Q-Switched Ytterbium-Doped Fiber Laser Using Black Phosphorus as Saturable Absorber

We demonstrate a Q-switched ytterbium-doped fiber laser （YDFL） using a newly developed multi-layer black phosphorous （BP） saturable absorber （SA）. The BP SA is prepared by mechanically exfoliating a BP crystal and sticking the acquired BP flakes onto a scotch tape. A small piece of the tape is then placed between two ferrules and incorporated in a YDFL cavity to achieve a stable Q-switched operation in a 1.0 μm region. The laser has a pump threshold of 55.1 mW, a pulse repetition rate that is tunable from 8.2 to 32.9 kHz, and the narrowest pulse width of 10.8 μs. The highest pulse energy of 328 nJ is achieved at the pump power of 97.6 mW. Our results show that multi-layer BP is a promising SA for Q-switching laser operation.

Wavelength-Tunable Single Frequency Ytterbium-Doped Fiber Laser with Loop Mirror Filter

By using a loop mirror filter, a novel wavelength-tunable single-frequency ytterbium-doped fiber laser is developed to select single longitudinal modes in a linear cavity. The output wavelength could be tuned 2.4 nm intervals range from 1063.3 to 1065.Tnrn with the temperature change of the fiber Bragg grating. The maximum output power could reach 32 m W while the pump power increases to 120 m W. The corresponding optical-to-optical conversion efficiency is 26.7% and the slope efficiency is 33.9%, respectively. The output power fluctuation is below 2%, and its highest signal-to-noise ratio is 60 dB.

A kW Continuous-Wave Ytterbium-Doped All-Fiber Laser Oscillator with Domestic Fiber Components and Gain Fiber

We demonstrate a kW continuous-wave ytterbium-doped all-fiber laser oscillator with M1 domestic fiber compo- nents： a 7× I fused fiber bundle combiner, a fiber Bragg grating and a double-clad gain fiber. The oscillator operates at 1079.48nrn with 80.94% slope efficiency and shows no limit of temperature and nonlinear effects. These indicate that the passive fiber components and the gain fiber are all qualified for the high power environ- ment. No evidence of the signal power roll-over shows that this oscillator possesses the capacity to higher output with available pump power.

Optical properties of ytterbium-doped tandem-pumped fiber oscillator

With the rapid development of ytterbium-doped fiber lasers, some obtrusive limitations on power scaling appeared. In order to avoid these problems, a scheme called tandem pumping is introduced into the fiber laser field. In this paper, the optical properties of an ytterbium-doped tandem-pumped fiber oscillator are presented. According to the oscillator profile, the proper gain fiber type and pump wavelength range are picked out, under the comprehensive consideration of laser conversion efficiency and beam quality. In addition, the photodarkening performances of tandem pumping lasers and conventional ones are compared based on practical application, with all possible impact parameters taken into account. Moreover, an all-fibered tandem-pumped oscillator centered at 1079.5 nm is built, in the way of clad pumping by a 1030-nm fiber laser. The laser power of the oscillator reaches 7 W, with an opto-optic efficiency of 82.4%.

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.

Low-Threshold Broadband Spectrum Generation by Amplification of Cascaded Stimulated Raman Scattering in an Ytterbium-Doped Fiber Amplifier

We present an experimental study on low-threshold broadband spectrum generation mainly due to the amplirfication of the cascaded stimulated Raman scattering （SRS） effect in a four-stage fiber master oscillator power amplifier system. The cascaded SRS is achieved by using a long passive fiber pumped by a pulsed fiber laser cen： tered at wavelength 1064 nm. The amplified spontaneous emission during the amplification process is efficiently suppressed by cutting the length of the passive fiber and by using a double-clad ytterbium-doped fiber amplifier. The generated broadband spectrum spans from 960nm to 1700nm with maximum average output 13.6 W and average spectral power density approximately 17. 7 mW/nm.

2×3 kW bidirectional output fiber oscillator employing spindle-shaped ytterbium-doped fiber

A 2×3 kW-level bidirectional output fiber oscillator is realized by combining the specially designed spindle-shaped ytterbium-doped fiber,non-wavelength-stabilized 976-nm LDs,and grating bandwidth optimization to balance transverse mode instability and stimulated Raman scattering.The maximum output powers at both ends are 3265 and 2840 W,respectively,with a total efficiency of 73.2%.The M^(2) factors of the lasers at both ends are about 1.98 and 2.38,respectively.The beam profile at both ends shows that a bidirectional output annular beam fiber oscillator has been realized,which has great potential in practical applications.

Novel constant-cladding tapered-core ytterbium-doped fiber for high-power fiber laser oscillator

Power scaling based on traditional ytterbium-doped fibers(YDFs)is limited by optical nonlinear effects and transverse mode instability(TMI)in high-power fiber lasers.Here,we propose a novel long tapered fiber with a constant cladding and tapered core(CCTC)along its axis direction.The tapered-core region of the fiber is designed to enhance the stimulated Raman scattering(SRS)threshold and suppress higher-order mode resonance in the laser cavity.The CCTC YDF was fabricated successfully with a modified chemical vapor deposition(MCVD)method combined with solution doping technology,which has a cladding diameter of 400µm and a varying core with a diameter of~24μm at both ends and~31μm in the middle.To test the performance of the CCTC fiber during high-power operation,an all-fiber laser oscillator based on a CCTC YDF was investigated experimentally.As a result,a maximum output power of 3.42 kW was achieved with an optical-to-optical efficiency of 55.2%,although the TMI effect was observed at an output power of~3.12 kW.The measured beam quality(M^(2)factor)was~1.7,and no sign of the Raman component was observed in the spectrum.We believe that CCTC YDF has great potential to simultaneously mitigate the SRS and TMI effects,and further power scaling is promising by optimizing the structure of the YDF.

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.

Passively Q-switched ytterbium-doped fiber laser using the evanescent field interaction with bulk-like WTe_2 particles

The potential of bulk-like WTe2 particles for the realization of a passive Q-switch operating at the 1 μm wavelength was investigated. The WTe2 particles were prepared using a simple mechanical exfoliation method together with Scotch tape. By attaching bulk-like WTe2 particles, which remained on the top of the sticky surface of a small segment of the Scotch tape, to the flat side of a side-polished fiber, a saturable absorber（SA） was readily implemented. A strong saturable absorption was then readily obtained through an evanescent field interaction with the WTe2 particles. The modulation depth of the prepared SA was measured as ~2.18% at 1.03 μm. By incorporating the proposed SA into an all-fiberized ytterbium-doped fiber ring cavity, stable Qswitched pulses were readily achieved.

272 W quasi-single-mode picosecond pulse laser of ytterbium-doped large-mode-area photonic crystal fiber

A large-mode-area（LMA） ytterbium-doped photonic crystal fiber（PCF） with core NA of 0.034 and core diameter of 50 μm was made by the stack-and-draw technique. The core is formed by Yb3+/Al3+/F-/P5+ co-doped silica glass containing 0.09 mol% Yb2O3 with an absorption coefficient at 976 nm up to 3.2 d B/m. The core glass with homogeneous distribution of Yb3+ ions and refractive index difference of 4 × 10-4 compared with pure silica was prepared by the sol-gel method and heat homogenization at 2000°C. Laser power amplification of this LMA PCF was studied using a seed source of 21 ps pulse duration and 48.7 MHz repetition rate at 1030 nm wavelength. With pump power of 520 W, a maximum 272 W（266 k W peak power） quasi-single-mode laser output with M2 of 2.2 was achieved in a 4.7 m fiber length bent at a diameter of 47 cm with slope efficiency of 52%, and no obvious mode instability, stimulated Raman scattering, or thermal damage on the end facet of the fiber were observed.

Tunable passively Q-switched ytterbium-doped fiber laser with mechanically exfoliated GaSe saturable absorber

A tunable passively Q-switched ytterbium-doped fiber laser using few-layer gallium selenide（GaSe） as a saturable absorber（SA） is demonstrated.The few-layer GaSe SA,which is fabricated by the mechanical exfoliation method,is able to generate a Q-switched fiber laser that has a maximum repetition rate of 92.6 kHz and a minimum pulsed width of 2.3 μs.The highest pulse energy exhibited by the generated pulse is 18.8 nJ with a signal to noise ratio of ~40 dB.The tunability of the proposed laser covers from 1042 to 1082 nm,giving a tuning range of 40 nm.

Mode-locked ytterbium-doped fiber laser with zinc phthalocyanine thin film saturable absorber

A stable mode-locked laser was demonstrated using a newly developed zinc phthalocyanine(ZnPc)thin film as passive saturable absorber(SA)in ytterbium-doped fiber laser(YDFL).The ZnPc thin film was obtained using a casting method and then inserted between the two fiber ferrules of a YDFL ring cavity to generate mode-locked pulses.The resulting pulsed laser operated at a wavelength of 1034.5 nm having a repetition rate of 3.3 MHz.At pump power of 277 mW,the maximum output power and pulse energy are achieved at 4.92 mW and 1.36 nJ,respectively.ZnPc has a high chemical and photochemical stability,and its significance for use as a potential SA in a mode-locked laser is reported in this work.

Optimization of spectral distortion in a ytterbium-doped mode-locked fiber laser system

A method for optimizing the spectral distortion of an ultrafast pulse in a polarization-maintaining picosecond linear-cavity fiber laser with a one-stage fiber amplifier is proposed and demonstrated. The mechanism of control of the spectral distortion in the fiber system has been investigated. The experimental and theoretical results illustrate that the filtering effect of a fiber Bragg grating can effectively decrease the spectral oscillatory distortion accumulated by self-phase modulation. Injected into a Nd:YAG regenerative amplifier, the ultrafast pulse could produce high pulse energy of 1.2 mJ at a repetition rate of 1 kHz.

Synthesis and Characterization of Neodymium and Ytterbium-doped Yttrium Aluminum Garnet Nano-powder

Nd/Yb-co-doped YAG transparent ceramic nano-powder was prepared by a sol-gel combustion method.The structure,morphology and properties were characterized by thermogravimetric-differential thermal analysis,X-ray diffraction,transmission electron microscopy,infrared spectroscopy,absorption analysis and fluorescence spectroscopy,respectively.The results show that the mass loss of the powder calcinated at 900 ℃ for 3 h is 49.56%.A well-crystallized Nd/Yb:YAG nano-powder with the superior sintering performance and high purity is obtained,and the morphology of the particles with the average diameter in the range of 60-100 runs appears regular.The nano-powder exhibits an intense absorption at 808 nm,corresponding to the 4I/9/2-4F7/2 transition of Nd^(^(3+) ions,which is suitable to absorb the wavelength of 808 nm from a laser diode source.The emission peak at 1046 nm of the Nd/Yb:YAG powder is more intense than that of Nd^(^(3+):YAG powder.It is indicated that the energy absorbed by Yb^(^(3+) ions from the laser diode source can be transmitted to Nd^(^(3+) ions based on the cross relaxation process of[(4F3/2)Nd,(2F7/2)Yb]-[(479/2)Nd,(2F5/2)Yb].

Investigation on Material Response of 55% SiCp/Al Composites Induced by Pulsed Laser

Silicon carbide particle reinforced aluminum matrix composites(SiCp/Al composites)are widely used in aviation,aerospace and electronic package.However,low machining efficiency,severe tool wear and poor surface quality are severe during the machining of SiCp/Al composites.Laser-induced oxidation is capable to improve the machinability of SiCp/Al composites.The material response of 55%(volume fraction)SiCp/Al composites induced by a nanosecond pulsed laser is studied.A metamorphic layer which is composed of an oxide layer and sub-layer is produced.The effects of reaction surrounding and laser average power on the microstructure and thickness of the oxide layer and sub-layer are investigated.Experimental results show that:A thicker oxide layer and a sub-layer are formed in an oxygen-rich atmosphere.The oxides are mainly composed of 2Al2O3·SiO2(mullite).A positive correlation between the laser average power and thicknesses of oxide layers and sub-layers is found.A loose oxide layer of 138μm and a sub-layer of 21μm are formed at the laser average power of 6 W,laser scanning pitch of 10μm,and laser scanning speed of 1 mm/s under an oxygen-rich atmosphere.The high efficient machining of Si Cp/Al composites can be realized by laser-induced oxidation.

Demonstration of multi-Watt all-fiber superfluorescent source operating near 980 nm

The superfluorescent Yb-doped fiber source operating near 980 nm is studied. The design requirement is theoretically discussed aiming to suppress the amplified spontaneous emission around 1030 nm in the 980-rim superfluorescent fiber source. Based on the theoretical study, a multi-Watt, all-fiber, bi-directional, pumped, superfluorescent source operating near 980 nm is designed and experimentally demonstrated for the first time, to the best of our knowledge. The recorded 8.38-W combined output power is obtained with a 3-dB bandwidth about 3.5 nm. The power scaling of the 980-nm superlfuorescent fiber source is limited by the parasitic laser oscillation.

Photomechanical Ablation of 304L Stainless Steel, Aluminum Oxide (Al2O3) Thin Film, and Pure Silicon

Recently, a number of studies have focused on micro-manufacturing processes, which find use in a variety of applications, including the production of microelectromechanical systems (MEMS). The process of ablation in materials is mainly governed by the laser source and scanning speed. The rate of material ablation is influenced by chemical and physical properties. In this work, the energy from a CO2 laser was used to ablate three different materials, namely, stainless steel 304L, a thin film of amorphous aluminum oxide (Al2O3), and pure silicon, due to their wide use in MEMS technology. The laser parameters used were an average power of 18 W and a spot size of 200 μm. The maximum depth during the photomechanical ablation process was 72 μm in the case of 304L steel and 77 μm in the case of the Al2O3 thin film for a scan rate of 24 mm/min. However, at the same scan rate, silicon did not exhibit any penetration. As expected, while increasing scanning speed the ablation depth decreases due to reduced interaction time between laser and material. The theoretical ytterbium fiber laser shown in this study can thus be employed in the manufacturing of a wide variety of materials used in the production of MEMS as well as those used in clean energy technologies.

5 kW-level single-mode fiber amplifier based on low-numerical-aperture fiber

A low-numerical-aperture(NA)concept enables large-mode-area fiber with better single-mode operation ability,which is beneficial for transverse mode instability and nonlinear effects suppression.In this contribution,we reported a high-power fiber amplifier based on a piece of self-developed large-mode-area low-NA fiber with a core NA of 0.049 and a core/inner cladding diameter of 25/400μm.The influence of the pump wavelength and fiber length on the power scaling potential of the fiber amplifier is systematically investigated.As a result,an output of 4.80 kW and a beam quality factor of~1.33 were finally obtained,which is the highest output power ever reported in a fiber amplifier exploiting the low-NA fiber.The results reveal that low-NA fibers have superiority in power scaling and beam quality maintenance at high power levels.

High-efficiency bismuth borate-based optical parametric chirped pulse amplifier with approximately 2.1 mJ,38 fs output pulses at approximately 2150 nm

We present a compact and cost-effective mJ-level femtosecond laser system operating at a center wavelength of approximately 2.15μm.An affordable two-stage ytterbium-doped yttrium aluminum garnet(Yb:YAG)chirped pulse amplifier provides more than 10 mJ,approximately 1.2 ps pulses at 1030 nm to pump a three-stage optical parametric chirped pulse amplifier(OPCPA)based on bismuth borate crystals and to drive the supercontinuum seed in the YAG crystal.The energy of the amplified pulses in the wavelength range of 1.95–2.4μm reached 2.25 mJ with a pump-tosignal conversion efficiency of approximately 25%in the last OPCPA stage.These pulses were compressed to 38 fs in a pair of Suprasil 300 glass prisms.