Linear and cross-linked polymeric solid-state dye lasers based on 8-substituted alkyl analogues of pyrromethene 567

The lasing properties of analogues of the commercial laser dye pyrromethene 567 (PM567) incorporated (dissolved or copolymerized) into polymeric matrices have been studied using both linear and cross-linked methyl methacrylate-based copolymers with different degrees of functionalization. All synthesized dyes have the chromophore core of PM567 but with an ω-acyloxypolymethylene chain at position 8. In general, the new materials exhibited laser emission with higher efficiencies and much higher photostabilities than those containing the commercial dye PM567 under the same experimental conditions. Lasing efficiencies of up to 40% were obtained under transversal pumping at 534 nm. The highest photostabilities, with the laser output remaining stable or dropping by less than 15% after 100 000 pump pulses at the same position of the sample, were reached in cross-linked materials with dyes covalently linked to the polymeric chains. When the polymeric samples were incorporated into a grazing-incidence grating oscillator, narrow-line-width operation with tuning ranges of up to 40 nm was obtained. These results show that efficient and photostable solid-state dye lasers competitive with their liquid counterparts can be developed by adequate chemical modifications in the dye molecules, as well as by the selection of appropriate polymeric formulations.     

Efficient and highly photostable solid-state dye lasers based on modified dipyrromethene.BF2 complexes incorporated into solid matrices of poly(methyl methacrylate)

We report on the laser action of modified dipyrromethene.BF₂ complexes both dissolved in poly(methyl methacrylate) and copolymerized with methyl methacrylate. All recently synthesized dyes have the chromophore core of laser dye pyrromethene 567, differing in the substituent in position 8. The new dyes showed important and most significant increases in both lasing efficiency and photostability. When the laser samples were pumped transversely at 534 nm, laser emission was obtained with efficiencies of over 30% in most cases, to be compared with a lasing efficiency of 12% exhibited by reference dye pyrromethene 567 under the same experimental conditions. Some of the materials exhibited highly photostable laser action, with no sign of degradation in the laser output after 60000 pump pulses at the same position of the sample at a repetition rate of 10 Hz, whereas the laser emission of reference dye pyrromethene 567 dropped to zero after less than 40000 pump pulses. Received: 19 November 2002 / Revised version: 20 February 2003 / Published online: 9 April 2003 RID="*" ID="*"Corresponding author. Fax: +34-91/564-2431, E-mail: acostela@iqfr.csic.es     

Laser performance of pyrromethene 567 dye in solid matrices of methyl methacrylate with different comonomers

Laser performance of pyrromethene 567 (PM567) dye dissolved in pure poly(methyl methacrylate) homopolymer and its copolymers with 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, 1-vinyl-2-pyrrolidone, 2-phenoxyethyl acrylate, and 2,2,2-trifluoromethyl methacrylate has been investigated. The chosen monomers were selected to mimic solvents used in a previous study on the photophysical and lasing properties of PM567 in liquid solution in order to establish correlations between the lasing properties of PM567 in liquid and solid solutions. The vol/vol proportion of the different comonomers in each copolymer formulation was systematically varied, and the effect of each composition on the lasing properties of PM567 was evaluated. The laser samples were transversely pumped at 534 nm with 5.5-mJ pulses from a frequency-doubled Q-switched Nd:KGW laser. Lasing efficiencies of up to 30% and good photostabilities, with a drop of the initial laser output of 20% after 10000 pump pulses in some of the solid samples, were demonstrated. Received: 2 June 1999 / Revised version: 18 July 1999 / Published online: 3 November 1999     

Laser emission from mixtures of dipyrromethene dyes in liquid solution and in solid polymeric matrices

Laser emission from binary mixtures of different dyes both in liquid solution and incorporated into solid polymeric matrices, covering the spectral region from green to red, is investigated. Mixtures of two synthesized dyes, analogs of the commercial dye Pyrromethene 567 (PM567), allowed covering the spectral range from green to orange. Tuning ranges in solid state of up to 42 nm with good photostabilities were demonstrated. To extend the tuning range to the red, binary mixtures of the dyes Pyrromethene 597 (PM597)/Pyrromethene 650 (PM650), PM567/DCM, and PM597/DCM were also studied. In liquid solution, a mixture of dyes PM567 and DCM allowed for narrow-linewidth laser emission continuously tunable over a range of 85 nm. In solid-state, mixtures of dyes PM597 and PM650 allowed laser emission tunable over two separate spectral regions up to a wavelength of 619 nm.     

Photophysical properties and laser characteristics of a new rigid aminocoumarin dye lasing in the blue-green region

The photophysical properties of a new dye, 7-Diethyl AminoCoumarin with a Rigid substitution in the 3-position (referred to as DARC) have been studied in three solvents: dioxane, DMF and DMSO. The dye has been found to have a fluorescence quantum efficiency (_fl) between 0.40 and 0.80 in these solvents. The dye-laser performance of this dye has also been investigated in dioxane, DMF and DMSO, under nitrogen-laser pumping and compared with that of the commercially available standard laser dye, Coumarin 515 (C-515). A tuning range of nearly 70 nm was obtained in the blue-green region with an efficiency up to 80% of that of the standard dye. The observed characteristics of the dye are explained in terms of the sructural rigidization of the dye in the 3-position which inhibits the formation of the Twisted Intramolecular Charge Transfer (TICT) conformation in the excited state leading to an enhancement of the _fl and a considerable improvement in the laser performance.Research carried out at U.D.C.T., Bombay, India     

Two-photon absorption-induced optical properties of a new lasing dye in two solvents

Pumped by an infrared lasing and its frequency-doubling source, the fluorescence and superradiance emission properties of a new lasing dye trans-4-[4^′-(N,N-diethylamino)styryl]-N-methyl pyridinium methyl sulfate (abbreviated DEASPS), have been studied in benzyl alcohol and chloroform. The two-photon absorption (TPA) and emission properties of DEASPSare influenced by the solvents used. The emission wavelength of the dye in benzyl alcohol is redshifted relative to that in chloroform. The lifetime of two-photon absorption-induced fluorescence is about 529 ps in benzyl alcohol, whereas it is 340 ps in chloroform. Correspondingly, the one-photon-excited fluorescence lifetimes in the two solvents are also given. The upconversion efficiency of DEASPS in chloroform is higher than in benzyl alcohol. Finally, the effective molecular two-photon absorption cross-sections were measured by the nonlinear transmittance method. It is found that the optical limiting effect of the dye in benzyl alcohol is stronger than that in chloroform. Received: 3 May 2001 / Revised version: 6 July 2001 / Published online: 19 September 2001     

High efficiency lasing of a dye-doped polymer laser with 1.06 μm pumping

For the first time, tunable lasing from a dye laser with an active polymer medium has been obtained using 1.06 μm pumping. The conversion efficiency of 43% and the tunable range of Δλ=63 nm have been reached with the use of polymethine dye in a polyurethane matrix. Received: 20 April 2001 / Revised version: 16 July 2001 / Published online: 19 September 2001     

Photophysical and lasing properties of pyrromethene 567 dye in solid poly(trifluoromethyl methacrylate) matrices with different degrees of crosslinking

The effect of increasing the rigidity of the host matrix by controlled crosslinking of the polymeric chains on the lasing and photophysical properties of pyrromethene 567 (PM567) was evaluated. To this end, the dye was dissolved in 2,2,2-trifluoromethyl methacrylate (TFMA) together with different amounts of the crosslinking monomer ethylene glycol dimethacrylate (EGDMA). Increasing the concentration of this crosslinker monomer resulted in significant increases in both lasing efficiency and photostability. Good correlation between fluorescence and lasing properties has been observed, indicating the existence of an optimum degree of crosslinking for which lasing efficiency and photostabilty reach their highest values. These new solid materials show lasing efficiencies up to 18% when transversely pumped at 534 nm and good photostabilities, with a decrease in the initial laser output of 45% after 10000 pump pulses. Received: 16 February 2001 / Revised version: 9 April 2001 / Published online: 8 June 2001     

Studies on laser action from polymeric matrices doped with coumarin 503

Received: 20 December 1997/Revised version: 10 February 1998     

Structural influence of the inorganic network in the laser performance of dye-doped hybrid materials

We report a systematic study of the influence on the laser action of Rhodamine 6G (Rh6G) of the composition and structure of new hybrid matrices based on 2-hydroxyethyl methacrylate (HEMA) as organic monomer and different weight proportions of dimethyldiethoxysilane (DEOS) and tetraethoxysilane (TEOS) as inorganic part. We selected mixtures of di- and tetra-functionalized alkoxides trying to decrease, in a controlled way, the rigidity of the three-dimensional network by making use of the flexibility provided by the linear chains acting as a spacer of the inorganic domains. The organization of the molecular units in these nanomaterials was studied through a structural analysis by solid-state NMR. The different reactivity exhibited by di- and tetra-functionalized silanols generates a non-homogeneous tri-dimensional network. Thus, the laser performance in dye-doped hybrid materials is improved when the inorganic phase is composed of a unique alkoxide.This revised version was published online in August 2005 with a corrected cover date.     

Laser properties of a new average-power Nd-doped phosphate glass

The Nd-doped phosphate laser glass described herein can withstand 2.3 times greater thermal loading without fracture, compared to APG-1 (commercially available Average-Power Glass from Schott Glass Technologies). The enhanced thermal loading capability is established on the basis of the intrinsic thermomechanical properties (expansion, conduction, fracture toughness, and Young's modulus), and by direct thermally induced fracture experiments using Ar-ion laser heating of the samples. This Nd-doped phosphate glass (referred to as APG-t) is found to be characterized by a 29% lower gain cross section and a 25% longer low-concentration emission lifetime. Other measurements pertaining to the concentration quenching, thermal lensing, and saturation of the extraction are also described in this article. It is note-worthy that APG-t offers increased bandwidth near the peak of the 1054 nm gain spectrum, suggesting that this material may have special utility as a means of generating and amplifying ultrashort pulses of light.     

Optical properties of dye-doped zirconia films by spectroscopic ellipsometry

The optical properties of zirconia films doped with rhodamine 6G and oxazine 725 by the sol-gel process were investigated using spectroscopic ellipsometry (SE). Accurate refractive index n and the extinction coefficient k were determined using a three-oscillator classical Lorentz model in the wavelength range of 300-800 nm. The derived refractive index of dye-doped films exhibited anomalous dispersion in the absorption region. Wavelength tunable output lasing action yellow and near-infrared wavelength region was achieved by DFB configuration using zirconia films doped with R6G and oxazine 725.     

Single-longitudinal-mode selection in a nanosecond-pulsed dye laser

We investigate the dynamics of the excited-state population, the cavity photon number, and the spectrum of an optically pumped nanosecond-pulsed dye laser containing bandwidth-narrowing elements in the cavity. We show that, in order to achieve single-mode operation, the pump-pulse duration has to be long enough and the dye concentration sufficiently high. This is partly due to the frequency shift of the laser spectrum during the decrease of the excited-state population towards its steady-state value. We demonstrate a single-mode dye laser, where single-mode selection is realised with the aid of an intracavity Fox–Smith interferometer. In this way we have obtained 5-ns-long pulses at the wavelength of 590 nm with a pulse energy of 6 mJ and a spectral width of 100 MHz (FWHM). Received: 3 December 2001 / Published online: 14 March 2002     

Distributed-feedback laser actions in zirconia-ORMOSIL waveguides based on energy transfer between co-doped laser dyes

Laser dyes such as pyrromethene 567 (PM567), perylene red (P-red) and coumarin 540A (C540A) were doped into zirconia-organically modified silicate (ORMOSIL) materials prepared by low temperature sol-gel technique. Narrow line-width distributed feedback (DFB) laser actions were induced in the PM567 and/or P-red doped sol-gel planar waveguide. Tuning of the output wavelength was achieved by varying the period of the gain modulation generated by a nanosecond Nd:YAG laser at 532 nm. Compared with those of PM567 and P-red solely doped thin films, tuning range of C540A, PM567 and P-red co-doped sol-gel planar waveguide was greatly extended, from 564.5 nm to 635.1 nm.     

Spectroscopic characterisation of LaGaO3:Er3+ crystals

LaGaO₃ crystals doped with Er³⁺ ions were grown by the Czochralski method and their optical properties were examined. The Er³⁺ energy levels have been determined from the low-temperature absorption and emission spectra. The results of Judd–Ofelt analysis are presented and compared with experimental data. The emission cross sections are determined for the ⁴ I _13/2→⁴ I _15/2 (1.55 μm) and ⁴ I _11/2→⁴ I _13/2 (2.85 μm) transitions of erbium. Received: 6 December 1999 / Revised version: 10 February 2000 / Published online: 27 April 2000     

Passive Q-switching at 1.54 μm of an Er–Yb: GdCa4O(BO3)3 laser with a Co2+: MgAl2O4 saturable absorber

We report, for the first time to our knowledge, efficient passive Q-switching of the 1.54-μm laser transition in an Er–Yb-doped crystalline medium. The laser configuration is a compact microchip design that is suitable for a range of practical applications such as range finding and lidar. The slope efficiency of 11.6%, pulse duration of 5–6 ns and average output power of 88 mW are all comparable with standard Er–Yb:glass lasers.     

Time-resolved thermal lens study on the heat dissipation effects in solid polymeric matrices used as laser dyes

A dual-beam pulsed-laser time-resolved thermal lens (TRTL) has been used to study the heat dissipation effects in solid polymers employed as laser dyes. The laser-dye samples studied are polymer solutions of rhodamine 6G (Rh6G), namely homopolymers of methyl methacrylate (MMA) and copolymers of methyl methacrylate and 2-hydroxyethyl methacrylate (HEMA) with MMA:HEMA compositions 1:1 and 7:3 vol./vol., where the dye is either dissolved or modified and copolymerized with methacrylate monomers. The long-term stability of the laser material is independent of the thermal diffusivity of the samples, as determined by the TRTL technique. This suggests that the rate of heat dissipation does not play a major role in the photostability of the samples. In contrast, the TRTL experiments have revealed permanent changes in the optical properties of the polymers when subjected to a large number of laser pulses. This is explained in terms of permanent plastic deformation of the matrices. Received: 19 June 2002 / Revised version: 1 August 2002 / Published online: 15 November 2002 RID="*" ID="*"Dedicated to Prof. S.E. Braslavsky on the occasion of her 60th birthday. This work was presented at the V Congreso de Fotoquímica, Torremolinos, Spain, 2001 RID="**" ID="**"Corresponding author. Fax: +34-93/205-6266, E-mail: s.nonell@iqs.es     

Cooperative up-conversion luminescence of ytterbium doped yttrium lanthanum oxide transparent ceramic

The up-conversion luminescence of Yb³⁺-doped yttrium lanthanum oxide transparent ceramic was investigated. It was ascribed to cooperative luminescence originated from the coupled states of the Yb³⁺ ion pairs. The proper doping of La₂O₃ can remove the cooperative luminescence of Yb³⁺ ion. But excessive La₂O₃ (at least 10 at.%) the cooperative up-conversion of Yb³⁺:Y₂O₃ is obtained again, and the intensity of up-conversion luminescence strengthens with the increase of La₂O₃ content.     

Efficient Pumping Scheme by Direct Excitation of Upper Laser Level in Nd:CNGG

We report an efficient pumping scheme which involves a direct excitation of the upper lasing level of a four-level laser in a Nd-doped Ca₃(NbGa)_2-xGa₃O₁₂ (Nd:CNGG) by using a tunable Ti:sapphire, 700-920nm, cw pump source. The slope efficiency is improved from 10.5% of the traditional band pumping at 808nm to 21.8% of the direct pumping at 882nm. The influence of pumping wavelength on lasing is discussed. We present a scheme of double pumping for lasing.     

Enhanced efficiency and extended wavelength range of dye lasers operated with DCM

It is observed that the efficiency of the DCM dye dissolved in ethylene glycol benzyl alcohol can be enhanced if the dye is preheated at a temperature of 150 °C. Peak powers as high as 1.5 W have been achieved with a single-mode ring dye laser at 640 nm when pumped by 9 W (all lines) from an argon-ion laser. The wavelength region has been also extended beyond both ends of the tuning curve compared to a conventionally prepared DCM dye. Received: 3 September 1999 / Revised version: 9 December 1999 / Published online: 23 February 2000