Resolution of photon-recoil structure of the 6573-Å calcium line in an atomic beam with optical Ramsey fringes

Abstract
The photon‐recoil components of the Ca 6573‐Å line have been resolved using the three‐zone optical Ramsey interference technique with an atomic beam. Linewidths as narrow as 3 kHz HWHM (line Q of 8×1010) are reported for zone separations up to 7 cm. An indication of the light‐shift‐induced contraction of the recoil splitting predicted by C.J. Bordé is obtained. Techniques are discussed which should lead to an optical wavelength/frequency standard with an accuracy of better than 10−14.