Iulian Ionita

Femtosecond laser: the finest tool for hard tissue ablation

We report oral cavity specific hard tissue ablation experiments at different fluence values using femtosecond laser. The set-up was composed by a high energy femtolaser, optical and mechanical equipment for focusing and displacement of the beam on the sample surface. Using a lens to focus the beam we have obtained fluence range between 75 J/cm2 and 0.21 J/cm2. Samples were human extracted teeth and mandible bone. Created structures were rows. Characterization of ablated structures was made by scanning electron microscope and optical microscope. Ablation areas images show crystalline and regular structures. There are not evidences of material burning under 75 J/cm2. Generated structures are reproducible, dependent on tissue quality and surface roughness. Dimensions of structures are of tens microns, dependent on beam fluence and material hardness. We appreciate the potential of the method to about 1 micron precision. The results are positive considering the advantages of the method: ablation precision and no collateral damage.

Teeth material ablation by femtosecond laser

In this work we made teeth ablation experiments using a laser microprocessing set-up coupled with an amplified femtosecond laser system with 200 fs pulse duration. The experiments were performed at different laser fluences, from 0.21 J/cm2 up to 64 J/cm2. Structures with computer controlled geometries were created as single round craters, large square craters shapes, and parallel lines. Irradiation was made in single-pulse, multi-pulse, and quasi-continuous (2 kHz) mode at different laser scanning speeds. Characterization of ablated structures was made by optical microscopy and scanning electron microscopy. Ablation areas images show crystalline and regular structures. There are not evidences of material burning under 64 J/cm2. Generated structures are reproducible, dependent on dental quality. Enamel ablation threshold under 3 J/cm2 was measured. Dimensions of the ablated structures are of tens of micrometers, depending on beam fluence, focusing optics, and material hardness. When a 10x microscope objective was used, craters with about 5-7 micrometers were obtained. Better resolution of the structures can be obtained down to about 1 micron, however more difficult is to observe and work with such ablated structures. Femtosecond laser ablation demonstrates to be a promising method for teeth treatment due to its advantages: ablation precision and no collateral damages.

Bone tissue ablation by femtosecond laser beam

We report here bone tissue ablation experiments performed with femtosecond laser. We determined ablation threshold value of human mandible which is the hardest bone of the skull.

Occlusal caries detection using polarized Raman spectroscopy

The tooth enamel, because of its hydroxyapatite composition, must present a Raman spectrum with strong polarization anisotropy. Carious lesions of the enamel will produce an alteration of local symmetry and will increase much more scattering of light. This will reduce the anisotropy of the Raman spectra. Because of the difference between high sensitivity to polarization of the 959 cm-1 Raman peak in sound enamel and low sensitivity in carried enamel, Raman polarized spectroscopy could be a useful method to early detect teeth caries.

Compared NIR and UV hard tissue drilling by femtosecond laser beam

Bone tissue drilling experiments performed with the same femtosecond laser at NIR and UV wavelength are reported. The ablation threshold value of human mandible, which is the hardest bone of the skull, was also determined. It was not found significant difference between thresholds. UV ablation is more precise.

New polarimetric investigations on human tissues using ultra-short laser imaging polarimetry

We report in this paper some new polarimetric investigations made on pathologically modified human tissues, using the ultra-short laser imaging polarimetry. This technique can be applied for a wide variety of objects with polarization inhomogeneous structure. Real biological tissues have an optically inhomogeneous structure, so any changes produced in the optical polarization state of a light beam passing through such samples (or reflected by them) can reveal important information about the respective biological tissue. The influence of the geometrical architectonics of a cancerous liver tissue on the polarization properties of an ultra-short laser beam who passes through such a sample is radical and can be seen both in the transmitted polarized light, as well as in the SHG (second harmonic generation) polarized light. We used a polarization sensitive imaging system, whose basic optical scheme has been previously published, this time a modified version of the experimental set-up being used. The biological tissue investigated in this paper was a slide of liver tumor. The polarization sensitive intensities for the transmitted and SHG light were measured with two detectors for different polarimetric configurations of the set-up. Experiments show a significant difference between transmitted and, respectively, SHG light behavior.

Monte Carlo Simulation of Photon Way in Clinical Laser Therapy

The multiple scattering of light can increase efficiency of laser therapy of inflammatory diseases enlarging the treated area. The light absorption is essential for treatment while scattering dominates. Multiple scattering effects must be introduced using the Monte Carlo method for modeling light transport in tissue and finally to calculate the optical parameters. Diffuse reflectance measurements were made on high concentrated live leukocyte suspensions in similar conditions as in-vivo measurements. The results were compared with the values determined by MC calculations, and the latter have been adjusted to match the specified values of diffuse reflectance. The principal idea of MC simulations applied to absorption and scattering phenomena is to follow the optical path of a photon through the turbid medium. The concentrated live cell solution is a compromise between homogeneous layer as in MC model and light-live cell interaction as in-vivo experiments. In this way MC simulation allow us to compute the absorption coefficient. The values of optical parameters, derived from simulation by best fitting of measured reflectance, were used to determine the effective cross section. Thus we can compute the absorbed radiation dose at cellular level.

Biotissue structure investigation using ultra-short pulsed laser polarimetry

This paper presents the experimental analysis of different pathologically modified tissues, using the ultra-short laser polarimetry. Any changes produced in the polarization state of a light beam passing through a sample that posses a polarization inhomogeneous structure, will depend on both the interfaces and the internal structures of the respective sample. The ultra-short laser polarimetry, as a new polarization imagery technique, is able to provide more in-depth increased resolution images of the samples.

Femtonics and Medical Applications

Femtonics is a new branch of Photonics. It means applications of the ultrashort pulsed laser. The paper shows three possible applications of femtolaser in medical diagnosis and treatment. The most commonly used phenomenon is two‐photon absorption with two main applications: TPFM and SHGM. Other possible applications of femtolaser are OCT and nano‐surgery.