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Steady-state and time-resolved laser spectroscopies are used to investigate the energy transfer between Cr(super 3+) and Nd(super 3+) ions in Cr(super 3+), Nd(super3+):YAl3(BO3)(sub 4) (YAB) codoped crystals. The analysis has showed that 80% of the Cr(super 3+) forward arrow Nd(super 3+) energy transfer in YAB has taken place without the assistance of lattice phonons whereas almost 20% has taken place through multiphonon emission.

Spectroscopic measurements were used to undertaken a systematic optical characterization of the NdA13(BO)3 (NAB) crystal.

The spectroscopic and laser properties of neodymium-doped yttrium aluminium borate are examined.

Nd3+ doped Ca3Ga2Ge3O12 spectral and laser properties were studied for different Nd concentrations.

UV laser radiation is shown to be produced using Nd3+:YAB crystals and argon laser end-pumped cavities.

A pressure-induced shift of the emission spectrum corresponding to the near infrared 4F3/2 → 4I9/2 transition of Nd3+ ions in a calcium gadolinium germanium garnet was obtained in the interval from ambient conditions up to 23 GPa in order to test its suitability as an optical pressure sensor. Although several Nd3+ non-equivalent centers are present in this garnet, which complicates the assignation of the optical transitions, the R1,R2 → Z5 transitions are unequivocally characterised and fit the requirements of an ideal optical pressure sensor. Results obtained for these emission peaks indicate large pressure coefficients of -8.8 and -10.8 cm-1 GPa-1; meanwhile, the rest of the R1,R2 → Z1-4 emissions remain almost unchanged under pressure. This behaviour is ascribed to the influence of the crystal-field at high pressure on the Z5 Stark level of the ground state and can be easily reproduced exclusively by varying the cubic term of fourth rank of the crystal-field Hamiltonian, which accounts for the Nd3+ ions and is related to medium Nd3+-oxygen distances. These coefficients are larger than those found for the R-lines of Cr3+ in ruby, -7.56 cm-1 GPa-1, suggesting that this system may be a good candidate for a luminescence pressure sensor. [ABSTRACT FROM AUTHOR]

In this paper, we present an iterative method which merges experimental μ-Raman measurements and numerical simulations to describe femtosecond written waveguides in LiNbO3 crystals. This method is based on the deformation potential theory, and uses the finite element method to analyze elastic deformations after femtosecond laser micro-explosions in x-cut Mg:LiNbO3 crystals. The resultant strain and refractive index field after laser interaction were estimated and yielded similar values to those obtained in other works. The LiNbO3 Raman deformation potential constants were also estimated in this work. [ABSTRACT FROM AUTHOR]

We report on the evaluation of rare earth (Er3+, Eu3+, and Tb3+ ions) SiO2 sub-micrometric spheres as potential optically controllable temperature sensors. Details about fabrication, optical manipulation and spectroscopic characterization of the sub-micrometric spheres are presented. The fluorescence properties of the micros-spheres in the biological range (25-60 °C) have been systematically investigated. From this systematic study, the thermal resolution potentially achieved in each case has been determined and compared to previous works. [ABSTRACT FROM AUTHOR]

Temperature control of the devitrification process in an erbium doped oxyfluoride glass under laser irradiation is reported. The green upconversion emissions around 525 and 545 nm originated from the thermalized 2H11/2 and 4S3/2 levels were studied when the glass structure changes to glass ceramic during irradiation with a laser beam. Power dependence of the fluorescence intensity ratio was used to determine the temperature of the irradiated zone. The transition from glass to glass ceramic takes place under 2300 mW of laser power with an estimated temperature around 783 K. This result agrees with the one obtained in the samples devitrified under conventional furnace treatment. Therefore, the estimation of the temperature of the irradiated zone through the fluorescence intensity ratio method allows a controlled devitrification. Moreover, an irradiated line has been written in the glass showing an important diffusion of the Pb2+ and F- ions. These results confirm that nanocrystals have been created due to the laser action. [ABSTRACT FROM AUTHOR]

We report on the thermal stability of both structural and optical micromodifications created by ultrafast laser written filaments in sapphire crystals. By using the Cr3+ traces as optical probes, we have concluded that the filaments are constituted by both reversible and nonreversible defects with very different spatial locations. The strain field measured from the analysis of R lines has been found to be erased at the same time when the reversible centers are recombined (∼1100 °C). This fact seems to indicate that these defects act as pinning centers for the induced stress. Furthermore, we have found that the waveguide generated in the proximity of the filament disappear for annealing temperatures above 1100 °C. This clearly supports the assumption that waveguiding is produced by the strain stress induced refractive index increment based on the dominant electronic polarizability enhancement. [ABSTRACT FROM AUTHOR]

We report on the fabrication and microspectroscopy imaging of femtosecond laser written double-filament based Nd3+:MgO:LiNbO3 optical waveguides. The waveguiding high refractive-index regions are identified by blueshifts of the Nd3+ ion fluorescence lines with no deterioration in the fluorescence efficiency, whereas filamentary low-index regions are identified by both a Nd3+ line redshift and a fluorescence efficiency reduction. The lattice structural micromodifications at the origin of both waveguide formation and Nd3+ fluorescence changes have been investigated by means of confocal micro-Raman experiments. We have found that the direct laser written filaments are mainly constituted by a large density of defects, together with a marked axial compression perpendicular to the filaments (along the optical c-axis). Conversely, the high-index waveguiding regions are characterized by a pronounced anisotropic dilatation of the LiNbO3 lattice xy-planes. [ABSTRACT FROM AUTHOR]

We report on the confocal microspectroscopic characterization of planar optical waveguides fabricated in yttrium vanadate (YVO4) crystals by thermal diffusion of neodymium ions. We have found that the waveguide formation is accompanied by Nd3+ fluorescence quenching and by a redshift of the Nd3+ sub-Stark transitions. These effects have been explained in terms of the high Nd3+ concentrations achieved close to the diffusion surface, which lead to the appearance of nonradiative processes, as well as to a local compression in the surroundings of the indiffused Nd3+ ions. By comparing with previous works, we have estimated an equivalent residual stress of 0.1 GPa. The possible mechanisms at the origin of waveguide formation have been also discussed. [ABSTRACT FROM AUTHOR]

The laser performance of poled and unpoled neodymium-doped strontium barium niobate crystals has been compared. We have found that the random distribution of microferroelectric domains, characteristic of as-grown crystals, leads to a relevant improvement in the laser performance. From the analysis of the optical distortion effects induced by both poled and unpoled crystals we have concluded that the compensation effects taking place between adjacent microdomains inside the active volume are at the origin of this improvement. [ABSTRACT FROM AUTHOR]

In this work the anisotropic thermal lens (TL) effect was studied in Nd3+ doped SrxBa1-xNb2O6 crystals with two different stoichiometries (x=0.47 and 0.61). TL measurements were carried out as a function of temperature from 30 up to 140 °C so that the effect of phase transition was investigated. A strong enhancement in the TL effect during the ferro-to-paraelectric phase transition has been observed. Additionally, we have found an inversion of the TL signal with the crystal stoichiometry. This fact is explained in terms of a different thermal expansion along the c axis for both crystals, as measured by x-ray diffraction experiments. The obtained results open the possibility to tailor a crystal stoichiometry that minimizes the TL effects. [ABSTRACT FROM AUTHOR]

We report on femtosecond laser modification of Nd:SBN crystals. Basic properties such as the ablation threshold have been obtained from the analysis of the ablation depths at different laser fluences. The induced micromodifications have been investigated by optical microscopy as well as by microphotoluminescence and micro-Raman experiments. We have found that in the vicinity of the ablated volume material amorphization can be induced along different directions. Furthermore, we have found that this material amorphization is accompanied by a strong inhibition of the Nd3+ luminescence. The analysis of the spatial extension of the luminescence inhibition as a function of the laser fluence has been used to elucidate the origin of the femtosecond laser induced material amorphization. [ABSTRACT FROM AUTHOR]

In this work the origin of the phase transition induced gain depression in diode pumped Nd3+ doped Sr0.6Ba0.4(NbO3)2 lasers has been systematically investigated. The mechanisms capable of intracavity beam distortions are discussed and their relative contribution to the gain depression is investigated. We also provide evidence of two effects: a phase transition induced polarization switching and an enhancement in the laser performance when phase transition is overcome. [ABSTRACT FROM AUTHOR]

The depth-resolved micromodification of single-crystalline femtosecond laser irradiated Nd3+ doped MgO:LiNbO3 crystals is investigated by means of micro-Raman and microluminescence experiments. We have found that a permanent tensile stress of the order of 2 GPa is induced in the vicinity of ablated volume as a consequence of the pressure-wave propagation due to the thermoelastic relaxation of the laser irradiated material. Microluminescence experiments have revealed that, as a consequence of the permanent laser induced microstress, a localized redshift of the 4F3/2→4I9/2 luminescence band of Nd3+ ions also takes place due to a crystal field modification. The analysis of Raman and fluorescence bandwidths indicates that a slight lattice disorder and densification is induced by femtosecond laser irradiation. [ABSTRACT FROM AUTHOR]

The energy transfer between Cr3+ and Nd3+ ions in Cr3+, Nd3+:YAl3(BO3)4 (YAB) codoped crystals has been investigated by means of steady-state and time-resolved laser spectroscopies. The mainly nonradiative character of the energy transfer has been evidenced from the comparison between the emission spectra and the donor fluorescence decays. The analysis of the donor decay profiles has been used to determine the main dipole–dipole character of the transfer, in excellent agreement with the predictions made from the Dexter [J. Chem Phys. 21, 836 (1953)] model, as well as with the dependence of the energy-transfer rates on the acceptor concentration. The temperature behavior of the transfer rate has been analyzed considering the thermal-induced population redistribution between the 2E and 4T2 states of Cr3+ ions and the existence of the phonon-assisted energy transfer. We have obtained that 80% of the Cr3+→Nd3+ energy transfer in YAB is taking place without the assistance of lattice phonons whereas almost 20% is taking place through multiphonon emission. [ABSTRACT FROM AUTHOR]

The temperature dependence of the Nd3+→Yb3+ energy-transfer rate in the YAl3(BO3)4 nonlinear laser crystal has been investigated from the analysis of fluorescence decay curves recorded in the 10–600 K range. Three different regimes, independent on the dopant concentration, have been observed in the thermal behavior of the Nd3+→Yb3+ energy-transfer rate. By comparing experimental results with theoretical predictions based on the Dexter model [J. Chem. Phys. 21, 836 (1953)], the origin of these different regimes has been explained. In addition, the influence of temperature and of both Nd3+ and Yb3+ concentrations on the Nd3+←Yb3+ energy back-transfer rate has been also investigated, concluding that it is a migration-assisted energy-transfer process. Finally, the populations of both Nd3+ and Yb3+ metastable states achieved after continuous-wave Nd3+ excitation have been calculated and measured and results have been explained in terms of the thermal behavior of both forward- and back-transfer rates. [ABSTRACT FROM AUTHOR]

A first spectroscopic characterization of Yb3+ ions in Sr0.6Ba0.4(NbO3)2 nonlinear crystal is presented. From low temperature emission and absorption spectra the energy level diagram of Yb3+ ions in this crystal has been built up. The ground state splitting has been found to be as high as 940 cm-1 allowing for potential quasi-four-level laser operation. In order to assess the ability of this system as a tunable solid state laser the main parameters of relevance in laser dynamics have been obtained and compared to those reported for other Yb3+ doped lasers. Optical microscopy has been used to study the ferroelectric domains appearing in the as-grown crystals. A relatively broad distribution of domain sizes (around 3 μm) will, in principle, allow for broadband noncritical second-harmonic generation of fundamental radiation by quasiphase matching. The obtained results make this crystal a promising candidate for tunable laser generation in the visible domain. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The Nd[sup 3+] multicenter distribution in a Ca[sub 3]Sc[sub 2]Ge[sub 3]O[sub 12] garnet laser crystal has been analyzed by low temperature site-selective laser spectroscopy. Two nonequivalent Nd[sup 3+] centers have been identified and characterized in this host lattice. The effect of codoping the crystal with MgO on the Nd[sup 3+] center distribution has also been investigated, since this codoping enables considerable enhancement of the doping levels of these crystals. Three different centers were observed in the codoped crystals, together with a reduction of inhomogeneous emission broadening. The nature of the optical centers present in both cases is discussed by considering the charge compensation mechanisms involved in accommodation of Nd[sup 3+] ions. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A diode-end-pumped intracavity frequency doubled Nd[sup 3+]:Ca[sub 3]Ga[sub 2]G[sub 3]O[sub 12]/KTiOPO[sub 4] green laser is demonstrated. The infrared laser output and pump-to-green conversion efficiency have been investigated as a function of crystal length and Nd[sup 3+] concentration. Results show that optimum ion concentration is around 2-3 at. %, in excellent agreement with theoretical predictions. Due to the broad absorption bands of this crystal, output power does not depend on diode temperature within a 12 °C range. The influence of Nd[sup 3+] concentration on the [sup 4]F[sub 3/2] quantum efficiency has been also analyzed. We have found that for optimum ion concentration quantum efficiency is as high as 0.7. Finally, the spectral distribution of green light is explained in terms of a combination of both second harmonic and frequency mixing processes between the two infrared oscillating lines. [ABSTRACT FROM AUTHOR]

We report on a full spectroscopic characterization of the Nd[sup 3+] ion doped Ca[sub 3]Ga[sub 2]Ge[sub 3]O[sub 12] garnet laser host for different ion concentrations ranging from 2.5×10[sup -2] up to 2 at. %. The Judd–Ofelt formalism has been applied, from which the stimulated emission cross section corresponding to the [sup 4]F[sub 3/2]→[sup 4]I[sub 11/2] laser channel has been determined. Excited state absorption cross section in the 1020–1090 nm region has been measured by using two beam spectroscopy, demonstrating that the 1060 and 1065 nm laser emissions are not affected by excited state absorptions. Finally, once the basic parameters are known, we have applied the mode overlap formalism in order to determine the Nd[sup 3+] concentration and crystal length which optimize the laser performance of an end diode pumped laser system. We have concluded that the maximum output power is reached when the Nd[sup 3+] concentration and crystal length are around 0.75 at. % and 0.6 mm, respectively © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magneto-optic (MO) studies are performed on regular arrays of Fe(100) micrometric squares, where the elements are patterned with different sizes (2.5–10 μm) and separations (0.2–0.6 μm). When a laser beam is focused inside the patterned structure a Bragg diffraction pattern is produced allowing MO studies on both reflected and diffracted spots. The magnetic anisotropy has been analyzed by in-plane MO hysteresis loops finding that, for square sizes below 2.5 μm, it is not consistent with the Fe crystalline cubic anisotropy, presenting a uniaxial-like behavior. The magnitude of the corresponding anisotropy constants has been determined by analyzing the array response (on reflected and diffracted spots) to a rotational magnetic field in a magneto-optical torque setup. For square sizes of 10 μm the anisotropy induced by patterning is negligible whereas for the small squares (2.5 μm) the uniaxial magnetic constant has been found to be roughly 0.2 times the Fe cubic anisotropy constant. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this work a systematic optical characterization of the NdAl[sub 3](BO[sub 3])[sub 4] (NAB) crystal has been carried out by means of spectroscopic measurements. The energy levels (118) of the Nd[sup 3+] constituent ions have been identified and labeled by appropriate crystal field quantum numbers (μ=1/2 or μ=3/2). Laser site selective experiments revealed the presence of two nonequivalent environments for the Nd[sup 3+] ions. From room temperature absorption and emission spectra and using the Judd–Ofelt formalism the emission cross sections and quantum efficiency (η=0.1) of the metastable state [sup 4]F[sub 3/2] have been determined. By further modeling we have estimated the crystal length and output coupler transmittance which optimize laser efficiency of a diode pumped NAB laser. The optimum crystal length found in all cases is around 100 μm. Finally, the high laser efficiencies predicted (up to 61% and 45% for laser oscillation at 1.06 and 1.34 μm, respectively) make NAB an excellent candidate to be incorporated in a diode pumped microchip laser device. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The impact of temperature on the controlling of the local devitrification process taking place in an oxyfluoride glass doped with [Er.sup.3+] ions under diode laser irradiation is analysed. The formation of nanocrystals due to the observed laser action is also discussed.

The fabrication and microspectroscopy imaging of femtosecond laser written double-filament based [Nd.sup.3+]:MgO:LiNb[O.sub.3] optical waveguides is described. The lattice structural micromodifications at the origin of both waveguide formation and [Nd.sup.3+] fluorescence changes are examined by using confocal micro-Raman experiments.

The laser performance of poled and unpoled neodymium-doped strontium barium niobate crystals is analyzed and compared. The optical distortion effects induced by both poled and unpoled crystals have shown that the compensation effects taking place between adjacent microdomains inside the active volume are the origin of this improvement.

The origin of the phase transition induced gain depression in diode pumped [Nd.sup.3+] doped [Sr.sub.0.6][Ba.sub.0.4][(Nb[O.sub.3]).sub.2] lasers is investigated. The mechanisms capable of intracavity beam distortions are discussed and evidence is provided for two effects, a phase transition induced polarization switching and an enhancement in the laser performance when phase transition is overcome.

The continuous-wave tunable laser light generation from a diode-pumped Nd(super 3+) - doped Ba2NaNb5O15 nonlinear crystal is presented. The characteristic cationic disorder of this system leads to a broad emission band allowing for continuous wavelength selection in the infrared and in the green through self-frequency doubling.

Quasiphase-matching second-harmonic-generation experiments are performed on the Nd(super 3+) doped strontium barium niobate multiself-frequency-converter nonlinear crystals. A broad distribution of domain sizes is obtained and this gives the possibility of broadband second-harmonic generation in the 800-1200 nm range.

Infrared laser gain experiments under diode pumping is performed on NCGC crystals with different ion concentrations. A combination of second harmonic and frequency mixing processes is used to explain the spectral and spatial characteristics of green radiation.

A full spectroscopic characterization of the Nd(super 3+) ion doped Ca3Ga2Ge3O12 garnet laser host for different ion concentrations is reported. The mode overlap formalism results show that the maximum output power is reached when the Nd(super 3+) concentration and crystal length are around 0.75 at.% and 0.6 mm, respectively.

We report on continuous-wave tunable laser light generation from a diode-pumped Nd3+-doped Ba2NaNb5O15 nonlinear crystal. The characteristic cationic disorder of this system leads to a 4F3/2→4I11/2 broad emission band, allowing for continuous wavelength selection from 1055 nm up to 1095 nm in the infrared, and from 527 nm up to 546 nm in the green via self-frequency doubling. This broad tuning range makes Nd3+:Ba2NaNb5O15 a promising system for tunable frequency conversion as well as for short pulse generation. [ABSTRACT FROM AUTHOR]

Quasiphase-matching second-harmonic-generation experiments have been performed on the Nd[sup 3+]-doped strontium barium niobate multiself-frequency-converter nonlinear crystals. Optical microscopy has been used to determine the size dispersion of cylindrical ferroelectric domains appearing in as-grown crystals. A broad distribution of domain sizes (ranging between 1.5 and 8 µm) has been obtained. This gives the possibility of broadband second-harmonic generation in the 800-1200 nm range. The dependence of second-harmonic efficiency on crystal temperature has been found to be correlated with the thermal behavior of the spontaneous polarization, so that second-harmonic efficiency is almost temperature independent in the 25-50 °C range. [ABSTRACT FROM AUTHOR]

In this work, we experimentally demonstrate continuous wave laser generation in the 330–380 nm range by intracavity self-frequency-sum-mixing processes in a Nd[sup 3+]:YAl[sub 3](BO[sub 3])[sub 4] crystal. Ultraviolet laser radiation has been obtained from a simple hemispherical linear cavity by nonlinear interaction between the pump radiation from an argon laser and the infrared laser radiations at 1.06 or 1.33 μm of Nd[sup 3+] ions. In nonoptimal preliminary experiments, up to 0.2 mW of ultraviolet laser power has been obtained at 250 mW of absorbed pump power. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]