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The investigated Q-switching technique is based on the spectral overlap between a Fabry-Perot (F-P) filter and a fiber Bragg grating. This Q-switching concept is implemented in a ring erbium (Er)-doped fiber laser configuration. We use a traveling-wave analytical model to study the peak power and the time duration of the output pulses with respect to the cavity parameters, such as the Er-doped fiber length, the pumping power, and the scanning frequency of the fiber F-P tunable filter. Experimental results are used to validate the proposed Q-switched fiber laser model. [ABSTRACT FROM AUTHOR]

Organic materials are attracting attention for their potential applications due to their large third-order optical nonlinearities. A passive fiber Q-switching laser has been demonstrated based on an erbium/ytterbium codoped amplifier and an acetone solution saturable absorber (SA). When pump power was increased from 120 to 155 mW, the repetition rate increased from 5.68 to 16.67 kHz, while the pulse width decreased from 24.1 to 15 µs. These results indicate that acetone solution can be used as an effective SA for pulsed lasers. [ABSTRACT FROM AUTHOR]

A dumbbell-shaped fiber laser with dual-functional pulsed outputs is demonstrated using a filmy polyvinyl alcohol-based gold nanorods (GNRs) saturable absorber (SA), which can deliver mode-locked soliton and multiwavelength Q-switched pulse. The GNRs-SA is fabricated by seed-mediated method with a modulation depth of 4.1% and nonsaturable loss of 32.9%. When the fiber laser operates in mode-locked regime, stable fundamental solitons with a temporal width of 910 fs and repetition rate of 2.88 MHz are directly generated from the laser cavity. The corresponding spectrum is located at 1560.1 nm with a 3-dB bandwidth of 3.08 nm. When the laser operates in Q-switched regime, more than 5-wavelength oscillation is achieved. The repetition rate of Q-switched monotonically increases from 13.4 to 31.7 kHz and the pulse duration can be significantly narrowed from 6.07 to 3.12 μs by varying the pump power from 128 to 154 mW. The results further expand the applications of GNRs-SA to obtain versatile pulse sources in ultrafast laser field. [ABSTRACT FROM AUTHOR]

We demonstrate the laser performance of a gadolinium scandium gallium garnet (GSGG) single crystal with 10 at.% Yb3+-doping concentration. In the case of continuous-wave operation, the laser wavelength was blueshifted in the range from 1067.1 to 1027.2 nm with increasing the transmission of the output coupler from 0.5% to 30%. The maximum output power produced was 3.2Wwith 3% output transmission. By employing a Cr4+∶YAG crystal as the saturable absorber, a stable Q-switched laser beam with 21-ns pulse duration and 38-μJ single-pulse energy was achieved at a 20-kHz repetition rate. This laser crystal should be a promising candidate for nanosecond pulse generation especially in harsh environments, such as outer space, due to its wide absorption and emission spectral bandwidths and strong radiation resistance. [ABSTRACT FROM AUTHOR]

The portable laser is indispensable for handheld laser-induced breakdown spectroscopy (LIBS) instruments. We developed a passive, Q-switched pulsed, Nd:YAG laser system with small size and low cost. The maximum pulse energy of the laser was 10 mJ and the pulse duration was <2 ns. The peak power was >5 MW. The laser exhibited very high stability without any cooling system and its relative standard deviation of the pulse energy was <0.2 %. The laser was also used as a light source of LIBS to measure the concentrations of Cr, Cu, Mn, and Ni in alloys. The experimental results show that the determination coefficient of the calibration curves for these four elements is all better than 0.99. For its shorter pulse duration, the laser can decrease the plasma shield effect to improve the coupling of laser pulse and the target and stability of spectra intensity. The portable laser developed is a good laser source for handheld LIBS instruments. [ABSTRACT FROM AUTHOR]

stable passive Q-switched ytterbium-doped fiber laser (YDFL) operating at 1057.4 and 1044.5 nm is demonstrated using two types of topological insulator-based saturable absorbers (SAs): bismuth (III) selenide (Bi2Se3) and bismuth (III) telluride (Bi2Te3). These materials are embedded in polyvinyl alcohol film and incorporated in the YDFL cavity. Using Bi2Se3 SA, the YDFL obtains a stable train of pulses with a repetition rate that is tunable from 48.83 to 102 kHz. Meanwhile, the corresponding pulse width decreases from 8.9 to 3.48 μs as the pump power increases from 67.6 to 88.3 mW. For the Bi2Te3-based Q-switched YDFL, the repetition rate grows from 43.25 to 93.63 kHz and the pulse width shrinks from 5.65 to 2.01 μs as the 980-nm pump power rises from 72.8 to 98.4 mW. The maximum pulse energy is obtained with the Bi2Te3 SA at 29.95 nJ. [ABSTRACT FROM AUTHOR]

A polycrystalline ceramic based on an Nd; Y:SrF2 single crystal was successfully fabricated and its laser performance was experimentally investigated. We obtained dual-wavelength continuous-wave operation at the wavelengths of 1050.5 and 1058.0 nm. The maximum output power and slope efficiency were 750 mW and 31.5%, respectively. In the passively Q-switched operation, the shortest pulse with a 169-ns duration was also obtained, and the corresponding maximum repetition rate and single pulse energy were 7.3 kHz and 19.2 μJ, respectively. [ABSTRACT FROM AUTHOR]

Due to an enormous potential of pulsed lasers in applications such as manufacturing, metrology, environmental sensing, and biomedical diagnostics, a high-power and stable Q-switched erbium-ytterbium codoped double-clad fiber laser (EYDFL) incorporating of multiwall carbon nanotubes (MWCNTs) saturable absorber (SA) made based on polyvinyl alcohol (PVA) with a 3:2 ratio is demonstrated. The SA was fabricated by mixing a dilute PVA solution with an MWCNTs homogeneous solution. Subsequently, the mixture was sonicated and centrifuged to produce a homogeneous suspension that was left to dry at room temperature to form the MWCNTs-PVA film. The SA was formed by inserting the film between a pair of FC/PC fiber connectors. Then, it was integrated into the EYDFL's ring cavity, which uses a 5-m-long erbium-ytterbium codoped fiber (EYDF). The lasing threshold for the Q-switched EYDFL was at 330 mW. At the maximum available pump power of 900 mW, the proposed EYDFL produced Q-switched pulses with a repetition rate of 74.85 kHz, pulsewidth of ~3.6 μs, and an average output power of about 5 mW. The maximum energy per pulse of ~85 nJ was obtained at pump power of ~700 mW with peak power of 21 mW. [ABSTRACT FROM AUTHOR]

A midinfrared (mid-IR) saturable absorber mirror (SAM) was fabricated by coating aluminum film on FeEr2+ :ZnSe crystal, based on the vacuum evaporation method. By employing the prepared SAM, we demonstrated a high-power passively Q-switched Er3+-doped ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber laser at 2.8 μm. The highest output power in excess of 1.01Wwas obtained with a pulse energy of 11.37 μJ and pulse duration of 0.73 μs, corresponding to a repetition rate of 88.84 kHz. To the best of our knowledge, these values represent the highest output power/pulse energy from a passively Q-switched ZBLAN fiber laser around 2.8 μm. Our results demonstrate that FeEr2+ :ZnSe SAM is a promising device for high-power/high-energy pulse generation in compact mid-IR fiber lasers. [ABSTRACT FROM AUTHOR]

We report on the generation of 152-nJ Q-switched pulses in all-polarization-maintaining Er-doped fiber laser. The laser is passively modulated by the antimony telluride (Sb2Te3) layer sputtered on a surface of the side-polished fiber in order to exploit the evanescent field interaction in optically nonlinear material. The laser cavity is designed in an extremely simple way comprising, in addition to fibers, only one component and the saturable absorber, forming a robust, compact, and stable source of short pulses. The repetition rate might be tuned from 42 kHz up to 132 kHz. The shortest recorded pulse duration was the 857 ns. [ABSTRACT FROM AUTHOR]

We demonstrate a passively Q-switched Yb3+-doped ScBO3 bulk laser using a black phosphorous (BP) saturable absorber, a two-dimensional semiconductor. The response spectra of BP show that it is suitable as a universal switcher in the spectral range from the visible to midinfrared band. Considering the saturable absorption properties of BP and emission properties of Yb3+-doped crystals, the passively Q-switched bulk laser pulses were realized with the Yb3+:ScBO3 crystal as a gain material and a fabricated BP sample as a Q-switcher. Because of the large energy storage capacity of Yb3+:ScBO3, the maximum output energy is obtained to be 1.4 μJ, which is comparable with the previous reported maximum energy of graphene Q-switched lasers. The obtained results identify the potential capability of BP as a pulse modulator in bulk lasers, and BP plays an increasingly important role in a wide range of its applications, including photonics and optoelectronics. [ABSTRACT FROM AUTHOR]

We report graphene mode-locked or Q-switched Tm/Ho-codoped fiber laser pumped by a 1212-nm phosphorus-doped fiber Raman laser. First, comparison experiments were performed for a continuous-wave 2 μm Tm/Ho-codoped fiber laser pumped by a 1565-nm laser or a 1212-nm laser, verifying that the 1212- nm pumping is more efficient than the conventional ~1560-nm pumping. Then, we further realized 1212-nm highly efficient pumped Tm/Ho-codoped fiber lasers mode-locked and Q-switched by a graphene saturable absorber, respectively. Using only 30-cm Tm-Ho gain fiber under the 1212-nm pumping, the passive Q-switching at a center wavelength of 1976 nm was efficiently generated with tunable repetition rate between 32.2 and 43.0 kHz and shortest pulse width of 1.41 μs. Moreover, the passive mode-locking at 1913.7 nm was stably achieved with a fundamental repetition rate of 19.978 MHz and pulse energy of ~20 pJ. To the best of our knowledge, it is the first demonstration of 2-μm pulsed fiber lasers high efficiently pumped by a 1212-nm laser. [ABSTRACT FROM AUTHOR]

We demonstrated a pulsed erbium-doped fiber laser (EDFL) based on a few-layer molybdenum disulfide saturable absorber (MoS2-SA). The MoS2-SA was fabricated into a film structure by evaporating the mixture of MoS2 nanosheets and polyvinyl alcohol. The Raman spectra and nonlinear optical characteristics were measured to confirm the quality of the as-prepared MoS2-SA. By inserting the MoS2-SA into an EDFL, the pulsed operation from the stable Q-switched to mode-locking regime could be achieved by simply increasing the pump power level. The Q-switched pulse duration and repetition rate could vary from 5.18 to 3.53 μs and from 72.74 to 86.39 kHz, respectively. The maximum pulse energy was 74.93 nJ. After the achievement of Q-switched operation, the ultrashort mode-locking pulse was obtained by further increasing the pump power. The results further demonstrate the excellent saturable absorption ability of the few-layer MoS2 at telecommunication waveband. [ABSTRACT FROM AUTHOR]

We report a tungsten diselenide (WSe2) polyvinyl alcohol (PVA)-based, saturable absorber and related experiment results of a Q-switched fiber laser. WSe2-PVA film is synthesized by liquid phase exfoliation method, and its saturable absorption is measured via a nonlinear transmission experiment. The result shows that WSe2-PVA saturable absorber has a modulation depth of 3.5%, which means it has potential for generating an ultrafast pulse laser. We apply this absorber into a ring-cavity erbium-doped fiber laser and obtain Q-switched pulses under appropriate pump power. Our work demonstrates the reliable nonlinear optical characteristics of WSe2 and the feasibility for this two-dimensional material to be applied in the field of nonlinear optics. [ABSTRACT FROM AUTHOR]

We demonstrate a high-peak-power and narrow pulse mid-infrared (MIR) laser with xenon-lamp pumping and La3Ga5SiO14 (LGS) Q-switching on the Cr,Er:YAP crystal grown by Czochralski method. X-ray powder diffraction and x-ray rocking curves suggest the crystal has high crystalline quality. Segregation coefficients of the Cr3 + and Er3 + in the as-grown Cr,Er:YAP crystal are 4.96 and 1.07, respectively. The absorption and fluorescence spectra indicate that the Cr,Er:YAP crystal is a promising material for MIR laser by xenon-lamp pumping. The fluorescence lifetimes of the upper (I11/24) and lower (I13/24) laser levels are 0.86 and 3.57 ms, respectively. A maximum energy of 632 mJ is acquired at 5 Hz by xenon lamp pumping. By the LGS electro-optic Q-switching technology, single pulse energy of 148.6 mJ is achieved at 5 Hz with a pulse width of 35.4 ns and peak power of 4.2 MW. The results show that the LGS Q-switched Cr,Er:YAP crystal pumped by xenon lamp possesses potential application as a short-pulse and high-energy laser device. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate a linearly polarized, passively Q-switched, erbium (Er)-doped fiber laser using a saturable absorber (SA) based on a composite consisting of a bulk-structured bismuth telluride (Bi2Te3) topological insulator (TI) and polyvinyl alcohol (PVA). The SA was constructed on a polarization maintaining (PM) fiber ferrule platform, which had a sandwich structure. Its saturation intensity and modulation depth were measured to be ~47.56 MW/cm2 and ~4.1%, respectively. Using the prepared Bi2Te3/PVA SA in a PM Er-doped fiber ring laser, stable Q-switched pulses with a degree of polarization of ~98.6% and an azimuth angle of ~ - 0.34 deg were demonstrated. The minimum pulse width was measured to be ~1.58 μs at a repetition rate of 47.1 kHz. This experimental demonstration verifies that a thin film based on a bulk-structured Bi2Te3 TI can fit into a sandwich-structured SA based on PM fiber ferrules [ABSTRACT FROM AUTHOR]

A continuous wave (CW) Tm:YAP laser resonantly pumped Ho:YLF laser in CW mode and passive Qswitched (PQS) mode with multilayer graphene as a saturable absorber is reported. A comparison analysis of laser performances with two different output couplers is carried out. In PQS mode, an maximum average output power of 2.26Wis obtained, corresponding to a slope efficiency of 20.7%. The minimum pulse width observed is 651.9 ns with a center wavelength of 2057.16 nm with a 300-mm radius curvature and 50% transmission output coupler. Meanwhile, the maximum pulse repetition frequency of 59.2 kHz is obtained. The beam quality factor of M² was 1.2, which is the near diffraction limit. The results show that multilayer graphene can be used as a saturable absorber in a Ho:YLF laser around a 2-µm wavelength. [ABSTRACT FROM AUTHOR]

A diode-pumped, passively Q-switched, intracavity-frequency-doubled YVO4/Nd:YVO4/KTP green laser has been realized with a monolayer graphene as the saturable absorber. Under an incident pump power of 10.5 W, the maximum output power of the passively Q-switched green laser was 516mWwith a repetition rate of 222 kHz and pulse width of 202 ns. The corresponding pulse energy and the peak power were 2.32 μJ and 11.5 W, respectively. [ABSTRACT FROM AUTHOR]

We demonstrated the efficient generation of a linearly polarized Ho:YAG laser pumped by a thulium fiber laser. Independent of the pumping power and without utilizing any dispersive optical element, the output radiation remained stable with a high degree of linear polarization. The output with 2044 nm wavelength and 0.12 nm bandwidth was measured. In the free-running generation, with respect to the incident pump power, we recorded more than 9 W of output power with 59% slope efficiency. In addition, in the pulsed generation, we obtained more than 2.2 mJ pulses with 50 ns time duration, and 44 kW peak power. [ABSTRACT FROM AUTHOR]

We present a high compact structure laser diode (LD) side-pumped all-solid-state Q-switched master oscillator power amplifier (MOPA) laser system with high beam quality. Bidirectional voltage-supplied Q-switched and MOPA technologies were introduced in the design. An in-center wavelength of 1064 nm with pulse width adjustability from 5 to 18 ns was obtained at the repetition rate of 500 Hz. Through multistage Nd:YAG amplifiers at the pulse width of 6 ns, the oscillator was scaled up to 145 W and the corresponding peak power reached 48.3 MW with single pulse energy fluctuation less than 0.45% in 1 h operation. [ABSTRACT FROM AUTHOR]

There is an increasing demand for high-intensity subnanosecond lasers for emerging industrial applications. While femtosecond and picosecond laser sources are considered promising, they suffer from the significant drawbacks of increased complexity and cost. In this regard, we demonstrate a unique edge-pumped passively Q-switched Nd:YAG/Cr4+:YAG microchip laser. The microchip is made of a Nd:YAG/Sm:YAG composite ceramic, and a Sm:YAG cladding is utilized as both the pump beam waveguide and amplified spontaneous emission absorber. With the use of a flat-concave laser cavity, we obtain single-pulse energy of 1.66 mJ for an absorbed pump energy of 24 mJ. Further, the resulting pulse width is 683 ps, and the repetition rate is 10 Hz. [ABSTRACT FROM AUTHOR]

We demonstrate the performance of a 968-nm laser-diode (LD) side-pumped Er,Pr:YAP laser in free-running and electro-optical (EO) Q-switched modes with emission at 2.7 μm, respectively. In the free-running mode, a maximum power of 11 W is achieved at a working frequency of 150 Hz and a pulse width of 200 μs, corresponding to the single pulse output energy of 73.3 mJ and slope efficiency of 13.3%. In the EO Q-switching mode, a giant pulse laser is obtained with pulse energy of 20.5 mJ, pulse width of 61.4 ns, and peak power of 0.33 MW at the highest working frequency of 150 Hz, corresponding to the energy extraction efficiency of 71.4%. In addition, dual-wavelength laser at 2713 and 2732 nm and beam quality factors Mx2/My2 of 6.62/6.66 are measured, respectively. The results indicate that a 2.7-μm laser with a high repetition rate and high peak power can be realized through LD side-pumped and EO Q-switched Er,Pr:YAP crystal. [ABSTRACT FROM AUTHOR]

We propose and demonstrate experimentally multimode Q-switched mode-locking (QML) fiber laser signal generation based on a long few-mode Er-doped fiber (FM-EDF). The erbium-doped profile of the fiber has been optimized to equalize the modal gain. The fiber supporting six modes has a total length of 5.5 m, a part of the fiber is used as a gain medium, and the unpumped part of the fiber is used as a saturable absorber. Multimode oscillation lasers in the state of the continuous wave laser operation, Q-switching, and QML state pulse laser operation were observed and measured at different pump powers by adjusting the polarization controller. A 1570-nm multimode QML pulse train was obtained, when the pump power was about 2.4 W. The width of the Q-switched envelope was 19 μs, and the repetition rate was 17.4 kHz. The stable mode-locked pulses repetition rate in Q-switched envelopes was 13.18 MHz. These temporal pulses can also be observed under the case of partly blocking the beam profile, and the part of the spectral signal gradually disappeared. The mode number in the laser was checked by a homemade mode selection photonic lantern. The results showed that the fiber laser had multimode oscillation, and the modes in generated signal were ≥5. The multiple transverse modes of the generated lasers are all in QML state at the same time. To the best of our knowledge, this is the first experimental demonstration of a multimode QML fiber laser using a long FM-EDF. [ABSTRACT FROM AUTHOR]

Acousto-optically Q-switched operation of a Ho:SSO laser is reported for the first time. An average power of 2.23 W was obtained at a pulse repetition frequency from 5 to 20 kHz, with a corresponding to optical-to-optical conversion efficiency of 14.4% and a slope efficiency of 20%. The highest energy per pulse of 0.44 mJ in 28 ns was achieved at 2112 nm with a repetition rate of 5 kHz and peak power of 15 kW. The lifetime of Ho3+ in the Sc2SiO5 crystal host was also measured. [ABSTRACT FROM AUTHOR]

Cylindrical vector-polarized vortex pulses from a passively Q-switched laser are demonstrated. Pump radiation reshaped into a size-controlled annular profile via circular Dammann grating produces an efficient excitation of the LG01 mode. The YAG / Nd : YAG / Cr4 + : YAG composite crystal structure is found to reduce the Q-switching threshold and significantly suppress thermal damage, thus allowing ability to obtain a passively Q-switched pulse. The threshold pumping power is found to be 4.35 W, with a slope efficiency of 23.1%. A maximum peak power of 3.24 kW, maximum pulse energy of 53.46 μJ, pulse width of 17.5 ns, and repetition rate of 2.695 kHz are obtained. Furthermore, a radially polarized output with a polarization degree of 88.9% is confirmed. Finally, mode and polarization tuning are also discussed. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editors discuss various reports within the issue on topics including the broadband saturable absorption property of graphene, the generation of Q-switched pulses, and the mode-locked erbium-doped fiber laser.