Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Introduction to theory of high-harmonic generation in solids: tutorial   High-harmonic generation (HHG) in solids has emerged in recent years as a
rapidly expanding and interdisciplinary field, attracting attention from both
the condensed-matter and the atomic, molecular, and optics communities. It has
exciting prospects for the engineering of new light sources and the probing of
ultrafast carrier dynamics in solids, and the theoretical understanding of this
process is of fundamental importance. This tutorial provides a hands-on
introduction to the theoretical description of the strong-field laser-matter
interactions in a condensed-phase system that give rise to HHG. We provide an
overview ranging from a detailed description of different approaches to
calculating the microscopic dynamics and how these are intricately connected to
the description of the crystal structure, through the conceptual understanding
of HHG in solids as supported by the semiclassical recollision model, and
finally a brief description of how to calculate the macroscopic response. We
also give a general introduction to the Berry phase, and we discuss important
subtleties in the modelling of HHG, such as the choice of structure and laser
gauges, and the construction of a smooth and periodic structure gauge for both
nondegenerate and degenerate bands. The advantages and drawback of different
structure and laser-gauge choices are discussed, both in terms of their ability
to address specific questions and in terms of their numerical feasibility.

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The categories of this paper are: astro-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-ph
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The categories of this paper are: nlin
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The categories of this paper are: nucl-th
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The categories of this paper are: dg-ga
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The categories of this paper are: patt-sol
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The categories of this paper are: chem-ph
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The categories of this paper are: adap-org
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The categories of this paper are: cs
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The categories of this paper are: comp-gas
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The categories of this paper are: bayes-an
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The categories of this paper are: chao-dyn
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The categories of this paper are: math-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: solv-int