Lasers for Raman Spectroscopy

Information about lasers for Raman spectroscopy

At Cobolt, we try to understand the specific needs that each customer has when it comes to laser usage. We have lasers that can be used in a broad range of applications.

In Raman spectroscopy, for example, the molecular fingerprint of the sample can be read by observing the inelastic scattering of vibrational and rotational transitions. The excitation source used to initiate these transitions will typically be a laser.

Laser specifications

Lasers for Raman spectroscopy need to meet certain performance criteria. Preferred, but not a pre requisite, is that the laser operates single longitudinal mode, has a very stable mode and has an accurate and stable wavelength. The advantage of using a laser operating single longitudinal mode is that the extremely weak Raman signals very close to the excitation wavelength can be resolved. A stable wavelength thus means there is lower chance the excitation wavelength will float around risking to engulf the weak Raman signal.

Laser wavelength selection

By far the most popular wavelength used for Raman spectroscopy is 785 nm, as it offers the best balance between avoiding fluorescence, absorption of the laser light (and Raman scattering) by the sample and therefore heating effects, and the limits to detector sensitivity. However, the choice of wavelength depends heavily on the specific application. In general, shorter wavelengths mean fluorescence is encountered more often but the intensity of Raman scattering increases quadratically (intensity shows a 1/l4 dependence), and longer wavelengths means less fluorescence but a weaker signal.

Furthermore, 785 nm lies at the edge of the detectors sensitivity (Silicon) before more expensive detectors need to be considered (InGaAs based with excitation at 1064 nm for example), which together with light absorption in the NIR by water itself, reduces somewhat the advantage of using yet longer excitation wavelengths. Hence selecting the correct laser excitation wavelength is critical to increase the chance of collecting a usable Raman spectrum.

Lastly, critical to both system integrators and researchers alike is that lasers for Raman spectroscopy are robust and reliable. Whatever the wavelength of laser chosen, they all come manufactured with our propriority method of HTCure™ for ultimate robustness and reliability.

 

See Cobolt’s lasers used for Raman spectroscopy: Cobolt 08-01 Series

 
 
 

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