High-power Solid-state Lasers Research Articles

Broadband mid-infrared generation by difference-frequency generation in strongly dispersive Bragg reflection waveguides

We present a novel scheme for generation of broadband mid-infrared (mid-IR) radiation using a quasiphase-matched difference-frequency-generation (DFG) process in a planar high index core symmetric Bragg reflection waveguide (BRW) geometry based on GaN/AlxGa1−xN system. By suitably tailoring the dispersion properties of the BRW so as to maintain the phase-matching condition over a broad range of pump wavelengths, we show that the pump acceptance bandwidth could be enhanced by nine to ten times for a DFG process. This manifests into a broadband mid-IR difference-frequency idler with greater than 280 nm bandwidth close to 4.35 μm wavelength. Since the design presented here exploits the dispersive features of the BRW; we can shift the broadband characteristics to any desired region of the mid-IR spectrum within the constraints imposed by transparency and nonlinearity of the constituent materials. The design also facilitates pumping by standard high-power solid-state laser sources.

A double-frequency solid-state laser on organic compounds

A double-frequency narrow-band tunable laser with a solid-state organic active medium pumped by the 2nd harmonic of a YAG–Nd3+ laser has been developed. The laser emits in the range from uv (with frequency doubling) to near ir wavelengths. The energy and lifetime characteristics of the laser suffice for its practical applications. It can be used as a master oscillator for a high-power narrow-band solid-state laser on organic compounds.

Efficient Nd3+→Yb3+ energy transfer in Nd3+,Yb3+:Gd3Ga5O12 multicenter garnet crystal

For seeking better laser crystals with good optical properties and high efficiency, especially for application in a high power solid-state laser, Yb3+,Nd3+:Gd3Ga5O12 crystal (abbreviated as Yb,Nd:GGG below) was grown by Czochralski method. A complete optical characterization was reported including absorption and emission spectra at different temperatures and fluorescence lifetimes. Very efficient Nd3+ F43/2→Yb3+ F25/2 energy transfer was found whereas the back transfer was completely quenched at low temperature (T<200 K). From the data of Nd3+ fluorescence lifetime and emission spectrum we achieved the energy-transfer efficiency as large as 94% at 77 K and 84% at 300 K, respectively. After fitting the decay curve we got the energy-transfer microparameter with a value of 2.1×10−39 cm6 s−1 at 300 K.

High-Power Fiber Lasers and Amplifiers Based on Multimode Interference

In this paper, high-power fiber lasers and amplifiers based on multimode interference (MMI) in active large-core multimode optical fibers are proposed and their properties are investigated. Experimental results and simulations indicate that such fiber lasers and amplifiers are promising candidates for high-power miniature solid-state lasers. Utilization of the MMI leads to remarkable spectral and spatial features of fiber lasers and amplifiers such as generation of high-power diffraction-free beams.

PRE-07 MECHANICAL DESIGN OF LARGE-APERTURE DISK AMPLIFIERS FOR A HIGH-POWER SOLID-STATE LASER(MM/Micro/Nano Precision Equipments III,Technical Program of Oral Presentations)

The main purpose of the paper is to describe mechanical design of large-aperture disk amplifiers for a high-power solid-state laser. The 400mm-aperture amplifiers use a modular and bottom-access design to facilitate replacement. The key components, such as laser slabs, central flashlamp cassettes, side flashlamp cassettes, reflectors and blast shields, are mounted in line-replaceable units (LRU) which are contained in a clean enclosure to maintain cleanliness. Flowing nitrogen gas is used to cool neodymium glass laser slabs and reduce the amplifier thermal recovery time.

高功率固体激光器冷却技术

高功率固体激光器冷却技术

Hybrid Laser-GMA Welding for Improved Affordability

Maturing high-power solid-state laser technology is fueling an interest in hybrid laser gas metal arc (laser-GMA) welding for shipyard fabrication activities. Hybrid laser-GMA welding has demonstrated an ability to both reduce the distortion of thin steel butt welds and increase the production rate of pipe welds relative to conventional joining techniques, both leading to improved affordability. The paper discusses the potential benefits of hybrid laser-GMA welding, results of experiments to address both distortion and production rate, and provides an overview of a hybrid pipe welding system recently installed in a shipyard.

Beam quality changes of radially and azimuthally polarized fields propagating through quartic phase plates

In terms of the so-called irradiance moments of a light field, the beam quality change, Δ Q, of radially and azimuthally polarized beams caused by propagation through a quartic phase plate (as occurs, for example, in strongly pumped laser rods used in high-power solid-state lasers) is studied. Analytical expressions for Δ Q are given, and a comparison between the scalar and vectorial regimes is also shown. The results are applied to several cases of interest.

Fluorescence properties and laser demonstrations of Nd-doped high silica glasses prepared by sintering nanoporous glass

Porous glass with high-SiO2 content was impregnated with Nd ions, and subsequently sintered at 1100 degrees C into a compact non-porous glass in air or reducing atmosphere. Sintering in a reducing atmosphere produced an intense violet-blue fluorescence at 394 nm. However, the sintering atmospheres almost did not affect the fluorescence properties in the infrared range. A good performance Nd3+-doped silica microchip laser operating at 1064 nm was demonstrated. The Nd-doped sintering glasses with high-SiO2 content are potential host materials for high power solid-state lasers and new transparent fluorescence materials. (c) 2007 Elsevier B.V. All rights reserved.

Cooling of Laser Slab by Forced Convection through a Heat Sink

The present study addresses a novel cooling scheme for the high-power solid-state laser slab. The scheme cools the laser slab by forced convection in a narrow channel through a heat sink. Numerical simulations were conducted to investigate the thermal effects of a Nd:YAG laser slab for heat sinks of different materials, including the undoped YAG, sapphire, and diamond. The results show that the convective heat transfer coefficient is non-uniform along the fluid flow direction due to the thermal entrance effect, causing a non-uniform temperature distribution in the slab. The heat sink lying between the coolant fluid and the pumped surface of the slab works to alleviate this non-uniformity and consequently improve the thermal stress distribution and reduce the maximum thermal stress of the slab. The diamond heat sink was found to be effective in reducing both the highest temperature and the maximum thermal stress; the sapphire heat sink was able to reduce the maximum thermal stress but not as effective in reducing the highest temperature; and the undoped YAG heat sink reduced the maximum thermal stress but tended to increase the highest temperature. Therefore, cooling with the diamond heat sink is most effective, and that with the sapphire heat sink follows; cooling with the undoped YAG heat sink may not apply if the highest temperature is a concern.

Thermal lens effect in solar-pumped high-power solid-state lasers

The thermal lens effect in the Nd:YAG laser rods pumped with a concentrated solar flux of the Big Solar Furnace of the NPO Fizika-Solntse of the Academy of Sciences of the Republic of Uzbekistan (Tashkent) is considered.

Thermal and Optical Properties of ${\hbox {Yb}}^{3+}$- and ${\hbox {Nd}}^{3+}$-Doped Phosphate Glasses Determined by Thermal Lens Technique

In this work, we study the thermal and optical properties of ion-doped phosphates glasses using the thermal lens (TL) technique. Three samples were characterized: Nd3+-doped Q-98; Nd3+-doped Q-100; and Yb3+-doped QX. We report multiwavelength TL measurements for a more accuracy determination of the fluorescence quantum efficiency and temperature coefficient of the optical path length change (ds/dT). In Nd-doped glasses, it was carried out using four discrete excitation wavelengths (between 514 and 872 nm) chosen to match with the ion absorption lines. In Yb-doped glass, the spectrum of heat generated along the Yb3+ transition (2 F 5/2rarr2 F 7/2) was obtained. In addition, parameters as thermal diffusivity and conductivity, thermal loading, etc were achieved. The advantages to obtain fluorescence quantum efficiency using the TL technique, mainly in Yb3+ doped materials, which are normally overestimated due to radiation trapping effect, are presented. The accuracy knowledge of these parameters is very important for design of high-power solid-state lasers, since these properties are directly related to the heat generation.

Recent Advances in Microwave and Millimeter-Wave Processing of Materials

We are using 2.45 GHz (S-Band) microwave systems and an 83-GHz, gytrotron-based, millimeter-wave beam system in material processing and other areas. We use one 2.45 GHz system in preparation of nanophase metals, metal mixtures and metal oxides, via the patented continuous microwave polyol process, with potential for large scale, low cost production. Of interest are precious metals, mixtures of magnetic and nonmagnetic metals, and mixed metal oxides for ceramic precursors. The other S-Band systems are used to develop repair techniques for ceramic matrix composites where the repairs are heated to 200-1000°C. A portable, battery-powered system is being developed for field repairs, and promises to be much more practical than alternative approaches (e.g., heating blankets). The 83-GHz system is being used in rapid sintering of polycrystalline ceramic materials intended for use in high power solid state lasers, where the requirement if for sintering to transparency with high optical quality and good lasing efficiency. Transparent Yb-doped yttria has been produced with hybrid conventional/millimeter-wave sintering of nanophase powders, as well as theoretically dense YAG. Another application for the millimeterwave beam system is in consolidation and bonding of hard coatings to light alloys, such as SiC on titanium, where the beam system allows heating of the coating to very high temperatures without overheating the metallic substrate. Finally, the millimeter-wave system is being used in the development of millimeter-wave plasma-assisted diamond deposition, where the quasi-optical system has significant advantages over conventional microwave plasma-assisted diamond deposition. Results for these various areas will be presented and discussed.

Diffractive Optical Elements for Laser Materials Processing

Recent developments of high-power and high-quality solid-state laser systems, in particular diode-pumped Nd: YAG lasers and fiber lasers, allow the development of various kinds of laser materials processing applicationsin production industries. Diffractive optical elements are employed as a key technology to achieve such applications. In this paper, the author describes the practical examples of a diffractive beam splitter, a diffractive beam homogenizer, a hybrid lens, and a long-focal-depth diffractive lens for a femtosecond laser.

Thermal lens study of energy transfer in Yb^3+/Tm^3+-co-doped glasses

Energy transfer (ET) and heat generation processes in Yb(3+)/Tm(3+)-co-doped low-silica calcium-aluminosilicate glasses were investigated using thermal lens and photoluminescence measurements. Stepwise ET processes from Yb(3+) to Tm(3+), with excitation at 0.976 mum, produced efficient emission in the mid-infrared range at around 1.8 mum, with high fluorescence quantum efficiency (~0.50) and relatively low thermal loading (</=0.42). An equation was deduced for the description of the thermal lens results which provided the absolute value of the ET efficiency and optimal Tm3+ concentration that result in population of the 1.8 mum Tm(3+) emitting level. These results suggest that the studied co-doped system would be a promising candidate for the construction of high-power diode-pumped solid-state lasers in the mid-infrared range, which are especially important for the purpose of medical procedures.

Influence of addition of B2O3 on properties of Yb3+-doped phosphate laser glass

The three host glasses doped with Yb3+ were prepared by means of conventional melt quenching technology, and the influence on physical and spectral properties of phosphate glass due to addition of B2O3 was investigated and compared with silicate glass. The results show that due to the existence of OH− impurities which induce the non-radiative route, the fluorescence lifetime of phosphate glass is shorter, so silicate glass has better spectral properties than phosphate glass. Silicate glass has more excellent thermal-mechanical properties than phosphate glass, but with the addition of B2O3, thermal-mechanical properties of phosphate glass are improved greatly without fluorescence quenching effect, and this kind of borophosphate glass will be the candidate to be used in high average power solid state laser.

Efficient Yb3+:Y3Al5O12 ceramic microchip lasers

Low-threshold and highly efficient continuous-wave (cw) Yb3+:Y3Al5O12 (Yb:YAG) ceramic laser with near-diffraction-limited beam quality was demonstrated at room temperature. Dual-wavelength operation at 1030 and 1049nm with 5% transmission of the output coupler was achieved by varying pump power intensity. Slope efficiencies of 79% at 1030nm and 67% at 1049nm were achieved for 1-mm-thick Yb:YAG ceramic plate (CYb=9.8at.%) under cw laser-diode pumping. The effect of pump power on the laser emission spectra of both wavelengths is addressed. Excellent laser performance indicates that Yb:YAG ceramic laser materials could be potentially used in high-power solid-state lasers.

Analysis on the temperature distribution and thermal effects in corner-pumped slab lasers

The temperature distribution and thermal effects in a high-power solid-state laser are investigated. The temperature distribution in a corner-pumped Yb:YAG/YAG composite slab is described analytically, and the thermal effects in that slab are deduced. Their influences to the resonator are also discussed. A corner-pumped Yb:YAG/YAG composite slab laser has achieved 1016 W continuous wave laser output. The experimental results support the calculated outcomes.

Efficient laser oscillation of Yb:Y3Al5O12 single crystal grown by temperature gradient technique

Low-threshold and highly efficient continuous-wave laser performance of Yb:Y3Al5O12 (Yb:YAG) single crystal grown by a temperature gradient technique (TGT) was achieved at room temperature. The laser can be operated at 1030 and 1049nm by varying the transmission of the output coupler. Slope efficiencies of 57% and 68% at 1049 and 1030nm, respectively, were achieved for 10at.% Yb:YAG sample in continuous-wave laser-diode pumping. The effect of pump power on the laser emission spectrum of both wavelengths is addressed. The near-diffraction-limited beam quality for different laser cavities was achieved. The excellent laser performance indicates that TGT-grown Yb:YAG crystals have very good optical quality and can be potentially used in high-power solid-state lasers.

Investigation on Structures and Properties of Yb 3+-Doped Laser Glasses

The Yb 3+-doped silicate, phosphate and borophosphate laser glasses were prepared by means of conventional melt quenching technology. The physical and spectral properties of the glasses were investigated. The results show that, due to the existence of OH −, the fluorescence lifetime of phosphate glass is shorter than that of silicate glass, so silicate glass has better spectral properties than phosphate glass. Silicate glass has better mechanical and thermal properties than phosphate glass, but with the addition of B 2O 3, mechanical and thermal properties of phosphate glass are improved greatly without fluorescence quenching effect. This kind of borophosphate glass can be used in high average power solid state lasers.