SBS suppression in high power fiber pulse amplifiers employing a superluminescence diode as seed source

SBS suppression in a high power ns fiber amplifier employing a pulsed SLD as seed source. It emits a 10nm FWHM spectrum free of longitudinal modes at 150mW peak power and 5ns rise / fall time

Suppression of stimulated Raman scattering in high-power fiber laser systems by lumped spectral filters

We present a systematic study on the inhibition of stimulated Raman scattering by lumped spectral filters both in passive optical transport fibers and in fiber amplifiers. This study reveals the parameters that have the strongest influence on the suppression of the Raman scattering (such as the attenuation at the Raman wavelength and the insertion losses at the signal wavelength). These parameters have to be optimized in order to achieve the desired Raman inhibition and/or to minimize the loss in amplifier efficiency. The study is concluded with realistic predictions on the use of spectral filtering elements for Raman scattering inhibition in real-world high power fiber amplifiers. Thus, using for example 10 lumped spectral filters with 20 dB effective Raman attenuation and less than 0.25 dB insertion losses, a maximum Raman threshold increase by a factor of 3 is expected. In this context, long period gratings are proposed as promising filtering elements for Raman inhibition in high power fiber amplifiers. In order to experimentally verify the theoretical predictions and the suitability of long period gratings, a fiber amplifier consisting of 2 m active Ytterbium doped fiber was built. Three long period gratings were consecutively inserted at different positions along the fiber, and the Raman threshold was determined for each situation. It is shown that, with three long period gratings, the Raman threshold (defined as the 20 dB ratio of Raman to signal output power) was increased by about 60%, which offers a good agreement with the theoretical predictions

Efficient high-power generation of visible and mid-infrared light by degenerate four-wave-mixing in a large-mode-area photonic-crystal fiber

An efficient and simple approach for converting pulsed near-IR laser radiation into visible and mid-IR light by exploiting degenerate four-wave-mixing in an endlessly single-mode, large-mode-area photonic-crystal fiber is presented. Coupling a 1 MHz, 200 ps, 8 W average power pulsed source emitting at 1064 nm into this fiber results in average powers of 3 W at 673 nm signal wavelength and of 450 mW at 2539 nm idler wavelength, respectively. The excellent pulse energy conversion efficiencies of 35% for the signal and 6% for the idler wavelength are due to the unique combination of characteristics of this type of fiber. (C) 2009 Optical Society of Americ

Modeling the suppression of stimulated Raman scattering in active and passive fibers by lumped spectral filtering elements

Stimulated Raman scattering in optical fibers can be suppressed by different techniques, which include the use of special fiber designs (that work as distributed spectral filters) or the use of lumped filtering elements. Fiber designs like the w-type profile are limited in maximum fiber core size and provide Raman attenuations of a few dB/m. These characteristics imply that these designs are not suitable for high power fiber amplifiers with short fiber lengths. In these applications lumped filters could provide a better and more flexible solution. Thus, in this work lumped filters will be evaluated as Raman suppression elements in passive fibers as well as in active Yb-doped fibers for amplifier and laser applications. Both the influence of the number of equidistant discrete filters in various setups and the impact of their insertion losses will be theoretically studied

Suppression of stimulated Raman scattering employing long period gratings in double-clad fiber amplifiers

We report on the suppression of stimulated Raman scattering (SRS) in a double-clad fiber amplifier using long-period gratings (LPGs). The LPGs, fabricated with a CO2 laser, achieve SRS suppression by coupling the Stokes wavelength from the active core into the cladding. With only three LPGs inserted into a fiber pulse amplifier, the extractable Raman-free output power was nearly doubled. A numerical simulation of the setup shows good agreement with the experimental results

Nonlinear compression of Q-Switched laser pulses to the realm of ultrashort durations

Mode-locked lasers have an undisputed position in the ultrafast domain, though they are fairly expensive for miscellaneous applications. Thus, laser consumers revert to more cost-effective systems like Q-switched lasers. Here we report on the nonlinear compression of passively Q-switched laser pulses that allows accessing the time domain of sub-10-picoseconds, which has been so far the realm of mode-locked lasers. Laser pulses with an initial duration of 100ps from a passively Q-switched microchip laser are amplified in a photonic crystal fiber and spectrally broadened from 20pm to 0.68nm by self-phase modulation. These pulses are compressed in a grating compressor to a duration of 6ps with a pulse energy of 13µJ

Sub-10 picosecond pulses from a fiber-amplified and optically compressed passively Q-switched microchip laser

We report on nonlinear optical compression of passively Q-switched pulses accessing sub-10 ps domain, which is so far dominated by mode-locked systems. The concept implements the SPM-induced spectral-broadening of passively Q-switched microchip pulses in optical waveguides and a supplementary compression with bulk optics e.g. a pair of diffraction gratings or a chirped-Bragg-grating. Used seed-source is a fiber-amplified, passively Q-switched microchip laser operating on a single longitudinal mode and consists of a monolithically bonded combination of Nd:YVO4-crystal and semiconductor saturable absorber mirror. The microchip laser provides pulses with durations of 100-150 ps, pulse energies of ~200 nJ at various repetition rates from hundreds of kilohertz to more than a megahertz, and line width of ~20 pm at wavelength of 1064nm. During the amplification process in the photonics crystal fiber, the pulses are spectrally broadened to up to ~0.7nm at energy of 17?J. Using a diffraction grating compressor with 1740 l/mm, the pulses are compressed to duration as short as 6ps assuming a numerically calculated de-convolution factor of 0.735. To the best of our knowledge, this is the first reported realization of nonlinear compression of the Q-switched pulses and the shortest pulses from a passively Q-switched laser system

Microdrilling of metals with an inexpensive and compact ultra-short-pulse fiber amplified microchip laser

We have investigated the ultra-fast microdrilling of metals using a compact and cheap fiber amplified passively Q-switched microchip laser. This laser system delivers 100-ps pulses with repetition rates higher than 100 kHz and pulse energies up to 80 μJ. The ablation process has been studied on metals with quite different thermal properties (copper, carbon steel and stainless steel). The dependence of the ablation depth per pulse on the pulse energy follows the same logarithmic scaling laws governing laser ablation with sub-picosecond pulses. Structures ablated with 100-ps laser pulses are accompanied only by a thin layer of melted material. Despite this, results with a high level of precision are obtained when using the laser trepanning technique. This simple and affordable laser system could be a valid alternative to nanosecond laser sources for micromachining applications. © 2008 Springer-Verlag

2 MHz repetition rate, 200 ps pulse duration from a monolithic, passively Q-switched microchip laser

We present a monolithic passively Q-switched microchip laser generating 200 ps pulses at a wavelength of 1064 nm with a repetition rate of up to 2 MHz. While maintaining transversal and longitudinal single-mode operation, the pulse energy can be changed from 130 nJ to 400 nJ by varying the pump conditions of the laser. To the best of our knowledge, the repetition rate of 2 MHz is by far the highest ever reported from such lasers operating in the sub-ns regime