Mid-infrared pulsed Er:ZBLAN fiber laser producing mode-switchable cylindrical vector beams.

We demonstrate the generation of both continuous-wave (CW) and Q-switched cylindrical vector beams (CVBs) from a mid-infrared Er3+-doped ZBLAN (Er:ZBLAN) fiber laser at ∼ 2.8 µm. A customized S-waveplate is incorporated as the intracavity mode converter to achieve the mid-infrared CVBs. Switchable modes of CVBs between the radially and azimuthally polarized beam can be realized easily by manipulating the cavity conditions. A maximum output power of ∼250 mW is achieved for the CW CVBs. In the short-pulsed CVBs operation regime, both the active and passive Q-switching modes are realized with a pulse duration of hundreds of nanoseconds. The proposed mid-infrared cylindrical vector lasers can have significant potential for applications in biomedicine, optical trapping, material processing and optical communication.

Electrocleavage Synthesis of Solution-Processed, Imine-Linked, and Crystalline Covalent Organic Framework Thin Films.

Developing a general, facile, and direct strategy for synthesizing thin films of covalent organic frameworks (COFs) is a major challenge in this field. Herein, we report an unprecedented electrocleavage synthesis strategy to produce imine-linked COF films directly on electrodes from electrolyte solutions at room temperature. This strategy enables the cathodic exfoliation of the COF powders to nanosheets by electrochemical reduction and protonation, followed by nanosheets migrating to the anode and reproducing the COF structures by anodic oxidation. Our method is adaptable with most imine-linked COFs by virtue of the low redox potential of the imine bonds, whereas the COF films possess high crystallinity and hierarchical porosity. We highlight these COF films as a superb platform for promoting mass transfer by demonstrating their extraordinarily rapid iodine adsorption with record-high rate constants.

60.4 W continuous-wave single-frequency laser output from a two-stage Nd:YAG single-crystal fiber amplifier.

A Nd:YAG single-crystal fiber amplifier for the amplification of continuous-wave single-frequency laser end-pumped by a laser diode (LD) is investigated. With a two-stage amplification configuration, an output power of 60.4 W under the total incident pump power of 200 W is achieved, which is, to our knowledge, the highest power from a continuous-wave single-frequency laser achieved with a single-crystal fiber scheme. The extraction efficiency reaches 41.6% in the second amplification stage, which is comparable with Innoslab amplifiers. The beam quality factors M2 at the maximum output power in the horizontal and vertical direction are measured to be 1.51 and 1.38, respectively. The long-term power instability for 1 hour is 0.97%.

High-power and high-efficiency short wavelength operation of a Tm:YLF laser at 1.83 µm.

A high-power and high-efficiency diode-end-pumped Tm:YLF laser at 1.83 µm is demonstrated for the first time, to our best knowledge. To make the laser operate at 1.83 µm, a simple way of controlling the transmittance of the output coupler is used, and the criteria of the transmittance of the output coupler at the emission peaks of Tm:YLF are theoretically analyzed, which are verified by experimental results. Based on the theoretical analysis, laser oscillation at only 1.83 µm is realized. Maximum output power at 1833 nm is 8.5 W with corresponding slope efficiency of 53.4% regarding absorbed pump power. In addition, tunability of this laser from 1827 nm to 1837 nm is obtained. Laser beam quality at 1833 nm is measured to be 1.4 at maximum output power. The achieved laser performance represents considerable improvement compared to any other bulk laser emitting around 1.83 µm.

Compact passively Q-switched RbTiOPO4 cascaded Raman operation.

Compact passively Q-switched RbTiOPO4 cascaded Raman laser operation has been investigated for the first time, to our knowledge. A Nd:YAG/Cr4+:YAG composite crystal was adopted for passively Q-switched fundamental laser generation. 440 mW multi-Stokes laser output with X(ZZ)X configuration according to the Porto notations was achieved under the incident pump power of 10 W. The measured spectra contained three wavelengths of 1149, 1165, and 1185 nm based on the Raman shift of 271 and 687 cm-1. Different from actively Q-switch cascaded Raman laser with Stokes wave from low order to high order oscillating in sequence, three intensity lines were output for the whole experiment in this passively Q-switched multi-Stokes laser. The output spectra could be varied and optimized based on the output coupler coating design. Output spectra not sensitive to incident pump power for passively Q-switched cascaded Raman laser have advantages in multiwavelength laser applications.

Efficient 1.7 µm light source based on KTA-OPO derived by Nd:YVO4 self-Raman laser.

An intra-cavity optical parametric oscillator (OPO) emitting at 1.7 µm derived by Nd:YVO4 self-Raman laser is demonstrated in this Letter, with a KTiOAsO4 (KTA) crystal used as nonlinear optical crystal. A laser diode end-pumped acousto-optic Q-switched Nd:YVO4 self-Raman laser at 1176 nm was employed as the pump source. At an incident pump power of 12.1 W and a pulse repetition frequency of 60 kHz, average output power up to 1.2 W signal light at 1742 nm was obtained, with diode-to-signal conversion efficiency of 10%. The pulse width was about 11 ns and spectral line width was less than 0.5 nm for the signal light. The results show that compact intra-cavity KTA-OPO derived by Nd:YVO4 self-Raman laser is an efficient method for 1.7 µm waveband laser generation, with potential applications in biological imaging, laser therapy, special materials processing, etc.

Propagation dynamics of super-Gaussian beams in fractional Schrödinger equation: from linear to nonlinear regimes.

We have investigated the propagation dynamics of super-Gaussian optical beams in fractional Schrödinger equation. We have identified the difference between the propagation dynamics of super-Gaussian beams and that of Gaussian beams. We show that, the linear propagation dynamics of the super-Gaussian beams with order m > 1 undergo an initial compression phase before they split into two sub-beams. The sub-beams with saddle shape separate each other and their interval increases linearly with propagation distance. In the nonlinear regime, the super-Gaussian beams evolve to become a single soliton, breathing soliton or soliton pair depending on the order of super-Gaussian beams, nonlinearity, as well as the Lévy index. In two dimensions, the linear evolution of super-Gaussian beams is similar to that for one dimension case, but the initial compression of the input super-Gaussian beams and the diffraction of the splitting beams are much stronger than that for one dimension case. While the nonlinear propagation of the super-Gaussian beams becomes much more unstable compared with that for the case of one dimension. Our results show the nonlinear effects can be tuned by varying the Lévy index in the fractional Schrödinger equation for a fixed input power.

Spectrum regulation for mid-infrared ultrafast pulses via a time-synchronization aperiodically poled LiNbO3.

Restricted to temporal separation during the coupled-waves interaction, aperiodically quasi-phase-matching (QPM) nonlinear crystals are primarily implemented for prechirped pulses, showing limited applications in ultrafast temporal scale. Under the proposed time-synchronization framework, pump and signal waves travel with identical group-velocity, which permits sustaining energy transfer in long aperiodically poled LiNbO3 crystals (APPLN) even with ultrafast pulse duration. With the help of this structure, adiabatic frequency conversion shows extra advantages compared with the common cases, which enables lower stretching ratio and smoother gain spectrum. Focusing on the typical mid-infrared wavelength of ~3 µm, we numerically study the potential performance of APPLN with chirp-free ultrabroad interacting waves. In contrast to the spectral shift and conversion efficiency degradation presented by its traditional Type-0 QPM counterpart, the proposed design demonstrated impressive ability to obtain arbitrary spectrum via a simple femtosecond OPA/OPO. Peculiarly, the QPM chirp rate sign plays a significant role to the output spectrum, and a positive chirp rate is preferential in delivering a bandwidth-controllable spectrum. The proposed design provides a promising technical route to achieve spectrum manipulation in ultrafast temporal scale.

Compact self-cascaded KTA-OPO for 2.6 µm laser generation.

We reported a compact self-cascaded KTA-OPO source for 2.6 µm coherent light generation. The OPO is driven in a diode end-pumped and Q-switched Nd:YVO4 laser cavity. Two OPO processes occurred in the same KTA crystal with non-critical phase matching. At an incident diode pump power of 8.7 W and a pulse repetition frequency of 60 kHz, the OPO can generate a maximum average output power of 445 mW at 2.59 µm. The slope efficiency was about 12.7%, and the power fluctuation was less than 8%. Therefore, the self-cascade OPO based on KTA offers a promise scheme for the rugged and compact mid-infrared 2.6 µm laser generation.

Efficient laser operation based on transparent Nd:Lu2O3 ceramic fabricated by Spark Plasma Sintering.

Efficient laser operation of Nd:Lu2O3 ceramic fabricated by Spark Plasma Sintering (SPS) was demonstrated. Transparent Nd:Lu2O3 ceramic was successfully fabricated by Spark Plasma Sintering and its laser experiment was done. On the 4F3/2 to 4I11/2 transition, the obtained maximum output is 1.25W at the absorbed pump power of 4.15W with a slope efficiency of 38% and two spectral lines at 1076.7nm and 1080.8nm oscillated simultaneously. The slope efficiency of 38% is near two times higher than the previously demonstrated SPSed Nd:Lu2O3 ceramic lasers. On the 4F3/2 to 4I13/2 transition, the laser operated at the wavelength of 1359.7nm and the maximum output of 200mW was obtained at the absorbed pump power of 2.7W.

NORMAL VAGINAL BACTERIAL FLORA OF GIANT PANDAS (AILUROPODA MELANOLEUCA) AND THE ANTIMICROBIAL SUSCEPTIBILITY PATTERNS OF THE ISOLATES.

In order to study the typical vaginal bacterial flora of giant pandas (Ailuropoda melanoleuca), we took vaginal swabs for the sake of bacterial isolation, from 24 healthy female giant pandas. A total of 203 isolates were identified, representing a total of 17 bacterial species. The most common bacteria isolated were Lactobacillus spp. (54.2%, 13 of 24), followed by Staphylococcus epidermidis (41.7%, 10 of 24) and Escherichia coli (33.3%, 8 of 24). Some opportunistic pathogenic bacteria, such as Peptostreptococcus spp., Klebsiella pneumoniae, and Proteus mirabilis, were also isolated but showed no pathology. Antimicrobial susceptibility testing of aerobic bacterial isolates was performed with disk diffusion method. Of the 152 isolates, resistance was most frequently observed with chloramphenicol (17.8%), followed by tetracycline (14.5%), ciprofloxacin (12.5%), streptomycin (11.8%), and florfenicol (11.8%), while 7.2% were multidrug resistant. This is the first report of the normal vaginal culturable bacterial flora of giant pandas, followed by the antimicrobial susceptibility patterns of the isolates.

NORMAL VAGINAL BACTERIAL FLORA OF GIANT PANDAS (AILUROPODA MELANOLEUCA) AND THE ANTIMICROBIAL SUSCEPTIBILITY PATTERNS OF THE ISOLATES.

To study the typical vaginal bacterial flora of giant pandas (Ailuropoda melanoleuca), we took vaginal swabs for the sake of bacterial isolation, from 24 healthy female giant pandas. A total of 203 isolates were identified, representing a total of 17 bacterial species. The most common bacteria isolated were Lactobacillus spp. (54.2%, 13/24), followed by Staphylococcus epidermidis (41.7%, 10/24) and Escherichia coli (33.3%, 8/24). Some opportunistic pathogenic bacteria, such as Peptostreptococcus spp., Klebsiella pneumoniae , and Proteus mirabilis , were also isolated but showed no pathology. Antimicrobial susceptibility testing of aerobic bacterial isolates was performed with the disk diffusion method. Of the 152 isolates, resistance was most frequently observed with chloramphenicol (17.8%), followed by tetracycline (14.5%), ciprofloxacin (12.5%), streptomycin (11.8%), and florfenicol (11.8%), whereas 7.2% were multidrug resistant. This is the first report of the normal culturable vaginal bacterial flora of giant pandas and the antimicrobial susceptibility patterns of the isolates.

First report of macrolide resistance gene erm(T) harbored by a novel small plasmid from Erysipelothrix rhusiopathiae.

The macrolide resistance gene erm(T) was identified for the first time in a porcine Erysipelothrix rhusiopathiae isolate from swine in China. The novel 3,749-bp small plasmid pER29, which carries erm(T), had a G+C content of 31% and four distinct open reading frames. The presence of pER29 increased by at least 128-fold the MICs of clindamycin and erythromycin for E. rhusiopathiae. The fitness cost of pER29 could be responsible for the low frequency of erm(T) in E. rhusiopathiae.

Two novel Salmonella genomic island 1 variants in Proteus mirabilis isolates from swine farms in China.

Four different Salmonella genomic island 1 (SGI1) variants, including two novel variants, were characterized in one Salmonella enterica serovar Rissen sequence type ST1917 isolate and three Proteus mirabilis isolates from swine farms in China. One novel variant was derived from SGI1-B with the backbone gene S021 disrupted by a 12.72-kb IS26 composite transposon containing the dfrA17-aadA5 cassettes and macrolide inactivation gene cluster mphA-mrx-mphR. The other one was an integron-free SGI1 and contained a 183-bp truncated S025 next to IS6100 and S044.

Stable and wavelength-locked Q-switched narrow-linewidth Er:YAG laser at 1645 nm.

A stable and wavelength-locked Q-switched narrow-linewidth Er:YAG laser with compact cavity structure, utilizing a volume Bragg grating (VBG) as a wavelength selector and a pump input mirror simultaneously, is reported. It yields high energy nanosecond pulse with pulse duration of 185 ns and pulse energy of 1.36 mJ at 1 kHz pulse repetition frequency for incident pump power of 21.6 W. The central wavelength of the Er:YAG laser is locked at 1645.3 nm with a spectral 3-dB linewidth of less than 0.08 nm, which coincides to the methane (CH4) absorption-line. The output has near diffraction-limited beam quality with M2 parameter of 1.08. Our work may provide an inroad for developing more miniaturized space-based integrated path differential absorption (IDPA) lidar transmitter.

Generation and evolution of mode-locked noise-like square-wave pulses in a large-anomalous-dispersion Er-doped ring fiber laser.

In a passively mode-locked Erbium-doped fiber laser with large anomalous-dispersion, we experimentally demonstrate the formation of noise-like square-wave pulse, which shows quite different features from conventional dissipative soliton resonance (DSR). The corresponding temporal and spectral characteristics of a variety of operation states, including Q-switched mode-locking, continuous-wave mode-locking and Raman-induced noise-like pulse near the lasing threshold, are also investigated. Stable noise-like square-wave mode-locked pulses can be obtained at a fundamental repetition frequency of 195 kHz, with pulse packet duration tunable from 15 ns to 306 ns and per-pulse energy up to 200 nJ. By reducing the linear cavity loss, stable higher-order harmonic mode-locking had also been observed, with pulse duration ranging from 37 ns at the 21st order harmonic wave to 320 ns at the fundamental order. After propagating along a piece of long telecom fiber, the generated square-wave pulses do not show any obvious change, indicating that the generated noise-like square-wave pulse can be considered as high-energy pulse packet for some promising applications. These experimental results should shed some light on the further understanding of the mechanism and characteristics of noise-like square-wave pulses.

Characteristics of Plasmids Coharboring 16S rRNA Methylases, CTX-M, and Virulence Factors in Escherichia coli and Klebsiella pneumoniae Isolates from Chickens in China.

The objective of this study was to characterize plasmids coharboring 16S rRNA methylases, blaCTX-M and virulence-associated genes in Escherichia coli and Klebsiella pneumoniae isolates from chickens in China. A total of 32 positive transconjugants exhibited coresistance to amikacin and cefotaxime in E. coli (24/281) and K. pneumoniae (8/93), and were identified by conjugation experiments and S1-pulsed-field gel electrophoresis. Polymerase chain reaction amplification assay detecting resistance genes showed that rmtB or armA gene accompanied with different blaCTX-M genes coexisted on 32 transferred plasmids. The blaCTX-M-98b gene was identified in chicken-derived E. coli and K. pneumoniae for the first time. The association between resistance genes and virulence genes was observed in the transferred plasmids; 68.8% (22/32) transferred resistance plasmids coharboring various virulence genes including traT, iutA, fyuA, msbB, and vagC genes with diverse proportions. Genetic stability tests revealed that 93.8% (30/32) transferred plasmids continued to exist in the host strain after continuous passage of 30 times in 15 days. Furthermore, 87.5% (28/32) conjugants showed no significant differences in growth rates compared with E. coli J53. Results of the growth competition assay showed that conjugants have low fitness cost, which indicated that there were no obvious negative effects on the host's growth. The combination of blaCTX-M-98b-rmtB-traT on 85-kb transferred IncF plasmids in E. coli, and blaCTX-M-14-rmtB-traT on 95-kb transferred IncF plasmids in K. pneumoniae were first identified in this study. These features of plasmids may contribute to the successful spread of resistance and virulence among pathogens of different sources and geographical origins.

Molecular characteristics of Salmonella genomic island 1 in Proteus mirabilis isolates from poultry farms in China.

Six out of the 64 studied Proteus mirabilis isolates from 11 poultry farms in China contained Salmonella genomic island 1 (SGI1). PCR mapping showed that the complete nucleotide sequences of SGI1s ranged from 33.2 to 42.5 kb. Three novel variants, SGI1-W, SGI1-X, and SGI1-Y, have been characterized. Resistance genes lnuF, dfrA25, and qnrB2 were identified in SGI1 for the first time.

Passive mode-locking performance of mixed Nd:La(0.11)Y(0.89)VO(4) crystal.

Passive mode locking of a diode pumped Nd:La(0.11)Y(0.89)VO(4) mixed crystal laser with a semiconductor saturable absorber mirror (SESAM) was experimentally investigated for the first time to our knowledge. Stable CW mode-locking has been achieved on both a-cut and c-cut mixed crystals. In case of the a-cut crystal, when a 2% output coupler (OC) was used, the shortest pulse obtained was 4.5 ps and the highest output power was 0.94 W, while when a 6% OC was used, the shortest pulse obtained was 6.8 ps and the highest output power was 5.16 W. In the latter case the optical conversion efficiency is 38% and the slope efficiency is 40.3%, respectively; with the c-cut crystal the shortest pulse achieved was 5.5 ps. Moreover, simultaneous mode locking at two close wavelengths of 1064.3 nm and 1066.2 nm was observed on the c-cut crystal. The mode locked pulse beating generated temporal interference fringe of 0.5 THz repetition rate.

Stable high-energy Q-switched resonantly diode-pumped Er:YAG laser at 1645 nm.

We demonstrate the generation of a stable high-energy Q-switched resonantly diode-pumped Er:YAG laser at 1645 nm in passive and active operation modes. For the passively Q-switched Er:YAG laser, the bi-layer graphene saturable absorber (SA), which was transferred onto the highly reflective cavity mirror by an improved method, was applied to deliver a stable pulse train with per-pulse energy of about 0.1 mJ. While in the active operation mode, the voltage-ON-type rubidium titanyl phosphate (RTP) Pockels cell as an electro-optic (EO) Q-switcher allows for the generation of a stable Q-switched pulse with per-pulse energy of up to 7.5 mJ. Our work may provide a basis for the development of a high-energy Er:YAG laser at 1645 nm to fulfill specific applications.