Fiber cladding mode stripping device with high-power high-attenuation stripping capability and negligible perturbation to signal light has been developed by employing Teflon-capillary segmental-etching fabrication method. By using different etchant solutions, surface roughening and cladding reducing structures can be obtained. The influence of the roughened length on the attenuation of cladding power has been studied experimentally, showing that roughened surface strips cladding light well at length below 5 cm, but becomes less effective beyond that. The impact of the cladding reduction has also been investigated, indicating that reduced cladding can help deplete the cladding light effectively, and the attenuation is able to be improved from 23.0 dB to 43.2 dB by etching the cladding diameter from 400 μm to 50 μm. By combining the roughened surface and reduced cladding structures, cladding mode stripper with 7 °C/kW of temperature rising rate on the etched area has been made, and stripped power up to 2.1 kW at 39 dB of attenuation has been demonstrated, with the device length merely 16 cm. The maximum temperature on the device housing at full operation power for the case water flux being 3.1 L/min and 5.6 L/min is 67 °C and 50 °C, respectively. To the best of our knowledge, this is the first report of >2-kW power cladding mode stripping device with 39-dB attenuation. All results indicate the effectiveness of the proposed fabrication technique to make cladding mode stripping device for high power and superior beam quality fiber laser systems.
A large-scale flexible X-ray detector based on a perovskite p–n homojunction is reported in this work. The addition of a Bi 3+ -doped MAPbI 3 layer would effectively suppress the dark current and noise while maintaining high sensitivity.
To incorporate sufficient pump energy from multi-hundred watt-level 976 nm commercial laser diodes, a new kind of (8 + 1)-type pump-gain integrated functional laser ((8 + 1)-PIFL) fiber was fabricated by our newly optimized special fiber assembly and coating techniques for the first time. This (8 + 1)-PIFL fiber allowed for 10.66 kW aggregated pump power at 976 nm from six counter-pump ports in a master oscillator power amplifier laser setup and stably presented 8.72 kW laser output at 1079.4 nm with a high optical-to-optical efficiency of 81.0%. This is the highest power of the fiber amplifiers pumped by commercial laser diodes that has been reported so far, and only limited by the available pump power. Up to this power level, pure output spectrum with narrow 3 dB bandwidth Δλ3 dB of 2.76 nm and without any sign of stimulated Raman scattering and amplified spontaneous emission was obtained. Neither roll over of output power nor obvious thermal issue was observed with increased pump power, indirectly justifying strong photodarkening and transverse mode instability suppression. With another ten pump ports to collect more pump power, a further power scaling towards 10 kW or above can be expected.
The influence of fluorescence on the absorption measurement of Yb-doped double-clad fiber was studied. The results show that the 976 nm fluorescence leads to a linear but slight decrease of absorption coefficient at 976 nm.
Abstract Metal halide perovskites have recently emerged as exceptional scintillator materials for ionizing radiation detection devices. Their chemical composition consists of elements with high atomic numbers, leading them to have a high attenuation coefficient. Their high attenuation coefficient, in combination with their excellent optoelectronic properties, versatile chemical tunability, and facile and low‐cost fabrication processes, makes them the ideal scintillator material. However, existing perovskite‐based scintillators suffer from poor material stability, especially in humid atmospheres. Moreover, current perovskite films have morphologies that have been optimized for photovoltaics, which results in the relatively long charge carrier lifetimes, a property that is detrimental for fast scintillation. Furthermore, existing reports of perovskite‐based scintillators have shown limited spatial resolution due to poor light transmittance that arises from light scattering from large aggregates of perovskite grains. To address these issues, this work introduces a template‐assisted in situ polymerization‐based process to prepare perovskite/polymer composite scintillators that simultaneously reduces afterglow effects, improves perovskite stability, and is industrially scalable. The optimized perovskite scintillators are then incorporated into X‐ray detection devices to investigate detection performance and device stability. Compared with existing commercial scintillators, the perovskite scintillators show superior detection performance metrics for imaging, indicating the great potential of perovskites for next‐generation, large‐area, and flexible scintillation screens.
Narrowband photodetectors have wide application potential in high-resolution imaging and encrypted communication, due to their high-precision spectral resolution capability. In this work, we report a fast response, high spectral rejection ratio, and self-filtered ultranarrowband photodetector with a new mechanism, which introduces bulk recombination by doping Bi3+ and cooperates with surface recombination for further quenching photogenerated charges generated by short-wavelength-light excitation in perovskite single-crystal. A perovskite film focused on collecting charges is fabricated on the single crystal by a lattice-matched solution-processed epitaxial growth method. Due to the formation of PN heterojunctions, a narrowband photodetector in this mechanism has remarkable spectral selectivity and detection performance with an ultranarrow full width at half-maximum (FWHM) of 7.7 nm and a high spectral rejection ratio of 790, as well as a high specific detectivity up to 1.5 × 1010 Jones, a fast response speed with a rise time and fall time of ∼8 and 137 μs. The ultrafast and ultranarrow spectra response of self-filtered narrowband photodetector provides a new strategy in high-precision and high-resolution photoelectric detection.
CTFBGs with different center wavelengths are cascaded to broad the bandwidth to 20 nm (FWHM). The homemade duplexed CTFBG assists a 20.88 kW output of single fiber laser system with 18.6 dB of SRS suppression.
Abstract Substance discrimination beyond the shape feature is urgently desired for x‐ray imaging for enhancing target identification. With two x‐ray sources or stacked two detectors, the two‐energy‐channel x‐ray detection can discriminate substance density by normalizing the target thickness. Nevertheless, the artifacts, high radiation dose and difficulty in image alignment due to two sources or two detectors impede their widespread application. In this work, we report a single direct x‐ray detector with MAPbI 3 /MAPbBr 3 heterojunction for switchable soft x‐ray (<20 keV) and hard x‐ray (>20 keV) detection under one x‐ray source. Systematic characterizations confirm soft and hard x‐ray deposit their energy in MAPbI 3 and MAPbBr 3 layer, respectively, while working voltages can control the collection of generated charge carriers in each layer for selective soft/hard x‐ray detection. The switching rate between soft and hard x‐ray detection mode reaches 100 Hz. Moreover, the detector possesses a moderate performance with ~50 nGy s −1 in limit‐of‐detection, ~8000 μC Gy −1 cm −2 in sensitivity and ~7 lp/mm in imaging resolution. By defining the attenuation coefficient ratio ( 𝜇 L /𝜇 H ) as substance label, we effectively mitigate the influence of target thickness and successfully discriminate substances in the acquired x‐ray images. image
An optical resonator with a spiral-phase defect is proposed for vortex laser generation. Theoretical models and calculations were conducted to predict the topological charge distribution of the emitted vortex laser. Utilizing a reflective spatial light modulator that creates a spiral-phase defect of variable radius and azimuthal phase modulation, vortex beams with controllable topological charges and intensity distributions were demonstrated experimentally.
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