Near-infrared Femtosecond Laser Pulses Research Articles

Femtosecond laser-induced dissociation (fs-LID) as an activation method in mass spectrometry

We report the photolysis of biomolecules in a Fourier-transform ion cyclotron resonance mass spectrometer by intense near-infrared femtosecond laser pulses. Photo-fragmentation was accompanied by photo-ionization and created a large number and variety of charged fragments, which could be identified with high confidence due to the outstanding resolving power and mass accuracy of the mass spectrometer. Fragmentation patterns were sufficient for peptide sequence analysis. Fragments formed by non-ergodic cleavage retained labile post-translational modifications.

Terahertz generation from reduced graphene oxide

We firstly investigate the generation of terahertz (THz) wave from reduced graphene oxide (RGO) illuminated with femtosecond near-infrared laser pulse. Experiment results show that the THz generation from RGO can be enhanced by increasing the reduction degree and reducing the film thickness. The former can be attributed to the increase of sp2 carbon region, which has much smaller band gap and graphene-like photoelectric properties. The latter is due to the suppression of the light-induced lateral currents in the surface of RGO layers. The linear dependency of the THz electrical field on the pump power confirms that the THz emission from RGO is governed by second-order nonlinear properties. When exciting laser irradiates from opposite sample sides, π phase shift of the generated THz wave has been observed, suggesting the transient photocurrent related to THz emission is induced by the photon drag effect. The conclusion has been further confirmed by the well fitting of the experiment and theoretical calculation based on the symmetry of RGO. This work makes it clear the THz generation mechanism of RGO and paves a way for developing new THz sources.

Fragmentation of endohedral fullerene Ho3N@C80 in an intense femtosecond near-infrared laser field

The fragmentation of gas phase endohedral fullerene, $\mathrm{H}{\mathrm{o}}_{3}\mathrm{N}@{\mathrm{C}}_{80}$, was investigated using femtosecond near-infrared laser pulses with an ion velocity map imaging spectrometer. We observed that $\mathrm{H}{\mathrm{o}}^{+}$ abundance associated with carbon cage opening dominates at an intensity of $1.1\ifmmode\times\else\texttimes\fi{}{10}^{14}\phantom{\rule{0.16em}{0ex}}\mathrm{W}/\mathrm{c}{\mathrm{m}}^{2}$. As the intensity increases, the $\mathrm{H}{\mathrm{o}}^{+}$ yield associated with multifragmentation of the carbon cage exceeds the prominence of $\mathrm{H}{\mathrm{o}}^{+}$ associated with the gentler carbon cage opening. Moreover, the power law dependence of $\mathrm{H}{\mathrm{o}}^{+}$ on laser intensity indicates that the transition of the most likely fragmentation mechanisms occurs around $2.0\ifmmode\times\else\texttimes\fi{}{10}^{14}\phantom{\rule{0.16em}{0ex}}\mathrm{W}/\mathrm{c}{\mathrm{m}}^{2}$.

Spectral broadening and conical emission of near-infrared femtosecond laser pulses in air

Spectral and spatial properties of infrared femtosecond laser pulses with a wavelength between 1.2 and 1.6 μm propagating in air are investigated both, experimentally and theoretically. It is shown that under tight focusing conditions laser pulses experience asymmetric spectral broadening (SB) and a strong blue-shift with respect to the incident laser wavelength. The observed blue-shifted radiation is emitted conically, in contrast to the weaker red-shifted on-axis emission. The SB and frequency shifts were interpreted in terms of ionization-induced effects.

Unexpected Sensitivity of Nitrogen Ions Superradiant Emission on Pump Laser Wavelength and Duration.

Nitrogen molecules in ambient air exposed to an intense near-infrared femtosecond laser pulse give rise to cavity-free superradiant emission at 391.4 and 427.8nm. An unexpected pulse duration-dependent cyclic variation of the superradiance intensity is observed when the central wavelength of the femtosecond pump laser pulse is finely tuned between 780 and 820nm, and no signal occurs at the resonant wavelength of 782.8nm (2ω_{782.8 nm}=ω_{391.4 nm}). On the basis of a semiclassical recollision model, we show that an interference of dipolar moments of excited ions created by electron recollisions explains this behavior.

Direct Laser Writing of LaBGeO5 Crystal-in-Glass Waveguide Enabling Frequency Conversion

We report on a technique of femtosecond laser-induced crystallization of glass, allowing improvement in the homogeneity of continuous crystalline tracks formed in lanthanum borogermanate glass using a focused beam with the elliptical-shaped waist cross section instead of a conventional circular one. Second harmonic generation produced by near-infrared femtosecond laser pulses was demonstrated in the waveguiding mode for the laser written crystalline track. The structure of the fabricated single crystalline waveguides is investigated with high resolution transmission electron microscopy and micro-Raman spectroscopy.

Resonance switching using ultrafast laser in THz plasmonic devices based on hybrid structure of semiconductor and carbon nanotube

We demonstrate all-optical switching of plasmonic resonance patterned on the carbon nanotube films supported on the silicon substrates. A considerable suppression of terahertz wave was observed in the transmission resonance, when the near-infrared femtosecond laser pulse is irradiated. A Fourier-transformed terahertz spectrum reveals that the resonance feature that was governed by the geometry of the slot antenna are almost completely removed with the laser irradiation having sufficiently high pulse energy reaching 18 μJ. A screening of terahertz field was analyzed in terms of the free carrier generation originating from the photoexcitation in semiconductor film.

Determining the Range of Noninvasive Near-Infrared Femtosecond Laser Pulses for Mammalian Oocyte Nanosurgery

Determining the Range of Noninvasive Near-Infrared Femtosecond Laser Pulses for Mammalian Oocyte Nanosurgery

50-nanometer femtosecond pulse laser induced periodic surface structures on nitrogen-doped diamond

Ultrashort pulse laser interaction with nitrogen-doped type I-b diamond was investigated with near-infrared femtosecond laser pulses at repetition rates of 5kHz and 11MHz. High spatial frequency laser-induced periodic surface structures with periodicities of 50 and 200nm were generated perpendicular to the polarization of the electric field. The novel 50nm features are found to be due to a phase transition from crystalline diamond to a graphitic phase in contrast to the 200nm laser-induced periodic surface structures consisting still of crystalline material.

State-selective preparation of Ar2+ and Kr2+ by resonantly enhanced two-photon double ionization via intermediate Rydberg states using high-order harmonics

Simultaneous two-electron emission processes of Ar induced by high-order harmonics of near-infrared femtosecond laser pulses were investigated by coincidence photoelectron spectroscopy. Two-photon double ionization processes via the $3s3{p}^{6}np\phantom{\rule{0.16em}{0ex}}(n\ensuremath{\sim}25)$ intermediate resonances of Ar were observed, which selectively created the $3s3{p}^{5}\phantom{\rule{0.16em}{0ex}}^{1}P$ state of $\mathrm{A}{\mathrm{r}}^{2+}$. The similar double ionization processes were also observed in Kr. The selective creation indicates that the core electron configuration of the doubly ionized state tends to be the same as that of the intermediate state and that the emitted two electrons tend to form the singlet state.

Possible flat band bending of the Bi1.5Sb0.5Te1.7Se1.3 crystal cleaved in an ambient air probed by terahertz emission spectroscopy.

We investigate an evolution of the surface electronic state of the Bi1.5Sb0.5Te1.7Se1.3 single crystal, which is one of the most bulk insulating topological insulators, by examining terahertz light emitted from the sample surface upon the illumination of the near-infrared femtosecond laser pulses. We find that the surface state with a flat band bending can appear in the course of the natural maturation process of the surface state in an ambient air. Furthermore, we demonstrate that the evolution of the surface electronic state can be accelerated, decelerated, or even stopped by controlling environmental conditions to contain different amount of H2O, in particular.

Au-Ag core-shell nanoparticles for simultaneous bacterial imaging and synergistic antibacterial activity

Au@Ag nanoparticles (NPs) were recently found to display giant two-photon photoluminescence (2PPL) enhancement, with an enhancement factor up to 815 fold upon aggregate formation. Based on this finding, two-photon imaging of bacteria by Au@Ag NPs under near-infrared (NIR) femtosecond laser pulses was demonstrated in this study, as positively charged Au@Ag NPs can form aggregates on the negatively charged bacterial surface, yielding strong 2PPL emission. The aggregation-enhanced 2PPL of Au@Ag NPs stemmed from higher two-photon excitation efficiency, implying strong two-photon photothermal effects. Au@Ag NPs showed strong antibacterial activity (minimum inhibition concentration as low as 7.5pM against Staphylococcus aureus) and negligible toxicity to human dermal fibroblasts. Their bactericidal activity was further enhanced under NIR irradiation due to strong two-photon photothermal effects. Au@Ag NPs effectively removed 85% of the notorious bacterial biofilm within 4 min under NIR irradiation. These Au@Ag NPs can potentially be used as imaging and antibacterial agents.

Laser-triggered release of encapsulated molecules from polylactic-co-glycolic acid microcapsules.

The controlled release of encapsulated molecules from a microcapsule is a promising method of targeted drug delivery. Laser-triggered methods for the release of encapsulated molecules have the advantage of spatial and temporal controllability. In this study, we demonstrated the release of encapsulated molecules from biodegradable polymer-based microcapsules using near-infrared femtosecond laser pulses. The polylactic-co-glycolic acid microcapsules encapsulating fluorescein isothiocyanate-dextran molecules were fabricated using a dual-coaxial nozzle system. Irradiation of femtosecond laser pulses enhanced the release of the molecules from the microcapsules, which was accompanied by a decrease in the residual ratio of the microcapsules. The laser-induced modification of the surface of the shell of the microcapsules indicated the potential for sustained release as well as burst release.

Intravital multiphoton photoconversion with a cell membrane dye.

Photoconversion, an irreversible shift in a fluorophore emission spectrum after light exposure, is a powerful tool for marking cellular and subcellular compartments and tracking their dynamics in vivo. This paper reports on the photoconversion properties of Di-8-ANEPPS, a commercially available membrane dye. When illuminated with near-infrared femtosecond laser pulses, Di-8-ANEPPS undergoes multiphoton photoconversion as indicated by the supralinear dependence of the conversion rate ρpc on the incident power (ρpc∝Iexc2.27), and by the ability to photoconvert a thin optical section in a three-dimensional matrix. The characteristic emission spectrum changed from red to blue, and ratiometric analysis on single cells in vitro revealed a 65-fold increase in the blue to red wavelength ratio after photoconversion. The spectral shift is preserved in vivo for hours, making Di-8-ANEPPS a useful dye for intravital cell marking and tracking applications.

Formation of luminescent and nonluminescent silver nanoparticles in silicate glasses by near-infrared femtosecond laser pulses and subsequent thermal treatment: the role of halogenides

It is shown experimentally that the near-infrared femtosecond laser irradiation and subsequent thermal treatment of silver-containing silicate glasses result in the formation of luminescent silver molecular clusters (MCs) and silver nanoparticles (NPs). In glasses doped also with halides (mostly Br), the nonluminescent silver NPs are formed because of the presence of halogenide shells on their surfaces, whereas, in glasses with no Br ions, the luminescent silver nanoparticles provides an emission in the 600- to 750-nm range. Two possible mechanisms of luminescence of glass with silver NPs are considered: (i) luminescence of silver NPs without halogenide shell and (ii) the luminescence of silver MCs <inline-formula< <mml:math display=inline xmlns:mml=http://www.w3.org/1998/Math/MathML< <mml:mrow< <mml:msub< <mml:mi<Ag</mml:mi< <mml:mi<m</mml:mi< </mml:msub< </mml:mrow< </mml:math< </inline-formula< (<inline-formula< <mml:math display=inline xmlns:mml=http://www.w3.org/1998/Math/MathML< <mml:mrow< <mml:mi<m</mml:mi< <mml:mo<=</mml:mo< <mml:mn<1</mml:mn< </mml:mrow< </mml:math< </inline-formula< to 4) remaining even after the formation of silver NPs.

Biodegradable microsphere-mediated cell perforation in microfluidic channel using femtosecond laser.

The use of small particles has expanded the capability of ultrashort pulsed laser optoinjection technology toward simultaneous treatment of multiple cells. The microfluidic platform is one of the attractive systems that has obtained synergy with laser-based technology for cell manipulation, including optoinjection. We have demonstrated the delivery of molecules into suspended-flowing cells in a microfluidic channel by using biodegradable polymer microspheres and a near-infrared femtosecond laser pulse. The use of polylactic-co-glycolic acid microspheres realized not only a higher optoinjection ratio compared to that with polylactic acid microspheres but also avoids optical damage to the microfluidic chip, which is attributable to its higher optical intensity enhancement at the localized spot under a microsphere. Interestingly, optoinjection ratios to nucleus showed a difference for adhered cells and suspended cells. The use of biodegradable polymer microspheres provides high throughput optoinjection; i.e., multiple cells can be treated in a short time, which is promising for various applications in cell analysis, drug delivery, and ex vivo gene transfection to bone marrow cells and stem cells without concerns about residual microspheres.

Intravital Imaging Study on Photodamage Produced by Femtosecond Near-infrared Laser Pulses In Vivo.

Ultrashort femtosecond pulsed lasers may provide indispensable benefits for medical bioimaging and diagnosis, particularly for noninvasive biopsy. However, the ability of femtosecond laser irradiation to produce biodamage in the living body is still a concern. To solve this biosafety issue, results of theoretical estimations as well as the in vitro and in situ experiments on femtosecond biodamage should be verified by experimental studies conducted in vivo. Here, we analyzed photodamage produced by femtosecond (19, 42 and 100 fs) near-infrared (NIR; ~800 nm) laser pulses with an average power of 5 and 15 mW in living undissected Drosophila larvae (in vivo). These experimental data on photodamage in vivo agree with the results of theoretical modeling of other groups. Femtosecond NIR laser pulses may affect the concentration of fluorescent biomolecules localized in mitochondria of the cells of living undissected Drosophila larva. Our findings confirm that the results of the mathematical models of femtosecond laser ionization process in living tissues may have a practical value for development of noninvasive biopsy based on the use of femtosecond pulses.

Femtosecond Er-doped fiber laser based on divided-pulse nonlinear amplification

A high-power erbium-doped fiber amplifier was realized by using a spatially and temporally divided pulse amplification technique. Pulse amplification and compression were simultaneously achieved in a double-clad Er-doped fiber by controlling the pulse gain and dispersion, generating a slope efficiency of 19.2% for the divided pulse amplification. The spectrum and pulse evolutions for nonlinear amplification and compression in the double-clad gain fiber were studied both in theory and experiment. Then 680 mW near-infrared femtosecond laser pulses were obtained by using 0.45 m single-mode fiber to compress amplified pulses. Frequency doubling was further carried out with a periodically poled lithium niobate (PPLN) crystal, generating 790 nm laser pulses with 110 mW average power and 95.7 fs pulse duration.

Optical reprogramming of human somatic cells using ultrashort Bessel-shaped near-infrared femtosecond laser pulses.

We report a virus-free optical approach to human cell reprogramming into induced pluripotent stem cells with low-power nanoporation using ultrashort Bessel-shaped laser pulses. Picojoule near-infrared sub-20 fs laser pulses at a high 85 MHz repetition frequency are employed to generate transient nanopores in the membrane of dermal fibroblasts for the introduction of four transcription factors to induce the reprogramming process. In contrast to conventional approaches which utilize retro- or lentiviruses to deliver genes or transcription factors into the host genome, the laser method is virus-free; hence, the risk of virus-induced cancer generation limiting clinical application is avoided.

Femtosecond Laser-Controlled Tip-to-Tip Assembly and Welding of Gold Nanorods.

Directed assembly of gold nanorods through the use of dithiolated molecular linkers is one of the most efficient methodologies for the morphologically controlled tip-to-tip assembly of this type of anisotropic nanocrystals. However, in a direct analogy to molecular polymerization synthesis, this process is characterized by difficulties in chain-growth control over nanoparticle oligomers. In particular, it is nearly impossible to favor the formation of one type of oligomer, making the methodology hard to use for actual applications in nanoplasmonics. We propose here a light-controlled synthetic procedure that allows obtaining selected plasmonic oligomers in high yield and with reaction times in the scale of minutes by irradiation with low fluence near-infrared (NIR) femtosecond laser pulses. Selective inhibition of the formation of gold nanorod n-mers (trimers) with a longitudinal localized surface plasmon in resonance with a 800 nm Ti:sapphire laser, allowed efficient trapping of the (n – 1)-mers (dimers) by hot spot mediated photothermal decomposition of the interparticle molecular linkers. Laser irradiation at higher energies produced near-field enhancement at the interparticle gaps, which is large enough to melt gold nanorod tips, offering a new pathway toward tip-to-tip welding of gold nanorod oligomers with a plasmonic response at the NIR. Thorough optical and electron microscopy characterization indicates that plasmonic oligomers can be selectively trapped and welded, which has been analyzed in terms of a model that predicts with reasonable accuracy the relative concentrations of the main plasmonic species.