Kontorovich–Lebedev transform
In mathematics, the Kontorovich–Lebedev transform is an integral transform which uses a Macdonald function (modified Bessel function of the second kind) with imaginary index as its kernel. Unlike other Bessel function transforms, such as the Hankel transform, this transform involves integrating over the index of the function rather than its argument.
Source: Wikipedia — Kontorovich–Lebedev transform (CC BY-SA 4.0)