Laser apparatus and method for controlling the linewidth of the emitted laser beam

A laser apparatus comprising:

• a laser diode configured to emit a laser beam, wherein the laser diode is further configured for frequency modulation of the laser beam;
• a sensor unit configured to receive a first portion of the laser beam, wherein the sensor unit is further configured for measuring variations of the frequency of the first portion of the laser beam;
• a phase shifter arranged in a path of a second portion of the laser beam, and configured to generate a phase shift of the second portion of the laser beam propagating through the phase shifter;
• wherein the laser apparatus is configured to output the second portion of the laser beam having propagated through the phase shifter;
• and
• wherein the laser apparatus is configured to acquire, by the sensor unit, a plurality of measurements of the variations of the frequency during frequency modulation at a plurality of different phase shifts generated by the phase shifter, and to control the phase shifter based on the plurality of measurements so as to control the variations of the frequency, whereby the laser apparatus is configured to control a linewidth of the laser beam in dependence of an external reflection of the second portion of the laser beam being output, received by the laser apparatus.