Showing papers by "Uwe Griebner published in 1999"

Laser operation with nearly diffraction-limited output from a Yb:YAG multimode channel waveguide

Abstract: We report laser action of a crystal channel-waveguide laser consisting of a diffusion-bonded Yb:YAG–YAG core–cladding structure. By use of diode bars a side-pumped arrangement adapted to the channel-waveguide geometry was realized, resulting in up to 1-W output power and a low threshold. With a rectangular core with a 100??m cross section, nearly diffraction-limited performance is demonstrated. The influence of the guiding properties of the channel waveguide on the resonator mode was studied with a nearly concentric resonator.

Ultra-short laser pulse characterisation method uses multi-channel correlation technique with matrix of phase elements for providing Fabry-Perot effect generating characteristic interference rings

Abstract: The characterisation method uses a multi-channel correlation technique in which parts of the beam are superimposed on themselves via a matrix (2) of phase elements (3a,3b) supported by a transparent substrate, with the phase elements and the substrate having different refractive indices, for total internal reflection within the phase elements for providing a Fabry-Perot effect, generating characteristic interference rings (5). Different phase elements or phase element groups have different phase profiles for multi-channel processing of the beam, with detection of the interference patterns via a detector (7) in the form of a matrix camera. An Independent claim for a device for characterisation of ultra-short laser pulses is also included.

Generation of thin film micro-optics by crossed deposition through wire-grid masks

Abstract: Shading masks consisting of regular grids of thin metallic wires have been used for the vacuum deposition of micro-optical thin film components. The fabrication of cylindrical microlenses with single- and two-step procedures has beendemonstrated. Refractive as well as partially reflective arrays with pitches 50 tm have been realized with Si02 and Si02:Hf02 layers on glass, quartz and polymer substrates. The thickness profiles have been characterized interferometrically.Keywords: Microoptics, thin film, vacuum deposition with masks, microlenses. 1. INTRODUCTION To realize small-scale optical systems for laser beam shaping, coupling and multi-channel applications, it is necessaryto develop simple, cost-effective fabrication technologies. Photolithographic structuring of thin films which early hasbeen investigated [1] and is now known as a well-established technique [2-5] allows a very precise processing, however itis a time-consuming multi-step procedure. One promising approach as a simpler and faster method is the mask-supportedvacuum deposition of transparent or reflecting continuous-relief thin film microoptics. Different kinds of masks havebeen designed to generate spherical as well as non-spherical microlenses and micro-mirrors by shaping the depositeddielectric single layers or multilayer systems [6-1 1]. As we could show in good agreement with the theory, it is possibleto fabricate microlens arrays with very high fill factors (near 1) by a crossed deposition of cylindrical microlenses [7]. Toreach further improvements, we proposed to combine the advantages of a crossed deposition with the additional degreesof freedom which are obtained by properly designed depths functions (3D-mask shading, curved edges) [7]. The mostsimple special case of curved edges which should also be the most interesting one from practical reasons is given by acircular shape of the mask bars (wires) [1 1]. Theoretical and experimental results concerning the deposition of micro-optical elements with shading arrays ofthin wires (wire-grid masks) are reported here.

Laserverstärkersystem mit zeitproportionaler Frequenzmodulation

Abstract: Bei einem Laserverstarkersystem mit zeitproportionaler Frequenzmodulation, aufweisend einen Laseroszillator, der ultrakurze Impulse erzeugt, einen passiven, dispersiven Lichtwellenleiter, der diese ultrakurzen Impulse zeitlich dehnt, und mindestens eine mit aktiven Ionen dotierte Doppelmantelfaser zur Verstarkung dieser Impulse, sowie einen dispersive Komponenten aufweisenden optischen Kompressor, der die aus der verstarkenden Doppelmantelfaser empfangenen gedehnten Impulse komprimiert, ist erfindungsgemas die verstarkende Doppelmantelfaser im Kern und in der ersten Mantelschicht mit aktiven Ionen dotiert, wobei die Dotierungskonzentration des Kerns groser ist als die der ersten Mantelschicht und in Ausbreitungsrichtung des Lichtimpulses uber die Faserlange im Kern konstant ist oder zunimmt, der optische Kompressor zur Ausbildung einer variablen Impulsbreite aus auf einem Metalltrager angeordneten Gittern gebildet, wobei die gekuhlten Gitter computergesteuert in definierte Abstande verfahrbar ausgebildet sind, und ein Modulator zur Einstellung einer variablen Folgefrequenz zwischen Laseroszillator und Kompressor angeordnet. In einer Ausfuhrungsform sind passiver dispersiver Lichtwellenleiter und verstarkende Doppelkernfaser in einer Faser integriert.

Short-pulse KrF laser with M2 reduction by a super-Gaussian mirror

Abstract: To improve the beam properties of a short-pulse KrF excimer laser (FWHM < 3.8 ns) with a low number of roundtrips (2...3) and limited magnification (< 5), unstable resonator designs have been developed. Resonators containing mirrors with super-Gaussian reflectivity distributions of different super-Gaussian orders have been investigated theoretically by beam propagation method as well as experimentally by measuring the near- and far-field beam profiles. Mirrors with radially varying multilayer systems have been fabricated by mask-shaded vacuum deposition of dielectric layers with planetary rotation of the substrate. It has been demonstrated that the (delta) -factor of the laser can be significantly improved with compact resonator configurations. For a resonator length of 400 mm, a beam spot size on the output coupler of 2 w equals 1.6 mm and a magnification of M equals 5, the optimum operation characteristics has been found for a super-Gaussian order of about k equals 10. Compared with a plane-parallel system, the (delta) -factor was enhanced by a factor of up to 7. The characteristic beam parameter M2 (times-diffraction- limited-factor) could be reduced in x- and y-directions by factors of 4 and 2, respectively. The experimental results are in good agreement with our theoretical predictions.

Zinc oxide thin films for autocorrelation studies of femtosecond pulses

Abstract: Summary form only given. We report on a study of autocorrelation and frequency doubling of thin polycrystalline ZnO films using 20 fs pulses. These films show an effective second order nonlinearity larger than that of beta-barium borate (BBO) and negligible group velocity dispersion (GVD) for input wavelengths around 800 nm.

Diffusion bonded Yb-YAG rectangular waveguide laser

Abstract: Summary form only given. We report laser performance of an end pumped 100 /spl mu/m Yb:YAG rectangular waveguide. This configuration offers an excellent confinement of the pump field achieved by waveguiding of the slow axis of the diode pump and nonguiding of the fast axis.

Laser amplifier system with time-proportional frequency modulation

Abstract: The invention relates to a laser amplifier system with time-proportional frequency modulation comprising a laser oscillator, which generates ultrashort pulses, a passive dispersive optical waveguide, which temporally stretches these ultrashort pulses, and at least one double-sheathed fiber, which is doped with active ions and which is provided for amplifying these pulses. The laser amplifier system is also equipped with an optical compressor, which comprises dispersive components and which compresses the stretched pulses that are received from the amplifying double-sheathed fiber. According to the invention, the amplifying double-sheathed fiber is doped with active ions in the core and in the first sheath layer, whereby the dopant concentration of the core is greater that that of the first sheath layer and, in the core, is constant or increases over the length of the fiber in a direction of propagation of the light pulse. In order to form a variable pulse width, the optical compressor is constructed of gratings that are arranged on a metal support, whereby the cooled gratings are designed such that they can displaced with defined intervals in a computer-controlled manner. The inventive laser amplifier system also comprises a modulator which is provided for adjusting a variable repetition rate and which is arranged between the laser oscillator and the compressor. In one embodiment, passive dispersive optical waveguides and amplifying double-sheathed fibers are integrated in one fiber.