Fabrication of surface nanoscale axial photonics structures with a femtosecond laser

Surface nanoscale axial photonics (SNAP) structures are fabricated with a femtosecond laser for the first time, to the best of our knowledge. The inscriptions introduced by the laser pressurize the fiber and cause its nanoscale effective radius variation. We demonstrate the subangstrom precise fabrication of individual and coupled SNAP microresonators having the effective radius variation of several nanometers. Our results pave the way to a novel ultraprecise SNAP fabrication technology based on the femtosecond laser inscription.

Contraction et filamentation des décharges micro-ondes entretenues à la pression atmosphérique : application à la détoxication des gaz à effet de serre

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Femtosecond laser inscription of fiber bragg gratings with low insertion loss and minor polarization dependence

The inscription of low insertion loss and negligibly polarization dependent fiber Bragg gratings inscribed using a femtosecond laser system is reported. Insertion losses were <0.4dB/20mm and polarization wavelength shift of <5pm, with transmission changes <0.1dB. © 2010 Optical Society of America.

All fibre femtosecond pulse generation using an intracavity 45°-tilted fibre grating

We demonstrate an all-fibre erbium doped fibre laser mode-locked by using an intracavity 45°-Tilted Fibre Grating as a polarization element. The laser produces soliton-like pulses with ~600fs pulse duration and ~1nJ output energy at a repetition rate of 10.34MHz. © 2010 Optical Society of America.

Flat-top supercontinuum and tunable femtosecond fiber laser sources at 1.9-2.5 μm

We report the high-energy flat-top supercontinuum covering the mid-infrared wavelength range of 1.9-2.5 μm as well as electronically tunable femtosecond pulses between 1.98-2.22 μm directly from the thulium-doped fiber laser amplifier. Comparison of experimental results with numerical simulations confirms that both sources employ the same nonlinear optical mechanism - Raman soliton frequency shift occurring inside the Tm-fiber amplifier. To illustrate that, we investigate two versions of the compact diode-pumped SESAM mode-locked femtosecond thulium-doped all-silica-fiber-based laser system providing either broadband supercontinuum or tunable Raman soliton output, depending on the parameters of the system. The first system operates in the Raman soliton regime providing femtosecond pulses tunable between 1.98-2.22 μm. Wide and continuous spectral tunability over 240 nm was realized by changing only the amplifier pump diode current. The second system generates high-energy supercontinuum with the superior spectral flatness of better than 1 dB covering the wavelength range of 1.9-2.5 μm, with the total output energy as high as 0.284 μJ, the average power of 2.1 W at 7.5 MHz repetition rate. We simulate the amplifier operation in the Raman soliton self-frequency shift regime and discuss the role of induced Raman scattering in supercontinuum formation inside the fiber amplifier. We compare this system with a more traditional 1.85-2.53 μm supercontinuum source in the external highly-nonlinear commercial chalcogenide fiber using the Raman soliton MOPA as an excitation source. The reported systems1 can be readily applied to a number of industrial applications in the mid-IR, including sensing, stand-off detection, medical surgery and fine material processing.

Contraction et filamentation des décharges micro-ondes entretenues à la pression atmosphérique : application à la détoxication des gaz à effet de serre

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Morphology and structure of particles produced by femtosecond laser ablation of fused silica

The aim of the present work was to study the morphology and structure of the nanoparticles produced by femtosecond laser ablation of fused silica. Ultrashort laser pulses of 1030 nm wavelength and 550 fs duration were tightly focused by a high numerical aperture microscope objective at the surface of fused silica samples while scanning the sample in relation to the stationary laser beam. Laser tracks were created with pulse energies in the range 5-100 mu J, resulting in ablation debris of different morphologies. The debris were examined by scanning and transmission electron microscopy for their morphology and crystal structure in relation to the incident laser pulse energy. Ejected particles with sizes ranging from a few nanometers to a few microns were found. Their morphologies can be broadly classified into three categories: very fine round nanoparticles with diameters lower than 20 nm, nanoparticles with intermediate sizes between 50 and 200 nm, and big irregular particles with typical size between 0.5 and 1.5 mu m. The fine nanoparticles of the first category are predominantly observed at higher pulse energies and tend to aggregate to form web-like and arborescent-like structures. The nanoparticles with intermediate sizes are observed for all pulse energies used and may appear isolated or aggregated in clusters. Finally, the larger irregular particles of the third category are observed for all energies and appear normally isolated.

Characterization of nanoparticle mediated laser transfection by femtosecond laser pulses for applications in molecular medicine

Background: In molecular medicine, the manipulation of cells is prerequisite to evaluate genes as therapeutic targets or to transfect cells to develop cell therapeutic strategies. To achieve these purposes it is essential that given transfection techniques are capable of handling high cell numbers in reasonable time spans. To fulfill this demand, an alternative nanoparticle mediated laser transfection method is presented herein. The fs-laser excitation of cell-adhered gold nanoparticles evokes localized membrane permeabilization and enables an inflow of extracellular molecules into cells. Results: The parameters for an efficient and gentle cell manipulation are evaluated in detail. Efficiencies of 90% with a cell viability of 93% were achieved for siRNA transfection. The proof for a molecular medical approach is demonstrated by highly efficient knock down of the oncogene HMGA2 in a rapidly proliferating prostate carcinoma in vitro model using siRNA. Additionally, investigations concerning the initial perforation mechanism are conducted. Next to theoretical simulations, the laser induced effects are experimentally investigated by spectrometric and microscopic analysis. The results indicate that near field effects are the initial mechanism of membrane permeabilization. Conclusion: This methodical approach combined with an automated setup, allows a high throughput targeting of several 100,000 cells within seconds, providing an excellent tool for in vitro applications in molecular medicine. NIR fs lasers are characterized by specific advantages when compared to lasers employing longer (ps/ns) pulses in the visible regime. The NIR fs pulses generate low thermal impact while allowing high penetration depths into tissue. Therefore fs lasers could be used for prospective in vivo applications.

Switchable dual-wavelength erbium-doped fibre laser utilizing two-channel fibre Bragg grating fabricated by femtosecond laser

We propose and demonstrate a switchable dual-wavelength erbium-doped fibre ring laser. Competition between the lasing wavelengths in erbium-doped fibre laser at room temperature is suppressed by incorporating a two-channel fibre Bragg grating (TC-FBG), which consists of two highly localized sub-gratings fabricated by femtosecond laser in single mode fibre. Wavelengths and polarization states of the lasing lines are selected by the TC-FBG. Laser output can be switched between single- and dual-wavelength operations by simply adjusting the polarization controller. Stable dual-wavelength output is verified at room temperature with a power fluctuation less than 0.27 dB, and wavelength fluctuation less than 0.004 nm.

SERS substrate for detection of explosives

A novel gold coated femtosecond laser nanostructured sapphire surface – an “optical nose” - based on surface-enhanced Raman spectroscopy (SERS) for detecting vapours of explosive substances was investigated. Four different nitroaromatic vapours at room temperature were tested. Sensor responses were unambiguous and showed response in the range of 0.05 – 15 uM at 25 °C. The laser fabricated substrate nanostructures produced up to an eight-fold increase in Raman signal over that observed on the unstructured portions of the substrate. This work demonstrates a simple sensing system that is compatible with commercial manufacturing practices to detect taggants in explosives which can undertake as part of an integrated security or investigative mission.

Indications of energetic consequences of decoherence at short times for scattering from open quantum systems

Decoherence of quantum entangled particles is observed in most systems, and is usually caused by system-environment interactions. Disentangling two subsystems A and B of a quantum systemAB is tantamount to erasure of quantum phase relations between A and B. It is widely believed that this erasure is an innocuous process, which e.g. does not affect the energies of A and B. Surprisingly, recent theoretical investigations by different groups showed that disentangling two systems, i.e. their decoherence, can cause an increase of their energies. Applying this result to the context of neutronCompton scattering from H2 molecules, we provide for the first time experimental evidence which supports this prediction. The results reveal that the neutron-proton collision leading to the cleavage of the H-H bond in the sub-femtosecond timescale is accompanied by larger energy transfer (by about 3%) than conventional theory predicts. It is proposed to interpreted the results by considering the neutron-proton collisional system as an entangled open quantum system being subject to decoherence owing to the interactions with the “environment” (i.e., two electrons plus second proton of H2).

Second-harmonic generation from biological tissues : effect of excitation wavelength

We report on the measurement of second-harmonic signals from hyperplastic parenchyma and stroma in malignant human prostate tissue under femtosecond pulsed illumination in the wavelength range from 730 to 870 nm. In particular, the relationship of the second-harmonic generation to the excitation wavelength is measured. The result in these two regions behaves considerably differently and thus provides a possible indicator for identifying tissue components and malignancy.