Diode-pumped continuous-wave and passively Q-switched 1.06 μm YVO4/Nd:GdVO4 laser

In this letter, a diode-pumped continuous-wave and passively Q-switched 1.06 μm laser with a novel composite YVO₄/Nd:GdVO₄ crystal was demonstrated for the first time. Theoretical calculations showed that the temperature distribution in YVO₄/Nd:GdVO₄ crystal was lower than that in GdVO₄/Nd:GdVO₄ and Nd:GdVO₄ crystals under the same conditions. After optimizing the mode matching degree, a CW output power of 5.6 W of YVO₄/Nd:GdVO₄ laser was obtained at the incident pump power of 12 W when the output coupler with transmission of 30% was employed. Using Cr^4 +:YAG crystals with initial transmission (T₀) of 80% and 90% as saturable absorbers, the pulsed YVO₄/Nd:GdVO₄ laser characteristics were investigated. At the incident pump power of 12 W, the maximum average output power of 2.76 W and the maximum repetition rate of 189 kHz was achieved when T₀ = 90% Cr^4 +:YAG was used. The shortest pulse width was 28.1 ns when the initial transmission of the used Cr^4 +:YAG was 80%.     

Multi-criteria optimization in CO2 laser ablation of multimode polymer waveguides

High interconnection density associated with current electronics products poses certain challenges in designing circuit boards. Methods, including laser-assisted microvia drilling and surface mount technologies for example, are being used to minimize the impacts of the problems. However, the bottleneck is significantly pronounced at bit data rates above 10 Gbit/s where losses, especially those due to crosstalk, become high. One solution is optical interconnections (OI) based on polymer waveguides. Laser ablation of the optical waveguides is viewed as a very compatible technique with ultraviolet laser sources, such as excimer and UV Nd:YAG lasers, being used due to their photochemical nature and minimal thermal effect when they interact with optical materials. In this paper, the authors demonstrate the application of grey relational analysis to determine the optimized processing parameters concerning fabrication of multimode optical polymer waveguides by using infra-red 10.6 µm CO₂ laser micromachining to etch acrylate-based photopolymer (Truemode^™). CO₂ laser micromachining offers a low cost and high speed fabrication route needed for high volume productions as the wavelength of CO₂ lasers can couple well with a variety of polymer substrates. Based on the highest grey relational grade, the optimized processing parameters are determined at laser power of 3 W and scanning speed of 100 mm/s.     

1.34 μm fluorescence and laser properties of Nd:La0.11Y0.89VO4 crystal

For Nd:La_xY_1−xVO₄ (x = 0.11) crystal, the ⁴F_3/2 → ⁴I_13/2 transition property was investigated for the first time. The fluorescence peak of Nd:La_0.11Y_0.89VO₄ crystal exhibited obvious inhomogeneous broadening comparing with that of Nd:YVO₄ crystal. With laser diode array as pump source, 1.34 μm continuous-wave (CW) and active Q-switched laser operations based on ⁴F_3/2 → ⁴I_13/2 transition were realized. For CW laser operation, the maximum output power of 2.47, 2.13 W is obtained with slope efficiencies of 29.4%, 27.6%, and optical to optical conversion efficiency of 26.2%, 24.7%, respectively for a, c cut crystal samples. For acousto-optic (AO) Q-switched laser operation, the shortest pulse width, highest peak power and maximum pulse energy came from the a-cut sample, which were 13 ns, 2.69 kW and 35 μJ, respectively.     

An eye-safe KTiAsO4 intracavity optical parametric oscillator driven by a diode pumped composite Nd:YAG/Cr4+:YAG laser

A mini eye-safe KTiAsO₄ intracavity optical parametric oscillator (IOPO) employing the shared cavity configuration and driven by a diode-end-pumped composite Nd:YAG/Cr⁴⁺:YAG laser is demonstrated in this paper. Under an incident laser diode power of 11 W, a maximum average output power of 424 mW at 1534 nm was obtained. The corresponding signal pulse width and repetition rate were 1.2 ns and 16.7 kHz, respectively. The fluctuation of the average signal output power over long-term operation was found to be ±3.0%. A theoretical model for the compact IOPO was also presented in this paper.     

High-peak-power,short-pulse-width,LD end-pumped,passively Q-switched Nd:YAG 946 nm laser

High-peak-power, short-pulse-width diode pumped 946 nm Nd:YAG laser in passively Q-switching operation with Cr⁴⁺:YAG is reported. The highest average output power reaches 3.4 W using the Cr⁴⁺:YAG with initial transmissivity T₀=95%. When the T₀=90% Cr⁴⁺:YAG is employed, the maximum peak power of 31.4 kW with a pulse width of 8.3 ns at 946 nm is generated.     

Mechanisms for Ce3+ excitation at energies below the zero-phonon line in YAG crystals and nanocrystals

Excitation of YAG:Ce³⁺ crystals and nanocrystals was performed at λ_exc=473–584 nm over a wide temperature range. It was observed that the luminescence of both nano- and single-crystal YAG:Ce samples is efficiently excited with photon energies well below the Ce³⁺ absorption band and at least 1650 cm^?1 below the ZPL of the 4f¹(²F_5/2)?4f⁰5d¹ transition, located at 489 nm. The studies of Ce³⁺ fluorescence spectra as a function of temperature and excitation wavelength and of their temporal evolution point to the role of phonon-assisted nonradiative energy transfer between different groups of Ce³⁺ centers in the excitation mechanism.     

Growth and characterization of pure and doped bis thiourea zinc acetate: Semiorganic nonlinear optical single crystals

Metal–organic coordination complex single crystals bis thiourea zinc acetate (BTZA) and Cd²⁺ doped BTZA have been synthesized and grown successfully by slow-cooling technique from their aqueous solutions. Single crystals of pure and Cd²⁺ doped BTZA with dimensions of 35 × 4 × 2 mm³ and 10 × 5 × 6 mm³, respectively were obtained with well defined morphology. The as grown single crystals are characterized by single crystal XRD studies and melting point measurements which reveal the incorporation of metallic dopants has not changed the structure of the parent crystal. The powder X-ray diffractogram of the grown crystals has been recorded and the various planes of reflection identified shows shift in the peak positions. The metal coordination with thiourea through sulphur in pure and Cd²⁺ doped BTZA were ascertained by FTIR studies and optical absorption study to identify the UV cut-off range. The presence of metals in pure and Cd²⁺ doped BTZA crystal lattice were confirmed by atomic absorption spectroscopy (AAS). The thermal decomposition of pure and Cd²⁺ doped BTZA crystals were investigated by thermo gravimetric analyses (TGA) and differential thermal analysis (DTA) indicate that doped crystals are more stable than pure crystals. The dielectric response of the crystals were studied in the frequency range 100 Hz–5 MHz at different temperatures and the results are discussed. Second harmonic generation (SHG) measurement confirms that the pure and Cd²⁺ doped BTZA have nonlinear optical (NLO) property. Laser damage threshold value of 12.44 MW/cm² has been determined using Q-switched Nd:YAG laser operating at 1064 nm and with 8 ns pulses in single shot mode for pure BTZA single crystal is reported for the first time.     

YAG laser-induced β-BaB2O4 crystalline dot formation in Sm2O3–BaO–B2O3 glasses

A continuous-wave (CW) YAG laser (power: 0.75–0.9 J/s, irradiation time: 15 s–15 min) with a wavelength of 1064 nm is irradiated to 11.1Sm₂O₃·44.4BaO·44.4B₂O₃ glass, and the formation of β-BaB₂O₄ (β-BBO) crystalline dots with a diameter of 30–150 μm is confirmed from micro-Raman spectra. β-BBO crystals with around 200 μm length grow towards the interior of the glass. The incorporation of Sm³⁺ into β-BBO crystalline dots is suggested from micro-Raman and fluorescence spectra. The second harmonic generation is detected from the array (10×10=100 dots) of β-BBO crystalline dots, indicating that each crystalline dot formed by YAG laser irradiation is a nonlinear optical crystal. CW YAG laser irradiation to glass with Sm³⁺ ions is a nice technique for a spatially controlled crystal growth.     

Passively Q-switched diode-pumped Raman laser with third-order Stokes eye-safe oscillation

We demonstrate a passively Q-switched all-solid-state laser system with intracavity Raman frequency conversion to the eye-safe spectral region. Laser oscillation at the 1.064 μm wavelength with a pulse repetition rate of several kilohertz was provided by a Nd:YAG crystal and a Cr:YAG passive absorber. Third Stokes oscillations at the 1.599 and 1.494 μm wavelengths were obtained in Ba(NO₃)₂ and PbWO₄ crystals with output pulse energies of 5 μJ and 6 μJ, respectively. The results of the numerical simulation of the pulse dynamics are in good agreement with the experimental data.     

Effect of XeCl laser irradiation on the defect structure of Nd:YAG crystals

This paper presents the effect of XeCl laser irradiation on Nd:YAG single crystal samples with various number of pulses at different repetition rates and laser fluences. Effects of the irradiation on the optical and structural properties of the crystal are analyzed by UV–vis-NIR spectroscopy. Annihilation of some point defects of the crystal structure is observed following laser irradiation at a fluence of 100 mJ cm⁻² with 100 and 500 pulses. Increasing the laser fluence and pulse numbers leads to saturation and new defects are found to be formed in the crystal. Additional absorption spectra of the irradiated samples show that oxygen vacancies in the Nd:YAG crystals are removed during the low-dose irradiation. The laser irradiation is compared to the thermal annealing process for Nd:YAG crystal modification. Additional absorption spectrum of an annealed sample reveals that induced negative absorption band at 236 nm is correlated with the annihilation of the oxygen vacancy center. Our results also demonstrate that XeCl laser treatment has several advantages upon annealing at high temperatures in the Nd:YAG crystal quality improvement. Thus, the present work can give a new approach to modify Nd:YAG crystals to be used in a wide variety of solid-state laser engineering.     

Highly efficient upconversion emission and luminescence switching from Yb3+/Tm3+ co-doped water-free low silica calcium aluminosilicate glass

We present highly efficient 480 and 800 nm upconversion emissions in Tm³⁺/Yb³⁺ co-doped water-free low silica calcium aluminosilicate glass under excitation at 976 nm. As a result of this efficient upconversion process, a luminescent switching with the excitation intensity has been observed. The switching is explained and discussed using rate equations analysis and saturation effects. By means of fitting of the experimental data point, it was possible to obtain the value of the energy transfer parameter related to the transition ²F_5/2, ³H₄→²F_7/2, ¹G₄. The value of this parameter is higher than that of materials like YLF. This switching mechanism could be used in the development of sensors and networks for optical processing and optical communications.     

Upconversion luminescence in Tm3+/Yb3+co-doped lead tungstate tellurite glasses

This work reports the upconversion luminescence properties of Tm³⁺/Yb³⁺ ions in lead tungstate tellurite (LTT) glasses. Judd–Oflet intensity parameters have been obtained from the absorption band intensities of Tm³⁺ singly-doped and Tm³⁺/Yb³⁺ co-doped LTT glasses. The spontaneous emission probabilities, radiative lifetimes and branching ratios for ¹G₄ and ³H₄ emission levels of Tm³⁺ have been determined. Upconversion luminescence has been observed by exciting the samples at 980 nm (Yb³⁺:²F_7/2→²F_5/2) at room temperature. Four upconversion emission bands corresponding to the ¹G₄→³H₆ (477 nm), ¹G₄→³F₄ (651 nm), ¹G₄→³H₅ (702 nm) and ³H₄→³H₆ (810 nm) transitions have been identified. The relative variation in the intensities of upconversion bands, the different channels responsible for upconversion spectra and the effect of Yb³⁺ ions concentration on the upconversion luminescence of Tm³⁺ ions have also been discussed.     

Enhanced infrared to visible upconversion emission in Er3+ doped phosphate glass: Role of silver nanoparticles

Phosphate glasses with compositions (59.5–x)P₂O₅–MgO–xAgCl–0.5Er₂O₃ (0.0≤x≤1.5 mol%) containing fixed concentration of Er³⁺ ion with and without silver nanoparticles (NPs) are prepared using melt quenching technique. The amorphous nature of the glass is confirmed using the X-ray diffraction method. The homogeneous distribution of spherical Ag NPs (average size ～37 nm) in the glassy matrix is evidenced from the transmission electron microscopy (TEM) analyses. The UV–vis–NIR absorption spectra shows 10 bands corresponding to ⁴I_13/2, ⁴I_11/2, ⁴I_9/2, ⁴F_9/2, ⁴S_3/2, ²H_11/2, ⁴F_7/2, ⁴F_5/2, ²G_9/2, ⁴G_11/2 transitions in which the most intense bands are ²H_11/2 and ⁴G_11/2. The absorption spectrum of Er³⁺ ions free glass sample containing Ag NPs displays a prominent surface Plasmon resonance (SPR) band located at 528 nm. The infrared to visible frequency upconversion (UC) emission under 797 nm excitation shows two emission bands green (⁴S_3/2–⁴I_15/2) and red (⁴F_9/2–⁴I_15/2) centered at 540 nm and 634 nm, respectively, corresponding to Er³⁺ transitions. An enhancement in UC emission intensity of green band (⁴S_3/2–⁴I_15/2) is observed in the presence of silver NPs and the maximum enhancement occurred for 1.5 mol% AgCl. However, the enhancement of emission intensity of the red band (⁴F_9/2–⁴I_15/2) is smaller. The enhancement of UC emission is understood in terms of the intensified local field effect due to silver NPs.     

Spectroscopic characteristics of Tm3+ in Tm and Tm,Nd, Yb:Sc2O3 ceramic

The spectroscopic investigation of Tm³⁺ or (Nd, Yb, Tm)-doped Sc₂O₃ transparent ceramics, as laser-active media for visible and IR emission, was performed. The spectra are dominated by Tm³⁺ ions in sites of C₂ symmetry and an energy level scheme and other spectral parameters were determined. The strong concentration quenching of ³H₄ level emission in Tm:Sc₂O₃ at 300 K is discussed by considering the resonant cross-relaxation (³H₄→³F₄)?(³H₆→³F₄) process and multipolar interactions of various orders. The main energy-transfer processes leading to the blue upconversion emission from the ¹G₄ Tm³⁺ level in (Tm, Nd, Yb):Sc₂O₃ ceramic, under pulsed pumping at 808.3 nm were evidenced.     

Optically stimulated second-order optical susceptibilities of self-assembled multi-layers film samples

In the present paper for the first time we study the influence of simultaneous polarized optical treatment (10 ns Nd: YAG lasers with power density 0.6 GW/cm²) together with electrostatic dc electric field (up to 8 kV/cm) on self-assembled multi-layer films samples. The second-order optical susceptibility (SOS) achieves the maximal values after one minute simultaneous dc-electrical-optical treatment. Further treatment will not enhance the values and even leads to the decrease of SOS. The independent measurement of the local temperature shows that local heating do not excess 8.6 K.     

Laser operated elasto-optical features of La2CaB10O19:Pr3+ polymer nanocomposites

We have discovered a principal role of the polymer matrices on the spectral dependences of piezooptical coefficients of La₂CaB₁₀O₁₉:Pr³⁺ (LCBO:Pr) nanocomposites formed by polymethylmethacrylate (PMMA) and polycarbonate (PC) matrices. It was established that the optical treatment by the 10 ns Nd:YAG laser can cause substantial changes of the dispersion of the piezooptical coefficients within the spectral wavelength 1400–1600 nm. The optimal content of the LCBO:Pr with sizes ranging from 40 to 110 nm corresponds to 4–6% in weighing units. Following the performed quantum chemical simulations, the observed changes are caused by different polarizabilities of the polymer matrices.     

White LED based on nano-YAG:Ce3+/YAG:Ce3+,Gd3+ hybrid phosphors

Nano-YAG:Ce³⁺ and YAG:Ce³⁺,Gd³⁺ phosphors were synthesized by glycothermal method. The X-ray diffraction (XRD) measurements showed that the samples can be well-crystallized at 600 °C. The transition electron microscope (TEM) showed that the particles have sizes mostly in the range between 35 and 100 nm. The YAG:Ce nano-phosphor had a wide emission band ranging from blue to yellow peaking at 532 nm, due to the transition from the lowest 5d band to ²F_7/2, ²F_5/2 states of the Ce³⁺ ion. Red-shift of emission peak wavelength from 532 nm to 568 nm has been achieved as doping Gd³⁺ ions into the YAG:Ce³⁺ to substitute some Y³⁺ ions. White LEDs were fabricated by combining GaN (460 nm) chip with the YAG:Ce³⁺ and YAG:Ce³⁺,Gd³⁺. Color rendering index of the white LED as a function of the ratios of theses two kinds of phosphors was studied. As the ratio of YAG:Ce³⁺,Gd³⁺ phosphor increased, the color rendering index of the LED improved significantly under the forward bias of 20 mA. As the ratio of YAG:Ce³⁺ and YAG:Ce³⁺,Gd³⁺ was 11:9, the white LED had a color rendering index, CIE chromaticity coordinates and color temperature T_c of 85, (0.3116, 0.3202) and 6564 K, respectively.     

Structural and luminescence properties of Nd3+-doped PbO–B2O3–TiO2–AlF3 glass for 1.07 μm laser applications

Trivalent neodymium doped multi-component lead borate titanate aluminumfluoride (LBTAFNd) glasses were prepared and characterized as a function of Nd³⁺ ions concentration through optical absorption, NIR luminescence and decay measurements. The intensity (Ω_2,4,6) and other radiative parameters were determined within the frame work of Judd–Ofelt theory. The intensities of absorption bands were expressed in terms of experimental oscillator strengths. Reasonably small root mean square deviation of ±0.384×10^?6 obtained between the experimental and calculated oscillator strengths indicates the validity of intensity parameters. Upon 805 nm laser excitation, the NIR emissions at 0.92 μm (⁴F_3/2→⁴I_9/2), 1.07 μm (⁴F_3/2→⁴I_11/2) and 1.35 μm (⁴F_3/2→⁴I_13/2) were observed. The spectroscopic quality factor has been determined from the Ω₄ and Ω₆ intensity parameters as well as the intensities of emission bands centered at 1.07 and 1.35 μm. The decay curves of the ⁴F_3/2 excited state were recorded by monitoring the emission and excitation wavelengths at 1.07 μm and 805 nm, respectively. The decay curves exhibit single exponential behavior for all the glasses. The laser characteristic parameters of ⁴F_3/2→⁴I_11/2 (1.07 μm) transition were determined and compared with other reported glasses.     

Single crystals of LnFeAsO1−xFx (Ln = La,Pr, Nd,Sm, Gd) and Ba1−xRbxFe2As2: Growth,structure and superconducting properties

A review of our investigations on single crystals of LnFeAsO_1?xF_x (Ln = La, Pr, Nd, Sm, Gd) and Ba_1?xRb_xFe₂As₂ is presented. A high-pressure technique has been applied for the growth of LnFeAsO_1?xF_x crystals, while Ba_1?xRb_xFe₂As₂ crystals were grown using a quartz ampoule method. Single crystals were used for electrical transport, structure, magnetic torque and spectroscopic studies. Investigations of the crystal structure confirmed high structural perfection and show incomplete occupation of the (O, F) position in superconducting LnFeAsO_1?xF_x crystals. Resistivity measurements on LnFeAsO_1?xF_x crystals show a significant broadening of the transition in high magnetic fields, whereas the resistive transition in Ba_1?xRb_xFe₂As₂ simply shifts to lower temperature. The critical current density for both compounds is relatively high and exceeds 2 × 10⁹ A/m² at 15 K in 7 T. The anisotropy of magnetic penetration depth, measured on LnFeAsO_1?xF_x crystals by torque magnetometry is temperature dependent and apparently larger than the anisotropy of the upper critical field. Ba_1?xRb_xFe₂As₂ crystals are electronically significantly less anisotropic. Point-Contact Andreev-Reflection spectroscopy indicates the existence of two energy gaps in LnFeAsO_1?xF_x. Scanning Tunneling Spectroscopy reveals in addition to a superconducting gap, also some feature at high energy (～20 meV).     

Spectroscopic analysis of Cr,Er:Gd3Ga5O12 crystals as candidates of potential xenon lamp pumped ~ 2.7 μm laser

A series of Cr,Er:Gd₃Ga₅O₁₂ crystals with high concentrations of Er^3 + were grown by Czochralski method. The absorption spectra, the up-conversion, near infrared (NIR) and mid-infrared (Mid-IR) luminescence spectra as well as the luminescence decay curves of Er: ⁴I_13/2 and ⁴I_11/2 levels were measured at room temperature. The spectroscopic properties of Cr,Er:Gd₃Ga₅O₁₂ crystals and Cr–Er energy transfer processes were investigated. The spectroscopy of the Er^3 +:⁴I_11/2 → ⁴I_13/2 transition was centralized to discuss, and the important optical parameters including luminescence lifetimes and the Cr–Er energy transfer efficiency are presented. Based on the comprehensive spectral analyses, 0.6 at.%Cr/50 at.%Er:GGG crystal is preferred as candidate of potential xenon lamp pumped ~ 2.7 μm laser in this work.