Near-infrared Femtosecond Laser Irradiation Research Articles

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.

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.

Near-infrared femtosecond laser-triggered nanoperforation of hollow microcapsules

Fabrication of a nanopore in a hollow microcapsule was demonstrated using near-infrared femtosecond laser irradiation. The shape of the irradiated microcapsules was kept spherical except for a pore in the shell owing to the nonthermal processing by a femtosecond laser. The simulation results for the near-field and far-field scattering around a microcapsule revealed that highly-enhanced optical intensity can be generated at a spot on the shell of a microcapsule, which would in turn contribute to localized ablation. To the best of our knowledge, this is the first demonstration of the nanoperforation of transparent hollow microcapsules by a near-infrared laser without any doping with absorbing metals or dyes that may cause cell toxicity. The presented method is a promising approach for safer drug delivery and the controlled release of therapeutic drugs.

Three-dimensional micronanofabrication via two-photon-excited photoisomerization

In this letter, laser micronanofabrication via two-photon absorption initiated isomerization was proposed and explored. Experimentally a cis-form rich poly[2,5-dihexyloxy-1,4-phenylene] vinylene)-alt-(2,5-diphenyl-1,4-phenylene vinylene)] (DPO-PPV) was used as the precursory material, which underwent pinpoint molecular conformational change upon the near-infrared femtosecond laser irradiation. Due to pronouncedly reduced solubility of trans-configuration molecules, the precipitate at the tiny volumes was implemented as voxels to construct two- and three-dimensional micronanostructures. This mechanism may provide an alternative enabling tool other than two-photon absorption initiated polymerization of resins for designable micronanofabrication of photonic or optoelectronic devices including organic electroluminescent devices, particularly those based on PPV and its derivatives.

A femtosecond laser pacemaker for heart muscle cells

The intracellular effects of focused near-infrared femtosecond laser irradiation are shown to cause contraction in cultured neonatal rat cardiomyocytes. By periodic exposure to femtosecond laser pulse-trains, periodic contraction cycles in cardiomyocytes could be triggered, depleted, and synchronized with the laser periodicity. This was observed in isolated cells, and in small groups of cardiomyocytes with the laser acting as pacemaker for the entire group. A window for this effect was found to occur between 15 and 30 mW average power for an 80 fs, 82 MHz pulse train of 780 nm, using 8 ms exposures applied periodically at 1 to 2 Hz. At power levels below this power window, laser-induced cardiomyocyte contraction was not observed, while above this power window, cells typically responded by a high calcium elevation and contracted without subsequent relaxation. This laser-cell interaction allows the laser irradiation to act as a pacemaker, and can be used to trigger contraction in dormant cells as well as synchronize or destabilize contraction in spontaneously contracting cardiomyocytes. By increasing laser power above the window available for laser-cell synchronization, we also demonstrate the use of cardiomyocytes as optically-triggered actuators. To our knowledge, this is the first demonstration of remote optical control of cardiomyocytes without requiring exogenous photosensitive compounds.

Blue emission from Eu2+-doped high silica glass by near-infrared femtosecond laser irradiation

Eu 2 + -doped high silica glass (HSG) is fabricated by sintering porous glass which is impregnated with europium ions. Eu2+-doped HSG is revealed to yield intense blue emission excited by ultraviolet (UV) light and near-infrared femtosecond laser. The emission profile obtained by UV excitation can be well traced by near-infrared femtosecond laser. The upconversion emission excited by 800 nm femtosecond laser is considered to be related to a two-photon absorption process from the relationship between the integrated intensity and the pump power. A tentative scheme of upconverted blue emission from Eu2+-doped HSG was also proposed. The HSG materials presented herein are expected to find applications in high density optical storage and three-dimensional color displays.

Progress on the Photoresponse of Chalcogenide Glasses and Films to Near-Infrared Femtosecond Laser Irradiation: A Review

This paper reviews ongoing progress in exploring the mechanistic origins of photoinduced structural modification in chalcogenide glasses (ChGs). These findings, reported by groups at the University of Central Florida, Clemson University, and throughout other research programs within the United States and abroad, have examined the relationship between the network modification and other photoresponse of IR glasses upon exposure to near-infrared (NIR) femtosecond laser exposure. Contained is a review on the principles of femtosecond laser writing in glass, the photoinduced phenomena, and a summary of the main models predicting photoinduced material response. We compare the photoresponse of As- and Ge-based films, taken as example, following NIR femtosecond laser irradiation that results in near-surface photoexpansion and an increase or decrease of the refractive index, respectively. This difference in photoresponse has been related to the layered network of the As-based glass that leads to the breaking and formation of bonds during laser exposure as compared to the 3-D network of Ge-based glass that leads only to a modification of the bond arrangements. Last, an explanation of the need to control the photoresponse of ChGs by aging, changing the glass thermal history, adding modifiers, or replacing the anions forming the network is discussed.

Three-photon-induced luminescence of gold nanoparticles embedded in and located on thesurface of glassy nanolayers

We report on the multiphoton-induced luminescence of gold nanoparticlesembedded in thin glassy silicate–titanate films. The glassy layers dopedwith gold(III) chloride are synthesized by a sol–gel coating process. Goldnanoparticles are generated by subsequent annealing of the thin films at300 °C. Intensive near-infrared femtosecond laser irradiation also initiates the formation ofgold particles, providing the possibility of spatially resolved photoactivation ofthe film. The reduction of gold ions to gold nanoparticles is monitored by AuL3-edge x-ray absorption near edge spectroscopy (XANES), UV–vis absorptionspectroscopy, scanning electron microscopy (SEM) and transmission electronmicroscopy (TEM). The particle sizes and shapes can be tuned by changing themetal concentration in the matrix. We demonstrate that the particles exhibit anefficient, long time stable, white luminescence during near-infrared Ti:sapphirefemtosecond laser excitation. The laser power-emission intensity law indicates that theluminescence is induced by the absorption of three laser photons. Cross-sectional TEMimages show that gold nanoparticles are both embedded in the glassy matrix andlocated on the film surface. Hence, the particles should be accessible for viableapplications, for example as sensor materials, and could therefore become a powerfulalternative to organic and semiconducting fluorophores in biological imaging.

Photochemical Hole Burning of Sm2+ in Sodium Borate Glasses Induced by Near-Infrared Femtosecond-Laser Irradiation.

We report on photochemical hole burning of Sm2+ in sodium borate glasses irradiated with femtosecond-laser pulses of 800nm wavelength. The irradiation of Sm3+-doped sodium borate glasses with femtosecond-laser pulses causes electron-trapped Sm3+, i.e., Sm2+ and point defects such as an oxygen hole center and an electron trapped near Na+. The measurements of spectral hole burning were carried out for the 5D0-7F0 transition of Sm2+ using a DCM dye laser. Photoionization hole burning is observed at 77K to room temperature for the glasses exposed to femtosecond-laser pulses, and also for the glasses prepared by melting under reducing conditions. The hole-burning efficiency of Sm2+ produced by the photoinduced process is about twice higher than that by the thermal process. It is thought that the metastable Sm2+ ions and oxygen hole centers induced by femtosecond-laser irradiation are responsible for the observed phenomenon. We propose that the efficient photoionization hole burning is caused by the photostimulated recombination of the electron trapped by Sm3+ with the oxygen hole center.