observed as an oscillatory magneto­striction in the metal crystal.

Dr. Green and Dr. Chandrasekhar ex­perimented with a single crystal of bis­muth, which was maintained at the tem­perature of liquid helium, a few degrees above the absolute zero of temperature. The magnetic field was produced by a superconducting magnet, a coil of niobi­um-zirconium alloy which loses all its electric resistance at the temperature of liquid helium and therefore consumes no power in spite of fifteen amperes of cur­rent flowing through it. This coil, eight inches long and two inches in inside di­ameter, produces more than 30,000 gauss of magnetic field strength and is one of the largest superconducting magnets in use today.

As the field was varied changes in the length of the bismuth crystal were measured by a very sensitive electrical method which could detect changes in the length of one part in a billion. The length of the crystal did indeed oscillate, in a manner which agreed in all respects with the theoretical predictions.

This new effect is essentially similar to oscillations in certain magnetic prop­erties, also in bismuth which were dis­covered in 1930 by the Dutch physicists De Haas and Van Alphen. These effects have provided a very powerful tool in understanding the detailed electronic structure of metals: how the electrons move among the atoms of metals. The new effect observed by Dr. Green and Dr. Chandrasekhar has certain additional features which should further our under­standing of the behavior of electrons in a metal, with possible applications to the technology of materials.

Pulsed gas laser yields high power Peak powers of over 50 watts have been achieved with a new pulsed gas laser at Martin-Orlando research laboratories, Baltimore, Md., and outputs in the kilo­watt range may be imminent. The achieve­ment of such output levels brings the gas laser from a low-power laboratory device into the intermediate power range with practical use as a system component for auto-tracking optical radars, reconnais­sance systems, and missile guidance ap­plication. The Martin research effort is aimed at the development of optical radar.

The Martin experimental helium-neon laser is 3 cm in diameter, reportedly the largest in current use in this country and larger than the only other one (in Eng­land) producing such power levels. It uses a pulse repetition frequency of 2,000 cps and a pump input of 50-kv peak voltage in 0.25-μsec pulses. Output pulse width is 0.7 μsec at the half-power point.

The high power and pulse repetition frequency of the laser are attributed to a "rapid inversion" technique developed by Martin scientists. In a continuous-wave gas laser, power output is limited by the time necessary for the neon atoms to return to ground state after being pumped to the high energy level where emission occurs. The energy levels through which the atoms must pass on the way

back down tend to be metastable and, consequently, become heavily populated, inhibiting inversion.

The pulsed gas laser, on the other hand, is able to take advantage of the fact that the build-up of the population of the different energy levels is sequen­tial. This allows inversion of the laser levels before the population of the ter­minal level of the laser transition has built up to its equilibrium level. Laser action is thus achieved during the period when the population of the neon one-S levels is low compared to that existing during continuous-wave operation.

Considerable experimentation with the pulsed gas laser has demonstrated its high potential as a key component in an optical radar. Results indicate effective ranges of up to 10 kilometers for non-cooperative targets and over 100 kilome­ters for cooperative targets.

Magnetometer used to locate suriken ships An instrument normally used to plot the earth's magnetic field is being used to wrest tightly held secrets from Davy Jones' locker.

A report of tests made with a proton magnetometer last year off Cape Ca­naveral and the Florida Keys has been turned over to a Florida-based marine archaeology organization. The report de­tails the results of Operation Lodestone, a marine archaeological survey carried out during the summer of 1962 under direction of Charles Harnett, of Orlando, Fla.

While establishing the value of the proton magnetometer in locating ancient vessels, the project also proved the in­strument's usefulness in detecting sunken ships of modern date. During Operation Lodestone, a modern freighter was de­tected on the ocean floor five miles off Cape Canaveral. A search of records showed that the freighter sank in 1927 while transporting a cargo of Model-T Fords south along the coast.

Never previously used in a marine archaeological application, the proton magnetometer was provided for the re­search project by its west coast manu­facturer. It has since been used to de­tect the location of sunken aircraft off the California coast. Current U.S. Navy search for the sunken submarine Thresh­er now is being conducted with an im­proved model of the instrument used in Operation Lodestone.

The proton magnetometer indicates the presence of iron masses lying on the ocean bottom. Spanish galleons carried tons of iron materials, from spikes and fittings to cannon.

Since Operation Lodestone, Harnett has made significant strides to improve search and survey techniques. Other in­struments operated in conjunction with the magnetometer now provide data not only on presence and location of a wreck, but also on the approximate size and shape of the sunken mass.

The key to successful undersea search operations is the ability to navigate straight paths parallel to one another

over a given search area and without benefit of landmarks. Wind, currents, rough sea, and tides combine to prevent navigation of a straight-line course even for the seasoned pilot. In early investi­gations Hartnett used buoys equipped with flags, radio transmitters, sonar and lights to provide homing sources for the search vessel. But even the best of these allowed an error of 75 feet on either side from the intended search path, a handicap for electronic search. After six months of study, he now has developed an optical device that enables a vessel to traverse search paths with deviations from course of only five to ten feet.

Traveling-wave maser uses superconducting magnet A 70-kmc traveling-wave maser that uses a superconducting magnet for the applied field is being developed by the Westinghouse Electric Corp. The super­conducting magnet, now in use, provides the high-field uniformity that is impor­tant to high-gain maser operation of broad bandwidth, high frequency and high sensitivity. The new maser device, with a pump frequency of 118 kmc, will be used to investigate advanced radiome­ters, radar, and communications equip­ment.

Gains of more than 20 db at 10-mc bandwidth have been achieved. To ob­tain high-frequency amplification at low noise levels, temperatures approaching zero Κ are required. The iron-doped titanium dioxide (rutile) maser operates at 4.2 K. This temperature environment is ideal for the operation of a supercon­ducting magnet. Without iron-doped ti­tanium dioxide, the maser would require a pump frequency of 140 instead of 118 kmc, at which it operates.

The niobium-zirconium superconduct­ing magnet used in this maser system produces a 5,000-gauss field having a field deviation of less than one gauss perpendicular to the 1.5-inch length of the traveling-wave maser element. The magnet is constructed with iron pole faces and return paths that are finished within a few wavelengths of light of exact dimensions. The magnet weighs approximately three pounds and is equipped with a persistent switch for op­eration in the persistent mode. During this mode of operation, the supercon­ducting magnet does not require any external power since the niobium-zir­conium wire has zero resistance at liquid helium temperature.

The advantages of using a supercon­ducting magnet in the 70-kmc traveling wave tube maser include substantial re­duction in size and weight, high-field uniformity and intensity, and ability to disconnect the power sources, making the unit portable. The superconducting mag­net provides a tunable feature for maser operation in that the field can be varied according to any desired value. Once the selected value is reached, the magnet can be operated in the persistent mode. This assures high-field stability and, at the same time, eliminates the need for the 12-volt d-c battery power supply.

694 ELECTRICAL ENGINEERING · NOVEMBER 1963