Femtosecond Inscription of a Fiber Bragg Grating Spectral Array in the Same Spatial Location.

A five fiber Bragg grating (FBG) array is inscribed at the same spot with a single uniform phase-mask (PM). The inscription setup consists of a near-infrared femtosecond laser, a PM, a defocusing spherical lens and a cylindrical focusing lens. The tunability of the center Bragg wavelength is achieved by a defocusing lens, and by translating the PM, which results in a different magnification of the PM.

Large-mode-area multicore Yb-doped fiber for an efficient high power 976 nm laser.

We present an efficient 976 nm laser generation from an ytterbium (Yb)-doped step-index multicore fiber (MCF) with six cores placed in a ring shape. Each of the six cores has a large-mode-area (LMA) and a low numerical aperture (NA), which makes the MCF equipped with the features of a large core-to-cladding area ratio and differential bending loss for wavelength and mode selection. Hence, the Yb-doped MCF benefits 976 nm laser generation by simultaneously suppressing unwanted 1030 nm emission and higher-order modes (HOMs).

Tissue post-classification using the measured acoustic signals during 355 nm laser atherectomy procedures.

The current laser atherectomy technologies to treat patients with challenging (to-cross) total chronic occlusions with a step-by-step (SBS) approach (without leading guide wire), are lacking real-time signal monitoring of the ablated tissues, and carry the risk for vessel perforation. We present first time post-classification of ablated tissues using acoustic signals recorded by a microphone placed nearby during five atherectomy procedures using 355 nm solid-state Auryon laser device performed with an SBS approach, some with highly severe calcification. Using our machine-learning algorithm, the classification results of these ablation signals recordings from five patients showed 93.

Applying tiling and pattern theory in the design of hollow-core photonic crystal fibers for multi-wavelength beam guidance.

We apply tiling and pattern theory in the design of hollow-core photonic crystal fibers for guiding light in multiple spectral bandgaps. By combining two different glass apexes in a single [3;3.4.

Characterization of sub-nanosecond pulsed laser amplification with Er:Yb co-doped phosphate glass fibers.

We present an experimental characterization of the amplification of sub-nanosecond duration laser pulses at a wavelength of 1538 nm in short custom-made Er:Yb phosphate glass fibers with different core diameters. The fibers vary in their diameter from 100 µm (highly multi-mode) down to 12 µm (single-mode). The peak power, energy per pulse, and spectral shape of the amplified signal are presented.

Femtosecond Bragg grating inscription in an Yb-doped large-mode-area multicore fiber for high-power laser applications.

We demonstrate a direct inscription of a fiber Bragg grating (FBG) in the active cores of an Yb-doped large mode area multicore fiber (MCF). An ultrashort pulsed laser is used to inscribe the FBG simultaneously in all six cores. In order to validate the FBG reflection and uniformity, the FBG is incorporated as a rear mirror in a fiber laser oscillator setup.

Use of Co:MgAlO transparent ceramics in passive Q-switching of an Er:Glass laser at 1.534 µm.

We present the implementation of Co:MgAlO transparent ceramics as passive Q-switching elements in an Er:Glass laser at 1.534 µm. Linearly polarized pulsed output was obtained by Brewster angle inclination of the material Q-switching plate relative to the laser axis.

Radiative and non-radiative transitions of excited Ti cations in sapphire.

We have measured the fluorescence quantum efficiency in Ti:sapphire single crystals between 150 K and 550 K. Using literature-given effective fluorescence lifetime temperature dependence, we show that the zero temperature radiative lifetime is (4.44 ± 0.

High-efficiency Raman conversion in SF- and CF-filled hollow-core photonic bandgap fibers.

We present a comparative experimental investigation of vibrational stimulated Raman scattering in hollow-core photonic bandgap fibers pressurized with sulfur hexafluoride (${{\rm SF}_6}$SF) and tetrafluoromethane (${{\rm CF}_4}$CF) gases. Nanosecond-duration pulses at a wavelength of 1030 nm are coupled into the gas-filled fiber, and the first and second Stokes orders are measured at the fiber output. We characterize the conversion process as a function of gas, fiber length, and input power.

Femtosecond inscription of fiber Bragg gratings through the coating with a Low-NA lens.

Fiber Bragg grating (FBG) inscription in standard fibers with femtosecond (fs) laser pulses was first reported nearly two decades ago. FBG fs inscription through the fiber polymer coating was recently demonstrated with a phase mask (PM) and High Numerical Aperture (High-NA) cylindrical lenses. In this work, we report on a new technique for FBG inscription through the acrylate polymer coating of optical fibers using a Low-NA lens and the PM.

In situ tissue classification during laser ablation using acoustic signals.

We suggest a novel method to classify the type of tissue that is being ablated, using the recorded acoustic sound waves during pulsed ultraviolet laser ablation. The motivation of the current research is tissue classification during vascular interventions, where the identification of the ablated tissue is vital. We classify the acoustic signatures using Mel-frequency cepstral coefficients (MFCCs) feature extraction with a Support Vector Machine (SVM) algorithm, and in addition, use a fully connected deep neural network (FC-DNN) algorithm.

Inscribing an output coupler grating directly through the fiber coating with a 266 nm femtosecond laser.

We inscribe with 266 nm femtosecond pulses a ∼0.75% output coupler for a 1550 nm fiber laser directly through the coating of an SMF-28. The output coupler was inscribed with the phase-mask technique without H loading.

Characterizing the effect of femtosecond photo-treatment on the center wavelength of fiber Bragg gratings.

Various types of pre- and post-treatments to optical fibers are typically used to improve and/or change the properties of fiber Bragg grating (FBG). Here, we investigate experimentally the effects of NIR femtosecond (fs) laser pulses used for pre- and post-treatment on the refractive index of the fiber, and the resulting center wavelength shift of an fs inscribed FBG. We observe "red"-shift when applying a suitable pre-treatment, and both "blue"- and "red"-shifts when applying post-treatment.

Strain-assisted femtosecond inscription of phase-shifted gratings.

Two slightly shifted gratings are inscribed, one over the other, while exploiting fiber strain in a single-mode fiber. The inscription is done with a near-infrared femtosecond laser, a phase mask, and a cylindrical focusing lens. The first fiber Bragg grating (FBG) is inscribed under normal fiber tension, while the second overlapping FBG is inscribed under higher fiber tension.

115 W fiber laser with an all solid-structure and a large-mode-area multicore fiber.

We investigate mode-area scaling by means of supermode operation in an all-solid multicore fiber. To obtain a large-mode area (LMA), we designed and fabricated an active double-clad multicore fiber, where each ytterbium-doped core is 19 μm in diameter and has a numerical aperture of 0.067, comparable to the core of the largest available commercial LMA fibers.

Competing radiative and nonradiative decay of embedded ions states in dielectric crystals: theory, and application to Co:AgClBr.

We present a generally applicable theoretical model describing excited-state decay lifetime analysis of metal ions in a host crystal matrix. In contrast to common practice, we include multi-phonon non-radiative transitions competitively to the radiative one. We have applied our theory to Co ions in a mixed AgClBr crystal, and as opposed to a previous analysis, find excellent agreement between theory and experiment over the entire measured temperature range.

Ns-duration transient Bragg gratings in silica fibers.

We demonstrate, for the first time to our knowledge, fast all-optical switching in standard silica fibers, based on a transient Bragg grating. The grating is implemented in the fiber using an immunization photo-pretreatment process, followed by side illumination with femtosecond laser pulses through a suitable phase mask. Each pulse is nonlinearly absorbed, creating a thermal grating that is washed out by thermal diffusion.

Atherectomy using a solid-state laser at 355 nm wavelength.

Peripheral arterial disease (PAD), caused by atherosclerotic processes, is allied with an increased risk of ischemic events, limb loss, and death. Recently, the use of a solid-state laser at 355 nm within a hybrid catheter was suggested for that purpose. In this work, short nanosecond pulses of a solid-state laser at 355 nm delivered through a hybrid catheter, composed of optical fibers and a blunt mechanical blade, are used to conduct a pre-clinical study and two clinical cases.

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.

Nonlinear wave interactions between short pulses of different spatio-temporal extents.

We study the nonlinear wave interactions between short pulses of different spatio-temporal extents. Unlike the well-understood mixing of quasi-monochromatic waves, this configuration is highly non-intuitive due to the complex coupling between the spatial and temporal degrees of freedom of the interacting pulses. We illustrate the process intuitively with transitions between different branches of the dispersion curves and interpret it in terms of spectral exchange between the interacting pulses.

Femtosecond inscription of phase-shifted gratings by overlaid fiber Bragg gratings.

Two slightly shifted gratings are inscribed, one over the other, in an SMF fiber with a femtosecond laser and a phase mask. The transmission spectrum of the complex structure is similar to that of a phase-shifted grating; yet, the fabrication process is fast and simple compared to standard methods. High-quality semi-phase-shifted gratings with -24  dB transmission loss and <100  pm transmission bandwidth are presented.

Effect of femtosecond photo-treatment on inscription of fiber Bragg gratings.

Pre- and post-treatment of optical fibers is typically used to improve the fiber Bragg grating (FBG) fabrication process. Here, we investigate experimentally the effects of femtosecond photo-treatment on the ability to inscribe and erase FBGs in standard, non-sensitized, silica SMF fibers. We observe "immunity" to inscription after applying a suitable pre-treatment to the fiber and full "erasure" of the FGB after applying a suitable post-treatment.

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

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

Objective: Proof of concept for using a solid-state pulsed laser at 355 nm with a hybrid catheter in LE.

Methods: A hybrid catheter was used comprising optical fibers for the delivery of 355 nm laser pulses at 30 Hz and 6 J/cm(2) combined with a blunt mechanical blade.

Effect of spatial coherence on damage occurrence in multimode optical fibers.

We investigate the influence of spatial coherence on damage occurrence in highly multimode optical fibers using ultraviolet (UV) nanosecond pulses, with the aim of delivering high fluence in the UV. In some cases, the optical damage is initiated below the fiber facet damage threshold and takes place along the propagation path; such damage is believed to be caused by local constructive interference, creating "hot spots." In order to reduce the degree of spatial coherence, we used a large-diameter core (1.

Highly efficient 10 cm long fiber laser.

We investigate an innovative multipass-pumping technique in a short photonic crystal fiber laser. The technique is based on simple optical elements and shows, in a power oscillator configuration, highly efficient CW and Q-switched operation of an extremely short fiber laser. We report significantly higher absorption of the pump light, compared to a single-pass configuration, which results in an impressive fourfold increase in slope efficiency, up to 60%.