Therefore, the spectral noise level will be significantly affected by changes in the slot configuration. The higher the slot setting, the lower the noise in the spectrum. The smaller the slot setting, the greater the noise in the spectrum. Above are spectra that show the results of a lack of resolution.
The concave mirror E then focuses the light on the outlet slot F, forming a spectrum across the outlet slot. A number of users have also experimented with slit widths and have even constructed mechanically variable slots, a difficult task. Some simple instruments, for example the common Spectronic 20, have fixed slot widths, but most research-grade instruments have user-controllable slot widths. As the width of the slot decreases, the slot increasingly blocks light traveling at a large angle to the optical axis (the central axis of symmetry of the optical processing system).
This spreadsheet demonstrates the spectral distribution of the slit function, transmission and measured light for a simulated dispersive absorption spectrophotometer with a continuous light source, adjustable wavelength, mechanical slot width, reciprocal linear dispersion, spectral bandpass, absorber, average width spectral, concentration, path length and unabsorbed scattered light. This simulation, Effect of slot width on the signal-to-noise ratio in absorption spectroscopy, shows how these opposing factors combine: decreasing the observed absorbance and the linearity of the analytical curve versus increasing the intensity of light and the signal-to-noise ratio as the width of the slot increases. This increases the importance of choosing the slot width, since it will be difficult and expensive to install a new slot once the spectrometer has been assembled. However, the signal-to-noise ratio decreases as the slot width decreases, so it is not always practical to use the smallest possible slot width.
There is a geometric mismatch between the slot and the outlet of the lens, especially in the case of thinner slits, which are very narrow rectangles. Results The PLab 3.0 kit conveniently includes sampling of slit widths such as accurate, high-contrast photographic film images that provide an opportunity to test theories about the effect of slot width on measurement resolution.
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