Geng Ai-Cong

High-average-power third harmonic generation at 355 nm with CsB3O5 crystal

A 17.7 W average power output at 355 nm by the third harmonic generation (THG) of 1064 nm light has been obtained with the nonlinear optical crystal CsB3O5 (CBO). The fundamental light source is a diode-pumped Nd:YAG laser with a pulse duration of 70 ns and a repetition rate of 7 kHz. A CBO crystal cut for type-II PM angles is used in the experiment. The THG energy conversion efficiency with CBO is twice as large as that with LBO. As a THG crystal, CBO has better performance than that of LiB3O5 crystal (LBO).

Reducing Thermal Effect in End-Diode-Pumped Laser Crystal by Using a Novel Resonator

We report a new way, i.e. double-end-pumping, to extend the stability range of a laser resonator, in advantage of making the thermal loading be effectively divided between the ends of the laser crystal to reduce the thermal effect, thus to extend the stability range. Using this new way, we experimentally obtained a 2.7-W cw laser source at 671 nm by intracavity frequency doubling of 1342 nm of a Nd:YVO4 laser based on the nonlinear crystal LiB3O5. The maximum pump power is 28 W, which is higher than 13 W of the single-end-pumping.

1.15kW continuous-wave generation by diode-side-pumped two-rod Nd:YAG laser

A high power and high efficiency laser head with five dual-line diode arrays for the side-pumped Nd:YAG rod is developed. By mounting two laser heads of this kind and a quartz 90-degree rotator into a thermally-near-unstable symmetrical flat–flat resonator, a continuous-wave power output of 1157W at 1064nm is obtained with a beam quality factor M2 of ~39. To the authors knowledge, this is the highest power output at 1064 nm for the diode-side-pumped two-rod Nd:YAG laser.

High Beam Quality Green Generation with Output 140 W Based on a Thermally-Near-Unstable Flat–Flat Resonator

By using a diode-side-pumped Q-switched Nd:YAG rod laser based on a thermally-near-unstable flat-flat resonator, an intracavity-frequency-doubled green beam generation is investigated. Output power 140 W is obtained at a repetition rate of 10 kHz and a pulse width of 110 ns. The green beam quality factors M-x(2) and M-y(:)2 which are measured by a laser beam analyser, are 10.65 and 10.85, respectively. at output, power of 124 W.

Passively Q-Switched Nd:KLuW Laser with Semiconductor Saturable Absorber

A simplified n- ZnO/ p- Si heterojunction has been prepared by growing n- type ZnO rods on p- type silicon wafer through the chemical vapour deposition method. The reflectance spectrum of the sample shows an independent absorption peak at 384 nm, which may be originated from the bound states at the junction. In the photoluminescence spectrum a new emission band is shown at 393 nm, besides the bandedge emission at 380 nm. The electroluminescence spectrum of the n- ZnO/ p- Si heterojunction shows a stable yellow luminescence band centred at 560 nm, which can be attributed to the emission from trapped states. Another kind of discrete ZnO rod has also been prepared on such silicon wafer and is encapsulated with carbonated polystyrene for electroluminescence detection. This composite structure shows a weak ultraviolet electroluminescence band at 395 nm and a yellow electroluminescence band. These data prove that surface modification which blocks the transverse movement of carriers between neighbouring nanorods plays important roles in the ultraviolet emission of ZnO nanorods. These findings are vital for future display device design.

A 4.8-W M-2=4.6 continuous-wave intracavity sum-frequency diode-pumped solid-state yellow laser

A yellow continuous wave with beam quality M-2 = 4.6 and output power of 4.8 W at 589 nm is generated by intracavity sum-frequency mixing of 1064 nm and 1319 nm radiations of ND:YAG laser. To achieve high beam quality at high power, thermally near-unstable flat-flat resonators with two-rod birefringence compensation are designed to obtain the large fundamental mode size inside the ND:YAG rods and the same beam width inside the KTP crystal. The optimal intracavity power ratio of both 1064 nm and 1319 nm beams is also considered. The output power fluctuation of the yellow laser remains less than 5% in four hours.

Generation of 2.1 W Continuous Wave Blue Light by Intracavity Doubling of a Diode-End-Pumped Nd:YAG Laser in a 30 mm LBO

A folded four-mirror cavity with a composite Nd:YAG rod is optimized to obtain high efficient cw 473 nm blue output. The laser could operate stably in the region of the thermal-lens focal length from 20 mm to 70 mm. LBO is used for intracavity frequency doubling of the 946 nm transition of Nd:YAG and the optimum LBO length is investigated. A maximum output power of 2.1 W in the blue spectral range at 473 nm is achieved with 30-mm-long LBO, corresponding to an optical conversion efficiency of 9.1%.

A 18-W Signal Average Power Nanosecond LiB3O5 Optical Parametric Oscillator around 860 nm and the Beam Quality

We report a compact high average power optical parametric oscillator (OPO) pumped by an all-solid-state nanosecond 532-nm laser. Based on the merit of non-critically phase-matched crystals without walk-off effect, a 60-mm-long LiB3O5 (LBO) crystal is used as the OPO nonlinear crystal to enhance the conversion efficiency and to increase the output power. The maximum average power of signal output is up to 18 W at 860 nm for pump power of 65 W. This is the highest signal average power generated by a nanosecond OPO in single bulk LBO, to the best of our knowledge. The dynamic characteristics of beam quality are investigated. Our experimental results demonstrate that good OPO conversion efficiency and high output power can be obtained even with relatively poor pump beam quality.

218 W,M 2 = 20.2 green beam generation by intracavity-frequency-doubled diode-pumped Nd:YAG laser

By employing a thermally near-unstable cavity design with two-rod birefringence compensation, average power of 218 W with beam quality of M2 = 20.2 was achieved by intracavity frequency doubling a diode-pumped Nd:YAG laser.

Beam divergence effects on high power optical parametric oscillation

The beam divergence effects of the input pump laser on a high power nanosecond optical parametric oscillator (OPO) have been numerically simulated. The OPO conversion efficiency is affected due to the angular deviation of real laser beams from ideal phase matching conditions. Our theoretical model is based on the decomposition of the Gaussian beam and assumes each component has a single deviation angle and thus a particular wave vector mismatch. We take into account the variable intensity profile in the spatial and temporal domains of the Gaussian beam, the pump depletion effects for large-signal processes as well as the oscillatory effects of the three waves. Two nonlinear crystals β-BaB2O4 (BBO) and LiB3O5 (LBO) have been investigated in detail. The results indicate that the degree of beam divergence strongly influences the maximum pump intensity, optimum crystal length and OPO conversion efficiency. The impact of beam divergence is much more severe in the case of critical phase-matching for BBO than in the case of non-critical phase-matching for LBO. The results provide a way to choose the optimum parameters for a high power ns OPO such as the nonlinear material, the crystal length and the pump intensity, etc. Good agreement is obtained with our experimental results.