The calcium optical frequency standard: present status

An optical frequency standard based on a dye laser stabilized to the Lamb dip of the Doppler-broadened Ca intercombination line is reported. The measured depth of the Lamb dip depends strongly on the laser power and the excitation geometry and can be explained quantitatively by calculation of the transition probability. The stabilized laser frequency can be made reproducible to better than 300 Hz by stabilizing the same laser to two independent thermal atomic beams with the possibility of laser cooling one of the atomic beams.<
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