Wearing masks has been a recommended protective measure due to the risks of coronavirus disease 2019 (COVID-19) even in its coming endemic phase. Therefore, deploying a "smart mask" to monitor human physiological signals is highly beneficial for personal and public health. This work presents a smart mask integrating an ultrathin nanocomposite sponge structure-based soundwave sensor (≈400 μm), which allows the high sensitivity in a wide-bandwidth dynamic pressure range, i.e., capable of detecting various respiratory sounds of breathing, speaking, and coughing. Thirty-one subjects test the smart mask in recording their respiratory activities. Machine/deep learning methods, i.e., support vector machine and convolutional neural networks, are used to recognize these activities, which show average macro-recalls of ≈95% in both individual and generalized models. With rich high-frequency (≈4000 Hz) information recorded, the two-/tri-phase coughs can be mapped while speaking words can be identified, demonstrating that the smart mask can be applicable as a daily wearable Internet of Things (IoT) device for respiratory disease identification, voice interaction tool, etc. in the future. This work bridges the technological gap between ultra-lightweight but high-frequency response sensor material fabrication, signal transduction and processing, and machining/deep learning to demonstrate a wearable device for potential applications in continual health monitoring in daily life.
Received Month X, XXXX; revised Month X, XXXX; accepted Month X, XXXX; posted Month X, XXXX (Doc. ID XXXXX); published Month X, XXXXWe demonstrate the generation of high-energy, mid-IR, picosecond pulses in a high-harmonic-cavity optical parametric oscillator (OPO) that has a relatively compact cavity with a length that is a small fraction of that required to match the pump repetition rate. The OPO, based on an MgO-doped periodically poled LiNbO 3 crystal, is pumped by a fiber master-oscillatorpower-amplifier system employing direct amplification and delivering 11 μJ, 150 ps pulses at 1035 nm. For a 1.554-m long OPO cavity, resonating near-infrared signal pulses with a repetition rate that is the 193rd harmonic of the 1 MHz pump are demonstrated. The mid-infrared idler output pulses, tunable from 2300nm to 3500nm, are generated at a 1 MHz repetition rate and have energies as high as 1. Tunable sources of short pulses in the mid-infrared (mid-IR) are useful for a number of applications, as this part of the spectrum corresponds to characteristic vibrational absorptions of organic materials [1,2]. In particular, short pulses with μJ-level energies in the mid-IR are interesting for organic material processing techniques such as resonant infrared pulsed laser deposition (RIR-PLD) [3,4]. Optical parametric generators (OPGs) are commonly used to generate high-energy pulses in the mid-IR, taking advantage of low-repetition rate, high-energy pump sources and high-nonlinearity crystals [5][6][7]. However, OPGs have a broad spectral output that limits their range of potential applications. Injection-seeded optical parametric amplifiers (OPAs) can effectively reduce the spectral bandwidth, but in order to generate widely tunable mid-IR pulses, tunable seed laser sources are required [8][9][10]. On the other hand, synchronously pumped optical parametric oscillators (OPOs) are attractive, due to their good efficiency and wide tunability, but pumping with the low repetition rate sources required for high pulse energies would normally demand very long cavity lengths to match the condition for synchronous pumping. Ultrashort pulses with energies as high as 0.65 μJ in the near-IR and 0.19 μJ in the mid-IR have been reported from low-repetition (<20 MHz) OPOs using either relay-imaging and cavity-dumping in a free-space resonator, or by employing an intracavity feedback optical fiber to take up most of the required cavity length [11][12][13].In this letter we describe the use of a harmonic cavity as an alternative route to utilizing high-energy, lowrepetition rate pump sources whilst maintaining a compact overall design, as the cavity length is set to be a small but exact fraction of that required for true synchronous pumping. Previous work has concentrated on the use of such cavities to generate high-repetition-rate short pulses at the signal wavelength in femtosecond (fs) OPOs up to 1 GHz [14][15][16]. In addition, for picosecond (ps) OPOs with an extended-cavity, in which the ratio of pump cavity length and the OPO cavity lengt...
We report a compact, stable, gain-switched-diode-seeded master oscillator power amplifier (MOPA), employing direct amplification via conventional Yb(3+)-doped fibers, to generate picosecond pulses with energy of 17.7 μJ and 97-W average output power (excluding amplified spontaneous emission) at 5.47-MHz repetition frequency in a diffraction-limited and single-polarization beam. A maximum peak power of 197 kW is demonstrated. Such a high-energy, high-power, MHz, picosecond MOPA is of great interest for high-throughput material processing. With 13.8-μJ pulse energy confined in the 0.87-nm 3-dB spectral bandwidth, this MOPA is also a promising source for nonlinear frequency conversion to generate high-energy pulses in other spectral regions. We have explored the pulse energy scaling until the stimulated Raman Scattering (SRS) becomes significant (i.e. spectral peak intensity exceeds 1% of that of the signal).
Abstract:We report a high-energy picosecond optical parametric generator/amplifier (OPG/A) based on a MgO:PPLN crystal pumped by a fiber master-oscillator-power-amplifier (MOPA) employing direct amplification. An OPG tuning range of 1450-3615 nm is demonstrated with pulse energies as high as 2.6 μJ (signal) and 1.2 μJ (idler). When seeded with a ~100 MHz linewidth diode laser, damage-limited pulse energies of 3.1 μJ (signal) and 1.3 μJ (idler) have been achieved and the signal pulse time-bandwidth product is improved to ~2 times transformlimited. When seeded with a 0.3 nm-bandwidth filtered amplified spontaneous emission source, crystal damage is avoided and maximum pulse energies of 3.8 μJ (signal) and 1.7 μJ (idler) are obtained at an overall conversion efficiency of 45%.
Abstract-We report supercontinuum generation using a mode-locked VECSEL emitting 400-fs pulses at a 3-GHz repetition rate, amplified with a cascaded ytterbium-doped fiber amplifier system up to 40 W of average power. The pulses were then recompressed to their original duration via a high throughput transmission grating compressor, and used to generate supercontinuum in two samples of photonic crystal fiber (PCF); an all-normal dispersion PCF, and a PCF with a zero dispersion wavelength of 1040 nm, creating 20 dB spectral bandwidths of 200 nm and 280 nm respectively.
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