Compensation of thermal expansion in mirrors for high power radiation beams

A multilayer front reflecting mirror compensated for thermal expansion caused by absorption of incident radiation comprising:

• an optically transmissive substrate having first and second surfaces;
• a source of radiant energy in the optical frequency range to which said substrate is transmissive and providing an output beam of radiation of said radiant energy;
• said output beam being directed toward said first surface;
• a coating on said first surface of said substrate operative to reflect the majority of the radiant energy in said output beam to absorb a small portion of the incident radiation to produce a thermal change in size along said first surface and to transmit to said second surface a small portion of the radiant energy in said output beam;
• a coating on said second surface of said substrate operating to absorb a portion of the radiant energy transmitted from said first surface to said second surface to produce a thermal change in size along said second surface compensatory to the change is size along said first surface.

A photoexcitation system comprising:

• an optically transmissive substrate having first and second surfaces;
• a source of radiant energy in the optical frequency range to which said substrate is transmissive and providing an output beam or radiation of said radiant energy;
• said output beam being directed toward said first surface;
• a coating on said first surface of said substrate operative to reflect the majority of the radiant energy in said output beam to absorb a small portion of the incident radiation to produce a thermal change in size along said first surface and to transmit to said second surface a small portion of the radiant energy in said output beam;
• a coating on said second surface of said substrate operating to absorb a portion of the radiant energy transmitted from said first surface to said second surface to produce a thermal change in size along said second surface compensatory to the change is size along said first surface;
• said source of radiant energy including means for providing radiant energy of one or more frequencies in which at least one frequency is selected for producing isotopically selective photoexcitation of a material;
• and
• means responsive to radiant energy reflected by said coating on said first surface for producing isotopically selective photoexcitation in response thereto.