YVO4 Crystal Research Articles

Effects of Selective Laser Modification and Al Deposition on the Hot Corrosion Resistance of Ceria and Yttria-Stabilized Zirconia Thermal Barrier Coatings

The air-plasma-sprayed ceria and yttria-stabilized zirconia (CYSZ) coating was modified by selective laser remelting and Al deposition to enhance hot corrosion resistance. The dotted coating was obtained after selective laser remelting. Magnetron sputtering was used to deposit an Al film on the dotted coating, and a vacuum heat treatment was subsequently performed to produce a dense α-Al2O3 overlay. Hot corrosion behavior of the following three types of coatings was investigated: plasma-sprayed, dotted, and dotted coatings combined with Al deposition (DA). Hot corrosion behaviors were evaluated in a mixture of 55 wt % V2O5 and 45 wt % Na2SO4 molten salts at 1000 °C for 30 h. The hot corrosion reaction between molten salts and zirconia stabilizers (Y2O3 and CeO2) led to the generation of monoclinic zirconia, YVO4, and CeVO4 plate-shaped crystals, and the mineralization of CeO2. The results indicated that the hot corrosion resistance of the DA coating was the best, and the dotted coating had superior hot corrosion resistance in comparison with the plasma-sprayed coating. The minimal surface roughness and dense dotted units improved the hot corrosion resistance of the dotted coating. The dense α-Al2O3 overlay with chemical inertness effectively inhibited the infiltration of molten salts, which led to the optimal hot corrosion resistance of the DA coating.

Photo-conversions in Ho3+/Yb3+ co-doped pairs under pulsed high magnetic fields

The optical up-conversion and down-conversion (or quantum cutting) processes in Ho3+/Yb3+ co-doped YVO4 and GdVO4 crystals, particularly cross relaxation and emission channels, were investigated with the help of magnetic fields. Cross-relaxation and emission channels were addressed with the help of magnetic field. The results demonstrated that cross relaxation processes between the donor Ho3+(Yb3+) ions and acceptor Yb3+(Ho3+) ions play positive roles in up-conversion, but negative roles in quantum cutting transitions. In addition, the conversion efficiency of the co-doped pairs depended on the hosts though could be distinctively modulated by a magnetic field. The results are helpful in understanding cross-relaxation processes and identifying the emissions originating in bi- (multi-) rare earth ion-doped luminescent materials, and also helpful in improving their efficiency in application.

High-power dual-color yellow–green solid-state self-Raman laser

A compact dual-color solid-state self-Raman laser with adjustable power-ratio between yellow and green emissions is demonstrated by using a specially coated Nd:YVO4 crystal. The Nd:YVO4 crystal is coated to replace a cavity mirror for minimizing the cavity losses and to reflect the backward green–yellow emission for avoiding the absorption. Two different lithium triborate (LBO) crystals are employed to produce the SHG of the 1176 nm Stokes field and the 1064 nm fundamental wave for the yellow and green emissions. The temperature of the LBO crystal for yellow generation is controlled at the optimal phase-matching to maximize the efficiency. The temperature of the LBO crystal for green generation is precisely varied to adjust the power-ratio between the yellow and green emissions. At the temperature for balanced emissions, both of 532 nm and 588 nm output powers can simultaneously achieve 4.0 W at a pump power of 31.6 W.

Anomalous effect of growth ambience on the optical absorption characteristics of Cr-co-doped Nd:YVO4 crystal

Single crystals of Cr-co-doped 0.7 at.% Nd:YVO4 were grown using the optical floating zone method with varied Cr doping concentrations (0.7, 1.0, 1.4 and 2.0 at.%) in different oxygen partial pressures. The lattice parameters are unaffected by Cr doping. Further, the effect of the doping concentration and the growth atmosphere on the optical absorption, particularly for the 2A1→2B2 transition, which is due to the pentavalent state of Cr ion, has been investigated under two orthogonally polarized lights (i.e., E ⊥ [001]) and E ǁ [001]). This transition is important as it results in saturable absorption that is used for self-Q-switching of laser output. The observation suggests that the concentration of the desired pentavalent Cr increases to 1.4 and 2.0 at.% Cr as the oxygen partial pressure in the growth ambience increases, whereas for 0.7 and 1.0 at.% of Cr, the increase in the oxygen partial pressure results in an adverse effect. This finding suggests that on the basis of the concentration of Cr5+ required in Nd:YVO4 to attain the desired level of saturable absorption, the growth ambience should be chosen judiciously so that it is in line with the result presented here.

High power diode-pumped passively mode-locked Nd:YVO4 laser at repetition rate of 3.2 GHz**Project supported by the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB16030200), the National Natural Science Foundation of China (Grant Nos. 11774410 and 61575217), the National Key Scientific Instruments Development Program of China (Grant No. 2012YQ120047), and the Key Research Program of Frontier Sciences

A compact high power diode-pumped passively mode-locked Nd:YVO4 laser with high repetition rate is realized. Using an Nd:YVO4 crystal and a semiconductor saturable absorber mirror (SESAM) in the oscillator, the picosecond pulse output with an average power of 1.38 W, a repetition rate of 3.24 GHz, and a pulse duration of 11.4 ps is achieved. After one stage of amplification, the final output power reaches 11.34 W, corresponding to a total optical-to-optical efficiency of about 32%. The root mean square (RMS) value of power fluctuation is demonstrated to be less than 0.6% in 24 hours, showing a superior stability with the compact configuration.

Tungsten disulfide saturable absorber for passively Q-Switched YVO4/Nd:YVO4/YVO4 laser at 1342.2 nm

By using both tungsten disulfide saturable absorber (WS2-SA) and YVO4/Nd:YVO4(0.3 at.%)/YVO4 crystal, a passively Q-switched laser centered at 1342.2 nm is first reported. Stable Q-switched pulses can be obtained. At the pump power of 12 W, a shortest pulse width of 550 ns and a pulse repetition rate of 97 kHz can be observed by a digital oscilloscope, corresponding to maximum pulse energy of 5.55 μJ and pulse peak power of 10.1 W. The results promote the promising applications of WS2-SA in all-solid-state laser at 1.3 μm.

Diode-Pumped Actively Q-Switched Nd:YVO4/RTP Intracavity Raman Laser at 1.49 µm

For the first time, a diode-pumped actively Q-switched Nd:YVO4/RbTiOPO4 (RTP) intracavity Raman laser at 1.49 µm was demonstrated to the best of our knowledge. Experimentally, a dual-end diffusion-bonded YVO4–Nd:YVO4–YVO4 crystal was employed as the laser medium to generate 1.34 µm laser radiation, and an RTP crystal as the Raman medium to enable the frequency conversion, by which radiation at 1.49 µm was achieved successfully. With an incident pump power of 10.4 W, an average output power of 502 mW was obtained at a pulse repetition rate of 15 kHz, corresponding to a conversion efficiency of 4.8%.

Construction of 879 nm direct intra-cavity pumped dual-wavelength laser operating at 912 nm and 1064 nm

A dual-wavelength continuous-wave laser with direct intra-cavity pumping using a 879 nm laser diode that utilizes Nd:GdVO4 and Nd:YVO4 crystals, is presented. To the best of our knowledge, this system completely eliminates the gain competition between the 912 nm and 1064 nm transitions for the first time. A theoretical model is introduced to describe this intra-cavity pumped dual-wavelength laser. The lasing threshold of the 912 nm Nd:GdVO4 laser is presented by considering the ground-state reabsorption loss effect. A total output power of 1.33 W at dual-wavelength operation with an absorbed pump power of 7.91 W is experimentally achieved. The individual output power for the 912 nm and 1064 nm emissions were 0.43 W and 0.9 W, respectively. Both wavelengths operate in TEM00 mode with a total slope efficiency >20%.

Cyclic Hot Corrosion Failure Behaviors of EB-PVD TBC Systems in the Presence of Sulfate and Vanadate Molten Salts

The cold gas dynamic spray (CGDS) method has been considered a promising technology to produce a metallic bond coat for thermal barrier coating (TBC) systems. In this study, CoNiCrAlY bond coats produced by CGDS method were coated with yttria-stabilized zirconia (YSZ) by electron beam physical vapor deposition (EB-PVD). TBCs were subjected to 50 wt % V2O5 and 50 wt % Na2SO4 molten hot corrosion salt combinations at 1000 °C. In the case of YSZ top coat on TBCs, the reaction between Na2SO4, V2O5, and Y2O3 salts generates YVO4 crystals, and these structures cause the transformation of tetragonal ZrO2 to monoclinic ZrO2. This situation occurs under operating conditions that lead to TBC failure. Hot corrosion behavior and the related failure mechanisms of TBC systems were investigated and discussed using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) analysis, and X-ray diffractometer (XRD).

Optical and spectral properties of Ho:Yb:YVO4 crystal irradiated by 6.0-MeV C ions

We report the Ho:Yb:YVO4 planar waveguide fabricated by 6.0-MeV C ions irradiation with fluences of 1.5 × 1014 cm−2 at room temperature. In this work, the prism-coupling measurement and reflectivity calculation method (RCM) were performed to study the guiding mode properties when the transverse electric (TE) modes were excited. The results indicate that the excited modes can be well confined by the 6.0-MeV-C-irradiated Ho:Yb:YVO4 waveguide at a wavelength of 632.8 nm. According to the upconversion (UC) photoluminescence investigation, the original fluorescence performances of Ho:Yb:YVO4 crystal can be well retained except that the emitting intensity slightly degrades after C ions irradiation.

First-Stokes Wavelengths at 1175.8 and 1177.1 nm Generated in a Diode End-Pumped Nd:YVO4/LuVO4 Raman Laser**Supported by the Zhejiang Provincial Natural Science Foundation of China under Grant No LY19F050012, the National Natural Science Foundation of China under Grant No 61505147, the Laboratory Open Project of Wenzhou University under Grant No 18SK31, and the Research Funds of College Student Innovation of Zhejiang

A diode end-pumped acousto-optic Q-switched Nd:YVO4/LuVO4 Raman laser is demonstrated. Both YVO4 and LuVO4 can work as Raman gain, and slightly different active vibration modes of both crystals can result in different first-Stokes wavelengths. The output characteristic as the Raman competition between YVO4 and LuVO4 crystals for the laser systems with both shared cavity and coupled cavity is experimentally investigated. For the shared cavity, simultaneous Raman conversion in both YVO4 and LuVO4 crystals is achieved with dual-wavelength emission at 1175.8 and 1177.1 nm. The maximum output power of 1.03 W and the conversion efficiency of 10.3% are obtained. The 0.84 W single first Stokes wavelength at 1177.1 nm with LuVO4 Raman conversion is achieved with the coupled cavity. The results show that the coupled cavity with short Raman cavity can obtain a narrow pulse width. The separated laser crystal and Raman gain media with different vanadates in shared cavity have advantages in achieving dual-wavelength lasers with small frequency intervals.

高重频高峰值功率窄线宽激光放大器

The laser with high repetition rate, high peak power and narrow line width has important application value in the field of laser radar. In the amplification of high repetition frequency and narrow line width laser, in order to achieve both high magnification and high beam quality laser output at high repetition rate, narrow line width of passively Q-switched laser used to be the seed source, high gain amplifier using 888 nm diode laser end pumped Nd:YVO4 crystal, side pumped Nd:YVO4 slab crystal thermal lens effect of two stage amplification scheme were designed. At the repetition rate of 10 kHz, the average power of 31.5 W, and the laser beam quality of M2 1.98 were obtained. The peak power was 5 MW, the line width was 154 pm and the pulse width was 0.6 ns. Thus, the design idea of amplifier with high magnification ratio and high beam quality control individually was verified.

Enhancement of hot corrosion resistance of thermal barrier coatings by using nanostructured Gd2Zr2O7 coating

Improvement of hot corrosion resistance in Na2SO4-V2O5 environments is one of the main goals in development of thermal barrier coatings (TBCs). In this study, nano-Gd2Zr2O7 (nano-GZ) powder was synthesized by co-precipitation method and then deposited with atmospheric plasma spray (APS) technique on Ni-based superalloy (IN738LC) substrates as a top coat with a CoNiCrAlY bond coat. Hot corrosion behavior of nano-GZ coated samples were studied and compared with those of CoNiCrAlY/conventional YSZ coatings. Hot corrosion resistance of the samples was investigated in a cyclic mode in which after each 4 h exposure to Na2SO4–55 wt% V2O5 salts at 950 °C. The results indicated that nano-GZ coatings have better hot corrosion resistance compared to conventional YSZ coatings. It was found that micro-cracks and pores played a main role in the molten salts infiltration into the TBCs during hot corrosion process. In the nano-GZ coating with nano zones structure which surrounded by fully molten parts could fill the aforementioned defects and could act as barrier for the corrosive molten salts penetration into the TBC. The main factor in destruction of the investigated coatings is the formation and growth of needle-like YVO4 and GdVO4 crystals, in both classes of the coatings.

A high-energy 1064-nm picosecond master oscillator laser with an optic-optic efficiency of 38%

A high-energy high optic-optic efficiency 808-nm diode-end-pumped 1064-nm Nd:YVO4 picosecond master oscillator laser was demonstrated, and a 3×3×7 mm Nd:YVO4 crystal with a doped concentration of 0.5% was adopted. A maximum output power of 3.39 W was obtained with a pulse width of 16.3 ps and a repetition rate of 29.36 MHz under a pump power of 8.92 W, corresponding to an optic-optic efficiency of 38.0%. Compared to the previously reported picosecond master oscillator solid-state lasers, the optic-optic conversion efficiency of 38% is in the leading level among the reported lasers.

High power 100 kHz electro-optic cavity empty green laser

A high repetition frequency high power and narrow pulse width laser output at 532 nm is realized by using the technology of electro-optical cavity emptying and cascade amplification in this paper. Using semiconductor laser end pump Nd:YVO4 crystal, and with electro-optical cavity emptying technology, the1064 nm seed laser output with power of 6 W, repetition frequency of 100 kHz and high beam quality is obtained. After six-stage amplification and double frequency crystal, the 532 nm laser output with frequency of 100 kHz, pulse of 3.77 ns and power of 60.2 W is obtained. The effective double frequency efficiency reaches 68.8%. The output power stability over 120 min is better than 3%.

A passively Q-switched YVO4 Raman laser with orthogonally polarized emission at 1175.4 nm and 1165.2 nm

We originally proposed a method for obtaining an orthogonally polarized dual-wavelength Raman laser via a polarized-dependent effect of Raman shifting. Pumping a-cut YVO4 crystal with a passively Q-switched Nd:YAG laser, the system not only emitted a conventional Raman emission at 1175.4 nm but also a Raman emission at 1165.2 nm, which originated from the Raman shifts of 890 cm−1 and 816 cm−1, respectively. The polarization directions of the emissions at 1175.4 nm and 1165.2 nm were found to be along the c-axis and b-axis of the YVO4 crystal respectively, which enabled the orthogonally polarized operation. With a type-II KTP crystal, their sum-frequency generation (SFG) was obtained for the first time, and this result proved that the pulse series of these two emissions were simultaneous.

Passive Q-Switching by Cr4+:YAG Saturable Absorber of Buried Depressed-Cladding Waveguides Obtained in Nd-Doped Media by Femtosecond Laser Beam Writing.

We report on laser performances obtained in Q-switch mode operation from buried depressed-cladding waveguides of circular shape (100 μm diameter) that were inscribed in Nd:YAG and Nd:YVO4 media by direct writing with a femtosecond laser beam. The Q-switch operation was realized with a Cr4+:YAG saturable absorber, aiming to obtain laser pulses of moderate (few μJ) energy at high (tens to hundreds kHz) repetition rate. An average power of 0.52 W at 1.06 μm consisting of a train of pulses of 7.79 μJ energy at 67 kHz repetition rate, was obtained from a waveguide realized in a 4.8 mm long, 1.1-at % Nd:YAG ceramics; the pulse peak power reached 1.95 kW. A similar waveguide that was inscribed in a 3.4 mm long, 1.0-at % Nd:YVO4 crystal yielded laser pulses with 9.4 μJ energy at 83 kHz repetition rate (at 0.77 W average power) and 1.36 kW peak power. The laser performances obtained in continuous-wave operation were discussed for each waveguide used in the experiments. Thus, a continuous-wave output power of 1.45 W was obtained from the circular buried depressed-cladding waveguide inscribed in the 1.1-at %, 4.8 mm long Nd:YAG; the overall optical-to-optical efficiency, with respect to the absorbed pump power, was 0.21. The waveguide inscribed in the 1.0-at %, 3.4 mm long Nd:YVO4 crystal yielded 1.85 W power at 0.26 overall optical efficiency. This work shows the possibility to build compact laser systems with average-to-high peak power pulses based on waveguides realized by a femtosecond (fs) laser beam direct writing technique and that are pumped by a fiber-coupled diode laser.

Passively Q-switched and mode-locked YVO4/Nd:YVO4/Nd:YVO4 laser based on a MoS2 saturable absorber at 1342.5 nm

We demonstrate a passively Q-switched and mode-locked (QML) laser with both YVO4/Nd:YVO4/Nd:YVO4 crystal and MoS2 saturable absorber (MoS2-SA) at ∼1342.5 nm. The MoS2-SA is fabricated with the liquid phase exfoliation (LPE) method. By inserting MoS2-SA into a Z-type resonator, we obtain a QML laser operation with the maximum average output power of 600 mW, the shortest envelope duration of 800 ns and the highest repetition rate of 98 kHz at 9 W. The energy of a Q-switched envelope is estimated to be about 6.12 μJ and the peak power is 39 W. The obtained envelope width and repetition rate are both superior to the results obtained from QML lasers with V3+:YAG and graphene at 1.34 μm. So far as we know, it is the first report on the QML laser at 1.34 μm with MoS2-SA, which proves the MoS2-SA is a good candidate for solid-state QML laser at 1.34 μm.

High power Stokes generation based on a secondary Raman shift of 259 cm−1 of Nd:YVO4 self-Raman crystal

A diode-end pumped passively Q-switched Nd:YVO4 self-Raman laser is demonstrated. A diffusion-bonded composite c-cut Nd:YVO4 crystal is used as the self-Raman medium. Based on a secondary Raman shift of 259 cm−1, the conversion from 1066 nm fundamental laser to 1097 nm first-Stokes Raman laser is achieved. The first-Stokes output power of 0.75 W is obtained under an incident diode power of 8.1 W. Thermal focal length formulas are given out for modeling the thermal effect of the self-Raman crystal. The characteristics including the spectrum, the pulse width, the repetition rate and the beam quality factors are studied for the Stokes laser.

Numerical analysis and experimental study of thermal lensing of standard and composite Nd:YVO4 crystal with temperature dependence of thermal conductivity tensor

A numerical analysis and experimental study of the temperature distribution and thermal lensing in six types and sizes of standard and composite Nd:YVO4 crystals with consideration of the temperature dependence of the thermal conductivity tensor is presented. In the first step to test the model, numerical results at 1064 nm and 1342 nm laser wavelengths are compared with previous experimental results in the literature. In these cases there was good agreement between them in comparison with constant thermal conductivity. In the second step, a diode end pumped Nd:YVO4 laser is constructed with three types of crystals. Single and double-end diffusion bounded crystals have shown equal efficiencies while standard crystal have lower efficiency. A comparison between theoretical and experimental results is done again and a perfect match between them is observed.