Low frequency noise blue external cavity diode laser

The development of precision laser spectroscopy around 420 nm for gas sensing, atomic clocks and laser cooling is slowed down by the lack of compact narrow linewidth laser sources allowing lab-to-market technology transfer. In the infrared (IR) part of the spectrum, the laser diode technology is mature to address those kind of specifications but for shorter wavelengths there are still technological issues. Commercial blue laser diodes have a wide multimode optical spectrum. To improve the frequency noise performances, the use of an external cavity has been proven to favor single mode behavior. Nevertheless, opto-mechanical instabilities of the external cavity limit the laser linewidth to a few MHz. To overcome this issue, we propose a compact and low-cost all-fiber-based locking setup for frequency noise suppression of a 420 nm external-cavity diode laser. This versatile and compact optical reference allows to reduce the laser frequency noise up to 40 dB associated with a linewidth reduction from 850 kHz to 20 kHz. To our knowledge this is the first demonstration of such a stabilization scheme in this wavelength range. The originality of our work is to point out that actual performances of fiber based photonic components around 420 nm, limit the noise reduction efficiency of such optoelectronic feedback loop scheme. This simple locking scheme might be implemented for a large range of wavelengths and can be integrated on a small footprint for embedded applications requiring narrow linewidth blue laser diodes.