Semiclassical Green functions and Lagrangian intersection. Applications to the propagation of Bessel beams in non-homogeneous media

Abstract

We study semi-classical asymptotics for problems with localized right-hand sides by considering a Hamiltonian $H(x,p)$ positively homogeneous of degree $m\geq1$ on $T^*{\bf R}^n\setminus0$. The energy shell is $H(x,p)=E$, and the right-hand side $f_h$ is microlocalized: (1) on the vertical plane $\Lambda_0=\{x=x_0\}$; (2) on the ``cylinder'' $\Lambda_0=\{(X,P)=\bigl(\varphi\omega(\psi),\omega(\psi)\bigr); \ \varphi\in {\bf R}, \omega(\psi)=(\cos\psi,\sin\psi)\}$. when $n=2$. Most precise results are obtained in the isotropic case $H(x,p)={|p|^m\over\rho(x)}$, with $\rho$ a smooth positive function. In case (2), $\Lambda_0$ is the frequency set of Bessel function $J_0({|x|\over h})$, and the solution $u_h$ of $(H(x,hD_x)-E)u_h=f_h$ when $m=1$, already provides an insight in the structure of ``Bessel beams'', which arise in the theory of optical fibers. We present in this work some extensions of A.Anikin, S.Dobrokhotov, V.Nazaikinskii, M.Rouleux, Theor. Math. Phys. 214(1): p.1-23, 2023. In Sect.3 we sketch the semi-classical counterpart of the construction of parametrices for the Cauchy problem with Lagrangian intersections, as is set up by R.Melrose and G.Uhlmann. This involves Maslov {\it bi-canonical operator}.