Coherence-selectable operation of external-cavity semiconductor diode laser by intracavity polarisation control

The operation of an external-cavity semiconductor diode laser with selectable coherence and a tunable wavelength has been successfully demonstrated through the control of the intracavity polarisation state. The laser has an intracavity half-wave plate that is able to rotate the orientation of the polarisation axis with regard to diffraction grating, where the grating acts as a polarisation- and wavelength-selective element. As a result, it was possible to continuously sweep the correlation widths from 230 kHz to 2.0 MHz by simply rotating the half-wave plate.