Micro-nanostructured films for high efficiency thermal light emitters

Abstract

Devices for emitting light in intended frequency ranges. Each device includes a thermal light source for generating light and a reflective film including holes for transmitting a portion of the light shorter than a cutoff wavelength and reflecting the rest of the light back to the light source. The thermal light source reabsorbs the reflected light and thereby increases the operational efficiency thereof.

1 . A device for emitting thermal radiation, comprising:
 a source for emitting thermal radiation; and   a reflective film including a plurality of openings formed therein, the size and shape of said openings being determined to transmit radiation having wavelengths shorter than a predetermined threshold wavelength and to reflect radiation having wavelengths exceeding said threshold wavelength back to said source such that said source absorbs at least a portion of the reflected radiation.   
   
   
       2 . A device as recited in  claim 1 , wherein said openings are holes having a generally circular shape and said threshold wavelength is about 2.5 times the diameter of said holes. 
   
   
       3 . A device as recited in  claim 1 , wherein said openings have a shape selected from a group of shapes consisting of circular, ellipsoidal, square, rectangular, rhomboidal, and polygonal. 
   
   
       4 . A device as recited in  claim 1 , wherein said device is an incandescent light bulb and said source is a filament, said filament being a helical wire or a coil formed of a helical wire. 
   
   
       5 . A device as recited in  claim 1 , wherein said device is an incandescent light bulb and said source is a planar filament that is formed of a tortuous wire in a plane. 
   
   
       6 . A device as recited in  claim 1 , wherein said device is an incandescent light bulb including a filament as said source and a bulb envelope that surrounds said filament and wherein said bulb envelope includes:
 a first portion having a first surface on which said reflective film is formed such that the radiation having wavelengths shorter than said predetermined threshold wavelength passes through said first portion, and   a second portion having a second surface on which a solid reflection film is formed, said solid reflection film being totally reflective to prevent the thermal radiation from passing through said second portion;   wherein at least one of said first and second portions includes a curved surface and said filament is located at a focal point of said curved surface.   
   
   
       7 . A device as recited in  claim 6 , wherein said first portion is a flat or curved plate and has a shape selected from a group of shapes consisting of circular, ellipsoidal, square, rectangular, rhomboidal, and polygonal and wherein said second portion includes a curved surface having a paraboloidal curvature. 
   
   
       8 . A device as recited in  claim 6 , wherein said first portion includes a curved surface having a circular cylindrical shape and said second portion has a flat disk shape. 
   
   
       9 . A device as recited in  claim 6 , wherein said first portion includes a curved surface having a spherical curvature and said second surface has a circular cylindrical shape. 
   
   
       10 . A device as recited in  claim 6 , wherein one of said first and second portions is a rectangular plate and the other includes a curved surface having a parabolic cylindrical shape. 
   
   
       11 . A device as recited in  claim 1 , wherein said reflective film is a metallic coating. 
   
   
       12 . A device as recited in  claim 1 , wherein the thickness of said reflective film is greater than 30 nm. 
   
   
       13 . A device for generating electric current, comprising:
 a source for generating heat energy;   a selective thermal emitter operative to receive said heat energy and to emit thermal radiation;   a housing enclosing said source and selective thermal emitter and having a transparent window through which the thermal radiation from the selective thermal emitter passes;   a photovoltaic cell located outside said cavity to receive the thermal radiation that has passed through the window and operative to convert the received thermal radiation into an electric current; and   a reflective film interposed between said window and said photovoltaic cell and including a plurality of openings formed therein, the size and shape of said openings being determined to transmit radiation having wavelengths shorter than a first predetermined threshold wavelength and to reflect radiation having wavelengths exceeding said first threshold wavelength back to the source such that said source absorbs at least a portion of the radiation reflected by said film.   
   
   
       14 . A device of  claim 13 , wherein said selective thermal emitter is made from a rare-earth ceramic. 
   
   
       15 . A device of  claim 13 , further comprising:
 a dichroic cold mirror interposed between said window and said photovoltaic cell and operative to transmit radiation having wavelengths exceeding a second predetermined threshold and to reflect radiation having wavelengths shorter than said second predetermined threshold back to said source such that said source absorbs at least a portion of the radiation reflected by said dichroic mirror, said second threshold wavelength being shorter than said first threshold wavelength;   wherein said first cutoff wavelength corresponds to the bandgap of said photovoltaic cell.   
   
   
       16 . A device of  claim 15 , wherein said reflective film is formed on a surface of said dichroic mirror facing said transparent window. 
   
   
       17 . A device of  claim 15 , wherein said reflective film is formed on a surface of said photovoltaic cell facing said transparent window.