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.

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.

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.

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.

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.