FAQ: Why are the Raman Responses not Near 0ns in the Temporal Range?

FAQ series: This series of publications explores some of the most frequently asked questions regarding Timegated® spectrometers and measurements without having you read page after page of text. 

Raman scattering is an almost instantaneous phenomenon and that is why this question comes up quite often: Why are the Raman responses not closer to 0ns in spectra which include the delay (time) axis?  As shown in the figure below, the recorded Raman signals are in a later part of the delay range.  

The Raman responses are recorded in the ca. 5-6ns delay range with this individual measurement setup.

Timegated® Raman spectrometers make use of pulsed lasers. Each pulse must first make its way from the laser source to the sample and after that through the collection pathway to the detector of the spectrometer. This is why the Raman signals are not recorded instantaneously after a pulse has been emitted but after a delay. It should be noted that the delay will vary depending on the optical pathway of each spectrometer and probe design. This is one reason Timegated® Raman spectrometers enable the user to choose and tune the delay range that is used for measurements. If necessary, the delay range where the signal is observed can be adjusted with hardware modifications that counter the delay caused by the optical path length. Read more about  Timegated® Raman Technology.

Raman responses are not recorded instantly as the light must first travel to the sample and after that to the detector. This is the main cause of a delay in the temporal range.

Author

This blog was written by Timegate Instruments’ Application Team Lead Bryan Heilala. Bryan is a young and energetic chemist with a degree in M.Sc. (chemistry) and experience and background in analytical chemistry.