A system comprising: a gas laser having a plurality of wavelengths, including an internal optical cavity, configured to emit an output beam and being a carbon dioxide laser; and an external optical feedback element configured to tune the output beam of the gas laser, the external optical feedback element comprising: a partially reflecting optical element positioned on a beam path of the output beam outside of the internal optical cavity of the gas laser; and a stage configured to support the optical element and configured to adjust 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; wherein the optical element is configured to partially reflect the output beam and feed back the partially reflected beam into the internal optical cavity of the gas laser via the beam path, the intensity of the reflected beam varies for the plurality of wavelengths, the stage is configured to adjust the intensity of the reflected beam for each of the plurality of wavelengths by changing the rotation, the horizontal tilt angle, and the vertical tilt angle of the optical element, thereby selecting a wavelength at which the output beam is fed back into the internal optical cavity of the gas laser and enhancing the output beam of the gas laser at the selected wavelength, and the optical element comprises a transparent substrate, characterized in that the optical element further comprises a dielectric coating configured to provide a reflectivity varying with the wavelength, the reflectivity having a minimum value of 0.5 % or lower at a wavelength of 10.6μm and increasing up to 75 % at a wavelength of 9.3 μm. a gas laser having a plurality of wavelengths, including an internal optical cavity, configured to emit an output beam and being a carbon dioxide laser; and an external optical feedback element configured to tune the output beam of the gas laser, the external optical feedback element comprising: a partially reflecting optical element positioned on a beam path of the output beam outside of the internal optical cavity of the gas laser; and a stage configured to support the optical element and configured to adjust 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; wherein the optical element is configured to partially reflect the output beam and feed back the partially reflected beam into the internal optical cavity of the gas laser via the beam path, the intensity of the reflected beam varies for the plurality of wavelengths, the stage is configured to adjust the intensity of the reflected beam for each of the plurality of wavelengths by changing the rotation, the horizontal tilt angle, and the vertical tilt angle of the optical element, thereby selecting a wavelength at which the output beam is fed back into the internal optical cavity of the gas laser and enhancing the output beam of the gas laser at the selected wavelength, and the optical element comprises a transparent substrate, characterized in that the optical element further comprises a dielectric coating configured to provide a reflectivity varying with the wavelength, the reflectivity having a minimum value of 0.5 % or lower at a wavelength of 10.6μm and increasing up to 75 % at a wavelength of 9.3 μm. a partially reflecting optical element positioned on a beam path of the output beam outside of the internal optical cavity of the gas laser; and a stage configured to support the optical element and configured to adjust 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; wherein the optical element is configured to partially reflect the output beam and feed back the partially reflected beam into the internal optical cavity of the gas laser via the beam path, the intensity of the reflected beam varies for the plurality of wavelengths, the stage is configured to adjust the intensity of the reflected beam for each of the plurality of wavelengths by changing the rotation, the horizontal tilt angle, and the vertical tilt angle of the optical element, thereby selecting a wavelength at which the output beam is fed back into the internal optical cavity of the gas laser and enhancing the output beam of the gas laser at the selected wavelength, and the optical element comprises a transparent substrate, characterized in that the optical element further comprises a dielectric coating configured to provide a reflectivity varying with the wavelength, the reflectivity having a minimum value of 0.5 % or lower at a wavelength of 10.6μm and increasing up to 75 % at a wavelength of 9.3 μm.