First demonstration of surface enhanced-stimulated Raman spectroscopy (SE-SRS) using low-power CW sources

Abstract

Using commercially available nanoparticles, continuous wave Surface-Enhanced Stimulated Raman spectroscopy (CW SE-SRS) is demonstrated for the first time using two Ti:Sapphire lasers producing a pump beam (785 nm, 100 mW) and appropriately varying probe/Stokes beams (860-870 nm, 120 mW). The Ti-Sapphire lasers are copumped by a 10 W low noise 532 nm Spectra Physics Millennia laser. Pulsed SE-SRS is also demonstrated using a Coherent Chameleon Ultra laser for the Stokes/probe (863-871 nm) beam and a Coherent Ultra II as the pump laser (785 nm). In both cases lock-in techniques are used to extract the small signal (1 in 10 9 ) successfully. These experiments convincingly demonstrate that SRS with CW sources is possible using appropriate nanoparticles, and this realization creates opportunities for a wider range of stimulated Raman spectroscopy applications.

Flickering nanometre-scale disorder in a crystal lattice tracked by plasmonic flare light emission

“…Because the coupled plasmon mode filters input white light into a single mode, we believe that when a flare occurs, the optical confinement is sufficiently high ( Supplementary Fig. 12) to generate CW SRS [67][68][69][70] at the redshifted coupled plasmon, even with incoherent illumination. As expected this emission is linear in both laser and white intensity.…”

“…As expected this emission is linear in both laser and white intensity. We can estimate the expected SRS enhancement for flare events as it scales as the 8th power of the field in the metal 71 meaning a nearly 2000-fold increase due to the enhanced field penetration for flares (using scaling as in Supplementary Note 3), and assuming analogous SRS mechanisms for metallic electrons as molecules. The range of gains observed at λ c varies from 100-2000% ( Supplementary Fig.…”

Continuous-Wave Coherent Raman Spectroscopy via Plasmonic Enhancement

“…Furthermore, as conventional SRS samples are usually in the micro-molar range, this adds more than three orders of magnitude to the enhancement. Therefore, one can expect to see a large enhancement in the pulsed SESRS signal compared to conventional SRS experiments 28,29 .…”

“…28 reported surface-enhanced stimulated Raman spectroscopy (SESRS) with femtosecond pulsed lasers using gold/silica nanoparticles. Previous studies on pulsed-SESRS show that one can detect a Raman signal for a sample of pico-molar concentration using nanoparticles enhancement and a power density of 0.01 MW cm − 2 28,29 . These values are three to four orders of magnitude lower than that required for conventional SRS.…”

“…We previously demonstrated the possibility of SESRS using cw laser sources (cwSESRS) and commercially available Oxonica nanoparticles for the first time 28 . It has been demonstrated that the surface enhancement leads to detecting samples using focused pump and Stokes beams with a power of around 100 mW 29 . In this paper, we describe the synthesis of gold/silica nanoparticles with a similar architecture employing embedded reporter molecules.…”