Z. Bay

LOCKING A LASER FREQUENCY TO THE TIME STANDARD

On the basis of high‐frequency modulation experiments and well‐known locking techniques, a scheme is described for stabilizing a visible laser frequency and simultaneously determining that frequency in terms of the time standard. The importance of this method for a refined determination of the velocity of light and the possibility of establishment of reference lines for spectroscopy and for length measurements, throughout the spectrum wherever laser lines are available, is discussed.

Electron-Multiplier as an Electron-Counting Device

IN an earlier communication1, I have described the possibility of using an electron multiplier, based on the secondary emission principle, for the detection of individual electrons by cooling the multiplier for the purpose of suppressing the thermal emission in liquid air. I stated there that this method of counting individual electrons does not necessarily require the use of liquid air, provided multiplying electrodes, with fairly great secondary emission factor and sufficiently high work function are used. There is a large discrepancy in the data of various papers published on the subject of work function and secondary emission of a surface. Experiments had to be carried out to determine whether a surface satisfying our requirements could be found, and we found the following surface satisfactory from the above point of view:Very thin layers of barium oxide on a nickel base activated by the method normally used for oxidecoated cathodes will easily give a multiplication factor of T = 2.5, with a primary electron velocity of 200 volts. A multiplication of about 10,000 times was achieved in a ten-stage multiplier. The thermionic emission (at room temperature) and field emission of the active surfaces in this multiplier are negligible.

The Constancy of the Velocity of Light and Prospects for a Unified Standardization of Time, Frequency and Length

The use of fundamental constants of nature for the definition of the units of physical measurements was suggested by M. Planck in 1906 (1). By assigning the value of unity to the four constants, c, h, k, and G the “natural units” of time, length, mass, and temperature can be defined. Albeit its great theoretical merit, that proposal could not be practical in 1906 since the large uncertainties in the known values of the constants would have propagated into the determination of the units.

Techniques and Teory of Fast Coincidence Experiments

A review of fast coincidence circuits, working in the millimicrosecond region, is presented. The main points covered are: 1) operating characteristics of the various types of coincidence circuits, 2) description of the various circuits, 3) differential coincidence method, 4) analysis of coincidence curves and the determination of time delays, 5) the resolving time, 6) effect of random time lags on coincidence curves, 7) experimental investigation of random time lags, 8) coincidence efficiency, and 9) statistical accuracy of time measurements.

Radar astronomy and the special theory of relativity

The measurements of Planetary Radar and Lunar Laser Ranging provide a complete experimental foundation of the Lorentz-group of the Special Theory of Relativity.

The speed of light and the new meter

New developments in the measurement of optical frequencies and the speed of light offer now the exciting possibility of creating a unified time-length measurement system and a highly accurate new meter.