Method to stabilize a wavelength of a tunable laser device, tunable laser device, and position measurement system provided with the tunable laser device

A method to stabilize a wavelength of a tunable laser device comprising:

• simultaneously providing a laser beam from a tunable laser source to a first interferometer having a mechanically stable reference axis and to a gas absorption cell;
• scanning a wavelength range with the laser beam from a first wavelength to a second wavelength;
• determining a transmission spectrum of the gas absorption cell as a function of the wavelength difference with respect to the first wavelength;
• using the first interferometer to determine a phase change as a function of the wavelength difference with respect to the first wavelength;
• determining a transmission spectrum as a function of the phase change using the transmission spectrum of the gas absorption cell and the phase change as a function of the wavelength difference;
• correlating the determined transmission spectrum as a function of phase change to a pre-calibrated transmission spectrum of the tunable laser device to provide an absolute laser wavelength as a function of the phase change;
• defining a phase setpoint corresponding to a wavelength setpoint;
• and
• using the phase setpoint to tune the tunable laser device to the wavelength setpoint.

A tunable laser device, comprising:

• a tunable laser source configured to provide a laser beam;
• a first interferometer comprising a mechanically stable reference axis adapted to receive the laser beam;
• a gas absorption cell adapted to receive the laser beam simultaneously with the interferometer;
• and
• a processor adapted for:
• scanning a wavelength range with the laser beam from a first wavelength to a second wavelength;
• determining a transmission spectrum of the gas absorption cell as a function of time;
• using the first interferometer to determine a phase change as a function of time;
• determining a transmission spectrum as a function of the phase change using the transmission spectrum of the gas absorption cell and the phase change as a function of time;
• correlating the determined transmission spectrum as a function of phase change to a pre-calibrated transmission spectrum of the tunable laser device to provide an absolute laser wavelength as a function of the phase change;
• defining a phase setpoint corresponding to a wavelength setpoint;
• and
• using the phase setpoint to tune the tunable laser device to the wavelength setpoint.