Lateral displacement of the mode axis in a misaligned Porro prism resonator.
The lateral shift of the mode axis in a misaligned Porro prism resonator is analyzed. A method to find the tilted mode axis in a misaligned Porro prism resonator is introduced. Expressions for the displacement of the mode axis are deduced. They predict that the lateral displacement of the mode axis is proportional to the horizontal misalignment angle beta and highly dependent of the prism azimuth angle theta. Experimental results obtained agree well with theory.
Jones matrix formulation of a Porro prism laser resonator with waveplates: theoretical and experimental analysis
This article presents the results of a detailed theoretical and experimental analysis carried out on a folded Z-shaped polarization coupled, electro–optically Q-switched laser resonator with Porro prisms and waveplates. The advantages of adding waveplates in a Porro prism resonator have been explored for creating high loss condition prior to Q-switching and obtaining variable reflectivity with fixed orientation of Porro prism. Generalized expressions have been derived in terms of azimuth angles and phase shifts introduced by the polarizing elements. These expressions corroborate with known reported results under appropriate substitutions. A specific case of a crossed Porro prism diode-pumped Nd:YAG laser has been theoretically and experimentally investigated. In the feedback arm, a 0.57λ waveplate oriented at 135° completely compensates the phase shift of a fused silica Porro prism and provides better tolerances than a BK-7 prism/0.60λ waveplate combination to stop prelasing. The fused silica prism/0.57λ combination with waveplate at 112° acts like a 100% mirror and was utilized for optimization of free running performance. The effective reflectivity was determined for various orientations of the quarter waveplate in the gain arm to numerically estimate the Q-switched laser pulse parameters through rate equation analysis. Experimental results match well with the theoretical analysis.
The German centenary of the First World War
In the run up to the 2014 centenary of the First World War, the German public was gripped by a heated debate on the origins of the war. This article explores the nature of this controversy and its role in shaping national commemoration of the Great War. It also draws parallels between the commemorations of the fiftieth anniversary of the outbreak of the war in 1964 and those of 2014. Through a comparison of Germany’s national memories of the war with those in Britain and France, the article also reveals how different and sometimes conflicting national interpretations of the history of the First World War have affected centenary commemoration. Memories of the First World War are nation-specific, constructed and developed over time to suit a particular view of a country’s past. Moreover, they can be instrumental in influencing that country’s future development and relations with its neighbours.