Raman scattering enhancement by dielectric spheres

Abstract

Raman scattering experiments were performed on Si(60 nm)/metal/substrate structures with and without silica microspheres (with a diameter between 0.5 and 5 mm) on top. Raman scattering from the thin Si layer exhibits enhancements (~20) due to the dielectric spheres, where the enhancement factors depend on the diameter of the spheres. The interaction between light and dielectric spheres has been simulated by finite difference time domain calculations (FDTD), wherein particularly the electric energy density (ED) distribution in the thin Si layer was of concern. For microspheres with a diameter less thañ 3 mm, the transverse ED distribution (perpendicular to the incident light direction) within the Si layer is characterised by a single peak centered on the optical axis. For larger diameters, a multimodal transverse ED distribution develops where the maximum is not centered on the optical axis. Using an ad-hoc approach for surface enhanced Raman scattering in combination with the FDTD calculations, the experimental Raman observations are well accounted for.

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

“…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, many researchers have involved in the fabrication of efficient and highly reproducible SERS substrates for studying the Raman scattering of single or a few molecules in real time. [3,4,11,12] On the other hand, some researchers have demonstrated the enhancement in Raman scattering signal using photonic nanojet [13][14][15][16] that is a narrow focused high intense electromagnetic beam emerging from the shadow side surface of a lossless dielectric microcylinder or microsphere illuminated by a non-resonant plane wave or Gaussian wave. [17][18][19][20][21][22][23][24] However, the maximum enhancement factor obtained using photonic nanojet (PNJ) is lower than 100.…”

Process engineering study of photonic nanojet from highly intense to higher propagation using FDTD method

“…Therefore the selection of the proper shape of microstructure depends on the field of various applications. Photonic nanojet is having wide range of applications such as imaging (microscopy [18,19] and Raman spectroscopy [20]), optical tweezing [21], micro etching [22], detection and sensing [23][24][25], laser surgery [17], optical data storage and switching [26,27] etc..…”

“…Theoretical investigations are mainly employed to know the behavior of change in light due to the desired structure. There are several methods employed to compute the solution of electromagnetic waves propagated from a finite structure such as transfer matrix method (TMM) [28], plane wave expansion (PWE) method [29], finite element method (FEM) [30], Boundary element method (BEM) [31], multiple multipole method (MMP) [7,8], finite difference time domain (FDTD) method [1][2][3][4][5][6][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] etc. Though there are several methods adopted for computation purpose, however FDTD method is frequently used because of user friendly simulation packages available in the market and to avoid empirical calculations [32].…”

Recent advances in linear and nonlinear Raman spectroscopy. Part VIII

“…Cardenas describes Raman scattering enhancement by dielectric spheres. Here, the interaction between light and dielectric spheres was simulated by finite‐difference time‐domain calculations wherein particularly, the electric energy density distribution in the thin Si layer was of concern . Funke and Wackerbarth investigate the role of the dielectric environment in SERS for the detection of a 4‐nitrothiophenol monolayer.…”