Near-infrared Femtosecond Laser Research Articles

Real-time observation of X-ray-induced intramolecular and interatomic electronic decay in CH2I2

The increasing availability of X-ray free-electron lasers (XFELs) has catalyzed the development of single-object structural determination and of structural dynamics tracking in real-time. Disentangling the molecular-level reactions triggered by the interaction with an XFEL pulse is a fundamental step towards developing such applications. Here we report real-time observations of XFEL-induced electronic decay via short-lived transient electronic states in the diiodomethane molecule, using a femtosecond near-infrared probe laser. We determine the lifetimes of the transient states populated during the XFEL-induced Auger cascades and find that multiply charged iodine ions are issued from short-lived (∼20 fs) transient states, whereas the singly charged ones originate from significantly longer-lived states (∼100 fs). We identify the mechanisms behind these different time scales: contrary to the short-lived transient states which relax by molecular Auger decay, the long-lived ones decay by an interatomic Coulombic decay between two iodine atoms, during the molecular fragmentation.

Single nanowire defined emission properties of ZnO nanowire arrays

We report on stimulated emission from vertically aligned, vapor transport grown, ZnO nanowire arrays, and pumped by three-photon absorption in intense near-infrared femtosecond laser pulses. In respect to single nanowires, arrays have the advantage of a higher light absorption and emission rate. The intensity and bandwidth of the emitted ultraviolet radiation as a function of the pump intensity is compared for nanowire arrays with different wire lengths, diameters, and spacing. The measured lasing thresholds for all arrays can be well described by the geometry of individual nanowire lasers, showing that coupling effects between the individual emitters in the arrays are negligible, even for the smallest 100 nm diameter wires with an average distance of 200 nm.

(Invited) Biological Multiphoton Imaging Techniques for Tracking Non-Fluorescent Carbon Nanomaterials

Multiphoton Microscopy (MPM) has enabled an unprecedented level of dynamic exploration within living cells and organisms. The physical principle behind this imaging technique involves the use of near-infrared femtosecond lasers to excite optical processes in fluorescent molecules using two or more photons1. The use of long wavelengths (700 nm – 1000 nm) enables deep tissue penetration (up to 1000 μm) without inducing harmful biological effects. Previous studies include the examination of membrane potentials on the single-molecule scale2, the non-invasive observation of embryo development3, and the simultaneous multiplane imaging of calcium transportation in transgenic mice4. An excellent review of this field can be found in the literature5. Herein we demonstrate a novel multiphoton-based technique for imaging negligible-to-non-fluorescent carbon-based nanomaterials such as C60 fullerenes, single-walled carbon nanotubes, and graphene, which usually can only be imaged by conjugation of specific fluorescent tracers thereby altering their inherent dynamics within biological systems. More specifically, we demonstrate optical and photoluminescent activity in water-soluble C60-serinol, highly enriched (95 %) metallic and semiconducting single-walled carbon nanotubes, and graphene. This multiphoton imaging technique was also applied to in vitro and in vivo animal model studies. Various concentrations of the above-mentioned nanomaterials were given to human pancreatic ductal adenocarcinoma (Panc-1) and hepatocellular carcinoma (Heb3B) cancer cell lines, as well as normal, healthy pancreatic ductal epithelial cells (HPDE). In all cases, imaging of these nanomaterials was possible using the MP imaging technique even though the nanomaterials exhibit weak, almost zero inherent fluorescent properties. We also examined the ability to image these nanomaterials, real-time, in vivo, using mice with orthotopic 4T1 breast tumors. Finally, we also include a range of spectroscopy data to examine the specific optical characteristics of the carbon nanomaterials. References Denk, W.; Strickler, J.; Webb, W. Science 1990, 248, (4951), 73-76.Peleg, G.; Lewis, A.; Linial, M.; Loew, L. M. Proceedings of the National Academy of Sciences 1999, 96, (12), 6700-6704.Chu, S.-W.; Chen, S.-Y.; Tsai, T.-H.; Liu, T.-M.; Lin, C.-Y.; Tsai, H.-J.; Sun, C.-K. Opt. Express 2003, 11, (23), 3093-3099.Cheng, A.; Goncalves, J. T.; Golshani, P.; Arisaka, K.; Portera-Cailliau, C. Nat Meth 2011, 8, (2), 139-142.Hoover, E. E.; Squier, J. A. Nat Photon 2013, 7, (2), 93-101.

Characterization of 20-fs VUV pulses by plasma-mirror frequency-resolved optical gating.

We demonstrate that vacuum ultraviolet (VUV) pulses (λ∼160 nm) with 20-fs duration can be fully characterized by plasma-mirror frequency-resolved optical gating. Plasma is formed as an ultrafast optical switch on a fused silica surface by irradiation of an intense near-infrared (NIR) femtosecond laser pulse. We measure the spectra of the VUV pulses reflected off plasma as a function of the delay with respect to the NIR pulse and reconstruct it to simultaneously extract a nearly Fourier-transform limited VUV pulse shape and a time-dependent reflectivity of plasma using the least-squares generalized projections algorithm. We show that there is almost no spatial dependence of the VUV pulse shape, whereas the plasma mirror reflectivity strongly depends on the spatial region.

Coherent modulation of superradiance from nitrogen ions pumped with femtosecond pulses

Singly ionized nitrogen molecules in ambient air pumped by 800 nm femtosecond laser give rise to superradiant emission. Here, we study this superradiance by injecting a pair of resonant seeding pulses at different intensity ratios inside the nitrogen gas plasma. Strong modulation of the 391.4 nm superradiant emission with a period of 1.3 fs is observed when the delay between the two seeding pulses is finely tuned. The modulation contrast is increased and then decreased with the delay time when the second seed pulse is stronger than the first one, and the maximum modulation contrast occurs at longer delay time when the second seeding pulse is stronger. This reveals the increase of the macroscopic polarization with time after the seeding pulse. Moreover, these observations provide a new level of control on the "air lasing" based on nitrogen ions, which can find potential applications in optical remote sensing.

Spectral broadening effects on metal photoemission by femtosecond laser pulses

Emitted electronic densities from an Al surface have been computed for various temporal shapes of near-infrared femtosecond laser pulses (less than or equal to 20 fs) over a wide range of low and intermediate laser intensities. At low intensities photoemission originates from the high-energy tail of the pulse spectrum leading to linear absorption in all cases, even if several photons are necessary to eject an electron at higher intensities. We propose an analytical method to calculate the transition intensity in which the behavior of emitted densities evolves from the single-photon ${I}_{m}$ slope to the multiphoton ${I}_{m}^{n}$ one (with ${I}_{m}$ the maximum intensity and $n$ the number of absorbed photons). We show that the use of a flat-top profile or at least of a super-Gaussian envelope enables strong electron emission at very low intensities for realistic pulse durations and should allow experimental observation of the transition between these two regimes of photoemission.

Abnormal elemental redistribution in oxyfluoride glasses induced by high repetition rate femtosecond laser

We report on the elemental redistribution behavior in oxyfluoride glasses with a high repetition rate near-infrared femtosecond laser. Elemental analysis by an electro-probe microanalyzer demonstrates that the redistributions of Ca2+ and Yb3+ ions change dramatically with pulse energy, which are quite different compared with previous reported results. Confocal fluorescence spectra of Yb3+ ions demonstrate that the luminescence intensity changes obviously with the elemental redistribution. The mechanism of the observed phenomenon is discussed. This observation may have potential applications in the fabrication of micro-optical devices.

Open-path gas detection using terahertz time-domain spectroscopy

We report on the development of an experimental setup for remote sensing of gas atmosphere in open air conditions using broadband terahertz pulses. Terahertz time-domain spectroscopy technique is used to solve the problems of gas detection and recognition in the presence of water vapor absorption lines. Acetonitrile vapors were detected and gas concentration was successfully estimated. Organic crystal with a 2% conversion efficiency pumped with near-infrared femtosecond laser pulses was used to generate single-cycle terahertz pulses with energies up to 10 µJ. Application of a novel high-power source of broadband terahertz radiation (0.2–3 THz) opens up new perspectives for further increasing the open space distances in remote sensing problem.

Discover Patent Landscape of Two-photon Polymerization Technology for the Production of 3D Nano-structure Using Claim-based Approach.

The TPP technology is a "nano-optics" 3D printing technology that develops in recent years. Compared with the traditional 3D printing technology, the TPP-3DP technique that takes near-infrared light femtosecond pulse laser as the light source can break through the limitation of optical diffraction and manufacture nanoscale 3D structures in arbitrary shapes with high resolution. The research develops a claim-based patent analysis method to identify technical features via the analysis of claim, especially the analysis of plural elements of independent claim. Furthermore, we analyze the subject matters and technical features of claims through claim-base analytical method to observe the patent trend of competitors and understand the current situation of competitors' technical distribution in related industries, in order to provide useful information for enterprises to determine R&D strategies. The result shows 3M Company possesses numerous patent portfolios that base on the diversified innovative applications of TPP technology. Nanoscribe Company has a long-term advantage in monopolizing this technology. The patents in TPP-3DP field can be grouped into five categories relating to application, including micro-optics device, photonic crystal, biomedical, microfluidics and MEMS. The findings of this review confirm the TPP-based 3D printing (TPP-3DP) technology has broad application prospects, of which the hydrogel material applied in tissue engineering and drug delivery is the future trend. Highly-initiated water-soluble initiators are particularly needed to increase its resolution and will be the direction of emerging technology in this domain.

Surface third and fifth harmonic generation at crystalline Si for non-invasive inspection of Si wafer's inter-layer defects.

Detection of inter-layer and internal defects in semiconductor silicon (Si) wafers by non-contact, non-destructive and depth-resolving techniques with a high lateral and depth resolution is one of the challenging tasks in modern semiconductor industry. In this paper, we report that nonlinear optical harmonic generation can be of great virtue therein because it enables non-invasive inspection of inter-layer defects with sub-micrometer depth resolution in extensive penetration depth over several millimeters. Compared to existing inspection methods for inter-layer defects, such as ultrasound, photoacoustic and photothermal imaging, the proposed technique provides higher lateral and depth resolution as well as higher interfacial selectivity. For in-depth understanding of nonlinear harmonic generation at Si wafer surfaces, the spectral power distributions of third and fifth harmonics from Si wafers with various crystal orientations and dopants were carefully analyzed under different incident polarizations and excitation depths using a near-infrared (NIR) femtosecond laser as the excitation light source. We finally demonstrated that inter-layer defects inside stacked Si wafers, such as delamination or stacking faults, can be inspected with a high lateral and depth resolution in a non-contact and non-destructive manner. These findings will pave the way for nonlinear optical harmonic generation to the fields of interfacial studies of crystalline materials, high-resolution detection of sub-diffraction-limit surface defects, and high-resolution imaging of internal structures in stacked semiconductor devices.

Spinal cord injury in zebrafish induced by near-infrared femtosecond laser pulses

BackgroundThe spinal cord is composed of a large number of cells that interact to allow the organism to function. To perform detail studies of cellular processes involved in spinal cord injury (SCI), one must use repeatable and specific methods to target and injure restricted areas of the spinal cord. New methodWe propose a robust method to induce SCI in zebrafish by laser light. With a 2-photon microscope equipped with a femtosecond near-infrared pump laser, we explored the effects of laser beam exposure time, area, and intensity to induce precise and repeatable SCI with minimized collateral damage to neighboring cells. ResultsThrough behavioral studies in zebrafish larvae, we assessed the functional outcome of intensive laser light directed at the spinal cord. Our experiments revealed that a laser pulse with wavelength 800 nm, duration 2.6 ms, and light intensity 390 mW was sufficient to induce controlled cell death in a single cell or a spinal cord segment. Collateral damage was observed if cells were exposed to laser pulses exceeding 470 mW. With these settings, we could induce precise and repeatable SCI in zebrafish larvae, resulting in loss of motor and sensory function. Comparison with existing method(s)Our method offers a simple and more controlled setting to induce SCI in zebrafish. We describe how the near-infrared femtosecond laser should be adjusted for achieving optimal results with minimal collateral damage. ConclusionsWe present a precise and robust method for inducing SCI in zebrafish with single-cell resolution using femtosecond near-infrared laser pulses.

Direct Laser Writing of Crystallized TiO2 and TiO2 /Carbon Microstructures with Tunable Conductive Properties.

Metal oxides are an important class of materials for optoelectronic applications. In this context, developing simple and versatile processes for integrating these materials at the microscale and nanoscale has become increasingly important. One of the major remaining challenges is to control the microstructuration and electro-optical properties in a single step. It is shown here that near-infrared femtosecond laser irradiation can be successfully used to prepare amorphous or crystallized TiO2 microstructures in a single step using a direct laser writing (DLW) approach from a TiO2 precursor thin film doped with a suitable dye. When laser writing is conducted under a nitrogen atmosphere, simultaneous to the crosslinking of the Ti-oxide precursor, the graphitization of the organic species embedded in the initial film is observed. In this case, a carbon network is generated within the TiO2 matrix, which significantly increases the conductivity. Moreover, the TiO2 /C nanocomposite exhibits piezoresistive behavior that is used in a pressure sensor device. Using this route, it is possible to use DLW to fabricate microsized pressure sensors.

Temperature and excitation wavelength-dependent photoluminescence of CH3NH3PbBr3 crystal.

We have investigated temperature and excitation wavelength-dependent luminescent properties of CH3NH3PbBr3 (MAPbBr3) perovskite crystal using steady-state and time-resolved photoluminescence (PL) spectroscopy. Optical spectroscopic results indicate that the PL intensity, peak wavelength, and full width at half maximum are jumped due to the phase transition from orthorhombic to tetragonal and cubic. As temperature increases, the peaks of above-bandgap and intrinsic PL have blueshift and redshift, respectively. The above-bandgap PL emerges under one-photon laser excitation and vanishes under the excitation of near-infrared femtosecond laser due to reabsorption. The initial redshift of PL peak and lifetime change at various wavelengths reveals the existence of a trap-assisted excitonic state. It is found that upconversion PL in all phases is composed of a photoinduced thermal-assisted and an intrinsic excitonic state, which produces the observation of biexponential dynamics. Our results can facilitate the understanding of the thermal effect of exciton recombination in hybrid perovskite crystal.

High spatial coherence in multiphoton-photoemitted electron beams

Nanometer-sharp metallic tips are known to be excellent electron emitters. They are used in highest-resolution electron microscopes in cold field emission mode to generate the most coherent electron beam in continuous-wave operation. For time-resolved operation, sharp metal needle tips have recently been triggered with femtosecond laser pulses. We show here that electrons emitted with near-infrared femtosecond laser pulses at laser oscillator repetition rates show the same spatial coherence properties as electrons in cold field emission mode in cw operation. From electron interference fringes, obtained with the help of a carbon nanotube biprism beam splitter, we deduce a virtual source size of less than (0.65 ± 0.06) nm for both operation modes, a factor of ten smaller than the geometrical source size. These results bear promise for ultrafast electron diffraction, ultrafast electron microscopy, and other techniques relying on highly coherent and ultrafast electron beams.

Strain-assisted femtosecond inscription of phase-shifted gratings.

Two slightly shifted gratings are inscribed, one over the other, while exploiting fiber strain in a single-mode fiber. The inscription is done with a near-infrared femtosecond laser, a phase mask, and a cylindrical focusing lens. The first fiber Bragg grating (FBG) is inscribed under normal fiber tension, while the second overlapping FBG is inscribed under higher fiber tension. The transmission spectrum of the complex structure is similar to that of a phase-shifted grating, yet the fabrication process is much faster and simpler compared to other standard methods. A high-quality phase-shifted grating with two -30 dB transmission dips, a 25dB transmission peak, and <50 pm transmission bandwidth is achieved. We observe polarization-dependent transmission in the phase-shifted gratings.

Photon Upconversion through a Cascade Process of Two-Photon Absorption in CsPbBr3 and Triplet–Triplet Annihilation in Porphyrin/Diphenylanthracene

Photon upconversion constitutes an exceptionally rich area of research in photonics and electronics, where low-energy light is converted to high-energy light through nonlinear processes represented by two-photon absorption (TPA) and triplet–triplet annihilation (TTA). Here, we report a cascade process of TPA in inorganic perovskite quantum dots (PQDs) of CsPbBr3 and TTA in an organic molecule (9,10-diphenylanthracene) mediated by an octaethylporphyrinatoplatinum(II) (PtOEP) sensitizer. This sequential energy transfer enables upconversion from four photons from a near-infrared femtosecond laser at 800 nm to one photon at 430 nm with a large anti-Stokes shift of ∼1.3 eV. We characterize the energy transfer from PQDs to PtOEP by picosecond lifetime spectroscopy and a Stern–Volmer plot of the steady-state photoluminescence while considering dynamic and static quenching as well as trivial absorption and Forster (fluorescence) resonance energy transfer. The serial connection of TPA and TTA achieved in a simple ...

Strong-field optoelectronics in solids

Perturbative optical nonlinearities induced by static electric fields1 have proven useful in visualizing dynamical function in systems including operating circuits2,3, electric and magnetic domain walls4, and biological matter5, and in controlling light for applications in silicon photonics6. Here, we extend field-induced second-harmonic generation to the non-perturbative regime. We demonstrate that static or transient fields up to terahertz (THz) frequencies applied to silicon and ZnO crystals generate even-order high harmonics. Images of the even harmonics confirm that static fields delivered with conventional electronics control the spatial properties of the high-harmonic emission. Extending our methodology to higher-harmonic photon energies7,8 paves the way for realizing active optics in the extreme ultraviolet and will allow imaging of operating electronic circuits9, of Si-photonic devices10 and of other functional materials11,12, with higher spatio-temporal resolution than perturbative methods. For THz spectroscopy, our method has the bandwidth to allow measurement of attosecond transients imprinted on THz waveforms. Near-infrared femtosecond laser pulses are sent to a Si or ZnO crystal to generate high-harmonic waves via static or transient field-induced optical nonlinearities. The beam profile of the high-harmonic emission is controlled by electronic methods.

Natural zeolite for adsorbing and release of functional materials.

Using multiphoton microscopy (MPM), we demonstrated that effective inducing of two-photon excited luminescence and second-harmonic generation signals in nano/microparticles of clinoptilolite type of zeolite (CZ) by femtosecond near-infrared laser excitation can be successfully utilized in multiphoton imaging of the drug adsorption processes. Adsorption of photodynamic active dyes (hypericin, chlorin e6, methylene blue, and fluorescein) and their release from CZ pores in the presence of biomolecules, such as collagen from bovine Achilles tendon, albumin, and hemoglobin, were investigated by absorption and fluorescence spectrometry. To quantify the experimental results on hypericin release, here we use a kinetic curves fitting approach and calculate hypericin release rates in different environments. This approach allows to compare various mathematical models and uses more parameters to better characterize drug release profiles. In addition, magnetic CZ particles were fabricated and proposed as a promising material for drug delivery and controlled release in biological systems. Optical spectrometry and MPM are effective approaches that may reveal potential of natural zeolites in controlled drug delivery and biomedical imaging.

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.

Bragg Gratings in Suspended-Core Photonic Microcells for High-Temperature Applications

We report a novel type-II photonic crystal fiber Bragg grating for high-temperature applications. The Bragg grating is inscribed in a low-loss in-fiber structure named suspended-core photonic microcell, which is postprocessed from a commercial pure-silica photonic crystal fiber. Grating samples with core diameters of about 4 μm were made by using a focused near-infrared femtosecond laser and a phase mask, and then tested in a tube furnace from room temperature to about 1200 °C. The thermal response of the Bragg resonant wavelength was measure to be about 12 and 16 pm/°C, respectively, at the temperature around 100 °C and 1000 °C. The grating spectrum remained stable in a 10-h isothermal annealing at 1000 °C and started decaying at about 1120 °C with the rate of about 0.02 dB/min. This type of grating possesses flexibilities in both waveguide and grating structure design, exhibits good high-temperature performance, hence would be promising platform for building wavelength-division-multiplexed fiber sensors and tunable devices with a wide working temperature range.