Near-infrared Femtosecond Laser Research Articles

Nonlinear dynamics of femtosecond laser interaction with the central nervous system in zebrafish

Understanding the photodamage mechanism underlying the highly nonlinear dynamic of femtosecond laser pulses at the second transparent window of tissue is crucial for label-free microscopy. Here, we report the identification of two cavitation regimes from 1030 nm pulses when interacting with the central nervous system in zebrafish. We show that at low repetition rates, the damage is confined due to plasma-based ablation and sudden local temperature rise. At high repetition rates, the damage becomes collateral due to plasma-mediated photochemistry. Furthermore, we investigate the role of fluorescence labels with linear and nonlinear absorption pathways in optical breakdown. To verify our findings, we examined cell death and cellular responses to tissue damage, including the recruitment of fibroblasts and immune cells after irradiation. These findings contribute to advancing the emerging nonlinear optical microscopy techniques and provide a strategy for inducing precise, and localized injuries using near-infrared femtosecond laser pulses.

Two-Dimensional Projected-Momentum Covariance Mapping for Coulomb Explosion Imaging.

We introduce projected-momentum covariance mapping, an extension of recoil-frame covariance mapping for 2D ion imaging studies. By considering the two-dimensional projection of the ion momenta as recorded by the detector, one opens the door to a complex suite of analysis tools adapted from three-dimensional momentum imaging studies. This includes the use of different frames of reference to unravel the dynamics of fragmentation and the application of fragment momentum constraints to isolate specific fragmentation channels. The technique is demonstrated on data from a two-dimensional ion imaging study of the Coulomb explosion of the cis and trans isomers of 1,2-dichloroethene, following strong-field ionization by an intense near-infrared femtosecond laser pulse. Classical simulations are used to guide the interpretation of projected-momentum covariance maps. The results offer a detailed insight into the distinct Coulomb explosion dynamics for this pair of isomers and lay the groundwork for future time-resolved studies of photoisomerization dynamics in this molecular system.

Femtosecond laser writing of fiber Bragg gratings using the phase mask technique: a geometrical optics analysis based on the Bravais refractive index

Material modification is produced inside silica-based optical fibers of different diameters using tightly focused near-infrared (central wavelength at 800 nm) femtosecond laser pulses and the phase mask technique which is often employed for laser inscription of fiber Bragg gratings. 1st-, 2nd-, and 3rd-order phase masks designed for the operation at 800 nm are used in the experiments. The inscription is performed at different distances from the fiber’s front surface by translating the focusing cylindrical lens along the laser beam propagation direction. The results show that the material modification produced by means of the 2nd- and 3rd-order phase mask can be positioned at any predetermined distance from the fiber’s front surface. In contrast, when the 1st-order mask is used for laser writing, the maximum distance from the fiber’s front surface at which material modification can be produced is limited and determined by three main parameters: the diffraction angle of the phase mask, the refractive index of the fiber and the diameter of the fiber.

Multi-shot near-infrared femtosecond laser tuning of silicon microring resonators

We studied multi-shot femtosecond laser surface modification as a permanent tuning technique for obtaining the desired resonance wavelengths for silicon microring resonators. In this multi-shot tuning approach, each microring resonator was irradiated with 10 or 100 laser pulses in the same location of the waveguide with selected laser fluence. The laser beam has 800 nm wavelength, 130 fs pulse duration, a Gaussian spatial profile with a beam waist radius of 13.1μm, and pulse energies of 12 nJ to 186 nJ to generate the applied range of laser fluences. The silicon microring resonators used in the study have a 15μm diameter and are coupled to a waveguide of 500 nm in width with a gap of 260 nm. We found that the multi-shot tuning curves (resonance wavelength shifts as a function of laser fluences) do not monotonically increase with laser fluences: they first increase, then plateau, and finally decrease. We observed that the laser energies required for the multi-shot case to obtain the onset of crystalline modifications and ablation are several times below the single-shot case because of the incubation effect. With proper control we can achieve both positive and negative resonance wavelength shifts with acceptable induced roundtrip waveguide losses.

Direct laser microprinting of hydroxyapatite-clad structures by photoreduction-triggered nanomaterial deposition

Hydroxyapatite-based micropatterns were fabricated via near-infrared femtosecond laser irradiation. The micropatterns had a hierarchical cross-section comprising an Ag-based core and an overlying thick layer of non-photosensitive hydroxyapatite nanoparticles. Such micropatterns were continuously formed by the translation of the laser focus in hydroxyapatite nanoparticle-containing AgNO3 solution. A pattern more than quadruple in width was obtained by adding nanoparticles to the solution, despite the same laser irradiation conditions. Raman spectroscopy indicated that the hydroxyapatite nanoparticles retained their crystalline nature even after laser printing. Furthermore, we demonstrate the fabrication of hydroxyapatite-clad patterns on the inner walls of glass capillaries using laser printing.

Multi-Electron Ionization and Coulomb Explosion of the IBr Molecule in the Near-Infrared Femtosecond Laser Field

Multi-Electron Ionization and Coulomb Explosion of the IBr Molecule in the Near-Infrared Femtosecond Laser Field

Study on electron response to near-infrared, ultraviolet and extreme ultraviolet femtosecond laser by first-principle

The phenomenon of laser-induced electronic evolution in semiconductors is an essential issue in laser fabrication, which has been extensively investigated within the near-infrared and visible spectral ranges. However, electronic evolution at short wavelength laser has neither been systematically investigated. In this paper, time-dependent density functional theory is employed to investigate the response in silicon under laser irradiation of different wavelengths. The result shows that shorter wavelength induces the excitation of electrons to higher energy levels, consequently leading to increased impact ionization rates. Such a moderate excitation of energetic electrons even at low-medium intensity is considered as a distinctive feature of extreme ultraviolet light laser, which is expected to further enhance the quality of laser processing.

Near-infrared femtosecond laser direct writing of microchannel and controlled surface wettability

The application of femtosecond laser in fabricatingpoly (methyl methacrylate) microchannels and the alteration of wettability by inducing a change in chemical functional groups has already been established and reported in literature.However, studies on the application of femtosecond laser for modification of surface wettability without significant chemical modification,are yet to be reported. The paper reports work on an expedition of femtosecond (Ytterbium-doped fiber) laser ablation working at the near-infrared wavelength (1030 nm) tuning the wettability behavior comprising of hydrophilic and hydrophobic state on the basis of the surface morphology created below the focal beam diameter. The initial part revolves around the investigation of near-infrared femtosecond laser ablation for achieving microcavity and microchannel below the focal beam diameter. The latter part deals with laser surface modification for attaining both hydrophilic and hydrophobic surfaces. The study obtained a high degree of hydrophobicity, with a maximum water contact angle of 129.05°at a laser energy of 40 μJ and pulse laser overlap of 96%. It was also possible to attain a minimum water contact angle of 56.35°using a laser pulse energy of 40 μJ and pulse overlap of 0 %. The reported work avoids surface chemical modification for controlling the wettability.

Generation of high-energy near-infrared femtosecond laser pulses by optical parametric amplification in YCOB crystals

"The energy of near-infrared femtosecond laser pulses generated by optical parametric amplification (OPA) in β-barium borate (BBO) crystals pumped by femtosecond Ti:sapphire lasers is restricted to few-mJ due to the 20 mm limited diam- eter of available crystals. In a type I collinear OPA with an yttrium calcium oxoborate (YCOB) crystal, pumped with femtosecond Ti:sapphire lasers at 800 nm wavelength, the 1300 nm signal wavelength and 2080 nm idler wavelength are located in the normal and anomalous group velocity dispersion range, respectively. Due to the small group velocity mismatch (GVM) between signal and idler pulses, as broad as 27 THz gain bandwidth can be obtained in a 3-mm YCOB crystal at 100 GW/cm2 pump intensity. A high parametric gain is the result of the increased parametric interaction length due to the different signs of GVM between pump-signal and pump-idler pulses. More than 10-mJ energy femtosecond laser pulses at 1300 nm wavelength can be generated by OPA in YCOB crystals with larger than 50 mm clear aperture."

Rhenium diselenide nanosheets as an excellent bi-color probe for intracellular two-photon imaging

Recently two-dimensional (2D) nanomaterials-mediated photothermal therapy (PTT) has become an important tool for treating cancer. However, visually monitoring the localization of nanoagents in cancer cells remains a key challenge. Herein, exploring high photostability, and high biocompatibility probes for monitoring PTT are still highly desirable. In this study, a novel optical probe named PEG@ReSe2 nanosheets (polyethylene glycol, PEG; rhenium diselenide, ReSe2) was prepared and employed to perform in vivo two-photon imaging for monitoring PTT in esophageal cancer cells. Under the illumination of a near-infrared (NIR) femtosecond laser at 820 nm with the output power as low as 5 mW, the PEG@ReSe2 nanosheets showed significant two-photon features, producing a significant photoluminescence emission band at 637 nm. In addition, the prepared PEG@ReSe2 nanosheets exhibited high resistance to photobleaching. Also, the PEG@ReSe2 nanosheets showed low cytotoxicity for cancer cells, providing a high viability of more than 90%. More importantly, the PEG@ReSe2 nanosheets could enter cancer cells and work as a two-photon probe for visually displaying the PTT process. After 12 h incubation, the PEG@ReSe2 nanosheets produced strong two-photon signals in KYSE150 cancer cells, enabling them to perform in vivo bi-channel bioimaging. In light of its photothermal effects, the PEG@ReSe2 nanosheets also could serve as a sensor for monitoring PTT under low-power infrared laser irradiation. This study suggests that, the PEG@ReSe2 nanosheets could serve as a superior two-photon biosensor for monitoring the PTT process in cancer nanomedicine.

Femtosecond pulse laser-engineered glass flexible structures instrumented with an in-built Bragg grating sensor.

The advent of near-infrared femtosecond pulse laser has enabled the highly-resolved manufacturing of micro/nano structures in various materials including glass. In this paper, we make use of an automated femtosecond laser system, so-called Femtoprint, to design a monolithic self-instrumented mechanism that we use for in-built strain sensing. To that aim, a flexible structure is designed and produced from a silica planar substrate. It has a flexural joint in which an optical waveguide and a Bragg grating have been directly inscribed using femtosecond pulse laser. The latter provides a non-destructive and non-intrusive measurement tool. The axial strain sensitivity of the in-built Bragg grating has been experimentally determined to be 1.22 pm/μ ϵ, while its temperature sensitivity is 10.51 pm/°C. The demonstration of such instrumented glass flexible mechanisms paves the way towards a new class of highly integrated sensors suitable for applications at the microscale or in harsh environments.

High Harmonic Generation near the Low-Frequency Edge of a Plateau under Nonlinear Propagation of 1.24-μm Near-Infrared Femtosecond Laser Radiation in a Dense Argon Jet

High (15–25) harmonic generation in the vacuum ultraviolet spectral range (83–50 nm) has been realized by focused (NA = 0.033) near-infrared femtosecond laser radiation (wavelength λ = 1.24 μm) with a vacuum intensity of ~7.5 × 1014 W/cm2 irradiating a dense gas jet. It has been shown experimentally that the use of such a high-numerical aperture focusing requires high (up to 10 bar) gas jet pressures to optimize phase matching. The use of the dense gas jet results in a noticeable manifestation of nonlinear propagation effects for generating radiation, which affect the generation process through the change in the phase matching conditions. Furthermore, it has been shown that the prechirping of the generating pulse makes it possible to compensate a chirp appearing due to self-phase modulation and to increase the harmonic generation efficiency because of the nonlinear compression of the generating pulse. This approach has allowed 17th (73 nm) harmonic generation with an energy of 2 pJ in a pulse and a generation efficiency of 5.4 × 10–9. The estimates obtained have shown that this radiation can be used for single-pulse maskless photolithography in the extreme ultraviolet range.

Light-Induced Metastable Hidden Skyrmion Phase in the Mott Insulator Cu2 OSeO3.

The discovery of a novel long-lived metastable skyrmion phase in the multiferroic insulator Cu2 OSeO3 visualized with Lorentz transmission electron microscopy for magnetic fields below the equilibrium skyrmion pocket is reported. This phase can be accessed by exciting the sample non-adiabatically with near-infrared femtosecond laser pulses and cannot be reached by any conventional field-cooling protocol, referred as a hidden phase. From the strong wavelength dependence of the photocreation process and via spin-dynamics simulations, the magnetoelastic effect is identified as the most likely photocreation mechanism. This effect results in a transient modification of the magnetic free energy landscape extending the equilibrium skyrmion pocket to lower magnetic fields. The evolution of the photoinduced phase is monitored for over 15 min and no decay is found. Because such a time is much longer than the duration of any transient effect induced by a laser pulse in a material, it is assumed that the newly discovered skyrmion state is stable for practical purposes, thus breaking ground for a novel approach to control magnetic state on demand at ultrafast timescales and drastically reducing heat dissipation relevant for next-generation spintronicdevices.

Strong-field photoionization/dissociation of vinyl bromide in near-infrared and ultraviolet femtosecond laser fields

Ionization of polyatomic molecules in strong femtosecond laser fields is a pivotal process that may induce a variety of highly nonlinear molecular physical phenomena. We performed an experimental study on photoionization and dissociation of vinyl bromide molecules in 800 nm or 400 nm femtosecond strong laser fields using a time-of-flight mass spectrometer. The dependence of the ion yields on laser intensity and polarization was investigated, and the results are compared in different wavelength laser fields. The kinetic energy releases from Coulomb explosion of vinyl bromide, and the angular distributions of different fragment ions were obtained. The mechanism of strong-field ionization/dissociation of vinyl bromide in different laser fields is discussed based on the experimental results.

Design of refractive–diffractive hybrid lenses for space–time focusing ultrashort laser pulses

We propose a simple formulation for the baseline design of a hybrid lens, consisting of refractive and diffractive elements, intended for focusing ultrashort laser pulses. Lens dispersions up to the second order are considered to obtain easy-to-use formulas. Using this formulation, we designed a refractive–diffractive triplet for near-infrared femtosecond laser pulses and observed that once radius-dependent temporal distortions are removed, chromatic distortions are removed as well, and vice versa. Furthermore, we found that the derived equations for removal of pulse distortions can be readily transformed to traditional lens design equations for optical imaging. This finding facilitates the design of hybridized triplets for ultrafast focusing optics.

Two-Photon Stereolithography—Optical Nanolithography

Free-radical photopolymerization has been widely used in additive technologies, in particular, stereolithography using single- and two-photon initiated polymerization. The single-photon stereolithography affords the objects with about 100 μm resolution. The two-photon stereolithography initiated with a femtosecond near-infrared laser can afford arbitrary 3D microstructures with ultrahigh resolution at micro- and nanoscale level (~100 nm). Herein each of the mentioned method and the mechanisms of single- and two-photon excitation are reviewed. The recent results on the components of the photopolymerizable resin as well as the approaches to decrease the size of the elements of objects and accelerate their formation have been generalizated and systematized.

Mesoporous Silica-Encapsulated Gold Nanorods for Drug Delivery/Release and Two-Photon Excitation Fluorescence Imaging to Guide Synergistic Phototherapy and Chemotherapy.

Photothermal therapy is a promising light-based medical treatment that relies on light absorption agents converting light irradiation into localized heat to destroy cancer cells or other diseased tissues. It is critical to enhance the therapeutic effects of cancer cell ablation for their practical applications. This study reports a high-performance combinational therapy for ablating cancer cells, including both photothermal therapy and chemotherapy to improve therapeutic efficiency. The prepared AuNR@mSiO2 loading molecular Doxorubicin (Dox) assemblies were highlighted by merits of facile acquisition, great stability, easy endocytosis, and rapid drug release in addition to improved anticancer capability upon irradiation with a femtosecond pulsed near-infrared (NIR) laser, where AuNR@mSiO2 nanoparticles afforded a high photothermal conversion efficiency of 31.7%. Two-photon excitation fluorescence imaging was introduced into confocal laser scanning microscope multichannel imaging to track the drug location and cell position in real time for monitoring the process of drug delivery in killing human cervical cancer HeLa cells and then to realize imaging-guiding cancer treatment. These nanoparticles exhibit widespread potential in photoresponsive utilizations including photothermal therapy, chemotherapy, one- and two-photon excited fluorescence imaging, and 3D fluorescence imaging and cancer treatment.

Femtosecond Inscription of a Fiber Bragg Grating Spectral Array in the Same Spatial Location.

A five fiber Bragg grating (FBG) array is inscribed at the same spot with a single uniform phase-mask (PM). The inscription setup consists of a near-infrared femtosecond laser, a PM, a defocusing spherical lens and a cylindrical focusing lens. The tunability of the center Bragg wavelength is achieved by a defocusing lens, and by translating the PM, which results in a different magnification of the PM. A first FBG is inscribed, followed by four cascading FBGs, which are inscribed exactly at the same spot only after the translation of the PM. The transmission and reflection spectra of this array are measured, showing a second-order Bragg wavelength at ~1.56 µm with a transmission dip of ~-8 dB. The spectral wavelength shift between each consecutive FBG is ~2.9 nm, and the total wavelength shift is ~11.7 nm. The reflection spectrum of the third-order Bragg wavelength is measured at ~1.04 µm, showing a wavelength separation of ~1.97 nm between neighboring FBGs, and the total spectral span between the first FBG and the last one is ~8 nm. Finally, the wavelength sensitivity to strain and temperature is measured.

Nanoscale local modification of PMMA refractive index by tip-enhanced femtosecond pulsed laser irradiation

Tip-enhanced optical effects have enabled a wide palette of nanoscale investigation techniques and recently they were successfully used to modify and manipulate matter with nanoscale spatial resolution. We contribute to this latter area by reporting a viable method to modify the refractive index of polymethyl methacrylate (PMMA). Local surface changes of the refractive index are accomplished by focusing a femtosecond pulsed near-infrared laser beam on the apex of a metalized nanosized tip, traditionally used in scanning probe microscopy (SPM). The refractive index is changed over a circular area with diameter <200 nm under 790 nm illumination, representing a four-fold increase in resolution compared to the current state-of-the-art. These results are obtained at low laser pulse energies (<0.5 nJ), which represents a two orders of magnitude advantage over previously reported methods. Besides enabling modifications of the refractive index with high lateral resolution, this method can pave the way towards other important applications such the fabrication of photonic crystal lattices and surface waveguides.

Room-temperature synthesis of CsPbBr3@CsPb2Br5 microcrystals and their upconversion luminescence

In this work, a convenient and environmental-friendly aqueous-phase method is used to synthesize CsPbBr3@CsPb2Br5 microcrystals (MCs) at room temperature, of which structural and optical properties are characterized by powder X-ray diffraction (PXRD), absorption, and photoluminescence (PL) spectroscopic techniques. Two obvious absorption peaks at 307 and 515 nm are attributed to CsPb2Br5 matrix and CsPbBr3 impurity, respectively. Full-width at half-maximum (FWHM) of PL for MCs is 83.5 meV at room temperature, and its emission peak is observed at 518 nm. With the temperature changed from 80 to 340 K, the fitted value of the exciton binding energy is 84.1 meV from temperature-dependent steady-state PL. Upconversion luminescence (UCL) can be observed obviously under near-infrared femtosecond laser pulse excitation, which is compared with normal luminescence from steady-state and time-resolved PL measurements. The experimental investigations show that CsPbBr3@CsPb2Br5 MCs have excellent stability against thermal, water and light irradiation, which will provide a new choice for the commercial applications to lasering and displaying.