Nikoletta Anastasopoulou

Comparative evaluation of HP oxide glass fibers for Q-switched and free-running Er:YAG laser beam propagation

The radiation transmission of a Q-switched and a free-running Er:YAG laser, emitting at 2.94 μm, through high power (HP) oxide glass fibers of 450 μm and 250 μm core diameter was studied. Attenuation measurements were obtained as a function of the laser energy input and as a function of the curvature. The output beam quality was also studied using a beam profiler. Experiments with the same Er:YAG laser but with a 1000 μm core diameter cyclic olefin polymer coated silver hollow glass (COP/Ag) waveguide as the delivery system were performed for comparison. The results are promising as far as the delivery of Q-switched Er:YAG laser radiation is concerned. The fibers exhibited an attenuation below 0.7 dB/m, good output beam profiles, while no damage was observed after extended use.

Q-switched Er:YAG radiation transmission through fluoride glass fibers and dielectric-coated metallic hollow waveguides

The radiation transmission of a Q-switched Er:YAG laser, through fluoride glass fibers of 450 and 600 μm core diameter, and through a cyclic olefin polymer coated silver hollow glass waveguide (COP/Ag), of 1 mm inner diameter, was investigated. Attenuation measurements were obtained as a function of the laser energy input and as a function of curvature, at 90° and 180° bending angle. The results are promising for the delivery of Q-switched Er:YAG laser radiation, as the fibers exhibited attenuation of 0.9 dB/m and the waveguide 1.9 dB/m, and no damage of them was observed.

Pulsed HF and Er:YAG laser radiation transmission through sapphire and fluoride glass fibers

A pulsed Er:YAG laser and a preionized pulsed HF laser were used for the evaluation of the transmission properties of sapphire fibers and fluoride glass fibers. Both lasers provided an output of 100 mJ/pulse, with a repetition rate of 1Hz at 3 micrometers wavelength. The pulse duration of the two lasers was 200 ns for the HF and 80 microsecond(s) for the Er:YAG. The sapphire fibers were 0.25 m long with diameters varying from 585 to 850 micrometers . The fluoride fibers were flexible, 1.6m long, with inner diameters varying from 350 to 600 micrometers . The evaluation of the fiber properties include both straight and bend loss characteristics, the influence of the input power to the output power and the permitted misalignment of the fiber in respect to the optical axis.

Laser excited autofluorescence for discrimination of atherosclerosis

Experiments on atherosclerotic plaque diagnosis were carried out using laser induced fluorescence (LIF) spectroscopy on carotid plaque specimens. The excitation laser was a nitrogen laser, emitting pulses at a wavelength of 337 nm. Over 10 samples were examined in vitro and several spectra were obtained from each sample. Results were compared with conventional clinical techniques, such as histopathological diagnosis, which showed three areas of different composition on the pathological samples: fibrous tissue, lipid constituents and calcified plaque. An effort was made to distinguish the composition of the sample from the obtained spectra. Also, the results were compared with our previous work using longer excitation wavelengths. Spectral morphology of UV excited fluorescence reveals multi-peaks lineshapes, as a result of the superposition of different tissue chromophore signals. However, there was no observed specific wavelength where spectra corresponding to fibrous tissue, calcified tissue and lipid constituents have peaks.

Pulsed 3-μm laser radiation transmission through hollow plastic and hollow glass waveguides

The transmission properties of four different waveguides were investigated: (1) dielectric coated silver hollow glass waveguides, with diameters varying from 0.7 mm to 1 mm, (2) polyamide waveguides, with diameters varying from 0.7 mm to 1 mm, (3) a silica glass waveguide, with a 0.7 mm diameter and (4) a plastic waveguide, with a 0.7 mm diameter. Two different lasers were used for the evaluation of these waveguides: (1) a pulsed Er:YAG laser, emitting at 2.96 micrometers and (2) a corona preionized pulsed HF laser, emitting at 2.78 micrometers . Both straight and bent loss characteristics of the waveguides were studied.

Q-switched Er:YAG radiation transmission through medical COP-coated silver hollow glass waveguide

Transmission measurements of Q-switched Er:YAG laser radiation, through cyclic olefin polymer-coated silver hollow glass waveguides, were performed under straight and bent conditions and the beam quality at the output of the waveguide was studied.

Output beam quality investigation of medical infrared and midinfrared waveguides and fibers

The effect of the mid-infrared laser radiation propagation through waveguides and fibers on the quality of the laser beam is investigated. Fluorocarbon fibers and metallic hollow waveguides with dielectric coating were investigated, using an Er:YAG laser (2.94 micrometers ), an HF laser (2.78 micrometers ) and a CO2 laser (10.6 micrometers ). A comparison was made between the different waveguides and fibers, regarding the quality of the output beam.

Development and in-vitro/in-vivo trials of an endoscopic laser diagnosis/surgery prototype

A laser laboratory prototype for laparoscopic, endoscopic or angioplastic surgery was developed, incorporating an Er:YAG laser as the therapeutic tool in endoscopic/laparoscopic surgery and angioplasty and a N2 laser induced fluorescence system in order to monitor the surgical process. Additionally, a laser radiation transmission system with waveguides and fibers was developed, to transmit the laser radiation, through an endoscope or laparoscope. The system was used in in vivo animal trials, giving promising results for the application of the device in semi-operative applications, in combination with systems of improved endoscopic imaging.

Pulsed HF laser radiation transmission through fluorocarbon-polymer-coated silver hollow glass waveguides

Flexible fluorocarbon polymer-coated silver hollow glass waveguides, devised for the delivery of 3.0 micrometers radiation, were evaluated sing a plasma cathode HF laser emitting at 2.78 micrometers , in a 180 ns duration, at a 1 Hz repetition rate. A multimode beam of 10 mrad divergence at FWHM, was focused into the 700 micrometers diameter, 986 mm long waveguide and was transmitted through it under straight and various bent conditions. The straight transmission loss was found to be 0.9 dB/m, while the bent transmission losses varied from 2.0 dB/m (90 degree(s) bent -35 cm bending radius) to 2.4 dB/m (180 degree(s) bent -10 cm bending radius), for the range of measurements attempted. Transmission as a function of the laser energy input was also measured. Losses increased from 1.5 dB/m at 3 mJoules to 7.0 dB/m at 20 mJoules laser input. These attenuation characteristics at the wavelength of 2.78 micrometers make these waveguides very promising for pulsed radiation and tissue interactions in in vitro and in vivo trials.

Laser-induced fluorescence as a diagnostic tool in atherosclerosis

Experiments on atherosclerotic plaque diagnosis were carried out using laser induced fluorescence. Different excitation wavelengths were tested: 488 nm and 457.9 nm of a c.w. Ar+ laser as well as 476 nm and 407 nm of a c.w. Kr+ laser. Over 15 samples were examined and several spectra were obtained from each sample. Results were cross- examined with conventional clinical techniques, such as histopathological diagnosis, which showed three main components of the atherosclerotic plaque: fibrous tissue, lipid constituents and calcified plaque. An effort was made to distinguish the composition of the sample from the obtained spectra. Fluorescence spectra corresponding to calcified plaque present their maximum in the area of 530 nm - 550 nm. However, there was not observed a specific wavelength where spectra corresponding to fibrous tissue and lipid constituents present maximum. Full width half maximum of the fluorescence spectra was also measured and the ratio of the fluorescence intensity at 600 nm over the intensity at 576 nm, I(600)/I(576), was calculated.