Single-mode VCSELs for Atomic Clock Pumping
Single-mode VCSELs are key components in the manufacture of miniaturized rubidium or cesium atomic clocks. The idea is a wrist-worn atomic clock based on MEMS technology.
VCSEL
The preparation of the dark states (i.e. the pumping of the atomic clock) in thermal atomic Cs vapors requires two phase-stable light beams at 852 nm. The light beams should have a difference in frequency of 9.2 GHz – the hyper fine splitting of the ground state structure of Cs. These are achieved by current modulation of a laser diode.
How does this application differ from common spectroscopic applications? For one, a certain line must be hit precisely without the other lines even being at the user’s disposal (as is the case in spectroscopy). A tight wavelength is selected by the manufacturer and the stabilization and control of the working point of the diode by the customer. For another, as the diode must be modulated in the GHz range, common TO assemblies can only be used at an experimental stage. These tight specifications justify the individual section inside the VCSEL family.
This groundbreaking research was conducted by Svenja Knappe during her post-graduate studies at the University of Bonn in the late ‘90s. Today, Dr. Knappe works at the NIST in Boulder, Colorado.
