Zhenhua Cong

Comparison of c-Nd:YVO4/YVO4 raman lasers and c-Nd:YVO4 self-Raman lasers

Raman lasers based on c-Nd:YVO4 crystals can generate 1178 nm Stokes line, which can be frequency-doubled to realize 589 nm sodium lasers. We make comparative experimental studies of c-Nd:YVO4/YVO4 Raman lasers and c-Nd:YVO4 self-Raman lasers. About these two kinds of lasers, the output characteristics of power, center wavelength and beam quality are measured and compared.

Diode-side-pumped intracavity frequency-doubled Nd:YAG/BaWO4 Raman laser generating average output power of 3.14 W at 590 nm.

We report a linear-cavity high-power all-solid-state Q-switched yellow laser. The laser source comprises a diode-side-pumped Nd:YAG module that produces 1064 nm fundamental radiation, an intracavity BaWO(4) Raman crystal that generates a first-Stokes laser at 1180 nm, and a KTP crystal that frequency doubles the first-Stokes laser to 590 nm. A convex-plane cavity is employed in this configuration to counteract some of the thermal effect caused by high pump power. An average output power of 3.14 W at 590 nm is obtained at a pulse repetition frequency of 10 kHz.

Dual-wavelength passively mode-locked Nd:LuYSiO 5 laser with SESAM

A diode-end-pumped dual-wavelength mode-locked laser based on Nd:LuYSiO5 crystal is demonstrated. With a SESAM, simultaneous mode locking at the 1075.8 nm and 1078.1 nm is achieved and the dual-wavelength mode locked pulses have a pulse width of 8.9 ps. Due to frequency beating, ultrahigh repetition rate ultrafast pulses with 997 fs pulse width and 0.59 THz repetition rate are further formed. Under 12.7 W absorbed pump power 1.7 W mode-locked output power was obtained, the slope efficiency of the mode locked laser was 24.3%.

Theoretical and experimental study on the Nd:YAG/BaWO 4 /KTP yellow laser generating 8.3 W output power

A diode-side-pumped actively Q-switched intracavity frequency-doubled Nd:YAG/BaWO(4)/KTP Raman laser is studied experimentally and theoretically. Rate equations are used to analyze the Q-switched yellow laser by considering the transversal distributions of the intracavity photon density and the inversion population density. An 8.3 W 590 nm laser is obtained with a 125.8 W 808 nm pump power and a 15 kHz pulse repetition frequency. The corresponding optical conversion efficiency from diode laser to yellow laser is 6.57%, much higher than that of the former reported side-pumped yellow laser. The output powers with respect to the incident pump power are in agreement with the theoretical results on the whole.

Highly efficient diode-pumped actively Q-switched Nd:YAG-SrWO(4) intracavity Raman laser.

A highly efficient diode-pumped actively Q-switched intracavity Raman laser with SrWO(4) as the Raman-active medium is presented. As high as 23.8% diode-to-Stokes optical conversion efficiency is obtained with an incident pump power of 7.17 W and a pulse repetition rate of 15 kHz.

Efficient diode-end-pumped actively Q-switched Nd:YAG/SrWO4/KTP yellow laser.

An efficient intracavity frequency-doubled Raman laser was obtained by using an SrWO(4) Raman medium, an Nd:YAG ceramic gain medium, and a KTP frequency-doubling medium. Three laser cavities, including a two-mirror cavity, a three-mirror coupled cavity, and a folded cavity, were investigated. With the coupled cavity, a 2.93 W, 590 nm laser was obtained at an incident pump power of 16.2 W and a pulse repetition frequency of 20 kHz; the corresponding conversion efficiency was 18.1%. The highest conversion efficiency of 19.2% was obtained at an incident pump power of 14.1 W and a pulse repetition frequency of 15 kHz. The obtained maximum output power and conversion efficiency were much higher than the results previously obtained with intracavity frequency-doubled solid-state Raman lasers.

Terahertz parametric oscillator based on KTiOPO 4 crystal

KTiOPO₄ (KTP) crystal is used as the nonlinear medium in a surface-emitted terahertz-wave parametric oscillator for the first time. The oscillating Stokes beam propagates along the x axis of the KTP crystal, the pumping beam propagates with a small incident angle θ(ext) to the x axis, and the polarizations of the pumping beam, the Stokes beam, and the THz wave are along the z axis. When θ(ext) is changed from 1.250° to 6.000°, the THz wave is intermittently tuned from 3.17 to 3.44 THz, from 4.19 to 5.19 THz, and from 5.55 to 6.13 THz. The maximum output of the THz wave is 336 nJ, obtained at 5.72 THz with a pumping energy of 80 mJ. The two frequency gaps, from 3.44 to 4.19 THz and from 5.19 to 5.55 THz, are located in the vicinities of the A₁ modes of 134 and 178.7  cm⁻¹, which are strongly infrared absorbing.

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.

High efficiency Nd:YAG ceramic eye-safe laser operating at 1442.8 nm

We report on a diode-pumped Nd:YAG ceramic laser operating at 1442.8 nm for the first time. In our experiment, two different Nd:YAG ceramics with the Nd-doped concentrations of 1.0 and 0.6 at. % and a Nd:YAG with the Nd-doped concentration of 1.0 at. % were used as the laser gain mediums, respectively. At a pump power of 20.7 W, a maximum output power of up to 3.96 W with optical-to-optical efficiency of up to 19.1% was obtained by using the 1.0 at. % Nd-doped ceramic as the laser gain medium. To the best of our knowledge, this is the highest output power of a LD-pumped 1.44 μm Nd:YAG ceramic laser and the highest optical-to-optical efficiency of a LD-pumped 1.44 μm Nd-doped crystal laser.

Simultaneous dual-wavelength operation of Nd:YVO 4 self-Raman laser at 1524 nm and undoped GdVO 4 Raman laser at 1522 nm

A diode-pumped, actively Q-switched dual-wavelength laser employing Nd:YVO(4) self-Raman emission at 1524 nm and undoped GdVO(4) Raman emission at 1522 nm is demonstrated. With a pump power of 21.5 W and pulse repetition frequency of 20 kHz, a maximum dual-wavelength output power of 1.62 W was obtained, comprising a 0.54 W, 1522 nm Raman component and 1.08 W, 1524 nm self-Raman component. The corresponding dual-wavelength Raman pulse width was 5.6 ns. The experimental results indicate that this laser, with quite small wavelength separation, was effective by virtue of simultaneous self-Raman and Raman shifts.