See also Debye's Asymptotic Representation, Watson-Nicholson Formula, Weyrich's Formula
References
Arfken, G. ``Hankel Functions.'' §11.4 in Mathematical Methods for Physicists, 3rd ed.
Orlando, FL: Academic Press, pp. 604-610, 1985.
Morse, P. M. and Feshbach, H. Methods of Theoretical Physics, Part I. New York: McGraw-Hill, pp. 623-624, 1953.