External optical feedback element for tuning a multi-wavelength gas laser

A method of tuning an output beam of a gas laser having a plurality of wavelengths, comprising:

• a partially reflective optical element that is supported by a stage and positioned on a beam path of the output beam outside of an internal optical cavity of the gas laser;
• varying intensity of the reflected output beam for the plurality of wavelengths;
• adjusting the intensity of the reflected output beam for each of the plurality of wavelengths by adjusting a rotation, a horizontal tilt angle, and a vertical tilt angle of the optical element with respect to the beam path of the output beam, thereby selecting a wavelength at which the output beam is fed back into the internal optical cavity of the gas laser, wherein the partially reflective optical element has a transparent substrate and a dielectric coating which gives a reflectivity which varies according to the wavelength, and the reflectivity being in the range between 0.5% and 75% at a wavelength between 10.6 μm and 9.3 μm;
• feeding back the reflected output beam at the selected wavelength into the internal optical cavity of the gas laser;
• and
• enhancing the output beam of the gas laser at the selected wavelength.

An external optical feedback element for tuning an output beam of a gas laser having a plurality of wavelengths, comprising:

• a first partially reflecting optical element positioned on a beam path of the output beam outside of an internal optical cavity of the gas laser;
• and
• wavelength dependent optical element (WDOE);
• and
• a second partially reflecting optical element positioned in the beam path;
• and
• a series of detectors, each spaced to accept specific wavelength bands;
• and
• a controller connected to the WDOE and the series of detectors, wherein the output beam is partially reflected at the first partially reflecting optical element and fed through the WDOE to the second partially reflecting optical element which retro-reflects a portion of the beam back to the laser and transmits a portion of the beam to the series of detectors,
• the controller adjusts the WDOE such that the beam reflected back to the laser has a wavelength that can be stabilized and controlled such that the laser can operate at any of the specific wavelength bands.