Jin-Long Xu

Graphene saturable absorber mirror for ultra-fast-pulse solid-state laser.

High-quality graphene sheets with lateral size over 20 μm have been obtained by bath sonicating after subjecting the wormlike graphite marginally to mixed oxidizer. To date, to our knowledge, they are the largest graphene sheets prepared by exfoliation in the liquid phase. A saturable absorber mirror was fabricated based on these sheets. We exploited it to realize mode-locking operation in a diode-pumped Nd:GdVO(4) laser. A pulse duration of 16 ps was produced with an average power of 360 mW and a highest pulse energy of 8.4 nJ for a graphene mode-locked laser.

Large energy laser pulses with high repetition rate by graphene Q-switched solid-state laser

We demonstrated that the graphene could be used as an effective saturable absorber for Q-switched solid-state lasers. A graphene saturable absorber mirror was fabricated with large and high-quality graphene sheets deprived from the liquid phase exfoliation. Using this mirror, 105-ns pulses and 2.3-W average output power are obtained from a passively Q-switched Nd:GdVO(4) laser. The maximum pulse energy is 3.2 μJ. The slope efficiency is as high as 37% approximating to 40% of the continue-wave laser, indicating a low intrinsic loss of the graphene.

Efficient graphene Q switching and mode locking of 1.34 μm neodymium lasers

We demonstrate that few-layered graphene sheets used as a saturable absorber can provide efficient Q-switching and mode-locking modulation in 1.34 μm Nd:GdVO(4) bulk lasers. The minimum Q-switched pulses were 450 ns for 260 mW average power, 43 kHz repetition rate, and 2.5 μJ pulse energy. For the mode-locked laser, an average power of 1.29 W was achieved with 11 ps pulse duration and 13 nJ pulse energy. To our knowledge, this average power is the highest yet obtained from a graphene mode-locked laser, and the corresponding optical-optical efficiency of 23% is the best result among 1.3 μm neodymium mode-locked lasers. The quality factor M(2) of the Q-switched beam was 1.4 and 1.6 in the horizontal and longitudinal planes, respectively, and the M(2) of the mode-locked beam reached 1.1 and 1.0. These results clearly indicate the advantages of few-layered graphene as a saturable absorber.

Diode-pumped passively Q-switched Nd:LuVO 4 laser at 1.34μm with a V 3+ :YAG saturable absorber

We report a diode-pumped passively Q-switched Nd:LuVO4 laser at 1.34μm using V3+:YAG as saturable absorber. The characteristics of a-cut and c-cut Nd:LuVO4 passive Q-switching operation were studied. The average output power of 1.02W was obtained under the pump power of 12.88W, corresponding to the optical conversion efficiency of 8% and slope efficiency of 10% in c-cut Nd:LuVO4 laser. The maximum pulse energy of 17.6μJ and the highest peak power of 820W were obtained at pulse width of 21ns and pulse repetition rate of 22.4kHz in a-cut Nd:LuVO4 laser.

V 3+ :YAG as the saturable absorber for a diode-pumped quasi-three-level dual-wavelength Nd:GGG laser

The performance of a diode-end-pumped passively Q-switched dual-wavelength Nd:GGG laser operating at 932.9 and 936.5 nm with V(3+):YAG as the saturable absorber was demonstrated for the first time to the best of our knowledge. The maximum dual-wavelength average output power of 150 mW was achieved with a T = 2% output coupler under the absorbed pump power of 2.55 W, corresponding to the optical-to-optical conversion and slope efficiency of 5.9% and 8.0%, respectively. The minimum pulse width was 395 ns with the pulse repetition frequency of 140 kHz, which was attained with a T = 5% output coupler under the absorbed pump power of 2.55 W.

Performance of large-area few-layer graphene saturable absorber in femtosecond bulk laser

Using large-area graphene sheets of 1-10 layers prepared by the improved liquid phase exfoliation technique, the mode locking operation of a diode-pumped Yb:KGW laser was demonstrated. Near-transform-limited 428 fs pulses were yielded at 1031.1 nm with an output power of 504 mW, corresponding to the slope efficiency of 27% and peak power of 13.8 kW. The output power ratio and the slope efficiency ratio of mode locking to free running were as high as 93% and 100%, respectively. This demonstration may open a proper way to achieve low-cost and efficient femtosecond bulk laser.

Diode-pumped passively Q-switched Nd:Gd 0.5 Y 0.5 VO 4 laser at 1.34μm with V 3+ :YAG as the saturable absorber

The performance of a diode-pumped passively Q-switched Nd:Gd(0.5)Y(0.5)VO(4) laser at 1.34 microm with V(3+):YAG as the saturable absorber was demonstrated for the first time to the best of our knowledge. The focal lengths of thermal lens in the diode-end-pumped Nd:Gd(0.5)Y(0.5)VO(4) laser for the 1.34 microm transition was experimentally investigated, with the corresponding proportion constant estimated to be approximately1.5x10(4) W/mm. For the passive Q-switching operation, the maximum average output power of 0.96 W was achieved under the pump power of 7.28 W, corresponding to optical-to-optical conversion and slope efficiency of 13.2% and 17.6%, respectively. The minimum pulse width attained was 47.8 ns with the pulse repetition frequency of 76 kHz, with the single pulse energy and peak power estimated to be 8.7 microJ and 182 W, respectively.

Benefit of Pr 3+ ions to the spectral properties of Pr 3+ /Er 3+ :CaGdAlO 4 crystal for a 2.7 μm laser

The spectra of Er3+:CaGdAlO4 and Pr3+/Er3+:CaGdAlO4 crystals were measured under the same conditions. With the presence of Pr3+ ions, the intensities of the green, red upconversion and near-infrared emissions are dramatically reduced to 1/20, 1/150, and 1/8.5 of those for Er3+:CaGdAlO4. Furthermore, the lifetimes of 4I11/2 upper and 4I13/2 lower laser levels fall from 450 and 982 μs to 84.8 and 74.3 μs. It is obvious that the self-saturation for Er3+ 2.7 μm laser is effectively suppressed. The energy transfer efficiencies and coefficients of Er3+→Pr3+ are also calculated. These results indicate that Pr3+ codoping is beneficial in achieving 2.7 μm laser in Pr3+/Er3+:CaGdAlO4 crystal.

Diode-end-pumped passively Q-switched 1.33 µm Nd:Gd 3 Al x Ga 5-x O 12 laser with V 3+ : YAG saturable absorber

We demonstrated the 1.33 microm laser performance with Nd:Gd(3)Al(x)Ga(5-x)O(12) (x = 0.94) (Nd:GAGG) laser crystals for the first time. Continuous-wave (cw) output power of 2.45 W was obtained with the optical-optical conversion efficiency of 21.8% and slope efficiency of 23.3%. In the passive Q-switching regime, the highest output power, the shortest pulse width, largest pulse energy and highest peak power were achieved to be 326 mW 18.2 ns, 36.3 microJ and 2.0 kW, respectively, with V(3+):YAG crystal as the saturable absorber.

Self-Q-switched, orthogonally polarized, dual-wavelength laser using long-lifetime Yb 3+ crystal as both gain medium and saturable absorber

A novel self-Q-switched and orthogonally polarized dual-wavelength laser has been investigated with Yb³⁺-doped CGB disordered crystals. By slightly inclining output coupler to introduce the Fresnel loss, we realized simultaneously dual-wavelength laser operation at 1052.6 nm in E//b polarization and 1057.7 nm in E//c polarization with a frequency difference of 1.38 THz. Self-Q-switched pulse generation was observed in this free-running laser, originating from the nonlinear reabsorption effect of Yb:CGB as well as the strong storage of inversion population induced by the long excited-state lifetime (~1 ms). Pulse duration of 287 ns was obtained with an output average power of 416 mW and a repetition rate of 35 kHz. The self-Q-switching effect increased the peak power by 100 times the average power. This very simple laser, free from the complexity and high-cost of additional intracavity polarization modulator and Q-switcher, may be applied for constructing miniature, integrated and portable laser system.