Method and apparatus for wavelength calibration

A method for determining the absolute wavelength of a narrowed spectral emission around 157 nm of a narrow band laser system including a wavelength selection and tuning unit for selecting one of multiple closely-spaced characteristic molecular fluorine emission lines around 157 nm by optically suppressing non-selected lines of The multiple closely-spaced characteristic molecular fluorine emission lines, and for tuning a central wavelength of the arrow band output beam from the laser within the selected line, a wavelength calibration system including a module containing a medium including at least one optically interacting species having one or more optical transition lines within the emission spectrum of said laser, and a wavelength monitoring module calibrated to the one or more optical transition lines of the medium contained within said module of said wavelength calibration system, comprising the steps of:

• providing a narrow band output laser beam around 157 nm from said laser system;
• directing said output beam through the module including said optically interacting species;
• detecting at least one of the optical transition lines when the narrowed emission is tuned within the emission spectrum of the laser;
• determining the absolute wavelength of the narrowed emission at at least one tuning position corresponding o at least one of the one or more optical transition lines based on the at least one detected transition;
• calibrating the wavelength monitoring module based on the absolute wavelength determination;
• and
• tuning the wavelength of the narrowed spectral emission to a desired wavelength by controlling the wavelength selection and tuning unit according to information received from the wavelength monitoring module which is calibrated to the absolute wavelength standard, such that the wavelength is moved away from an interaction wavelength with the absolute wavelength standard based on information received from the wavelength monitoring module as the wavelength is tuned to the desired wavelength within the selected line of the multiple closely-spaced characteristic molecular fluorine emission lines around 157 nm.

A method for determining the absolute wavelength of a narrowed spectral emission of a narrow band gas discharge laser system including a gas mixture comprising molecular fluorine, a wavelength selection and tuning unit for selecting one of multiple closely-spaced characteristic molecular fluorine emission lines around 157 nm by optically suppressing non-selected lines of the multiple closely-spaced characteristic molecular fluorine:

• emission lines, and for tuning a central wavelength of the narrow band output beam from the laser within the selected line, a wavelength calibration system including a module containing a medium including an optically interacting species having an optical transition line within the emission spectrum of said laser, and a wavelength monitoring module calibrated to the one or more optical transition lines of the medium contained within said module of said wavelength calibration system, comprising the steps of:
• providing a narrow band output laser beam from said excimer or molecular fluorine laser system;
• directing said output beam through the module including said optically interacting species;
• detecting the optical transition line when the narrowed emission is tuned within the emission spectrum of the laser;
• and
• determining the absolute wavelength of the narrowed emission based on the detected transition;
• calibrating the wavelength monitoring module based on the absolute wavelength determination;
• and
• tuning the wavelength of the narrowed spectral emission to a desired wavelength by controlling the wavelength selection and tuning unit according to information received from the wavelength monitoring module which is calibrated to the absolute wavelength standard, such that the wavelength is moved away from an interaction wavelength with The absolute wavelength standard based on information received from the wavelength monitoring module as the wavelength is tuned to the desired wavelength with the selected line of the multiple closely-spaced characteristic molecular fluorine emission lines around 157 nm, and
• wherein said optically interacting species includes platinum.