Mechanically tunable organic vertical-cavity surface emitting lasers (VCSELs) for highly sensitive stress probing in dual-modes.

Herein, we report a straight forward stress probing method based on mechanically tunable organic VCSELs via dual detecting-modes. By designing the active layer thickness, uploaded stress was measured simultaneously by the laser wavelength and mode separations, facilitating highly sensitive stress detection in broad ranges. Single-mode laser emission with low threshold and narrow line-width was characterized, which could be tuned continuously within 8 nm. The probing sensitivity and resolution were estimated to be 60 Pa and 5.6 nm/KPa respectively, which were ~160-folds higher than previous results.

Straightforward synthetic protocol for the introduction of stabilized C†nucleophiles in the BODIPY core for advanced sensing and photonic applications.

A straightforward synthetic protocol to directly incorporate stabilized 1,3-dicarbonyl C nucleophiles to the meso position of BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) is reported. Soft nucleophiles generated by deprotonation of 1,3-dicarbonyl derivatives smoothly displace the 8-methylthio group from 8-(methylthio)BODIPY analogues in the presence of Cu(I) thiophenecarboxylate in stoichiometric amounts at room temperature. Seven highly fluorescent new derivatives are prepared with varying yields (20-92%) in short reaction times (5-30 min). The excellent photophysical properties of the new dyes allow focusing on applications never analyzed before for BODIPYs substituted with stabilized C nucleophiles such as pH sensors and lasers in liquid and solid state, highlighting the relevance of the synthetic protocol described in the present work. The attainment of these dyes, with strong UV absorption and highly efficient and stable laser emission in the green spectral region, concerns to one of the greatest challenges in the ongoing development of advanced photonic materials with relevant applications. In fact, organic dyes with emission in the green are the only ones that allow, by frequency-doubling processes, the generation of tunable ultraviolet (250-350 nm) radiation, with ultra-short pulses.

First highly efficient and photostable E and C†derivatives of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) as dye lasers in the liquid phase, thin films, and solid-state rods.

A new library of E- and C-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivatives has been synthesized through a straightforward protocol from commercially available BODIPY complexes, and a systematic study of the photophysical properties and laser behavior related to the electronic properties of the B-substituent group (alkynyl, cyano, vinyl, aryl, and alkyl) has been carried out. The replacement of fluorine atoms by electron-withdrawing groups enhances the fluorescence response of the dye, whereas electron-donor groups diminish the fluorescence efficiency. As a consequence, these compounds exhibit enhanced laser action with respect to their parent dyes, both in liquid solution and in the solid phase, with lasing efficiencies under transversal pumping up to 73 % in liquid solution and 53 % in a solid matrix. The new dyes also showed enhanced photostability. In a solid matrix, the derivative of commercial dye PM597 that incorporated cyano groups at the boron center exhibited a very high lasing stability, with the laser emission remaining at the initial level after 100 000 pump pulses in the same position of the sample at a 10 Hz repetition rate. Distributed feedback laser emission was demonstrated with organic films that incorporated parent dye PM597 and its cyano derivative. The films were deposited onto quartz substrates engraved with appropriate periodical structures. The C derivative exhibited a laser threshold lower than that of the parent dye as well as lasing intensities up to three orders of magnitude higher.

Blue-to-orange color-tunable laser emission from tailored boron-dipyrromethene dyes.

A series of meso-substituted boron-bipyrromethene (BODIPY) dyes are synthesized and their laser and photophysical properties systematically studied. Laser emission covering a wide visible spectral region (from blue to orange) is obtained by just changing the electron donor character of the heteroatom at position 8. The additional presence of methyl groups at positions 3 and 5 results in dyes with a photostability similar to that of the unsubstituted dye but with much improved efficiency. Correlation of the lasing properties of the different dyes to their photophysical properties provides inklings to define synthetic strategies of new BODIPY dyes with enhanced efficiency and modulated wavelength emission over the visible spectral region.

Synthesis and optical and redox properties of symmetric and asymmetric BODIPYs.

Herein, we present the synthetic route and the photophysical, electrochemical as well as laser properties of novel red-emitting boron-dipyrromethenes (BODIPYs) bearing arylethyne moieties. Such functionality is added along the main axis of the chromophore leading to single- and double-substituted derivatives. The relationship between the dye structure and the lasing properties is studied in detail with the help of the photophysical and electrochemical properties as well as quantum mechanical simulations. The asymmetric substitution of the parent dye induces inhomogeneities in the charge distribution, which leads to an overall loss of the fluorescence capacity, mainly in polar media. Such non-radiative deactivation processes can be softened by decreasing the electron-donor ability of the substituent or even avoided by symmetrical substitution. Thus, grafting of the arylethyne moieties at the longitudinal axis of the indacene core results in an effective strategy to develop red-edge BODIPYs with highly efficient and photostable laser emission.

Click assembly of dye-functionalized octasilsesquioxanes for highly efficient and photostable photonic systems.

New hybrid organic-inorganic dyes based on an azide-functionalized cubic octasilsesquioxane (POSS) as the inorganic part and a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BDP) chromophore as the organic component have been synthesized by copper(I)-catalyzed 1,3-dipolar cycloaddition of azides to alkynes. We have studied the effects of the linkage group of BDP to the POSS unit and the degree of functionalization of this inorganic core on the ensuing optical properties by comparison with model dyes. The high fluorescence of the BDP dye is preserved in spite of the linked chain at its meso position, even after attaching one BDP moiety to the POSS core. The laser action of the new dyes has been analyzed under transversal pumping at 532 nm in both the liquid phase and when incorporated into solid polymeric matrices. The monosubstituted new hybrid dye exhibits high lasing efficiency of up to 56 % with high photostability, with its laser output remaining at the initial value after 4×10(5) pump pulses in the same position of the sample at a repetition rate of 30 Hz. However, functionalization of the POSS core with eight fluorophores leads to dye aggregation, as quantum mechanical simulation has revealed, worsening the optical properties and extinguishing the laser action. The new hybrid systems based on dye-linked POSS nanoparticles open up the possibility of using these new photonic materials as alternative sources for optoelectronic devices, competing with dendronized or grafted polymers.

New 8-amino-BODIPY derivatives: surpassing laser dyes at blue-edge wavelengths.

The development of highly efficient and stable blue-emitting dyes to overcome some of the most important shortcomings of available chromophores is of great technological importance for modern optical, analytical, electronic, and biological applications. Here, we report the design, synthesis and characterization of new tailor-made BODIPY dyes with efficient absorption and emission in the blue spectral region. The major challenge is the effective management of the electron-donor strength of the substitution pattern, in order to modulate the emission of these novel dyes over a wide spectral range (430-500 nm). A direct relationship between the electron-donor character of the substituent and the extension of the spectral hypsochromic shift is seen through the energy increase of the LUMO state. However, when the electron-donor character of the substituent is high enough, an intramolecular charge-transfer process appears to decrease the fluorescence ability of these dyes, especially in polar media. Some of the reported novel BODIPY dyes provide very high fluorescence quantum yields, close to unity, and large Stokes shifts, leading to highly efficient tunable dye lasers in the blue part of the spectrum; this so far remains an unexploited region with BODIPYs. In fact, under demanding transversal pumping conditions, the new dyes lase with unexpectedly high lasing efficiencies of up to 63 %, and also show high photostabilities, outperforming the laser action of other dyes considered as benchmarks in the same spectral region. Considering the easy synthetic protocol and the wide variety of possible substituents, we are confident that this strategy could be successfully extended for the development of efficient blue-edge emitting materials and devices, impelling biophotonic and optoelectronic applications.

Development of excellent long-wavelength BODIPY laser dyes with a strategy that combines extending π-conjugation and tuning ICT effect.

By comparison and combination of two strategies, extending π-conjugation and tuning Intramolecular Charge Transfer (ICT) effect, new long-wavelength BODIPY dyes have been efficiently synthesized. The new chromophores exhibit good optical properties: high fluorescence quantum yields, exceptionally large molar extinction coefficients, narrow red-emission bands, and relatively large Stokes shifts etc., in polar or apolar solvents. Besides, the new dyes, under transversal pumping at 532 nm, exhibit highly efficient and stable laser emission tunable from the green to NIR spectral region (570-725 nm). Moreover, one of these new BODIPY derivatives shows cell membrane permeability and bright intracellular red fluorescence. These advantageous characteristics assure the potential of these dyes for biophotonic applications.

Difluoro-boron-triaza-anthracene: a laser dye in the blue region. Theoretical simulation of alternative difluoro-boron-diaza-aromatic systems.

The synthesis, photophysical and laser properties of a difluoro-boron-triaza-anthracene (BTAA) compound are analyzed in the present paper. The molecular structure of this dye is an anthracene-like core with N atoms at 4a, 9 and 10a positions where two of them (4a and 10a) are linked through a BF(2)-bridge group. This structure is reminiscent of aza-BODIPY dye with an s-indacene core, BODIPY being one of the most commonly used laser dye family in the Vis region. The main absorption and emission bands of the new dye are localized in the blue part of the Vis region of the electromagnetic radiation, a spectral region practically unexploited by the BODIPY chromophore. Moreover, the new dye presents a higher laser efficiency and photostability than other commercial laser dyes operating in the same spectral region. In order to look for new molecular structures with potential laser emission covering the whole Vis spectral region, the spectroscopic properties of other different chromophoric systems based on BF(2)-linking aromatic groups are theoretically simulated by quantum mechanical calculations.

Controlling optical properties and function of BODIPY by using asymmetric substitution effects.

Asymmetrically substituted BODIPY analogues of the dye PM567 have been synthesised from 2-acylpyrroles and pyrroles that bear indene, fluorene or difluorene units. The type of linkage between the fluorene and the BODIPY core plays an important role in the photophysics of the BODIPY chromophore. Indeed, an aliphatic bridge gives rise to an energy-transfer process between the chromophores, whereas a vinyl spacer allows an electronic interaction between them, leading to a large red shift of the spectral bands. The laser action of the new dyes has been analysed under transversal pumping at 10 Hz repetition rate, in both liquid phase and incorporated into solid polymeric matrices. Lasing efficiencies of up to 40% were reached with high photostabilities with the laser output remaining at the initial level after 1×10(5) pump pulses in the same position of the sample. The laser action of the new dyes outperforms the laser behaviour of commercial dyes that emit in the same spectral region. The replacement of fluorene by indene quenches the fluorescence and laser emission, but allows the development of an iron cation fluorescent sensor.

Conventional unidirectional laser action enhanced by dye confined in nanoparticle scatters.

The synthesis, structural characterization, and lasing properties of new dye-sensitized organic scattering gain medium based on Rhodamine 6G (Rh6G) confined in polymeric nanoparticles are reported. We have demonstrated coherent laser action from amplifying random media using dye confined into polymeric nanoparticles as scattering centers and gain media. Lasing efficiency and photostability were significantly enhanced by nonresonant feedback of the emission by multiple scattering.

Efficient red-edge materials photosensitized by Rhodamine 640.

We report on tunable, highly efficient and photostable solid-state dye laser emitting around 640 nm based on Rhodamine 640 incorporated into homopolymers, linear and cross-linked copolymers, and silicon-modified organic matrices. The effect on the lasing properties of both dye concentration and environmental conditions was analyzed. Under transversal pumping at 532 nm with 5.5 mJ/pulse, high-lasing efficiencies of up to 42% were recorded. The laser operation was highly stable with a drop in the laser output of approximately 20% after 100 000 pump pulses at the same position of the sample at 10 Hz repetition rate. To the best of our knowledge, these results are the topmost achieved to date for organic, inorganic, and hybrid materials doped with rhodamine 640. When the samples were incorporated into a grazing-incidence grating oscillator, narrow-line-width operation with tunning ranges of up to 40 nm was obtained.

Synthesis, photophysical properties, and laser behavior of 3-amino and 3-acetamido BODIPY dyes.

The asymmetrically substituted BODIPY dyes 9a and 9b have been synthesized through a key redox step involving the alpha-nitroso derivative of the starting pyrrol. Both dyes emit fluorescence with quantum yields of ca. 0.7, but only 8b behaves as a good laser dye, with an efficiency of 48% in ethanol solution.

On-line laser radiation controlled to the removal of adhesive on teeth after bracket debonding.

BACKGROUND AND AIMS: After bracket debonding a correct removal of the adhesive from tooth surfaces without causing any iatrogenic damage to the enamel is needed. However, conventional techniques do not allow a selective removal process. The present article focuses on the removal of adhesive on teeth after bracket debonding by using laser radiation at 355 nm (third harmonic wavelength of a Q-switched Nd:YAG). MATERIAL AND METHODS: Brackets were bonded to 10 extracted human premolars from young patients and removed after a storage period of 2 months. As real-time diagnostic technique, laser-induced breakdown spectroscopy (LIBS) elemental analysis was applied for precisely controlling the removal of the adhesive and morphological analysis of the etched surfaces was carried out by scanning electron microscopy (SEM). RESULTS: LIBS technique allowed an on-line precise control in the adhesive removal process. SEM analysis revealed the capability of the 355 nm UV laser radiation to complete the removal of the adhesive on the tooth with no signs of damage on the enamel. CONCLUSION: Laser ablation process at 355 nm monitored by the LIBS technique allows to carry out efficient removal of the adhesive on teeth.

In vitro evaluation of Nd:YAG laser radiation at three different wavelengths (1064, 532, and 355 nm) on calculus removal in comparison with ultrasonic scaling.

OBJECTIVE: The aim of this study was to investigate the effectiveness of laser treatment for calculus removal at different wavelengths and compare it with that of ultrasonic scaling (US). BACKGROUND DATA: Conventional methods of treatment of periodontal tissues can be limited by morphology, root anatomy, and the periodontal pocket. In the search for an effective therapy to achieve a biocompatible root surface, laser treatment appeared in the field of periodontology. METHODS: Radiation from a Nd:YAG laser operating at the fundamental (1064 nm), second harmonic (532 nm) and third harmonic (355 nm) wavelengths was used for calculus removal. Environment scanning electron microscopy (ESEM) was used for the morphological analysis of the treated surfaces. The wavelength dependence of the ablation thresholds for calculus and cementum was evaluated by applying a photoacoustic technique. RESULTS: US achieved complete calculus removal, leaving a smooth and regular surface in a more efficient way than laser treatment. ESEM examination and photoacoustic methods confirmed a nonselective removal of material that entails partial cementum ablation of the root surface with the laser treatment. CONCLUSION: UV radiation at 355 nm can constitute an adjunctive therapy to US, by eliminating toxic agents and the contaminated layer of cementum.

Circularly polarized laser emission induced in isotropic and achiral dye systems.

The production of efficient, tunable, and switchable circularly polarized laser emission would have far reaching implications in optical communications or biophotonics. In this work, it is demonstrated the direct generation of circularly polarized (CP) laser emission in achiral and isotropic dye laser systems without the use of extracavity polarizing elements, and without resorting to chiral dyes, chiral liquid crystal matrices, or interferometric methods. The origin of this ellipticity arises from the dynamic birefringence induced by the strong and polarized laser pumping and the subsequent orientation anisotropy of the excited molecular dipoles. A complete polarimetric characterization of the polarization state of conventional dye laser oscillators as a function of different experimental parameters is performed and it is shown that the generated light always possesses a certain level of circularity that changes in a distinctive way with pump energy and polarization. These results demonstrate that it is possible to generate and modulate CP laser light from efficient and photostable conventional laser dyes.

A borane laser.

Emission from electronically excited species forms the basis for an important class of light sources-lasers. So far, commercially available solution-processed blue-emitting laser materials are based on organic compounds or semiconductor nanocrystals that have significant limitations: either low solubility, low chemical- and/or photo-stability and/or uncompetitive prices. Here we report a novel and competitive alternative to these existing laser materials that is based on boron hydrides, inorganic cluster compounds with a rich and diverse chemistry. We demonstrate that solutions of the borane anti-B18H22 show, under pulsed excitation, blue laser emission at 406 nm with an efficiency (ratio of output/input energies) of 9.5%, and a photostability superior to many of the commercially available state-of-the-art blue laser dyes. This demonstration opens the doors for the development of a whole new class of laser materials based on a previously untapped resource for laser technology-the boranes.

Photophysical and laser properties of cassettes based on a BODIPY and rhodamine pair.

This work deals with the synthesis and the photophysical and laser properties of new BODIPY-rhodamine cassettes. These dyads differ in their rigid and conjugated spacer group (phenyl or acetylenephenyl) and in their linking positions (meta or para). The photophysical properties of these cassettes are controlled by the formation/opening of the spirolactone ring, which, in turn, switches off/on an energy-transfer process between the chromophores. Herein, we thoroughly describe the influence of the attached spacer group, as well as the distance and orientation between the donor-acceptor pair, on the excitation energy transfer. The observed fast dynamics and efficiency suggest that the process mainly takes place "through-bond", although the "through-space" mechanism also contributes to the whole process. As a result, efficient laser emission from the rhodamine is achieved upon excitation of the BODIPY, in particular for the cassette that contains an acetylenephenyl spacer group in a para disposition.

Reaction of amines with 8-methylthioBODIPY: dramatic optical and laser response to amine substitution.

A thorough study of the photophysical and laser properties of 8-aminoboron dipyrromethene dyes was undertaken to determine the role of amine substitution and spatial disposition on the properties of the dyes. It was found that the fluorescent and laser response varied significantly. Although primary amines give rise to highly fluorescent products at the blue edge of the visible region, secondary amines yield nonfluorescent analogues in polar media. The crystal structures of two analogues are reported and described. Steric hindrance and the higher electron-releasing ability of the amine favor the formation of a quenching intramolecular charge-transfer state. Accordingly, boron dipyrromethene derivatives with primary amines exhibited laser emission with efficiencies of up to 44%. Besides, the more efficient derivative was also the most photostable, leading to a significant improvement in the lasing performance with regard to previously reported 8-aminoboron dipyrromethene derivatives. An increase in the solvent polarity, and mainly the presence of tertiary cyclic amines, led to a dramatic decrease or even the loss of the laser action.

Influence of the light source and bleaching gel on the efficacy of the tooth whitening process.

OBJECTIVE: To examine the whitening efficacy of three whitening agents in combination with six different photoactivation systems. BACKGROUND: Bleaching techniques have achieved significant advances using photoactivation with coherent or incoherent radiation sources. METHODS: Quick White, Ena White Power, and Opalescence Endo bleaching agents, all containing 35% hydrogen peroxide, were stimulated with halogen lamp, light-emitting diode (LED), low-power diode laser, and neodymium: yttrium-aluminum-garnet (Nd:YAG), second harmonic of Nd:YAG, and Er:YAG lasers. One hundred twenty-six extracted human incisors were treated, and color change, pulpal temperature, and enamel morphological alterations were evaluated. RESULTS: Only the groups that were photoactivated using a diode laser, halogen lamp, and LED showed statistically significant differences (p < 0.005) in color change when compared with the control group (without photoactivation). All whitening protocols were safe with regard to the increase in pulpal temperature. Scanning electron microscopy showed no evidence of effects on the integrity of enamel. CONCLUSIONS: The source of irradiation is more relevant than the bleaching agent for efficient tooth whitening. In addition, photoactivation with LED was found to be the best choice: it yielded significant change in color with only a minor increase in pulpal temperature.