Beat Note Frequency Research Articles

Long-term stability of two diode-laser-pumped nonplanar ring lasers independently stabilized to two Fabry–Perot interferometers

We have locked two 1064-nm diode-laser-pumped Nd:YAG lasers to two ultralow-expansion glass-ceramic Fabry-Perot interferometers by using the Pound-Drever discriminator technique. The interferometers have finesses of approximately 200,000 and 5-kHz linewidths and are housed in separate temperature-stabilized vacuum vessels. Allan variance measurements of the beat note between the two lasers are as low as 10(-14) for delay times between 0.5 and 2 s and increase with the time interval for times longer than 2 s, an improvement of 4 orders of magnitude over the free-running performance. Daily variations of the beat-note frequency are less than 1 MHz, which corresponds to a relative temperature change of approximately 100 mK between the interferometers.

Improved deuterium bromide 1-0 band molecular constants from heterodyne frequency measurements

Abstract Heterodyne frequency measurements have been made on selected deuterium bromide 1-0 band transitions ranging from P (20) to R (17). Difference frequency beat notes between a tunablediode laser whose frequency was locked to the DBr absorption lines and a CO laser whose frequency was either locked or adjusted to a reference synthesized from CO 2 laser frequency standards were measured. The beat note frequency was then combined with the measured CO laser frequency to give the DBr frequency. For two of the measurements, frequency-doubled CO 2 laser radiation was substituted for the CO laser radiation. The measurements included electric quadrupole split triplets comprising the R (0) and P (1) transitions in the D 79 Br isotope. New DBr constants have been determined, and a table of frequencies is presented for the calibration of spectrometers and tunable lasers in the wavenumber range 1600 to 1990 cm −1 . A table of far-infrared frequencies is also given for DBr covering the range from 50 to 206 cm −1 .

The Dielectric Constant of Air at Radio Frequencies

A radio frequency method has been used to measure the dielectric constant $K$ of dry air free from C${\mathrm{O}}_{2}$, the value obtained being 1.0005893 for standard conditions of temperature and pressure. The probable error in $K\ensuremath{-}1$ due to accidental variations is 0.34 percent. The method is a modification of the usual heterodyne beat arrangment. Capacity changes produced when the pressure in the test condenser is changed are compensated by a suitable condenser in parallel. The beat note frequency is compared with that of a fork by means of Lissajous' figures. The test condenser is made of invar to avoid temperature effects. Short connecting wires are used to minimize lead-inductance effects. A few preliminary measurements made with a large direct current voltage superimposed on the high frequency voltage across the condenser indicate no change in the dielectric constant of air, hydrogen, or ammonia. There is some indication that a discharge through the gas decreases its dielectric constant but the effect is probably spurious.