Intracavity iodine cell spectroscopy with an extended-cavity laser diode around 633 nm

The purpose of the work described was to develop a tunable laser diode which is as easy to use as a He-Ne laser stabilized on iodine. The particularity of this experiment is the use of I₂ cell placed inside the extended cavity laser (ECL). The experimental set-up mounted takes the form of a lambdameter which gives the wavelength to one part in 10⁶, a Fabry-Perot (FP) interferometer for mode analysis and a beat-frequency measurement system. The FP interferometer has the particular feature of a second I₂ cell which makes it possible to detect the iodine transitions by simple visual inspection of an oscilloscope. Many transitions, some much more intense than the usual R(127)11-5 transition, are under study. We worked mainly on P(33) 6-3 since this is inside the range of our beat-frequency system. Results are promising: the free running relative frequency stability is about three parts in 10¹⁰ and the locked-laser relative frequency stability about three parts in 10¹¹ after 80 s. This is already good enough for use as a wavelength standard for length and for interferometric measurement