Fig. 1
(Reprinted with permission from Ref. [53])
a Schematic of different configurations of laser excitation and Raman scattered light collection with respect to the WG of length L oriented in the light guiding z direction. Excitation is either (i) in plane via coupling to the WG mode or (ii) out-of-plane from the top. Collection is either in the (I) forward, (II) backward, or (III) out-of-plane scattered direction. b Schematic of laser excitation and Raman scattered light collection in free space. Excitation is in the forward direction and Raman scattered light is collected in the backward direction. The Gaussian beam is propagating in the z direction with waist diameter D0 and depth of focus b.