Interference filter-stabilized external cavity diode lasers(ECDLs) have properties of simple configurations, high stabilities, and narrow linewidths. However, the interference filter used in common ECDL designs requir...Interference filter-stabilized external cavity diode lasers(ECDLs) have properties of simple configurations, high stabilities, and narrow linewidths. However, the interference filter used in common ECDL designs requires an ultra-narrow bandwidth(about 0.3 nm) to achieve mode selection, that is considerably expensive and not yet available for a wide range of wavelengths. In this paper, a robust ECDL using an available broad bandwidth(about 4 nm) interference filter as the wavelength discriminator is constructed and tested. The ECDL demonstrated a narrow Lorentzian fitted linewidth of 95 kHz and a spectral purity of 2.9 MHz. The long-term frequency stability of the ECDL reaches 5.59×10^(-12).展开更多
Narrow linewidth light source is a prerequisite for high-performance coherent optical communication and sensing.Waveguide-based external cavity narrow linewidth semiconductor lasers(WEC-NLSLs)have become a competitive...Narrow linewidth light source is a prerequisite for high-performance coherent optical communication and sensing.Waveguide-based external cavity narrow linewidth semiconductor lasers(WEC-NLSLs)have become a competitive and attractive candidate for many coherent applications due to their small size,volume,low energy consumption,low cost and the ability to integrate with other optical components.In this paper,we present an overview of WEC-NLSLs from their required technologies to the state-of-the-art progress.Moreover,we highlight the common problems occurring to current WEC-NLSLs and show the possible approaches to resolving the issues.Finally,we present the possible development directions for the next phase and hope this review will be beneficial to the advancements of WEC-NLSLs.展开更多
Nonlinear spectroscopy has become a useful tool in laser cooling,frequency stabilization and so on.We use the 455.5 nm light beam output of an external cavity diode laser to perform the saturation spectroscopy signal ...Nonlinear spectroscopy has become a useful tool in laser cooling,frequency stabilization and so on.We use the 455.5 nm light beam output of an external cavity diode laser to perform the saturation spectroscopy signal and polarization spectroscopy signal on the 6S_(1/2)→7P3/2 transition in cesium.The measured linewidth of the F4→4,5 transition is as narrow as 1.40 MHz and that of the F3→2,3 transition is 1.67 MHz.Both of them are very close to the natural linewidth of about 1.2 MHz.Our result is the narrowest measured linewidth of Cs 455 nm saturation spectroscopy signal to our knowledge.展开更多
An experiment setup for narrow linewidth superradiant laser based on the mechanism of an active optical clock is proposed with optical lattice trapped 40 Ca.We obtain the threshold pumping rate analytically and deduce...An experiment setup for narrow linewidth superradiant laser based on the mechanism of an active optical clock is proposed with optical lattice trapped 40 Ca.We obtain the threshold pumping rate analytically and deduce the linewidth of the superradiant laser in a bad cavity regime.The proposed laser has an extremely narrow linewidth at millihertz level and a power level of order 10^(-9) W.展开更多
Objective:To explore the implementation of gastrointestinal endoscopy technology and endoscopic narrow-band imaging(NBI)in the early screening of gastric cancer and to observe and study their application effects.Metho...Objective:To explore the implementation of gastrointestinal endoscopy technology and endoscopic narrow-band imaging(NBI)in the early screening of gastric cancer and to observe and study their application effects.Methods:During the period from March 2023 to August 2023,312 patients who received gastroscopy in the Kunming Guandu District People’s Hospital were selected,and they underwent both conventional gastroscopy and endoscopic NBI,with clinicopathological tissue biopsy serving as the gold standard.The application value for early screening of gastric cancer was observed and analyzed.Results:The scoring data showed that the clarity of gastric mucosal glandular tube structure,microvascular structure clarity,and lesion contour scoring data of conventional gastroscopy were lower than those of the NBI technology(P<0.05).The screening rate of pathological biopsy in 312 patients was 18.59%(58 cases).Conventional gastroscopy showed a screening rate of 11.53%(36 cases),while NBI technology examined a screening rate of 17.63%(55 cases),and the two-by-two comparison of the screening rate data of the three groups was not statistically significant(P>0.05).The sensitivity,specificity,accuracy,positive predictive value,and negative predictive value of conventional gastroscopy appeared to be lower than those of NBI technology(P<0.05).Conclusion:In the early screening of gastric cancer,endoscopic NBI technology can be applied to patients.Compared with conventional gastroscopy,it provides a clearer visualization of the structure of the gastric mucosal glandular structure and microvascular structure,with a certain screening rate.Additionally,its sensitivity,specificity,accuracy,positive predictive value,and negative predictive value are higher,demonstrating outstanding effectiveness.展开更多
We report here a high-power, wavelength tunable and narrow linewidth 1.5 μm all-fiber laser amplifier based on a tunable diode laser and Er-Yb co-doped fibers. The laser wavelength can be precisely tuned from 1535 nm...We report here a high-power, wavelength tunable and narrow linewidth 1.5 μm all-fiber laser amplifier based on a tunable diode laser and Er-Yb co-doped fibers. The laser wavelength can be precisely tuned from 1535 nm to 1580 nm, which covers many absorption lines of mid-infrared laser gases, such as C2 H2, HCN, CO, and HI. The maximum laser power is >11 W, and the linewidth is about 200–300 MHz, which is close to the absorption linewidth of the above-mentioned gases. This work provides a suitable pump source for high-power wavelength tunable mid-infrared fiber gas lasers based on low-loss hollow-core fibers.展开更多
Optically pumped lasers based on solution-processed thin-film gain media have recently emerged as low-cost,broadly tunable,and versatile active photonics components that can fit any substrate and are useful for,e.g.,c...Optically pumped lasers based on solution-processed thin-film gain media have recently emerged as low-cost,broadly tunable,and versatile active photonics components that can fit any substrate and are useful for,e.g.,chemo-or biosensing or visible spectroscopy.Although single-mode operation has been demonstrated in various resonator architectures with a large variety of gain media-including dye-doped polymers,organic semiconductors,and,more recently,hybrid perovskites-the reported linewidths are typically on the order of a fraction of a nanometer or broader,i.e.,the coherence lengths are no longer than a few millimeters,which does not enable high-resolution spectroscopy or coherent sensing.The linewidth is fundamentally constrained by the short photon cavity lifetime in the standard resonator geometries.We demonstrate here a novel structure for an organic thin-film solid-state laser that is based on a vertical external cavity,wherein a holographic volume Bragg grating ensures both spectral selection and output coupling in an otherwise very compact(,cm3)design.Under short-pulse(0.4 ns)pumping,Fourier-transform-limited laser pulses are obtained,with a full width at half-maximum linewidth of 900 MHz(1.25 pm).Using 20-ns-long pump pulses,the linewidth can be further reduced to 200 MHz(0.26 pm),which is four times above the Fourier limit and corresponds to an unprecedented coherence length of 1m.The concept is potentially transferrable to any type of thin-film laser and can be ultimately made tunable;it also represents a very compact alternative to bulky grating systems in dye lasers.展开更多
We propose and demonstrate a novel single-longitudinal-mode(SLM) erbium-doped fiber laser(EDFL) capable of operating at fixed-wavelength lasing mode with a tunable range more than 54 nm, an ultra-narrow linewidth of 4...We propose and demonstrate a novel single-longitudinal-mode(SLM) erbium-doped fiber laser(EDFL) capable of operating at fixed-wavelength lasing mode with a tunable range more than 54 nm, an ultra-narrow linewidth of 473 Hz and an ultra-high optical signal-to-noise ratio(OSNR) more than 72 dB, or operating at wavelength-swept mode with tunable sweep rate of 10—200 Hz and a sweep range more than 50 nm. The excellent features mainly benefit from a triple-ring subring cavity constructed by three optical couplers nested one another and a fiber Fabry-Pérot tunable filter which can be driven by a constant voltage or a periodic sweep voltage for fixed or wavelength-swept operation, respectively. The proposed EDFL has potential applications in high-resolution spectroscopy and fiber optic sensing.展开更多
Yb-doped fiber laser(YDFL) is a promising kind of laser source due to high efficiency, excellent beam quality, robust configuration, diverse applications and so on. The progress of large-mode-area double cladding acti...Yb-doped fiber laser(YDFL) is a promising kind of laser source due to high efficiency, excellent beam quality, robust configuration, diverse applications and so on. The progress of large-mode-area double cladding active fiber and high power laser diodes have been continuously promoting the power scaling of the YDFLs. However, the further power scaling is blocked by some physic issues including nonlinear effect, thermal-induced mode instability(MI), optical damage and so forth. So, newlydesigned fibers with special structures are invented to address or relieve these limitations. The tapered fiber, which has changed mode area along its longitudinal direction, has been demonstrated to benefit suppressing the nonlinear effect, especially the stimulated Brillouin scattering(SBS) effect. In this paper, we will review the previous work done to explore the advantages of the tapered fiber for high power output, and then for the first time to our knowledge, demonstrate an all-fiberized high power narrow linewidth fiber laser based on a homemade tapered Yb-doped fiber(T-YDF). As a result, an output power of 260 W with a narrow linewidth of ~2 GHz is obtained, with SBS effectively suppressed owing to gradually increased mode area of the T-YDF as well as continuously changed Brillouin frequency shift dependent on the core diameter. Further power scaling is limited by MI, and the features of MI are studied in detail. It is pointed out that, the MI seems the primary and durative limitation factor of the tapered fiber amplifier for high power narrow linewidth output due to the gradually increased effective numerical aperture(NA) and the excitation of the high-order modes, even although it has the advantage to reduce other nonlinear effects. At last,worthwhile discussion about the optimization of the T-YDF and the whole fiber laser system for both SBS and MI suppression is conducted based on the previous and our results. It is concluded that the small diameter at the small-diameter end and low optical NA are preferred in the design of a T-YDF to ensure good beam quality and improve the MI threshold. The good splicing quality and proper coiling or bend state are also necessary.展开更多
We present a quantum-theoretical treatment of cavity linewidth narrowing with intracavity electromagnetically induced transparency(EIT). By means of intracavity EIT, the photons in the cavity are in the form of cavity...We present a quantum-theoretical treatment of cavity linewidth narrowing with intracavity electromagnetically induced transparency(EIT). By means of intracavity EIT, the photons in the cavity are in the form of cavity polaritons:bright-state polariton and dark-state polariton. Strong coupling of the bright-state polariton to the excited state induces an effect known as vacuum Rabi splitting, whereas the dark-state polariton decoupled from the excited state induces a narrow cavity transmission window. Our analysis would provide a quantum theory of linewidth narrowing with a quantum field pulse.展开更多
We investigate the resonance fluorescence spectrum of an atomic three-level ladder system driven by two laser fields.We show that such a system emulates to a large degree a V-type atom with parallel dipole moments-the...We investigate the resonance fluorescence spectrum of an atomic three-level ladder system driven by two laser fields.We show that such a system emulates to a large degree a V-type atom with parallel dipole moments-the latter being a system that exhibits spontaneously generated coherence and can display ultrasharp spectral lines.We find a suitable energy scheme in a 85Rb atom and experimentally observe the narrowing of the central peak in a rubidium atomic beam.The corresponding spectrum can convincingly demonstrate the existence of spontaneously generated coherence.展开更多
A novel configuration of the tunable fiber laser with uniform wavelength spacing in dense wavelength division multiplexing (DWDM) application is proposed.The ring type tunable fiber laser consists of an all-fiber comb...A novel configuration of the tunable fiber laser with uniform wavelength spacing in dense wavelength division multiplexing (DWDM) application is proposed.The ring type tunable fiber laser consists of an all-fiber comb filter which determines the wavelength spacing,and a piece of adjustable fiber grating to select the discrete lasing wavelength for DWDM application.The proposed all-fiber ring type tunable laser has potential application in the DWDM and other optical systems due to its advantages such as narrow linewidth,easy tuning,uniform wavelength interval,etc..展开更多
The output characteristics of a narrow linewidth, no-gain competition, dual-wavelength solid-state laser using an intra-cavity pumped method are reported. This system consists of an intra-cavity pumped Nd:YVO4 laser e...The output characteristics of a narrow linewidth, no-gain competition, dual-wavelength solid-state laser using an intra-cavity pumped method are reported. This system consists of an intra-cavity pumped Nd:YVO4 laser emitting at 1064 nm, using a 912 nm Nd:GdVO4 laser. A Fabry-Perot etalon is used to compress the linewidth that located at the common cavity of 912 nm and 1064 nm laser. Theoretical analysis and experimental verification were carried out. When the pump power is 32.8 W, the output of 912 nm and 1064 nm theoretical value is 0.036 W and 0.046 W, and the experimental value is 0.017 W and 0.016 W, respectively. The change trend of the theoretical simulated output power value was the same as the actual measured value in the experiment. In addition to this, the experimental measurement shows when the etalon with an angle of 15?, corresponding minimum linewidths were 0.284 nm and 0.627 nm, respectively.展开更多
A single-/dual-wavelength switchable and tunable erbium-doped fiber laser(EDFL) with super-narrow linewidth has been proposed and experimentally demonstrated at room temperature. The fiber laser is based on a compound...A single-/dual-wavelength switchable and tunable erbium-doped fiber laser(EDFL) with super-narrow linewidth has been proposed and experimentally demonstrated at room temperature. The fiber laser is based on a compound cavity simply composed of a ring main cavity and a two-ring subring cavity(TR-SC). Regardless of single- or dual-wavelength operation, the EDFL could always work well in single-longitudinal-mode(SLM) state at every oscillating wavelength. In dual-wavelength operation, the spacing could be tuned from 0 nm to 4.83 nm. In single-wavelength operation, the EDFL could lase at a fixed wavelength of 1 543.65 nm or another wavelength with a tunable range of 4.83 nm. The super-narrow linewidths of 550 Hz and 600 Hz for two wavelengths are obtained. The proposed EDFL has potential applications in microwave/terahertz-wave generation and high-precision distributed fiber optical sensing.展开更多
We propose a novel approach for generating a high-density,spatially periodic narrow electron beam comb(EBC)from a plasma grating induced by the interference of two intense laser pulses in subcritical-density plasma.We...We propose a novel approach for generating a high-density,spatially periodic narrow electron beam comb(EBC)from a plasma grating induced by the interference of two intense laser pulses in subcritical-density plasma.We employ particle-in-cell(PIC)simulations to investigate the effects of cross-propagating laser pulses with specific angles overlapping in a subcritical plasma.This overlap results in the formation of a transverse standing wave,leading to a spatially periodic high-density modulation known as a plasma grating.The electron density peak within the grating can reach several times the background plasma density.The charge imbalance between electrons and ions in the electron density peaks causes mutual repulsion among the electrons,resulting in Coulomb expansion and acceleration of the electrons.As a result,some electrons expand into vacuum,forming a periodic narrow EBC with an individual beam width in the nanoscale range.To further explore the formation of the nanoscale EBC,we conduct additional PIC simulations to study the dependence on various laser parameters.Overall,our proposed method offers a promising and controlled approach to generate tunable narrow EBCs with high density.展开更多
Narrow bipolar events(NBEs)are intriguing intra-cloud discharge that have attracted enormous interest in the lightning community.They come with two polarities that dominate at different altitudes in thunderclouds.The ...Narrow bipolar events(NBEs)are intriguing intra-cloud discharge that have attracted enormous interest in the lightning community.They come with two polarities that dominate at different altitudes in thunderclouds.The sources of negative NBEs are usually located near the top of thunderclouds;those of positive NBEs are at the middle levels.NBEs may occur at the onset of lightning.The electrical properties of NBEs remain poorly understood.We present here the first comparative study of the electrical characteristics of negative and positive NBEs.To derive electrical parameters from the fast electric field change waveforms of 1673 positive NBEs and 364 negative NBEs recorded by the Jianghuai Area Sferic Array(JASA)in China,we use an improved method based on the transmission line model.This approach concludes that negative NBEs occurring at high altitudes tend to produce a narrower current pulse and take a shorter time to traverse the channel than their positive counterparts.Moreover,compared to positive NBEs,a larger portion of negative NBEs are associated with slightly greater peak current moments but smaller overall charge moments.The differences reported herein between electrical properties of negative and positive NBEs suggest that charge distribution in NBE-producing thunderstorms tends to vary systematically with altitude.展开更多
Background: The burden of cataract and glaucoma has been increasing. Primary angle closure occurs as a result of crowded anterior segment anatomy causing appositional contact between peripheral iris and trabecular mes...Background: The burden of cataract and glaucoma has been increasing. Primary angle closure occurs as a result of crowded anterior segment anatomy causing appositional contact between peripheral iris and trabecular meshwork. Lens extraction has been proposed as a method of deepening anterior chamber and managing intraocular pressure. Purpose: To assess changes in anterior chamber depth after phacoemulsification with intraocular lens implantation in narrow angle eyes. Design: Prospective controlled trial (before-after) study. Method: The study was conducted from March 2015 to August 2017 among the patients of department of Ophthalmology of BSMMU who were diagnosed as cataract with narrow angles. Anterior chamber angle grading of 2 or less (Shaffer grading) in 3 or more quadrants was considered narrow angle (NA). The purposive type sampling technique was applied to collect sample from the study population, as per inclusion and exclusion criteria. Complete clinical evaluation including history, physical examination, relevant ocular examinations and systemic examinations were performed. In this prospective study, subjects underwent phacoemulsification with foldable lens implantation. A scan ultrasonography was performed preoperatively and 10<sup>th</sup> and 30<sup>th</sup> postoperative days of surgery. Results: Thirty eyes of 29 patients included in the study, male: female ratio was 1:1, with an overall mean age of 62.03 ± 8.95 years. The mean preoperative central ACD was 2.95 ± 0.35 mm. At 10<sup>th</sup> and 30<sup>th</sup> POD mean central ACD were 3.94 ± 0.32, and 3.92 ± 0.28 mm respectively. Mean of increase in central ACD at final follow-up was 0.96 mm (p Conclusion: Phacoemulsification with posterior chamber in bag lens implantation can deepen the anterior chamber depth in patients with narrow angles. Based on these findings, it is concluded that phacoemulsification with foldable intraocular lens implantation is an effective tool in deepening the anterior chamber.展开更多
Spectrally-selective photodetection plays a crucial role in various applications,including target imaging and environmental monitoring.Traditional deep-ultraviolet(DUV)narrowband photodetection systems consist of broa...Spectrally-selective photodetection plays a crucial role in various applications,including target imaging and environmental monitoring.Traditional deep-ultraviolet(DUV)narrowband photodetection systems consist of broadband photodetectors and filters,which complicates the architecture and constrains imaging quality.Here,we introduce an electronic-grade diamond single-crystal photodetector exhibiting an exceptionally narrow spectral response in the DUV range with a full width at half maximum of 8 nm.By examining diamond photodetectors with varying dislocation densities,we propose that mitigating the defect-induced trapping effect to achieve charge collection narrowing,assisted by free exciton radiative recombination,is an effective strategy for narrowband photodetection.The superior performance of this device is evidenced through the imaging of DUV light sources,showcasing its capability to differentiate between distinct light sources and monitor human-safe sterilization systems.Our findings underscore the promising potential applications of electronicgrade diamond in narrowband photodetection and offer a valuable technique for identifying electronic-grade diamond.展开更多
基金Project supported by the Foundation of Based Technology of China(Grant No.YXBGD20151JL01)the National Natural Science Foundation of China(Grant Nos.61376049,61604007,11674016,61378058,61575008,and 61574011)+1 种基金the Natural Science Foundation of Beijing City,China(Grant Nos.4172009 and4152003)the Beijing Municipal Commission of Education of China(Grant Nos.PXM2017 014204 500034 and PXM2016 014204 500018)
文摘Interference filter-stabilized external cavity diode lasers(ECDLs) have properties of simple configurations, high stabilities, and narrow linewidths. However, the interference filter used in common ECDL designs requires an ultra-narrow bandwidth(about 0.3 nm) to achieve mode selection, that is considerably expensive and not yet available for a wide range of wavelengths. In this paper, a robust ECDL using an available broad bandwidth(about 4 nm) interference filter as the wavelength discriminator is constructed and tested. The ECDL demonstrated a narrow Lorentzian fitted linewidth of 95 kHz and a spectral purity of 2.9 MHz. The long-term frequency stability of the ECDL reaches 5.59×10^(-12).
基金Jiangsu Province Key R&D Program(Industry Prospect and Common Key Technologies)(No.BE2014083)Jiangxi Natural Science Foundation Project(No.2019ACBL20054)。
文摘Narrow linewidth light source is a prerequisite for high-performance coherent optical communication and sensing.Waveguide-based external cavity narrow linewidth semiconductor lasers(WEC-NLSLs)have become a competitive and attractive candidate for many coherent applications due to their small size,volume,low energy consumption,low cost and the ability to integrate with other optical components.In this paper,we present an overview of WEC-NLSLs from their required technologies to the state-of-the-art progress.Moreover,we highlight the common problems occurring to current WEC-NLSLs and show the possible approaches to resolving the issues.Finally,we present the possible development directions for the next phase and hope this review will be beneficial to the advancements of WEC-NLSLs.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10874009 and 11074011.
文摘Nonlinear spectroscopy has become a useful tool in laser cooling,frequency stabilization and so on.We use the 455.5 nm light beam output of an external cavity diode laser to perform the saturation spectroscopy signal and polarization spectroscopy signal on the 6S_(1/2)→7P3/2 transition in cesium.The measured linewidth of the F4→4,5 transition is as narrow as 1.40 MHz and that of the F3→2,3 transition is 1.67 MHz.Both of them are very close to the natural linewidth of about 1.2 MHz.Our result is the narrowest measured linewidth of Cs 455 nm saturation spectroscopy signal to our knowledge.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10874009 and 11074011.
文摘An experiment setup for narrow linewidth superradiant laser based on the mechanism of an active optical clock is proposed with optical lattice trapped 40 Ca.We obtain the threshold pumping rate analytically and deduce the linewidth of the superradiant laser in a bad cavity regime.The proposed laser has an extremely narrow linewidth at millihertz level and a power level of order 10^(-9) W.
文摘Objective:To explore the implementation of gastrointestinal endoscopy technology and endoscopic narrow-band imaging(NBI)in the early screening of gastric cancer and to observe and study their application effects.Methods:During the period from March 2023 to August 2023,312 patients who received gastroscopy in the Kunming Guandu District People’s Hospital were selected,and they underwent both conventional gastroscopy and endoscopic NBI,with clinicopathological tissue biopsy serving as the gold standard.The application value for early screening of gastric cancer was observed and analyzed.Results:The scoring data showed that the clarity of gastric mucosal glandular tube structure,microvascular structure clarity,and lesion contour scoring data of conventional gastroscopy were lower than those of the NBI technology(P<0.05).The screening rate of pathological biopsy in 312 patients was 18.59%(58 cases).Conventional gastroscopy showed a screening rate of 11.53%(36 cases),while NBI technology examined a screening rate of 17.63%(55 cases),and the two-by-two comparison of the screening rate data of the three groups was not statistically significant(P>0.05).The sensitivity,specificity,accuracy,positive predictive value,and negative predictive value of conventional gastroscopy appeared to be lower than those of NBI technology(P<0.05).Conclusion:In the early screening of gastric cancer,endoscopic NBI technology can be applied to patients.Compared with conventional gastroscopy,it provides a clearer visualization of the structure of the gastric mucosal glandular structure and microvascular structure,with a certain screening rate.Additionally,its sensitivity,specificity,accuracy,positive predictive value,and negative predictive value are higher,demonstrating outstanding effectiveness.
基金supported by the National Natural Science Foundation of China(No.11274385)
文摘We report here a high-power, wavelength tunable and narrow linewidth 1.5 μm all-fiber laser amplifier based on a tunable diode laser and Er-Yb co-doped fibers. The laser wavelength can be precisely tuned from 1535 nm to 1580 nm, which covers many absorption lines of mid-infrared laser gases, such as C2 H2, HCN, CO, and HI. The maximum laser power is >11 W, and the linewidth is about 200–300 MHz, which is close to the absorption linewidth of the above-mentioned gases. This work provides a suitable pump source for high-power wavelength tunable mid-infrared fiber gas lasers based on low-loss hollow-core fibers.
基金the Agence Nationale de la Recherche(grant ANR-12-EMMA-0040‘‘Vecspresso’’project)the Region Ile de France(DIMNano’K)the LABEX SEAM for funding this work.
文摘Optically pumped lasers based on solution-processed thin-film gain media have recently emerged as low-cost,broadly tunable,and versatile active photonics components that can fit any substrate and are useful for,e.g.,chemo-or biosensing or visible spectroscopy.Although single-mode operation has been demonstrated in various resonator architectures with a large variety of gain media-including dye-doped polymers,organic semiconductors,and,more recently,hybrid perovskites-the reported linewidths are typically on the order of a fraction of a nanometer or broader,i.e.,the coherence lengths are no longer than a few millimeters,which does not enable high-resolution spectroscopy or coherent sensing.The linewidth is fundamentally constrained by the short photon cavity lifetime in the standard resonator geometries.We demonstrate here a novel structure for an organic thin-film solid-state laser that is based on a vertical external cavity,wherein a holographic volume Bragg grating ensures both spectral selection and output coupling in an otherwise very compact(,cm3)design.Under short-pulse(0.4 ns)pumping,Fourier-transform-limited laser pulses are obtained,with a full width at half-maximum linewidth of 900 MHz(1.25 pm).Using 20-ns-long pump pulses,the linewidth can be further reduced to 200 MHz(0.26 pm),which is four times above the Fourier limit and corresponds to an unprecedented coherence length of 1m.The concept is potentially transferrable to any type of thin-film laser and can be ultimately made tunable;it also represents a very compact alternative to bulky grating systems in dye lasers.
基金supported by the Natural Science Foundation of Hebei Province(No.F2016201023)the Technology Foundation for Selected Overseas Chinese Scholar of Ministry of Human Resources and Social Security of China(No.CG2015003006)the Advanced Talents Program of Hebei Educational Committee(No.GCC2014020)
文摘We propose and demonstrate a novel single-longitudinal-mode(SLM) erbium-doped fiber laser(EDFL) capable of operating at fixed-wavelength lasing mode with a tunable range more than 54 nm, an ultra-narrow linewidth of 473 Hz and an ultra-high optical signal-to-noise ratio(OSNR) more than 72 dB, or operating at wavelength-swept mode with tunable sweep rate of 10—200 Hz and a sweep range more than 50 nm. The excellent features mainly benefit from a triple-ring subring cavity constructed by three optical couplers nested one another and a fiber Fabry-Pérot tunable filter which can be driven by a constant voltage or a periodic sweep voltage for fixed or wavelength-swept operation, respectively. The proposed EDFL has potential applications in high-resolution spectroscopy and fiber optic sensing.
基金supported by the National Natural Science Foundation of China(Grant Nos.61322505 and 61705264)the Foundation for the Author of National Excellent Doctoral Dissertation of China(Grant No.201329)
文摘Yb-doped fiber laser(YDFL) is a promising kind of laser source due to high efficiency, excellent beam quality, robust configuration, diverse applications and so on. The progress of large-mode-area double cladding active fiber and high power laser diodes have been continuously promoting the power scaling of the YDFLs. However, the further power scaling is blocked by some physic issues including nonlinear effect, thermal-induced mode instability(MI), optical damage and so forth. So, newlydesigned fibers with special structures are invented to address or relieve these limitations. The tapered fiber, which has changed mode area along its longitudinal direction, has been demonstrated to benefit suppressing the nonlinear effect, especially the stimulated Brillouin scattering(SBS) effect. In this paper, we will review the previous work done to explore the advantages of the tapered fiber for high power output, and then for the first time to our knowledge, demonstrate an all-fiberized high power narrow linewidth fiber laser based on a homemade tapered Yb-doped fiber(T-YDF). As a result, an output power of 260 W with a narrow linewidth of ~2 GHz is obtained, with SBS effectively suppressed owing to gradually increased mode area of the T-YDF as well as continuously changed Brillouin frequency shift dependent on the core diameter. Further power scaling is limited by MI, and the features of MI are studied in detail. It is pointed out that, the MI seems the primary and durative limitation factor of the tapered fiber amplifier for high power narrow linewidth output due to the gradually increased effective numerical aperture(NA) and the excitation of the high-order modes, even although it has the advantage to reduce other nonlinear effects. At last,worthwhile discussion about the optimization of the T-YDF and the whole fiber laser system for both SBS and MI suppression is conducted based on the previous and our results. It is concluded that the small diameter at the small-diameter end and low optical NA are preferred in the design of a T-YDF to ensure good beam quality and improve the MI threshold. The good splicing quality and proper coiling or bend state are also necessary.
基金This work is supported by the International Science and Technology Cooperation Program of China （2012DFA10730） and Natural Science Foundation of China （61307101 and 61205083）.
基金supported by the National Natural Science Foundation of China(Grants Nos.11204080,11274112,91321101,and 61275215)the Fundamental Research Fund for the Central Universities of China(Grants No.WM1313003)
文摘We present a quantum-theoretical treatment of cavity linewidth narrowing with intracavity electromagnetically induced transparency(EIT). By means of intracavity EIT, the photons in the cavity are in the form of cavity polaritons:bright-state polariton and dark-state polariton. Strong coupling of the bright-state polariton to the excited state induces an effect known as vacuum Rabi splitting, whereas the dark-state polariton decoupled from the excited state induces a narrow cavity transmission window. Our analysis would provide a quantum theory of linewidth narrowing with a quantum field pulse.
基金Project supported by the National Basic Research Program of China (Grant No. 2011CB921603)the National Natural Science Foundation of China (Grant Nos. 11074097,10904048,10974071,and 11004080)
文摘We investigate the resonance fluorescence spectrum of an atomic three-level ladder system driven by two laser fields.We show that such a system emulates to a large degree a V-type atom with parallel dipole moments-the latter being a system that exhibits spontaneously generated coherence and can display ultrasharp spectral lines.We find a suitable energy scheme in a 85Rb atom and experimentally observe the narrowing of the central peak in a rubidium atomic beam.The corresponding spectrum can convincingly demonstrate the existence of spontaneously generated coherence.
基金The work was supported by the Foundation of the Backbone Teachers of the Ministry of Education of Chinathe Natural Science Foundation of Fujian Province (No.A0010004).
文摘A novel configuration of the tunable fiber laser with uniform wavelength spacing in dense wavelength division multiplexing (DWDM) application is proposed.The ring type tunable fiber laser consists of an all-fiber comb filter which determines the wavelength spacing,and a piece of adjustable fiber grating to select the discrete lasing wavelength for DWDM application.The proposed all-fiber ring type tunable laser has potential application in the DWDM and other optical systems due to its advantages such as narrow linewidth,easy tuning,uniform wavelength interval,etc..
文摘The output characteristics of a narrow linewidth, no-gain competition, dual-wavelength solid-state laser using an intra-cavity pumped method are reported. This system consists of an intra-cavity pumped Nd:YVO4 laser emitting at 1064 nm, using a 912 nm Nd:GdVO4 laser. A Fabry-Perot etalon is used to compress the linewidth that located at the common cavity of 912 nm and 1064 nm laser. Theoretical analysis and experimental verification were carried out. When the pump power is 32.8 W, the output of 912 nm and 1064 nm theoretical value is 0.036 W and 0.046 W, and the experimental value is 0.017 W and 0.016 W, respectively. The change trend of the theoretical simulated output power value was the same as the actual measured value in the experiment. In addition to this, the experimental measurement shows when the etalon with an angle of 15?, corresponding minimum linewidths were 0.284 nm and 0.627 nm, respectively.
基金supported by the Youth Foundation of Hebei Educational Committee(No.QN2015235)the Technology Foundation for Selected Overseas Chinese Scholar of Ministry of Human Resources and Social Security of China(No.CG2015003006)the Special Funding of Comprehensive Capability Enhancement Program from Hebei University
文摘A single-/dual-wavelength switchable and tunable erbium-doped fiber laser(EDFL) with super-narrow linewidth has been proposed and experimentally demonstrated at room temperature. The fiber laser is based on a compound cavity simply composed of a ring main cavity and a two-ring subring cavity(TR-SC). Regardless of single- or dual-wavelength operation, the EDFL could always work well in single-longitudinal-mode(SLM) state at every oscillating wavelength. In dual-wavelength operation, the spacing could be tuned from 0 nm to 4.83 nm. In single-wavelength operation, the EDFL could lase at a fixed wavelength of 1 543.65 nm or another wavelength with a tunable range of 4.83 nm. The super-narrow linewidths of 550 Hz and 600 Hz for two wavelengths are obtained. The proposed EDFL has potential applications in microwave/terahertz-wave generation and high-precision distributed fiber optical sensing.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.12174410,11991072,11991074,12225411,and 12105353)the CAS Project for Young Scientists in Basic Research(Grant No.YSBR060)the State Key Laboratory Program of the Chinese Ministry of Science and Technology,and the CAS Youth Innovation Promotion Association(Grant Nos.Y201952 and 2022242).
文摘We propose a novel approach for generating a high-density,spatially periodic narrow electron beam comb(EBC)from a plasma grating induced by the interference of two intense laser pulses in subcritical-density plasma.We employ particle-in-cell(PIC)simulations to investigate the effects of cross-propagating laser pulses with specific angles overlapping in a subcritical plasma.This overlap results in the formation of a transverse standing wave,leading to a spatially periodic high-density modulation known as a plasma grating.The electron density peak within the grating can reach several times the background plasma density.The charge imbalance between electrons and ions in the electron density peaks causes mutual repulsion among the electrons,resulting in Coulomb expansion and acceleration of the electrons.As a result,some electrons expand into vacuum,forming a periodic narrow EBC with an individual beam width in the nanoscale range.To further explore the formation of the nanoscale EBC,we conduct additional PIC simulations to study the dependence on various laser parameters.Overall,our proposed method offers a promising and controlled approach to generate tunable narrow EBCs with high density.
基金The authors would acknowledge financial support from the National Key Laboratory on Electromagnetic Environmental Effects and Electro-optical Engineering(NO.JCKYS2022LD6)the National Natural Science Foundation of China(42005068 and 42375074)+1 种基金the Project of Stable Support for Youth Team in Basic Research Field CAS(YSBR-018)the Joint Open Fund of Mengcheng National Geophysical Observatory(MENGO-202208).
文摘Narrow bipolar events(NBEs)are intriguing intra-cloud discharge that have attracted enormous interest in the lightning community.They come with two polarities that dominate at different altitudes in thunderclouds.The sources of negative NBEs are usually located near the top of thunderclouds;those of positive NBEs are at the middle levels.NBEs may occur at the onset of lightning.The electrical properties of NBEs remain poorly understood.We present here the first comparative study of the electrical characteristics of negative and positive NBEs.To derive electrical parameters from the fast electric field change waveforms of 1673 positive NBEs and 364 negative NBEs recorded by the Jianghuai Area Sferic Array(JASA)in China,we use an improved method based on the transmission line model.This approach concludes that negative NBEs occurring at high altitudes tend to produce a narrower current pulse and take a shorter time to traverse the channel than their positive counterparts.Moreover,compared to positive NBEs,a larger portion of negative NBEs are associated with slightly greater peak current moments but smaller overall charge moments.The differences reported herein between electrical properties of negative and positive NBEs suggest that charge distribution in NBE-producing thunderstorms tends to vary systematically with altitude.
文摘Background: The burden of cataract and glaucoma has been increasing. Primary angle closure occurs as a result of crowded anterior segment anatomy causing appositional contact between peripheral iris and trabecular meshwork. Lens extraction has been proposed as a method of deepening anterior chamber and managing intraocular pressure. Purpose: To assess changes in anterior chamber depth after phacoemulsification with intraocular lens implantation in narrow angle eyes. Design: Prospective controlled trial (before-after) study. Method: The study was conducted from March 2015 to August 2017 among the patients of department of Ophthalmology of BSMMU who were diagnosed as cataract with narrow angles. Anterior chamber angle grading of 2 or less (Shaffer grading) in 3 or more quadrants was considered narrow angle (NA). The purposive type sampling technique was applied to collect sample from the study population, as per inclusion and exclusion criteria. Complete clinical evaluation including history, physical examination, relevant ocular examinations and systemic examinations were performed. In this prospective study, subjects underwent phacoemulsification with foldable lens implantation. A scan ultrasonography was performed preoperatively and 10<sup>th</sup> and 30<sup>th</sup> postoperative days of surgery. Results: Thirty eyes of 29 patients included in the study, male: female ratio was 1:1, with an overall mean age of 62.03 ± 8.95 years. The mean preoperative central ACD was 2.95 ± 0.35 mm. At 10<sup>th</sup> and 30<sup>th</sup> POD mean central ACD were 3.94 ± 0.32, and 3.92 ± 0.28 mm respectively. Mean of increase in central ACD at final follow-up was 0.96 mm (p Conclusion: Phacoemulsification with posterior chamber in bag lens implantation can deepen the anterior chamber depth in patients with narrow angles. Based on these findings, it is concluded that phacoemulsification with foldable intraocular lens implantation is an effective tool in deepening the anterior chamber.
基金supports from Natural Science Foundation of Guangdong Province for Distinguished Young Scholars(Grant No.2021B1515020105).
文摘Spectrally-selective photodetection plays a crucial role in various applications,including target imaging and environmental monitoring.Traditional deep-ultraviolet(DUV)narrowband photodetection systems consist of broadband photodetectors and filters,which complicates the architecture and constrains imaging quality.Here,we introduce an electronic-grade diamond single-crystal photodetector exhibiting an exceptionally narrow spectral response in the DUV range with a full width at half maximum of 8 nm.By examining diamond photodetectors with varying dislocation densities,we propose that mitigating the defect-induced trapping effect to achieve charge collection narrowing,assisted by free exciton radiative recombination,is an effective strategy for narrowband photodetection.The superior performance of this device is evidenced through the imaging of DUV light sources,showcasing its capability to differentiate between distinct light sources and monitor human-safe sterilization systems.Our findings underscore the promising potential applications of electronicgrade diamond in narrowband photodetection and offer a valuable technique for identifying electronic-grade diamond.
