maintain an adequate erection during sexual activity. The prevalence of ED is strongly correlated with age, affecting about 40% of men at age 40 and nearly 70% at age 70. A variety of chronic diseases, including diabetes, ischemic heart disease, congestive heart failure, hypertension, depression, chronic renal failure, obstructive sleep apnea, prostate disease, gout, and sleep disorder, were reported to be associated with ED. In this study, data retrieved from a subset of the National Health Insurance Research Database of Taiwan were used for designing the clinical decision support system (CDSS) for predicting ED incidences in men. The positive cases were male patients aged 20-65 who were diagnosed with ED between January 2000 and December 2010 confirmed by at least three outpatient visits or at least one inpatient visit, while the negative cases were randomly selected from the database without a history of ED and were frequency (1:1), age, and index year matched with the ED patients. Data of a total of 2832 ED patients and 2832 non-ED patients, each consisting of 41 features including index age, 10 comorbidities, and 30 other comorbidity-related variables, were retrieved for designing the predictive models. Integrated genetic algorithm and support vector machine was adopted to design the CDSSs with two experiments of independent training and testing (ITT) conducted to verify their effectiveness. In the 1st ITT experiment, data extracted from January 2000 till December 2005 (61.51%, 1742 positive cases and 1742 negative cases) were used for training and validating and the data retrieved from January 2006 till December 2010 were used for testing (38.49%), whereas in the 2nd ITT experiment, data in the training set (77.78%) were extracted from January 2000 till Deceber 2007 and those in the testing set (22.22%) were retrieved afterward. Tenfold cross validation and three different objective functions were adopted for obtaining the optimal models with best predictive performance in the training phase. The testing results show that the CDSSs achieved a predictive performance with accuracy, sensitivity, specificity, g-mean, and area under ROC curve of 74.72%-76.65%, 72.33%-83.76%, 69.54%-77.10%, 0.7468-0.7632, and 0.766-0.817, respectively. In conclusion, the CDSSs designed based on cost-sensitive objective functions as well as salient comorbidity-related features achieve satisfactory predictive performance for predicting ED incidences.

Narrowing spectral linewidth in passively mode-locked solid-state lasers.

A novel scheme to realize a mode-locked laser with a narrow spectral linewidth is demonstrated by exploiting a reflected Fabry-Perot (FP) cavity to introduce an intense FP effect. Stable continuous-wave mode-locked operation is achieved with the repetition rate of 48 MHz and the maximum average output power of 2.6 W under an incident pump power of 11.9 W. The mode-locked pulse width is systematically investigated by varying the optical thickness of the reflected FP cavity. The pulse duration is experimentally found to be in a range of 0.8 to 2.6 ns. The experimental results reveal that the reflected FP cavity is the key factor leading to the pulse generation in the nanosecond regime. This Letter is believed to provide a promising method for generating optical pulses with narrow spectral linewidths.