A Graphene-Based Passively Q-Switched Ho：YAG Laser

A 2.09-μm in-band pumped passively Q-switched Ho： YAG laser is demonstrated. Single layer graphene deposited on a quartz substrate is used as the saturable absorber for the Q-switched operation. The minimum pulse width of 2.11μs is obtained at an average output power of lOOmW, corresponding to a pulse repetition frequency of 57.1 kHz and the pulse energy of 1.75 μJ. The beam quality factors M^2 of the Q-switched laser are 1.18 and 1.22 in the horizontal and longitudinal direction, respectively. The optical-to-optical conversion efficiency of the passively Q-switched laser is 4.3%, which is the highest conversion efficiency in the 2 μm wavelength, to the best of our knowledge. It shows clearly that the Ho： YAG crystal is a potential gain medium in the 2 μm range for the graphene application.     

Q-switched Er-doped fiber laser with low pumping threshold using graphene saturable absorber

We propose a Q-switched Er-doped fiber laser(EDFL) with a threshold pumping power as low as 7.4 mW, and demonstrate using graphene polyvinyl alcohol(PVA) thin film as a passive saturable absorber(SA). The SA is fabricated from graphene flakes, which is synthesized by electrochemical exfoliation of graphite at room temperature in 1% sodium dodecyl sulfate aqueous solution. The flakes are mixed with PVA solution to produce a thin film, which is then sandwiched between two ferrules to form a SA and integrated in the EDFL ring cavity to generate a stable Q-switched pulse train. The pulse train operates at 1560 nm with a threshold pump power of 7.4 mW. At maximum 1480 nm pump power of 33.0 mW, the EDFL generates an optical pulse train with a repetition rate of 27.0 kHz and pulse width of 3.56 μs. The maximum pulse energy of 39.4 nJ is obtained at a pump power of 14.9 mW. This laser can be used as a simple and low-cost light source for metrology, environmental sensing, and biomedical diagnostics.     

Q-Switched Tm：YAG Laser Intracavity-Pumped by a 1064nm Laser

We report a Q-switched 2-μm Tm：YAG laser based on intracavity-pumped by a 1064-nm Nd：YAG laser operating at room temperature for the first time. An average output power of 5.1W is obtained with the repetition rate of 30kHz and a pulse width of 300ns. In addition, we demonstrate a 12.5-W continuous-wave 2-μm Tm：YAG laser, which is, to our best knowledge, the highest power for intracavity-pumping configuration.     

2-μm mode-locked nanosecond fiber laser based on MoS_2 saturable absorber

We demonstrated a 2-μm passively mode-locked nanosecond fiber laser based on a MoS_2 saturable absorber(SA).Owing to the effect of nonlinear absorption in the MoS_2 SA, the pulse width decreased from 64.7 to 13.8 ns with increasing pump power from 1.10 to 1.45 W. The use of a narrow-bandwidth fiber Bragg grating resulted in a central wavelength and 3-dB spectral bandwidth of 2010.16 and 0.15 nm, respectively. Experimental results show that MoS_2 is a promising material for a 2-μm mode-locked fiber laser.     

Wavelength tunable passively Q-switched Yb-doped double-clad f iber laser with graphene grown on SiC

A passively Q-switched tunable Yb-doped double-clad fiber laser is demonstrated with graphene epitaxially grown on SiC.The spectral tuning of the Q-switched fiber laser is implemented by rotating a quartz plate filter inside the cavity.The central wavelength of the fiber laser can be continuously tuned from 1038.54 to 1056.22 nm.The maximum pulse energy of 0.65 μJ is obtained at the pump power of 4.08 W,and the corresponding pulse duration and average output power are 1.60 μs and 35 mW,respectively.     

Green Output of 1.5 W from a Diode-Pumped Intracavity Frequency-Doubled Self-Q-Switched and Mode-Locked Cr,Nd：YAG Laser

We report a diode-pumped intracavity frequency-doubled self-Q-switched and mode-locked Cr,Nd：YAG/KTP green laser with a Z-type cavity, which produces 1.5 W of average power at 532nm with incident pump power 14.2 W. The individual mode-locked green pulse duration is about 560ps with 149 MHz repetition rate. Almost 100% modulation depth of the mode-locked green pulses is achieved at an incident pump power of 4.13 W. The maximum energy of Q-switched green pulse is 19.8μJ. The experimental results of pulse duration and pulse energy of Q-switched green pulse agree well with the theoretical calculations.     

6.5-ns actively Q-switched Nd:YVO_4 laser operating at 1.34 μm

With a plano-concave cavity,diode-pumped continuous-wave(CW) and actively Q-switched Nd:YVO4 laser operating at 1.34 μm is demonstrated.Maximum CW output power of 4.76 W and Q-switched average output power of 2.64 W are obtained with output coupler(transmission T = 3.9%).For the Q-switching operation,the theoretically calculated pulse energy and pulse width,with a pulse repetition frequency(PRF) range of 5-40 kHz,coincide with the experimental results.With a T = 11.9% output coupler,the maximum peak power of 24.3 kW and minimum pulse width of 6.5 ns are obtained when the PRF is 10 kHz.To the best of our knowledge,this is the shortest actively Q-switched pulse duration ever obtained in a 1.3-μm Nd-doped vanadate laser.     

Experimental study of continuous-wave and Q-switched laser performances of Ho:YVO4 crystal

In this letter, we report a Ho:YVO4 laser pumped by a 1.94-μm laser in both continuous-wave(CW)and Q-switched modes. The output performance of the Ho:YVO4 laser is compared with different output coupler transmissions. By use of the output coupler transmissions of T =30%, we obtain the maximum CW output power of 3.9 W at 2052 nm, with beam quality factor of M2=1.09 for the absorbed pump power of 12.5 W. For the Q-switched mode, we achieve maximum output energy per pulse of 0.38 mJ and the minimum pulse width of 25 ns, corresponding to the peak power of 15.2 kW.     

Mode-locked 2 μm fiber laser with a multi-walled carbon nanotube as a saturable absorber

We propose and demonstrate a passively mode-locked fiber laser operating at 1951.8 nm using a commercial thulium-doped fiber(TDF) laser, a homemade double-clad thulium–ytterbium co-doped fiber(TYDF)as the gain media, and a multi-walled carbon nanotube(MWCNT) based saturable absorber(SA). We prepare the MWCNT composite by mixing a homogeneous solution of MWCNTs with a diluted polyvinyl alcohol(PVA) polymer solution and then drying it at room temperature to form a film. The film is placed between two fiber connectors as a SA before it is integrated into a laser ring cavity. The cavity consists of a 2 m long TDF pumped by a 800 nm laser diode and a 15 m long homemade TYDF pumped by a 905 nm multimode laser diode. A stable mode-locking pulse with a repetition rate of 34.6 MHz and a pulse width of 10.79 ps is obtained when the 905 nm multimode pump power reaches 1.8–2.2 W, while the single-mode 800 nm pump power is fixed at 141.5 m W at all times. To the best of our knowledge, this is the first reported mode-locked fiber laser using a MWCNT-based SA.     

Suppression of multi-pulse formation in all-polarization-maintaining figure-9 erbium-doped fiber mode-locked laser

We report on a novel architecture to suppress the multi-pulse formation in an all-polarization-maintaining figure-9 erbium-doped fiber laser under high pump power. A 2×2 fiber coupler is introduced into the phase-biased nonlinear amplifying loop mirror to extract part of intracavity laser power as a laser output, and the dependence of output couple ratio of fiber coupler on the mode-locking state is experimentally investigated. The intracavity nonlinear effect is mitigated by lowering the intracavity laser power, which is conducive to avoiding the multi-pulse formation. In the meantime, the loss-imbalance induced by fiber coupler is helpful in improving the self-starting ability. With the proposed laser structure,the multiple pulse formation can be suppressed and high power single pulse train can be obtained. The laser emits three pulse trains which is convenient for some applications. Finally, the output power values of three ports are 5.3 m W, 51.3 m W,and 13.2 m W, respectively. The total single pulse output power is 69.8 m W, which is more than 10 times the result without OC2. The total slope efficiency is about 10.1%. The repetition rate of three pulse trains is 21.17 MHz, and the pulse widths are 2.8 ps, 2.63 ps, and 6.66 ps, respectively.     

Reflective graphene oxide absorber for passively mode-locked laser operating at nearly 1μm

A low cost and simply fabricated reflective graphene oxide is successfully made. By using this absorber, as well as an end reflector, we obtain a passively mode-locked Yb:LuYSiO5 laser operating at nearly 1 μm. When the pump power is increased up to 5.73 W, stable mode locking is achieved. The central wavelength of the laser spectrum is 1043.2 nm with a pulse duration of 5.0 ps. When the pump power reaches 8.16 W, dual-wavelength mode locking laser pulses at 1036.3 nm and 1043.5 nm are simultaneously detected.     

A novel 2-μm pulsed fiber laser based on a supercontinuum source and its application to mid-infrared supercontinuum generation

A new method to achieve 2-μm pulsed fiber lasers based on a supercontinuum(SC) is demonstrated. The incident pump light is a pulsed SC which contains a pump light and a signal light at the same time. The initial signal of the seed laser is provided by the incident pump light and amplified in the cavity. Based on this, we obtain a 2-μm pulsed laser with pulse repetition rate of 50 kHz and pulse width of 2 ns from the Tm-doped fiber laser. This 2-μm pulsed laser is amplified by two stages of fiber amplifiers, then the amplified laser is used for mid-infrared(mid-IR) SC generation in a 10-m length of ZrF4–BaF2–LaF3–AlF3–NaF(ZBLAN) fiber. An all-fiber-integrated mid-IR SC with spectrum ranging from 1.8 μm to4.3 μm is achieved. The maximal average output power of the mid-IR SC from the ZBLAN fiber is 1.24 W(average output power beyond 2.5 μm is 340 mW), corresponding to an output efficiency of 6.6% with respect to the 790-nm pump power.     

Q-Switching Pulse Operation in 1.5-μm Region Using Copper Nanoparticles as Saturable Absorber

We demonstrate a passively Q-switched erbium-doped fiber laser(EDFL)using a copper nanoparticle(CuNP)thin film as the saturable absorber in a ring cavity.A stable Q-switched pulse operation is observed as the CuNP saturable absorber(SA)is introduced in the cavity.The pulse repetition rate of the EDFL is observed to be proportional to the pump power,and is limited to 101.2 kHz by the maximum pump power of 113.7 mW.On the other hand,the pulse width reduces from 10.19 ps to 4.28 ps as the pump power is varied from 26.1 mW to 113.7 mW.The findings suggest that CuNP SA could be useful as a potential saturable absorber for the development of the robust,compact,efficient and low cost Q-switched fiber laser operating at 1.5-μm region.     

Holmium Oxide Film as a Saturable Absorber for 2μm Q-Switched Fiber Laser

This work reports on the use of the holmium oxide(Ho_2 O_3) polymer film as a saturable absorber(SA) for generating stable Q-switching pulses operating in a 2-μm region in a thulium-doped fiber laser cavity. The SA is prepared by diluting a commercial Ho_3 O_2 powder and then mixing it with polyvinyl alcohol(PVA) solution to form a Ho_2 O_3-PVA film. A tiny part of the film about 1 mm×1 mm in size is sandwiched between two fiber ferrules with the help of index matching gel. When incorporated in a laser cavity driven by a 1552-nm pump,stable Q-switching pulses are observed at 1955 nm within the pump power range of 363-491 mW. As the pump power increases within this range, the repetition rate rises from 26 kHz to 39 kHz, as the pulse width drops from4.22μs to 2.57μs. The laser operates with a signal-to-noise ratio of 47 dB, and the maximum output power and the pulse energy obtained are 2.67 mW and 69 nJ, respectively. Our results successfully demonstrate that the Ho_2 O_3 film can be used as a passive SA to generate a 2-μm pulse laser.     

Diode-pumped,narrow-linewidth,linearly polarized,passively Q-switched 1645 nm Er:YAG laser

We demonstrate a narrow-linewidth linearly polarized 1645 nm Er:YAG laser, directly diode-pumped by a fibercoupled continuous-wave laser diode at 1532 nm. Passive Q-switching is realized by a few-layer graphene saturable absorber. A maximum polarized average output power of 3.13 W is achieved at 23.28 W incident pump power. A pulse energy of as much as 58.8 μJ and pulse width of 4.21 μs are yielded at a 53.2 k Hz pulse repetition rate. The spectrum and linewidth of the output beams are measured to be 1645.34 and 0.05 nm, respectively.This laser can be useful in the detection of atmosphere pollutants.     

Q-Switched Large-Mode-Area Yb-Doped Fibre Laser Using GaAs as Saturable Absorber

A passive Q-switched large-mode-area Yb-doped fibre laser is demonstrated using a GaAs wafer as the saturable absorber. A high Yb doping concentration double-clad fibre with a core diameter of 30μm and a numerical aperture of 0.07 is used to increase the laser gain volume, permitting greater energy storage and higher output power than conventional fibres. The maximum average output power is 7.2W at 1080nm wavelength, with the shortest pulse duration of 580ns and the highest peak power of 161W when the laser is pumped with a 25W diode laser operating at 976nm. The repetition rate increases with the pump power linearly and the highest repetition rate of 77kHz is obtained in the experiment.     

Graphene oxide for diode-pumped Tm:YLF passively Q-switched laser at 2 μm

A diode-pumped Tm:YLF passively Q-switched laser at 2 μm was first demonstrated by using graphene oxide(GO) as a saturable absorber(SA).In this letter,continuous-wave(CW) laser and pulse laser performances were studied meticulously and systematically.It reasonably showed the dependence of the pulse duration,pulse energy,and pulse repetition rate on the absorbed power.A maximum repetition rate of 38.33 kHz and a single pulse energy of 9.89 μJ were obtained.     

High-repetition-rate 1.5 μm passively Q-switched Er:Yb:YAl_3(BO_3)_4 microchip laser

End-pumped by a 976 nm diode laser,a high-repetition-rate Er:Yb:YAl_3(BO_3)_4 microchip laser passively Q-switched by a Co~(2+):MgAl_2 O_4 crystal is reported.At a quasi-continuous-wave pump power of 20 W,a 1553 nm passively Q-switched laser with the repetition rate of 544 kHz,pulse duration of 8.3 ns,and pulse energy of 3.9 μJ was obtained.To the best of our knowledge,the 544 kHz is the highest reported value for the 1.5 μm passively Q-switched pulse laser.In the continuous-wave pumping experiment,the maximum repetition rate of 144 kHz with the pulse duration of 8.0 ns and pulse energy of 1.7 μJ was obtained at the incident pump power of 6.3 W.     

Efficient Laser-Diode End-Pumped Passively Q-Switched Mode-Locked Yb：LYSO Laser Based on SESAM

We report an efficient Q-switched laser action based on a semiconductor saturable absorber mirrors （SESAMs） as passively Q-switched laser starter and a Yb：LYSO alloyed crystal as gain material pumped directly by 974nm InGaAs laser diodes. The output pulse duration is measured to be about 7μs, while the average power and the repetition rate of the pulse chain are about 0.92 W and 6.2 kHz, respectively, under 12.5 W absorbed pumping power. The Q-switched mode-locked pulse train is also observed in this setup. The laser performance shows that Yb：LYSO is a promising laser gain medium for laser-diode pumped compact solid-state lasers.     

High peak power 1.0 μm and tri-wavelength 1.3 μm Nd:ScYSiO_5 crystal lasers

With a Nd:ScYSiO_5 crystal, a high peak power electro-optically Q-switched 1.0 μm laser and tri-wavelength laser operations at the 1.3 μm band are both investigated. With a rubidium titanyle phosphate(RTP) electro-optical switcher and a polarization beam splitter, a high signal-to-noise ratio 1.0 μm laser is obtained, generating a shortest pulse width of 30 ns, a highest pulse energy of 0.765 mJ, and a maximum peak power of 25.5 kW,respectively. The laser mode at the highest laser energy level is the TEM200 mode with the Mvalue in the X and Y directions to be M_x~2= 1.52 and M_y~2= 1.54. A tri-wavelength Nd:ScYSiO_5 crystal laser at 1.3 μm is also investigated. A maximum tri-wavelength output power is 1.03 W under the absorbed pump power of7 W, corresponding to a slope efficiency of 14.8%. The properties of the output wavelength are fully studied under different absorbed pump power.