Extremely short external cavity semiconductor laser: profilometry via wavelength tuning

Summary form only given. We are studying wavelength tuning profilometry based on direct optical feedback to a laser diode. In this system, the front facet of a semiconductor laser is brought close to the sample surface (for example the recorded surface of an optical disk) so that some of the light emitted by the laser is reflected back into the laser cavity (i.e. laser´s front facet and the reflective sample surface form an external cavity). As the surface is scanned, this reflection strength varies with the variations of the sample´s surface depth. The laser reacts to this variation by changing its operation point, which causes changes in bias voltage, optical output power and wavelength. The changes in the laser´s optical properties are monitored via the light emitted through the back facet of the laser. We measured the depth information of surface relief structures by monitoring the laser´s wavelength with optical spectrum analyzer, as the surface was scanned.