3.5 W long-wave infrared ZnGeP2 optical parametric oscillator at 9.8 µm.

We demonstrated a high-power long-wave infrared optical parametric oscillator at 9.8 µm based on a type-I phase-matching ${{\rm ZnGeP}_2}$ZnGeP2 crystal. By using a ${Q}$Q-switched 2091 nm Ho:YAG laser with pulse repetition frequency of 10 kHz as the pump source, the maximum average output power of 3.51 W at 9.8 µm was achieved with incident pump power of 90 W, corresponding to a slope efficiency of 4.81% and conversion efficiency at maximum pump power of 3.9%. The pulse width of 19.6 ns and linewidth of 142 nm were obtained at maximum output level. In addition, the beam quality factor ${M^2}$M2 was measured to be ${\sim}{2.2}$∼2.2.

High repetition rate 102 W middle infrared ZnGeP2 master oscillator power amplifier system with thermal lens compensation.

We demonstrate a 102 W middle infrared ZnGeP2 (ZGP) optical parametric amplifier (OPA) pumped by a 2097-nm Q-switched Ho:YAG laser at a pulse repetition frequency of 10 kHz. The seed middle infrared laser was produced by a ZGP optical parametric oscillator. Its average power was 28.4 W pumped by a 50 W 2097-nm laser. By thermal lens compensation, the beam factor M2 reduced from 3.1 to 2.1. When the incident Ho pump power was 120 W, the middle infrared ZGP OPA yielded the maximum average output power of 102 W and slope efficiency of 61.7%. The overall optical conversion efficiency of 60% from Ho to middle infrared was obtained for the whole middle infrared laser system. In addition, at the maximum average output power, the beam quality factors of the middle infrared ZGP OPA were measured to be about 2.7 and 2.8 for horizontal and vertical directions, respectively.

231 W dual-end-pumped Ho:YAG MOPA system and its application to a mid-infrared ZGP OPO.

A high-efficiency and high-brightness Ho:YAG master-oscillator power-amplifier (MOPA) system dual-end pumped by Tm:YLF lasers was demonstrated. The maximum output power of 231 W at a wavelength of 2090.7 nm was achieved with pulse repetition frequency of 10 kHz and pulse width of 22.9 ns, corresponding to pulse energy of 23.1 mJ and peak power of ∼1 MW. The extraction efficiency of the amplifier system was more than 60%. The beam quality factor M2 was measured to be ∼1.05. Using the Ho:YAG MOPA system as the pump source, the ZnGeP2 optical parametric oscillator delivered an output power of 110 W, corresponding to slope efficiency of 62%.

High power, tunable mid-infrared BaGa4Se7 optical parametric oscillator pumped by a 2.1 µm Ho:YAG laser.

We, for the first time, demonstrate a tunable mid-infrared BaGa4Se7-based optical parametric oscillator pumped by a acousto-optical Q-switched Ho:YAG laser at 2090.6 nm. Up to 1.55 W of average power was generated in the 3-5 µm range, corresponding to an optical-to-optical conversion efficiency of 14.4% and a slope efficiency of 19.9%. The mid-IR radiation spectra were also seriously researched at different phase-matched angles. The tunable range was 3.49-4.13 µm for the signal, and 5.19-4.34 µm for the idler.

A 41-W ZnGeP2 optical parametric oscillator pumped by a Q-switched Ho:YAG laser.

We reported a high-power ZnGeP2 (ZGP) optical parametric oscillator (OPO) pumped by a Q-switched Ho:YAG laser. The maximum output power of the ZGP OPO was 41.2 W at 107.0 W incident Ho pump power, corresponding to a slope efficiency of 44.6%. The ZGP OPO produced 16-ns mid-IR pulse laser in the 3.74-3.98 µm and 4.38-4.76 µm spectral regions simultaneously. The beam quality was measured to be M²<4.37. The continuous wave maximum average output power of the Ho:YAG laser was 128 W, corresponding to a slope efficiency of 65.8%.

Spectral properties and laser performance of Ho:Sc2SiO5 crystal at room temperature.

Holmium doped scandium silicate (Ho:SSO) bulk crystal grown by Czochralski technique is reported. The absorption cross section of 4.8 × 10(-21) cm2 at pumping wavelength 1940 nm and emission cross section of 5.56 × 10(-21) cm2 at lasing wavelength 2112 nm were calculated, respectively. Lifetime was measured to be 1.51 ms at 300 K and 0.92 ms at 77 K. Continuous-wave laser was operated by using a diode-pumped Tm:YAP laser as pump source with central wavelength of 1940 nm. Output power of 385 mW at 2112 nm was primarily obtained.

103 W in-band dual-end-pumped Ho:YAG laser.

An efficient 2 µm in-band pumped Ho:YAG laser was demonstrated. The resonator involves two Ho:YAG crystals, each of which was dual-end-pumped by two orthogonally polarized diode-pumped Tm:YLF lasers. The maximum continuous wave output power of 103 W was achieved, corresponding to a slope efficiency of 67.8% with respect to the incident pump power and an optical-to-optical conversion efficiency of 63.5%. Under Q-switched mode, we obtained 101 W laser output at 30 kHz, corresponding to a slope efficiency of 66.2%. The beam quality or M2 factor was found to be less than 2.

Resonantly pumped high efficiency Ho:YAG laser.

High-efficient CW and Q-switched Ho:YAG lasers resonantly dual-end-pumped by two diode-pumped Tm:YLF lasers at 1908 nm were investigated. A maximum slope efficiency of 74.8% in CW operation as well as a maximum output power of 58.7 W at 83.2 W incident pump power was achieved, which corresponded to an optical-to-optical conversion efficiency of 70.6%. The maximum pulse energy of 2.94 mJ was achieved, with a 31 ns FWHM pulse width and a peak power of approximately 94.7 kW.

High-efficiency resonantly pumped room temperature Ho:YVO4 laser.

An efficient 2 µm room temperature Ho:YVO(4) laser resonantly pumped by a 1.94 µm Tm:YAP laser is demonstrated, for the first time to our knowledge, in this Letter. Up to 8.58 W of laser output at 2053 nm is obtained with the optical-to-optical conversion efficiency as much as 41.2%. The output beam had quality of M2 factor with Mx(2) of 3.58 and My(2) of 1.76 at 8 W output level. In addition, we also obtained 4.18 W laser output at 2066 nm and 7.04 W at 2040 nm from the Ho:YVO(4) laser with conversion efficiency of 27.8% and 33.8%, respectively.

Room temperature efficient actively Q-switched Ho:YAP laser.

We report on efficient actively Q-switched Ho:YAP laser double-pass pumped by a 1.91-microm laser. At room temperature, when the incident pump power was 20.9 W, a maximum average output power of 10.9 W at 2118 nm was obtained at the repetition rate of 10 kHz, and this corresponds to a conversion efficiency of 52.2% and a slope efficiency of 63.5%. Moreover, a maximum pulse energy of approximately 1.1 mJ and a minimum pulse width of 31 ns were achieved, with the peak power of 35.5 kW.

Continuous-wave laser action around 2-microm in Ho3+:Lu2SiO5.

Continuous-wave (cw) laser action around 2 microm in Ho(3+)-doped Lu(2)SiO(5) (LSO) was demonstrated in this paper. Cryogenically cooled by liquid nitrogen, a 10-mm long Tm-sensitized (6% at.) Ho(0.4% at.):LSO produced a maximum output power of 3 W at 2.07 microm for incident diode power of 11 W at 786 nm, and a slope efficiency of 35% with respect to incident pump power. To achieve room-temperature operation of Tm, Ho:LSO laser, a 1-mm long microchip crystal was pumped by a high brightness diode, generating an output power of greater than 80 mW and a slope efficiency of 26% at 2.08 microm. Using a 1.91 microm Tm:YLF laser as an in-band pump source, room-temperature cw operation of singly-doped Ho: Lu(2)SiO(5) laser at 2106 nm was attained with a maximum output power of 2.8 W and a slope efficiency of 35% corresponding to absorbed pump power.

Diode-pumped continuous wave and Q-switched operation of a c-cut Tm,Ho:YAlO(3) laser.

We report on a diode-pumped, cryogenic and room temperature operation of a Tm,Ho:YAlO3 (c-cut) laser. In a temperature of 77 K, an optical-optical conversion efficiency of 27% and a slope efficiency of 29% were achieved with the maximum continuous-wave (CW) output power of 5.0 W at 2.13 microm. Acousto-optic switched operation was performed at pulse repetition frequency (PRF) from 1 kHz to 10 kHz, the highest pulse energy of 3.3 mJ in a pulse duration of 40 ns was obtained. In room temperature (RT), the maximum CW power of Tm,Ho:YAlO3 laser was 160 mW with a slope efficiency of 11% corresponding to the absorbed pump power.

Continuous-wave and Q-switched operation of a resonantly pumped Ho:YAlO3 laser.

We demonstrated continuous-wave (CW) and Q-switched operation of a room-temperature Ho:YAlO(3) laser that is resonantly end-pumped by a diode-pumped Tm:YLF laser at 1.91 microm. The CW Ho:YAlO(3) laser generated 5.5 W of linearly polarized (EII c ) output at 2118 nm with beam quality factor of M(2) approximately 1.1 for an incident pump power of 13.8 W, corresponding to optical-to-optical conversion efficiency of 40%. Up to 1- mJ energy per pulse at pulse repetition frequency (PRF) of 5 kHz, and the maximum average power of 5.3-W with FWHM pulse duration of 30.5 ns at 20 kHz were achieved in Q-switched mode.

Diode-pumped efficient Tm,Ho:GdVO(4) laser with near-diffraction limited beam quality.

A diode-pumped efficient 2.05-mum Tm,Ho:GdVO(4) laser with high beam quality is reported. The cavity configuration was optimized for weakening influence of thermal effect to resonator stability and mode-coupling. A conversion efficiency of 46% and a slope efficiency of 50% were obtained with continuous-wave (CW) output power of 10.5 W at 77 K. A repetitively Q-switched laser also achieved 10.1 W of output power at 10 kHz. A beam quality factor of M(2) < 1.1 was measured by the traveling knife-edge method. In addition, the energy per pulse of 1.9 mJ was obtained at 5 kHz, corresponding to the peak power of 0.14 MW.

Gain-switched Tm3+-doped double-clad silica fiber laser.

A gain-switched Tm-doped double-clad silica fiber laser operating at a wavelength of approximately 2microm with moderate output energy of 14.7mJ per pulse and a slope efficiency of 39.5% (with respect to launched pump energy) is realized pumped at 1.064microm from a Nd:YAG laser. The gain-switched fiber laser pulses are built up by a series of relaxation spikes, and every spike pulse duration is nearly 1micros. The output wavelength becomes longer, and the slope efficiency increases with the increase in fiber length.

Performance of AO Q-switched Tm,Ho:GdVO4laser pumped by a 794nm laser diode.

Acousto-optically Q-switched operation of Tm (5 at. %), Ho(0.5 at. %):GdVO4 laser was reported in this paper. The Tm,Ho:GdVO4 crystal was cooled by liquid nitrogen and end-pumped by a 13.6 W fiber-coupled laser diode at 794 nm. Average power of 3.9W was obtained at pulse repetition frequency (PRF) from 10 to 50 kHz, with corresponding to optical-to-optical conversion efficiency of 29 %, and slope efficiency of 35%. The highest energy per pulse of 1.1 mJ in 23 ns was achieved at 3 kHz with peak power of 46 kW.

[Effects of nitrogen application rate on soil nitrate nitrogen accumulation under vegetable-paddy rice rotation system].

A 2-year field experiment of mustard-cabbage-early rice rotation was conducted to investigate the effects of nitrogen application on yield and accumulation of nitrate nitrogen in the soil. The results showed that the applications of 150 kg N x hm(-2) for mustard and cabbage respectively and 90 kg N x hm(-2) for early rice were the best economic application mode, which could increase the net profit by 0.2%-75.6% compared with other application modes. Nitrogen application rates were positively correlated with NO3(-)-N concentration in the soil and in the percolating water. The vegetable-paddy rice rotation decreased the surplus of nitrogen in the soil. The average soil NO3(-)-N concentration was 29.7 mg x kg(-1) under the rotation of mustard-cabbage-early rice, which was only 84.4% of that under the continuous cropping of mustard-cabbage. The average NO3(-)-N concentration in the percolating water under mustard-cabbage-early rice rotation was little different from that in basal soil. Therefore, with the optimum nitrogen application mode, the vegetable-paddy rice rotation could gain the best economic benefit while significantly decrease the accumulation of nitrate nitrogen in the soil to effectively control non-point source pollution of nitrogen from vegetable fields.

7.3 W of single-frequency output power at 2.09 mum from an Ho:YAG monolithic nonplanar ring laser.

Single-frequency output power of 7.3 W at 2.09 mum from a monolithic Ho:YAG nonplanar ring oscillator (NPRO) is demonstrated. Resonantly pumped by a Tm-doped fiber laser at 1.91 mum, the Ho:YAG NPRO produces 71% of slope efficiency with respect to absorbed pump power and nearly diffraction-limited output with a beam quality parameter of M(2) approximately 1.1.