Compact conical beam shaper and freeform segmented reflector for SERS analysis

Abstract

We present a Raman spectroscopy setup containing a conical beam shaper in combination with a freeform segmented reflector for surface enhanced Raman scattering (SERS) analysis. The freeform segmented reflector and the conical beam shaper are designed by numerical approaches and fabricated by means of ultra-precision diamond tooling. The segmented reflector has a numerical aperture of 0.984 and a working distance of 1mm for SERS measurements. We perform systematic simulations using non-sequential ray tracing to assess the detecting abilities of the designed SERS-based system. We implement a proof-of-concept setup and demonstrate the confocal behavior by measuring the SERS signal of 10µM rhodamine B solution. The experimental results agree well with the simulations concerning the misalignment tolerances of the beam shaper with respect to the segmented reflector and the misalignment tolerances of the collecting fiber. In addition, we conduct benchmark SERS measurements by using a 60× objective lens with a numerical aperture of 0.85. We find that the main Raman intensity of rhodamine B at 1502 cm-1 obtained by our segmented reflector working together with the conical beam shaper is approximately 30% higher compared to the commercial objective lens.

Optical Feedback for Sensitivity Enhancement in Direct Raman Detection of Liquids

“…us, we realized an enhancement factor of 5.6 in the Raman spectroscopic measurement on ethanol. Compared with the reported methods [12,13,18,19], our "F+2f" scheme has a simplest design and low-cost configuration, which produces even higher enhancement. Although we employed pure ethanol and R6G in water as the analytes in this experimental work, the most important motivation is to find effective and practical approaches for improving the sensitivity of Raman spectroscopy, which can be potentially utilized in the direct detection of pollutant molecules in environmental water.…”

“…However, Raman-scattering signal is very weak, which has an intensity lower than (10 −6 ) that of the excitation. erefore, approaches for enhancing the Raman-scattering signals are always important for improving and realizing the related detection techniques [11][12][13].…”

“…ese approaches may include single-channel multiplex optrode [21,22], liquid core waveguides [23,24], and fiber probes [25]. Parabolic reflection mirror and multipass schemes have been reported for the Raman spectroscopic systems, which enabled large enhancement of the detection sensitivity [12,13,18,19].…”