Sensitivity

Sensitivity in spectroscopy is the ability of a spectroscopic system to collect low levels of light, being that as we are getting lower in the amount of light we can detect we are getting higher sensitivity. Is an essential feature of a detection system on a spectrometer, which depends from two fundamental parameters: quantum efficiency and signal-to-noise ratio. Great sensitivity is specially relevant in applications such as Fluorescence and Raman.

Quantum Efficiency

 The quantum efficiency of a detector is a parameter that defines the probability of a photon with a given energy originates an electron. A CCD detector does not exhibit a constant quantum efficiency over the operational wavelength range, however it is possible to achieve a maximum quantum efficiency (in the visible region) close to 40% for front-illuminated CCD’s. But when looking to the maximum quantum efficiency Sarspec can offer the best solution with the SENSE Spectrometer it’s possible to reach 90% quantum efficiency (at peak) and more that 60% efficiency in a region from 400 to 850nm.

 

How Detector Temperature Control Influences Sensitivity?

 

 

 The sensitivity of a CCD’s detector is proportional to the radiation exposure and, therefore, can be increased by increasing the integration time. Long integration times are generally selected when the sample emission is weak. However, this approach is limited by the noise of the CCD’s detector (dark counts). Dark counts have generally a thermal origin and correspond to the signal that is measured by the detector in the absence of radiation. Thus, it can be reduced by cooling the detector using a thermoelectric (TE) system. Cooling the detector means that the signal of the dark counts does not change with the variation of the ambient temperature, resulting, therefore, in a better signal-to-noise ratio.

Sensitivity Depends Only on Spectrometer?

Although the quantum efficiency and signal-to-noise ratio of the detector are essential, sensitivity is also influenced by the changes made in internal and external components of the spectroscopic system. Thus, choose optical fibers with a larger core, using collecting lenses, increase the width of the slit or choose a diffraction grating with the efficiency maximum near the wavelength of interest are options needed to correctly select on the spectroscopic system, when sensitivity is wanted. Depending on the application, the power of the light source may be also a key factor for sensitivity increase, this is esily verifiable in Fluorescence and Raman measurements.

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