Frequency measurements in the optical range: current status and prospects

Abstract

The vibrational constants of the c 'C: and x 'Xi states of the e x system of the N P + molecule have been determined from the spectrum obtmned by passing a condensed &scharge through a mixture of lSN2 and hekum. These constants have been compared with those calculated by using I4Na instead of 16N2. The agreement is very good. The isotope shfts for indimdual bands have also been calculated. A few bands of the (I4, Is!9 + molecule, which appear during the study of W2+, have been analysed.

Calibration of a Michelson-type laser wavemeter and evaluation of its accuracy

“…A more fundamental problem with secondary length standards is that they must be regularly calibrated against a reference laser with higher stability in frequency to obtain a high degree of accuracy in the measurements. There are a number of reviews published on the techniques of laser frequency/wavelength measurements [3,4]. One of the most common techniques implements optical heterodyne interferometry in which the output beam of the secondary standard is combined with the output of the primary standard on the active area of a fast photodetector and the frequency difference between the two lasers is generated as the electrical signal of the photodetector.…”

Optical frequency/wavelength references

“…The accuracies to which optical atomic frequencies have been determined relative to primary Cs frequency standards are illustrated in figure 2 [18][19][20][21][22][23]. For the plot we have arbitrarily chosen the starting date as 1972, the year when the 3.39 µm methane-stabilized HeNe laser was first measured, but, in fact, there were a few measurements of far-infrared and CO 2 laser frequency references prior to that date.…”

The measurement of optical frequencies

“…There are even two books devoted to the technology and applications of optical frequency metrology [41,42]. Equally interesting are key early papers on optical frequency measurements that contain a wealth of information along with the unique perspective of their time [5,8,10,18,21,30,31,[43][44][45][46][47][48][49][50].…”