Direct comparison of infrared and ultraviolet wavelength matrix-assisted laser desorption/ionization mass spectrometry of proteins

In an effort to gain an understanding of the processes governing matrix-assisted laser desorption/ionization (MALDI), we made a direct comparison of ultraviolet (UV)- and infrared (IR)-MALDI linear time-of-flight mass spectra of proteins obtained from the same samples and matrices (on the same sample surface), using two different lasers, each having short duration (<10-ns) pulses, i.e., a tunable wavelength Nd:yttrium aluminum garnet (YAG) pumped optical parametric oscillator laser operating at 2.94 µm and a Nd:YAG laser operating at 355 nm. We observed that (1) the IR-MALDI and UV-MALDI spectra of a given protein from the same matrix were strikingly similar; (2) protein ions produced by IR-MALDI experienced less fragmentation than those produced by UV-MALDI; and (3) photochemical adducts produced during UV-MALDI were absent in IR-MALDI. These results lead us to speculate on the mechanisms for the ionization process in UV- and IR-MALDI. Because photons with a wavelength of ～3 µm are unlikely to effect electronic excitation of the matrix at the irradiance used for MALDI, we propose that ionization in IR-MALDI occurs as a natural consequence of the solid-to-gas phase transition induced by the IR irradiation, and involves proton transfer reactions in the intermediate phase between solid and gas. The strikingly similar UV- and IR-MALDI mass spectra leads us to the additional proposal that ionization in UV-MALDI may also be a natural consequence of the phase transition and that electronic excitation may not play a primary role in the ionization process.     

Experimental determination of laser induced breakdown thresholds of metals under nanosecond Q-switched laser operation

Laser-induced breakdown thresholds for several pure metals were determined using a nanosecond laser. A Q-switched pulsed Nd:YAG laser operating at infrared (1064 nm), visible (532 nm) and ultraviolet (266 nm) wavelengths has been used. The plasma was generated by focusing the Nd:YAG laser on the target in air at atmospheric pressure. The dispersed plasma light was detected using a two-dimensional intensified charge-coupled device (CCD) detector. The studied elements were chosen according to their different thermal and physical properties, particularly boiling point, melting point and thermal conductivity. The effect of wavelength on the plasma threshold has been discussed. Laser fluence thresholds in the ultraviolet were larger than those obtained using visible and infrared radiation, while the energy threshold is larger using infrared radiation. Correlations between the plasma threshold of metal targets and the melting point and boiling point at 266, 532 and 1064 nm have been established. The results indicate that thermal effects have an important influence on the ablation behavior of metals at the three wavelengths used.     

Single-beam Z-scan measurement of the third-order optical nonlinearities of azo dyes

Organic dyes are very attractive optical materials for photonics and biophotonic applications. To quantitatively characterize their third-order nonlinear coefficients we have performed the experiments on two different azo dyes using a diode-pumped Nd:YAG laser at 532 nm. The |chi(3)| is of the order of 10(-6) esu. The relative contributions from nonlinear absorption (NLA) and nonlinear refraction (NLR) are dependent on the chemical structure and linear absorption of the dyes.     

Cooperative phenomena in two-pulse, two-color laser photocoagulation of cutaneous blood vessels.

A novel laser system has been developed to study the effects of multiple laser pulses of differing wavelengths on cutaneous blood vessels in vivo, using the hamster dorsal skin flap preparation and in vitro, using cuvettes of whole or diluted blood. The system permits sequenced irradiation with well-defined intrapulse spacing at 532 nm, using a long-pulse frequency-doubled Nd:YAG laser, and at 1064 nm, using a long-pulse Nd:YAG laser. Using this system, we have identified a parameter space where two pulses of different wavelengths act in a synergistic manner to effect permanent vessel damage at radiant exposures where the two pulses individually have little or no effect. Using a two-color pump-probe technique in vitro, we have identified a phenomenon we call greenlight-induced infrared absorption, where a pulse of green light causes photochemical and photothermal modifications to the chemical constituents of blood and results in enhanced infrared absorption. We identify a new chemical species, met-hemoglobin, not normally present in healthy human blood but formed during laser photocoagulation which we believe is implicated in the enhanced near-infrared absorption.     

Nonlinear optical properties of tetrapyrazinoporphyrazinato indium chloride complexes due to excited-state absorption processes

The multiphoton absorption properties of the axially substituted tetrapyrazinotetraazaporphyrinato complex Pyz(4)TAPInCl (1) are reported and interpreted. In particular, the nonlinear optical transmission of the complex and the excited states involved in the nonlinear absorption have been determined at the frequency of the second harmonic generation of a Nd:YAG laser in the nanosecond time regime. Pyz(4)TAPInCl has an excited-state absorption cross section larger than its ground state in the 460-540 nm spectral region, and it shows an optical limiting (OL) behavior at 532 nm, which derives from a sequential two-photon absorption with a larger absorption cross section of the excited triplet state with respect to the ground state. It results that the absorption cross section of 1 in the excited triplet state is 7.8 x 10(-18) cm(2) vs 0.9 x 10(-18) cm(2) of the ground state at the wavelength of OL analysis.     

Study of laser ablation of brass materials using inductively coupled plasma atomic emission spectrometric detection

A XeCl laser and a Q-switched Nd:YAG laser operating at 1064, 532, 355 and 266 nm were used to ablate brass materials with varying concentrations of Zn and Cu. The ablated material was transported to an inductively coupled plasma for further atomization, excitation and ionization with an atomic emission spectrometric detection. A Zn enhancement was observed, which could be suppressed by using a Nd:YAG laser working at 266 nm with fluences higher than 400 J cm⁻² (equivalent to 80 GW cm⁻²). In contrast, a lack of linearity was observed for Cu as a function of the concentration, regardless of the wavelength and the fluence. The Cu problem seemed to occur during the ablation and was related to the structure of the brass material. Lack of linearity was also observed for Zn and other contained elements when samples from different origins were used.     

Development of a multi-frequency laser for use in MALDI-TOFMS

The application of a multi-frequency laser source for the use in matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOFMS) is described. An elliptically polarized beam of a Nd:YAG laser emitting at 355 nm (200 mJ) is focused into a Raman shifter, filled with high pressure hydrogen. As a result, numerous Raman lasers (including vibrational and rotational Raman emissions for hydrogen; 4155 and 587 cm⁻¹ shifts, respectively) were generated with a total power of ∼100 mJ. Using this multi-frequency laser as an ionization source, methionine enkephalin (MW 573.7), angiotensin I (MW 1296.5) and oxidized insulin chain B (MW 3495.9) were examined, as model compounds using α-cyano-4-hydroxycinnamic acid (CHCA), sinapinic acid (SA) and activated charcoal as the matrix, respectively. As a result, the S/N ratios were improved when the multi-frequency laser was used, compared to the single light source of the Nd:YAG laser (355 nm), irrespective of the type of matrix used. This is because the multi-frequency laser provides multi-line for absorption, where the traditional N₂ laser only provides single wavelength (at 337 nm) for absorption.     

Two-photon induced uncaging of a reactive intermediate. Multiphoton in situ detection of a potentially valuable label for biological applications

[reaction: see text] Two-photon induced Wolff rearrangement of a terphenyl diazoketone 1 was achieved by using focused laser pulses of 532 nm from a Q-switched Nd:YAG laser. The nonfluorescent terphenyl diazoketone 1 was transformed into a fluorescent ester derivative 4, which can be detected in situ using the focused laser pulses at 532 nm. Laser power dependence studies show that the Wolff rearrangement is induced by two-photon absorption of the terphenyl diazoketone 1, but suggests that more than two photons of 532 nm are involved (a multiphoton process) in excitation of the ester derivative 4.     

Investigation of optical nonlinearities of an azo dye using a 532nm diode-pumped Nd:YAG laser

Solid-state dye-doped polymers are attractive alternatives to the conventional liquid dye systems. In this paper, the third order nonlinear optical property of Sudan III, an azo dye in solvents and dye doped polymer films measured using the Z-scan technique is reported. Multiple diffraction rings were observed when the dye doped in both the liquid and solid media was exposed to a diode-pumped Nd:YAG laser at 532nm.     

Influence of the laser fluence in infrared matrix-assisted laser desorption/ionization with a 2.94 microm Er : YAG laser and a flat-top beam profile

The dependence of the signal intensity of analyte and matrix ions on laser fluence was investigated for infrared matrix-assisted laser desorption/ionization (IR-MALDI) mass spectrometry using a flat-top laser beam profile. The beam of an Er : YAG laser (wavelength, 2.94 microm; pulse width, 90 ns) was coupled into a sapphire fiber and the homogeneously illuminated end surface of the fiber imaged on to the sample by a telescope. Three different laser spot sizes of 175, 350 and 700 microm diameter were realized. Threshold fluences of common IR matrices were determined to range from about 1000 to a few thousand J m(-2), depending on the matrix and the size of the irradiated area. In the MALDI-typical fluence range, above the detection threshold ion signals increase strongly with fluence for all matrices, with a dependence similar to that for UV-MALDI. Despite the strongly different absorption coefficients of the tested matrices, varying by more than an order of magnitude at the excitation laser wavelength, threshold fluences for equal spot sizes were found to be comparable within a factor of two. With the additional dependence of fluence on spot size, the deposited energy per volume of matrix at threshold fluence ranged from about 1 kJ mol(-1) for succinic acid to about 100 kJ mol(-1) for glycerol.     

Nonlinear optical response of chloroaluminiumphthalocyanine encapsulated by silica core-shell particles

We report for the first time on the synthesis of core-shell particles containing chloroaluminiumphthalocyanine (ClAlPc) prepared using a sol-gel technique. These particles have the dye molecules at the core, encapsulated by silica shell. The mean size of the particle is determined from HRTEM studies and is found to be approximately 0.08 microm. The surface and bulk compositions of the core-shell particles are studied by XPS and EDAX measurements, respectively. Time-resolved fluorescent measurements indicate a decrease in fluorescence lifetime for the core-shell particles as compared to that of bare dye dissolved in ethanol. This is analyzed on the basis of available theoretical models. Third-order nonlinear optical effects are investigated by the Z-scan technique using 8 ns pulses at a wavelength of 532 nm from a frequency-doubled Nd:YAG laser. The analysis indicates that both singlet and triplet excited-state absorption contribute to nonlinear absorption.     

Wavelength dependence of polyyne preparation by liquid-phase laser ablation using pellet targets

The amount of polyynes produced by Nd:YAG laser (355, 532, and 1064 nm) ablation of fullerene and graphite pellet targets was the largest for 1064 nm ablation, contrary to the powder target in the previous report. This result is believed to come from the difference in the main polyyne-production area in liquids in the optical cell, depending on the pellet and powder targets.     

Highly resolved luminescence measurements for traces of 1,3-dibetanato europium(III) and terbium(III) complexes using a microscope laser Raman spectrometer toward the forensic discrimination.

The emission spectra of luminescent trivalent europium (Eu3+) and terbium (Tb3+) complexes were measured using a microscope laser Raman spectrometer with a doubled Nd:YAG laser (532 nm) and an Ar laser (488 nm). Excitation at 532 and 488 nm corresponded to wavelengths of the 7F1 --> 5D1 band of Eu3+ and the 7F6 --> 5D4 band of Tb3+, respectively. The Eu3+ and Tb3+ complexes were discriminated by high-resolution emission spectra more distinctly and sensitively than by fluorescence spectrometry, the usual analytical method.     

Laser-induced breakdown spectroscopy of solid aerosols produced by optical catapulting

Laser-induced breakdown spectroscopy of particles ejected by optical catapulting is discussed for the first time. For this purpose, materials deposited on a substrate were ejected and transported from the surface in the form of a solid aerosol by optical catapulting using a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser at 1064 nm. A Q-switched Nd:YAG laser at 532 nm was used for chemical characterization of the particles by laser-induced breakdown spectroscopy. Both lasers were synchronized in order to perform suitable spectral detection. The optical catapulting was optimized and evaluated using aluminum silicate particles, nickel spheres, and quartz and stainless steel particles. Experimental parameters such as the interpulse delay time, the sampling distance, the laser fluence, the sampling rate and the particle size have been studied. A correlation between these parameters and the particle size is reported and discussed.     

Fluorescence and Nonlinear Optical Response of Graphene Quantum Dots Produced by Pulsed Laser Irradiation in Toluene

Graphene quantum dots (GQDs), the zero dimensional (0D) single nanostructures, have many exciting technological applications in diversified fields such as sensors, light emitting devices, bio imaging probes, solar cells, etc. They are emerging as a functional tool to modulate light by means of molecular engineering due to its merits, including relatively low extend of loss, large outstretch of spatial confinement and control via doping, size and shape. In this article, we present a one pot, facile and ecofriendly synthesis approach for fabricating GQDs via pulsed laser irradiation of an organic solvent (toluene) without any catalyst. It is a promising synthesis choice to prepare GQDs due to its fast production, lack of byproducts and further purification, as well as the control over the product by accurate tuning of laser parameters. In this work, the second (532 nm) and third harmonic (355 nm) wavelengths of a pulsed nanosecond Nd:YAG laser have been employed for the synthesis. It has been found that the obtained GQDs display fluorescence and is expected to have potential applications in optoelectronics and light-harvesting devices. In addition, nonlinear optical absorption of the prepared GQDs was measured using the open aperture z-scan technique (in the nanosecond regime). These GQDs exhibit excellent optical limiting properties, especially those synthesized at 532 nm wavelength.     

非线性光学材料──水草酸铵

一水草酸铵（简称ＡＯＭ）是一种优良的电光晶体￣［１］。文献￣［１，２］报道了该晶体的晶体结构，化学式为（ＮＨ＿４）＿２Ｃ＿２Ｏ＿２·Ｈ＿２Ｏ，属正交晶系，Ｐ２２２空间群，晶胞参数ａ＝０．８０３５ｎｍ，ｂ＝１。０３１ｎｍ，ｃ＝０．３８０１ｎｍ，ｚ＝２。本文拟报道ＡＯＭ单晶生长，热化学分析，透过波段以及非线性光学性质的初步研究。     

Time-resolved imaging of the plume dynamics in infrared matrix-assisted laser desorption/ionization with a glycerol matrix

The dynamics of the expanding material plume after irradiation of a matrix sample with two different infrared (IR) lasers, an Er:YAG laser of ca. 100 ns and an optical parametric oscillator (OPO) laser system of 6 ns pulse duration, were investigated by imaging the plumes with nanosecond time resolution. Both lasers emitted at an identical wavelength of 2.94 microm. Laser exposure parameters were typical for infrared matrix-assisted laser desorption/ionization mass spectrometry (IR-MALDI-MS); glycerol was employed as a liquid matrix to provide a homogeneous sample and reproducible plume formation. A Nd:YAG laser (532 nm; 8 ns) was used as the illumination source and a CMOS camera with a ten-bit dynamic range served for recording of the images. Dark-field as well as scattered light illumination was employed to preferentially image the gaseous and particulate components of the plume, respectively. During the initial phase of its expansion (ca. 1 micros) the plume appears to consist of a continuous cloud of material of varying density. At later times after exposure, individual particles of several micrometers in size dominate the images. For both laser pulse durations material ejection was observed for times as long as 100 micros postexposure. Subtle but distinct differences in the plume dynamics are observed for the two different pulse durations. They are related to a transition between the regimes below and above acoustic confinement. The experimental findings are compared to results obtained in two previous studies by photoacoustic analysis of the desorption process and IR-laser postionization of the plume.     

Third-order nonlinear optical studies of newly synthesized polyoxadiazoles containing 3,4-dialkoxythiophenes

The third-order nonlinear optical properties of newly synthesized soluble polyoxadiazoles containing 3,4-dialkoxythiophenes were investigated by using Z-scan and degenerate four-wave mixing (DFWM) techniques. The measurements were performed at 532 nm with 7 ns pulses from a Nd:YAG laser. We found a good agreement between the values of χ⁽³⁾ determined from both the experiments. Z-scan results indicate a negative nonlinear refractive index, n₂, whose magnitude is of the order of 10⁻¹⁰ esu for all the copolymers. The variation of nonlinear response among the copolymers clearly indicates the dependence of χ⁽³⁾ on donor and acceptor type of units present in these copolymers. The copolymers exhibit strong reverse saturable absorption and good optical limiting properties at 532 nm.     

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.     

四甲川苯乙烯菁染料的合成及其激光性能

合成了一系列四甲川苯乙烯菁染料。以Nd:YAG锁模激光倍频(532nm)作泵浦源,测定了染料的激光性能,包括激光调谐范围、中心激光波长、激光转换效率及稳定性。探讨了该类分子结构与其激光性能之间的关系。