Nd-doped Crystals Research Articles

Improvement of Doubly Q-Switching and Mode-Locking Performance with Nd-Doped Mixed Vanadate Crystals

Improvement of Doubly Q-Switching and Mode-Locking Performance with Nd-Doped Mixed Vanadate Crystals

Phase diagram and weak-link behavior in Nd-doped CaFe2As2

The transport properties, phase diagram, and dopant distribution are investigated in systematically Nd-doped CaFe2As2 single crystals. Coexistence of two superconducting (SC) phases with different critical transition temperature (Tc) is observed. The low-Tc phase emerges as x ≥ 0.031, and the Tc value increases to its maximum value of about 20 K at x = 0.083, the maximum doping level in our study. As x ≥ 0.060, the high-Tc phase with a Tc value of about 40 K is observed. The structure transition (STr) from tetragonal to orthorhombic phase vanishes suddenly around x = 0.060, where a new STr from tetragonal to collapsed tetragonal phase begins to turn up. Compared to the low-Tc phase, the end point of SC transition of the high-Tc phase is more sensitive to the magnetic field, showing a characteristic of Josephson weak-link behavior. Possible scenarios about this system are discussed based on our observations. We also find that the non-uniform SC properties cannot be attributed to the heterogeneous Nd distribution on the micro scale, as revealed by the detailed energy dispersive x-ray spectroscopy measurements.

Luminescence and scintillation properties of rare-earth-doped LuF3 scintillation crystals

The Nd-doped and Er-doped LuF3 single crystals were grown by the micro-pulling-down method to study their scintillation properties in the vacuum-ultraviolet (VUV) region. The doubly Nd–Er codoped single crystal was grown to study possibility of scintillation performance improvement by energy transfer from Er3+ to Nd3+ ions. The LiF flux was to avoid phase transition below melting temperature. The 1%Nd-doped sample showed the highest overall scintillation efficiency under X-ray excitation which was 7 times as high as that of the LaF3:Nd 8% standard. The leading Nd3+ 5d–4f emission was situated at 176nm, while the Er3+ 5d–4f emission for Er-doped samples was observed at 163nm, which better matches the sensitivity of some VUV-sensitive photodetectors. The optimum Er concentration was determined to be around 1–3mol%. No Er3+ 5d–4f emission was observed for the doubly Er,Nd-codoped sample due to energy transfer from the Er3+ to Nd3+ ions. Slight improvement of the light yield was observed in the doubly-doped sample with respect to the Nd-only doped one.

Passively mode-locked femtosecond laser with an Nd-doped La₃Ga₅SiO₁₄ disordered crystal.

We experimentally prove the broad emission band of Nd:LGS disordered crystal and demonstrate a diode-pumped passively mode-locked femtosecond Nd-doped La₃Ga₅SiO₁₄ (Nd:LGS) laser for the first time. With a birefringent filter inserted into the cavity, the tunable continuous wave (CW) laser of over 60 nm from 1045.2 nm to 1105.3 nm is achieved, which is the widest tuning range with Nd-doped crystals to our knowledge. Further in mode-locked operation, femtosecond pulses with pulse duration of 381 fs, average output power of 75 mW and repetition rate of 134.4 MHz are obtained at the central wavelength of 1066 nm. It is suitable to be a compact seed for femtosecond laser amplifiers.

Spectroscopic, thermal and laser characteristics of Nd:LiLuF4 for 1314 nm laser

Nd-doped LiLuF4 crystal was grown by the traditional Czochralski method. Room-temperature polarized spectroscopic characteristics of Nd3+ ions in LiLuF4 crystal were investigated. The maximum emission cross-sections are 5.45 × 10−20 cm2 at 1320 nm and 2.34 × 10−20 cm2 at 1313 nm for π-polarization and σ-polarization, respectively. The thermal expansion coefficient, specific heat, thermal diffusion coefficient and the thermal conductivity of Nd:LiLuF4 crystal were systematically studied, which, to the best of our knowledge, is the first time for this crystal thus far. Laser operation in an Nd:LiLuF4 single crystal at 1314 nm with laser-diode pumping was demonstrated. We obtained 3.7 W output power at 1314 nm with a slope efficiency of near 32%. The results of our study indicate that Nd:LiLuF4 crystal is a very promising crystal for application as a high-peak power laser.

Photoinduced nonlinear optical effects in Nd-doped δ-BiB3O6 crystals

The studies of the second harmonic generation, Pockels effect and piezoelectricity were performed for the new synthesized δ-BiB3O6 single crystals. The incorporation of Nd3+ ions into these crystals plays an important role for the increasing of the photoinduced nonlinear optical properties. Temperature dependences of the optical and piezoelectric features showed existence of some anomalies in the vicinity of 160K and 220K. This may confirm a principal role of the photopolarization and of the localized impurity states which give additional contribution into the observed effect. It is crucial that the effect is dependent on the number of the photoinducing pulses. The effect is completely reversible after switching off of the photoinducing laser beam.

Tm3+ and Nd3+ singly doped LiYF4 single crystals with 3-5 \mu m mid-infrared luminescence

Mid-infrared (MIR) emissions of 2.4 and 3.5 m from Tm3+:LiYF4 single crystals attributed to 3H4->3H5 and 3H5->3F4 transitions as well as MIR emissions of 4.2, 4.3, and 4.5 \mu m from Nd3+: LiYF4 lasers attributed to 4I15/2->4I13/2,4I13/2->4I11/2, and 4I11/2->4I9/2 transitions, respectively, are observed. LiYF4 single crystals possess high transmittance of over 85% in the 2.5-6 \mu m range. The large emission crosssections of Tm-doped crystals at 2.4 \mu m (1.9\times 10-20 cm2) and Nd-doped crystals at 4.2 \mu m (0.84\times 10-20cm2) as well as the high rare-earth doping concentrations, excellent optical transmission, and chemicalphysical properties of the resultant samples indicate that Nd3+ and Tm3+ singly doped crystals may be promising materials for application in MIR lasers.

Development of Growth Technologies for the Photonic Single Crystals by the Czochralski Method at Institute for Single Crystals, NAS of Ukraine

The present paper brie y overviews the application of the Czochralski method for growth of a set of oxide crystals for photonics, as well as the design of equipment at the Institute for Single Crystals, NAS of Ukraine. The examples of crystal growth and their characterization are described. The simultaneous Q-switched lasing and self-Raman frequency conversion were demonstrated in Nd-doped PbWO4 and PbMoO4 crystals grown by the Czochralski method. The slope lasing e ciency obtained for a PbMoO4:Nd 3+ laser is the best result for all the crystals with the scheelite-type structure. A detection unit with high scintillation characteristics based on a large volume (V ≈ 350 cm) CdWO4 crystal was produced. Crystal growth procedures and properties of new double tungstate and vanadate crystals are presented, too.

Lasing threshold of Nd-doped crystal, ceramic, and glass lasers under spatially inhomogeneous diode pumping

The effect of transverse mode locking on the dependence of the threshold pump power on the cavity length in Nd-doped media lasers with longitudinal inhomogeneous diode pumping is experimentally and theoretically studied in the cavity stability region. An essentially nonmonotonic behavior of the dependence of the threshold pump power on the cavity length is detected. The dependences of the threshold pump power on the cavity length are calculated using the method based on the expansion of the complex field amplitude in Laguerre-Gaussian modes of a cold cavity. The best agreement with calculated results is observed for lasers with Nd:YLF active elements.

Growth and optical properties of Nd:LaVO4 monoclinic crystal

Abstract

Growth and spectroscopic characteristics of Nd-doped PbWO4 crystal

Nd-doped PbWO4 crystals are grown by using the modified Bridgman method. The spectroscopic properties of the crystals are investigated. The changes of the absorption band at 350 nm are discussed for samples annealed at 740 °C and 1040 °C. The radiative lifetime of the 4F3/2 level is calculated by using the Judd-Ofelt theory according to the absorption spectrum of 0.5 at.% Nd-doped PbWO4 crystal. The spontaneous Raman scattering properties of the crystals are analysed.

Broad near‐infrared fluorescence properties of Nd‐doped PbClF crystals

AbstractNd‐doped PbClF crystals were grown with modified Bridgman method. Broad and flat emission band at 1.0 μm was observed. The FWHM value of 0.0091 wt.% Nd3+‐doped PbClF crystal at 1064 nm reached up to 30 nm with the peak emission cross‐section of 1.05×10‐19 cm2. All the results indicated that Nd‐doped PbClF crystal should be a promising tunable and ultrafast laser material. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Orthogonally polarized dual-wavelength Nd:LuVO_4 laser at 1086 nm and 1089 nm

A comparison between the fluorescence spectra of the Nd-doped vanadate crystals (Nd:YVO4, Nd:GdVO4, Nd:LuVO4) for the 4F3/2 → 4I11/2 transition is studied. We numerically analyze the condition of gain-to-loss balance via an uncoated intracavity etalon to achieve the dual-wavelength operation. We further experimentally demonstrate the orthogonally polarized dual-wavelength laser with a single Nd:LuVO4 crystal. The simultaneous dual-wavelength Nd:LuVO4 laser at 1085.7 nm in σ polarization and 1088.5 nm in π polarization is realized. At an incident pump power of 12 W, the average output power obtained at 1085.7 nm and 1088.5 nm is 0.4 W and 1.7 W, respectively.

Radio-luminescence and absence of trapping defects in Nd-doped YAG single crystals

Nd-doped yttrium aluminum garnet (NdYAG) is an important solid-state laser material due to Nd3+ interconfigurational transitions which result in intense infrared emission. This work shows that NdYAG crystals also emit visible radio-luminescence in response to exposure to beta particles due to other Nd3+ interconfigurational 4f–4f transitions. Additionally, thermo-luminescence spectroscopy reveals the absence of traps in NdYAG, making it a potentially superior scintillation material. The fact that Nd is present in only one valence state in NdYAG leads to charge balance and results in the suppression of defect formation. This finding reveals fundamental understanding regarding defect formation in ionic crystals.

Growth and scintillation properties of Nd-doped Lu3Al5O12 single crystals by Czochralski and micro-pulling-down methods

The Nd-doped Lu3Al5O12 (Nd:LuAG) single crystal was grown by the Czochralski (CZ) method. In XRC profiles, the full-width at half-maximum (FWHM) value was 58arcsec, which was much higher than that of the μ-PD (194arcsec). In photo and radio-luminescence spectra, the CZ grown sample showed strong emission peaks attributed to Nd3+ 4f–4f transitions in visible wavelengths longer than 400nm. The Nd:LuAG grown with the CZ method showed light yield of 7900 photons/MeV, which is comparable with the standard BGO and energy resolution of 14% under 137Cs γ-ray excitation.

Continuous-wave and passively Q-switched Nd:LYSO lasers

Continuous-wave (CW) and passively Q-switched performance of a Nd-doped oyorthosilicate mixing crystal, (Nd0.005Lu0.4975Y0.4975)2SiO5 (Nd:LYSO), were reported. As a result, new dual-wavelength all-solid-state lasers at 1075 and 1079 nm were achieved. When the absorbed pump power was 3.87 W, the CW laser produced 1.1 W output, corresponding to an optical conversion efficiency of 28.4% and a slope efficiency of 32.4%. By using a Cr4+:YAG wafer as the saturable absorber, we achieved Q-switching operation of Nd:LYSO crystal. The maximal average output power, shortest pulse width, largest pulse energy and highest peak power were measured to be 294 mW, 27.5 ns, 34.3 μJ and 1.18 kW, respectively. By difference frequency, these dual-wavelength lasers have potential applications for the generation of a broadband coherent radiation from 0.7–1.3 THz.

Assessment of gadolinium calcium oxoborate (GdCOB) for laser applications

AbstractIncreasing demand for growing high quality laser crystals puts a question about their most important parameters that one should concentrate on to get a desired product which will exhibit best properties in practical use. And by no means, this is a simple question. Apart of the usual lasing properties associated with a special dopant in the host material itself, one needs to consider another two lasing phenomena, namely second (SHG) and higher harmonic generation, and self-frequency doubling (SFD). Not necessarily all of these three can meet altogether in the same host material to yield in its best appearance in every case. We have made a review of basic properties of gadolinium oxoborate GdCa4O(BO3)3 (GdCOB) crystal and came to the conclusion that, currently, as a host material this is probably the best in all of its lasing applications. Although GdCOB has low thermal conductivity, which requires a suitable cooling, on the other hand it has got small thermo-optic coefficients which govern good operation in SHG and SFD experiments.Two inch dia. Nd-doped crystals were grown by the Czochralski technique. Since a large discrepancy in the literature exists on exact values of nonlinear coefficients, one is never sure about this whether theoretically predicted phase-matching angles (PMA) are those that are really optimal. Besides, none has yet measured the values of nonlinear coefficients as a function of doping concentration. Therefore we have not decided to cut numerous differently oriented samples for generation of different wavelengths in SHG and SFD, but rather tried to generate different wavelengths from the same samples. We have also not paid special attention to get highest possible conversion efficiencies. However, we have concentrated our attention on potential use of the core region in laser technique. Unlike in YAG crystals, when the core is by all means a parasitic structure, we discovered that the core region in GdCOB, that majority of investigators are even not aware of its presence in the crystal, can be also useful in laser technique. According to our best knowledge, a SHG of red light in this work is the second reported case in the world-wide literature.

Diode-pumped Nd:BaY_2F_8 picosecond laser mode-locked with carbon nanotube saturable absorbers

Picosecond pulse generation near 1-μm wavelength has been achieved with a Nd:BaY2F8 (Nd:BaYF) laser mode-locked using a single-walled carbon nanotube saturable absorber (SWCNT-SA). The laser was operated at its main 1049-nm transition, generating 8.5-ps pulses with ≈70-mW output power for ≈570-mW absorbed pump power. This is the first demonstration of cw mode-locking in the picosecond regime with Nd-doped crystals and SWCNT-SAs. The requirements on the SWCNT-SA for successful mode-locking in relatively narrow-band neodymium lasers are reviewed and their implications are discussed.

Crystal growth, VTE treatment, and characterizations of Nd-doped LiTaO3

Congruent 0.2 and 0.5mol% Nd-doped LiTaO3 single crystals were grown by the conventional Czochralski technique. Near-stoichiometric lithium-tantalate wafers were also produced from these crystals by the vapor-transport equilibration (VTE) process. The crystals were characterized by the measurements of composition (by inductively coupled plasma atomic emission spectroscopy (ICP-AES)), UV absorption edge, Curie temperature, and thermal diffusivity. From the ICP-AES study, we found that Li/Ta ratio increased by the VTE treatment, while Nd/Ta ratio was found to decrease with crystal length. Blue-shift in the absorption edge was observed in the VTE treated crystals as compared with the congruent ones. The Curie temperature decreased with increasing Nd concentration, while thermal diffusivity was found to increase after the VTE treatment.

Energetic Bessel–Gauss pulses from diode-pumped solid-state lasers

We discuss the generation of Bessel–Gauss pulses directly from a diode-pumped solid-state laser. The laser resonator has a plano–concave configuration with the concave end mirror replaced with a diffractive phase element. As the active material, Nd-doped yttrium lithium fluoride (YLF) and GdVO4 crystals have been used. The pulsed operation is obtained by passively Q-switching the laser using Cr4+:yttrium aluminum garnet (YAG) crystals with different unsaturated transmission coefficients. When guiding the pulses out from the resonator through the laser crystal, 5–10 ns long pulses with energies of 40–50 μJ and peak powers on the order of 10 kW are obtained. Even 70 μJ is possible, but this is achieved at the expense of slightly deteriorated beam quality in the far field.