An energy transfer kinetic probe for OH-quenchers in the Nd(3+):YPO4 nanocrystals suitable for imaging in the biological tissue transparency window.

Tetragonal xenotime-type yttrium orthophosphate (YPO4) Nd(3+) doped nanoparticles suitable for biomedical applications were prepared by microwave-hydrothermal treatment. We applied the energy transfer probing based on the analysis of kinetics of impurity quenching to determine the presence and spatial position of -OH fluorescence quenching acceptors in the impurity-containing nanoparticles. We show that the impurity quenching kinetics of the 0.1 at% Nd(3+) doped YPO4 nanoparticles is a two stage (ordered and disordered) static kinetics, determined by a direct energy transfer to the -OH acceptors. Analyzing the ordered stage, we assume that the origin of the -OH groups is the protonation of the phosphate groups, while analyzing the disordered stage, we assume the presence of water molecules in the mesopores. We determine the dimension of the space of the -OH acceptors as d = 3 and quantify their absolute concentration using the disordered Förster stage of kinetics. We use the late stage of kinetics of fluorescence hopping (CDD ≫ CDA) quenching (the fluctuation asymptotics) at 1 at% Nd(3+) concentration as an energy transfer probe to quantify the relative concentration of -OH molecular groups compared to an optically active rare-earth dopant in the volume of NPs, when energy migration over Nd(3+) donors to the -OH acceptors accelerates fluorescence quenching. In doing so we use just one parameter α = γ(A)/γ(D) = n(A)√[C(DA)]/n(D)√[C(DD)], defined by the relation of concentration of the -OH acceptors to the concentration of an optically active dopant. The higher is the α, the higher is the relative concentration of -OH acceptors in the volume of nanoparticles. We find α = 2.95 for the 1 at% Nd(3+):YPO4 NPs that, according to the equation for α, and the results obtained for the values of the microparameters CDD(Nd-Nd) = 24.6 nm(6) ms(-1) and CDA(Nd-OH) = 0.6 nm(6) ms(-1), suggests twenty times higher concentration for acceptors other than donors. As the main result we have established that the majority of -OH acceptors is located not on the surface of the Nd(3+):YPO4 nanoparticles, as many researchers assumed, but in their volume, and can be either associated with crystal structure defects or located in the mesopores.

Dysprosium-doped PbGa2S4 laser generating at 4.3 µm directly pumped by 1.7 µm laser diode.

In this Letter, we demonstrate the pulsed and CW operation of the Dy:PbGa(2)S(4) laser directly pumped by the 1.7 µm laser diode. In the pulsed regime (pulse duration 5 ms; repetition rate 20 Hz), the maximum mean output power of 9.5 mW was obtained with the slope efficiency of 9.3% with respect to the absorbed pump power. The generated wavelength was 4.32 µm, and the laser beam cross section was approximately Gaussian on both axes. Stable CW laser generation was also successfully obtained with the maximum output power of 67 mW and the slope efficiency of 8%. Depopulation of the lower laser level by 1.7 µm pump radiation absorption followed by 1.3 µm upconversion fluorescence was demonstrated. These results show the possibility of construction of the compact diode-pumped solid-state pulsed or CW laser generating at 4.3 µm in the power level of tens mW operating at room temperature.

Diode-pumped Er:CaF2 ceramic 2.7 µm tunable laser.

Spectroscopic and laser properties of a newly developed high optical quality Er:CaF2 hot-formed ceramic were investigated. Under pulsed 968 nm laser diode pumping, the mid-infrared (2.7 µm) radiation was obtained with a slope efficiency of 3%. Laser tunability was reached using a birefringent filter and the laser tuning range of 118 nm, from 2687 up to 2805 nm, was demonstrated. The maximal output energy reached was 0.48 mJ at 2730 nm for the absorbed pumping energy 34 mJ.

Dysprosium-doped PbGa2S4 laser excited by diode-pumped Nd:YAG laser.

We realized a compact mid-IR room temperature operating Dy(3+):PbGa(2)S(4) laser, excited by a diode-pumped Nd:YAG laser at a wavelength of 1318 nm. The pumping laser was operating in pulsed mode with a pulse length of 4 ms and repetition rate of 20 Hz. Maximum pumping energy at a wavelength of 1318 nm was 15 mJ. Energy up to 90 µJ and mean output power of 1.8 mW was obtained at a wavelength of 4290 nm with a slope efficiency with respect to absorbed pumping energy better than 3%.

Oscillation properties of dysprosium-doped lead thiogallate crystal.

The room-temperature laser-oscillation properties of lead thiogallate crystals doped with dysprosium ions PbGa(2)S(4):Dy(3+) without additional codoping and codoped with potassium ion for excessive charge compensation were investigated. A slope efficiency of 1% was obtained for the codoped crystal. YAP:Er -1.66 microm laser resonant pumping of PbGa(2)S(4):Dy(3+) laser was compared with YAG:Nd -1.32 microm nonresonant pumping. The maximum energy obtained was 57 microJ with the negligible influence of the atmosphere.

Laser and self-Raman-laser oscillations of PBMoO4:Nd3+ crystal under laser diode pumping.

Different regimes of laser operation and stimulated Raman scattering (SRS) for a laser diode (LD)-pumped PbMoO4:Nd3+ crystal have been investigated. Under 1.5 W LD pumping, the output power of the PbMoO4:Nd3+ laser in the free-running mode at 1056 nm reached 0.65 W with a slope efficiency of up to 53%. Using different LiF: F-2 saturable absorbers, we achieved a maximum pulse energy of 11 microJ at a 1.4 ns pulse duration and a maximum output power of 0.35 W (10 microJ) at a 7 ns pulse width in the passively Q-switched mode. PbMoO4:Nd3+ self-Raman-laser operation at 1163 nm (first Stokes) was obtained for the first time, to our knowledge. The self-Raman-laser output pulse energy was measured to be as high as 6 microJ and the pulse duration was estimated to be shorter than 500 ps.