Iodine stabilized diode laser using Noise-Immune Cavity-Enhanced Optical Heterodyne Molecular Spectroscopy for the practical realisation of the meter at 633 nm

Abstract

In this thesis a new practical realization of the meter at a wavelength of 633 nm with a diode laser stabilized on iodine is investigated, with the aim of replacing the old technology of He-Ne lasers with more effective diode lasers. The frequency of an external cavity diode laser is stabilized to the Doppler-free hyperfine transitions of iodine (127^I_2) using noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) technique. The performance of the system was investigated in comparison to a primary Cs atomic clock via a frequency comb. The diode laser is stabilized by using the NICE-OHMS method to a 14 cm external cavity containing a 10 cm long iodine cell. It achieves a short time frequency instability of 1.4 · 10^(−12) for an averaging time of 1 s, an improvement by a factor of four compared to an iodine stabilized He-Ne laser, which is widely used as practical realization of the meter. The uncertainty of the NICE-OHMS system is 28 kHz. Practical experiments as well as simulations are performed to identify effects that influence the frequency of the laser. To replace two-mode or Zeeman-stabilized He-Ne lasers, also a shoe box size diode laser system stabilized to Doppler broadened iodine lines is investigated. This system, which uses a 3 cm iodine cell, covers a frequency range of several 100 GHz, and achieves an output power of 5 mW. It automatically stabilizes to iodine lines and has a frequency instability of 2·10^(−10) for averaging times of 1 s, which is adequate for industrial interferometry applications.