Angular momentum flux of twisted light in paraxial and nonparaxial regimes
We present a theoretical framework for the derivation of the $z$-directed total angular momentum density of a Bessel wave and of the corresponding intercepted angular momentum flux in an ideal perfectly absorbing disk model. Exact expressions for these quantities are obtained in both paraxial and nonparaxial regimes. We then analyze several experimentally relevant setups in the large-argument asymptotic of the Bessel functions. By varying the beam wavelength, polarization, and cone angle, we identify several distinct regimes of the intercepted angular momentum flux. Within the ideal absorber model, this intercepted flux may be identified with the corresponding mechanical torque. The results suggest potential applications for size-sensitive probing and controlled flux manipulation within the idealized macroscopic model.