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Ultrafast response of harmonic modelocked THz lasers
摘要： The use of fundamental modelocking to generate short terahertz (THz) pulses and THz frequency combs from semiconductor lasers has become a routine affair, using quantum cascade lasers (QCLs) as a gain medium. However, unlike classic laser diodes, no demonstrations of harmonic modelocking, active or passive, have been shown in THz QCLs, where multiple pulses per round trip are generated when the laser is modulated at the harmonics of the cavity’s fundamental round-trip frequency. Here, using time-resolved THz techniques, we show for the ?rst time harmonic injection and mode-locking in which THz QCLs are modulated at the harmonics of the round-trip frequency. We demonstrate the generation of the harmonic electrical beatnote within a QCL, its injection locking to an active modulation and its direct translation to harmonic pulse generation using the unique ultrafast nature of our approach. Finally, we show indications of self-starting harmonic emission, i.e., without external modulation, where the QCL operates exclusively on a harmonic (up to its 15th harmonic) of the round-trip frequency. This behaviour is supported by time-resolved simulations of induced gain and loss in the system and shows the importance of the electronic, as well as photonic, nature of QCLs. These results open up the prospect of passive harmonic modelocking and THz pulse generation, as well as the generation of low-noise microwave generation in the hundreds of GHz region.
关键词： harmonic modelocking,ultrafast response,THz QCLs,terahertz pulses,quantum cascade lasers
更新于2025-09-23 15:21:01
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Ultrafast Response Polyelectrolyte Humidity Sensor for Respiration Monitoring
摘要： Respiration monitoring is important for evaluating human health. Humidity sensing is a promising way to establish a relationship between human respiration and electrical signal. This work describes polymer humidity sensors with ultrafast response for respiration monitoring. The humidity-sensitive polyelectrolyte is in situ crosslinked on the substrate printed with interdigitated electrodes by a thiol-ene click reaction. The polyelectrolyte humidity sensor owns rapid water adsorption/desorption ability, excellent stability and repeatability. The sensor with ultrafast response and recovery (0.29 s/0.47 s) when changing humidity between 33% and 95% shows good application prospects in breath monitoring and touchless sensing. Different respiration patterns can be distinguished and the breath rate/depth of detection subjects can also be determined by the sensor. In addition, the obtained sensor can sense the skin evaporation by a non-contact way.
关键词： breath monitoring,in situ preparation,ultrafast response,click reaction,polyelectrolyte humidity sensors
更新于2025-09-19 17:15:36
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Ultrafast and broadband photodetectors based on a perovskite/organic bulk heterojunction for large-dynamic-range imaging
摘要： Organic-inorganic hybrid perovskite (OIHP) photodetectors that simultaneously achieve an ultrafast response and high sensitivity in the near-infrared (NIR) region are prerequisites for expanding current monitoring, imaging, and optical communication capabilities. Herein, we demonstrate photodetectors constructed by OIHP and an organic bulk heterojunction (BHJ) consisting of a low-bandgap nonfullerene and polymer, which achieve broadband response spectra up to 1 μm with a highest external quantum efficiency of approximately 54% at 850 nm, an ultrafast response speed of 5.6 ns and a linear dynamic range (LDR) of 191 dB. High sensitivity, ultrafast speed and a large LDR are preeminent prerequisites for the practical application of photodetectors. Encouragingly, due to the high-dynamic-range imaging capacity, high-quality visible-NIR actual imaging is achieved by employing the OIHP photodetectors. We believe that state-of-the-art OIHP photodetectors can accelerate the translation of solution-processed photodetector applications from the laboratory to the imaging market.
关键词： Organic-inorganic hybrid perovskite,ultrafast response,photodetectors,high-dynamic-range imaging,broadband response,near-infrared
更新于2025-09-19 17:13:59
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Ultrahigh Stability 3D TI Bi <sub/>2</sub> Se <sub/>3</sub> /MoO <sub/>3</sub> Thin Film Heterojunction Infrared Photodetector at Optical Communication Waveband
摘要： Infrared (IR) detection at 1300–1650 nm (optical communication waveband) is of great significance due to its wide range of applications in commerce and military. Three dimensional (3D) topological insulator (TI) Bi2Se3 is considered a promising candidate toward high-performance IR applications. Nevertheless, the IR devices based on Bi2Se3 thin films are rarely reported. Here, a 3D TI Bi2Se3/MoO3 thin film heterojunction photodetector is shown that possesses ultrahigh responsivity (Ri), external quantum efficiency (EQE), and detectivity (D*) in the broadband spectrum (405–1550 nm). The highest on–off ratio of the optimized device can reach up to 5.32 × 104. Ri, D*, and the EQE can reach 1.6 × 104 A W?1, 5.79 × 1011 cm2 Hz1/2 W?1, and 4.9 × 104% (@ 405 nm), respectively. Surprisingly, the Ri can achieve 2.61 × 103 A W?1 at an optical communication wavelength (@ 1310 nm) with a fast response time (63 μs), which is two orders of magnitude faster than that of other TIs-based devices. In addition, the device demonstrates brilliant long-term (>100 days) environmental stability under environmental conditions without any protective measures. Excellent device photoelectric properties illustrate that the 3D TI/inorganic heterojunction is an appropriate way for manufacturing high-performance photodetectors in the optical communication, military, and imaging fields.
关键词： photodetectors,Bi2Se3 thin films,infrared optical communication wavebands,heterojunction structures,ultrafast response times
更新于2025-09-16 10:30:52