14.1 W continuous-wave dual-end diode-pumped Er:Lu_(2)O_(3)laser at 2.85μm

We present our efforts towards power scaling of Er:Lu_(2)O_(3)lasers at 2.85μm.By applying a dual-end diode-pumped resonator scheme,we achieve an output power of 14.1 W at an absorbed pump power of 59.7 W with a slope efficiency of 26%.In a single-end pumped resonator scheme,an output power of 10.1 W is reached under 41.9 W of absorbed pump power.To the best of our knowledge,this is the first single crystalline mid-infrared rare-earth-based solid-state laser with an output power exceeding 10 W at room temperature.

High-power free-running single-longitudinal-mode diamond Raman laser enabled by suppressing parasitic stimulated Brillouin scattering

A continuous-wave(CW)single-longitudinal-mode(SLM)Raman laser at 1240 nm with power of up to 20.6 W was demonstrated in a free-running diamond Raman oscillator without any axial-mode selection elements.The SLM operation was achieved due to the spatial-hole-burning free nature of Raman gain and was maintained at the highest available pump power by suppressing the parasitic stimulated Brillouin scattering(SBS).A folded-cavity design was employed for reducing the perturbing effect of resonances at the pump frequency.At a pump power of 69 W,the maximum Stokes output reached 20.6 W,corresponding to a 30%optical-to-optical conversion efficiency from 1064to 1240 nm.The result shows that parasitic SBS is the main physical process disturbing the SLM operation of Raman oscillator at higher power.In addition,for the first time,the spectral linewidth of a CW SLM diamond Raman laser was resolved using the long-delayed self-heterodyne interferometric method,which is 105 kHz at 20 W.

Large-diameter indium antimonide microwire based broadband and robust optical switch

Various nanophotonic devices based on semiconductor wires with a diameter of several ten nanometers have been studied.Nevertheless,studying the optoelectronics properties and performance of such devices based on large-diameter wires is interesting and meaningful.Here,we successfully grew the micronsized indium antimonide(InSb) wires,and examined their nonlinear optical properties by Z-scan and I-scan(power-dependent) methods within the wavelength range of 0.8-2.8 μm.Furthermore,we demonstrated InSb micro wires(MWs) working as an effective and robust optical switch within 1-2.8 μm wavelength.The findings can open possibilities for research on more large-diameter MWs made from other semiconductor materials for photonic and electronic devices.

Rare-earth ions-doped mid-infrared(2.7-3 μm)bulk lasers:a review[Invited]

Mid-infrared (MIR) laser sources operating in the 2.7–3μm spectral region have attracted extensive attention for many applications due to the unique features of locating at the atmospheric transparency window,corresponding to the"characteristic fingerprint"spectra of several gas molecules,and strong absorption of water.Over the past two decades,significant developments have been achieved in 2.7–3μm MIR lasers benefiting from the sustainable innovations in laser technology and the great progress in material science.Here,we mainly summarize and review the recent progress of MIR bulk laser sources based on the rare-earth ions-doped crystals in the 2.7–3μm spectral region,including Er3+-,Ho3+-,and Dy3+-doped crystalline lasers.The outlooks and challenges for future development of rare-earth-doped MIR bulk lasers are also discussed.

Nanosecond-pulsed, dual-wavelength, passively Q-switched ytterbium-doped bulk laser based on few-layer MoS2 saturable absorber

A compact saturable absorber mirror（SAM） based on few-layer molybdenum disulfide（MoS2） nanoplatelets was fabricated and successfully used as an efficient saturable absorber（SA） for the passively Q-switched solid-state laser at 1 μm wavelength. Pulses as short as 182 ns were obtained from a ytterbium-doped（Yb:LGGG） bulk laser Q-switched by the MoS2 SAM, which we believe to be the shortest one ever achieved from the MoS2 SAs-based Q-switched bulk lasers. A maximum average output power of 0.6 W was obtained with a slope efficiency of 24%,corresponding to single pulse energy up to 1.8 μJ. In addition, the simultaneous dual-wavelength Q-switching at 1025.2 and 1028.1 nm has been successfully achieved. The results indicate the promising potential of few-layer MoS2 nanoplatelets as nonlinear optical switches for achieving efficient pulsed bulk lasers.

Broadband rhenium disulfide optical modulator for solid-state lasers

Rhenium disulfide （ReS2）, a member of group VII transition metal dichalcogenides （TMDs）, has attracted increasing attention because of its unique distorted 1T structure and electronic and optical properties, which are much different from those of group VI TMDs （MoS2, WS2, MoSeg, WSe2, etc.）. It has been proved that bulk ReS2 behaves as a stack of electronically and vibrationally decoupled monulayers, which offers remarkable possibilities to prepare a monolayer ReS2 facilely and offers a novel platform to study photonic properties of TMDs. However, due to the large and layer-independent bandgap, the nonlinear optical properties of ReS2 from the visible to midinfrared spectral range have not yet been investigated. Here, the band structure of ReS2 with the introduction of defects is simulated by the ab initio method, and the results indicate that the bandgap can be reduced from 1.38 to 0.54 eV with the introduction of defects in a suitable range. In the experiment, using a bulk ReS2 with suitable defects as the raw material, a few-layered broadband ReS2 saturable absorber （SA） is prepared by the liquid phase exfoliation method. Using the as-prepared ReS2 SA, passively Q-switched solid-state lasers at wavelengths of 0.64, 1.064, and 1.991 μm are investigated systematically. Moreover, with cavity design, a femtosecond passively modelocked laser at 1.06μm is successfully realized based on the as-prepared ReS2 SA for the first time. The results present a promising alternative for a rare broadband optical modulator and indicate the potential of ReS2 in generating Q-switched and mode-locked pulsed lasers. It is further anticipated that this work may be helpful for the design of 2D optoelectronic devices with variable bandgaps.

High-power and high-efficiency 4.3 μm ZGP-OPO

In this paper,a high-power and high-efficiency 4.3μm mid-infrared(MIR)optical parametric oscillator(OPO)based on ZnGeP_(2)(ZGP)crystal is demonstrated.An acousto-optically Q-switched Ho Y_(3)Al_(5)O_(12) laser operating at 2.1μm with a maximum average output power of 35 W and pulse width of 38 ns at a repetition rate of 15 kHz is established and employed as the pump source.A doubly resonant OPO is designed and realized with the total MIR output power of 13.27 W,including the signal and idler output power of 2.65 W at 4.07μm and 10.62 W at 4.3μm.The corresponding total optical-to-optical and slope efficiencies are 37.9%and 67.1%,respectively.The shortest pulse width,beam quality factor,and output power instability are measured to be 36 ns,M_(x)^(2)=1.8,M_(y)^(2)=2.0,and RMS<1.9%at 8 h,respectively.Our results pave a way for designing high-power and high-efficiency 4–5μm MIR laser sources.

Two-dimensional tellurium saturable absorber for ultrafast solid-state laser

Two-dimensional(2 D) Te nanosheets were successfully fabricated through the liquid-phase exfoliation(LPE) method. The nonlinear optical properties of 2 D Te nanosheets were studied by the open-aperture Z-scan technique. Furthermore, the continuous wave mode-locked Nd:YVO4 laser was successfully realized by using 2 D Te as a saturable absorber(SA) for the first time, to the best of our knowledge. Ultrashort pulses as short as 5.8 ps were obtained at 1064.3 nm with an output power of 851 m W. This primary investigation indicates that the 2 D Te SA is a promising photonic device in the fields of ultrafast solid-state lasers.

Nonlinear optical absorption properties of InP nanowires and applications as a saturable absorber

Indium phosphide(InP)nanowires(NWs)have attracted significant attention due to their exotic properties that are different from the bulk counterparts,and have been widely used for light generation,amplification,detection,modulation,and switching,etc.Here,high-quality InP NWs were directly grown on a quartz substrate by the Au-nanoparticle assisted vapor-liquid-solid method.We thoroughly studied their nonlinear optical absorption properties at 1.06μm by the open-aperture Z-scan method.Interestingly,a transition phenomenon from satu-rable absorption(SA)to reverse saturable absorption(RSA)was observed with the increase of the incident laser intensity.In the analysis,we found that the effective nonlinear absorption cofficient(βeff-10^2 cm/MW)under the SA process was 3 orders of magnitude larger than that during the RSA processes.Furthermore,the SA proper-ties of InP NWs were experimentally verified by using them as a saturable absorber for a passively Q-switched Nd:YVO4 solid-state laser at 1.06μm,where the shortest pulse width of 462 ns and largest single pulse energy of 1.32μJ were obtained.Moreover,the ultrafast carrier relaxation dynamics were basically studied,and the intraband and inter-band ultrafast carrier relaxation times of 8.1 and 63.8 ps,respectively,were measured by a degenerate pump-probe method with the probe laser of 800 nm.These results well demonstrate the nonlinear optical absorption properties,which show the excellent light manipulating capabilities of InP NWs and pave a way for their applications in ultrafast nanophotonic devices.

Ta_(2)NiSe_(5) nanosheets as a novel broadband saturable absorber for solid-state pulse laser generation

Two-dimensional(2D)ternary chalcogenides have attracted great attentions because of their novel chemical and physical properties arising from the synergistic effect and stoichiometric variation with the additional third element compared with their binary counterparts.Here,high-quality 2D tantalum nickel selenide(Ta_(2)NiSe_(5))nanosheets are successfully fabricated by a liquid-phase exfoliation(LPE)method.The ultrafast excited carrier relaxation time and nonlinear optical absorption response are investigated and reveal that the prepared 2D Ta_(2)NiSe_(5)nanosheets have excellent broadband saturable absorption properties,which are further illustrated by three passively Q-switched(PQS)allsolid-state lasers operating at 1.0,2.0 and 2.8μm with the Ta_(2)NiSe_(5)nanosheet-based saturable absorber(SA).Furthermore,mode-locked laser operation with the pulse width as short as 356 fs is also realized at 1.0μm.This work not only demonstrates the excellent nonlinear optical proprieties and optical modulation performance of Ta_(2)NiSe_(5),but also paves the way for exploring the photonic and optoelectronic proprieties of ternary chalcogenide materials.

Spectroscopic and laser properties of Er^(3+),Pr^(3+)co-doped LiYF_(4)crystal

In this paper,the absorption and fluorescence spectra of Er^(3+),Pr^(3+)co-doped LiYF_(4)(Er,Pr:YLF)crystal were measured and analyzed.The Pr^(3+)co-doping was proved to effectively enhance the Er^(3+)∶^(4)I_(11/2)→^(4)I_(13/2)mid-infrared transition at the 2.7μm with 74.1%energy transfer efficiency from Er^(3+)∶^(4)I_(13/2)to Pr^(3+)∶^(3)F_(4).By using the Judd–Ofelt theory,the stimulated emission cross section was calculated to be 1.834×10^(-20)cm^(2)at 2685 nm and 1.359×10^(-20)cm^(2)at 2804.6 nm.Moreover,a diode-end-pumped Er,Pr:YLF laser operating at 2659 nm was realized for the first time,to the best of our knowledge.The maximum output power was determined to be 258 m W with a slope efficiency of 7.4%,and the corresponding beam quality factors m^(2)_x=1.29 and m^(2)_(y)=1.25.Our results suggest that Er,Pr:YLF should be a promising material for 2.7μm laser generation.

Dual-wavelength synchronously mode-locked Tm-doped bulk laser with terahertz frequency beating

A dual-wavelength synchronously mode-locked homogeneously broadened bulk laser operating at 1985.6 and1989 nm is presented for the first time, to the best of our knowledge, which delivers a maximum output power of 166 m W and a repetition rate of 85 MHz. The pulse duration was measured to be 16.8 ps by assuming a sech2 pulse shape. The recorded autocorrelation trace showed frequency beating signals with an interval of 3.8 ps and a full width at half-maximum duration of 2 ps, corresponding to an ultrahigh beating frequency of about0.26 THz, which agrees well with the frequency difference of the emitted two spectral peaks. The results indicated that such a kind of dual-wavelength mode-locked Tm:YAlO3 laser could be potentially used for generating terahertz radiations.

Ultrafast carrier dynamics and nonlinear optical response of InAsP nanowires

Indium arsenide phosphide(In As P)nanowires(NWs),a member of theⅢ–Ⅴsemiconductor family,have been used in various photonic and optoelectronic applications thanks to their unique electrical and optical properties such as high carrier mobility and adjustable band gap.In this work,we synthesize In As P NWs and further explore their nonlinear optical properties.The ultrafast carrier dynamics and nonlinear optical response are thoroughly studied based on the nondegenerate pump probe and Z-scan experimental measurements.Two different characteristic carrier lifetimes(~2 and~15 ps)from In As P NWs are observed during the excited-carrier relaxation process.Based on the physical model analysis,the relaxation process can be ascribed to the carrier cooling process via carrier-phonon scattering and Auger recombination.In addition,based on the measured excited-carrier lifetime and Pauli-blocking principle,we discover that In As P NWs show strong saturable absorption properties at the wavelengths of 532 and 1064 nm.Last,we demonstrate for the first time a femtosecond(~426 fs)solid-state laser based on an In As P NWs saturable absorber at 1.04μm.We believe that our work provides a better understanding of the In As P NWs optical properties and will further advance their photonic applications in the near-infrared range.