Spatial mode cleaning and efficient nonlinear pulse compression to sub-50†fs in a gas-filled multipass cell.

We demonstrate a gas-filled multipass cell (MPC) that cleaned the spatial mode of a spatial-filter-free 250 W, 100 kHz, 445 fs driven source based on an Innoslab amplifier and compressed the pulse duration to 41 fs simultaneously. The multipass cell acted as a spatial filter and benefited from its discrete waveguide nature, in which the input beam quality factor M2 was improved from 1.53 to a near-diffraction-limited value of 1.21 at 96% transmission.

Dual-slab Yb:KGd(WO4)2 regenerative amplifier for spectral shaping and high-power output.

A high-power regenerative amplifier (RA) based on dual-slab Yb:KGd(WO4)2 (Yb:KGW) was demonstrated, which provided a maximum average power of 33.7 W at a repetition rate of 75-200 kHz before compression with a central wavelength of 1039 nm, corresponding to an optical-to-optical conversion efficiency of 51.4%. To the best of our knowledge, this is the highest average power from the Yb:KGW solid-state RA. The compressed pulse duration of 205 fs was realized under the maximum output power. By adjusting the gain of the crystals, respectively, the spectral shaping can be achieved. A combination spectrum with root-mean-square (RMS) bandwidth of 4.5 nm was generated with a central wavelength of 1035 nm at an output power of 20 W, the compressed pulse duration was 159 fs. Meanwhile, effective mitigation of thermal effects by dual-slab configuration guaranteed the nearly diffraction-limited beam quality: M x2 = 1.17 and M y2 = 1.20.

417†W, 2.38†mJ Innoslab amplifier compressible to a high pulse quality of 406†fs.

We demonstrate a 417 W, 175 kHz Innoslab chirped pulse amplification laser compressible to short and clean 406 fs pulse duration. A spectral bandwidth (full width at half maximum, FWHM) of ∼3 nm was maintained at full pump power, and the pulses exhibited good pulse quality in a wide tunable pulse energy range from 1.7 mJ to a maximum of 2.38 mJ. At the maximum output power, the compressed pulses were nearly pedestal free. The comprehensive effects of residual high-order dispersion from the front end, the gain shaping effects of the amplifier, and the slight mismatch of third-order dispersion (TOD) between the stretcher (CFBG) and the gating compressor, along with the small nonlinear phase shift accumulated in the amplifier, could have facilitated the high pulse quality. To the best of our knowledge, this is the shortest pulse duration from the Innoslab amplifiers at hundreds of watts average power in the millijoule energy regime.

Efficient high-power orthogonal dual-slab Yb:KGd(WO4)2 laser oscillator with a TEM00 mode.

We demonstrated a TEM00 mode orthogonal dual-slab Yb:KG(WO4)2(Yb:KGW) laser oscillator with high average power. Polarization anisotropy of thermal lenses was investigated and alleviating the astigmatism based on orthogonal dual-slab. In addition, the laser polarization was directly controlled by adjusting the net gain of the two crystals. The maximum output power was highly enhanced compared with single crystal due to effective thermal distribution. For an absorbed pump power of 52.4 W, this oscillator delivered an average power of 26.5 W, corresponding to an optical-to-optical conversion efficiency of 50.6%. Meanwhile, the ellipticity of the output laser was optimized to 0.940. Nearly diffraction-limited beam quality was measured to be M x2 = 1.19 and M y2=1.18.

Wavelength shift with a diode-pumped continuous-wave Yb:CALGO laser.

The dependence of an emission wavelength on the crystal temperature was first investigated for a diode-pumped continuous-wave ${{\rm Yb}^{3 + }}$Yb3+-doped ${{\rm CaGdAlO}_4}$CaGdAlO4 (Yb:CALGO) laser. A maximum output power of 11 W was obtained, corresponding to a slope efficiency of 19.8%. The output wavelength varied from 1051.10 nm to 1054.72 nm with increased absorbed pump power. This wavelength shift is attributed to a change in the crystal temperature. This observation is, to our best knowledge, an original conclusion about this phenomenon in a Yb:CALGO laser. We use a temperature-dependent model to explain the emission wavelength shifts that can be generalized to any such quasi-three-level materials.

[Water quality comparison between Lake Taihu and contribute river during high water-level period].

Thirty-two main rivers around Lake Taihu were sampled during high water period in 2008 to investigate river's vital impact on Lake water quality. Different forms of nitrogen and phosphorus were analyzed for the 32 river water samples according to nutrients function to algae. The aim of this study is to provide the basic information for river rehabilitation. Based on the results, the nutrients and suspended substance (SS) concentrations of Wangyu River were the highest, its water quality was below the V grade (Chinese water quality criterion). Water quality of northern rivers was also below the V grade, organic matter and enzymatically hydrolysable phosphate (EHP) concentration were the highest. The EHP concentration was 0.240 mg/L, and accounted for 62.4% of total phosphorus (TP). Nitrite nitrogen (NO2(-) -N) concentration was exceptionally high in western rivers and the average concentration was 0.270 mg/L, it was 2-3 times higher than that of other rivers. The northern rivers' nitrogen, phosphorus and organic concentration were markedly higher than those in the north Lake region, while the western rivers' nitrogen was markedly higher than that in the west Lake region. It can also be concluded that algae and suspended sediment were able to bring more phosphorus to water by comparing the ratio of total nitrogen(TN) and TP in these rivers and Lake Taihu.