X.H. Gong

2.0W diode-pumped Er:Yb:YAl3(BO3)4 laser at 1.5–1.6μm

An efficient and high output power laser has been realized for an Er:Yb:YAl3(BO3)4 crystal end pumped by a 970nm diode laser. Under the absorbed pump power of 15.5W, quasi-continuous-wave output power of 2.0W at 1.5–1.6μm has been obtained in a hemispherical cavity. The laser had an absorbed pump threshold power of 4.7W and a slope efficiency of 21%. The influence of the laser output power and output coupler transmission on the output laser spectra has also been investigated.

Highly efficient Nd3+:LaB3O6 cleavage microchip laser

The improvement of the laser performances of an unprocessed 5.6at.% Nd3+:LaB3O6 cleavage microchip has been reported. Pumped by a Ti:sapphire laser at 871nm, quasi-cw output laser power up to 395mW around 1060nm wavelength with slope efficiency near 52% has been obtained in an end-pumped plano-plano resonator. The influence of the ratio between the cavity mode and pump beam area on the laser performances and laser spectra at various output powers has been investigated. The experimental results have shown that the cleavage technique can become a practical and effective method to obtain the microchip laser medium easily and directly.

Site-selective excitation and emission of Eu 3+ -doped transparent glass ceramic containing Ca 5 (PO 4 ) 3 F nanocrystals

An Eu3+-doped transparent oxyfluoride glass ceramic containing Ca5(PO4)3F nanocrystals was prepared by melt quenching and subsequent thermal treatment. The transmittance of the glass ceramic with a thickness of 1.92 mm is up to 80.5% in the visible range at room temperature. Site-selective excitation and emission spectra indicate that Eu3+ ions in the Ca5(PO4)3F nanocrystals occupy two types of sites, A and B, with a same point symmetry Cs. As for Eu3+ ions at site A, the crystal field is more deformed and stronger. The crystal field may appear in the form of a ligand ion F- being replaced by O2- in accordance with the charge compensation scheme: Ca2+ + F-→Eu3+ + O2-. As for Eu3+ ions at site B, the possible charge compensation scheme is 3Ca2+→2Eu3+ + Vacancy. Furthermore, an energy transfer process from Eu3+ ions at site A to that at site B in the glass ceramic at low temperature was also discussed.

Effect of Ce 3+ doping on the spectroscopic properties and 1.55 μm laser operation of Er:Yb:Ce:NaY(WO 4 ) 2 crystal

Er:NaY(WO4)2 and Er:Yb:Ce:NaY(WO4)2 crystals were grown by the Czochralski method. Er:Yb:NaY(WO4)2, Er:Ce:NaY(WO4)2, and Yb:NaY(WO4)2 crystal powders were synthesized by means of the solid-state reaction. The spectroscopic properties of the crystals were investigated, including the absorption and fluorescence spectra and fluorescence decay. The energy transfer efficiency from Yb3+ to Er3+ in Er:Yb:NaY(WO4)2 and Er:Yb:Ce:NaY(WO4)2 was calculated and analyzed. End-pumped by a diode laser at 970 nm in a hemispherical cavity, a 1.84 W quasi-continuous-wave laser around 1.55u2009μm with a slope efficiency of 17% and an absorbed pump threshold of 1.60 W was achieved in a 1.04 mm thick c-cut Er:Yb:Ce:NaY(WO4)2 crystal. The results show that the Er:Yb:Ce:NaY(WO4)2 crystal with high Ce3+ doping is a candidate for gain medium of low threshold 1.55u2009μm laser.

Spectral properties and 1.5–1.6 μm laser operation of Er:Yb:NaCe(WO4)2 crystal

An Er:Yb:NaCe(WO4)2 crystal was grown by the Czochralski method. Spectral properties of the crystal were investigated and compared with those of the Er:Yb:Ce:NaGd(WO4)2 crystal. The green up-conversion was not observed when the Er:Yb:NaCe(WO4)2 crystal was excited by a diode laser at 970 nm. The efficiency of energy transfer from Yb3+ to Er3+ in the Er:Yb:NaCe(WO4)2 crystal was calculated to be about 93%. End-pumped by a diode laser at 970 nm in a hemispherical cavity, 0.95 W quasi-CW laser at 1.5–1.6 μm was achieved in a 1.47-mm-thick c-cut Er:Yb:NaCe(WO4){ia2} crystal, the slope efficiency was 11%, and the threshold was 2.83 W.

Passively Q-switched laser operation of Nd:LaB3O6 cleavage microchip

Pumped by a Ti:sapphire laser, a passively Q-switched laser oscillation from an unprocessed Nd:LaB3O6 cleavage microchip with a Cr4+:YAG saturable absorber has been demonstrated. The influence of the transmission of the output coupler on the pulse width and repetition rate at various absorbed pump powers has been investigated. A pulse with 2.8μJ energy, 2.2ns duration, and 29kHz repetition rate at 1060nm was obtained at the absorbed pump power of 1.25W and output coupler transmission of 3.2%, which results in 1.25kW peak power. The polarization and spectral properties of laser radiation were measured.

Efficient diode-pumped acousto-optic Q-switched Er:Yb:GdAl(3)(BO(3))(4) pulse laser at 1522 nm.

End-pumped by a continuous-wave 976 nm diode laser, efficient 1522 nm laser operation was demonstrated in an Er:Yb:GdAl(3)(BO(3))(4) crystal when a sapphire crystal was used as a heat diffuser. A continuous-wave 1522 nm laser with a maximum output power of 750 mW and slope efficiency of 36% was realized at an absorbed pump power of 4.1 W. The pulse performances of an acousto-optic Q-switched laser with various repetition frequencies were investigated in detail. In a repetition frequency range of 1-10 kHz, 1522 nm pulse lasers with a slope efficiency of about 10%, peak output power at the kilowatt level, and width of about 50 ns were first obtained in an Er:Yb:GdAl(3)(BO(3))(4) crystal pumped by a continuous-wave diode laser. The results indicate that the crystal is a promising gain medium for an actively Q-switched 1.5 μm laser.

Enhanced performance of acousto-optic Q-switched Er:Yb:RAl3(BO3)4 (R = Y and Lu) pulse lasers at 1580 nm

By using mirrors with specially designed transmissions in a diode end-pumped hemispherical cavity, laser oscillations except for 1580xa0nm were suppressed and an enhanced pulse performance of an acousto-optic Q-switched laser at a single wavelength of 1580xa0nm was realized for Er:Yb:RAl3(BO3)4 crystals. When the absorbed pump power was 13.5xa0W and the pulse repetition frequency was 1xa0kHz, 250xa0μJxa0Q-switched pulse energy with a width of 215xa0ns and 350xa0μJxa0Q-switched pulse energy with a width of 125xa0ns were achieved in Er:Yb:YAl3(BO3)4 and Er:Yb:LuAl3(BO3)4 crystals, respectively. The pulsed laser performances of both the crystals were also compared and investigated in detail.

Characterization of periodic extreme ultraviolet multilayer based on multi-objective evolutionary algorithm

In order to refine the layered structure of extreme ultraviolet multilayers, a multi-objective evolutionary algorithm which is post-hybridized with the standard Levenberg-Marquardt algorithm is applied to analyze the grazing incidence X-ray reflectivity (GIXR) and the normal incidence extreme ultraviolet reflectance (EUVR). In this procedure, the GIXR data and EUVR data are simultaneously fitted as two objectives, and the high sensitivities of these two sets of data to layer thicknesses and densities are combined. This set of mathematical procedures is conducive to obtain a more correct model of periodic multilayers which can simultaneously describe both GIXR and EUVR measurements. As a result, the layered structure of Mo/Si multilayers with a period of about 7.0u2009nm is obtained.