Watt-level output power and near-diffraction-limit beam quality mid-infrared Ho:GdVO4 self-Raman laser at 2.5†µm.

We demonstrate an efficient active Q-switched Ho:GdVO4 self-Raman laser at 2500 nm for the first time, to our knowledge. Using Ho:GdVO4 crystal as the gain medium for both the 2048nm fundamental laser and the 2500 nm Raman laser, the output performances of a new mid-infrared self-Raman laser were investigated. The maximum average output power of 1.45 W was achieved at an incident pump power of 22.5 W, with a slope efficiency of 25.8%, for an output transmittance of 30% and a pulse repetition frequency of 15 kHz. The maximum single pulse energy of 96.7 µJ with a pulse width of 11.35 ns was obtained, corresponding to the peak power of 8.5 kW. The beam quality was near diffraction limited with the M2 factors of 1.15 and 1.06 along the x and y directions. Moreover, adopting the two-end output way of the fundamental laser and the Raman laser, the Raman gain coefficient of Ho:GdVO4 crystal was estimated to be 1.14 cm/GW at 2048nm. This work shows that Ho:GdVO4 is an excellent self-Raman laser crystal for the generation of high power Raman laser at 2.5 µm.

High-power, gigahertz repetition frequency self-mode-locked Ho:GdVO4 laser resonantly pumped by a Tm-doped fiber laser.

A self-mode-locked Ho:GdVO4 laser with the GHz pulse repetition frequency oscillation near 2.06 µm was demonstrated for the first time to our knowledge. The output performances of the self-mode-locked Ho:GdVO4 laser were investigated for a few output coupler transmittances at the pulse repetition frequency of 1.89 GHz. At the incident pump power of 8.12 W, the maximum average output power was as high as 2.28 W, corresponding to the slope efficiency and optical-to-optical efficiency of 36.3% and 28.1%, respectively. This is the maximum average output for the 2 µm self-mode-locked solid-state laser with a GHz pulse repetition frequency. This work provides a new way for generating an efficient and a high-power ultrafast pulse laser with a GHz repetition frequency in the 2 µm wave band.

High average output power, dual-wavelength synchronously self-mode-locked Ho:LLF laser operating at 2068.5 and 2069.2†nm.

A dual-wavelength synchronously self-mode-locked Ho:LLF laser operating at 2068.5 and 2069.2 nm was demonstrated. The maximum average output power was as high as 2.6 W with a pulse repetition frequency of 3.03 GHz. Meanwhile, the output power ratio of the dual-wavelength lasers can be effectively controlled by varying the incident pump power. To the best of our knowledge, this is the first dual-wavelength synchronously self-mode-locked Ho-doped fluoride solid state laser; moreover, our current experimental results represent the highest average output power from a GHz self-mode-locked oscillator in the 2 µm wave band.

Power balanced orthogonally polarized dual-wavelength Ho:GdVO4 laser with a difference frequency of 1 THz.

A power balanced orthogonally polarized dual-wavelength Ho:GdVO4 laser was demonstrated for the first time. Without inserting any other devices into the cavity, the power balanced simultaneous orthogonally polarized dual-wavelength laser at π-polarization 2048nm and σ-polarization 2062nm was successfully achieved. At the absorbed pump power of 14.2 W, the maximum total output power was 1.68 W, and the output powers of 2048nm and 2062nm were 0.81 W and 0.87 W, respectively. The interval between the two wavelengths in the orthogonally polarized dual-wavelength Ho:GdVO4 laser was nearly 14nm, corresponding to the frequency separation of 1 THz. This power balanced orthogonally polarized dual-wavelength Ho:GdVO4 laser can be applied to generate the terahertz wave.

Dual-wavelength passively Q-switched Ho:GdVO4 self-Raman laser operating at 2473†nm and 2520†nm.

A dual-wavelength passively Q-switched Ho:GdVO4 self-Raman laser in the 2.5 µm wave band was demonstrated with Cr:ZnS as a saturable absorber. Synchronized dual-wavelength pulsed laser outputs at 2473 nm and 2520 nm were acquired, corresponding to Raman frequency shifts of 808 cm-1 and 883 cm-1, respectively. The maximum total average output power of 114.9 mW was obtained at an incident pump power of 12.8 W with a pulse repetition rate of 3.57 kHz and a pulse width of 16.36 ns. The maximum total single pulse energy was 32.18 µJ, corresponding to a total peak power of 1.97 kW. The power ratios of the two Raman lasers can be controlled by varying the incident pump power. To the best of our knowledge, this is the first time a dual-wavelength passively Q-switched self-Raman laser in the 2.5 µm wave band has been reported.

Compact dual-crystal Tm,Ho:YLF laser with balanced orthogonal polarization output power.

The compact dual-crystal orthogonally polarized Tm,Ho:YLF laser with balanced orthogonal polarization output power was reported for the first time, to the best of our knowledge. Two pieces of a-cut Tm,Ho:YLF crystals were placed compactly with their c-axis perpendicular. The maximum multimode total output power of 460 mW was obtained with the slope efficiency of 28.2%, and the M2 factor value was measured to be 1.07. By adjusting the pump focus position along the optical axis in the process of changing pump power, the balanced output powers in the two orthogonal polarization directions were successfully achieved, and the maximum output powers of the P-polarization and S-polarization states were both 215 mW. Inserting two uncoated solid state etalons into the resonator, the dual-wavelength single-longitudinal-mode laser with orthogonal polarization was obtained. The output powers at P-polarized 2052.1 nm and S-polarized2065 nm were 71mW and 62mW, respectively, and the M2 factor was 1.26. The orthogonally polarized dual-wavelength laser at 2 µm can be used as a seed laser for differential absorption lidars and coherent THz wave generation.

Theoretical and experimental investigation of polarization coexistence and switching in an optical bistability Tm,Ho:LLF laser.

We first investigate the polarization coexistence and switching between the orthogonal π- and σ-polarization states in a free running optical bistability Tm,Ho:LLF laser. The output performances of the optical bistability Tm,Ho:LLF laser is numerically simulated, based on a new rate equation theory model taking into account the influences of polarization-dependent gain and losses. The simulation results show the polarization coexistence and switching of output laser in the process of decreasing pump power. The physical mechanism of polarization coexistence and switching is clarified by analyzing the polarization-dependent net-gain coefficients. Furthermore, the polarization coexistence and switching are experimentally realized in the optical bistability Tm,Ho:LLF laser, which validates the theoretical analysis. The theoretical model can be applied to analyze the polarization coexistence and switching in other kinds of (quasi-) three-level optical bistable lasers.

Cr:ZnS saturable absorber passively Q-switched mode-locking Tm,Ho:LLF laser.

We first report on a diode-end-pumped passively Q-switched mode-locking Tm,Ho:LLF laser at 2053 nm by using a Cr:ZnS saturable absorber. A stable Q-switched mode-locking pulse train with a nearly 100% modulation depth was achieved. The repetition frequency of the Q-switched pulse envelope increased from 0.5 to 12.3 kHz with increasing pump power from 1 to 4.36 W. The maximum average output power of 145 mW was obtained, and the width of the mode-locked pulse was estimated to be less than 682 ps with a 250 MHz repetition frequency within a Q-switched pulse envelope of about 700 ns.

Ordering Ag nanowire arrays by spontaneous spreading of volatile droplet on solid surface.

Large-area Ag nanowires are ordered by spontaneous spreading of volatile droplet on a wettable solid surface. Compared with other nanowires orientation methods, radial shaped oriented Ag nanowires in a large ring region are obtained in an extremely short time. Furthermore, the radial shaped oriented Ag nanowires are transferred and aligned into one direction. Based on the hydrodynamics, the coactions among the microfluid, gravity effect and the adhesion of substrate on the orientation of the Ag nanowires are clearly revealed. This spreading method opens an efficient way for extreme economic, efficient and "green" way for commercial producing ordered nanowire arrays.