Amir Herzog

Wavelength conversion of nanosecond pulses to the mid-IR in photonic crystal fibers

We investigate degenerate four wave mixing with nanosecond pulses in fused silica photonic crystal fibers. Phase-matching curves are calculated taking into account the material and waveguide dispersion. Experiments with a nanosecond pulsed Nd:YAG pump laser and relatively short fiber lengths show more than an octave spanning conversion to idler and signal wavelengths at 3.105 μm and 0.642 μm, respectively. Conversion efficiency depends on the fiber length and pump intensity and is limited in our experiments by damage of the fiber input facet. Our results represent a new stretch towards the limit of the silica transmission window in the mid-infrared (IR).

Selective tissue ablation using laser radiation at 355 nm in lead extraction by a hybrid catheter; a preliminary report.

Current lead extraction (LE) devices can harm the blood vessel endothelium, increasing the risk of perforation.

Shaping photomechanical effects in tissue ablation using 355 nm laser pulses.

We investigate the influence of the cladding diameter of an optical delivery fiber on the ablation dynamics of porcine aorta immersed in tetracycline antibiotic solution using 355 nm nanosecond pulses. We manipulate the pressure transients by enforcing a rear rigid interface (applied by an enlargement of the cladding diameter) to the ablated area, which leads to enhanced ablation efficiency along with a reduction in tissue disruption effects. Numerical simulations, based on the finite elements method, are used to study the propagation of the pressure transients within the suggested scheme. Ultrasonic transducers are used for measuring the increased pressure in front of the fibers facet and the reduced pressure at the fibers circumference in the presence of large diameter cladding. The increase and decrease are both found to be by a factor of ˜1.8. The width of the cavitation bubble is measured by high-speed photography. An enlargement of 13.8% is demonstrated, at the expense of backward expansion along the fibers axis. A histopathological in vitro study demonstrates an average enhancement of 12.27% in the diameter of the ablated crater, as well as significant reduction in the disruption effects. Our study sheds light on the potential to improve the ablation efficiency without additional energy cost, along with attaining improved safety for interventional medical procedures.

Reduced tissue disruption effects by manipulating pressure transients of UV nanosecond laser pulses

Reduced tissue disruption and enhanced ablation efficiency are demonstrated using a pulsed 355nm laser. This was achieved by innovative engineering of the end facet of the delivering fiber to stir pressure transients initiated during ablation.

Lead extraction by selective operation of a nanosecond-pulsed 355nm laser

Lead extraction (LE) is necessary for patients who are suffering from a related infection, or in opening venous occlusions that prevent the insertion of additional lead. In severe cases of fibrous encapsulation of the lead within a vein, laser-based cardiac LE has become one of the foremost methods of removal. In cases where the laser radiation (typically at 308 nm wavelength) interacts with the vein wall rather than with the fibrotic lesion, severe injury and subsequent bleeding may occur. Selective tissue ablation was previously demonstrated by a laser operating in the UV regime; however, it requires the use of sensitizers (e.g.: tetracycline). In this study, we present a preliminary examination of efficacy and safety aspects in the use of a nanosecond-pulsed solid-state laser radiation, at 355 nm wavelength, guided in a catheter consisting of optical fibers, in LE. Specifically, we demonstrate a correlation between the tissue elasticity and the catheter advancement rate, in ex-vivo experiments. Our results indicate a selectivity property for specific parameters of the laser radiation and catheter design. The selectivity is attributed to differences in the mechanical properties of the fibrotic tissue and a normal vein wall, leading to a different photomechanical response of the tissue’s extracellular matrix. Furthermore, we performed successful in-vivo animal trials, providing a basic proof of concept for using the suggested scheme in LE. Selective operation using a 355 nm laser may reduce the risk of blood vessel perforation as well as the incidence of major adverse events.

A Route to Laser Angioplasty in the Presence of Fluoroscopy Contrast Media, Using a Nanosecond-Pulsed 355-nm Laser

We examine the efficacy of flushing the fluoroscopy contrast media during laser-angioplasty prior to the laser operation, when using nanosecond pulses at a wavelength of 355 nm, guided in an optical fiber. We investigate the acoustic transients of the ablation in blood, saline, and contrast media in relation to the absorption spectra of the three. Ex vivo results of ablation in porcine aorta samples showed only minor disruption effects in samples which were immersed in contrast media, and none when immersed in saline. These results are in contrast to the severe disruption effects witnessed in previous reports, using an excimer laser at a wavelength of 308 nm within contrast media. Numerical simulations based on the finite-elements method analyzed the pressure and temperature distributions, and supported the experimental findings. Our study indicates a feasibility of using nanosecond-pulsed laser sources at 355 nm in percutaneous vascular laser interventions that include fluoroscopy contrast media.

Spatial-coherence effect on damage occurrence in multimode optical fibers using nanosecond pulses

We investigate high peak power delivery in highly multimode optical fibers. By altering the spatial-coherence of the input beam, we demonstrate the transmission of 120mJ ns pulses at 355nm through a multimode fiber.

Chalcogenide waveguides on a sapphire substrate for 3-5 μm wavelengths applications

As2S3 Chalcogenide strip waveguides on a sapphire substrate were fabricated and characterized. The waveguides enable an efficient transmission of 3-5μm wavelengths, and numerical simulations reveal benefits over silica and silicon substrates.