Lasers for Raman Spectroscopy

Compact high performance lasers advances Raman spectroscopy

The ”inelastic scattering of light,” or Raman effect, was observed in practice for the first time in 1928 by C.V. Raman for which he was awarded the Nobel Prize in 1930. In Raman spectroscopy an incident laser beam (in the UV visible-near IR spectral range) is frequency shifted by this inelastic scattering in the material or substance studied.

The frequency shift (Stoke shift) originates from interactions of the laser beam with molecular vibrations, phonons or other excitations in the material and the resulting spectrum provides quantitative and spatial information about the chemical compound distribution in the material. A main advantage of Raman spectroscopy is its capability to offer label-free biochemical and material analysis. The increasing availability of high performance compact DPSS lasers across a broad range of wavelengths from the UV to the NIR has strongly contributed to making Raman microscopes and spectrometers a powerful and increasingly popular analytical tool not only for material science in laboratory environment but also for on-line quality and process control in e.g pharmaceutical and semiconductor and chemical industries.

The Raman signal is very weak and must be carefully discriminated from the excitation beam, Rayleigh scattering and the back-ground fluorescence. However, the introduction of new types of Raman spectroscopy such as surface-enhanced Raman (SERS), resonant Raman, tip-enhanced Raman etc has helped to increase the strength of the Raman signal significantly and enabled rapid penetration of Raman into new applications areas such as biomedical analysis and medical diagnosis. High performance Raman spectroscopy puts very high demands on the spectral purity and spectral stability of the laser sources used.

The Cobolt DPSS lasers on the 04-01, 05-01 and 08-01 platforms are perfectly suited for demanding Raman spectroscopy applications. Stable single-frequency operation combined with the ultra-robust thermo-mechnical architecture of HTCure provides narrow linewidth (<1MHz), extremely low spectral drift (<2 pm over 8 hs) and a spectral purity better than 60 dB, which allows for very high resolution Raman spectroscopy and a possibility to detect low frequency Raman signals even down in the THz regime.

lasers for raman spectroscopy An example of the resonance Raman effect; by choosing 355 nm rather than 473 nm laser excitation the observed Raman signals are much stronger, thus providing improved resolution. (Co W.R. Browne, Institute for Chemistry, University of Groningen, The Netherlands

 

neural_3spaltNeural cell imaging with Raman confocal microscopy using the Cobolt Samba 532 nm (Co Renishaw, New Mills, UK)
asprin_3spaltMedical compound distribution in aspirin pill; generated by Raman microscopy using the Cobolt Samba 532 nm
06Dpl_3spaltCobolt 08-01 series; Ultra-compact, all integrated, single-frequency 532 nm lasers up to 200 mW, Ideal for high performance Raman spectroscopy.