Analytical instruments like UV-Vis spectrophotometers and atomic absorption spectrometers rely on collimated light. A lens or curved mirror, called a collimator, turns light from a lamp or laser into a collimated beam. This happens before the light passes through the sample and into the monochromator, the part that selects a single wavelength.
Collimation matters because of the Beer-Lambert law, which chemists use for quantitative absorbance measurements. This law assumes every photon travels the same, well defined path length through the sample. If some rays were not parallel, they would travel slightly different distances through the sample.
This would introduce scattered light and measurement error into the results. Collimation is also essential in several other techniques. Nephelometry, which measures how a sample scatters light, needs a well defined beam.
Laser based detectors and X-ray diffraction also depend on a beam with a precise direction and cross section. This precision gives accurate, repeatable results. A poorly collimated beam can make a spectrophotometer’s calibration curve bend away from a straight line at high absorbance.
Telescopes and laser pointers also use collimating lenses to keep their light from spreading out over long distances. Optical alignment tools called collimators help technicians check and adjust a beam’s parallelism before an experiment begins.