Raman spectroscopy: important considerations

Getting the best from your Raman system

While Raman spectroscopy has many advantages, it can present some challenges. There are ways we can address some of the issues encountered during its use.

Raman is a weak effect

Renishaw's Raman systems overcome this by using highly efficient optical designs and ultra-sensitive detectors.

Photoluminescence (PL) is a strong effect that can mask Raman information

By using a multiple laser system you can switch to a different excitation wavelength. This maximizes your chances of producing spectra whose Raman features are not masked. For example, switching from a visible to a near-infrared laser (e.g. 785 nm) usually reduces PL.

Chemical glassware, such as glass cuvettes or microscope slides, can mask the Raman signals of your samples

You can avoid this by using a metal microscope slide rather than a glass one. When you have to use a transparent vessel, you can select a glass type with a weak Raman signal (e.g. quartz is weaker and less intrusive at 785 nm than standard glass). In some cases, you can use replacement materials such as CaF₂ or MgF₂. These produce a few narrow Raman bands, typically located in a different part of the spectrum to those of the material you are studying.

The inVia is a confocal Raman microscope. This enables the sampling volume to be minimised, helping to counteract any unwanted contributions from substrate or container materials.

Renishaw is leading the way in avoiding sample damage

Lasers are used to generate Raman scattering. The Raman signal is typically proportional to the amount of laser power, so more power usually means a stronger signal. All samples have a laser power density threshold beyond which structural or chemical modification may occur.

Renishaw's Raman systems provide unrivalled laser control performance; you can be confident your sample has not changed. inVia confocal Raman microscopes do this by using 16 or more repeatable and software-controlled power levels, combined with multiple focus modes such as spot focus, line focus, and enlarged spot focus. Together with inVia's market-leading sensitivity, these produce the highest Raman signals at the lowest possible power densities. Sample integrity is maintained and data collection speeds are fully optimised.

Control the volume of sample analysed

Renishaw's Raman systems use powerful microscope lenses to collect the Raman scattered light. These have high numerical apertures and efficiently collect the light scattered, over a wide range of angles, from a tiny region of the sample. This is in comparison with bulk analysis systems which typically use lower magnification lenses and sample larger volumes.

Renishaw's systems are fully configurable, enabling both bulk analysis and confocal microscopy operation, without compromise. This is achieved using integrated fibre probe options and fast averaging modes incorporated within the StreamLine™ Slalom option. Averaging is performed on the detector and readout noise is minimised.