Diode-pumped wavelength-switchable visible Pr^(3+):YLF laser and vortex laser around 670 nm

Here we developed a novel wavelength-switchable visible continuous-wave(CW)Pr^(3+):YLF laser around 670 nm.In single-wavelength laser operations,the maximum output powers of 2.60 W,1.26 W,and 0.21 W,the maximum slope efficiencies of 34.7%,27.3%,and 12.3%were achieved with good beam qualities(M^(2)<1.6)at 670.4 nm,674.2 nm,and 678.9 nm,respectively.Record-high output power(2.6 W)and record-high slope efficiency(34.7%)were achieved for the Pr^(3+):YLF laser operation at 670.4 nm.This is also the first demonstration of longer-wavelength peaks beyond 670 nm in the^(3)P_(1)→^(3)F_(3)transition of Pr^(3+):YLF.In multi-wavelength laser operations,the dual-wavelength lasings,including 670.1/674.8 nm,670.1/679.1 nm,and 675.0/679.4 nm,were obtained by fine adjustment of one/two etalons within the cavity.Furthermore,the triple-wavelength lasings,e.g.672.2/674.2/678.6 nm and 670.4/674.8/679.4 nm,were successfully demonstrated.Moreover,both the first-order vortex lasers(LG_(0)^(+1)and LG_(0)^(-1)modes)at 670.4 nm were obtained by off-axis pumping.

Mid‐infrared all‐fiber gain‐switched pulsed laser at 3μm

Mid-infrared(MIR)fiber pulsed lasers are of tremendous application interest in eye-safe LIDAR,spectroscopy,chemical detection and medicine.So far,these MIR lasers largely required bulk optical elements,complex free-space light alignment and large footprint,precluding compact all-fiber structure.Here,we proposed and demonstrated an all-fiberized structured gain-switched Ho3+-doped ZBLAN fiber laser operating around 2.9μm.A home-made 1146 nm Raman fiber pulsed laser was utilized to pump highly concentrated single-cladding Ho3+-doped ZBLAN fiber with different lengths of 2 m or 0.25 m.A home-made MIR fiber mirror and a perpendicular-polished ZBLAN fiber end construct the all-fiberized MIR cavity.Stable gain-switched multiple states with a sub-pulse number tuned from 1 to 8 were observed.The effects of gain fiber length,pump power,pump repetition rate and output coupling ratio on performance of gain-switched pulses were further investigated in detail.The shortest pulse duration of 283 ns was attained with 10 kHz repetition rate.The pulsed laser,centered at 2.92μm,had a maximum average output power of 54.2 mW and a slope efficiency of 10.12%.It is,to the best of our knowledge,the first time to demonstrate a mid-infrared gain-switched Ho3+:ZBLAN fiber laser with compact all-fiber structure.

Watt-level acousto-optically Q-switched Pr:YLF laser at 639 nm

We present a study on a watt-level acousto-optically Q-switched Pr:YLF laser at three different repetition rates(10 kHz,20 kHz,and 50 kHz)for the first time,to the best of our knowledge.The corresponding average output powers and pulse widths were measured to be 1.14 W,1.2 W,and 1.32 W,and 40 ns,52 ns,and 80 ns,respectively.A maximum pulse energy of0.11 mJ was obtained,corresponding to a peak power of up to 2.8 kW at a repetition rate of 10 kHz.The simulated dynamics of a fast Q-switched Pr:YLF laser is in agreement with the experiment.The laser's ability to generate stable pulses with high peak power and short pulse width makes it highly desirable for various practical applications,such as laser machining and material processing.

Dual ligands relay-promoted transformation of unstrained ketones to polyfluoroarenes and nitriles

C-C bond activation has emerged as a powerful tool for the construction of complex molecules.Herein,we report a dual ligands relay-promoted transformation of unstrained aryl,alkenyl and alkynyl ketones to the corresponding polyfluoroarenes and nitriles via C-C(=O)bond cleavage and subsequent decarboxylative arylation process.Various polyfluoroarene and nitrile products are obtained in one pot under cyanide-free conditions.The protocol features high atom economy,broad functional group tolerance and excellent heterocyclic compatibility.The late-stage functionalization of the drug and natural product demonstrated the synthetic utility of our protocol.Furthermore,the decisive role of the dual ligands was clarified and the mechanistic rationale including theβ-C elimination as the rate-limiting step was supported by detailed density functional theory(DFT)studies.

Watt-level laser operation of Pr^(3+):YLF at 696 and 698 nm

We report continuous-wave deep red lasers at 696.6 and 698.6 nm in a Pr^(3+):YLF crystal pumped by an InGaN laser diode.A Lyot filter was inserted into the cavity as a birefringent filter to select wavelength;the lasers at 696.6 and 698.6 nm were obtained with a maximum output power of 1.36 and 3.11 W,separately.To the best of our knowledge,the output powers of these two lasers are the highest to date,and this is the first scaling of the output power of the Pr^(3+):YLF laser to the watt level at around 696 nm.In addition,the corresponding theoretical analysis and simulation were carried out to explain the experimental phenomena.

Diode-pumped high-power continuous-wave intracavity frequency-doubled Pr^(3+):YLF ultraviolet lasers around 349 nm

High-power continuous-wave ultraviolet lasers are useful for many applications.As ultraviolet laser sources,the wavelength switching capability and compact structure are very important to extend the applicability and improve the flexibility in practical applications.In this work,we present two simple and relatively compact schemes by laser diode pumping to obtain a watt-level single-wavelength 348.7-nm laser and discrete wavelength tunable ultraviolet lasers around 349 nm(from 334.7 to 364.5 nm)by intracavity frequency doubling based on Pr^(3+):YLF andβ-BBO crystals.The maximum output power of the single-wavelength 348.7-nm laser is 1.033 W.The output powers of the discrete wavelength tunable lasers are at the level of tens of milliwatts,except for two peaks at 348.7 and 360.3 nm with output powers of approximately 500 mW.In addition,simulations are carried out to explain the experimental results and clarify the tuning mechanisms.

Direct generation of an ultrafast vortex beam in a CVD-graphene-based passively mode-locked Pr:LiYF4 visible laser

We report on the direct generation of passively mode-locked vortex lasers in the visible spectral region, for the first time to the best of our knowledge, using a Pr :Li YF4(Pr:YLF) crystal as the gain medium. A stable mode-locked TEM00 mode has been achieved with a maximum average output power of 75 m W using a graphene saturable absorber mirror. The mode-locked pulse width is measured to be as short as about 73.4 ps at a repetition rate of about 140 MHz, and the laser wavelength is at about 721 nm with spectral width of about 0.5 nm. By slightly misaligning the laser resonator, a first-order Laguerre-Gaussian mode(LG0,1) has also been obtained with output power reduced to about 22 m W. The achieved LG0,1 mode has been verified via a home made improved Fizeau interferometer. This work provides a simple and universal method for direct generation of an ultrafast vortex laser,which can be readily extended to other spectral regions by using different laser gain mediums.

Self-Q-switched and wavelength-tunable tungsten disulfide-based passively Q-switched Er:Y2O3 ceramic lasers

We report on diode-pumped Er:Y_2O_3 ceramic lasers at about 2.7 μm in the tunable continuous-wave, selfQ-switching and tungsten disulfide(WS2)-based passively Q-switching regimes. For stable self-Q-switched operation, the maximum output power reaches 106.6 m W under an absorbed power of 2.71 W. The shortest pulse width is measured to be about 1.39 μs at a repetition rate of 26.7 kHz at maximum output. Using a spin-coated WS2 as a saturable absorber, a passively Q-switched Er:Y_2O_3 ceramic laser is also realized with a maximum average output power of 233.5 m W(for the first time, to the best of our knowledge). The shortest pulse width decreases to 0.72 μs at a corresponding repetition rate of 29.4 kHz, which leads to a pulse energy of 7.92 μJ and a peak power of 11.0 W. By inserting an undoped YAG thin plate as a Fabry–Perot etalon, for the passive Q switching, wavelength tunings are also demonstrated at around 2710, 2717, 2727, and 2740 nm.

Visible Raman and Brillouin lasers from a microresonator/ZBLAN-fiber hybrid system

Raman and Brillouin lasers based on a high-quality(high-Q) whispering gallery mode microresonator(WGMR)are usually achieved by employing a tunable single-frequency laser as a pump source. Here, we experimentally demonstrate visible Raman and Brillouin lasers using a compact microresonator/ZrF4-BaF2-LaF3-AlF3-NaF(ZBLAN)-fiber hybrid system by incorporating a WGMR with a fiber-compatible distributed Bragg reflector/fiber Bragg grating to form a Fabry–Perot(F-P) fiber cavity and using a piece of Pr:ZBLAN fiber as gain medium.The high-Q silica-microsphere not only offers a Rayleigh-scattering-induced backreflection to form the ~635 nm red laser oscillation in the F-P fiber cavity, but also provides a nonlinear gain in the WGMR itself to generate either stimulated Raman scattering or stimulated Brillouin scattering. Up to six-order cascaded Raman lasers at0.65 μm, 0.67 μm, 0.69 μm, 0.71 μm, 0.73 μm, and 0.76 μm are achieved, respectively. Moreover, a Brillouin laser at 635.54 nm is clearly observed. This is, to the best of our knowledge, the first demonstration of visible microresonator-based lasers created by combining a Pr:ZBLAN fiber. This structure can effectively extend the laser wavelength in the WGMR to the visible waveband and may find potential applications in underwater communication, biomedical diagnosis, microwave generation, and spectroscopy.

Enantioselective synthesis of indenopyrazolopyrazolones enabled by dual directing groups-assisted and rhodium(Ⅲ)-catalyzed tandem C-H alkenylation/[3+2] stepwise cycloaddition

The Cp;Rh(Ⅲ)-catalyzed asymmetric cascade C-H coupling/intramolecular cyclization of azomethine imines with propargyl carbonates has been developed, affording a variety of chiral tetracyclic indenopyrazolopyrazolone frameworks with good substrate/functional group tolerance and enantioselectivity(up to 97:3 er). Combined experimental studies and DFT calculations revealed the Rh(Ⅲ)-catalyzed stepwise annulation process and clarified the synergy coordination mode of dual directing groups in tuning the selectivity.