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A statistical ensemble of laser light is defined. Based on the Fresnel-integration a approach to compute the ensemble elements was developed. Using the approach numerical studies of the transverse mode behaviour were carried out. The approach and some results are presented.

(AlGaIn)(AsSb) ridge-waveguide tapered diode lasers with separately contacted ridge and tapered sections, emitting at 1.93 µm, have been analyzed in pulsed mode with respect to their high-power capability and wavelength tunability. Operating the ridge section above saturation, a variation of the current through this section resulted in a change in lasing wavelength, while changing the current injected into the tapered section at a constant ridge current allowed to vary the output power at constant lasing wavelength. Furthermore, the optical power required to saturate the tapered amplifier section has been derived from a comparison of the experimental characteristics with beam propagation method calculations.

High-power laser beam welding in industrial environment often suffers from process induced contamination of laser focusing optics. Especially exposed to this contamination is the plane protection glass which is positioned directly above the process to protect the expensive lenses from contaminations such as spatter and metal vapor. Locally increased absorption due to con-tamination leads to a temperature rise in the protection glass and a corresponding change of its optical characteristics. This results in a reduced beam quality and a shift of the focus position. Both effects lead to a reduced intensity of radiation on the workpiece causing a lower welding penetration depth. In this article we present laser beam measurements using laser processing optics with protection glasses of different materials and different grades of contamination. Welds in mild steel illustrate the extraordinary advantage of sapphire protection glasses, allowing a constant welding depth even when they are strongly contaminated. Welding results, beam caustic measurements and an estimation of economic efficiency will be shown.

© 2014 The Authors. Published by Elsevier B.V. The direct use of diode lasers for cutting sheet metal has high potential to decrease operational costs, but, currently, implementation in industrial environments is constrained by beam quality. In this paper the performance of a novel direct diode laser (DDL) with increased beam quality is documented for both fusion and flame cutting and compared to conventional CO2 and fiber laser sources. Experimental tests were carried out for steel and aluminium based on a Design of Experiments approach. Furthermore, an analytical model, focusing on the absorption of lasers in metals, is described here, which predicts and clarifies performance variation. Although the observed laser beam quality is still lower than the other studied technologies, industrially relevant cutting speeds, with acceptable surface quality, are achievable with DDL, as validated by our results ispartof: pages:901-908 ispartof: 8TH INTERNATIONAL CONFERENCE ON LASER ASSISTED NET SHAPE ENGINEERING (LANE 2014) vol:56 issue:C pages:901-908 ispartof: 8th International Conference on Laser Assisted Net Shape Engineering (LANE) location:Furth, GERMANY date:8 Sep - 11 Sep 2014 status: published

Summary Background The amount of backscattered electrons depends on the thickness of the backscattering metal. The electron backscatter increases with the increase in thickness of the metal until a saturation level is reached and thereafter no change in scatter enhancement is noticed. Aim Electron backscatter effects at metallic interfaces were analysed in this study. High energy electron beams ranging from 6 to 20 MeV were used. Materials/Methods Measurements were carried out with a PTW thin-window parallel plate ionization chamber and an RDM-1F electrometer. Thin sheets of aluminium, copper and lead were used as inhomogeneities. The chamber was positioned below the inhomogeneities with the gantry maintained under the couch. Results The electron backscatter factor (EBSF) increases with increase in energy for aluminium, copper and lead. With low atomic number materials EBSF increases with increase in scatterer thickness and for lead it attains saturation within a few millimetres. Conclusions The information from this study could be useful in predicting the increase in dose at the metal-tissue interface due to electron backscatter.

A number of laser propagation codes have been assessed as to their suitability for modeling Army High Energy Laser (HEL) weapons used in an anti- sensor mode. We identify a number of areas in which systems analysis HEL codes are deficient. Most notably, available HEL scaling law codes model the laser aperture as circular, possibly with a fixed (e.g. 10%) obscuration. However, most HELs have rectangular apertures with up to 30% obscuration. We present a beam-quality/aperture shape scaling relation which can be useful when applying these codes to realistic designs for HELs. Originator supplied keywords: High energy lasers; Laser propagation; Beam quality; Diffraction; Laser aperture; Pupil function; Thermal blooming US Army Tradoc, Operations Research Activity http://archive.org/details/laserpropagation00rock MLPR# TRASANA 5029 NA

A model for calculating the index of refraction of atomic species present in the cavity of a Xenon Fluoride Laser is applied to Neon and Neon*(3s) . The model considers the variation from unity to be a function of the absorption cross section. Below the ionization threshold, the cross section is a set of discrete transitions between the various energy levels of the specie of concern. Above the 5p level, the discrete transitions become indistinct and the continuum cross section function is extended into this region. The continuum cross section function is a polynomial function fitted to independent research results. The results for Neon I agree with previous theoretical and experimental results. The model is extended to Neon*(3s). Comparison with the results of independent research of the polarizability and cavity phase shift derived from the calculation indicate accuracy is within ten percent. Defense Advanced Research Projects Agency, ARPA Order Number 3747, N0001479WR90174, Proj Elem 62301E Program Code 9E20 http://archive.org/details/asimplemodelforc1094518865 Defense Advanced Research Projects Agency, ARPA Order Number 3747, N0001479WR90174, Proj Elem 62301E Program Code 9E20 Captain, United States Army Approved for public release; distribution is unlimited.

Density gradients, which refract laser light within the cavity, degrade beam quality. In addition to wall influences and viscous effects which cause density gradients, there is another mechanism. This mechanism, which is due to wakes and compression waves from heat (vibration energy to translation and rotation) addition in a supersonic stream, appears to have been overlooked. This appropriate equation is stated and discussed. A semigraphical solution procedure is outlined. Contours of constant density have been calculated for circular and rectangular cavities. Graphs of the isodensity contours are given. (Author) http://archive.org/details/densityinhomogen00fuhs NA

Various schemes of geometrical coupling between optical resonator and gain medium were investigated for a 10-kW class Chemical Oxygen-Iodine Laser (COIL). Starting from theory, different types of resonator layouts were designed and optimized for COIL with a rectangular gain medium and an output coupling of about 10%. Hybrid resonators match these coupling conditions more easily than concentric unstable resonators. Compared to the negative branch type, the positive branch hybrid resonator shows very high sensitivity to the optical alignment in the unstable direction but avoids a focal line within the resonator. The obtained output power of both hybrid resonators is compared to the output power of the COIL device in a conventional stable resonator configuration. Measured margins for the sensitivity of resonator setup and alignment were found in close agreement with numerical calculations. Power density distributions were measured in the near field and in the far field. The divergence of the emitted laser beam in the unstable direction was nearly diffraction limited.

High brightness performance of chemical oxygen iodine lasers (COIL) requires resonator concepts that enable efficient power extraction from low gain medium while the beam quality is close to the diffraction limit. The resonator shall provide straightforward alignment procedures and stable output performance for efficient laser operation. Such resonator configurations are theoretically designed and implemented in a 10 kW-class COIL. Different resonator concepts are pre-evaluated by numerical methods with regard to their design and alignment sensitivities. Promising candidates are tested for their alignment performance and brightness parameters. Among others, hybrid resonators are found to be of straightforward optical architecture meeting the above challenges. Theoretical predictions and experimental results are in excellent agreement. Therefore, further promising design approaches, like multi-pass hybrid resonators or the modified negative-branch unstable resonator, will be depicted and discussed within this paper.