Link to publicationCitation for published version (APA): Balcou, P., Dederichs, A. S., Gaarde, M., & L'Huillier, A. (1999). Quantum-path analysis and phase matching of high-order harmonic generation and high-order frequency mixing processes in strong laser fields. Journal of Physics B: Atomic, Molecular and Optical Physics, 32(12), 2973-2989. DOI: 10.1088 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal Abstract. We study phase-matching conditions for high-order harmonic generation as well as high-order sum-and difference-frequency mixing processes in strong laser fields, using a graphical approach described in Balcou et al (1997 Phys. Rev. A 55 3204-10). This method is based on the analysis of the different quantum paths that contribute, with different phase properties, to the single-atom response. We propose a simple numerical method to disentangle the quantum paths contributing to the generation process. We present graphical maps of the phase matching around the laser focus, which allow one to predict the geometries that optimize the conversion efficiency of the process considered. The method is applied to the study of sum-and difference-frequency mixing processes. The qualitative predictions of the graphical phase-matching approach are confirmed by numerical propagation calculations.

Little is known on the evacuation characteristics of children. Current literature on evacuation is mostly based on studies on adults. The aim of this study is to investigate the movement of children during evacuation, focusing on flow, densities and walking speeds. Ten Danish daycare centers participated in full scale evacuation experiments where two age groups 0 to 2 years and 3 to 6 years were analyzed separately. It was found that flow through doors, walking speeds and densities were age-dependent and differed strongly from the data in existing literature. The results showed higher walking speeds in spiral stairs when the children were familiar with the evacuation path. Higher person densities and faster flow through doors were obtained among the children than found in the current literature on adults. Children in the younger age group were generally slower than the older children. The children walked slower in horizontal plane than adults, however they were keen to run during the evacuations, in the latter case their travel speed increased and exceeded the adults'. Since the evacuation characteristics of children differ in many ways from those of adults, nowadays models badly comprehend the evacuation behavior of children.

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