Spectroscopy Knowledge Base
Spectroscopy Terms
Resolution
The resolution of a spectrometer describes its ability to distinguish between two closely spaced wavelengths. It is typically expressed as the Full Width at Half Maximum (FWHM), which represents the wavelength difference at half the height of a spectral peak. Factors such as grating, slit width, wavelength range, and detector pixel count influence resolution. A smaller FWHM indicates better performance.
Stray Light
Stray light refers to unwanted light that reaches the detector due to internal scattering, reflection, or refraction. It is commonly evaluated by measuring residual light at a blocked wavelength, for example using a high‑pass filter. Lower stray‑light levels improve measurement accuracy.
Dark Noise
Dark noise is the electronic noise generated by the detector and readout electronics when no light is present. It is usually measured as the RMS voltage output during a short integration period in complete darkness. Lower dark noise enhances sensitivity, particularly for low‑light measurements.
Signal-to-Noise Ratio (SNR)
The signal‑to‑noise ratio compares the detector’s maximum measurable signal to the noise present in the system. A higher SNR results in a cleaner, more stable output and improves the detection of small intensity variations. It is often calculated using the full‑scale detector signal divided by the RMS noise.
Integration Time
Integration time is the duration over which the spectrometer collects light to generate a single spectrum. Longer integration times increase signal intensity and improve SNR, while very short times are limited by the characteristics of the CCD or CMOS sensor. Typical user‑defined ranges span from milliseconds to more than one minute.
Dynamic Range
Dynamic range expresses the ratio between the smallest and largest signals a spectrometer can measure accurately. A larger dynamic range allows the simultaneous detection of both weak and strong signals without saturation or loss of detail.
Thermal Stability
Thermal stability refers to how consistently a spectrometer performs across varying temperatures. Evaluations are typically made within a defined temperature range to ensure stability in wavelength and intensity under different environmental conditions.