Reducing the phase noise in diode lasers.

Diode lasers are widely used in atomic physics given their narrow linewidth and wavelength tunability. Nevertheless, although they present low noise for their intensity, excessive noise in the phase limits their application in quantum optics. Looking for reduction of this phase noise, we built and characterized a ring laser, using a semiconductor-tapered amplifier as the gain medium. We were able to reduce the phase noise of a diode laser to a factor of 10 above shot-noise level, bringing it closer to a useful coherent state for applications in quantum information.