The $L^2$ Behavior of Eigenfunctions Near the Glancing Set

Let $M$ be a compact manifold with or without boundary and $H\subset M$ be a smooth, interior hypersurface. We study the restriction of Laplace eigenfunctions solving $(-h^2{\mathrm{\Delta }}_g-1)u=0$ to $H$. In particular, we study the degeneration of $u{\mathrm{\mid }}_H$ as one microlocally approaches the glancing set by finding the optimal power $s_0$ so that $(1+h^2{\mathrm{\Delta }}_H{)}_{+}^{s_0}u{\mathrm{\mid }}_H$ remains uniformly bounded in $L^2(H)$ as $h\to 0$. Moreover, we show that this bound is saturated at every $h$-dependent scale near glancing using examples on the disk and sphere. We give an application of our estimates to quantum ergodic restriction theorems.