Production of highly aligned microfiber bundles from polymethyl methacrylate via stable jet electrospinning for organic solid-state lasers

The fabrication of micron-sized poly(methyl methacrylate) (PMMA) polymer optical fibers doped with rhodamine B as an organic dye is demonstrated. Highly aligned and defect-free fibers are fabricated by using the stable jet electrospinning (SJES) method and systematically varying critical parameters such as solvent type and polymer concentration. At optimal conditions, for example, a polymer concentration of 35 wt% of PMMA in butanone, ribbon-shaped fibers with a smooth surface and diameter of about 20 μm could be spun using SJES mode and deposited on a rotating drum as target in a highly aligned manner. Photoluminescence spectra of the doped fibers excited longitudinally and transversely with a laser show an excitation peak with full-width-at-half-maximum of only 5.05 nm and a low lasing threshold at a pump energy of 0.55 μJ, indicating that SJES could become a new source of amplified optics components or organic solid-state fiber lasers.     

Lab-on-a-chip with integrated optical transducers

Taking the next step from individual functional components to higher integrated devices, we present a feasibility study of a lab-on-a-chip system with five different components monolithically integrated on one substrate. These five components represent three main domains of microchip technology: optics, fluidics and electronics. In particular, this device includes an on-chip optically pumped liquid dye laser, waveguides and fluidic channels with passive diffusive mixers, all defined in one layer of SU-8 polymer, as well as embedded photodiodes in the silicon substrate. The dye laser emits light at 576 nm, which is directly coupled into five waveguides that bring the light to five different locations along a fluidic channel for absorbance measurements. The transmitted portion of the light is collected at the other side of this cuvette, again by waveguides, and finally detected by the photodiodes. Electrical read-out is accomplished by integrated metal connectors. To our knowledge, this is the first time that integration of all these components has been demonstrated.     

SnO2/SiO2 and Sn/Sb-oxide/SiO2 gel-derived composites. Part 1: Structural evolution from a Mössbauer study

The lasing photostability of the red perylimide dye (RPD) in various solid matrices was measured under frequency-doubled Nd:YAG laser excitation. The RPD: composite glass laser intensity decayed to 50% of its initial value after approximately 20,000 pump pulses of 13 mJ/pulse. The output of RPD:ormosil glass and RPD:PMMA glass lasers decayed to 50% of their initial value after 1,200 and 1,000 pump pulses of the same energy, respectively. For rhodamine-6G:silica-gel and rhodamine-6G:ormosil glass lasers, the 50% decay occurred already after 1,000 and 300 pulses, respectively. The decay was non-exponential, suggesting that the dye bleaching was not a single-photon process. The average laser output decay rates increased linearly with the pump energy. Singlet-singlet excited state absorption of the RPD dye in the solid matrices was also measured between 550 and 730 nm. At ～600 nm the cross section was ～2×10^?16 cm²/molecule. The excited-state absorption competes with the lasing, and is a main factor that limits the laser efficiency.     

Dual amplified spontaneous emission as evidence for superexciplex from the dye LD473

Pulsed laser excitation of certain laser dye solutions prepares the sample molecules in a condition, unavailable under steady state lamp excitation. Excited molecules in large concentration obtainable under intense pulse laser pumping appear to undergo superexciplex interaction in which two excited molecules form an association with a solvent molecule acting as a link. This paper shows some of the important features of such superexciplexes with LD473 dye molecule as a reference.     

Efficient Preparation of D2 Molecules in v=2 by Stimulated Raman Pumping

We report the preparation of D₂ molecules in v=2 level in molecular beam condition. A single longitudinal mode laser system was used for excitation of D₂ from (v=0, j=0) to (v=2, j=0) with the scheme of stimulated Raman pumping. An excitation efficiency of 25.2% has been achieved, which was determined by the scheme of resonance-enhanced multiphoton ionization. Dependence of relative excitation efficiency on laser energy has been measured. We found that the increasing rate of excitation efficiency became slower as pulse energy of Stokes laser increase, while the excitation efficiency still increases approximately linearly with pump pulse energies up to 60 mJ. The spectral line shapes of Raman transition was also measured at different laser energies and considerable dynamical Stark effect was observed. A single peak was found on the three dimension surface of relative excitation efficiency, indicating the process occurred in the present study is a process of stimulated Raman pumping instead of stimulated adiabatic Raman passage.     

Photostablity and amplified spontaneous emission in dye-activated new organic-inorganic hybrid material

This paper reports on the lasing action of some dyes (pyrromethene 597, pyrromethene 567 and Rhodamin B) incorporated into a new organic-inorganic hybrid material. The amplified spontaneous emission (ASE) was studied under 532 nm, laser excitation in transverse pumping configuration for the prepared rod samples. The influence of the dye concentration on the amplified spontaneous emission peak wavelengths, the output energies, the gain and the energy conversion efficiencies were studied. Relatively high efficiencies (up to ∼64%) were obtained with good photostabilities where a decrease to ∼30% of the initial amplified spontaneous emission output energy were observed after pumping by 60,000 shots at relatively high repetition rate (10 Hz) and energy (15 mJ).     

LASER MEDIATED RELEASE OF DYE FROM LIPOSOMES

Liposomes made from phospholipids and containing sulforhodamine dye (1-50 mM) have been irradiated with nanosecond and picosecond laser pulses. Individual liposomes were locally heated by laser absorption of dye dimers during a single laser pulse, and heating was sufficient to release the liposome contents. The extent of dye release produced by a single laser pulse was shown to be quantitatively dependent on several interdependent variables, including dye concentration, liposome size, laser excitation parameters and initial temperature of the dye-liposome system. Fluorescence lifetime data having three components have been obtained and analyzed in terms of three dye environments. Quantitative estimates support a photo-induced thermal mechanism for liposome lysis and release of its contents. These results may be useful for laser induced delivery of therapeutic agents or other applications of lasers in biological systems.     

PDMS 2D optical lens integrated with microfluidic channels: principle and characterization

In this paper, the fabrication and characterization of PDMS 2D-optical lenses are reported. These lenses are designed in order to improve the performance of fluorescent spectroscopy detection performed on a portable chip using optical fibers. The fabrication process of the PDMS layer is first detailed, and the patterns are then checked with a SEM. By comparing various interfacial structures, it is shown that the beam properties of the light coming out from the fiber can be modified depending on the lens curvature radius. As a consequence, for a constant dye concentration, the use of such lenses can increase the intensity of fluorescent response close to the fiber or far from the fiber, compared to the same design with a flat interface. This excitation improvement corresponding to a stronger response from the dye then consequently leads to around three times higher sensitivity of the on-chip detection method for fluorescent spectroscopy.     

The potential of laser-induced breakdown spectrometry for real time monitoring the laser cleaning of archaeometallurgical objects

In this work, an orthogonal double pulse (DP) laser-induced breakdown spectroscopy configuration as a diagnostic tool for the restoration of archaeometallurgical samples has been developed and evaluated. Although laser-induced breakdown spectroscopy has been extensively tested in this kind of applications, this study presents an alternative method in terms of controlling the laser cleaning process of metallic object as well as real time laser-induced breakdown spectroscopy monitoring of the emission signal of the ablated material (pollutants and the structural materials). Several experimental parameters such as interpulses delay time, second laser to target distance and second pulse energy delay have also been accomplished in ancient Alexandrian coins. An enhancement of the signal emission is observed when both cleaning and analyzing lasers are combined, while no spectra signal is achieved when both lasers are operating independently. The restoration of ancient object by means of both conventional and double pulse laser cleaning arrangements is also discussed.     

高荧光量子效率的分子分散型聚芴衍生物的放大自发发射特性

通过将掺杂剂单元用化学键接到聚芴的侧链上,实现了掺杂剂单元在高分子主体中的分子水平分散,开发了一种新型的基于掺杂剂/主体材料体系的分子分散型蓝光聚芴衍生物.与纯聚芴相比,这种新的分子分散型蓝光聚芴衍生物具有很高的荧光量子效率.以这种新的分子分散型蓝光聚芴衍生物为增益介质的激光器件,在Nd:YAG 355 nm脉冲激光泵浦下,获得了较好的放大自发发射光谱,阈值达到0.25 m J/(pulse cm2).从光物理的角度对薄膜的光学增益和光学损耗进行了定量运算和分析,经过拟合发现,当泵浦能量为0.06m J/pulse时,该聚芴衍生物增益系数可达23.08 cm-1,损耗系数为6.96 cm-1.优良的放大自发发射特性表明该聚芴衍生物是非常好的有机激光增益介质材料.     

双光子共振四波差频产生的真空紫外激光特性研究

The character of tunable Vacuum-Ultraviolet（VUV）laser generated by two-photon resonant four wave difference frequency mixing in Xenon was studied. The intense VUV laser was generated in the wavelength range of 151-171 nm using 6P［1/2,0］level of Xe atom as the two-photon resonant state. The pulse intensity of VUV laser was estimated to be 0.2 μJ,and the conversion efficiency relative to the wavelength-fixed laser was determined to be 0.1%. The line width of VUV laser was found to be 0.3 cm-1 from the laser-induced fluorescence spectrum of A-X（0,0）rotational line profiles of jet-cooled CO,which was much broader than those of the two employed dye lasers（0. 1 cm-1）,mainly due to the saturation broadening of Xe level by intense laser field. The dependencies of VUV intensity on Xe pressure and two dye laser intensities were also investigated in this experiment.     

Processing and Photostability of Pyrromethene 567 Polycerams

Polyceram materials are attractive hosts for laser dyes because they can have high optical transparencies, high laser damage thresholds, and the ability to tailor optical properties by varying the composition and synthetic routes. Pyrromethene 567 has been successfully incorporated within silica: polydimethylsiloxane (PDMS) Polycerams to obtain polishable, crack-free, transparent monoliths using the sol-gel process. Fluorescence photostability was measured by pumping with aQ-switched, frequency doubled Nd: YAG laser (532 nm) at a pulse rate of 10 Hz. Fluorescence intensity dropped to 50% after approximately 50,000 pulses at a fluence of 0.10 J/cm². UV degradation studies were performed on Polycerams with different polymer contents, and the absorption photostability is related to the solubility and type of caging of the dye.     

Polymer-filled nanoporous silica aerogels as hosts for highly stable solid-state dye lasers

New hybrid solid-state dye laser materials based on highly porous silica aerogels have been synthesized. The open porous network of the aerogel was saturated with laser dyes dissolved in appropriate organic monomers, and polymerization took place inside the silica structure. The resulting polymer-filled nanoporous aerogel (PFNPA) was cast in a cylindrical shape, forming monoliths that were used as gain media in solid-state dye lasers. When the PFNPA incorporated pyrromethene dyes, highly photostable laser emission with good lasing efficiency was obtained. Under the demanding conditions of tightly focused transversal pumping with 532 nm, 5 mJ pulses at 10 Hz repetition rate, the commercial dye Pyrromethene 567 exhibited laser action with only a 10% drop in the laser output after 10(6) pump pulses in the same position of the sample.     

Raman amplification spectroscopy using pulsed dye lasers

A picosecond laser system consisting of a mode-locked argon-ion laser synchronously pumping two dye lasers is used for studies of Raman amplification spectra. The two dye laser beams, one kept constant in frequency while the other is tunable, coincide in the Raman sample. Recording the gain or the loss in intensity of one of the lasers as a function of frequency difference produces the Raman spectrum. Good signal to noise ratios have been obtained for a variety of liquids and solids. Fluorescing samples can be studied in the Inverse Raman method where the loss on the higher frequency laser is monitored.     

Theoretical considerations of laser induced fluorescence and ionization spectrometry: how close to single atom detection

The potential capability of detecting single atoms and/or of approaching the intrinsic detection limit, i.e. the limit where all external causes of noise in the system are eliminated, is discussed with respect to laser induced fluorescence and ionization spectrometry. These approaches have been chosen because of their widespread use in laboratories involved in analytical laser spectroscopy. Among the lasers, tunable dye lasers pumped by N₂, Nd-YAG, Excimer, Cu vapor lasers and flashlamps are considered, and flames, graphite furnaces, plasmas and low pressure glow discharges are considered as atom reservoirs. From practical considerations, it is shown that none of the conventional analytical approaches used can satisfy the requirement of a true single atom detection technique, the only exception being provided by the ionization method coupled with atomization under vacuum.     

RAPID COMMUNICATION

Abstract— We show that the calcium fiuorophore Indo-1 can be excited by simultaneous absorption of three-photons at 885 nra, a wavelength readily available from Ti:sapphire lasers. Three-photon excitation was demonstrated by the emission intensity of Indo-1 which depended on the cube of the laser power, and by a higher anisotropy than was observed for two-photon excitation. Excitation of Indo-1 becomes a two-photon process when the wavelength is decreased to 820 nm. Three-photon excitation was accomplished at a low 17μ concentration of Indo-1. Examination of the spatial profile of the excited Indo-1 showed a smaller volume for three- versus two-photon excitation. These results suggest that three-photon excitation may be useful in fluorescence microscopy using the long wavelength output of Tksapphire lasers, and may provide higher spatial resolution than available using two-photon excitation.     

1．5μm波段连续单频光纤激光器的研究进展

连续单频光纤激光器在光纤通信、光纤传感、引力波探测、激光雷达、非线性频率转换、光谱学等领域有着广泛的应用前景,发展十分迅速．近20年来,1．5μm波段连续单频光纤激光性能不断提高,如激光线宽从兆赫兹到千赫兹、功率从毫瓦到近百瓦量级,但激光器的噪声抑制、放大线宽展宽、输出功率等仍有待进一步研究．本文回顾了获得1．5μm波段连续单频激光输出的关键技术,总结了本课题组基于磷酸盐玻璃光纤短腔Bragg反射（DBR）结构实现1．5μm波段连续单频光纤激光性能,以及单频激光功率放大的研究进展．     

Cooperative photoproduction of Xe2+Cl− in liquid Cl2/Xe solutions: Stimulated emission and gain measurements

Cooperative photogeneration of Xe₂⁺Cl⁻ can be accomplished by near UV laser excitation of Cl₂/Xe solutions with a high quantum efficiency. Gain measurements on the Xe₂⁺Cl⁻ (4²Γ) transition are reported. The liquid phase rare gas halides should be regarded as a family of ideal “dye” lasers.     

Studies of dyestuffs in fibres by Fourier Transform Raman spectroscopy

FT Raman spectroscopy is shown to be a powerful tool for the direct observation of low levels of dyestuffs in acrylic fibres. In the systems studied here, it is also found to yield more specific information than the complementary infrared technique. In contrast to conventional Raman spectroscopy with visible excitation, the near infrared laser used here does not induce fluorescence in the dye. Acrylic polymer bands can be efficiently subtracted to yield superbly detailed spectra of the dye in its physiochemical state in the fibre. The subtraction spectra provide valuable information on the nature of the dye and can be compared with spectra of pure dyes. Caution should be taken when subtracting spectra since small shifts in the frequency of the excitation laser line passing through the interferometer can generate artefacts in the final subtraction spectrum.     

Stark quantum beat spectroscopy: The vibrational dependence of the dipole moment in the A1Σ+ state of BaO

The method of quantum beat spectroscopy following pulsed dye laser excitation is applied to measure electric field splittings in excited states of the ¹³⁸Ba¹⁶O molecule. Stark quantum beats were observed in the fluorescent decay of the A¹Σ⁺ (ν′ = 0, 1, 2, 3, J′ = 1) states. From the observed beat frequencies values of electric dipole moments in different vibrational states were derived. The results are: μ(ν′ = 0) = 2.98(7) D, μ(ν′ = 1) = 2.66(7) D, μ(ν′ = 2)3.15(8) D and μ(ν′ = 3) = 3.18(8) D.