Single-mode thulium fiber laser (TFL) at 1.94 μm with optimal energy and pulse settings has potential benefits for lithotripsy over the presently used Ho:YAG laser. A fiber Bragg grating-based, all-fiber, continuous-wave and modulated TFL at 1.94 μm is configured to deliver up to 30 W of laser power with efficiency of 50%. The TFL operating in the range of repetition rate 10 Hz-1 kHz and corresponding pulse energy 2 J-1.05 mJ is irradiated on urinary stone for in-vitro evaluation of fragmented particle size and retropulsion. TFL irradiation at higher repetition rate fragments the stones into smaller particle size (average size of few hundreds microns) resulting reduced retropulsion.
A focused laser beam at wavelength of strong water absorption at 1.94 μm can be a good scalpel for precision soft tissue surgery. A fiber Bragg grating-based, all-fiber, continuous-wave as well as modulated, cladding pumped, thulium-doped fiber laser at 1.94 μm has been configured to deliver up to 10 W of laser power under pumping at 793 nm having an efficiency of 32 %. The laser was exposed to freshly sacrificed chicken breast at different power level and exposure time. The formalin-fixed samples were examined by microscopy to identify the ablation region, carbonization and necrosis region for laser parameter optimization.
We report fabrication of a segmented cladding fiber (SCF) in silica-based glass. An SCF with a uniform core of pure silica and cladding of periodically arranged pure silica and fluorine-doped silica in an angular direction has been fabricated by using the stack-and-draw technique. The fabricated fiber has been characterized by capturing its near-field intensity pattern at 633 nm wavelength. The number of modes has been estimated from the captured near-field intensity pattern by using neural network analysis. A four-segment SCF of 30-μm core diameter and 0.43% relative index differences between the high- and low-index segments shows few-mode operation by filtering out higher-order modes of an otherwise highly multimode fiber.
Strong water absorption at 2 μm generated recent interest in lasers at this wavelength for soft tissue surgery. A fiber
Bragg grating-based, all-fiber, continuous-wave, cladding pumped, thulium-doped fiber laser at 1.95 μm is configured.
The thulium-doped active fiber with octagonal-shaped inner cladding is pumped at 808 nm (total power of 17 W) with
six laser diodes through a combiner. The laser power of 3.3 W (after elimination of unabsorbed pump power through a
passive fiber) with slope efficiency of 23% (against launched pump power) is achieved. The linear variation of laser
power with pump offers scope of further power scaling.
Rare earth (RE) doped optical fibers have shown tremendous progress for producing high power fiber lasers for industrial, medical and strategic applications. However, fabrication of large core, high Yb-doped fiber is still a challenge through conventional process due to poor repeatability and limitation regarding core size. This paper presents successful fabrication of Yb-doped fibers through vapor phase doping technique. Preform fabrication was carried out using a specially constructed MCVD system containing High Temperature Vapor Delivery Unit with sublimators for Al and Yb precursors. The novelty of the present work lies in deposition of Al2O3 and Yb2O3 in vapor phase simultaneously with silica during formation of sintered core layer which result in uniform dopants distribution in the preform. The fibers exhibited lasing efficiency of 76% with low ‘photodarkening effect’.
Radiation resistance property of a series of optical preforms/fibers of different compositions including those available
commercially has been investigated to find out a suitable fiber in the UV-Visible wavelength range. The fibers drawn
from commercial preforms exhibit feeble transmission in the UV zone prior to the radiation exposure and considerable
darkening even with very low dose of radiation; although the preforms contain high OH in the core and it is claimed that
higher OH content provides better transmission and radiation tolerance in the UV region. Radiation Induced Attenuation
(RIA) dynamics for the wavelength range of 200 to 850 nm has been characterized 'real-time' under γ radiation.
Dependence of RIA on the OH concentration in the core has been analyzed for wavelength band of 400-500 nm and at
630 nm. The generation of E' and NBOH color centers is responsible for the absorption at the above two wavelength
bands respectively and is strongly influenced by the fiber composition. The effect of dose rate up to the accumulated
dose of 1MRad has been studied. This systematic study led to the fabrication of a fiber with better radiation resistance
characteristics in the wavelength range of 400-700 nm with out any radiation induced absorption peak at 630 nm.
Large flattened mode optical fiber with raised index ring around the outer edge of the fiber core has been fabricated
through modified chemical vapour deposition process to raise the threshold for non-linear interaction in high power laser
fiber. The conversion of the fundamental mode shape from a Bessel function to a top hat function, enhances the effective
area of the core intersected by the mode without increasing the physical size of the core. The shape of the fundamental
mode is observed to be strongly dependent on the width of the raised index ring from the modal analysis. Suitable fiber
parameters have also been estimated through the modal field analysis. Fabrication process steps have been optimized to
achieve the desired fiber parameters. Modal field distribution, transmission properties and bending loss of the fabricated
fibers have been characterized.
In this paper Tm/Yb doped microspheres have been successfully created through melting the ends of fibre cores etched
from single mode Tm/Yb fibres designed and fabricated specifically for the laser emission centred at mid-infrared region.
When coupled with a fibre taper, a microsphere fibre laser cavity can thus be configured creating a system when pumped
by a ~1600nm laser source using a monochromator to monitor the spectral characteristics of the laser output produced.
The performance and characteristics of the Tm/Yb microsphere lasers are discussed in detail in the paper. The laser has
shown low threshold in terms of the pump power making it well suited to potential optical fibre sensor applications.