Diode-pumped Nd<Superscript>3+</Superscript>:YAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> laser at 1338 nm

A high-power diode -pumped Nd³⁺:YAl₃(BO₃)₄ (Nd:YAB) laser emitting at 1338 nm is described. At the incident pump power of 9.8 W, as high as 734 mW of continuous-wave (CW) output power at 1338 nm is achieved. The slope efficiency with respect to the incident pump power was 9.0%. To the best of our knowledge, this is the first demonstration of such a laser system. The output power stability over 60 min is better than 2.6%. The laser beam quality M ² factor is 1.21.     

Spectroscopic properties of Nd<Superscript>3+</Superscript>:CaNb<Subscript>2</Subscript>O<Subscript>6</Subscript> crystal

The absorption spectra, fluorescence spectrum and fluorescence decay curve of Nd³⁺ ions in CaNb₂O₆ crystal were measured at room temperature. The peak absorption cross section was calculated to be 6.202×10⁻²⁰ cm² with a broad FWHM of 7 nm at 808 nm for E//a light polarization. The spectroscopic parameters of Nd³⁺ ions in CaNb₂O₆ crystal have been investigated based on Judd-Ofelt theory. The parameters of the line strengths Ω _t are Ω ₂=5.321×10⁻²⁰ cm²,Ω ₄=1.734×10⁻²⁰ cm²,Ω ₆=2.889×10⁻²⁰ cm². The radiative lifetime, the fluorescence lifetime and the quantum efficiency are 167 μs, 152 μs and 91%, respectively. The fluorescence branch ratios are calculated to be β ₁=36.03%,β ₂=52.29%,β ₃=11.15%,β ₄=0.533%. The emission cross section at 1062 nm is 9.87×10⁻²⁰ cm².     

Quasi-three level laser based on diode-pumped Nd<Superscript>3+</Superscript>:YAlO<Subscript>3</Subscript> crystal

We describe the output performances of the 930 nm ⁴ F _3/2 → ⁴ I _9/2 transition in Nd³⁺:YAlO₃ (Nd:YAP) under in-band pumping with diode laser at the 803 nm wavelength. An end-pumped Nd:YAP crystal yielded 1.13 W of continuous-wave (CW) output power for 17.8 W of incident pump power. Moreover, intracavity second-harmonic generation has also been achieved with a power of 172 mW at 465 nm by using a LiB₃O₅ (LBO) nonlinear crystal. The blue beam quality factor M ² was less than 1.3. The blue power stability was less 3% in 60 min.     

Growth and optical properties of Pr<Superscript>3+</Superscript>:KLu(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> laser crystal: a candidate for red emission laser

A Pr³⁺:KLu(WO₄)₂ crystal with dimension of 30 × 30 × 15 mm³ was grown in the K₂W₂O₇ flux. A slice was cut from the crystal, and the polarized absorption and fluorescence spectra were measured at room temperature. Based on the J-O theory, the oscillator intensity parameters Ω _t (t = 2, 4, 6), spontaneous emission probabilities and branch ratios were estimated and good results had been obtained. Furthermore, the crystal has a relatively large emission cross-section in the region of 615–630 nm with the highest value of 14.5 × 10^?20 cm², which indicates that the crystal is good for the application in red emission laser. The emission decay time for ¹D₂ and ³P₀ multiplets was discussed. By adapting the I-H model to fit the emission decay curves, the lifetime for ¹D₂ at 607 nm and ³P₀ at 615 nm are 19.72 μs and 8.95 μs, respectively. Then the corresponding fluorescence quantum efficiencies of the two multiplets reach 83.7 % and 87.9 %, respectively. All the studies illustrate that this crystal is potential in red emission laser application.     

Spectroscopy and laser properties of Tm<Superscript>3+</Superscript>:KY(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystal

The polarized absorption spectra of Tm³⁺-doped potassium yttrium tungstate (Tm:KY(WO₄)₂) crystal at room temperature were measured. The emission spectrum and lifetime of the ³ F ₄ excited state were determined. Using standard and modified Judd–Ofelt theories, the intensity parameters and the radiative lifetimes were calculated and good agreement with the experimental results was obtained for both theories. Continuous-wave laser operation in Tm:KYW crystal under laser diode pumping at 802 nm and 1750 nm was demonstrated with slope efficiency of 53% and 28% and output power of about 555 mW and 86 mW, respectively. PACS 42.55.Xi; 42.60.Pk; 42.70.Hj     

Growth,spectroscopic and laser properties of Yb<Superscript>3<Emphasis Type="Bold">+</Emphasis></Superscript>-doped GdAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> crystal: a candidate for infrared laser crystal

Yb³⁺:GdAl₃(BO₃)₄ (hereafter Yb³⁺:GAB) crystals with large sizes and good optical quality have been grown by the top-seed solution growth (TSSG) method. The polarized absorption and emission spectra have been investigated at room temperature. For the σ-polarization, the intensities of both absorption and emission spectra are stronger than those for the π-polarization, the σ-absorption cross section of Yb³⁺ in GAB being 3.43×10^-20 cm² at 977 nm, and the σ-emission cross section being 0.98×10^-20 cm² at 1045 nm. The fluorescence lifetime of the ² F _5/2→² F _7/2 transition was measured to be 800 μs in the 5% doped sample used for our laser experiments, 993 μs in a 10% doped sample and 569 μs in a 0.5% doped sample. The laser parameters were estimated as: β_min=0.022, I_sat=10.4 kW/cm² and I_min=0.23 kW/cm². About 0.4 W laseroutput at the wavelength of 1043 nm was achieved when the Yb³⁺:GAB crystal was pumped by a 974 nm laser diode, with 27.4% slope efficiency. PACS 42.55.-f; 42.70.Hj; 78.20.-e; 81.10.Dn     

Luminescence and electronic excitations in Li<Subscript>6</Subscript>Gd(BO<Subscript>3</Subscript>)<Subscript>3</Subscript>: Ce<Superscript>3+</Superscript> crystals

This paper reports on a study of the luminescence emitted by Li₆Gd(BO₃)₃: Ce³⁺ crystals under selective photoexcitation to lower excited states of the host ion Gd³⁺ and impurity ion Ce³⁺ within the 100–500-K temperature interval, where the mechanisms of migration and relaxation of electronic excitation energy have been shown to undergo noticeable changes. The monotonic 10–15-fold increase in intensity of the luminescence band at 3.97 eV has been explained within a model describing two competing processes, namely, migration of electronic excitation energy over chains of Gd³⁺ ions and vibrational energy relaxation between the ⁶ I _j and ⁶ P _j levels. It has been shown that radiative transitions in Ce³⁺ ions from the lower excited state 5d ¹ to ² F _5/2 and ² F _7/2 levels of the ground state produce two photoluminescence bands, at 2.08 and 2.38 eV (Ce1 center) and 2.88 and 3.13 eV (Ce2 center). Possible models of the Ce1 and Ce2 luminescence centers have been discussed.     

Luminescence and thermally stimulated recombination processes in Li<Subscript>6</Subscript>Gd(BO<Subscript>3</Subscript>)<Subscript>3</Subscript>:Ce<Superscript>3+</Superscript> crystals

The luminescence and thermally stimulated recombination processes in lithium borate crystals Li₆Gd(BO₃)₃ and Li₆Gd(BO₃)₃:Ce have been studied. The steady-state luminescence spectra under X-ray excitation (X-ray luminescence), temperature dependences of the intensity of steady-state X-ray luminescence (XL), and thermally stimulated luminescence (TSL) spectra of these compounds have been investigated in the temperature range of 90–500 K. The intrinsic-luminescence 312-nm band, which is due to the ⁶ P _J → ⁸ S _7/2 transitions in Gd³⁺ matrix ions, dominates in the X-ray luminescence spectra of these crystals; in addition, there is a wide complex band at 400–420 nm, which is due to the d → f transitions in Ce³⁺ impurity ions. It is found that the steady-state XL intensity in these bands increases several times upon heating from 100 to 400 K. The possible mechanisms of the observed temperature dependence of the steady-state XL intensity and their correlation with the features of electronic-excitation energy transfer in these crystals are discussed. The main complex TSL peak at 110–160 K and a number of minor peaks, whose composition and structure depend on the crystal type, have been found in all crystals studied. The nature of the shallow traps that are responsible for TSL at temperatures below room temperature and their relation with defects in the lithium cation sublattice are discussed.     

Diode-pumped continuous-wave Nd<Superscript>3+</Superscript>:YAlO<Subscript>3</Subscript> intracavity-doubled red laser

It is reported that efficient continuous-wave (CW) red laser generation at 670 nm in a LBO crystal at type-I phase matching direction performed with a diode-pumped Nd³⁺:YAlO₃ (Nd:YAP) laser. With incident pump power of 15.6 W, output power of 273 mW at 670 nm has been obtained using a 10 mm-long LBO crystal. At the output power level of 273 mW, the output stability is better than 3.7%.     

Mode-locked and Q-switched laser operation of the Yb-doped Li<Subscript>6</Subscript>Y(BO<Subscript>3</Subscript>)<Subscript>3</Subscript> crystal

We report for the first time pulsed laser operation of the Yb-doped Li₆Y(BO₃)₃ (Yb-LYB) crystal in the nanosecond as well as in the femtosecond regime. Pulse durations as short as 355 fs have been obtained in passively mode-locked operation and pulse energies up to 140 μJ in Q-switched operation. PACS 42.70Hj; 42.55Xi; 42.60Gd; 42.65Re     

On the Luminescence of Ce<Superscript>3+</Superscript>, Eu<Superscript>3+</Superscript>, and Tb<Superscript>3+</Superscript> in Novel Borate LiSr<Subscript>4</Subscript>(BO<Subscript>3</Subscript>)<Subscript>3</Subscript>

This paper reports on the photoluminescence (PL) and time-resolved properties of Ce³⁺, Eu³⁺, and Tb³⁺ in novel LiSr₄(BO₃)₃ powder phosphors. Ce³⁺ shows an emission band peaking at 420 nm under 350-nm UV excitation. Energy transfer from Ce³⁺ to Mn²⁺ takes place in the co-doped samples. Eu³⁺ shows red emission under near UV excitation. LiSr₄(BO₃)₃:Eu³⁺ phosphor could be a suitable candidate for phosphor-converted solid state lighting. The luminescence lifetime is 2.13 ms for Eu³⁺ in LiSr₄(BO₃)₃:0.001Eu³⁺. As Eu³⁺ concentration increasing, the decay curves deviate from exponential behavior. Tb³⁺ shows the strongest ⁵D₄→⁷ F₅ emission line at 540 nm. Decay curves of ⁵D₄→⁷ F₅ and ⁵D₃→⁷ F₅ emission with different Tb³⁺ concentrations were also measured. Cross-relaxation process is discussed based on the decay curves.     

Growth and characterization of a LaCa<Subscript>4</Subscript>O(BO<Subscript>3</Subscript>)<Subscript>3</Subscript> crystal

The non-linear optical (NLO) crystal LaCa₄ O(BO₃)₃ (LaCOB ) has been grown by the Czochralski method. X-ray diffraction experiments show that LaCOB crystal possesses the space group Cm, and its unit cell constants have been measured to be a=0.8168(3) nm,b=1.6081(7) nm and c=0.3630(6) nm, with an angle =101.39°. The thermal properties of LaCOB have been studied; the specific heat of the crystal is 321.9 J/molK at 330 K, and the three principal coefficients of thermal expansion of the principal axes have been calculated from the measured data to be 5.61×10^-6 K^-1, 7.21×10^-6 K^-1 and 11.01×10^-6 K^-1, respectively. The transmission spectrum shows that LaCOB crystal has a wide transparency wavelength range, and may be used as a NLO crystal. PACS 81.10.Fq; 65.40.Ba; 65.40.De     

Diode-pumped CW Nd<Superscript>3+</Superscript>:YAlO<Subscript>3</Subscript> laser at 1339 nm

A diode-pumped Nd³⁺:YAlO₃ (Nd:YAP) laser emitting at 1339 nm is described. At the incident pump power of 17.8 W, as high as 3.4 W of continuous-wave (CW) output power at 1339 nm is achieved. The slope efficiency with respect to the incident pump power was 23.6%. The output power stability over 60 min is better than 3.5%. The laser beam quality M ² factor is 1.33.     

Magnetic properties of the Nd<Subscript>0.5</Subscript>Gd<Subscript>0.5</Subscript>Fe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> single crystal

The magnetic properties of the Nd_0.5Gd_0.5Fe₃(BO₃)₄ single crystal have been studied in principal crystallographic directions in magnetic fields to 90 kG in the temperature range 2–300 K; in addition, the heat capacity has been measured in the range 2–300 K. It has been found that, below the Néel temperature T _N = 32 K down to 2 K, the single crystal exhibits an easy-plane antiferromagnetic structure. A hysteresis has been detected during magnetization of the crystal in the easy plane in fields of 1.0–3.5 kG, and a singularity has been found in the temperature dependence of the magnetic susceptibility in the easy plane at a temperature of 11 K in fields B < 1 kG. It has been shown that the singularity is due to appearance of the hysteresis. The origin of the magnetic properties of the crystal near the hysteresis has been discussed.     

Thermal and optical properties of Tm<Superscript>3+</Superscript>:NaLa(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystal

A Tm³⁺-doped NaLa(WO₄)₂ single crystal with a dimension of Φ20 mm×40 mm was grown by the Czochralski method. Anisotropic thermal expansion coefficients of this crystal were investigated. Polarized absorption spectra, emission spectra and decay curve were recorded at room temperature. The absorption and emission cross-section were presented. Based on the Judd–Ofelt analysis, we obtained the three intensity parameters: Ω₂=10.21×10^-20, Ω₄=2.66×10^-20, and Ω₆=1.46×10^-20 cm². The radiative probabilities, radiative lifetimes, and branch ratios of Tm³⁺:NaLa(WO₄)₂ were calculated, too. Luminescence lifetime of the ³ H ₄ level was measured to be 220 μs. The stimulated emission cross-section for the ³ F ₄→³ H ₆ transition were determined using the reciprocity method, potential laser gain for this transition were also investigated, the gain curves implied that the tunable range is up to 200 nm. PACS 42.70.Hj; 78.20.-e     

Spectral properties of a Nd<Superscript>3+</Superscript>-doped Li<Subscript>3</Subscript>Ba<Subscript>2</Subscript>Gd<Subscript>3</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>8</Subscript> crystal

The spectral properties of a promising laser material, ternary molybdate Li₃Ba₂Gd₃(MoO₄)₈:Nd³⁺, are studied (i.e., its optical absorption spectra, luminescence spectra, kinetic of luminescence decay, and temperature dependence of luminescence). Luminescence of the crystalline matrix is detected, and the temperature dependence of its intensity and reabsorption by neodymium are investigated.     

Influence of magnetic ordering on electronic structure of Tb<Superscript>3+</Superscript> ion in TbFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> crystal

Optical absorption spectra of trigonal crystal TbFe₃(BO₃)₄ have been studied in the region of ⁷F₆ → ⁵D₄ transition in Tb³⁺ ion depending on temperature (2–220 K) and on magnetic field (0–60 kOe). Splitting of the Tb³⁺ excited states, both under the influence of the external magnetic field and effective exchange field of the Fe-sublattice, have been determined. Landé factors of the excited states have been found. Stepwise splitting of one of the absorption lines has been discovered in the region of the Fe-sublattice magnetic ordering temperature. This is shown to be due to the abrupt change of equilibrium geometry of the local Tb³⁺ ion environment only in the excited state of the Tb³⁺ ion. In general, the magnetic ordering is accompanied by temperature variations of the Tb³⁺ local environment in the excited states. The crystal field splitting components have been identified. In particular, it has been shown that the ground state (in D ₃ symmetry approximation) consists of two close singlet states of A ₁ and A ₂ type, which are split and magnetized by effective exchange field of the Fe-sublattice. Orientations of magnetic moments of the excited electronic states relative to that of the ground state have been experimentally determined in the magnetically ordered state of the crystal. A pronounced shift of one of absorption lines has been observed in the vicinity of the TbFe₃(BO₃)₄ structural phase transition. The temperature interval of coexistence of the phases is about 3 K.     

Passive Q-switching of a laser-diode-pumped intracavity-frequency-doubling Nd:Nd<Superscript>3+</Superscript>:NaY(WO<Subscript>4</Subscript>)<Subscript>2</Subscript>/KTP laser with Cr<Superscript>4+</Superscript>:YAG saturable absorber

Nd³⁺:NaY(WO₄)₂, known as Nd:NYW, is a new type crystal. By using laser-diode as pump source, a passive Q-switching of intracavity-frequency-doubling Nd:NYW/KTP laser has been realized with Cr⁴⁺:YAG saturable absorber. The dependence of pulse repetition rate, pulse energy, pulse width, and peak power on incident pump power for different small-signal transmissions of Cr⁴⁺:YAG are measured. The coupled rate equations are used to simulate the Q-switched process of laser, and the numerical solutions agree with the experimental results.     

Spectroscopy of NaLa(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript>: Tm<Superscript>3+</Superscript> and NaGd(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript>: Tm<Superscript>3+</Superscript> crystals as advanced laser materials

Single crystals of double sodium-containing lanthanum and gadolinium molybdates doped with Tm³⁺ ions were synthesized by the Czochralski method. The spectroscopic properties of these crystals were investigated from the viewpoint of their use as active media in diode-pumped lasers. The polarized spectra of absorption on the ³ H ₄ and ³ F ₄ levels and the polarized spectra of luminescence due to the ³ F ₄-³ H ₆ laser transition were recorded, and the lifetimes of the ³ H ₄ and ³ F ₄ excited states of the Tm³⁺ ions were determined. The luminescence cross sections were calculated using the Füchtbauer-Ladenburg formula. The simulation of the decay curve of the ³ H ₄ excited state according to the Golubov-Konobeev-Sakun method revealed that, in the crystals under investigation, the interaction between Tm³⁺ ions predominantly occurs through the dipole-dipole mechanism.     

Polarized spectral properties of Er<Superscript>3+</Superscript> ions in NaGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystal

Polarized spectral properties of Er³⁺:NaGd(WO₄)₂ single crystal are reported. The crystal was grown by the Czochralski method. The Judd–Ofelt theory was applied to analyze the polarized absorption spectra and then calculate the spontaneous emission probabilities, radiative lifetimes, and branching ratios. Fluorescence decay curves of the ⁴ I _13/2, ⁴ I _11/2, and ⁴ S _3/2 multiplets for the Er³⁺ ions were measured. Stimulated emission cross-sections of the ⁴ I _13/2→⁴ I _15/2 transition obtained by the Fuchtbauer–Ladenberg formula and the reciprocity method were compared. Multi-phonon relaxation rates of the crystal were estimated. Green up-conversion fluorescence around 531 and 552 nm was observed, and the possible up-conversion mechanisms were proposed. PACS 78.20.-e; 42.70.Hj