Optical quantities and their measurement

If it's true that astronomy is the oldest of the sciences, then optics provided the first of all measuring instruments: gnomons, astrolabes, quadrants and other devices for locating the positions of stars are the ancestors of a long line of devices, whose field of action has progressively extended to almost all human activities.

In the following paragraphs, we'll look in more detail at the role played by optical metrology in both research and industry, but here are just a few examples of the influence optics has had on the development of our knowledge, and the close links it has always maintained with the other sciences.

For a long time, the only source of information we had on the movement and constitution of the heavens was the study of the light coming from them. These early observations led directly to our first measurements of time and, in particular, to our calendars. Even today, our cosmogonic theories evolve at the pace of optical observations, since exploration by man – or his robots – does not go beyond the stars closest to Earth. If the news is confirmed, it is to optics that we owe the discovery of the first planet in an extra-solar system.

In a related field, it was the study of light that opened the door to the two major theories of physics: relativity and quantum mechanics.

The failure of all attempts to demonstrate variations in the speed of light linked to the Earth's motion led Lorentz, Poincaré and then Einstein to give a new expression to the old principle of relativity formulated by Galileo.

The notion of the quantum, reluctantly introduced by Planck to explain how energy is distributed in the spectrum of light emitted by an incandescent body, is the basis of all our current conceptions of the structure and behavior of matter.

Should we also recall the decisive contribution made by the development of the – microscope, contemporary with the astronomical telescope – to the scientific revolution of the 17th century? Leuwenhoek's and Boyle's observations revealed the existence of "animalcules", unknown because they were invisible to the naked eye. They opened the door to the vast field of labiology and Earth sciences. For almost four centuries, biologists, physicians, geologists and metallurgists would have no other way of improving their knowledge of the infinitely small. In a curious twist of fate, the quest for ever-more sophisticated performance refined our ideas on one of the fundamental concepts of optics - image formation - and led to the most recent theories, such as Fourier optics, the mother of holography, the videodisc and, more recently, the infinite variety of CD ROMs. Without optics, would we be able to open up the "information superhighway"...