Diode-pumped Pr<Superscript>3+</Superscript>:YAlO<Subscript>3</Subscript>/LBO violet laser at 374 nm

We report a diode-pumped Pr³⁺:YAlO₃ laser emitting at 747 nm. A power of 232 mW at 747 nm has been achieved in continuous-wave operation with a diode emitting 2 W at 448 nm. Furthermore, intracavity second-harmonic generation in continuous-wave mode has also been demonstrated with a power of 52 mW at 374 nm by using a LBO nonlinear crystal. The fluctuation of the violet output power was better than 2.3%. The beam quality M ² value is 2.2.     

Switchable multiple lasing oscillations in an erbium-doped fiber ring laser using a single stage of a Sagnac loop mirror

A simple scheme for a switchable multi-wavelength erbium-doped fiber (EDF) ring laser is investigated by using a single stage of a Sagnac loop mirror. The multiple lasing outputs are obtained and switched readily by controlling the state of polarization (SOP). Since the transmission characteristics of the Sagnac loop mirror in terms of peak wavelengths and peak powers strongly depend on the SOP, the switching performance of the proposed multi-wavelength EDF laser can be effectively obtained. The proposed multi-wavelength EDF laser has versatile lasing outputs in states of a single-, dual-, triple-, and quadruple-wavelength oscillations. The multiple outputs are effectively switchable by adjusting the SOP.     

Effect of metallic and hyperbolic metamaterial surfaces on electric and magnetic dipole emission transitions

Spontaneous emission patterns of electric and magnetic dipoles on different metallic surfaces and a hyperbolic metamaterial (HMM) surface were simulated using the dyadic Green’s function technique. The theoretical approach was verified by experimental results obtained by measuring angular-dependent emission spectra of europium ions on top of different films. The results show the modified behavior of electric and magnetic dipoles on metallic and HMM surfaces. The results of numerical calculations agree well with experimental data.     

High repetition rate LiF<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack>: Color center laser

The efficient oscillation of LiF:F₂⁻ color center laser pumped by a compact LD-pumped Nd:YVO₄ acousto optically Q-switched laser with 30 kHz pulse repetition rate was demonstrated. The broadband oscillation with 75 μJ pulse energy and 37 kW peak power with the slope efficiency 20% was obtained. The average output power as high as 230 mW was reached. The narrow line tunable from 1.10 to 1.29 μm laser radiation with 10% conversion efficiency in the maximum of the tuning curve was achieved under pumping with 1.6 W average pump power.     

Efficient and compact intracavity-frequency-doubled Nd:LuVO<Subscript>4</Subscript>/LBO laser at 538 nm end-pumped by a fiber-coupled laser diode

We report a diode-pumped Nd:LuVO₄ laser emitting at 1076 nm, based on the ⁴ F _3/2−⁴ I _11/2 transition, generally used for a 1066 nm emission. A power of 689 mW at 1076 nm has been achieved in continuous-wave (CW) operation with a fiber-coupled laser diode emitting 17.8 W at 809 nm. Intracavity second-harmonic generation (SHG) in CW mode has also been demonstrated with a power of 105 mW at 538 nm by using a LiB₃O₅ (LBO) nonlinear crystal.     

Fabrication and characterization of double-wall carbon nanotube absorber for passive mode-locked Nd:GdVO<Subscript>4</Subscript> laser

Using the vertical evaporation technique we fabricated saturable absorbers by transferring the double-wall carbon nanotubes (DWCNT) onto a hydrophilic quartz substrate. The fast recovery time and the saturation intensity of the absorber were measured to be 228 fs and 130 μJ/cm², respectively, at 1060 nm. The modulation depth of the absorber was about 3.7%. Passive mode-locked Nd:GdVO₄ laser was demonstrated. The continuous wave mode-locked pulses pulse duration is 5.6 ps and the largest average output power is 1.2 W at the pump power of 9.5 W. To the best of our knowledge, this is the first demonstration of high power continuous wave mode locking laser with DWCNT absorber.     

Cooperative emission study in ytterbium doped NdVO4

The infrared and visible cooperative emissions of ytterbium ions are studied in Yb-doped NdVO₄ single crystals. The absorption of optical phonons allows the emissions at room temperature when a Nd:YAG laser is used. Low temperature emissions are observed due to the Nd³⁺→Yb³⁺ energy transfer following an argon ion laser excitation of the Nd³⁺ ions. Analysis of the cooperative emission at low doping concentration (1%) indicates that it is generated by distant pair forming Yb³⁺ ions while at high doping concentration (≥ 5%) close ions magnetically coupled and superexchange mechanisms prevail in the emitting process.     

Analytical study of an active piezoelectric absorber on vibration attenuation of a plate

The attenuation of the transverse vibration of a plate, subjected to a harmonic force, is studied. This goal can be achieved by using an active dynamic absorber. The active absorber is made of a pair of piezoelectric sheets, attached to both sides of the plate, and closed electric circuits. One piece of the piezoelectric material provides a sensor for detecting the motion of the plate. Another piece serves as an active dynamic absorber. The equations of motion of the composite plate, including the plate and the piezoelectric material, and the circuit equations of the sensor and the absorber are derived. The displacements of the plate and the currents in the circuits are calculated. The active absorber can successfully attenuate the vibration. The numerical results show that the proposed active absorber can offer more reduction than that using a passive absorber while the absorber is designed to suppress the resonance of a particular vibration mode. Moreover, the active absorber can also reduce the displacements corresponding to other uncontrolled modes. The effects of altering various parameters of the active absorber are studied and discussed.     

Spin-glass behavior and magnetocaloric effect in melt-spun TbCuAl alloys

Magnetic properties and magnetocaloric effects of amorphous and crystalline TbCuAl ribbons are investigated by measuring their ac susceptibilities including a nonlinear term and dc magnetizations. The in-phase third harmonic ac susceptibility is found to be negative. It can be well fitted by the expression at high temperatures, indicating a spin-glass behavior in amorphous TbCuAl alloy. ΔT_f(ω)/[T_f(ω)Δlog₁₀ω], a possible distinguishing criterion to judge the presence of a spin-glass behavior is ∼0.011. The frequency-dependent data can be well fitted by the conventional critical slowing down law and the spin-glass transition temperature is obtained to be 20.1 K. The maximum of magnetic entropy change reaches 4.5 J kg⁻¹ K⁻¹ for a field change of 0-50 000 Oe, while the crystalline TbCuAl compound experiences a simple ferromagnetic-to-paramagnetic phase transition. The peak value of magnetic entropy change is obtained at the Curie temperature and reaches 14.4 J kg⁻¹ K⁻¹ for the same field change, which is much larger than that of amorphous TbCuAl alloy.     

Vibrational spectroscopy studies of a pressure-induced disproportionation reaction of LaH2

The pressure-induced disproportionation reaction of LaH₂ was investigated by infrared reflection and Raman measurements at ambient temperature. The relative reflection intensity in the 4000-6000 cm⁻¹ region began to decrease significantly at a pressure of about 12 GPa and fell to 10% of the initial value at 20 GPa. Absorption peaks, which appeared around 1200 and 700 cm⁻¹ at pressures above 14 GPa, were assigned to the hydrogen vibrations at the tetrahedral and octahedral sites of the fcc metal lattice, respectively. The peak frequencies measured in the 14-30 GPa range were similar to those observed in LaH₃. These infrared results indicated insulating LaH₃ precipitated from metallic LaH₂. Above 20 GPa, a Raman peak related to the hydrogen vibration in the octahedral sites appeared around 700 cm⁻¹, and was likely due to lattice distortion. The disproportionation reaction of LaH₂ into and solid solution LaH_x (x<1) was confirmed.