Frequency-domain-resolved investigation of unitary h-shaped pulses.

We experimentally investigate the generation of h-shaped pulse in an all-polarization-maintaining (PM) and all-normal-dispersion (ANDi) mode-locked fiber laser. The generated pulse is demonstrated to be a unitary pulse, instead of a noise-like pulse (NLP). Furthermore, by employing an external filtering system, the obtained h-shaped pulse can be resolved into rectangular-shaped pulses, chair-like pulses, and Gaussian pulses. The authentic AC traces with a double-scale structure of unitary h-shaped pulses and chair-like pulses are observed on the autocorrelator. The chirp of h-shaped pulses is also proved similar to that of DSR pulses. To the best of our knowledge, this is the first time that the existence of unitary h-shaped pulse generation has been confirmed. Moreover, our experimental results reveal the close relationship of formation mechanisms of dissipative soliton resonance (DSR) pulses, h-shaped pulses, and chair-like pulses, which helps to unify the essences of such "DSR-like" pulses.

Mid-infrared ultrashort pulses generated from a hybrid mode-locked Er:ZBLAN fiber laser.

By combining nonlinear polarization rotation (NPR) and semiconductor saturable absorber, we report a hybrid mode-locked Er:ZBLAN fiber oscillator at 2.8 µm. Stable 325-fs mode-locked pulses with an average power of 131 mW and a record signal-to-noise ratio of 79 dB at the fundamental frequency of 55.4 MHz are generated. Numerical simulations are carried out based on the modified coupled nonlinear Schrödinger equations, and offer new insights into the underlying dynamics of pulse generation. The simulations indicate that compared with Er:ZBLAN fiber lasers mode-locked by NPR alone, the hybrid mode-locked Er:ZBLAN fiber oscillator allows a wider range and a lower threshold of the pump power while maintaining the ultrashort pulse width. Moreover, we numerically demonstrate that the hybrid mode-locked oscillator is less sensitive to the variation of polarization states, which will increase its robustness against environmental disturbance. This is the first time that the hybrid mode-locking technique is applied in the mid-infrared, opening up new opportunities for the development of stable ultrafast mid-infrared laser sources and practical applications outside the laboratory.

976†nm all-polarization-maintaining mode-locked fiber laser based on nonlinear polarization evolution.

An all-polarization-maintaining (PM) mode-locked fiber laser based upon nonlinear polarization evolution (NPE) that operates around 976 nm is presented. The NPE-based mode-locking is realized using a special section of the laser which comprises three pieces of PM fibers with specific deviation angles between the polarization axes and a polarization-dependent isolator. By optimizing the NPE section and adjusting the pump power, dissipative soliton (DS) pulses with a pulse duration of ∼6 ps, a spectral bandwidth of >10 nm and a maximum pulse energy of 0.54 nJ are generated. Self-starting, steady mode-locking operation is achievable within a pump power range of ∼2 W. Moreover, by incorporating a segment of passive fiber into the appropriate location in the laser resonator, an intermediate regime between stable single-pulse mode-locking and noise-like pulse (NLP) is realized in the laser. Our work expands the dimension of the research on the mode-locked Yb-doped fiber laser operating around 976 nm.

All-fiber 3.4-W 2.8-µm ultra-short pulse MOPA system seeded by the soliton self-frequency shift of 2-µm pulses.

We report an all-fiber 2.8-µm ultra-short pulse master oscillator power amplifier (MOPA) system seeded by a soliton self-frequency shift from a mode-locked thulium-doped fiber laser. This all-fiber laser source delivers 2.8-µm pulses with an average power of 3.42 W, a pulse width of 115 fs, and a pulse energy of 45.4 nJ. We demonstrate, to the best of our knowledge, the first femtosecond watt-level all-fiber 2.8-µm laser system. A 2.8-µm pulse seed was obtained via the soliton self-frequency shift of 2-µm ultra-short pulses in a cascaded silica and passive fluoride fiber. A novel, to the best of our knowledge, high-efficiency and compact home-made end-pump silica-fluoride fiber combiner was fabricated and used in this MOPA system. Nonlinear amplification of the 2.8-µm pulse was realized, and soliton self-compression was observed accompanied by spectral broadening.

High-energy femtosecond pulse generation from a hybrid mode-locked large-mode-area Er:ZBLAN fiber laser.

We report a hybrid mode-locked fiber laser at 2.8 µm based on a large-mode-area Er:ZBLAN fiber. Reliable self-starting mode-locking is achieved via the combination of nonlinear polarization rotation and a semiconductor saturable absorber. Stable mode-locked pulses with a pulse energy of 9.4 nJ and a pulse duration of 325 fs are generated. To the best of our knowledge, this is the highest pulse energy directly generated from a femtosecond mode-locked fluoride fiber laser (MLFFL) to date. The measured M2 factors are below 1.13, indicating a nearly diffraction-limited beam quality. Demonstration of this laser provides a feasible scheme for the pulse energy scaling of mid-infrared MLFFLs. Moreover, a peculiar multi-soliton mode-locking state is also observed, in which the time interval between the solitons varies irregularly from tens of picoseconds to several nanoseconds.

Tunable mode-locked Tm-doped fiber laser based upon cross-phase modulation.

We demonstrate the generation of soliton and dissipative soliton in an ultrafast thulium (Tm) doped fiber laser based upon cross-phase modulation (XPM) induced mode-locking. The mode-locking is realized by periodically modulating the 2-µm signal through XPM that is activated by an injected 1.5-µm pulsed laser. Such a mechanism enables the laser to be mode-locked in various operation regimes without any real or artificial saturable absorbers. Thanks to the XPM pulling effect, the wavelength of the Tm-doped fiber laser can be tuned by adjusting the repetition frequency of the 1.5-µm pulsed laser. The maximum tuning ranges achieved in this work for the soliton and dissipative soliton regimes are respectively 11 nm and 15 nm. The outcomes of this work not only provide a continuously and controllably wavelength-tunable ultrafast laser but also offer a passively synchronized dual-color fiber laser system, which is promised for many important applications such as Raman spectroscopy, nonlinear frequency conversion systems, and multi-color pump-probe systems.

Average-power (4.13 W) 59 fs mid-infrared pulses from a fluoride fiber laser system.

We report a high-average-power mid-infrared ultrafast laser system consisting of a fluoride fiber mode-locked oscillator and a nonlinear amplifier. A backward pumping scheme was used in the amplifier to simultaneously realize pulse amplification and self-compression. The input signal polarization was demonstrated to play an important role in the self-compression process. Through the optimization of input polarization, a 4.13 W average-power 59 fs pulse at 2.8 µm was achieved, with an estimated pulse energy of 42.2 nJ and a peak power of 715 kW. To the best of our knowledge, this is the highest average-power pulse with sub-100-fs duration generated from a mid-infrared fiber laser system to date.

Early diagnosis and critical management of wound botulism in the emergency department: a single center experience and literature review.

BACKGROUND: Clostridium botulinum remains a major threat to a select population of subcutaneous and intramuscular drug users. We conducted a retrospective study of patients who were diagnosed with wound botulism and their clinical presentations to the Emergency Department (ED). RESULTS: A total of 21 patients met the inclusion criteria and all had a confirmed history of heroin use disorder. Initial presentation to the ED included generalized weakness (n = 20, 95%), difficulty swallowing (n = 15, 71%), and speech/voice problems (n = 14, 79%). Sixteen patients (76%) also presented with visible skin wounds and fifteen (71%) required mechanical ventilation (MV). Patients who presented with dysphagia as well as dysarthria and/or dysphonia were more likely to require a percutaneous endoscopic gastrostomy (PEG) tube. Patients who required MV and PEG tubes were noted to have a longer hospital length of stay (LOS) due to the severity of the disease progression. CONCLUSIONS: Emergency physicians should remain vigilant about early recognition of wound botulism, especially in patients who inject drugs.