1,102 research outputs found
Large mode area fiber lasers and their applications
Full text linkThe area of fiber lasers has undergone rapid developments in recent years. Gone are the days when fiber lasers were seen as something of an irrelevant curiosity, offering interesting performance features, but always with power levels or other performance limitations, that made them unsuitable for all but a few applications. Improvements in the area of high-power, high-brightness semiconductor pump lasers, and the development of techniques, such as cladding-pumping, have changed this viewpoint markedly. Most significantly, fiber lasers have shed the "low power" label and it is now widely appreciated that the heat-dissipation characteristics of the fiber environment, coupled with the high efficiencies demonstrated (in excess of 80%), actually make fiber lasers a preferred candidate for many high-power applications. Moreover, major advances in fiber Bragg grating fabrication and more sophisticated fiber designs and pump coupling techniques, have at the same time improved device performance and increased the versatility, functionality and practicality of the technology; allowing the development of a broad range of robust, practical optical sources
Characteristics of Q-switched cladding-pumped ytterbium-doped fiber lasers with different high-energy fiber designs
No full textWe theoretically and experimentally analyze Q-switched cladding pumped ytterbium-doped fiber lasers designed for high pulse energies. We compare the extractable energy from two high-energy fiber designs: (1) single- or few-moded low-NA large mode area (LMA) fibers and (2) large-core multimode fibers, which may incorporate a fiber taper for brightness enhancement. Our results show that the pulse energy is proportional to the effective core area and, therefore, LMA fibers and multimode fibers of comparable core size give comparable results. However, the energy storage in multimode fibers is mostly limited by strong losses due to amplified spontaneous emission (ASE) or even spurious lasing between pulses. The ASE power increases with the number of modes in a fiber. Furthermore, spurious feedback is more difficult to suppress with a higher NA, and Rayleigh back-scattering increases with higher NA, too. These effects are smaller in low-NA LMA fibers, allowing for somewhat higher energy storage. For the LMA fibers, we found that facet damage was a more severe restriction than ASE losses or spurious lasing. With a modified laser cavity, we could avoid facet damage in the LMA fiber, and reached output pulse energies as high as 2.3 mJ, limited by ASE. Theoretical estimates suggest that output pulse energies around 10 mJ are feasible with a larger core fiber, while maintaining a good beam qualit
Characterization of a 10 GHz harmonically mode-locked erbium fiber ring laser using second harmonic generation frequency resolved optical grating
No full textActive harmonic mode-locking of Erbium Fiber Ring Lasers (EFRLs) is an established technique for obtaining short pulses at GHz repetition rates. To date all reports on the characterization of such lasers have used techniques that provide incomplete information on the pulse shape and quality, e.g. autocorrelation with optical spectrum, streak camera etc.. Whilst this is largely adequate, direct measurements of pulse amplitude and phase would be extremely useful, facilitating the optimization and detailed understanding of the operation of such lasers
Hexagonally poled lithium niobate: a two-dimensional nonlinear photonic crystal
No full textWe report on the fabrication of what we believe is the first example of a two-dimensional (2D) nonlinear photonic crystal [Berger, Phys. Rev. Lett. 81, 4136 (1998)], where the refractive index is constant but where the 2nd order nonlinear susceptibility is spatially periodic. Such crystals allow for efficient quasi-phase-matched 2nd harmonic generation using multiple reciprocal lattice vectors. External 2nd harmonic conversion efficiencies >60% were measured with picosecond pulses. The fabrication technique is extremely versatile and should allow for the fabrication of a broad range of 2D crystals including quasicrystals. <br/
Power scaling in passively mode locked large mode area fibre lasers
No full textWe report on a novel approach towards generating high peak powers in passively mode locked fibre lasers. By appropriate design the fibre's mode area is increased by a factor of ~30 compared to standard fibre. This increased area effectively decreases the nonlinearity thus increasing the power necessary to form stable soliton-like pulses
HeXLN, the first 2D nonlinear photonic crystal
No full textLinear photonic crystals are crystal in which the linear susceptibility of the material (χ1 or the index of refraction, n) is varied periodically. This periodic variation means that the modes of propagation for certain wavelength are strongly influenced by the structure. One example is a fibre Bragg grating, where the Bragg resonance reflects light within the bandwidth. The resonance condition in the crystals is often expressed in terms of k-space, where the k vector of the light must match a reciprocal lattice vector of the structure
High energy passive Q-switching of an erbium fiber laser using a nonlinear liquifying gallium mirror
No full textIt has been recently reported that the reflectivity of a gallium:glass interface becomes strongly nonlinear at temperatures close to, but below gallium's melting point of ~30°C. The nonlinearity is attributed to a surface-assisted, optically-induced structural phase transition from the stable phase of solid gallium (alpha-gallium) to some other, as yet unidentified, metastable phase of higher reflectivity. It has been observed both in the visible and the near infrared, and characterised fully at 1550 nm. Optical intensities of -1kW/cm are sufficient to change the optical reflectivity of a gallium:glass interface from 50% to 65% at 1550nm, with a turn-on time shorter than 10ns, and temperature dependent turn-off time in the range 10-1000 ns. Initial experiments had shown that this nonlinearity could be used for passive Q-switching of an erbium fiber laser ring cavity. Using a 15m cavity and a fiber butt-coupled gallium mirror we obtained 1 - 2 ps pulses with peak powers of 0.5 W. Whilst this was an important result, the first practical demonstration of the concept, the laser performance itself was not particularly impressive. In this paper we present more recent results with a more optimized cavity which show that liquefying gallium mirrors can be used to generate much shorter pulses of much higher intensity and indeed give comparable results to those achieved with state-of-the-art semiconductor saturable absorbers
Non-reciprocal transmission via phase conjugation in multimode optical fibres
Full text linkWe demonstrate a novel non-reciprocal transmission device based on photorefractive phase-conjugate distortion correction of the modal and polarisation scrambled fields in a highly multimode optical fibre
Passive Q-switching of fiber lasers using a broadband liquefying gallium mirror
No full textUsing a nonlinear cavity element, a liquefying gallium mirror, we demonstrate stable, self-starting, passive Q-switching of both erbium and ytterbium fiber laser cavities operating at wavelengths of 1550 and 1030 nm, respectively. The performance at 1550 nm is shown to be equivalent to that achieved with a state of the art semiconductor saturable absorber designed to work at this wavelength. The results highlight the suitability of this tremendously broadband, inexpensive nonlinear medium for a wide range of passive Q-switch applications
Letter: R.F. Pettigrew to H.L. Loucks, May 30, 1916
No full textR.F. Pettigrew articulates to H.L. Loucks his distaste for the book that Loucks recommended to him. Pettigrew also mentions that he would prefer to remain distanced from any conference with the author of the book. Pettigrew expresses great admiration and interest in Loucks' manuscript and desire to read it further
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