Enhancement of Raman scattering by two orders of magnitude using photonic nanojet of a microsphere

Abstract

The enhancement of Raman signal is observed on excitation through a single microsphere. The dependence of the enhancement ratio (ER) on various parameters viz., numerical aperture (NA) of the microscopic objective lens, pump wavelength, size and refractive index of the microsphere has been studied. The enhancement has been explained due to interaction of the increased field of the photonic nanojet emerging from the single microsphere. The photonic nanojet induced ER of Raman peaks of silicon wafer and cadmium ditelluride is reported here. It is observed for the first time that by suitable selection of the experimental parameters, it is possible to enhance the Raman signal by approximately two orders of magnitude.

Photonic nanojet‐mediated SERS technique for enhancing the Raman scattering of a few molecules

“…In this technique, the power of SERS Stokes radiation from N molecules in the effective volume of the SERS substrate is given by where σ is the Raman scattering cross section and | A ( ν pnj )| 2 and | A ( ν s )| 2 are the enhancement factors of PNJ and Raman scattered fields because of nanoplasmonic particles, respectively . I pnj is the intensity of PNJ emerging from an optical microsphere and its dependence on λ exc , n s and a can be found elsewhere …”

“…. In this arrangement, high intense PNJ is expected to be generated at the shadow side of the microsphere because of the constructive interference between incident and strong Mie scattered light by the microsphere, and the PNJ thus generated can excite LSP inside AuNPs. The coupled oscillation of the LSP induces intense hot spots on the surface of the AuNPs, and Raman scattered photons from MB molecules adsorbed at the hot spots were captured using same backscattering geometry.…”

“…On the other hand, some researchers have demonstrated the enhancement in Raman scattering signal using photonic nanojet that is a narrow focused high intense electromagnetic beam emerging from the shadow side surface of a lossless dielectric micro‐cylinder or microsphere illuminated by a non‐resonant plane wave or Gaussian wave . However, the maximum enhancement factor obtained using photonic nanojet (PNJ) is lower than 100 . Recently, Alessandri et al have reported the enhancement of Raman signal using smaller colloidal microspheres (size ~2 µm) dispersed on the SERS substrates (ultra‐thin layer of gold nanoisland on TiO 2 substrates) fabricated using the combination of atomic layer deposition and sputtering techniques .…”

Raman scattering enhancement by dielectric spheres

“…Notice, the EF of 80 that has been observed for d an order of magnitude larger than for the diameters in the present work fall off rapidly to similar values as in the present work when d approaches 5 micron. [20] Further, the metal simply behaves as a reflector and effectively screens the substrate from interacting with the light beam and is smooth; thus, plasmonic (due to rough surfaces) enhancement of the field intensity is not expected. Note that, the Raman signal from the Si/metal/substrate is compared to the sphere/Si/metal/ substrate.…”

Almost Periodic Lumped Elements Structure Modeling Using Iterative Method: Application to Photonic Jets and Planar Lenses

“…To date, several jet photonics-based applications have been considered and implemented for molecules detection [3], optical imaging, data storage [4] and high-resolution microscopy or nonlinear optical effects [5,6]. Among these applications, most studies and developed applications were based on obtaining a photonic jet from the interaction of an electromagnetic wave with obstacles having spherical [7,8], cylindrical [9] or elliptic shapes [10,11], but some of them are interested in producing of planar jets.…”