A Diode-Pumped Actively Q-Switched and Injection-Seeded Tm:LuAG Laser at Room Temperature

We elaborate a diode-end-pumped actively Q-switched injection-seeded Tm:LuAG laser. To achieve power scaling with good beam quality, we construct a more flexible laser with longer cavity accommodated strongly aberrated thermal lens in a Tm:LuAG laser and took special care in designing the laser resonator. Under Q-switched operation, we achieve a maximum output energy of 2.6 mJ with a pulse width of 318.2 ns at a pulse repetition frequency of 50 Hz. To control the spectral, temporal, and phase characteristics of the Tm:LuAG laser, the ring laser is injected by a seed laser, which provides a 50 mW single longitudinal-mode laser output at a wavelength of 2,022.6 nm. We achieve an output energy of 1.8 mJ with a pulse width of 293.0 ns after employing the injection seed.     

Luminescence and ESR characteristics of γ-irradiated Lu3Al5O12:Ce single crystalline film scintillators

The influence of γ-irradiation with a dose of ～10⁴ Gy on the characteristics of LuAG:Ce single crystalline films (SCF) was investigated using ESR and time-resolved luminescence spectroscopy under excitation by synchrotron radiation with the energies ranging from 3.7 to 12 eV. The origin of γ-ray induced radiation defects in LuAG:Ce SCF is discussed.     

Scintillation properties of Yb-doped garnet crystals

Luminescence properties of heavily Yb-doped Lu₃Al₅O₁₂ (Yb:LuAG) and Lu₃Ga₅O₁₂ (Yb:LGG) single crystals grown by micro-pulling-down method were characterized. Charge transfer luminescence of Yb³⁺ was observed in both crystals. Photoluminescence spectra, temperature dependence of emission intensity and decay kinetics of these crystals were studied. Mean decay time of about 24 ns at 90 K (Yb5%:LuAG) and 21 ns at 110 K (Yb5%:LuGG) were observed. Strong thermal quenching at room temperature was measured for both Yb:LuAG and Yb:LGG.     

Crystal growth, spectroscopic and laser properties of Tm:LuAG crystal

Tm:Lu₃Al₅O₁₂ (Tm:LuAG) crystal was grown by the Czochralski method. The segregation coefficient was measured by Inductively Coupled Plasma Atomic Emission Spectrometer. The cell parameters were analyzed with X-ray powder diffraction experiments. The absorption and fluorescence spectra of Tm:LuAG crystal at room temperature were investigated. With a 20 W fiber-coupled diode laser as pump source, the continuous-wave (CW) laser action of Tm:LuAG crystal was demonstrated. The maximum output power at 2020 nm was obtained to be 3.04 W, and the slope efficiency was 25.3%.     

Effect of thermal annealing in air on scintillation properties of LuAG and LuAG:Pr

Pure and Pr-activated Lu₃Al₅O₁₂ (LuAG) crystals have been grown by the Czochralski method. In order to improve the scintillation properties, several samples have been annealed in air. Various annealing temperatures and periods of time have been tested to determine optimal conditions in the way of scintillation yield and energy resolution enhancement. The largest increase of yield of LuAG:Pr (17%), accompanied by a distinct decrease of resolution, has been observed after annealing at 1100°C for 48 h. On the contrary, in case of undoped LuAG no significant changes following thermal annealing have been noticed.     

Luminescence spectroscopy of excitons and antisite defects in Lu3Al5O12 single crystals and single-crystal films

The nature of the intrinsic luminescence of the lutetium aluminum garnet Lu₃Al₅O₁₂ (LuAG) has been analyzed on the basis of time-resolved spectral kinetic investigations upon excitation of two model objects, LuAG single crystals and single-crystal films, by pulsed X-ray and synchrotron radiations. Due to the differences in the mechanisms and methods of crystallization, these objects are characterized by significantly different concentrations of Lu_Al antisite defects. The energy structure of luminescence centers in LuAG single crystals (self-trapped excitons (STEs), excitons localized near antisite defects, and Lu_Al antisite defects) has been established. For single-crystal LuAG films, grown by liquid-phase epitaxy from a Pb-containing flux, the energy parameters of the following luminescence centers have been determined: STEs in regular (unperturbed by the presence of antisite defects) sites of the garnet lattice and excitons localized near Pb²⁺ ions. The structure of the luminescence centers, related to the background emission of impurity Pb²⁺ ions, has also been established in the UV and visible ranges. It is suggested that, in contrast to the two-halide hole self-trapping, a self-trapped state similar to STEs in simple oxides (Al₂O₃, Y₂O₃) is formed in LuAG; this state is formed by self-trapped holes in the form of singly charged O^? ions and electrons localized at excited levels of Lu³⁺ cations.     

Effect of thermal annealing on light yield,low temperature thermoluminescence,and time profiles of LuAG:Pr scintillator crystals

Measurements of light yield, low temperature thermoluminescence, and scintillation time profiles, performed comparatively on “as grown” and thermally annealed LuAG:Pr samples, are reported. It is shown that traps play an efficient role in the scintillation of LuAG:Pr, being responsible for the yield decrease and introducing a long component to the time profiles. The trap concentrations in the annealed crystals are lower than in the non-annealed ones, which correlates with the yield enhancement.     

Comparative study of LD-pumped Tm:YAG and Tim:LuAG lasers

Widely tunable performances of Tm:YAG and Tm:LuAG lasers near 2 μm are demonstrated. The emission spectra of Tm³⁺ in these two single crystals are reported and analyzed. The lifetimes of the ³ F ₄ state in thulium-doped YAG and LuAG are 10.1 and 9.2 ms, respectively. In addition, it is proven that the Tm:YAG crystal with two bonded undoped YAG ends is promising for high-efficient operation.     

Nd-doped Lu3Al5O12 single-crystal scintillator for X-ray imaging

The optical and scintillation properties of Nd-doped Lu₃Al₅O₁₂ (Nd:LuAG) crystals grown by the Czochralski (Cz) method were examined under X-ray excitation. Their applicability for X-ray imaging was also inspected. The radioluminescence spectrum induced by X-rays showed a broad host emission and sharp Nd³⁺ 4f–4f emission peaks in the UV to visible wavelengths. The light output current of the Nd:LuAG was 85% of that of a standard CdWO₄ X-ray scintillator. The afterglow value measured 20 ms after X-ray irradiation was 1.5%. An X-ray radiographic image was successfully obtained using the Nd:LuAG scintillator coupled with the charge coupled device (CCD) photodetector.     

Tm:fiber laser in-band pumped Ho:LuAG laser with over 18 W output at 2124.5 nm

We describe efficient operation of a Ho:LuAG laser in-band pumped by a cladding-pumped narrow linewidth Tm fiber laser at ∼1907 nm. With 1.0 at % Ho³⁺-doped LuAG and an output coupler of 6% transmission, the laser had a threshold pump power of ∼0.85 W and generated 18.04 W of continuous-wave output power at 2124.5 nm for 35 W of incident pump power, corresponding to an average slope efficiency with respect to incident pump power of 53.4%.     

Luminescence of excitons and antisite defects in Lu<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Ce single crystals and single-crystal films

The luminescence of excitons and antisite defects (ADs) was investigated, as well as the specific features of the excitation energy transfer from excitons and ADs to the activator (Ce³⁺ ion) in phosphors based on Lu₃Al₅O₁₂:Ce (LuAG:Ce) single crystals and single-crystalline films, which are characterized by significantly different concentrations of ADs of the Lu _Al ³⁺ type and vacancy-type defects. The luminescence band with λ_max = 249 nm in LuAG:Ce single-crystal films is due to the luminescence of self-trapped excitons (STEs) at regular sites of the garnet lattice. The excited state of STEs is characterized by the presence of two radiative levels with significantly different transition probabilities, which is responsible for the presence of two excitation bands with λ_max = 160 and 167 nm and two components (fast and slow) in the decay kinetics of the STE luminescence. In LuAG:Ce single crystals, in contrast to single-crystal films, the radiative relaxation of STEs in the band with λ_max = 253.5 nm occurs predominantly near Lu _Al ³⁺ ADs. The intrinsic luminescence of LuAG:Ce single crystals at 300 K in the band with λ_max = 325 nm (τ = 540 ns), which is excited in the band with λ_max = 175 nm, is due to the radiative recombination of electrons with holes localized near Lu _Al ³⁺ ADs. In LuAG:Ce single crystals, the excitation of the luminescence of Ce³⁺ ions occurs to a large extent with the participation of ADs. As a result, slow components are present in the luminescence decay of Ce³⁺ ions in LuAG:Ce single crystals due to both the reabsorption of the UV AD luminescence in the 4f-5d absorption band of Ce³⁺ ions with λ_max = 340 nm and the intermediate localization of charge carriers at ADs and vacancy-type defects. In contrast to single crystals, in phosphors based on LuAG:Ce single-crystal films, the contribution of slow components to the luminescence of Ce³⁺ ions is significantly smaller due to a low concentration of these types of defects.     

1.57 MW peak power pulses generated by a diode-pumped Q-switched Nd:LuAG ceramic laser

The pulse characteristics of a laser diode dual-end-pumped electro-optic Q-switched Nd:LuAG ceramic laser at various repetition rates are presented. The largest output pulse energy of 11 mJ is realized at the repetition rate of 100 Hz with pump energy of 84.3 mJ, and the slope efficiency in respect to pump pulse energy is 18.6%. The single pulse peak power reaches up to 1.57 MW. Using Nd:LuAG ceramic as the amplification medium seeded by an Nd:YAG laser of 5.2 mJ, a 10.3 mJ amplified pulse is obtained with pump pulse energy of 42.8 mJ, corresponding to an extraction efficiency of 11.9%.     

Single-crystalline films of Ce-doped YAG and LuAG phosphors: advantages over bulk crystals analogues

Luminescent properties of phosphors based on single-crystalline films (SCF) of Y₃Al₅O₁₂:Ce (YAG:Ce) and Lu₃Al₅O₁₂:Ce (LuAG:Ce) garnet have been analyzed in comparison with single-crystal (SC) analogues. It has been shown that the main peculiarity of luminescent properties of YAG:Ce and LuAG:Ce SCF as compared to SC is determined by the extremely low concentration of Y_Al³⁺ and Lu_Al³⁺ antisite defects (AD) in SCF. The advantages of phosphors based on YAG:Ce and LuAG:Ce SCF are caused by the absence in these SCF the additional channels for dissipation of excitation energy connected with AD and vacancy-type defects.     

Yb:LuAG单晶光纤的连续及脉冲激光性能

单晶光纤是具有准一维结构的功能晶体材料,结合了体块单晶优异的物化性能和传统光纤材料比表面积大的结构优势,是一种极具潜力的激光增益介质.目前单晶光纤激光的研究主要集中于连续激光输出,关于脉冲激光性能的研究相对较少.我们采用微下拉法(μ-PD)制备的Yb:LuAG单晶光纤(SCF)作为增益介质,获得了输出功率大于4 W、斜...     

1.5 J high-beam-quality Nd:LuAG ceramic active mirror laser amplifier

A 1.5 J Nd:LuAG ceramic active mirror laser amplifier with a high beam quality is demonstrated in which a 0.8%(atomic fraction)Nd-doped Nd:LuAG ceramic disk with a diameter of 64 mm and a thickness of 5.5 mm is used as a laser gain medium.A maximum single-pass small-signal gain of 2.59 is measured when the pump energy is 11.5 J,with an injected seed energy of 0.4 J;a maximum output energy of 1.5 J is obtained at the repetition rate of 10 Hz.A far-field beam spot 1.25 times the diffraction limit(DL)is achieved by using a stimulated Brillouin scattering phase conjugation mirror(SBS-PCM)for wavefront correction.     

Synthesis and luminescent properties of LuAG : Ce3+ transparent ceramics by solvo-thermal method

The precursor powders of LuAG∶Ce3+ transparent ceramics were synthesized by solvo-thermal method.The crystal structure and morphology of powders were analyzed by means of Fourier transform infra-red spectroscopy,X-ray diffraction and scanning electron microscopy.The precursor powders were sintered into transparent ceramics in vacuum and then in nitrogen without any additive.The surface morphology of the transparent unpolished ceramics was characterized using scanning electron microscopy.Some factors that af...     

Comparison of Lu3Al5O12:Pr and Bi4Ge3O12 scintillators for gamma-ray detection

The scintillation properties of Lu₃Al₅O₁₂:Pr³⁺ (LuAG:Pr) single crystal grown by the Czochralski method with praseodymium concentration of 0.19 mol% were investigated. For a comparison, a good quality Bi₄Ge₃O₁₂ (BGO) single crystal grown by Bridgman method was also studied. The light yield and energy resolution were measured using photomultiplier tube (XP5200B PMT) readout. Moderate light yield of 15,900 photons per MeV was measured for the LuAG:Pr(0.19%) crystal. For 662 keV gamma rays (¹³⁷Cs source), an energy resolution of 6.5% obtained for LuAG:Pr(0.19%) is much better than that of 9.0% obtained for BGO. The light yield non-proportionality and energy resolution versus energy of gamma rays were measured and the intrinsic resolution of the crystals was determined after correcting the measured energy resolution for PMT statistics. The LuAG:Pr(0.19%) showed a good proportionality of the light yield within 5% over the energy range from 1274.5 keV down to 32 keV, which is much better than that of 14% for BGO. The photofraction was determined at 320 and 662 keV for both crystals and compared with the ratio of the cross-sections for the photoelectric effect to the total one calculated using WinXCOM program.     

Spectroscopy and efficient laser emission of Yb3+: LuAG single crystal grown by μ-PD

A LuAG shaped rod crystal, doped with Yb³⁺, has been grown by μ-PD technique. The crystal diameter was about 3 mm and the length around 130 mm. A complete spectroscopic investigation in the temperature range 10–300 K is reported and data has been utilized to model the laser behavior. In the laser experiment the Yb:LuAG sample was placed in an X cavity and pumped longitudinally obtaining an efficient CW laser emission. The Yb:LuAG laser yielded a maximum output power of 23 mW with a slope efficiency of 32% and a threshold around 35 mW, at lasing wavelength of 1030 nm. No significant depolarization effects were observed, indicating a crystal growth with negligible stress. The output beam profile was investigated, yielding M² ≈ 1.0 in both directions, further confirming the good optical quality of the sample.     

Efficient passively Q-switched Yb:LuAG microchip laser

An efficient passively Q-switched Yb:LuAG microchip laser with Cr4+:YAG as saturable absorber was demonstrated for the first time to our knowledge. Slope efficiencies of 40% and 28% were measured for the initial transmission of Cr4+:YAG, T(0)=95% and 90%, respectively. Laser pulses with a pulse energy of 19 microJ and a pulse width of 610 ps at the repetition rate of 12.8 kHz were achieved for T(0)=90%; the corresponding peak power of over 31 kW was obtained. The lasers oscillated at two or three longitudinal modes owing to the broad emission spectra of Yb:LuAG and mode selection by Cr4+:YAG thin plate acting as an intracavity etalon.     

Spectroscopic properties of nano-sized cerium-doped lutetium aluminum garnet phosphors via sol-gel combustion process

Nano-sized cerium-doped lutetium aluminum garnet (LuAG:Ce) phosphors were prepared via a sol-gel combustion process from a mixed aqueous solution of metal nitrates, using glycine as a fuel. The prepared LuAG:Ce phosphors were characterized by XRD, EPMA, and TEM, respectively. The spectroscopic properties of the phosphors were investigated. The as-prepared phosphors are agglomerated with a primary particle size of about 30 nm and have a foamy-like morphology. The pure crystalline LuAG:Ce with uniform size of 40 nm was obtained after calcined at 1000 °C for 2 h. The excitation spectrum shows two bands localized at 350 and 450 nm due to transitions from the 4f ground state to the excited 5d band. Both the photoluminescence excited by UV and the radioluminescence excited by X-ray show the same two emission bands, corresponding to transitions from the lowest 5d excited state (²D) to the 4f ground state of Ce³⁺ (²F_5/2,²F_7/2).