In recent years, several kinds of nanomaterials have been successfully used for passive mode-locking, but it is not fully understand how the mode-locking performance is influenced by the different ...characteristics of these saturable absorbers (SAs). In this paper, we numerically and experimentally investigate the effects of nanomaterial saturable absorption (e.g., modulation depth and saturation intensity) on a passively mode-locked fiber laser in an anomalous dispersion regime. First, by numerically solving the Ginzburg-Landau equation, we analyze the evolution of the output performances (spectral bandwidth, pulse duration, and peak power) of passively mode-locked Er 3+ -doped fiber laser as the SA's modulation depth or saturation intensity. Then, we fabricate four nanomaterial-based SAs, which have the different modulation depth from 1.8% to 19.1%, the different saturation intensity from 11 to 180 MW/cm 2 ,and the similar insertion loss of ~3 dB. Finally, we perform the experimental comparison of passively mode-locked Er 3+ -doped fiber laser using the four nanomaterial-based SAs, respectively. Our results reveal that: 1) as the modulation depth increases, the mode-locked spectral bandwidth becomes wide and the pulse duration becomes short; and 2) the SA's saturation intensity has little influence on the output performance. The experimental results are in good agreement with the numerical simulations. This work could provide a useful guideline for choosing proper nanomaterial-based SA for different practical applications.
The recent renaissance in pulsed lasers operating in the visible spectral region has been driven by their significant applications in a wide range of fields such as display technology, medicine, ...microscopy, material processing, and scientific research. Low-dimensional nanomaterials as saturable absorbers are exploited to create strong nonlinear saturable absorption for pulse generation at visible wavelengths due to their absorption peaks located in visible spectral region. Here we provide a detailed overview of visible-wavelength pulsed lasers based on low-dimensional nanomaterials, covering the optical properties and various integration strategies of these nanomaterials saturable absorbers, and their performance from solid-state as well as fiber pulsed lasers in the visible spectral range. This emerging application domain will undoubtedly lead to the rapid development of visible pulsed lasers.
We report the generation of tunable high-repetition-rate (0.1-1 THz) femtosecond pulses based on a quasi-continuous wave (CW) dual-pumped all-fiber cascaded four-wave-mixing (FWM) scheme without ...requiring a cavity resonator. By synchronously injecting two pulse-modulated lasers into an 85-m-long dispersion-flat highly nonlinear fiber, cascaded FWM processes under only ~30-mW average pump power are efficiently initiated to form the Kerr frequency combs near 1.56 μm. Phase locking of the Kerr combs is confirmed by real-time measurements using an autocorrelator, and stable ultrashort pulse trains are observed. The pulse repetition rate can be tuned continuously in the range of 0.1~1 THz by controlling the wavelength spacing between the two pump lasers. The pulse duration can be correspondingly adjusted from 1.66 ps to 262 fs. Such quasi-CW dual-pumped all-fiber cascaded-FWM frequency combs with the advantages of compactness and flexibility could provide a practical solution for generating ultrahigh-repetition-rate femtosecond pulses.
We report, to the best of our knowledge, the first visible-wavelength all-fiber passively mode-locked vortex laser by a figure-9 cavity in combination with <inline-formula><tex-math ...notation="LaTeX">\sim</tex-math></inline-formula>635 nm mode selective coupler, which can deliver picosecond optical vortex pulses with topological charges of OAM<inline-formula><tex-math notation="LaTeX">_{\pm 1}</tex-math></inline-formula>. The mode-locked vortex laser emits stable rectangular pulses with pulse duration tunable range from 85 to 510 ps and a 0.16-nm narrow linewidth at 634.36 nm. The maximum output power of the vortex laser reaches 1.3 mW with a high purity <inline-formula><tex-math notation="LaTeX">\sim 97.2\%</tex-math></inline-formula>. This work demonstrated the generation of picosecond pulsed vortex in visible passively mode-locked fiber laser, showing their potential for applications in particle trapping, optical tweezers, and high-resolution microscopy.
As deep-red semiconductor lasers are still in development, high-power deep-red lasers have traditionally relied on excimer or dye lasers, or nonlinear frequency conversion of near-infrared lasers, ...precluding efficient, compact, and affordable laser systems. Herein, the first compact watt-level all-fiber CW Pr<inline-formula><tex-math notation="LaTeX">^{3+}</tex-math></inline-formula>-doped laser operating in the deep-red waveband was developed to navigate the challenge. The all-fiber laser consists of a double-clad Pr<inline-formula><tex-math notation="LaTeX">^{3+}</tex-math></inline-formula>-doped fluoride fiber, two homemade visible fiber dichroic mirrors with a damaged intensity of <inline-formula><tex-math notation="LaTeX">\gt </tex-math></inline-formula>15 MW/cm<inline-formula><tex-math notation="LaTeX">^{2}</tex-math></inline-formula>, and a 443-nm high-power pump source with a multimode fiber-pigtail output. We exhaustively investigated the influences of the gain fiber length and the reflectivity of output mirrors on the deep-red laser performance by experiments and simulations. A maximum average power of 4.1 W at 717 nm was directly obtained under a pump power of 20.2 W, which is more than five times higher than previously reported. The laser slope efficiency is as high as 22.2%, and its power fluctuation is less than 0.93%. Such a compact high-power all-fiber deep-red laser holds promise for applications in biophotonics, biomedicine, and UV laser generation.
We report, to the best of our knowledge, the first all-fiber passively mode-locked laser around 800 nm wavelength. The laser with a figure-9 cavity configuration consists of a homemade 1146 nm Raman ...fiber laser as pump source, a 2.1 m-length Tm<inline-formula> <tex-math notation="LaTeX">^{3+} </tex-math></inline-formula>-doped ZBLAN fiber, a 0.8/<inline-formula> <tex-math notation="LaTeX">1.15~\mu \text{m} </tex-math></inline-formula> fiber end-facet dichroic mirror, and a nonlinear optical loop mirror (NOLM). The NOLM is not only employed as the output cavity mirror, and also initiates passive mode-locking. The mode-locked center wavelength is 816 nm with a 3-dB bandwidth of ~0.35 nm. The mode-locked rectangular pulse in the noise-like regime has a pulse duration of 486.7 ps with the 7.826 MHz repetition rate. The maximum average power is as high as 488.5 mW and the pulse energy is 62.4 nJ. This work represents an important step towards ~800 nm short-wavelength ultrafast fiber lasers and may has potential applications in biological imaging and medical treatment.
We report on the experimental observation of bidirectional 100-fs bound solitons from a nanotube-mode-locked dispersion-managed Er-fiber laser with an ultra-simple linear cavity. Two mode-locked ...pulse trains in opposite directions are delivered simultaneously from the linear cavity. Under the pump power of <74 mW, both the bidirectional outputs of the laser work at the single-soliton state with pulse duration of 173 fs and 182 fs, respectively. Once the pump power is more than 74 mW, both the bidirectional outputs evolve into the two-soliton bound states with soliton separation of 1.53 ps. Interestingly, the bidirectional operations can show the different bound states, i.e. the forward bound solitons with phase difference of + π/2, and the backward ones with phase difference of -π/2. This is, to the best of our knowledge, the first demonstration of such compact bidirectional soliton fiber laser with the sub-200 fs pulses.
Spatiotemporal mode‐locking (STML) in fiber lasers are of interest in applications such as optical communications, nonlinear imaging, and precision machining. To date, STML fiber lasers in the ...near‐infrared region have been well demonstrated, yet operation at visible wavelengths is still challenging. Here, a STML picosecond fiber laser at 635 nm with the implementation of Pr3+$^{3+}$/Yb3+$^{3+}$ co‐doped few‐mode fiber and nonlinear polarization rotation technology is reported. By solving the modified generalized multimode nonlinear Schrödinger equation, the 635 nm STML formation is theoretically predicted and analyzed. The stable 635 nm STML with a 9 ps pulse duration, which is two orders of magnitude narrower than previously reported, is realized experimentally. Moreover, spatiotemporal profiles are illustrated by investigating the locking of transverse and longitudinal modes simultaneously. By further establishing visible ultrafast fiber amplifier, the 635 nm average power is boosted up to 440 mW, corresponding to a maximum pulse energy and peak power of 4 nJ and 280 W, respectively. The experimental results are in good agreement with the numerical simulations. This work helps to understand nonlinear dynamics in STML fiber laser and directly generate large‐energy ultrashort pulses in visible region.
To date, spatiotemporal mode‐locking (STML) of fiber lasers in the near‐infrared region have been well demonstrated, yet operation at visible wavelengths is still challenging. Here, a 635 nm STML fiber laser is reported with a 9 ps pulse duration, and the average power is amplified up to 440 mW (corresponding to 4 nJ pulse energy).
Deep ultraviolet (DUV) lasers are essential elements to versatile applications such as spectroscopy and lithography, and several techniques including free-electron lasers, excimer lasers and ...high-order harmonic conversion have been developed for DUV laser generation, yet the wavelength tunability and compactness are still challenging. Here, for the first time, we experimentally demonstrate a compact tunable continuous-wave (CW) DUV laser source by direct intracavity frequency doubling of visible fiber lasers. Efficient green/yellow laser emission is enabled by the down-conversion in the Ho<inline-formula><tex-math notation="LaTeX">^{3+}</tex-math></inline-formula>- or Dy<inline-formula><tex-math notation="LaTeX">^{3+}</tex-math></inline-formula>-doped ZBLAN fibers while the miniaturized cavity consists of a home-made fiber pigtail mirror and diffraction grating. The second harmonic generation from visible to ultraviolet is subsequently implemented by utilizing a BBO module intracavity. The achieved CW DUV lasers yield wavelength tuning range of 269.5-275.4 nm and 283.6-289.9 nm in the presence of an ultra-narrow linewidth of <inline-formula><tex-math notation="LaTeX">< </tex-math></inline-formula>0.025 nm. The produced power at 272.6 nm reaches 1.36 mW and a maximum visible-to-DUV efficiency of 5.3‰ is estimated with the green laser excitation. Our work therefore provides new possibilities for the realization of a new class of compact, wavelength tunable, and cost-effective CW DUV laser sources.
We report a 790–1000 nm tunable femtosecond laser source by second harmonic generation (SHG) of a 1580–2000 nm soliton self-frequency shift (SSFS) fiber laser. The SSFS fiber laser with an all ...polarization-maintaining fiber configuration consists of passively mode-locked figure-9 Er-doped fiber oscillator, two-stage fiber amplifiers and a nonlinear fiber, delivering femtosecond Raman solitons in a tunable range of 1580 to 2016 nm. The tunable Raman solitons are further injected into a specifically-designed chirped periodically-poled lithium niobite (CPPLN) crystal for efficient SHG, and therefore femtosecond pulses with wide wavelength tuning from 790 to 1000 nm are obtained. The shortest pulse duration is < 100 fs at 890 nm, and the average power is 7.55 mW with a repetition rate of 44.9 MHz. This is, to the best of our knowledge, the first demonstration of a < 1000 nm broadband tunable fiber-based femtosecond source almost covering the whole short-wavelength near-infrared spectrum, which may have important applications in the nonlinear microscopy, biomedical imaging, and material processing.
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