Professor Receives Award For Invention of "Maser"

For his work in the development of the solid state maser--a super high fidelity amplifier of tremendous importance in radio astronomy and satellite communication systems--Nicolaas Bloembergen, Gordon McKay Professor of Applied Physics, will receive the Ballantine Medal of the Franklin Institute at the Institute's annual Medal Day award ceremony tonight.

Bloembergen's maser is used to amplify weak radiations of very short wavelength--for example, microwave radio signals. In use for a year-and-a-half on the Harvard College Observatory's 60-foot radio telescope, the maser has already helped double the known number of radio stars.

Winning a Franklin Institute Medal is viewed as a high honor in the scientific world. The Institute, a research center in Philadelphia, has been awarding medals for 113 years to promote "the recognition and encouragement of scientific invention."

Tonight's medal recipients will include architect Le-Corbusier, physicist James A. Van Allen, who was responsible for the discovery of the Van Allen radiation belts drdling the earth, and Donald A. Glaser, a Nobel Prize winner in physics last year for his work on the Bubble Chamber.

Bloembergen conceived the first practical solid state maser in 1956. The first operational version was completed in December, 1956 by a Bell Telephone scientist.

Masers amplify by way of a special effect of quantum physics known as "stimulated emission of radiation." (The name "maser" stands for "Microwave Amplification by Stimulated Emission of Radiation."

According to quantum theory, an electron in an atom can exist at any one of several discrete energy levels. When an electron falls from a higher level to a lower one, the atom gives off radiation at a specific frequency--for example, a microwave or a light wave.

Radiation "Triggers" Emission

If the electrons in an atom are already at the higher levels, incoming radiation of the proper frequency can "trigger" their fall, thus producing new radiation of the same frequency as the original signal and in effect amplifying it.

Obtaining a supply of atoms with electrons in the higher energy states is the chief problem in using stimulated emission to amplify.

The first maser, built by physicist Charles H. Townes at Columbia University in 1951, solved this problem by physically segregating the high energy atoms in a gas from the low energy ones. This gas maser, however, proved unsuitable for practical amplification.

Bloembergen's solution was to use a crystal instead of a gas and to devise a means for keeping a large proportion of the atoms in the crystal in the higher energy states.

A magnetic field surrounding the crystal and impurities introduced into the crystal make three discrete energy level available. A special generator directs microwave radiation towards the crystal so that electrons are continuously "pumped" from the first to the third level. The crystal is kept cold so that the maximum number of electrons is kept at the highest level.

When radiation of the frequency to be amplified strikes one of the excited atoms, the electron falls from the third to the second level, emitting new radiation. The electron later spontaneously returns to the first level to be pumped again to the top level.

Operates Near Absolute Zero

The actual maser in use on the radio telescope at the University's Harvard, Mass., Observatory is contained in a box about four feet long and one foot wide and deep. The crystal that is the heart of the maser is a synthetic ruby placed between the two poles of a magnet and kept in a both of liquid helium at a temperature about two degrees above absolute zero(--491* Fahrenheit.)

The Observatory maser has achieved a ten-fold increase in the sensitivity of the telescope, which is used to detect the radio waves emitted by stars and other sources scattered throughout the universe.

Because masers can be made that will permit the reception of signals 100 times weaker than the weakest radiation detectable by previous means, the devices have important applications in satellite communications systems, Here masers are used to amplify weak signals broadcast from satellites or bounced off them. Masers may thus one day make possible global TV networks, with television signals transmitted across the oceans by being bounced off satellites.

Bloembergen himself is continuing his work on masers with research on the basic physical mechanisms involved