A low temperature processable tin oxide interlayer via aminemodification for efficient and stable organic solar cells

The exploitation of proper electron transport layers(ETLs)and interface optimization can play a pivotal role to promote the performance of organic solar cells(OSCs).In this work,low temperature processable tin oxide(SnO_(2))colloidal nanoparticles with ethanolamine(EA)treatment are successfully employed for efficient and stable OSCs with light soaking free.The EA is chemically bonded with SnO_(2),and the ethanolamine treated tin oxide(E-SnO_(2))layer delivers a suitable work function of 4.10 eV and a unique surface texture with suspended polar moieties.The enhanced performance of E-SnO_(2) based OSCs can be attributed to the improved charge transport and electron extraction,which is correlated with the regulated energy level alignment and contact quality of E-SnO_(2)/active layer.As a result,considerable power conversion efficiencies(PCEs)of 10.30%,13.93%and 15.38%for PTB7-Th/PC_(71) BM,PM7/ITC6-4 F and PM6/Y6 based OSCs have been realized with E-SnO_(2) as ETL,respectively.Compared with ZnO based devices,the E-SnO_(2) based OSCs exhibit an improved light aging stability,which can retain 94.3%of their initial PCE of 15.38%after 100 h light aging for E-SnO_(2)/PM6/Y6 based OSCs.This work demonstrates that the enormous potential of E-SnO_(2) to serve as ETL for high-efficiency and stable OSCs.

An asymmetric A-D-π-A type non-fullerene acceptor enables high-detectivity near-infrared organic photodiodes

Narrow bandgap non-fullerene acceptors(NFAs)are relevant as key materials components for the fabrication of near-infrared(NIR)organic solar cells(OSCs)and organic photodiodes(OPDs)thanks to their complementary absorption,tunable energy levels,and enhanced stability.However,high-performance NIR photodetectors are still scarce due to the absence of narrow bandgap NFAs.Herein,an asymmetric A-D-π-A type NFA,named ABTPV-S,with a broad optical absorption approaching 1,000 nm is designed and synthesized through integrating alkylthio side chains and a vinyleneπ-bridge.The optimal inverted OPD device exhibits an excellent performance with a photoresponsivity of 0.39 AW-1,a noise current of 2.25×10^(-14)A Hz^(-0.5),a specific detectivity(D*)of 3.43×10^(12)Jones at 840 nm,and linear dynamic range(LDR)of 140 d B.In addition,the rise and fall times for ABTPV-S-based OPDs also reach 1.07 and 0.71μs,respectively.ABTPV-S-based OPDs exhibit a high D*over 1012Jones at 950 nm,which is a competitive result for the self-powered photodiode-type NIR OPDs.These findings highlight the outstanding potential of asymmetric A-D-π-A type NIR NFAs for high-performance OPDs competing with their silicon counterparts.

Mitigation of stimulated Raman scattering in a high-power fiber master oscillator power amplifier laser based on a dual-structure fiber grating

With the increasing power of fiber lasers,single chirped and tilted fiber Bragg gratings(CTFBGs)cannot completely mitigate continuously enhanced system-excited stimulated Raman scattering(SRS).Although improving the loss rate of a single CTFBG or cascading multiple CTFBGs can provide better suppression of the stronger SRS,excessive insertion loss may cause significant attenuation of the output power.Confronting the challenge,we firstly present an SRS mitigation method based on a dual-structure fiber grating in this paper.The dual-structure fiber grating comprises a CTFBG and a fiber Bragg grating structure,which were designed and fabricated on a passive 25/400 double-clad fiber.To evaluate the performance of the grating,a 3 kW fiber master oscillator power amplifier laser is established.The experimental results demonstrate that the SRS mitigation rate of the grating is greater than 30 dB(99.9%),whereas the insertion loss is only approximately 3%,thus allowing for minimal deterioration of the output power.This solves the contradiction between high suppression rate and high insertion loss faced by CTFBGs,which in turn makes dualstructure fiber gratings particularly suitable for mitigating SRS in 3-5 kW high-power fiber lasers.

Fabrication of kW-level chirped and tilted fiber Bragg gratings and filtering of stimulated Raman scattering in high-power CW oscillators

Suppression of stimulated Raman scattering(SRS)by means of chirped and tilted fiber Bragg gratings(CTFBGs)has become a key topic.However,research on high-power systems is still lacking due to two problems.Firstly,after the inscription,there are a large number of hydroxyl compounds and hydrogen molecules in CTFBGs that cause significant heating due to their strong infrared absorption.Secondly,CTFBGs can couple Stokes light from the core to the cladding and the coating,which causes serious heating in the coating of the CTFBG.Aimed at overcoming these bottlenecks,a process that combines constant-low-temperature and variable-high-temperature annealing is used to reduce the thermal slope of the CTFBG.Also,a segmented-corrosion cladding power stripping technology is used on the CTFBG to remove the Stokes light which is coupled to the cladding,which solves the problem of overheating in the coating of the CTFBG.Thereby,a CTFBG with both a kilowatt-level power-carrying load and the ability to suppress SRS in a fiber laser has been developed.Further,we establish a kW-level CW oscillator to test the CTFBG.Experimental results demonstrate that the power-carrying load of the CTFBG is close to 1 kW,the thermal slope is lower than 0.015 ℃/W,and the SRS suppression ratio is nearly 23 dB.

Alignment and efficiency-monitoring method of high-power fiber-to-fiber coupling

High-power fiber-to-fiber coupling is extensively used in fiber laser applications,and its performance is determined by coupling efficiency.We demonstrate a novel method for alignment and monitoring efficiency by detecting backscattering power at the fiber end cap.The relationship between alignment error and backscattering power is determined by simulations and experiments.Through this method,a state-of-the-art kW-level fiberto-fiber optic switch is developed(transmission efficiency>97%).It performs well for longer than 60 min.To the best of our knowledge,it is the first time to establish the mathematical model based on this method.Our results can provide guidance in high-power fiber-to-fiber coupling.

Utilizing phase-shifted long-period fiber grating to suppress spectral broadening of a high-power fiber MOPA laser system

Suppressing nonlinear effects in high-power fiber lasers based on fiber gratings has become a hotspot.At present,research is mainly focused on suppressing stimulated Raman scattering in a high-power fiber laser.However,the suppression of spectral broadening,caused by self-phase modulation or four-wave mixing,is still a challenging attribute to the close distance between the broadened laser and signal laser.If using a traditional fiber grating with only one stopband to suppress the spectral broadening,the signal power will be stripped simultaneously.Confronting this challenge,we propose a novel method based on phase-shifted long-period fiber grating(PS-LPFG)to suppress spectral broadening in a high-power fiber master oscillator power amplifier(MOPA)laser system in this paper.A PS-LPFG is designed and fabricated on 10/130 passive fiber utilizing a point-by-point scanning technique.The resonant wavelength of the fabricated PS-LPFG is 1080 nm,the full width at half maximum of the passband is 5.48 nm,and stopband extinction exceeds 90%.To evaluate the performance of the PS-LPFG,the grating is inserted into the seed of a kilowattlevel continuous-wave MOPA system.Experiment results show that the 30 dB linewidth of the output spectrum is narrowed by approximately 37.97%,providing an effective and flexible way for optimizing the output linewidth of highpower fiber MOPA laser systems.

Long-term variations of X-ray pulse profiles for the Crab pulsar:data analysis and modeling

The pulse profiles of the Crab pulsar(as well as some other pulsars)vary with time.They can lead to a major source of intrinsic timing noise,which lacks a detailed physical model.The phase separation?between the first left peak(P1)and the second right peak(P2)is a key parameter that shows the variations of pulse profiles for the Crab pulsar.It was found that the evolution of?has a tendency with increasing rates of 0.82?±0.25?,0.80?±0.54?,and 0.77?±0.28?per century for the 2-6,6-15,and15-60 ke V bands,respectively.Furthermore,the flux ratios(P2/P1)of X-ray pulse profiles in the three bands were calculated,and the derived flux ratios were consistent with the radio and X-ray measurements of the Insight-HXMT.In addition to discovering the physical origin of the pulse changes,the high-SNR X-ray pulse profiles were simulated in the annular gap model,and two model parameters(e.g.,the maximum emission heights of the two peaks)were observed to slightly affect the variations of peak separation.We fitted the long-term variations of emission heights of the two peaks and discovered that the emission heights showed increasing tendencies with time.Variations of these emission heights induced a characteristic period derivative,and a complete formula for both the magnetic dipole radiation and wind-particle-induced variations of the moment of inertia was used for the pulsar’s spin-down to obtain the variation rate˙αof the magnetic inclination angle,which was-1.60?per century.Intrinsic timing noise is observed to be mainly induced by the variations of pulse profiles,which might correlate with a characteristic spin period derivative arising from the fluctuations of the emission regions.This work will lay a foundation for understanding the origin of intrinsic timing noise and making high-precision timing models in the future.

Absolute surface form measurement of flat optics based on oblique incidence method

In this Letter, a test method based on oblique incidence is practically implemented in the interferometric measurement process. Three sets of wavefront data are achieved through cavity interference measurement with a Fizeau interferometer and one oblique incidence measurement. An iterative algorithm is applied to retrieve the absolute surface shape of the test flat. By adding two sets of measurements, the absolute surface error of the interferometer＇s reference flat can be obtained. The new method can not only calibrate the reference flat error of interferometer, but also provide the absolute measurement method for high precision optical components applied in high power laser systems.

Four-quadrant demodulation fiber sensor for wavelength monitoring of a wavelength phase-shifting interferometer

Real-time monitoring of wavelength is important for high-speed wavelength phase-shifting interferometry.In this paper,a wavelength sensor based on a polarization-maintaining fiber interferometer with four-quadrant demodulation was proposed.We built the wavelength sensing system with resolution better than 0.005 pm and 0.1 ms sampling interval and measured the response time of the tuned wavelength at 35 ms in the phase-shifting process of a commercial wavelength phase-shifting free-space interferometer,as well as the wavelength drift velocity of 0.01 pm per second in the hysteresis process.The optical fiber wavelength sensor with four-quadrant demodulation provides a real-time wavelength sensing scheme for high-speed wavelength phase-shifting interferometers.