The Atomic Structure of Matter

The most important of all chemical theories is the atomic theory. In 1805 the English chemist and physicist John Dalton (1766–1844), of Manchester, stated the hypothesis that substances consist of small particles of matter. He called these particles atoms, from the Greek word «atomos», meaning indivisible. This hypothesis gave a simple explanation or picture of previously observed but unsatisfactorily explained relations among the weights of substances taking part in chemical reactions with one another. It was necessary that the hypothesis be confirmed. Hadn't it been verified by further work in chemistry and physics it wouldn't have become the atomic theory. The existence of atoms is now accepted as a fact.

All ordinary matter consists of atoms. The exceptional kinds of matter are the elementary particles from which atoms are made (electrons, protons, neutrons) and similar sub-atomic particles (positrons, mesons). But atoms are the units which retain their identity when chemical reactions take place, and therefore they are important to us now. Atoms are the structural units of all solids, liquids, and gases. They are very small ‑ only about 2 Å to 5 Å in diameter.

This is indeed small. If a piece of rock, or anything else, one inch in diameter were magnified to the size of the earth, its constituent atoms would become about the size of golf balls or tennis balls.

Every atom consists of one nucleus and one or more electrons. The nucleus is a small, heavy particle containing almost all the mass of the atom. Nuclei are very small indeed. The nucleus of an atom is only about one ten-thousandth as great in diameter as the atom itself, and the volume of the nucleus is one million-millionth, of the volume of the atom.

If nuclei could be packed together side by side, they would give a form of matter with very great density. The electron is a particle with a small mass, 1/1845 that of the lightest nucleus, and with a negative electrical charge.

The electron itself is about as large as a nucleus, its diameter being about 10-12 cm. The electrons in an atom are attracted by the nucleus. The electrons in an atom move rapidly around in the space extending over a diameter of a few Å about the nucleus, and because they move about so fast they effectively fill this space in such a way as to repel any other atom which approaches to within this diameter.

Were it not for the rapid progress of scientific knowledge about atoms the evidence for the existence of atoms would not be so overwhelming.

Laser

The laser period opens with the achievement of the ruby laser. The acronym l.a.s.e.r.stands for light amplification by stimulated emission of radiation.

Physicist Theodore Harold Maiman invented the first operable laser. While employed at Hughes Research Laboratories as a section head in 1960, he developed, demonstrated, and patented a laser using a pink ruby medium, for which he gained worldwide recognition. Born in Los Angeles, California, Maiman, in his teens earned college money by repairing electrical appliances and radios. He attended the University of Colorado and received a B.S.* in engineering physics in 1949, then went on to do graduate work at Stanford University, where he received an M.S.* in electrical engineering in 1951 and a Ph.D.* in physics in 1955. In 1962 Maiman founded his own company, Korad Corporation, devoted to the research, development, and manufacture of lasers.

Early in 1961 the first continuously operating laser was announced by Ali Javan and coworkers at Bell Laboratories. This laser was the first to use a gas, a mixture of helium and neon, for the light emitting material. At the same years scientists from American Optical Company made the first neodymium-doped glass laser. In 1962 scientists at General Electric and International Business Machines (IBM) almost simultaneously demonstrated the first semiconductor junction laser.

In 1962 Basov and Oraevskii proposed that rapid cooling could produce population inversions in molecular systems. And in 1966, the first gas-dynamic laser was successfully operated at the Avco Everett Research Lab. Many new laser types were discovered, most notable among these are the semiconductor lasers. In these lasers electrical energy is converted directly into highly monochromatic radiation.

The 1970s years became the time of discovery of a free electron laser. Laser applications have also increased in variety. Clearly, most optical experiments can be done at least as well with lasers as with conventional light sources and many can be done much better. Experiments requiring really high intensities in narrow spectral regions can only be made with lasers. Outside the field of scientific experimentation many applications were found in medicine, communications, geophysical and space exploration, military and metals technology. The potential importance of these applications continues to stimulate new developments in the laser field.

The 1964 Nobel Prize in physics was awarded to Charles Townes and to the Russian scientists Nikolai Basov and Alexander Prokhorov for fundamental work in the field of quantum electronics, which has led to the construction of oscillators and amplifiers based on the maser-laser principle.

Maser

The devices known as masers and lasers serve as amplifiers and generators of radiation. Their common characteristic is that they make use of the conversion of atomic or molecular energy to electromagnetic radiation by means of the process known as stimulated emission of radiation. When the wavelength of the emitted radiation is in the vicinity of 1 cm we speak of microwave amplifiers or masers. Instruments which generate or amplify visible or nearly visible radiation are called optical masers or lasers.

The history of the invention or the evolution of these devices may be divided into the following periods.

The relevant phase of the premaser period started with the discovery of the existence of the stimulated emission process and ended with the recognition by many physicists of the possibility that this process might lead to a radiation amplifier. This period extends from 1916 to 1953. In 1917, it was Albert Einstein who was the first to recognize the existence of stimulated emission, but not until the 1950s when the first device was demonstrated.

The maser period begins with the publication of an article by Basov and Prokhorov and the construction of the first operating maser by Townes, Gordon, Zeiger. Basov and Prokhorov gave a detailed theoretical exploration of the use of molecular beams in microwave spectroscopy. The article of Basov and Prokhorov contained detailed calculations pertaining to the role of the relevant physical parameters, the effects of line-width, cavity dimensions, and the like. Thus the quantitative conditions for the operation of a microwave amplifier and generator were found.

In 1954 at Columbia University Charles Townes and two of his students announced the construction and operation of a device that may be used as a high resolution microwave spectrometer, a microwave amplifier, or a very stable oscillator. They named the device a “maser” – an acronym for microwave amplification by stimulated emission of radiation.

From 1958 on, many masers were constructed for applications in radio astronomy and as components of radar receivers. These masers were mostly of the ruby type. Their design became a part of the engineering art and research interest turned toward the extension of stimulated emission techniques in the visible and infrared regions. Arthur Schawlow of Bell Laboratories and Townes proposed extending the maser concept to the optical frequency range in 1958. Born in Greenville, South Carolina, Townes joined the technical staff of Bell Telephone Laboratories Inc. and worked on radar bombing systems during World War II. In 1948 he joined the faculty of Columbia University and three years later had the idea that resulted in the construction of the maser. From 1959 to 1961 Townes served as a vice president and a director of research of the Institute for Defense Analysis in Washington, D.C. He then was appointed the professor of physics at Massachusetts Institute of Technology.

The maser period extends from 1954 to 1960.