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.

It is an essential feature of a spectrometer detection system, which depends on two fundamental parameters: quantum efficiency and signal-to-noise ratio. Great sensitivity is especially 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 originating from 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 CCDs. But when looking at 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 than 60% efficiency in a region from 400 to 850nm.

How does Detector Temperature Control influence Sensitivity?

The sensitivity of a CCD 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 generally have a thermal origin and correspond to the signal 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 ambient temperature variation, resulting in a better signal-to-noise ratio.

Sensitivity Depends Only on Spectrometer?

Although the detector's quantum efficiency and signal-to-noise ratio are essential, sensitivity is also influenced by the changes in the spectroscopic system's internal and external components.

Thus, choosing optical fibers with a larger core, using collecting lenses, increasing the width of the slit, or choosing a diffraction grating with an 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 easily verifiable in Fluorescence and Raman measurements.