A. Lupei

Laser emission under resonant pump in the emitting level of concentrated Nd:YAG ceramics

The possibility of using the thermally activated optical absorption bands for a resonant pump in the emitting level of highly doped Nd laser materials is discussed. This potential is demonstrated by the continuous wave 1064 nm laser emission under 885 nm pump in concentrated (up to 6.8 at.u200a%) Nd:YAG ceramics.

Transparent Nd and (Nd, Yb)-doped Sc2O3 ceramics as potential new laser materials

Highly transparent Sc2O3 ceramics with uniform doping up to 0.5at.% Nd and with (Nd, Yb) codoping are reported. The spectroscopic and emission decay properties of Nd:Sc2O3 ceramics are similar to those of single crystals. Highly efficient Nd-to-Yb energy transfer is observed in the codoped ceramics. It is inferred that these materials have potential for construction of Nd or Nd-sensitised-Yb lasers.

Energy transfer between Nd3+ ions in YAG

Abstract The luminescence decay of the 4 F 3 2 level of Nd 3+ in YAG at room temperature for concentrations from 0.1 to 2.5 at .% is analyzed. Above 0.4 at.% Nd the decay shows an evident departure from an exponential law. An analysis of the non-exponential part of the decay reveals various time regimes of energy transfer which, for our samples, shows a rather monotonous variation along this range of concentrations. For less than 1.2 at.% Nd the energy transfer is essentially of direct donor-acceptor type. This energy transfer lowers the relative quantum efficiency by almost 10% for neodymium concentration increasing from 0.1 to 1.2 at.%.

Concentration effects on the up-conversion from the 4I132 level of Er3+ in YAG

Abstract A quantitative study of the up-conversion process ( 4 I 13 2 → 4 I 15 2 ) + ( 4 I 13 2 → 4 I 9 2 → 4 I case11 2 ) , essential in the 3 μm emission of Er3+ in YAG, over a large concentration range (0.1 to 100 at% Er3+) and pumping energy has been performed. The concentration and sample dependence of the “intrinsic” lifetime of 4I 13 2 and 4I 13 2 laser levels is tentatively explained by energy transfer to aleatory impurities. The quadratic concentration dependence of the up-conversion parameter, obtained experimentally, and the possibility to describe the up-conversion process by rate equations are explained by large migration effects and effective interactions between nearest neighbours.

High-resolution spectroscopy and emission decay in concentrated Nd:YAG ceramics

The high-resolution spectroscopic and emission-decay investigation of highly concentrated (up to 9 at.u2009%) Nd:YAG ceramics indicates that the state of the Nd3+ ion in these materials is similar to that of diluted crystals. The increased relative intensities of the spectral satellites connected with ensembles of Nd ions in near-lattice sites at high Nd concentrations CNd is consistent with the predictions of the statistics of the random placement of these ions at the available lattice sites. The room-temperature transmission spectra show that the resonant pump in the emitting level xa04F3/2, including the hot-band pump Z2→R1 and Z3→R2, can be efficient at high CNd, with important effects in the reduction of the pump quantum defect and of the corresponding heat generation under the pump. The accelerated xa04F3/2 emission decay at high CNd is consistent with the increased efficiency of the energy transfer, including the contribution of migration-assisted transfer processes. The calculated emission quantum efficiency η and the figure of merit ηCNd indicate that the concentrated Nd:YAG components can be used for construction of efficient solid-state lasers in free-generation or low-storage regimes, and, coupled with the hot-band resonant pump in the emitting level, they could enable the scaling of Nd:YAG lasers to high powers.

Spectroscopy and laser emission under hot band resonant pump in highly doped Nd:YAG ceramics

The high resolution spectroscopic and emission decay properties of Nd:YAG ceramics with up to 9 at.% Nd show that no major changes from the single crystals other than those induced by the increased Nd concentration occur and indicate that these materials can be used for construction of efficient and high power lasers. The laser emission of a 3.8 at.% Nd ceramic laser component under hot band resonant pump at 885 nm with a Ti:sapphire laser is demonstrated.

Resonant electron-phonon coupling of Yb3+ in YAG

Abstract An analysis of Yb3+ spectra in YAG in terms of the splitting of the zero-phonon lines in the case of near resonance between Stark levels and sharp peaks in the phonon spectrum is presented. The theoretical relations allow estimation of the position of the electronic level and vibronic coupling strength from the intensity ratio and spectral shifts. A new energy level scheme for the 2F5/2 Yb3+ multiplet in YAG is proposed.

ELECTRON-PHONON COUPLING FOR HEAVY RE3+ IONS IN CRYSTALS

Abstract The near resonant effects of electron-phonon coupling in the optical spectra of rare earth (RE) ions are analysed. A theoretical treatment that could describe effects such as splittings or temperature shifts and broadening of zero-phonon lines is presented. The main factors that determine the magnitudes of the near resonant effects are the strength of electron–phonon coupling and the peaks in the phonon density in the resonance region. Experimental data refer to heavy RE 3+ ions, i.e. Tm 3+ and Yb 3+ in Y 3 Al 5 O 12 (YAG), known as important laser systems. The fitting of experimental data with theory allows the identification of the electronic levels with a good approximation. The obtained data concerning the strength of the electron–phonon coupling show the tendency of increasing from Tm 3+ to Yb 3+ .

Effects of nearest‐neighbor pairs on the energy transfer in Nd:YAG

An analysis of the luminescence quenching of 4F3/2 level of Nd3+ in YAG is presented in terms of two models: uniform random distribution and nonuniform placement of activators. It is shown that the correlated placement model for Nd3+ ions, assuming the absence, based on ionic size arguments, of Nd3+ ions in nearest‐neighbor sites, is in contradiction with high resolution absorption spectra as well as quantum yield data. The anomalous decay can be described by energy transfer theory for a uniform distribution with a short‐range interaction connecting the nearest‐neighbor pairs and with dipolar interaction inside the other donor‐acceptor pairs.

Emission quantum efficiency and heating effects in YAG:Nd3+ lasers

The intrinsic limitations of emission quantum efficiency of Nd 31 in YAG that lead to heating of active element are analyzed. The main factors characteristic of the system of active ions that lead to heat are the quantum defect and the emission quenching due to energy trans- fer by cross-relaxation and multisite structure (especially for laser or di- ode pumping). It is shown that for concentrations of interest for lasers, the reduction of emission quantum efficiency by energy transfer is due to two types of interactions between active ions. The high-resolution data are used to explain the global behavior of metastable level emission kinetics and the concentration reduction of quantum efficiency. An ana- lytic expression for the fractional thermal load is obtained, imposing a lower limit at each concentration. The estimated values of emission quantum efficiency and fractional load are in agreement with reported measured values.