Collimated
Definition and meaning of Collimated in chemistry.
Collimated describes a beam of light or other radiation whose rays travel parallel to one another, so the beam neither converges nor diverges as it propagates. The opposite would be a divergent or convergent beam, such as light spreading out from a point source.
In more detail
In analytical instruments such as UV-Vis spectrophotometers and atomic absorption spectrometers, a lens or curved mirror called a collimator converts light from a lamp or laser into a collimated beam before it passes through the sample compartment and monochromator. This matters because quantitative absorbance measurements based on the Beer-Lambert law assume every photon travels the same, well-defined path length through the sample; stray divergent rays would traverse slightly different path lengths and distances, introducing scatter and measurement error. Collimation is also essential in techniques like nephelometry, laser-based detectors, and X-ray diffraction, where a well-defined beam direction and cross-section are required for accurate results.
Key facts
| Field | Analytical Chemistry |
|---|---|
| Achieved with | collimating lens or curved mirror (collimator) |
| Key purpose | ensures uniform, well-defined path length through a sample |
| Relevant law | Beer-Lambert law (absorbance measurements) |
In a UV-Vis spectrophotometer, light from a deuterium or tungsten lamp diverges from the source and is reflected off a collimating mirror to form a collimated beam before it enters the monochromator and passes through the sample cuvette.
Frequently asked questions
Why does collimated light matter for Beer-Lambert law measurements?
Absorbance calculations assume every photon travels the same path length through the sample; non-parallel rays create varying effective path lengths and stray light, which distorts the measured absorbance.
Is collimated light the same as monochromatic light?
No. Collimated describes the directional parallelism of the rays, while monochromatic describes a single wavelength. A beam can be collimated, monochromatic, both, or neither.