Raman spectroscopy is a non-destructive technique spanning a wide range of scientific and industrial applications. It is often used to characterize or identify the chemical composition and structure of an unknown material. Incident laser light, in the UV, visible or NIR, is scattered inelastically from molecular vibrational modes of the sample.
The frequency difference (measured in relative cm-1) between the incident and scattered photons is called the Raman shift. The majority of inelastically scattered photons are found at positive Raman shifts, corresponding to lower energies and longer wavelengths – this is referred to as Stokes scattering. The scattered photons are analyzed by a spectrometer to produce a Raman spectrum.
With Stokes scattering, the energy of the molecule increases and the Raman scattered photons are red-shifted. With Anti-Stokes, the energy of the molecule decreases – so therefore the molecules must have already been in a vibrationally excited state – and the Raman scattered photons are blue-shifted.
A New Dawn for NIR Spectroscopy
Featuring two revolutionary back-illuminated deep-depletion sensors, Teledyne Princeton Instruments BLAZE cameras for spectroscopy provide the highest near-infrared quantum efficiency, fastest spectral rates, and deepest thermoelectric cooling available in a CCD platform. Lower thermally generated dark noise, combined with…Read Full Article
Tip-Enhanced Raman Spectroscopy
TERS works in conjunction with scanning probe microscopy (SPM), a technique that utilizes a metal tip to probe the size and shape of samples at atomic dimensions.
The tip can be coated with silver or gold and, when brought close to a sample of molecules, excited with a laser yielding a spectra with greatly enhanced Raman signal.
TERS confines the signal enhancement to the near-field surrounding the very sharp SPM tip, allowing optical spatial resolution down to ~ 10 nm. The signal can be so strong that single molecules can be detected, ideal for samples that exhibit heterogeneities on the nanoscale.
Tip-Enhanced Raman Scattering (TERS)
The ability to identify small quantities of adsorbed analyte or structural features down to the few-molecule level is a key challenge in nanotechnology. Optical spectroscopy provides an attractive means to achieve such identification via non-invasive implementations and the potential for chemical sensitivity. Raman scattering has emerged as a particularly powerful technique due to its…Read Full Article
Coherent Anti-Stokes Raman Spectroscopy (CARS)
CARS is a nonlinear Raman spectroscopy technique that uses two very strong collinear lasers to irradiate a sample. The frequency is usually kept constant, with the second laser tuned so that the frequency difference between the two lasers equals the frequency of a Raman-active mode of interest.
To obtain a strong Raman signal, the second laser frequency should be tuned in such a way that its frequency is equivalent to the constant frequency of the first laser minus the frequency of a Raman-active rotational, vibrational, or other mode.
This will cause the frequency of the scattered light to be higher than that of the excitation frequency and so forms anti-Stokes frequency.
Ultra-Multiplex CARS Spectroscopic Imaging of Living Cells
Popular molecular imaging techniques are only able to reveal the distribution or behavior of specific molecules within the human body that have been labeled with pigments or fluorescent proteins. Raman spectroscopy, however, allows researchers to identify the components of…Read Full Article