1,721,178 research outputs found
Laser crystal waveguides
No full textOptically-pumped lasers and amplifiers can in principle benefit greatly from a guided-wave geometry in which the pump and lasing modes overlap tightly, the laser mode volume is minimized, and the product of optical intensity and interaction length is not limited by diffraction as in a bulk gain medium. This idea is most successfully embodied in the erbium-doped silica fibre amplifier, and many novel and efficient laser systems have been demonstrated in glass fibre form
Fibre and waveguide lasers
No full textThe guided-wave laser is almost as old as the laser itself. The first demonstration of laser action in glass made use of a multimode waveguide; a core rod encased in a cladding of lower refractive index so that confinement of the light would counteract the effect of the poor optical quality of the available glass, (Snitzer, 1961). However, although waveguiding has long been an essential feature of semiconductor diode lasers, in dielectric laser media by far the greatest research effort has gone into the development of bulk rods and slabs of high optical quality. Interest in the potential advantages of guided wave dielectric gain media was only quickened with the advent of high quality single mode optical waveguides, especially rare earth doped silica fibres, in which the propagation losses are so low that the benefits of optical confinement are fully realised. The most immediate advantage of the guided-wave geometry is that of reducing the cavity mode volume, and hence the pump power needed to reach threshold. Provided the guiding structure is designed so as to support only a single propagating mode at the gain wavelength, then the laser output will be spatially coherent, in a mode that is not affected, for example, by cavity misalignment. The guided-wave laser can be designed as a compact, stable, monolithic device, exploiting all the techniques of integrated optics, such as gratings, couplers, and modulators. Since the active region of a guided-wave laser is typically only a few µm in diameter, fabrication can involve a range of deposition techniques very different from those used to grow bulk media. The resulting gain medium may have a composition or dopant concentration not available to a bulk phase. On the other hand the advantages of a guided-wave structure are cancelled if propagation losses compete too effectively with the achievable gain. A further difficulty attending these optically pumped devices is the need to couple pump light into the waveguide core. The pump sources themselves must therefore emit spatially coherent beams, and expensive micropositioning techniques are required. The literature on fibre and planar dielectric waveguide lasers is now so extensive that a review of this type cannot attempt to be comprehensive. My aim is rather to sketch the principles of guided-wave laser design and operation, and introduce a few selected devices of particular current interest. I shall pay particular attention to the role that guided-wave systems may play in the effort to develop compact and efficient sources emitting high power diffraction-limited beams. Diode-bar lasers emitting many tens of watts are now readily available, but it remains a challenge to convert the highly asymmetric and multimode output from such a device into a usable beam in a simple and efficient way. It is not at first sight obvious that a guided wave laser should be particularly suitable for high power operation. Waveguides are characteristically devices in which high core intensity accompanies low overall power, and scaling up the core area leads to multimode propagation and loss of spatial coherence. Recently, however, the technique of cladding pumping of fibre lasers has been found to be strikingly effective in overcoming these limitations. It can be argued that planar waveguide structures are inherently highly compatible with high-power diode-bar pump lasers. Experimental investigation of such devices indicates that extremely compact sources, potentially able to handle 10 W or more of output, can be fabricated in this way. Control of the spatial mode is a central and difficult problem, and various technical approaches will be reviewed. Equally stringent is the necessity to couple pump radiation into the guide, whether longitudinally for greater efficiency, or transversely for a less divergent output and the possibility of power scaling. We shall see that with careful positioning this can be achieved without the use of any optical components whatsoever. If, moreover, the cladding-pumping principle is employed, then the position tolerances are significantly relaxed. Alternatively it may be possible to pump through the face of the device, and we shall review some practical schemes of this type
Spectroscopy - the changing face of physics: spectroscopy of materials for guided wave devices
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Optically-pumped vertical-external-cavity surface-emitting semiconductor lasers
No full textThe optically-pumped vertical-external-cavity surface-emitting semiconductor laser (OP-VECSEL) is a versatile laser source that can generate high average power in a circular diffraction-limited beam. The diode-pumping techniques developed for solid state lasers provide uniform pumping over a large laser mode area, without the problems of filamentation experienced by injection-pumped VCSELS, while an external cavity enforces TEM00 operation, and gives intracavity access to the laser mode. The OP-VECSEL thus combines many of the virtues of the diode-pumped solid state laser with the possibilities for engineering the wavelength, gain, dispersion and saturation characteristics offered by the semiconductor quantum-well gain medium. The gain medium incorporates a multilayer distributed Bragg reflector (DBR) adjacent to a number of quantum wells. Diode pump light is absorbed in the barrier regions either side of the quantum wells, generating carriers that are subsequently trapped in the wells. The interband barrier absorption is extremely broad compared to the pump bands of most dielectric laser media, conferring a relaxed pump diode wavelength specification. Our structures are grown by MOCVD on GaAs substrates, and designed to operate at ~1030 nm, with a GaAs/AlAs DBR and 6 or 7 strain-compensated InGaAs/GaAsP wells. The wafers are used without post-growth processing
Honorary Editor's introduction. Special issue in honour of the 60th birthday of Professor David Hanna FRS
No full textThe idea of pulling together a Cluster of papers in celebration of the 60th birthday of Professor David Hanna FRS was inspired by his award of the European Physical Society Quantum Electronics Prize 2000 for applied aspects. The prize citation recognises David's 'outstanding and numerous contributions to solid-state laser physics and non-linear optics', an evaluation warmly endorsed by those of us who have been lucky enough to work with him. Over the years, David Hanna has made immense personal contributions to the field of quantum electronics and has inspired many students and collaborators to go on to make their own contributions. His influence can be seen in many aspects of the field and those who have worked closely with him have gone on to make significant impacts in the fields of business and academia throughout the world.David Hanna, who was the 1993 recipient of the Max Born Medal and Prize, has served as Deputy Director of the Optoelectronics Research Centre at the University of Southampton since its foundation in 1989. His achievements over this period include major advances in the high-power operation of bulk, fibre and planar guided-wave lasers, and the refinement of the optical parametric oscillator into a versatile practical source. All of these areas are represented in this Cluster, in which many of the contributors are David's students and colleagues, past and present. In Some thoughts on 38 years of lasing David shares his unique perspective on the evolution of this important field of contemporary optics.We hope that the readers of Journal of Physics D: Applied Physics will enjoy sampling the range and depth of topics covered by this tribute to David Hanna. The publication of the Cluster coincides with developments in the board of the Journal where we intend to give greater prominence to developments in the field of what has become known as Photonics
Femtosecond semiconductor lasers
No full textPassive modelocking of surface-emitting semiconductor quantum well lasers can generate transform-limited optical pulses with duration comparable to the carrier-carrier scattering time. The presentation describes recent advances in this field
Cooperative luminescence and absorption in Ytterbium-doped silica fiber and the fiber nonlinear transmission coefficient lambda=980 nm with a regard to the Ytterbium ion-pairs' effect: comment
No full textRecently, significant power losses in ytterbium-doped fibers have been interpreted as resulting from the formation of ytterbium ion pairs [A. V. Kir’yanov et al., Opt. Express 14, 3981 (2006)]. However, there appears to be strong evidence against this model
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