Artur Shavlov

Artur Shavlov

Physicist
Date of Birth: 05.05.1921
Country: USA

Content:
  1. Biography of Arthur Leonard Schawlow
  2. Early Life and Education
  3. Early Career and Contributions
  4. Research on Supersymmetry and Lasers
  5. Later Career and Achievements
  6. Nobel Prize and Later Life

Biography of Arthur Leonard Schawlow

Early Life and Education

Arthur Leonard Schawlow, an American physicist, was born in Mount Vernon, New York. His father, also named Arthur Schawlow, immigrated from Riga, Latvia to the United States ten years before his birth. Settling in New York, his father became an insurance agent and married a Canadian citizen, Helen Mason. When Arthur was three years old, the family (including his younger sister) moved to Canada. Growing up in Toronto, Schawlow attended Winchester Public School, followed by a normal school and then Vaugan Road Collegiate Institute, which he graduated from in 1937. Despite his interest in natural sciences from a young age, Schawlow was unable to pursue his dream of becoming a radio engineer at the University of Toronto due to financial difficulties caused by the Great Depression. However, he earned an honorable scholarship in mathematics and physics.

Early Career and Contributions

Schawlow completed his bachelor's degree in 1941 and during World War II, he taught military personnel courses at the University of Toronto until 1944. Afterward, he joined a project working on the development of microwave antennas at a radar equipment factory. In 1945, Schawlow returned to the University of Toronto to work on his dissertation on optical spectroscopy under the guidance of Malcolm F. Crawford, whom he later described as an "extraordinarily creative individual." He received his doctorate in physics in 1949. A postdoctoral fellowship from Carbide and Carbon Chemicals allowed him to spend two years at Columbia University, working with Charles H. Townes on microwave spectroscopy problems.

Research on Supersymmetry and Lasers

In 1951, Schawlow became a researcher at Bell Labs in Murray Hill, New Jersey. His main area of research became superconductivity, a phenomenon discovered by Heike Kamerlingh Onnes in 1911, which involves the complete disappearance of electrical resistance in certain materials at extremely low temperatures near absolute zero (-273°C). Schawlow continued to collaborate with Townes during this time. They met regularly and worked on completing their book "Microwave Spectroscopy," which Schawlow started during his time at Columbia University. The book was published in 1955. Two years prior to this, Townes and his colleagues had developed a device they named the maser, which stood for "microwave amplification by stimulated emission of radiation." This stimulated emission was predicted by Albert Einstein in 1917. Based on a revolutionary quantum theory, they showed that atoms consist of electrons orbiting around a dense central nucleus (Niels Bohr's model). The movement of electrons is restricted to discrete allowed orbits, meaning they have specific energy values. In such cases, it is said that the atom exists in certain energy states (or energy levels) determined by the electron-nucleus interaction. The lowest level is called the ground state. By absorbing or emitting radiation, electrons can become excited and transition to higher levels. Since Max Planck showed that radiation consists of individual portions, which Einstein called quanta (now known as photons), energy differences between levels correspond to specific quanta or photons. Planck also showed that the frequency of radiation is proportional to the energy of the photon. An excited electron eventually returns to a lower energy level, emitting a photon with energy equal to the difference between these levels and producing characteristic emission spectra correlated with energy differences between levels that form a unique system for each atom.

Excited atoms usually emit photons of various wavelengths and frequencies randomly. Einstein theoretically showed that if a sufficient number of atoms could be excited to a specific energy level, the emission of photons with energies equal to the differences between this level and some lower atomic level could cause a cascade of transitions. Excited atoms on the upper level would transition back to the lower level, emitting a large number of photons with the same frequency and phase (at the same point in the frequency cycle). Townes experimentally confirmed this theoretical prediction using microwaves, whose photons had energy equal to the differences between the two levels of ammonia atoms, the substance he worked with. (Molecules also have energy levels associated with the states of atoms composing them and are determined by atomic interactions.) Since relatively weak microwave signals induce a relatively large output of photons with the same frequency, the result can be interpreted as signal amplification. Some of the released photons excite atoms, causing them to transition back to the upper energy level, turning the amplifier into a generator capable of sustaining continuous oscillations, not just a single burst. Microwaves have lower frequencies (lower photon energies) and therefore longer wavelengths (1-50 mm) than visible light (0.0004-0.0007 mm). In 1957-1958, Townes and Schawlow worked on finding a way to achieve the maser effect with visible light and in December 1958, they published the article "Infrared and Optical Masers" in the journal "Physical Review," explaining how it could be done. In 1960, American physicist Theodore Maiman from Hughes Aircraft Company demonstrated the first operational laser – an acronym for "light amplification by stimulated emission of radiation." In the same year, Schawlow and other physicists also succeeded in constructing lasers. During this period, masers and lasers were independently developed by Russian physicists Nikolay Basov and Alexander Prokhorov.

Later Career and Achievements

In 1960, Schawlow returned to Columbia University as a visiting professor. The following year, he became a professor of physics at Stanford University, where he remained for the rest of his career, serving as the dean of the Physical Sciences Division for five years. He continued to advance laser technology, aiming to achieve output of fully monochromatic (single-frequency) radiation with adjustable frequency (tunable lasers). However, in most of his work, Schawlow used lasers to study atoms and molecules. Since the early 1960s, he became one of the leading figures in the rapidly developing field of laser spectroscopy. Laser spectroscopy is based on the fundamental fact that atoms and molecules absorb and emit electromagnetic radiation at characteristic frequencies (photon energies) corresponding to energy differences between their different energy levels. Analyzing the frequency spectrum of emitted or absorbed radiation helps identify elements, determine the structure of atoms and molecules, and validate conclusions of fundamental theories of matter and radiation. The creation of a tunable laser was a significant achievement as the radiation from such a laser is virtually monochromatic (allowing precise frequency measurement), highly intense (allowing spectrum measurements with a relatively small number of atoms or molecules), and facilitates laser adjustment to desired frequencies.

In many types of spectroscopy, spectral lines (narrow frequency bands) are subject to the Doppler effect. The Doppler effect refers to the change in observed frequency when the radiation source moves relative to the observer. The frequency increases when the emitter approaches the observer and decreases when it moves away, with the amount of frequency shift depending on the speed of the source's approach or withdrawal. In the case of sound waves, the Doppler effect is responsible for the familiar increase or decrease in pitch of a passing train whistle or car horn. In spectroscopy, the frequencies emitted by atoms or molecules, which are always in motion due to their temperature, shift towards higher or lower frequencies depending on the direction of their motion. Since atoms and molecules move in different directions, the spectral line becomes broadened. In the case of absorption spectra, the "observer" is the atom or molecule being exposed to radiation. The "observed" frequency is higher or lower than the frequency of the external source, depending on whether the atom or molecule is approaching or moving away from the source. Spectral "lines" are actually peaks with diminishing edges. Due to line broadening, two closely spaced peaks may overlap, and a small peak may be difficult to discern against a larger neighboring one, remaining unnoticed.

Working with Theodore W. Hänsch at Stanford, Schawlow developed several methods to overcome the difficulties associated with Doppler broadening by selecting absorption spectra emitted by atoms whose velocity does not contain a component parallel to the laser beam. Since these atoms do not approach or move away from the radiation source, the Doppler effect is completely eliminated. In 1972, Schawlow and his team achieved the first optical spectra of atomic hydrogen that were not affected by the Doppler effect, allowing them to measure the Rydberg constant with unprecedented accuracy – one of the most important constants in physics.

Molecular spectra, in general, are much more complex than atomic spectra, and Schawlow used lasers to simplify molecular spectra using so-called laser "tags." Molecules are "pumped" into a specific energy state using laser radiation tuned to the desired frequency (photon energy), and then the experimenter observes their return to lower energy levels. Since this upper state is isolated from all the possible neighboring states, it is called a tagged state. Schawlow also developed a laser spectroscopy method for detecting trace elements in materials.

Nobel Prize and Later Life

In 1981, Schawlow, along with Nicholas Bloembergen, was awarded half of the Nobel Prize in Physics "for their contributions to the development of laser spectroscopy." The other half of the prize was awarded to Kai Siegbahn for his related work in electron spectroscopy. During the presentation ceremony, Ingvar Lindgren, representing the Royal Swedish Academy of Sciences, stated, "These methods have enabled the study of the internal structure of atoms, molecules, and solids in much greater detail than was previously possible."

In 1951, Schawlow married Aurelia Townes, the younger sister of Charles X. Townes. They have one son and two daughters. A devoted amateur clarinetist, Schawlow enjoys traditional jazz and has amassed a large collection of recordings. He is well-known as a lecturer and has contributed to the creation of educational films and television science programs.

In addition to the Nobel Prize, Schawlow received the Stuart Ballantine Medal and Award from the Franklin Institute (1952), the Thomas Young Medal from the Institute of Physics in London (1963), and the Frederic Ives Medal from the Optical Society of America (1976). He is a member of the National Academy of Sciences, the American Association for the Advancement of Science, the American Physical Society, the Optical Society of America, and the Institute of Electrical and Electronics Engineers. Schawlow has also been awarded honorary doctorates from Ghent State University, the University of Bradford, and the University of Toronto.

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