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The Tendency to Say Optical Maser is Growing

The following are some interesting words of wisdom from May 1961.[1]

“The optical maser is a source of coherent, monochromatic light. By modulating and amplifying this coherent light emission, it will be possible to use light as radio waves are used today. Until now, there were coherent sources of electromagnetic waves only for frequencies less than 105 Mc (1011 cycles). The optical maser has raised this limit almost 10,000 times. And not only has the frequency been increased but the sharpness or fractional bandwidth has also been improved.”

“The ruby optical maser as reported by Bell Telephone Laboratories and similar to the Hughes Research Group’s development consists of a Linde synthetic pink ruby rod 0.20 inch in diameter and 2 inches long. Both ends of the rod are optically polished to make them flat within 2 X 10-6 inches and parallel to within 10 seconds of arc. The end surfaces are made partially reflective, allowing only about 5% of the light striking them to pass through. A source of input power, a xenon-filled flash lamp, surrounds the ruby rod. It is pulsed by discharging a bank of capacitors through it. Charged to 4,000 volts, the bank delivers 3,000 joules to the lamp in about 1 millisecond. Fig. 1 shows both the mechanical and electrical details of the construction of a pulsed ruby optical maser. In the bottom section is a 0-4,000 volt power supply, used to charge the bank of four 100 μf 4,000 volt capacitors. The series resistor limits the charging current. Also shown is the supply for the 15kv transient that triggers the FT524 flash tube. A funnel-shaped cone holds the ruby rod axially within the helical coil of the flash tube. Surrounding the entire assembly of holder and lamp is a reflector. It can be either highly polished aluminum sheet or powdered magnesium oxide. It contains the flash lamp output so a large fraction of it will be absorbed by the ruby. The output of the flash lamp is white light but only the green and violet portions of it can be absorbed by the ruby. Besides the essential parts ruby, flash lamp and reflector a coolant for the ruby and flash tube, and opaque shields surrounding the exterior parts complete the maser.”

“With the development of these powerful, coherent and monochromatic light sources, many new uses of light will become possible. In the past, no light combined all three of these properties to the same extent and at the same time. One immediate application would be optical radar. Since the wavelength is so much shorter than that of present radars, the resolution could be much higher. Radar systems operating at 1 cm with antennas several meters in height have a beam width, and hence definition, of about 0.5°. This might be compared with an optical maser 1/2 cm in width, with a beam width of 0.05°, which through the addition of a simple optical lens system an inch or so in diameter could easily be reduced to 0.005°. With such a narrow beam width, radar systems could easily identify the actual shapes of aircraft.”

“Because of the vast new frequency space that will be opened in the future, the communications industry is vitally concerned with maser developments. At present, communications links operate up to about 104 Mc. The optical maser will extend that range to 1014 cycles. This advance is particularly striking when one remembers that all of the frequency span now available to us is contained in 10% of the new region. To appreciate the significance of this, it is only necessary to realize that a color TV channel requires a bandwidth of nearly 10 megacycles. If the existing channels were used in a 10% modulation system, about 100 channels would be available. This is certainly adequate for TV but there is no space left for data transmission or telephony. On the other hand, an optical maser at 108 Mc with a 10% bandwidth could handle 106 TV channels and still have a bandwidth of 107 Mc left for other uses.”

“The directional property of optical masers will be useful in earth-to-satellite, satellite-to-satellite and earth-to-moon links. For example, if the output of an optical maser were sent through a simple lens system 4 inches in diameter, the radiation would cover only 2 miles at the surface of the moon. This indicates the possibilities of private communications.”

“In addition to these applications, the optical maser might be used as a tool to effect chemical reactions. Maser emission is coherent; it can therefore be focused into an area of dimensions comparable to wavelengths of light. Under these conditions all the maser energy could be concentrated within single living cells and selective destruction of tissue (surgery) be performed.”

“The optical maser can extend greatly the range over which interferometric measurements can be made. Present optical interference measurements are limited to about 100 cm due to inherent line width and low power of monochromatic sources, but significant increases in length are now possible.”

The technology developed quicker than most thought and the history of the optical maser informs today’s R&D. It’s time to reconstruct some of these early experiments.

[1] R. J. Collins and D. F. Nelson, “Communications at 450,000,000 MC, How the revolutionary new optical maser works” p. 57-60 Radio Electronics, May 1961.