PhD abstract
This thesis describes the frequency stabilization of a 1.54 µm fiber laser on an iodine hyperfine line at 514 nm, after a frequency tripling process. An important part of this work is dedicated to the frequency tripling process (ω to 3ω), and to the development of an original approach of a phase modulation operated in the IR, while the Doppler free spectroscopy is operated at 1.54 µm. To do this, a phase modulation by an EOM, a power stabilization action by an AOM and two periodically polled wave guided Lithium Niobate nonlinear crystals are used. A harmonic power higher than 100 mW at 514 nm) is generated using a fundamental optical power less than 1 W at 1.54 µm. The optical setup is fully fibered. The total power consumption of this frequency tripling process is 20 W only. Using a specific operation mode, this laser setup emits simultaneously three frequency-stabilized and intense radiations at 1.54 µm, 772 nm and 514 nm. Following this development, a very compact laser spectroscopy setup was built, based on a short sealed quartz cell, which contains the molecular iodine vapor. An optical power lower than 10 mW in the green is sufficient to carry out the iodine vapor interrogation, and to detect the hyperfine saturation transitions, with a high quality factor around 514 nm (Q higher than 2×109). A frequency stability at the level of 3×10-14 τ-1/2 with a minimum value of 4×10-15 at 200 s is demonstrated using a phase modulation operated in the green. When the phase modulation is applied in the IR, a relative frequency stability at the level of 5×10-14 τ-1/2 was obtained. This work has allowed to identify the major key components, in order to develop in the near future, a fully fibered and compact stabilized laser prototype occupying a total optical volume less than 10 litres. We have pointed out an important limitation to the mid-term frequency stability due to the Zeeman Effect as 10-15/mGauss. Such frequency stabilized laser source could be used in numerous space projects that require ultra-stable frequency optical links, inter-satellite or ground to space, for space geodesy (GRICE), Earth gravitational field measurement (GRACE-FO, NGGM), gravitational waves detection (LISA), etc.
Key words
optical metrology, frequency stabilization, ultra-stable lasers, Iodine optical clock, nonlinear optics, frequency tripling, Telecom Laser, 1.5 μm, 514 nm, space, Zeeman effect