Solid-state Laser Applications Research Articles

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.

Optical and structural properties of lithium sodium borate glasses doped Dy3+ ions

Absorption and emission spectra of lithium sodium borate glass doped with different concentrations of Dy3+ have been reported. The concentration of Dy3+ was varied from 0.3 to 1.3mol%. The amorphous nature of the prepared samples was confirmed by the X-ray Diffraction (XRD). Fourier transforms infrared (FTIR) spectra, and other significant physical properties (energy band gap, density, ion concentration, molar volume, Polaron radius and inter-nuclear distance) have been analyzed in the light of the different oxidation states of the co-dopant ions. The absorption spectrum showed nine peaks with hypersensitive transition corresponding to 6F11/2+6H9/2 at 1256nm. As a result of 380nm excitation wavelength, the luminescence spectra showed two characteristic bands at 479nm and 587nm. These absorption bands were attributed to 6P15/2→6H15/2 and 6P15/2→6H13/2 transitions of trivalent Dy3+ ions. The current study indicates that Dy doped lithium sodium borate glasses are attractive for solid-state laser applications.

Anisotropic Ta2O5 waveguide etching using inductively coupled plasma etching

Smooth and vertical sidewall profiles are required to create low loss rib and ridge waveguides for integrated optical device and solid state laser applications. In this work, inductively coupled plasma (ICP) etching processes are developed to produce high quality low loss tantalum pentoxide (Ta2O5) waveguides. A mixture of C4F8 and O2 gas are used in combination with chromium (Cr) hard mask for this purpose. In this paper, the authors make a detailed investigation of the etch process parameter window. Effects of process parameters such as ICP power, platen power, gas flow, and chamber pressure on etch rate and sidewall slope angle are investigated. Chamber pressure is found to be a particularly important factor, which can be used to tune the sidewall slope angle and so prevent undercut.

Coherent characteristics of solid-state lasers with corner cubes.

A corner cube (CC) as a peculiar coherent combination element is first, to the best of our knowledge, theoretically and experimentally proved by the authors. When a CC is used as a total-reflecting mirror in the solid-state laser resonator it can improve the laser far-field energy focalization. Furthermore, the differences between the coherent characteristics of the lasers with a corner cube resonator (CCR) and those with a Fabry-Perot resonator have been investigated, respectively. Theoretical calculation and numerical simulation have proved that the symmetric output beams of the CCR laser are coherent and the adjacent output beams are partially coherent. Based on these special coherent characteristics, a new laser coherent combining configuration, in which a CC was utilized as a total-reflecting mirror, was proposed and experimentally investigated. In our experiments, the measured far-field intensity profiles of coherent combing laser arrays are in good agreement with the numerical simulation. These novel coherent characteristics of a CC may be important for applications in solid-state lasers and laser coherent combining systems, and coherent combination may be one of the development trends and future research directions for CCR lasers.

Mid-infrared emission in Dy:YAlO_3 crystal

In this work, we report on the spectroscopic properties of Dy3+ doped YAlO3 crystal grown by Czochralski technique. The Judd-Ofelt theory was performed based on the measured polarized absorption spectra. Under optical pumping at 1300 nm, Dy:YAP crystal exhibited a broad MIR emission centered at 3020 nm, with a bandwidth of 520 nm at full width half maximum. The decay lifetime of the 6H13/2 level was measured to be 8.88 ms, and the corresponding quantum efficiency evaluated was 57.9%. The studied optical gain properties indicate that Dy:YAlO3 crystal could be a potential candidate for solid-state mid-infrared laser applications.

Molecular Packing versus Strength and Effective Mass of the Emitting Exciton of β-1,1,4,4-Tetraphenyl-1,3-butadiene

Molecular packing in molecular crystalline solids and aggregates influences both the redistribution of oscillator strength between the excitons involved in optical transitions and also their effective masses. 1,1,4,4-Tetraphenyl-1,3-butadiene is taken into consideration because it is often used in light-emitting solid-state devices and it is also a promising material for solid-state laser applications, owing to the observed amplified spontaneous emission at room temperature of its β polymorph. This paper concerns a combined experimental and computational study of the photoluminescence emission of the β phase. The emission is demonstrated to originate from the lowest-energy exciton, which takes almost the whole available oscillator strength from the four molecules in the unit cell, and it is also the heaviest one in terms of effective mass. On the basis of the balance between nuclear relaxation energy, free-exciton Davydov splitting, and also exciton effective mass, as discussed in the framework of the recent reclassification reported in J. Chem. Phys. 2007, 127, 184703, the exciton–phonon coupling turns out to be effective in limiting the delocalization of this heavy exciton and in influencing the phonon progression in the emission spectra.

Functional organic single crystals for solid-state laser applications

Because of long-range order and high chemical purity, organic crystals have exhibit unique properties and attracted a lot of interest for application in solid-state lasers. As optical gain materials, they exhibit high stimulated emission cross section and broad tunable wavelength emission as similar to their amorphous counterpart; moreover, high purity and high order give them superior properties such as low scattering trap densities, high thermal stability, as well as highly polarized emission. As electronic materials, they are potentially able to support high current densities, thus making it possible to realize current driven lasers. This paper mainly describes recent research progress in organic semiconductor laser crystals. The building molecules, crystal growth methods, as well as their stimulated emission characteristics related with crystal structures are introduced; in addition, the current state-of-the-art in the field of crystal laser devices is reviewed. Furthermore, recent advances of crystal lasers at the nanoscale and single crystal light-emitting transistors (LETs) are presented. Finally, an outlook and personal view is provided on the further developments of laser crystals and their applications.

2.7 μm emission of high thermally and chemically durable glasses based on AlF3

AlF3-based glasses (AlF3-YF3-CaF2-BaF2-SrF2-MgF2) with enhanced thermal and chemical stability were synthesized and compared with the well-known fluorozirconate glass (ZBLAN). The 2.7 μm mid-infrared emission in the AlF3-based glasses was also investigated through the absorption and emission spectra. Both the temperature of glass transition and the characteristic temperatures (ΔT, Hr, kgl) of the fluoroaluminate glasses were much larger than those of the ZBLAN glasses. The corrosion phenomenon can be observed by naked-eye, and the transmittance dropped dramatically (0% at 3 μm) when the ZBLAN glass was placed into distilled water. However, the AlF3-based glass was relatively stable. The fluoroaluminate glasses possessed large branching ratio (20%) along with the emission cross section (9.4×10−21 cm−2) of the Er3+:4I11/2→4I13/2 transition. Meanwhile, the enhanced 2.7 μm emission in highly Er3+-doped AYF glass was obtained. Therefore, these results showed that this kind of fluoride glass has a promising application for solid state lasers at 3 μm.

Large-energy, narrow-bandwidth laser pulse at 1645 nm in a diode-pumped Er:YAG solid-state laser passively Q-switched by a monolayer graphene saturable absorber

Nonlinear transmission parameters of monolayer graphene at 1645 nm were obtained. Based on the monolayer graphene saturable absorber, a 1532 nm LD pumped 1645 nm passively Q-switched Er:YAG laser was demonstrated. Under the pump power of 20.8 W, a 1645 nm Q-switched pulse with FWHM of 0.13 nm (without the use of etalon) and energy of 13.5 μJ per pulse can be obtained. To the best of our knowledge, this is the highest pulse energy for graphene-based passively Q-switched Er:YAG laseroperating at 1645 nm, suggesting the potentials of graphene materials for high-energy solid-state laser applications.

Spectroscopic properties of Nd3+:Lu3ScAl4O12 single crystal

Nd:Lu3ScAl4O12 single crystal has been grown by the Czochralski method. The segregation coefficient of Nd3+ ions in LuSAG crystal is 0.22. X-ray powder diffraction (XRD) experiments show that the Nd:LuSAG crystal crystallizes in cubic structure with space group Ia3d and its cell parameters are a = 1.1953 nm. The absorption and fluorescence spectra of Nd:LuSAG crystal were investigated at room temperature. The spectral parameters were calculated based on Judd–Ofelt (J–O) theory, and the intensity parameters Ω2, Ω4 and Ω6 were obtained to be 0.14, 3.38, and 4.88 × 10−20 cm2, respectively. The calculated spontaneous radiative probabilities, branching ratios, radiative lifetime and quantum efficiency have been evaluated for the 4F3/2 excited state using the calculated intensity parameters. The results indicate that this crystal can be considered as a promising material for solid-state laser application.

Highly efficient Yb3+/Tm3+ co-doped NaYF4 nanotubes: Synthesis and intense ultraviolet to infrared up-conversion luminescence

Nanocrystals of up-conversion (UC) phosphor Yb3+/Tm3+ co-doped NaYF4 are prepared by a facile hydrothermal method using oleic acid as a stabilizing agent. The as-prepared nanocrystals are of hexagonal phase, and have tube-like morphology and strong ultraviolet (UV) and blue UC fluorescence intensity, which have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and luminescence spectroscopy. The effect of Yb3+ concentration on the UC emission properties is also analyzed. Our results reveal that the intensity of emission peaks can be controlled by varying the Yb3+ concentration and these NaYF4 nanotubes are highly efficient host material. The as-prepared NaYF4 nanotubes show potential applications in UV compact solid state lasers and multi-channel fluorescent label.

Ultrasensitive Polarized Up-Conversion of Tm3+–Yb3+ Doped β-NaYF4 Single Nanorod

Up-conversion luminescence in rare earth ions (REs) doped nanoparticles has attracted considerable research attention for the promising applications in solid-state lasers, three-dimensional displays, solar cells, biological imaging, and so forth. However, there have been no reports on REs doped nanoparticles to investigate their polarized energy transfer up-conversion, especially for single particle. Herein, the polarized energy transfer up-conversion from REs doped fluoride nanorods is demonstrated in a single particle spectroscopy mode for the first time. Unique luminescent phenomena, for example, sharp energy level split and singlet-to-triplet transitions at room temperature, multiple discrete luminescence intensity periodic variation with polarization direction, are observed upon excitation with 980 nm linearly polarized laser. Furthermore, nanorods with the controllable aspect ratio and symmetry are fabricated for analysis of the mechanism of polarization anisotropy. The comparative experiments suggest that intraions transition properties and crystal local symmetry dominate the polarization anisotropy, which is also confirmed by density functional theory calculations. Taking advantage of the REs based up-conversion, potential application in polarized microscopic multi-information transportation is suggested for the polarization anisotropy from REs doped fluoride single nanorod or nanorod array.

Synthesis of Er-doped Lu2O3 nanoparticles and transparent ceramics

Transparent rare earth-doped Lu2O3 ceramics have received much attention for use in solid-state scintillator and laser applications. The fabrication of these ceramics, however, requires ultrafine and uniform powders as precursors. Presented here is the synthesis of Er-doped Lu2O3 nanopowders by a solution precipitation method using Er-doped lutetium sulfate solution and hexamethylenetetramine as a precipitant and the fabrication of Er-doped Lu2O3 transparent ceramics from these nanopowders. The precipitated precursors were calcined at 1100°C for 4h in order to convert the precursors into Lu2O3 nanoparticles with an average particle size of 60nm. Thermal decomposition and phase evolution of the precursors were studied by simultaneous thermal analysis (STA), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Er-doped Lu2O3 transparent ceramics were fabricated from these nanopowders using vacuum sintering followed by hot isostatic pressing at 1700°C for 8h. The transparent ceramics exhibit an optical transmittance of 78% at a wavelength of 1.55μm.

50th anniversary of the Judd–Ofelt theory: An experimentalist's view of the formalism and its application

The theory on the intensities of 4f→4f transitions introduced by B.R. Judd and G.S. Ofelt in 1962 has become a centerpiece in rare-earth optical spectroscopy over the past five decades. Many fundamental studies have since explored the physical origins of the Judd–Ofelt theory and have proposed numerous extensions to the original model. A great number of studies have applied the Judd–Ofelt theory to a wide range of rare-earth-doped materials, many of them with important applications in solid-state lasers, optical amplifiers, phosphors for displays and solid-state lighting, upconversion and quantum-cutting materials, and fluorescent markers. This paper takes the view of the experimentalist who is interested in appreciating the basic concepts, implications, assumptions, and limitations of the Judd–Ofelt theory in order to properly apply it to practical problems. We first present the formalism for calculating the wavefunctions of 4f electronic states in a concise form and then show their application to the calculation and fitting of 4f→4f transition intensities. The potential, limitations and pitfalls of the theory are discussed, and a detailed case study of LaCl3:Er3+ is presented.

Er3+-doped fluoro-tellurite glass: A new choice for 2.7 μm lasers

A novel erbium ion doped fluoro-tellurite glasses were prepared, and 2.7μm emission properties, thermal stability and chemical durability were investigated. An intense 2.7μm emission was observed. It was also found that the thermal stability and chemical durability were greatly improved by introducing a small amount of TeO2 into fluoride glasses. In addition, the spontaneous transition probability (A) and branching ratios (β) of Er3+-doped fluoro-tellurite glasses were calculated and analyzed. The present Er3+-doped fluoro-tellurite glasses with large 2.7μm emission cross-sections (6.32×10−21cm2) indicate that it has a very promising application for solid state lasers around 3μm.

Citric acid-assisted hydrothermal synthesis of α-NaYF4:Yb3+,Tm3+ nanocrystals and their enhanced ultraviolet upconversion emissions

Tm3+ and Yb3+ ions co-doped α-NaYF4 nanocrystals (NCs) were prepared by a one step hydrothermal method with citric acid as the organic additive. The morphology of the as-prepared materials maintains a spherical shape when the surfactant amount, hydrothermal time, and hydrothermal temperature were varied. Under 980 nm excitation, intense ultraviolet (UV) and blue upconversion (UC) emissions were observed from the α-NaYF4 NCs and their intensities were much higher than those of the β-NaYF4 NCs modified by trisodium citrate. The intensities of the 5-photon UC emissions from the 1I6 level of Tm3+ ions were much stronger than those of the 4-photon UC emissions from the 1D2 level and the 3-photon UC emissions from the 1G4 level. It is for the first time, to our knowledge, that such intense UV UC emissions were obtained with α-NaYF4 NCs. The intense UV UC emissions and the relatively long fluorescent lifetimes for the 1I6, 1D2, and 1G4 levels of Tm3+ ions in α-NaYF4 NCs indicate that they could be one of the promising candidates for potential application in short-wavelength solid-state lasers.

Phase structure and vibrational spectra of rare-earth-oxide ceramics of Dy2(1−x)Tm2x O3

Rare-earth-sesquioxide ceramics have been found to possess potential applications in solid-state lasers due to their excellent physical and chemical properties as well as low cost. In this paper, composite powders with the composition of Dy2(1−x)Tm2xO3 were prepared by ball milling method and corresponding ceramics were obtained using the pressureless sintering technique. Phase structure and vibrational spectra were investigated using X-ray diffraction, Raman spectrometer, and FT-IR spectrometer. It is shown that the mixture of Dy2O3 and Tm2O3 converts to an ordered solid solution of body-centered cubic structure after heat treatment at 1,100 °C for 4 h. It is also found that the cell constants of ceramics decrease linearly with the increase of Tm2O3 content. Raman spectra analysis demonstrates that bond length plays a major role in determining the frequencies of Raman bands at high-frequency range and that peak positions exhibit a blue shift with the increase of Tm2O3 content due to decreasing cell constant. Similar phenomenon is also observed in infrared spectra, which shows linearly increasing infrared band frequency with decreasing cell volume. The ball milling method used for preparing composite powders and vibrational spectra analysis in this work provide some important references for the study of laser ceramics containing Dy2O3 and Tm2O3.

Cryogenic Yb^3+-doped materials for pulsed solid-state laser applications [Invited

We review recent progress in pulsed lasers using cryogenically-cooled Yb3+-doped gain media, with an emphasis on high average power. Recent measurements of thermo-optic properties for various host materials at both room and cryogenic temperature are presented, including thermal conductivity, coefficient of thermal expansion and refractive index. Host materials reviewed include Y2O3, Lu2O3, Sc2O3, YLF, YSO, GSAG and YVO4. We report on the performance of several cryogenic Yb lasers operating at 5-kHz pulse repetition frequency (PRF). A Q-switched Yb:YAG laser is shown to operate at 114-W average power, with 16-ns pulse duration. A chirped pulse amplifier achieves 115-W output using a Yb:YAG power amplifier. Output power of 73 W is obtained from a composite Yb:YAG/Yb:GSAG amplifier, with pulses that compress to 1.6 ps. Finally, a high-average-power femtosecond laser based on Yb:YLF is discussed, with results for a 10-W regenerative amplifier at 10-kHZ PRF.

Applications and performance of high power lasers and in the battlefield

This paper reviews the status and applications of a defensive weapon based on high power lasers, in the battlefield. Laser weapon is a novel concept which utilizes high power laser beam to traverse the distance into incoming objects at a speed of light, and then, destroy or disable it. Various types of lasers and configurations will be discussed in this review including gas lasers, solid state lasers, fiber lasers and the free-electron laser. We will discuss various configurations such as airborne laser (ABL), diode pumped crystals and disk lasers as well as heat-capacity lasers. Recent applications of ultrafast solid state lasers for non-lethal or low collateral damage applications will be presented.

Calculation of band offsets in Cd 1− xX xTe alloys, X = Zn, Mg, Hg and Mn and magnetic effects in CdMnTe

Due to the large variety of properties offered by the telluride binaries CdTe, ZnTe, MgTe, HgTe and MnTe as well as their mixed ternary alloys, an accurate knowledge of their electronic band parameters is crucial. These materials have been extensively studied but, some points bearing on several properties have never previously reported or are still not clear. In this paper, we report results on the conduction and valence band offsets of the pseudo-morphically strained Cd 1− x X x Te layer on relaxed Cd 1− y X y Te substrate, X = Zn, Hg, Mg and Mn. Based on the Van Der Walle model, calculations have been performed for the all range of material and substrate 0 ≤ x, y ≤ 1. These discontinuities have not yet calculated for X = Mg, Mn or Hg in the all range 0 ≤ x, y ≤ 1. For the CdMnTe diluted magnetic semiconductor which we focus more interest due to its considerable current interest for applications, calculations have been done without and with correction taking into account magnetic effect of magnesium ions Mn 2+. It is found that the introduction of only a few percent of Mn into CdTe provides a unique opportunity to combine two important fields in physics, semiconductivity and magnetism. We can take advantage both of possibility of applications in solid-state lasers and exceptional magnetic properties offered by this magnetic diluted semiconductor. This study presents important quantities that are required to model quantum structures and offers a fast and inexpensive way to check device designs and processes.