Influence of effective number of pulses on the morphological structure of teeth and bovine femur after femtosecond laser ablation

Femtosecond lasers have been widely used in laser surgery as an instrument for contact-free tissue removal of hard dental, restorative materials, and osseous tissues, complementing conventional drilling or cutting tools. In order to obtain a laser system that provides an ablation efficiency comparable to mechanical instruments, the laser pulse rate must be maximal without causing thermal damage. The aim of this study was to compare the different morphological characteristics of the hard tissue after exposure to lasers operating in the femtosecond pulse regime. Two different kinds of samples were irradiated: dentin from human extracted teeth and bovine femur samples. Different procedures were applied, while paying special care to preserving the structures. The incubation factor S was calculated to be 0.788 +/- 0.004 for the bovine femur bone. These results indicate that the incubation effect is still substantial during the femtosecond laser ablation of hard tissues. The plasma-induced ablation has reduced side effects, i.e., we observe less thermal and mechanical damage when using a superficial femtosecond laser irradiation close to the threshold conditions. In the femtosecond regime, the morphology characteristics of the cavity were strongly influenced by the change of the effective number of pulses. (C) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.JBO.17.4.048001]

Necrosis response to photodynamic therapy using light pulses in the femtosecond regime

One of the clinical limitations of the photodynamic therapy (PDT) is the reduced light penetration into biological tissues. Pulsed lasers may present advantages concerning photodynamic response when compared to continuous wave (CW) lasers operating under the same average power conditions. The aim of this study was to investigate PDT-induced response when using femtosecond laser (FSL) and a first-generation photosensitizer (Photogem) to evaluate the induced depth of necrosis. The in vitro photodegradation of the sensitizer was monitored during illumination either with CWor an FSL as an indirect measurement of the PDT response. Healthy liver of Wistar rats was used to evaluate the tissue response. The photosensitizer was endovenously injected and 30 min after, an energy dose of 150 Jcm-2 was delivered to the liver surface. We observed that the photodegradation rate evaluated via fluorescence spectroscopy was higher for the FSL illumination. The FSL-PDT produced a necrosis nearly twice as deep when compared to the CW-PDT. An increase of the tissue temperature during the application was measured and was not higher than 2.5 °C for the CW laser and not higher than 4.5 °C for the pulsed laser. FSL should be considered as an alternative in PDT applications for improving the results in the treatment of bulky tumors where higher light penetration is required.

Fabrication of micro-channels in optical fibers using femtosecond laser pulses and selective chemical etching

The fabrication of micro-channels in single-mode optical fibers is demonstrated using focused femtosecond laser processing and chemical etching. Straight line micro-channels are achieved based on a simple technique which overcomes limitations imposed by the fiber curved surface.

Point-by-point inscription of 250 nm period structure in bulk fused silica by tightly focused femtosecond UV pulses

By conducting point-by-point inscription in a continuously moving slab of pure fused silica at the optimal depth (170νm depth below the surface), we have fabricated a 250nm period nanostructure with 30nJ, 300fs, 1kHz pulses from a frequency-tripled Ti:sapphire laser. This is the smallest value for the inscribed period yet reported, and has been achieved with radical improvement in the quality of the inscribed nanostructures in comparison with previous reports.

Cascaded nonlinear absorption of femtosecond laser pulses in dielectrics

We investigated the energy deposition process leading to the waveguide inscription in transparent dielectrics both experimentally and theoretically. Parameters of multiphoton absorption process and inscription thresholds were measured in a range of materials including YAG, ZnSe, RbPb2Cl5 crystals, and in fused silica and BK7 glasses.

Point-by-point inscription of 250-nm-period structure in bulk fused silica by tightly-focused femtosecond UV pulses: experiment and numerical modeling

By conducting point-by-point inscription in a continuously moving slab of a pure fused silica at the optimal depth (170 μm depth below the surface), we have fabricated a 250-nm-period nanostructure with 30 nJ, 300 fs, 1 kHz pulses from frequency-tripled Ti:sapphire laser. This is the smallest value for the inscribed period yet reported, and has been achieved with radical improvement in the quality of the inscribed nanostructures in comparison with previous reports. The performed numerical modeling confirms the obtained experimental results.

Low loss depressed cladding waveguide inscribed in YAG:Nd single crystal by femtosecond laser pulses

A depressed cladding waveguide with record low loss of 0.12 dB/cm is inscribed in YAG:Nd(0.3at.%) crystal by femtosecond laser pulses with an elliptical beam waist. The waveguide is formed by a set of parallel tracks which constitute the depressed cladding. It is a key element for compact and efficient CW waveguide laser operating at 1064 nm and pumped by a multimode laser diode. Special attention is paid to mechanical stress resulting from the inscription process. Numerical calculation of mode distribution and propagation loss with the elasto-optical effect taken into account leads to the conclusion that the depressed cladding is a dominating factor in waveguide mode formation, while the mechanical stress only slightly distorts waveguide modes.

Fabrication of micro-channels in optical fibers using femtosecond laser pulses and selective chemical etching

The fabrication of micro-channels in single-mode optical fibers is demonstrated using focused femtosecond laser processing and chemical etching. Straight line micro-channels are achieved based on a simple technique which overcomes limitations imposed by the fiber curved surface. © 2005 Optical Society of America.

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.

Femtosecond carrier dynamics and saturable absorption in graphene suspensions

Nonlinear optical properties and carrier relaxation dynamics in graphene, suspended in three different solvents, are investigated using femtosecond (80 fs pulses) Z-scan and degenerate pump-probe spectroscopy at 790 nm. The results demonstrate saturable absorption property of graphene with a nonlinear absorption coefficient, beta of (similar to 2-9) x 10(-8) cm/W. Two distinct time scales associated with the relaxation of photoexcited carriers, a fast one in the range of 130-330 fs (related to carrier-carrier scattering) followed by it slower one in 3.5-4.9 ps range (associated with carrier-phonon scattering) are observed. (C) 2009 American Institute of Physics.