Aleksandr Prohorov Physicist Date of Birth: 11.07.1916 Country: Australia

1. Alexander Prokhorov: Russian Physicist and Nobel Laureate
2. Research and Discoveries
3. Contributions to Quantum Electronics
4. Later Career and Achievements

Alexander Prokhorov: Russian Physicist and Nobel Laureate

Alexander Mikhailovich Prokhorov, the son of Mikhail Ivanovich Prokhorov and Maria Ivanovna (nee Mikhailova) Prokhorova, was born in Atherton, Australia, where his family had relocated in 1911 after his parents escaped from Siberian exile. After the October Revolution, the Prokhorov family returned to the Soviet Union in 1923. Prokhorov graduated with honors from the Physics Department of Leningrad State University in 1939 and went on to pursue his postgraduate studies in the Laboratory of Oscillations at the Lebedev Physical Institute of the USSR Academy of Sciences in Moscow.

Research and Discoveries

During his time at the Lebedev Physical Institute, Prokhorov focused on studying the propagation of radio waves over the Earth's surface. Together with one of his supervisors, physicist V.V. Migulin, he developed a new method of using radio wave interference to study the ionosphere, one of the upper layers of the atmosphere. Prokhorov's experiments during his military service in the Red Army from June 1941 to 1944 resulted in new insights into frequency stabilization in vacuum tube generators.

In 1946, Prokhorov defended his candidate thesis on the theory of nonlinear oscillations, which earned him the L.D. Landau Prize, a prestigious award in Soviet radio physics, shared with two other physicists. In 1947, he began researching the radiation emitted by electrons in a synchrotron, a device in which charged particles, such as protons or electrons, move along expanding cyclic orbits, accelerating to very high energies. Prokhorov experimentally demonstrated that the radiation from electrons is concentrated in the microwaves region, with wavelengths on the order of centimeters.

Based on this work, Prokhorov completed his doctoral dissertation in 1951, which formed the basis for further research carried out by other scientists. In 1950, he was appointed Deputy Director of the Laboratory of Oscillations, where he shifted his research interests to the field of radio spectroscopy. He organized a group of young researchers to study the rotational and vibrational spectra of molecules using radar and radio technology developed primarily in the United States and England during and after World War II.

Prokhorov's research focused on a class of molecules called asymmetric tops, which have three different moments of inertia and are particularly challenging to analyze. In addition to spectroscopic studies, Prokhorov conducted theoretical analysis on the application of microwave absorption spectra to improve frequency and time standards. These findings led him to collaborate with Nikolay Basov in the development of molecular generators, now known as masers (microwave amplification by stimulated emission of radiation).

Contributions to Quantum Electronics

The principles of quantum physics state that atoms and molecules possess energies, arising from the arrangement and motion of their electrons, that are limited to discrete values or energy levels. According to another principle, electromagnetic radiation, such as light or radio waves, consists of discrete energy packets called photons, whose energy is proportional to the frequency. If a photon has energy equal to the difference in energy between two levels, an atom or molecule can absorb the radiation and undergo a transition from the lower level to the upper level. The atom or molecule then spontaneously transitions back to the lower energy level, emitting the energy difference in the form of emitted photon radiation.

In 1917, Albert Einstein, while studying the interaction of radiation with matter in a confined region, derived an equation that described the known processes of absorption and spontaneous emission. Einstein's equation also predicted a third process called stimulated emission, in which an excited atom or molecule transitions from a high-energy state to a lower-energy state due to the presence of radiation whose photons have energy equal to the energy difference between these two levels. The energy lost during the transition is emitted as photons of the same type as the stimulating photons.

Prokhorov and Basov proposed a method for utilizing stimulated emission. By separating the excited molecules from the molecules in the ground state using a non-uniform electric or magnetic field, it became possible to create a substance in which the molecules were in the upper energy level. If radiation with a frequency (photon energy) equal to the energy difference between the excited and ground levels fell on this substance, it would induce emission with the same frequency, leading to amplification. By diverting some of the energy to excite new molecules, it would be possible to convert the amplifier into a molecular generator capable of producing self-sustained emission. Prokhorov and Basov presented the possibility of creating such a molecular generator at the All-Union Conference on Radio Spectroscopy in May 1952, and their first publication on the topic was in October 1954. In 1955, they proposed the "three-level method" for creating a maser.

Charles H. Townes, an American physicist from Columbia University, independently came to similar conclusions and constructed a working maser ten months before Prokhorov and Basov published their article in 1954. Townes used a resonant chamber filled with excited ammonia molecules and achieved extraordinary microwave amplification at a frequency of 24,000 megahertz. In 1960, the three-level method was confirmed by Theodore Maiman, an American physicist working at Hughes Aircraft Company. He achieved amplification of light waves using a long synthetic ruby crystal as the resonant chamber, with a spiral tube filled with xenon gas. The gas discharge was accompanied by flashes capable of inducing stimulated emission. As Maiman used light, his device was named a "laser" (an abbreviation for light amplification by stimulated emission of radiation).

Later Career and Achievements

As the Director of the Laboratory of Oscillations at the Lebedev Physical Institute from 1954, Prokhorov established two new laboratories: Radio Astronomy and Quantum Radio Physics. He consulted numerous research institutes on quantum electronics and organized the Radio Spectroscopy Laboratory at the Research Institute of Nuclear Studies at Moscow State University, where he became a professor in 1957.

From the mid-1950s, Prokhorov focused his efforts on the development of masers and lasers and the search for crystals with suitable spectral and relaxation properties. His detailed studies on ruby, one of the best crystals for lasers, led to the widespread use of ruby resonators for microwave and optical wavelengths. To overcome some difficulties in creating molecular generators operating in the submillimeter range, Prokhorov proposed a new open resonator consisting of two mirrors. This resonator type proved particularly effective in creating lasers in the 1960s.

In 1964, Prokhorov and Basov, along with Townes, were awarded the Nobel Prize in Physics for their fundamental work in the field of quantum electronics, which led to the creation of generators and amplifiers based on the principles of maser-laser.

Prokhorov continued his research on laser physics, including their application in studying multi-quantum processes and thermonuclear fusion, while serving as Deputy Director of the Lebedev Physical Institute from 1973. He was elected a Corresponding Member of the USSR Academy of Sciences in 1960, a Full Member in 1966, and a member of the Presidium in 1970. He was an honorary member of the American Academy of Arts and Sciences. In 1969, he became the Chief Editor of the Great Soviet Encyclopedia. Prokhorov held the title of Hero of Socialist Labor, awarded by the Soviet government in 1969.

Alexander Prokhorov is married to Galina Alekseevna Shelepin, a geographer by profession, since 1941. They have one son.

Prokhorov is an honorary professor at Delhi University (1967) and Bucharest University (1971).