Solid-state Laser Applications Research Articles

Large area growth of monolayer MoS2 film on quartz and its use as a saturable absorber in laser mode-locking

Monolayer MoS2 film on quartz was fabricated by a home-made three-temperature zone chemical vapor deposition method. The photo, AFM image, Raman spectroscopy and HRTEM image showed that high quality as-grown MoS2 film completely covered the whole quartz substrate of a few cm2. A Nd:YVO4 laser with mode-locking operation was obtained by using the monolayer MoS2 on quartz as the saturable absorber (SA). To the best of our knowledge, this is the first report on large-area growth of high quality monolayer MoS2 film on transparent quartz substrate, and the first time that the CVD MoS2 SA was used in mode-locked solid state lasers. Because of the large area, high transmission, low non-saturable loss and high optical damage threshold of this material, it is very suitable for application in mode-locked solid state lasers.

Theoretical study of weakly-guided large-mode-area rib waveguides: single-mode condition, birefringence, and supermode generation

In this paper, single-mode large-mode-area rib waveguides have been systematically investigated aiming for high-power solid-state laser and amplifier applications. The single-mode criterion has been analyzed with a modified cut-off equation presented under the weakly guiding condition. The polarization characteristics has also been explored to achieve the zero-birefringence condition. Our results show that it is possible to achieve single-mode large-mode-area, up to a few hundred μm2, rib waveguides of excellent beam equality by careful design of the waveguide geometry to sustain substantially enhanced optical power. Finally, a two-dimensional rib-waveguide array structure to generate the fundamental supermode for further modal area breakthrough is proposed.

Enhanced optical, thermal and piezoelectric behavior in dye doped potassium acid phthalate (KAP) single crystal

Dye inclusion crystals have attracted researchers in the context of crystal growth for applications in solid state lasers. Pure and 0.1mol% amaranth doped KAP single crystals, were grown from aqueous solutions by slow evaporation technique at room temperature. The grown crystals are up to the dimension of 12×10×3mm3. Attempt is made to improve the growth rate, optical, piezoelectric and photoconductive properties of pure KAP single crystal with addition of amaranth dye as a dopant. Various characterization studies were made for both pure and dye doped KAP. Thermal stability of the crystals is tested from thermogravimetric and differential thermal analysis (TG/DTA). There is only one endothermic peak indicating decomposition point. Higher optical transparency for dye doped KAP crystal was identified from the UV–vis spectrum. Etching studies showed an improvement in the optical quality of the KAP crystal after doping with amaranth dye. The positive photoconductive nature is observed from both pure and amaranth doped KAP.

Fresnoite Ba2TiSi2O8: A novel stimulated Raman scattering active crystal

Large Ba2TiSi2O8 crystals were successfully grown by the Czochralski technique. The stimulated Raman scattering properties of the Ba2TiSi2O8 crystals were investigated for the first time, and the first (558 nm) and second (587 nm) Stokes lines were generated in an ultracavity single-pass configuration excited by 532 nm picosecond pulses. The output energy and conversion efficiency of the scattering process as functions of pump energy were studied, and the highest conversion efficiency was found to be 31.8%. The experiments indicate that Ba2TiSi2O8 is a novel active crystal suitable for solid-state Raman laser applications.

Synthesis and Applications of Lanthanide-Doped Nanocrystals

Lanthanide (Ln3+)-doped nanocrystals continue to receive significant interest due to the large number of applications in display devices, optical communication, solid-state lasers, catalysis, and biological labeling. It is well known that the Ln3+-doped nanocrystals can exhibit unique optical properties such as long fluorescence lifetime, large Stokes shift, single to multicolor emission and good luminescence efficiency combined with high photochemical stability of the hosts. Nano-sized phosphorescent or optoelectronic devices usually exhibit novel properties, depending on their structures, shapes, and sizes, such as tunable wavelengths, rapid responses, and high efficiencies. In terms of the mechanism of luminescence, the luminescence of Ln3+ ions can be divided into down-conversion and up-conversion emission processes. The down-conversion process is the conversion of higher-energy photons into lower-energy photons, which often requires two main components, an inorganic matrix (known as the host) and activated Ln3+ doping ions (activators). Among all the Ln3+-based host materials observed to date including oxides, phosphates, vanadates, oxides, and so on. The optical properties of Ln3+-doped nanocrystals depend critically on the hosts in which the Ln3+ reside, and thus it is important to seek for suitable host matrices to achieve desirable luminescence of Ln3+. In this review, we focus on the most recent advances in the development of the synthesis and applications of Ln3+-doped nanocrystals.

Luminescence behavior of Nd3 +-activated soda-lime-borate glasses for solid-state lasers applications

In this work, Nd3+-activated soda-lime-borate (SLBNd) glasses are prepared in a composition (65-x) B:10CaO:25Na2O:xNd2O3 (where x=0, 0.5, 1.0, 1.5, 2.0 and 2.5mol%) by conventional melt-quenching technique, which is its novel study for laser application. The prepared samples are studied by absorption and near-infrared (NIR) luminescence emission spectra and decay-time analysis. The Judd–Ofelt (JO) intensity parameter, Ωλ (λ=2, 4, 6), and radiative properties of the 4F3/2 level of Nd3+ ion are calculated from absorption spectra using JO theory. At 585-nm excitation wavelength, strong NIR emission, at 1.069μm, is observed corresponding to the 4F3/2→4I11/2, for all glass samples. Decay constants are found to be decreasing with increasing Nd3+ concentration due to the energy transfer through cross-relaxation process. The stimulated-emission cross-section (σ(λp), experimental branching ratio (βexp), gain bandwidth, and quantum efficiency (η) are measured as 4.0×10−20cm2, 68%, 1.48×10−25cm3 and 65%, respectively. Presented results revealed that Nd3+-activated soda-lime-borate glasses could be useful for 1.06-μm laser application.

Spectroscopic and thermal characterizations of Yb:LaF3 single crystal

A Yb3+ doped LaF3 laser crystal was detailed investigated by both spectroscopic and thermal measurements. A peak absorption at 974 nm with FWHM broader than 60 nm makes the crystal suitable to InGaAs LDs. Fluorescence spectrum and calculated spectroscopic parameters show potential of Yb:LaF3 crystal to laser operations around 1009 nm. A relatively long fluorescence lifetime of 2.92 ms was detected for Yb3+:2F5/2 manifold. The thermal diffusivity and specific heat capacity in the range of 300–575 K were studied to calculate the thermal conductivity of Yb:LaF3. The results indicate that the Yb:LaF3 crystal is a good candidate for diode-pumped ∼1 μm solid-state laser applications.

Resonantly pumped Er:YAG laser Q-switched by topological insulator nanosheets at 1617 nm

We demonstrated an in-band pumped 1617 nm Er:YAG solid-state laser passively Q-switched by self-assembled topological insulator Bi2Te3 nanosheets sandwiched by polymethyl methacrylate (PMMA) polymer. With the self-assembled Bi2Te3 saturable absorber, the laser can deliver Q-switched pulse centered at 1617 nm with a maximum single pulse energy 18.3 μJ for output power of 114 mW at repetition rate of 6.22 kHz and the maximum output power of 134 mW at a repetition rate of 11.6 kHz. The results suggest that the potential of topological insulator nonlinear modulator for broadband solid-state lasers applications.

Femtosecond solid-state laser based on a few-layered black phosphorus saturable absorber.

In this Letter, a high-quality, few-layered black phosphorus (BP) saturable absorber (SA) was fabricated successfully, and a femtosecond solid-state laser modulated by BP-SA was experimentally demonstrated for the first time, to the best of our knowledge. Pulses as short as 272 fs were achieved with an average output power of 0.82 W, corresponding to the pulse energy of 6.48 nJ and peak power of 23.8 MW. So far, these represent the shortest pulse duration and highest output power ever obtained with a BP-based mode-locked solid-state laser. The results indicate the promising potential of few-layered BP-SA for applications in solid-state femtosecond mode-locked lasers.

Investigations on the growth, optical, thermal, dielectric, and laser damage threshold properties of crystal violet dye-doped potassium acid phthalate single crystal

Influence of crystal violet dye with different concentration on potassium acid phthalate single crystal grown by conventional method has been studied. No change has been observed in the structure, whereas changes have been observed in the external morphology of the crystal when the dyes are incorporated in the crystal lattice. Thermogravimetric and differential thermal analyses show the onset decomposition temperatures to be at 302, 285, 284, and 285 °C for pure, 0.1, 0.3, and 0.5 mol% crystal violet-doped potassium acid phthalate crystals, respectively. The dielectric measurement was carried out on the grown crystals as a function of frequency at various temperatures. In addition, strong luminescent emission bands at 638, 648, and 640 nm were observed in which the relative intensity was found to be reversed as a result of doping concentration. The laser damage threshold value significantly increased for dye-doped crystal in comparison with pure crystal which may make it suitable for the solid-state dye laser applications.

Fluorescence characteristics of Nd3+ doped multicomponent fluoro-phosphate glasses for potential solid-state laser applications

The multicomponent fluoro-phosphate glasses of the type, 49.5P2O5–10AlF3–10BaF2–10SrF2–10PbO–10M (M=Li2O, Na2O, K2O, ZnO and Bi2O3) doped with 0.5mol% neodymium were prepared by melt quenching technique. Their structures were characterized by the X-ray diffraction with SEM analysis, Fourier transform infrared (FTIR), Raman spectroscopy and 31P and 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) techniques. XPS spectra were studied to know the bridging and non-bridging oxygen groups. X-ray absorption near edge spectroscopy (XANES) was used to study the electronic structure of neodymium in the host glass matrices. The Judd–Ofelt parameters (J–O) (Ω2, Ω4 and Ω6) were evaluated from the intensities of the absorption bands through optical absorption spectra. Further, J–O parameters have been used to calculate various radiative properties like probabilities of radiative transitions, radiative lifetimes and branching ratios for different fluoro-phosphate glasses. The luminescence kinetics from the excited neodymium levels have been studied upon selective excitation through photoluminescence measurements. Neodymium ion emits two near infrared laser emissions: 4F3/2→4I11/2 at 1.06μm and another one 4F3/2→4I13/2 at 1.32μm. The major intensity is observed for 1.06μm for the prepared fluoro-phosphate glasses. The lifetimes of these levels have been experimentally determined through decay profile studies. The above results suggest that the prepared lithium fluoro-phosphate glass system could be a suitable candidate for using it as 1.06μm laser source in the near infrared region of spectrum.

Upconversion flourescence characteristics of Er3+/Yb3+ codoped NaYF4 and LiYF4 microcrystals

Lanthanide-doped upconverting fluoride nano-and micro-materials have aroused much research interest due to their potential applications in phosphors, color displays, optical storages, solid-state lasers, solar cells and biomedical imaging. In order to synthesize Ln3+ doped crystals with favorable optical properties, such as high upconversion (UC) efficiency and controllable emission profile, the two major parameters that affect luminescence processes including host materials and lanthanide activator ions should be selected appropriately in the synthesis process. Majority of scientists deem that lanthanide doped fluoride nano-and micro-materials with low phonon energy are currently the efficient UC host materials. In this work, Yb3+ and Er3+ ions codoped NaYF4 and LiYF4 microcrystals are synthesized by a facile hydrothermal method with ethylene diamine tetraacetic acid (EDTA) as a chelator. The NaYF4:Yb3+/Er3+ and LiYF4:Yb3+/Er3+ microcrystals are characterized by X-ray diffraction (XRD), scanning electron microscope(SEM), and the photo-luminescence spectra method. The influences of EDTA on the crystal phase, shape and upconversion luminescence are explored in detail. According to the results of XRD and SEM, the pure hexagonal phased NaYF4:Yb3+/Er3+ rod-like microcrystals each with smooth surface are all around 12 m in the length. While the pure tetragonal phased LiYF4: Yb3+/Er3+ microcrystals each with smooth surface are octahedral in shape, and their average size is around 12 m. Under near infrared (NIR) 980 nm excitation, the two dominant emission peaks of Er3+ ions at 544 nm and at 650 nm are observed in NaYF4 and LiYF4 microcrystals, which can be assigned to the transitions of (2H11/2/4S3/2)4I15/2 and 4F9/24I15/2, respectively. It is found that the upconversion luminescence intensity of NaYF4:Yb3+/Er3+ microcrystals is about two times that of LiYF4:Yb3+/Er3+ microcrystals under the same excitation conditions. The ratio of red-to-green emission of Er3+ ions in LiYF4 microcrystals is higher than that of the NaYF4:Yb3+/Er3+microcrystals. The changes of the spectra in the different hosts could stem from two sources: one is that the nonradiation relaxation probability relative to phonon energy of matrix, the other is that the radiative transition probability relative to the site symmetry of the crystal field acting on the ion. The ratios between 5D07F1 and 5D07F2 transitions of Eu3+ ions in NaYF4:Yb3+/Eu3+ and LiYF4:Yb3+/Eu3+ microcrystals are employed to compare and elucidate the site symmetry of the crystal field for Ln3+ ions. Note that the ratio of 5D07F1 and 5D07F2 transitions in NaYF4:Yb3+/Eu3+ microcrystals is smaller than that of the LiYF4:Yb3+/Eu3+ microcrystals, which indicates a much higher radiative relaxation rate in NaYF4 microcrystals than in LiYF4 microcrystals. The organic ligands of EDTA on the surface of microparticles affect the properties of luminescence through changing the nonradiative relaxation rate, resulting in the different R/G ratios in NaYF4 and LiYF4 microcrystals. This result can be further supported by the comparison between NaYF4 and LiYF4 microcrystals without EDTA added in the preparation process. The micro-sized luminescence materials usually present stronger upconversion luminescence because of their higher degree of crystallinity and less surface quenching centers. Thus, the Er3+ codoped NaYF4 and LiYF4 microcrystals exhibit strong green upconversion emission, which has potential applications in full-color displays and microelectronic devices.

Comparison of MoS_2 nanosheets and hierarchical nanospheres in the application of pulsed solid-state lasers

We prepared multi-layered MoS2 nanosheets and hierarchical MoS2 nanospheres composed of ultrathin nanosheets via a facile hydrothermal method. The presence of excessive thiourea played a critical role in the formation of nanospheres. Both the passively Q-switched single- and dual-wavelength Yb3+:GdAl3(BO3)4 (Yb:GAB) laser were achieved by using the multi-layered nanosheets and hierarchical nanospheres as saturable absorbers (SAs). As far as we know, the saturable absorption characteristic of hierarchical nanospheres was reported for the first time. Compared with nanosheets, the as-prepared nanospheres SA exhibited improved saturable absorption property with shorter pulse width and higher pulse energy, which should be attributed to the unique hierarchical structure.

Synthesis and Luminescence Properties of Doped Magnesium Boro-Tellurite Ceramics

Glass has been widely utilized in the field of lighting, telecommunication and spectroscopy. Boro-tellurite is one of the suitable glasses used for solid state lighting and laser application. The investigation on the luminescence properties of rare earth doped ceramic is rarely used due to the opacity. In this paper boro-tellurite prepared in ceramic can show the better luminescence with the less advantage. The aim of this paper is to present the effect and advantages in luminescence results of boro-tellurite ceramics doped with the constant amount of rare earth. Doped magnesium boro-tellurite with Eu3+ and Dy3+ ceramic have been prepared using solid state reaction method with the compositions of xTeO2-(70-x)B2O3-30MgO with 10≤x≤40, and have been doped with Eu2O3 (1mol%) and Dy2O3 (1mol%) . The characterizations of the samples have been investigated by means of X-Ray diffraction, Raman, Infrared and Photoluminescence spectroscopy. From the X-ray diffraction results, two phases are assigned to MgTe2O5 and Mg2B2O5. Raman spectroscopy showed strong bands observed in the vicinity of 140, 175, 220, 266, 332, 403, 436, 646, 694, 723, 757 and 806 cm-1. FTIR spectra showed bands located in the range between 400-800 cm-1 are assigned to the bending mode of Te-O-Te, TeO3 and TeO4. In the range of 800-1400 cm-1,the bands are associated with B-O, B-O-B, BO3 and BO4 bonds. The emission transition 5D0-7F2 corresponded to the red emission (612 nm) was found to be the most intense in all the Eu3+-doped magnesium boro-tellurite ceramics.

The Latest Development of Laser Application Research in Plant Factory

Abstract Essential resource elements in crop production are light, water, carbon dioxide and fertilizer. Optimum design for air-conditioning and lightings in plant factory system is required to realize the economical operation of plant factory because most energy consuming elements of plant factory system are air-conditioning and lightings. In this sense application of solid state lighting sources such as LED in plant factory system have been promoted to expect some reduction of running cost in lighting. Research work of solid state laser application in plant factory has just started recently at Osaka Prefecture University Plant Factory Research Center. The latest development of laser application research in plant factory will be reported in this article.

A study on the growth, optical, thermal, mechanical, dielectric and piezoelectric properties of dye doped KAP single crystals

Potassium hydrogen phthalate single crystals have been grown by conventional and Sankaranarayanan–Ramasamy method. Dye inclusion crystals have attracted researchers in the context of crystal growth for applications in solid state lasers. The effect of crystal violet as dopant on the characteristic properties of KAP crystal was studied. Thermal stability of the crystals is tested using TG-DTA. There is only one endothermic peak which indicates the decomposition point. The optical transparency of the crystals was identified from the UV–vis spectrum. The mechanical strength of the crystals has been measured by Vickers micro hardness. The dielectric, piezoelectric and luminescence study is carried out for both pure and dye doped KAP crystals. The photoluminescence spectrum of the KAP induced by the dye-doping reveals an emission band peaking at 595nm.

Anisotropy of the spectroscopic, optical and thermo-mechanical properties of Li_6Eu_1-xGd_x(BO_3)_3 crystals optimized for heat-scintillation cryogenic bolometers

Optical, spectroscopic and thermo-mechanical properties of monoclinic Li6Eu1-xGdx(BO3)3 (x = 0,0.25,0.35) bulk single crystals, grown to be used in the design of heat-scintillation cryogenic bolometers (HSCBs), were investigated. The linear thermal expansion was determined along the a, b, c and c* directions over the temperature range 303–873 K, and its tensor principal coefficients were calculated for both x = 0.25 and x = 0. In addition, the anisotropic thermal conductivity was measured over the temperature range 20-400 K in Li6Eu0.75Gd0.25(BO3)3 (LGEB7, x = 0.25), and the principal components of its tensor at 300 K were established. Spectroscopic properties such as polarized absorption, polarized emission, Raman spectroscopy and optical refractive indices are also reported for the first time. Based on the polarized emission spectra, the line and oscillator strengths, the radiative lifetimes and fluorescent branching ratios were obtained. The intensity parameters Ωλ (λ = 2,4) were obtained and then predicted via the Judd–Ofelt theory. The crystal field parameters and the 7F1 level splitting were discussed using the simple overlap model (SOM) and the method of equivalent nearest neighbours (MENN). The 613 nm emission originates from the 5D0→7F2 transition and the associated stimulated emission peak cross section reaches its maximum value in π-polarization, ≈1.07 × 10−20 cm2 in LGEB7. The thermo-mechanical characterizations and spectroscopic analysis in LGEB7 suggest that this crystal has better optical properties than the Eu3+-doped Li6Y(BO3)3 crystals. However, its potential for solid-state laser applications is still quite speculative, unless a clever thermo-mechanical management of the crystal under laser operation is designed.

Challenges of high power diode-pumped lasers for fusion energy

Abstract This paper reviews the different challenges that are encountered in the delivery of high power lasers as drivers for fusion energy. We will focus on diode-pumped solid-state lasers and we will highlight some of the main recent achievements when using ytterbium, cryogenic cooling and ceramic gain media. Apart from some existing fusion facilities and some military applications of diode-pumped solid-state lasers, we will show that diode-pumped solid-state lasers are scalable to inertial fusion energy (IFE)’s facility level and that the all-fiber laser scheme is very promising.

Physical and optical properties of Dy3+: Li2O–K2O–B2O3 glasses

The luminescence, lasing and sensing properties of rare earth (RE) ions have drawn much interest among researchers. We have focussed on the physical and optical properties of Li2O–K2O–B2O3 (LKB) with different concentrations of dysprosium (Dy3+) ions. The glass samples were prepared using melt quenching method. The physical parameters of the prepared glass were determined. Optical measurements such as XRD, FTIR, absorption and photoluminescence spectra have been carried out. Dy3+: LKB glass showed eight absorption bands with hypersensitive transition located at 1265nm (6H15/2→6F11/2–6H9/2). Finally, Dy3+: LKB glass exhibited two intense luminescence emission at 481nm (4F9/2→6H15/2; blue) and 573nm (4F9/2→6H13/2; yellow) and feeble band at 683nm (4F9/2→6H11/2; red) with excitation wavelength at 370nm. The results obtained are prevalent with others studies and also point to its use in solid-state laser, optoelectronic devices and W-LEDs application.

Generation of Laguerre-Gaussian LGp0 beams using binary phase diffractive optical elements.

In recent years, considerable attention has been devoted to laser beams with specific intensity profile, i.e., non-Gaussian. In this work, we present a novel technique to generate high-radial-order Laguerre-Gaussian beams LG(p0) based on the use of a binary phase diffractive optical element (BPDOE). The latter is a phase plate made up of annular zones introducing alternatively a phase shift equal to 0 or π modeled on positions which do not coincide with the position of the zeros of the desired LG(p0) beam. The LG(p0) beams are obtained by transforming a fundamental Gaussian beam through an appropriate BPDOE. The design of the latter is based on the calculation of the Fresnel-Kirchhoff integral, and the diffracted intensity at the focus plane of a lens has been modeled analytically for the first time. The numerical simulations and experiment demonstrate a good beam quality transformation. Obtained LG(p0) are suitable for atom trap and pumping solid state laser applications.