Physics, Instrumentation and Sensing
Cold atom devices
Construction of an onboard laser source for cooling rubidium
Laser source under construction
In order to plan onboard applications of cold atoms, it is essential to develop high-performance laser sources that are immune to very disturbed mechanical environments.
Yet the laser diodes in cavities that are ordinarily used, while appropriate for cooling requirements (1 MHz beam width for 100 mW intensity), are very sensitive to environmental conditions like vibrations and temperature. There are robust sources developed for telecommunications requirements and meeting extremely severe and rigorous standards.
Unfortunately, these wavelengths (around 1.5 mm ) do not correspond to atomic transitions usable for cooling. The original idea we have developed consists in doubling the frequency of the light emitted by laser sources at 1.56 mm. The wavelength thus obtained is between 770 nm and 780 nm, which can be used to cool potassium and rubidium. Technically, we use an erbium-doped fiber laser with a spectral width less than 10 kHz. Its light is amplified by an erbium-doped amplifier and then sent into a nonlinear crystal (lithium niobate, periodically returned), which performs the frequency doubling function. After this, a part of the beam is used to slave the laser frequency to an atomic transition of rubidium. The source at 780 nm thus obtained has a spectral width of less than 10 kHz.
In a second phase, we tried to increase the usable power by different means: more powerful amplifier, waveguide crystal, placement in a doubling cavity, which made it possible to achieve densities of the order of a watt. This laser source today serves as a reference beam for the Girafon experiment, and is the embryo of its optical bench.
Onboard laser source
