Abstract
Raising the interest in remote chemical analysis, in particular through Raman and fluorescence spectroscopy, the opportunity of increasing the exposure represents an important step for an easier and more reliable spectrum analysis. However, the European directive 2006/25/EC defines the maximum permitted exposure (MPE) to artificial radiations according to exposure duration, wavelength, coherence of the radiation and beam divergence. Though the Raman cross section scales in general according to the fourth power of the excitation wavelength, promoting the use of deep UV radiation, a synergy between wavelength and exposure time can raise the Raman signal in the near UV or in the near IR if compliance to eye-safety directives is requested. In this work we will analyze the possibilities offered by commercially available components for enhancing the Raman scattering under eye-safe conditions.
Highlights
Laser spectroscopy represents a very useful tool for chemical analysis
Raman and fluorescence spectroscopy are successfully used in detection of biological in vivo analysis and standoff/proximal detection of unknown substances [1, 2]
Since the overall value of the noise depends on a variety of factors such as temperature, dark noise, readout noise and background illumination, a thorough discussion on Raman signal-to-noise ratio is beyond the aim of this work; as a rule of thumb we can say that if the detector noise does not grow dramatically with integration time the best strategy could be represented by sending more pulses in times as long as 10 s
Summary
Laser spectroscopy represents a very useful tool for chemical analysis. In particular, Raman and fluorescence spectroscopy are successfully used in detection of biological in vivo analysis and standoff/proximal detection of unknown substances [1, 2]. It is clear that if a single exposure of 1 s would be possible, the use of UVA region allows an MPE up to 178 times that associated to 1 ns, typical lower limit of the pulse duration in active Q-switched lasers.
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