Frequency stabilization of an external-cavity diode laser by offset frequency looking to a stabilized He-Ne laser

We present an external cavity diode laser which is frequency coupled to a stabilized He-Ne Laser with optical phase locked loop technology. For long term frequency stability the diode laser is locked with a fixed frequency offset to a stabilized He-Ne Laser at 633nm. A commercial PLL chip and the piezo-drive of the diode laser are used for precise frequency control. With this simple technique we develop a diode laser source which reach the frequency stability of a stabilized He-Ne Laser and still provide an optical output power of 5 mW or more. This high optical output power enables applications like multi axis homodyne interferometry with just one laser source.