635 nm femtosecond fiber laser oscillator and amplifier

Although visible femtosecond lasers based on nonlinear frequency conversion of Ti:sapphire femtosecond oscillators or near-infrared ultrafast lasers have been well developed,limitations in terms of footprint,cost,and efficiency have called for alternative laser solutions.The fiber femtosecond mode-locked oscillator as an ideal solution has achieved great success in the 0.9 to 3.5μm infrared wavelengths,but remains an outstanding challenge in the visible spectrum(390 to 780 nm).Here,we tackle this challenge by introducing a visible-wavelength mode-locked femtosecond fiber oscillator along with an amplifier.This fiber femtosecond oscillator emits red light at 635 nm,employs a figure-nine cavity configuration,applies a double-clad Pr3þ-doped fluoride fiber as the visible gain medium,incorporates a visible-wavelength phase-biased nonlinear amplifying loop mirror(PB-NALM)for mode locking,and utilizes a pair of customized high-efficiency and high-groove-density diffraction gratings for dispersion management.Visible self-starting mode locking established by the PB-NALM directly yields red laser pulses with a minimum pulse duration of 196 fs and a repetition rate of 53.957 MHz from the oscillator.Precise control of the grating pair spacing can switch the pulse state from a dissipative soliton or a stretched-pulse soliton to a conventional soliton.In addition,a chirped-pulse amplification system built alongside the oscillator immensely boosts the laser performance,resulting in an average output power over 1W,a pulse energy of 19.55 nJ,and a dechirped pulse duration of 230 fs.Our result represents a concrete step toward high-power femtosecond fiber lasers covering the visible spectral region and could have important applications in industrial processing,biomedicine,and scientific research.

Burst-mode pulse generation in passively mode-locked all-fiber green/orange lasers at 543 nm and 602 nm

We report on the experimental realization of,to the best of our knowledge,the first green and orange passively mode-locked all-fiber lasers.Stable mode-locking in the burst-pulse status is achieved at the wavelengths of 543.3 nm and 602.5 nm.The figure-9 cavity comprises the fiber end-facet mirror,gain fiber(Ho^(3+):ZBLAN fiber or Pr^(3+)/Yb^(3+):ZBLAN fiber),and fiber loop mirror(FLM).The FLM with long 460 HP fiber is not only used as an output mirror,but also acts as a nonlinear optical loop mirror for initiating visible-wavelength mode-locking.The green/orange mode-locked fiber lasers with the fundamental repetition rates of 3.779/5.662 MHz produce long bursts containing ultrashort pulses with the 0.85/0.76 GHz intra-burst repetition rates,respectively.The ultrashort intra-burst pulses stem from the dissipative four-wave-mixing effect in the highly nonlinear FLM as well as the intracavity Fabry–Perot filtering.Long bursts of 22.2/11.6 ns with ultrashort pulses of 87/62 ps are obtained in our experiment.The visible-wavelength passively mode-locked lasers in an all-fiber configuration and burst-mode would represent an important step towards miniaturized ultrafast fiber lasers and may contribute to the applications in ablation-cooling micromachining,biomedicine imaging,and scientific research.

3.6 W compact all-fiber Pr3+-doped green laser at 521 nm

Green semiconductor lasers are still undeveloped,so high-power green lasers have heavily relied on nonlinear frequency conversion of near-infrared lasers,precluding compact and low-cost green laser systems.Here,we report the first Watt-level all-fiber CW Pr3t-doped laser operating directly in the green spectral region,addressing the aforementioned difficulties.The compact all-fiber laser consists of a double-clad Pr3t-doped fluoride fiber,two homemade fiber dichroic mirrors at visible wavelengths,and a 443-nm fiber-pigtailed pump source.Benefitting from>10 MW∕cm2 high damage intensity of our designed fiber dielectric mirror,the green laser can stably deliver 3.62-W of continuous-wave power at∼521 nm with a slope efficiency of 20.9%.To the best of our knowledge,this is the largest output power directly from green fiber lasers,which is one order higher than previously reported.Moreover,these green all-fiber laser designs are optimized by using experiments and numerical simulations.Numerical results are in excellent agreement with our experimental results and show that the optimal gain fiber length,output mirror reflectivity,and doping level should be considered to obtain higher power and efficiency.This work may pave a path toward compact high-power green all-fiber lasers for applications in biomedicine,laser display,underwater detection,and spectroscopy.

Direct generation of 3.17 mJ green pulses in a cavity-dumped Ho^(3+)-doped fiber laser at 543 nm

High-energy pulsed lasers in the green spectral region are of tremendous interest for applications in space laser ranging,underwater detection,precise processing,and scientific research.Semiconductor pulsed lasers currently are difficult to access to the so-called“green gap,”and high-energy green pulsed lasers still heavily rely on the nonlinear frequency conversion of near-IR lasers,precluding compact and low-cost green laser systems.Here,we address this challenge by demonstrating,for the first time to the best of our knowledge,millijoule-level green pulses generated directly from a fiber laser.The green pulsed fiber laser consists of a 450 nm pump laser diode,a Ho^(3+)-doped ZBLAN fiber,and a cavity-dumping module based on a visible wavelength acousto-optic modulator.Stable pulse operation in the cavity-dumping regime at 543 nm is observed with a tunable repetition rate in a large range of 100 Hz–3 MHz and a pulse duration of 72–116 ns.The maximum pulse energy of 3.17 mJ at 100 Hz is successfully achieved,which is three orders of magnitude higher than those of the rare-earth-doped fiber green lasers previously reported.This work provides a model for compact,high-efficiency,and high-energy visible fiber pulsed lasers.

New ultrashort pulsewidth measurement technology based on interference jitter and FPGA platform

Conventional ultrashort pulsewidth measurement technology is autocorrelation based on second-harmonic generation;however,nonlinear crystals and bulky components are required,which usually leads to the limited wavelength range and the difficult adjustment with free-space light alignment.Here,we proposed a compact all-fiber pulsewidth measurement technology based on the interference jitter(IJ)and field-programmable gate array(FPGA)platform,without requiring a nonlinear optical device(e.g.nonlinear crystal/detector).Such a technology shows a wide measurement waveband from 1 to 2.15μm at least,a pulsewidth range from femtoseconds to 100 ps,and a small relative error of 0.15%-3.8%.In particular,a minimum pulse energy of 219 fj is experimentally detected with an average-power-peak-power product of 1.065×10^(-6)W^(2).The IJ-FPGA technology may offer a new route for miniaturized,user-friendly,and broadband pulsewidth measurement.