Efficient Laser Action Research Articles

Diode-pumped 1028 nm Ytterbium-doped fiber laser with near 90% slope efficiency

Highly efficient laser action from an Ytterbium-doped fiber (YDF) is demonstrated using a fiber Bragg grating (FBG) in conjunction with a 4% Fresnel reflection at room temperature. The YDF used is drawn from Yb2O3-doped preform, fabricated through deposition of porous layer of composition SiO2-GeO2 by the MCVD process in conjunction with a solution doping technique. The fabricated YDF has a core composition of 0.2 wt % of Yb2O3, 1.8 wt % of Al2O3 and 23 wt % of GeO2 with a pump absorption of 9.0 dB/m. The fiber laser operates at wavelength of 1028 nm with a slope efficiency of 88% with respect to the launched 976 nm pump power using the YDF length of 7 m.

Efficient diode pumped ytterbium-doped fibre laser

A highly efficient laser action from a ytterbium-doped fibre (YDF) is demonstrated using a fibre Bragg grating at room temperature. The YDF used is drawn from a Yb2O3-doped preform, fabricated through deposition of a porous layer of composition SiO2-GeO2 by the MCVD process in conjunction with a solution doping technique. The fibre laser operates at a wavelength of 1028 nm with maximum slope efficiency of 88% when pumped by a singlemode 977 nm laser diode.

Efficient lasing action from Rhodamine-110 (Rh-110) impregnated sol–gel silica samples prepared by dip method

Rhodamine-110/sol–gel samples are prepared by sol–gel technique using dip method. Concentration dependent photophysical studies of these samples have indicated about the least possibility of aggregate formation. The lasing action of Rh-110 in silica samples is studied as a function of dye concentration. An efficient laser emission is observed when the samples are transversely pumped at 337.1 nm and 1.5 Hz repetition rate using a nitrogen laser (400 μJ energy/pulse and 4 ns pulse duration). The maximum of 166% laser efficiency of dye doped sol–gel samples compared to Rhodamine-6G (Rh-6G) in methanol is achieved. The photostability is also measured by using N 2 laser at 1 Hz and it is found nearly 165 pulses. The possible reasons for the photodegradation of the dye molecules are discussed in detail.

Diode-pumped Nd:YVO_4/Yb:S-FAP laser emitting at 985 and 4925 nm

For the first time, to the best of our knowledge, Yb:S-FAP crystals have been intracavity pumped by a Nd:YVO(4) laser at 914 nm. This original pumping scheme allows efficient laser action on the three-level transition at 985 nm with 1.4 W output power. Second-harmonic generation is also presented with a total output power of 120 mW at 492.5 nm.

Low‐dose ion implanted active waveguides in Nd3+ doped near‐stoichiometric lithium niobate: promising candidates for near infrared integrated laser

AbstractBy applying low‐dose oxygen ion implantation, active planar waveguides in Nd3+ doped near‐stoichiometric lithium niobate laser crystals have been, for the first time to our knowledge, successfully produced. The waveguide exhibits good transmission properties with relatively low propagation loss of ∼2 dB/cm. The confocal micro‐luminescence investigations indicate that the emission properties of Nd3+ ions in the waveguide are well preserved with respect to the bulk, thus showing promising potentials for efficient waveguide laser action operating at the Nd3+ near‐infrared bands. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Random laser action of ZnO@mesoporous silicas

ZnO@mesoporous silica nanocomposite was prepared by the impregnation method, andvery efficient laser action was highlighted. As revealed by high-resolution transmissionelectron microscopy (HR-TEM), nanometric ZnO particles are confined insidethe mesochannels of CMI-1 mesoporous silicas. Upon excitation at 3.6 eV of afemtosecond pulsed laser and at low pumping intensity, the ZnO@mesoporous silicashowed a broad photoluminescence (PL) band corresponding to the excitonicrecombination of ZnO. When the pumping intensity is increased up to a threshold(2.5 mJ cm−2), the excitonic emission turns to stimulated emission through a mechanism which will bediscussed. The same threshold value was obtained with another excitation source andnanocomposites with different ZnO loadings inside the CMI-1 mesoporous silica. Theseresults allow a better understanding of the random laser effect in ZnO@mesoporoussilica and, consequently, a model has been proposed to explain this phenomenon.Based on these new observations, many new applications can be considered sinceshort-wavelength devices are required by industry to design new information storagesupports.

Efficient Laser-Diode End-Pumped Passively Q-Switched Mode-Locked Yb:LYSO Laser Based on SESAM

We report an efficient Q-switched laser action based on a semiconductor saturable absorber mirrors (SESAMs) as passively Q-switched laser starter and a Yb:LYSO alloyed crystal as gain material pumped directly by 974 nm In GaAs laser diodes. The output pulse duration is measured to be about 7μs, while the average power and the repetition rate of the pulse chain are about 0.92 W and 6.2kHz, respectively, under 12.5 W absorbed pumping power. The Q-switched mode-locked pulse train is also observed in this setup. The laser performance shows that Yb:LYSO is a promising laser gain medium for laser-diode pumped compact solid-state lasers.

Tm-doped LiLuF_4 crystal for efficient laser action in the wavelength range from 182 to 206 μm

Room-temperature continuous-wave laser action in a novel Tm-doped LiLuF(4) crystal emitting at around 1.9 microm is demonstrated. The crystal growth process, spectroscopic measurements, and laser performance are presented for different Tm concentrations. An overall tunability extending from 1817 to 2056 nm, a slope efficiency of 46%, and a maximum output power in excess of 1.1 W are reported.

New phenomenon in the channels of mesoporous silicate CMI-1: quantum size effect and two-photon absorption of ZnO nanoparticles

Quantum size effect (QSE) and very efficient laser action were observed in ZnO-mesoporous CMI-1 silica nanocomposites prepared through the incorporation of ZnO nanoparticles inside the channels of a silica mesoporous material CMI-1. The incorporation was made by direct impregnation of the mesoporous material in a zinc nitrate aqueous solution followed by calcination. The PL spectrum of the nanocomposites presents a significant blue-shift corresponding to the enhancement of the semiconductor band gap. Being excited by incident photons with energy of 1.82 eV, the ZnO nanoparticles exhibit spontaneous emission due to the excitonic recombination. In our samples, spontaneous emission turns to stimulated emission when the pumping intensity reaches a threshold value. This effect implies a two-photon excitation which was never observed with ZnO nanoparticles. This paper deals with results about the characteristics of the matrix and the nanocomposites and the lasing effect. A two-photon excitation phenomenon has been observed.

Continuous-wave diode-pumped Yb:glass laser with near 90% slope efficiency

Room temperature highly efficient laser action from an ytterbium-doped phosphate glass is demonstrated when end pumped by a 975nm fiber-coupled laser diode. Laser slope efficiencies as high as 88% have been obtained, leading to pump-to-laser conversion efficiencies greater than 50%. From the analysis of pumping threshold and laser slope efficiencies the authors have determined both the optical losses and emission cross section at laser wavelength (1028nm).

Auger upconversion energy transfer losses and efficient 1.06 μm laser emission in Nd3+ doped fluoroindogallate glass

In addition to efficient continuous wave laser action at 1.06 μm (4F3/2→4I11/2 transition), with a slope efficiency 30% and 30 mW pump power threshold, this work presents a throughout study of the spectroscopic, and thermo-optical properties of a 2.0 mol % Nd3+ doped fluoroindogallate glass. The characterization of the sample using the pump probe experimental technique indicated the presence of two broad excited state absorption bands from 0.94 to 1.05 μm (4F3/2→2D3/2, 2G9/2, 4G11/2, 2K15/2) and from 1.16 to 1.42 μm (4F3/2→4G9/2, 4G7/2, 2K13/2), found not to interfere with the stimulated emission at 1.06 μm, with a peak cross section value σSE = 2.55×10-21 cm2 and a full width at half maximum of 22 nm. Thermal lens measurements were performed to quantify the Auger upconversion parameter (γ=(1.26±0.09)×10-16 cm3/s) and evaluate the thermal loading in the sample in comparison to other commercial glasses.

Chiroptical Properties Induced in Chiral Photonic‐Bandgap Liquid Crystals Leading to a Highly Efficient Laser‐Feedback Effect

Highly efficient lasing action is obtained by exploiting the chiroptical characteristics of the ground and excited states of an achiral fluorescent dye doped in a cholesteric liquid crystal (CLC) medium (see figure). The highly efficient lasing action from the oblique dye-doped CLC cell is produced by tuning the ellipticity angle of the excitation beam while taking into consideration the molecular helical sense of the cholesteric host.

Efficient tunable diode-pumped Yb:LYSO laser

We demonstrated efficient laser action of a new ytterbium-doped oxyorthosilicate crystal Yb:LuYSiO(5) (Yb:LYSO) under high-power diode-pumping. The spectroscopic features and laser performance of the alloyed oxyorthosilicate crystal are compared with those of ytterbium-doped lutetium and yttrium oxyorthosilicates. In the continuous-wave laser operation of Yb:LYSO, a maximal slope efficiency of 96% and output power of 7.8 W were respectively achieved with different pump sources. The Yb:LYSO laser exhibits not only little sensitivity to the pump wavelength drift but also a broad tunability. By using a dispersive prism as the intracavity tuning element, we demonstrated that the continuous-wave Yb:LYSO laser exhibit a continuous tunability in the spectral range of 1014-1091 nm.

Efficient laser action of Yb:LSO and Yb:YSO oxyorthosilicates crystals under high-power diode-pumping

We report here on the efficient laser action of a new Yb-doped crystal Yb3+:Lu2SiO5 (Yb:LSO) under high power diode-pumping (15 W). Its performances were compared to another Yb-doped crystal belonging to the oxyorthosilicate family: the Yb:YSO. For both crystals, more than 7 W of laser radiation around 1 μm was obtained under 14.4 W of incident pump power at 978 nm, leading to high optical conversions of more than 50%. Finally, both crystals demonstrate little sensitivity to pump wavelength drift and exhibit broad tunability at a multiwatt level (more than 4 W over 50 nm and 60 nm, respectively for Yb:LSO and Yb:YSO).

74% Slope efficiency from a diode-pumped Yb3+:LiNbO3:MgO laser crystal

An optimization of the laser action performance from a diode-pumped Yb3+-doped LiNbO3:MgO crystal has been carried out. In this sense, efficient laser action at 1.06 μm when pumping with a fiber-coupled laser diode at 980 nm has been demonstrated, achieving laser slope efficiencies as high as 74%. The influence of output mirror transmittance on both pumping threshold and laser slope efficiency has been investigated, and the parameters of relevance in laser dynamics (emission cross section and optical losses) have been determined. Under the experimental conditions leading to maximum slope efficiency, the pump power at threshold was 300 mW, and the pump-to-laser conversion efficiency was 40%.

Spectroscopy and efficient laser action from diode pumping of a new broadly tunable crystal: Yb^3+:Sr_3 Y(BO_3)_3

The first demonstration of laser action in a Yb3+:Sr3Y(BO3)3 crystal is reported. This new material exhibits particularly broad absorption and emission bandwidths (6 and 60 nm, respectively) and hence is of particular interest for diode-pumped femtosecond and tunable laser sources. Efficient operation from diode pumping (1.4 W of cw laser power obtained with 3.6 W of diode pump power and as much as 3.4 W of peak power from high-power quasi-cw pumping) together with smooth tunability (over 50 nm FWHM) is reported. For the comparison, efficiency and thermal limitations of Yb:glass and Yb:Ca4GdO(BO3)3 have been investigated under the same conditions.

An efficient lasing action from pyrromethene 556 dye-doped organically modified silicates

Organically modified solid-state silicates (ORMOSILS) doped with a new laser dye 1,3,5,7,8-pentamethylpyrromethene-2,6-disulfonate–BF2 complex (pyrromethene 556) have been synthesized by a sol–gel method and the compositional effects on pore characteristics, fluorescence and lasing properties have been investigated. It is found that the use of dimethylsulfoxide and γ-glycidoxypropyltrimethoxysilane could greatly change the structure properties of sol–gel derived ORMOSILS cage, and thus the fluorescence and lasing properties of the materials could improve significantly. A successful laser oscillation from this dye-doped ORMOSILS sample has been achieved upon pumping with a Q-switched frequency-doubled Nd:YAG laser at 532nm. A slope efficiency of 54% with a useful lifetime greater than 10,000 shots has been demonstrated at a pump repetition rate of 1Hz and a pump intensity of 1J/cm2 by using the new ORMOSILS cage on our newly designed laser system. Our results have shown that it is possible to obtain a high-efficiency with a long-lifetime for a compact new laser device by low cost dye-doped solid-state ORMOSILS.

Efficient and stable dye laser action from modified dipyrromethene BF2 complexes

We report on the lasing action of modified dipyrromethene BF2 complexes in air-equilibrated liquid solutions. All recent dyes share a common chromophore core and were dissolved in apolar, polar nonprotic, and polar protic solvents. When pumped transversely at 534 nm, nearly solvent-independent laser emission was obtained with efficiencies well over 40% in most cases. Highest lasing efficiency was 59%. Under continuous ultraviolet irradiation some of these dyes demonstrated improved photostability as compared with commercial dye pyrromethene 567.

Novel class of pyrylium dyes with high efficiency in lasing and two-photon absorption fluorescence

We report the synthesis of a promising class of pyrylium dyes concerning laser and two-photon absorption action. Three representatives of this class, 4-(2,4-dichlorophenyl)-2,6-bisphenylpyrylium tetrafluoroborate, 4-phenyl-2,6-bis(4-methoxyphenyl)pyrylium tetrafluoroborate, and 4-(2,4-dichlorophenyl)-2,6-bis(4-biphenyl)pyrylium tetrafluoroborate, were investigated. Each dye was synthesized by a convenient and inexpensive method. Efficient laser action was shown at ∼500, ∼560, ∼615 nm. Changing the conjugation length i.e. the length of the oligophenyl moiety, or introducing various substituents on the aromatic rings, the emission maximum can be controlled. Two-photon absorption induced fluorescence was also observed. These pyrylium dyes constitute excellent candidates for laser technology and two-photon absorption applications.

Mechanism of efficient ultraviolet lasing in GaN/AlGaN separate-confinement heterostructures

We report the results of an experimental study on efficient laser action in an optically pumped GaN/AlGaN separate-confinement heterostructure (SCH) in the temperature range of 10–300 K. The lasing threshold was measured to be as low as 15 kW/cm2 at 10 K and 105 kW/cm2 at room temperature. Strongly polarized (TE:TM⩾300:1) lasing peaks were observed over the wavelength range of 358–367 nm. We found high-finesse lasing modes that originate from self-formed microcavities in the AlGaN and GaN layers. Through analysis of the relative shift between spontaneous emission and lasing peaks, combined with the temperature dependence of the lasing threshold, we conclude that exciton–exciton scattering is the dominant gain mechanism leading to low-threshold ultraviolet lasing in the GaN/AlGaN SCH over the entire temperature range studied. Based on our results, we discuss possibilities for the development of ultraviolet laser diodes with a GaN active medium.