Sourav Das Chowdhury

Yb-Doped Pedestal Silica Fiber Through Vapor Phase Doping for Pulsed Laser Applications

This letter describes successful fabrication and detail characterization of ytterbium (Yb)-doped pedestal aluminosilicate fibers through vapor phase doping technique using modified chemical vapor deposition system (MCVD). Fabricated preforms have uniform step-index profiles devoid of any profile ripples, central dip, and/or core-clad interface defects, which are very common to the preforms made by a solution doping method. Fibers with a pedestal design exhibit good optical properties, low photodarkening-induced losses, high SNR values, and higher efficiencies making them suitable for high-power pulsed laser applications as compared with normal Yb-doped fibers. One of the pedestal fibers has demonstrated the output energy of 186 μJ with the 1.86-W average power. The pulse has a width of 100 ns at a 10-kHz repetition rate, which provides a peak power of 1.86 kW.

Numerical and Experimental Study of Multi-peaked and Trimmed Pulses in an Actively Q-switched Fiber Laser

An analysis of „multi-peaked‟ and „trimmed‟ pulses of actively Q-switched fiber lasers based on a theoretical simulation has been reported. The simulated results were supported by experimental results which are well matched.

Broadband generation by multiple four-wave mixing process due to ASE Q-switching in high-power double-clad ytterbium-doped fiber amplifier

Broadband output from 1060nm to 1700nm and cascaded four-wave mixing generated red light pulsing is observed in a fiber amplifier set up consisting of a 5.5m double clad, double D shaped Ytterbium doped fiber, a single clad passive fiber for excess pump absorption and a splitter, both with and without a CW seed. Self-pulsing occurs from ASE due to passive Q-switching by saturable absorption effect of the active fiber and also depends on splice loss. The pulses generate broadband output by multiple four-wave mixing process with maximum broadening efficiency near 1300nm which is the zero dispersion wavelength for silica fiber. Pulses traveling both in forward and backward direction have enough peak power and energy to damage splice points and fiber components. When seeded the self-pulsing and broadband generation is often suppressed but again generate at increased pump powers.

All-fiber laser at 1.94 µm: effect on soft tissue

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.

Intensity Limitation of Nano-second Gaussian Optical Pulses in High Gain Fiber Amplifiers

The paper extrapolates experimental findings through a mathematical model that depicts the manifestation of large gain in fiber amplifiers for Nano-second Gaussian shaped optical pulses in limiting the maximum attainable intensity.

Yb-doped Pedestal Aluminosilicate Fiber through Vapor Phase Doping for High Power Laser Applications

Presenting fabrication process and characteristics of large core Yb-doped optical fibers with pedestal design using vapor phase doping technique. Preforms have uniform step-index profiles. Fibers exhibit good optical properties, suitable for high power laser applications.

Experimental study of backscattering pulses and broadband generation in a Q-switched MOPA

In a master oscillator fiber amplifier (MOPA) system, we have experimentally studied nonlinear phenomena originating in the amplifier Yb-fiber during amplification of Q-switched pulse. During amplification, the Yb-doped active fiber generated backscattered pulses followed by amplified pulse breaking and high peak power short pulse generation. The backscattered pulses were delayed maximum by 30ns and seed pulse of width 108ns was broadened to 140ns at 20KHz repetition rate due to different scattering effects in a 8m long Yb-doped double clad fiber. At higher pump power, the output pulse showed unstable pulse envelops and eventually broke into multiple short pulses. A broadband output was observed from 1050 to 1650nm. This unwanted pulse breaking was observed which caused catastrophic damage to the MOPA system occasionally.

Spatial, Spectral and Temporal Study of Self-pulsing in CW Yb-Fiber Laser due to Saturable Absorption Effect

Self-pulsing in a CW Yb-fiber laser due to saturable absorption (SA) is explored in spatial, spectral and temporal domain. Shorter active fiber length removed this effect at the cost of increased unabsorbed excess pump power.

All-fiber Tunable Ring Laser near 2 micron

A tunable continuous-wave thulium-doped fiber ring laser near 2 μm has been studied numerically and experimentally under in-band pumping at 1.6 μm and a tunable range > 30 nm has been demonstrated under cavity-loss variation.