Yuangeng Zhang

THz-wave generation via stimulated polariton scattering in KTiOAsO4 crystal.

A terahertz parametric oscillator based on KTiOAsO(4) crystal is demonstrated for the first time. With the near-forward scattering configuration X(ZZ)X + Δφ, the polarizations of the pump, the Stokes and the generated THz waves are parallel to the z-axis of the crystal KTA. When the incident angle θext of the pump wave is changed from 1.875° to 6.500°, the THz wave is intermittently tuned from 3.59 to 3.96 THz, from 4.21 to 4.50 THz, from 4.90 to 5.16 THz, from 5.62 to 5.66 THz and from 5.92 to 6.43 THz. The obtained maximum THz wave energy is 627 nJ at 4.30 THz with a pump energy of 100 mJ. It is believed that the terahertz wave generation is caused by the stimulated scattering of the polaritons associated with the most intensive transverse A(1) mode of 233.8 cm(-1). Four much weaker transverse A(1) modes of 132.9 cm(-1), 156.3 cm(-1),175.1 cm(-1), and 188.4 cm(-1) cause four frequency gaps, from 3.97 THz to 4.20 THz, from 4.51 to 4.89 THz, from 5.17 to 5.61 THz and from 5.67 to 5.91 THz, respectively.

Second-Stokes dual-wavelength operation at 1321 and 1325 nm ceramic Nd:YAG/BaWO 4 Raman laser

A diode-pumped, actively Q-switched second-Stokes dual-wavelength laser employing ceramic Nd:YAG as the gain medium and BaWO(4) as the Raman medium is demonstrated. The dual-wavelength Raman laser emission at 1321 and 1325 nm is based on the dual-wavelength fundamental laser emission at 1061 and 1064 nm. With a pump power of 18.4 W and pulse repetition frequency of 15 kHz, a maximum dual-wavelength output power of 1.67 W was obtained, comprising a 0.75 W, 1321 nm laser component and a 0.92 W, 1325 nm laser component. The corresponding dual-wavelength second-Stokes pulse width was 2.9 ns.

90-fs diode-pumped Yb:CLNGG laser mode-locked using single-walled carbon nanotube saturable absorber

A diode-pumped Yb:CLNGG laser is mode-locked with a single-walled carbon nanotube saturable absorber (SWCNT-SA) for the first time. Pulse durations as short as 90 fs are obtained at ~1049 nm with 0.4% output coupler, the shortest pulses to our knowledge for a diode-pumped 1-µm laser applying SWCNTs as saturable absorber. Using 3% output coupler, the maximum average output power reached 90 mW at a repetition frequency of 83 MHz.

Characteristics of the temperature-tunable Nd:YAG/YVO4 Raman laser.

We demonstrate a tunable crystalline Raman laser by varying the temperature of Raman crystal. Nd:YAG and YVO(4) crystals were selected as the laser and Raman gain media, respectively. The center wavelength of this Nd:YAG/YVO(4) Raman laser was tuned over a 0.49 nm range from 1175.76 to 1175.27 nm when the temperature of the Raman crystal was adjusted from 5 °C to 150 °C. The characteristics of this Raman laser including tunability, output power, and beam quality factors (M(2)) dependent on temperature were also studied in this paper.

Experiments with an intracavity BaTeMo2O9 Raman laser

A diode-side-pumped actively Q-switched intracavity Raman laser emitting at 1178 nm employing Nd:YAG as the gain medium and BaTeMo2O9 as the Raman medium is realized. With a pump power of 115 W and pulse repetition rate of 10 kHz, a maximum first-Stokes output power of 1.9 W is obtained. The corresponding diode-to-first-Stokes conversion efficiency is 1.7% and the first-Stokes pulse width is 35 ns. The preliminary experiments proved that an intracavity BaTeMo2O9 Raman laser is feasible.

Extracavity pumped BaWO 4 anti-Stokes Raman laser

The characteristics of a barium tungstate (BaWO(4)) anti-Stokes Raman laser at 968 nm are studied theoretically and experimentally. The BaWO(4) Raman resonator is pumped by a Q-switched Nd:YAG laser at 1064 nm with its axis tilted from the pumping laser axis. The non-collinear phase matching for the generation of the first anti-Stokes wave in the same BaWO(4) crystal is achieved. The output energy, temporal and spectral informations are investigated. At a pumping laser energy of 128 mJ, the anti-Stokes laser energy obtained is 2.2 mJ. The second Stokes radiation at 1324 nm as well as the first and the third Stokes waves at 1180 nm and 1509 nm is also generated at the same time. The maximum total Stokes energy output is 42.5 mJ. In the theory, the anti-Stokes laser intensity expression as a function of the pumping and the first Stokes laser intensities for the extracavity anti-Stokes Raman laser is deduced. The properties of the anti-Stokes Raman laser are simulated theoretically by solving the rate equations of the extracavity Raman laser and using the derived expression. The theoretical results are in good agreement with the experimental results.

Characteristics of diode-pumped dual-loss-modulated Q-switched and mode-locked Nd:Lu0.15Y0.85VO4 laser

A diode-pumped dual-loss-modulated Q-switched and mode-locked (QML) Nd:Lu0.15Y0.85VO4 laser with acousto-optic (AO) modulator and Cr4+:YAG saturable absorber is presented. The stable QML laser pulse with high peak power and complete modulation depth has been obtained. The QML laser characteristics such as the pulse width, single-pulse energy etc. have been measured for different small-signal transmissions (T0) of Cr4+:YAG, different reflectivity (R) of output coupler and modulation frequencies of the AO modulator (fp). The results show that the pulse energy increases with decreasing fp and increasing T0, while the pulse width decreases with decreasing fp and increasing T0. At fp = 10 kHz, R = 90%, and T0 = 91%, the highest pulse energy and peak power of mode-locked pulses is obtained.

Diode-Pumped Q-Switched and Mode-Locked Nd:LuVO4/KTP Green Laser with AO and Cr4+:YAG Saturable Absorber

A diode-pumped Q-switched and mode-locked (QML) Nd:LuVO4/KTP green laser with acousto-optic modulator (AOM) and Cr4+:YAG saturable absorber is presented. By inserting an AOM into the laser cavity, the stability of the QML green laser pulse with AO and Cr4+:YAG is improved, the modulation depth is increased and the pulse width of Q-switched pulse envelope is significantly compressed in comparison with that of the singly passively QML green laser with Cr4+:YAG. The experimental results show that the peak power of the doubly QML green laser pulse is much higher than that of the singly passively QML green laser pulse.

A frequency-doubled Nd:YAG/KTP laser at 561 nm with diode side-pumping

An intracavity KTiOPO4 (KTP) frequency doubling laser emitting at 561?nm is achieved within a diode side-pumped acousto-optically Q-switched Nd:YAG laser. A compact convex?flat straight cavity is employed to achieve the compact configuration, where coatings are specially designed to suppress unwanted lines. At the pump power of 147?W and the pulse repetition rate of 10?kHz, the output power of 8.1 W was obtained at 561?nm. The corresponding optical-to-optical conversion efficiency is 5.5%. The pulse width of a 561?nm wave is 210?ns. The M2 factors are measured to be 15.5 and 17.5 in the horizontal and vertical directions respectively.

200 ps pulse generation at 1180 nm with a SrWO4 Raman crystal pumped by a sub-nanosecond MOPA laser system

We are reporting Raman conversion experiments with a SrWO4 crystal in a single-pass traveling-wave setup. As a pump source we employed a master oscillator power amplifier (MOPA) laser system at 1064 nm, delivering 200 µJ, 500 ps long pulses at a 9 kHz maximum repetition rate with limited diffraction beam quality. At 2 kHz we obtained up to 45 µJ pulse energy and 200 ps pulse duration at 1180 nm, with a conversion efficiency of 22%. Up to the maximum incident average pump power of 1.35 W no serious beam quality degradation was observed, and we measured a factor M2 ≤ 1.5 for the Raman shifted beam.