= Alexander Dreischuh
{c}
\b[Alexander Dreischuh] is a physicist associated with the Department of Quantum Electronics at Sofia University. His author-hosted curriculum vitae records a professorship there beginning in 2004.<Curriculum vitae by Alexander Dreischuh>[Work experience, Sofia University appointments]{ref} His publication list documents experimental and theoretical work in <nonlinear optics> and structured light, including joint work with <Lyubomir Stoyanov> and <Gerhard G. Paulus>.
A useful theme is that an optical field has a spatial <wave phase> as well as a <light intensity>. An <optical vortex> has a phase singularity around which the <wave phase> winds. In an original local model $u(r,\varphi)=A(r)e^{im\varphi}$, with integer $m$ and vanishing central amplitude when $m\ne0$, a complete circuit changes the continuous phase by $2\pi m$. The <optical vortex charge> is therefore $m$; $m=2$ gives a $4\pi$ phase winding. The visible dark center alone does not determine the sign or magnitude of that winding.
Dreischuh coauthored the 2023 comparison of <Gouy phase> theory with measurements on <Bessel-Gaussian beams>. One apparatus used a 532 nm <laser>, two <spatial light modulators>, a <Mach-Zehnder interferometer> and a rail-mounted <camera> behind the focusing lens.<Gouy phase of Bessel-Gaussian beams: theory vs. experiment by Lyubomir Stoyanov and others>[p.13691, Figure 3(a) and caption]{ref}
The apparatus separates preparation from diagnosis: a <spatial light modulator> controls an optical field's spatial structure, while <interference (wave propagation)> with a reference converts phase differences into recorded intensity fringes. Changing the longitudinal camera position tests propagation through and beyond the focus. That makes the observed phase evolution a quantitative experimental question rather than something inferred solely from a single ring-shaped intensity image.
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