Science (from Latin scientia, meaning "knowledge") is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe.
From classical antiquity through the 19th century, science as a type of knowledge was more closely linked to philosophy. In the West, the term natural philosophy encompassed fields of study that are currently associated with disciplines such as classical physics, astronomy and medicine and was a precursor of modern natural sciences (life science and physical science). In the 17th and 18th centuries, scientists increasingly sought to formulate knowledge in terms of laws of nature. Over the centuries, the term science became associated with the scientific method, a systematic way of studying the natural world and particularly in the 19th century, multiple distinguishing characteristics of contemporary modern science began to take shape.
Modern science is typically divided into three major branches that consist of the natural sciences (e.g. biology, chemistry, physics), which study nature in the broadest sense; the social sciences (e.g. psychology, sociology, economics), which study individuals and societies; and the formal sciences (e.g. mathematics, logic, theoretical computer science), which study abstract concepts. There is disagreement, however, on the formal sciences being a science as they do not rely on empirical evidence. Disciplines that use science, such as engineering and medicine, are described as applied sciences.
Science is related to research and is commonly organized by academic and research institutions as well as government agencies and companies. The practical impact of scientific research has led to the emergence of science policies that seek to influence the scientific enterprise by prioritizing the development of commercial products, armaments, health care, and environmental protection.
An atomic line filter (ALF)
is an advanced optical band-pass filter
used in the physical sciences
for filtering electromagnetic radiation
with precision, accuracy, and minimal signal strength loss. Atomic line filters work via the absorption
or resonance lines
of atomic vapors and so may also be designated an atomic resonance filter (ARF).
The three major types of atomic line filters are absorption-re-emission ALFs, Faraday filters and Voigt filters. Absorption-re-emission filters were the first type developed, and so are commonly called simply "atomic line filters"; the other two types are usually referred to specifically as "Faraday filters" or "Voigt filters". Atomic line filters use different mechanisms and designs for different applications, but the same basic strategy is always employed: by taking advantage of the narrow lines of absorption or resonance in a metallic vapor, a specific frequency of light bypasses a series of filters that block all other light.