Wavelength-Tunable Rectangular Pulses Generated from All-Fiber Mode-Locked Laser Based on Semiconductor Saturable Absorber Mirror

The wavelength-tunable rectangular mode-locking operation is demonstrated in an all-fiber laser based on semi- conductor saturable absorber mirror. As the dissipative soliton resonance signature, the pulse duration varies from 5SOps to 2.1 ns as a function o~ the increasing pump power. Correspondingly, the maximum pulse energy is 9.11 n3. Moreover, it is found that the wavelength tunable operation with a range of approximately 10 nm could be obtained by properly adjusting the polarization controllers. The characteristics of the rectangular pulses at different wavelengths are similar to each other. The demonstration of the wavelength tunable rectangular pulses would be beneficial to some applications for many fields such as spectroscopy and sensing research.

Dual-Wavelength Passively Q-Switched Ytterbium-Doped Fiber Laser Based on Aluminum Oxide Nanoparticle Saturable Absorbers

We report on generation of a dual-wavelength, all-fiber, passively Q-switched ytterbium-doped fiber laser using aluminum oxide nanoparticle （Al2O3-NP） thin film. A thin film of Al2O3 was prepared by embedding Al2O3-NPs into a polyvinyl alcohol （PVA） as a host polymer, and then inserted between two fiber ferrules to act as a saturable absorber （SA）. By incorporating the Al2O3-PVA SA into the laser cavity, a stable dual-wavelength pulse output centered at 1050 and 1060.7nm is observed at threshold pump power of 80mW. As the pump power is gradually increased from 80 to 300mW, the repetition rate of the generated pulse increases from 16.23 to 59 kHz, while the pulse width decreases from 19 to 6μs. To the best of our knowledge, this is the first demonstration for this type of SA operating in the 1 μm region.

Sensitivity to Acidification of Forest Soils in Two Watersheds with Contrasting Hydrological Regimes in the Oil Sands Region of Alberta

Input of large amounts of N and S compounds into forest ecosystems through atmospheric deposition is a significant risk for soil acidification in the oil sands region of Alberta.We evaluated the sensitivity of forest soils to acidification in two watersheds(Lake 287 and Lake 185)with contrasting hydrological regimes as a part of a larger project assessing the role of N and S cycling in soil acidification in forest ecosystems.Fifty six forest soil samples were collected from the two watersheds by horizon from 10 monitoring plots dominated by either jack pine(Pinus banksiana)or aspen(Populus tremuloides).Soils in the two watersheds were extremely to moderately acidic with pH(CaCl_2)ranging from 2.83 to 4.91.Soil acid-base chemistry variables such as pH,base saturation,Al saturation,and acid-buffering capacity measured using the acetic acid equilibrium procedure indicated that soils in Lake 287 were more acidified than those in Lake 185. Acid-buffering capacity decreased in the order of forest floor>subsurface mineral soil>surface mineral soil.The most dramatic differences in percent Ca and Al saturations between the two watersheds were found in the surface mineral soil horizon.Percent Ca and Al saturation in the surface mineral soil in Lake 287 were 15% and 70%,respectively;the percent Ca saturation value fell within a critical range proposed in the literature that indicates soil acidification.Our results suggest that the soils in the two watersheds have low acid buffering capacity and would be sensitive to increased acidic deposition in the region.

Q-switched fiber laser based on saturable absorption of ferroferric-oxide nanoparticles

We demonstrate that ferroferric-oxide(Fe_3O_4) nanoparticles exhibit nonlinear saturable absorption property at1.55 μm, and fabricate two filmy saturable absorbers by embedding the nanoparticles into a polyvinyl alcohol(PVA) film or polyimide(PI) film separately. In the Fe_3O_4-PVA(Fe_3O_4-PI) Q-switched fiber laser, the pulse repetition rate increases from 8.5 kHz(5.5 kHz) to 28 kHz(49 kHz) and the pulse duration decreases from 23.5 μs(47 μs) to 6 μs(3.5 μs) by varying the pump power from 25 m W(23 mW) to 150 m W(650 mW). Experiment results indicate that PI-based saturable absorbers can afford larger powers than PVA-based saturable absorbers, which can be attributed to the higher fusion point of the PI film. The Fe_3O_4-PI saturable absorber exhibits features of high damage threshold, low cost, and good flexibility, which could be applied in fields of near-infrared pulse generation and frequency conversions.

Dual-wavelength rectangular pulse erbium-doped fiber laser based on topological insulator saturable absorber

We reported on the generation of the dual-wavelength rectangular pulse in an erbium-doped fiber laser(EDFL)with a topological insulator saturable absorber.The rectangular pulse could be stably initiated with pulse width from 13.62 to 25.16 ns and fundamental repetition rate of 3.54 MHz by properly adjusting the pump power and the polarization state.In addition,we verified that the pulse shape of the dual-wavelength rectangular pulse can be affected by the total net cavity dispersion in the fiber laser.Furthermore,by properly rotating the polarization controllers,the harmonic mode-locking operation of the dual-wavelength rectangular pulse was also obtained.The dual-wavelength rectangular pulse EDFL would benefit some potential applications,such as spectroscopy,biomedicine,and sensing research.

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.

Dual-wavelength single-longitudinal-mode fiber laser with switchable wavelength spacing based on a graphene saturable absorber

We propose and demonstrate a dual-wavelength single-longitudinal-mode(SLM) fiber laser with switchable wavelength spacing based on a graphene saturable absorber(GSA) and a Wave Shaper. By virtue of the excellent saturable absorption ability of graphene, the linewidths of the lasing wavelengths can be effectively reduced and eventually SLM operation can be obtained. The linewidths of both wavelengths are measured to be narrower than 7.3 kHz. The obtained results suggest that the graphene would be a good candidate nonlinear optical material for applications in related photonic fields, such as SLM oscillation generation for microwave generation and optical sensing.

High-power passively Q-switched 2 μm all-solid-state laser based on a Bi_2Te_3 saturable absorber

By using the ultrasound-assisted liquid phase exfoliation method, Bi_2Te_3 nanosheets are synthesized and deposited onto a quartz plate to form a kind of saturable absorber(SA), in which nonlinear absorption properties around 2 μm are analyzed with a home-made mode-locked laser. With the as-prepared Bi_2Te_3 SA employed,a stable passively Q-switched all-solid-state 2 μm laser is successfully realized. Q-switched pulses with a maximum average output power of 2.03 W are generated under an output coupling of 5%, corresponding to the maximum single-pulse energy of 18.4 μJ and peak power of 23 W. The delivered shortest pulse duration and maximum repetition rate are 620 ns and 118 k Hz under an output coupling of 2%, respectively. It is the first presentation of such Bi_2Te_3 SA employed in a solid-state Q-switched crystalline laser at 2 μm, to the best of our knowledge. In comparison with other 2 D materials suitable for pulsed 2 μm lasers, the saturable absorption performance of Bi_2Te_3 SA is proved to be promising in generating high power and high-repetition-rate 2 μm laser pulses.

Femtoseconds soliton mode-locked erbium-doped fiber laser based on nickel oxide nanoparticle saturable absorber

We demonstrate a femtosecond mode-locked erbium-doped fiber laser（EDFL） using a nickel oxide（Ni O） as a saturable absorber（SA）. Ni O nanoparticles are hosted into polyethylene oxide film and attached to fiber ferrule in the laser cavity. The Ni O-SA shows a 39% modulation depth with a 0.04 MW∕cm^2 saturation intensity. Our ring laser cavity based on erbium-doped active fiber with managed intracavity dispersion has the ability to generate ultrashort pulses with a full width at half-maximum（FWHM） of around 2.85 nm centered at 1561.8 nm.The pulses repeat at a frequency of 0.96 MHz and duration of 950 fs.