FAQs - Choice of wavelength and power requirements
- What is the best wavelength for Raman Spectroscopy?
It depends on the sample being analyzed: laser power considering weak Raman scatterers or thermally sensitive materials; any possible sample fluorescence; and the required spectral range in terms of Raman shift as significant to the Raman analysis of the sample.
The principles of Raman scatter dictate that, all other factors being the same, the Raman Scattering Cross-Section (the parameter which relates to the intensity of scattering) increases with decreasing wavelength.In other words, all other factors remaining constant, a sample will show higher scattering at 532 nm than it will at 785 nm. The intensity of scattering increases linearly with increasing laser power.
The probability of fluorescence is higher at lower wavelengths. In other words, a sample has higher probability of fluorescence at 532 nm, than at 785 nm (See figure).
The spectral range of the CCD is longer at 532 nm excitation (200-4000 cm-1) than that at 785 nm (200-3000 cm-1). However, most of the fingerprint region lies between 200-2700 cm-1, hence the additional benefit of an extended range is not significant.
While the choice of laser wavelength lies with the end-user, we strongly recommend a 785 nm system as the best choice for most samples.
- Is it possible to change the laser or have two lasers and be able to switch between them?
No. All optical components in the instrument are optimized for a particular wavelength.
- Is it possible to change the power level of the laser?
The 785 nm laser power level is controlled by software. Since it is a diode laser, power is easily adjustable by electronic means.
For a 532 nm system, the laser type is solid-state (DPSS) and cannot be adjusted. The 532 nm laser system operates at one power level only.
When operating either laser, we recommend the use of safety goggles which are supplied with the purchase of any Raman Systems spectrometer.
- Do we make our own lasers?
- Yes.
- Is the laser available as a stand-alone product?
- Yes. Click here RAM-LR Laser
