Mingwei Gao

Continuous-wave and Q-switched operation of a resonantly pumped U-shaped Er:YAG laser at 1617 and 1645 nm

Continuous-wave (CW) and Q-switched operation at 1617 and 1645 nm in a resonantly pumped Er:YAG laser is reported. A U-shaped resonator incorporating an acousto-optic Q-switch was used, and an etalon was employed to select the 1617 nm output. In CW operation the laser yielded 3.68 W at 1617 nm and 4.01 W at 1645 nm; in Q-switched operation the laser yielded 2.09 mJ at a 750 Hz repetition rate at 1617 nm and 2.07 mJ at a 1 kHz repetition rate at 1645 nm.

Experimental investigation of pulse diodes side-pumped 2 μm Tm:YAG lasers

The free running and Q-switched operation of 2 μm Tm:YAG lasers side-pumped by pulse laser diodes were reported. In the free running mode the maximum output energies were 102.5 mJ at 1 Hz and 94.6 mJ at 10 Hz, respectively. With an acousto-optic modulator in the laser resonator, 21 mJ 2 μm Q-switched pulse was obtained, with a pulse width of about 330 ns. The dependences of the output energy and the efficiency on the laser resonator parameters were investigated.

15 mJ single-frequency Ho:YAG laser resonantly pumped by a 1.9 µm laser diode

A 2.09 µm injection-seeded single-frequency Ho:YAG laser resonantly pumped by a 1.91 µm laser diode is demonstrated for the first time. The seed laser is a continuous wave (CW) Ho:YAG non-planar ring oscillator. 15.15 mJ single-frequency output energy is obtained from the injection-seeded Q-switched Ho:YAG laser, with a pulse repetition rate of 200 Hz and a pulse width of 109 ns. The half-width of the pulse spectrum is measured to be 4.19 MHz by using the heterodyne technique. The fluctuation of the center frequency of the single-frequency pulses is 1.52 MHz (root mean square (RMS)) in 1 h.

A diode-pumped tunable single frequency Tm:YAG laser at room temperature using two etalons

We report a diode pumped single frequency Tm:YAG laser with two coated fused silica etalons as mode selectors. The maximum single frequency output power was 681 mW with the pumping power of 4.83 W. The slope efficiency of single-frequency laser was 20.5% and the optical-to-optical conversion efficiency was 14.2%. According to the experimental results, we developed a prototype with the maximum single frequency output power of 249 mW and the slope efficiency of 23.1%. The frequency tuning was investigated by changing the temperature of the crystal. A tuning coefficient of 2.57 GHz/°C was obtained. The beam propagation factors M2 were measured as 1.01 in both directions. The linewidth of the single frequency was 40 kHz.

Single-frequency operation of a laser diode side-pumped Q-switched Tm:YAG laser using seeding injection technique

A laser diode (LD) side-pumped 2 μm single-frequency Q-switched Tm:YAG laser was demonstrated. The laser was injection seeded by a CW single frequency Tm:YAG laser with a twisted-mode cavity. The maximum single-frequency pulse energy was 16.3 mJ, with a pulse width of 570 ns and a pulse repetition rate of 10 Hz. The linewidth of the 2 μm single-frequency Q-switched laser was 0.68 MHz, measured by using the optical heterodyne technique. The M2 of the laser beam was measured to be 1.09 and 1.03 for x direction and y direction, respectively.

Characterization of laser beams by using intensity moments

Any coherent and partially coherent laser beams can be characterized by their intensity moments. Generally a laser beam has maximal 4 first order moments and 10 second order moments. The centers of gravity of the beam in the near field and the far field are determined by the first order moments. The beam radii, far field divergences, radii of curvature, beam orientations and M2-factors can be obtained from the second order moments. Beam twist which is related to the orbital angular momentum can be also obtained from the second order moments. The intensity moments and related laser beam parameters obey parabolic propagation laws in the first order optical systems. They are measurable by the caustic method or the Hartmann-Shack wavefront sensor method. The principle and technical problems of these methods were analyzed. As examples the beams emitted from high power diode stack and the astigmatic beam with twist were experimentally investigated.