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Anti-Reflection Coating
Katharine Blodgett at General Electric, working with Irving Langmuir, learned to build soap-like films one molecule-thick layer at a time. Stacking just enough layers onto glass, she made it nearly invisible: light reflected from the top of the film and from the glass beneath cancelled out.
**US 2,220,861**, "Reduction of surface reflection", Blodgett, assigned to General Electric, filed 16. June 1938, granted 5. November 1940: a coating whose "optical thickness … corresponds at least approximately to a quarter wave length of visible light" and whose refractive index is "intermediate" between air and the glass.
**You measure the reflection a coating removes**, design one in a notebook, and watch quarter-wave interference happen in a soap film.
Principiante
90 minutes
Instrucciones
1
1
Measure bare glass
Measure bare glass
Clip the solar cell to the multimeter (DC mA). In a dim room shine the laser straight onto the cell and note the current. Then bounce the beam off a clean microscope slide, close to perpendicular, onto the cell. Note that current. Never look along the beam.
Materiales para este paso:
Portaobjetos con cubreobjetos1 paquete
Solar Cell Mini - 350mV1 piezaHerramientas necesarias:
Puntero láser
Multímetro
Alligator to Alligator Cables2
2
Mix a film solution
Mix a film solution
Stir 1 part detergent and 1 part glycerin into 10 parts water in a jar. Bend copper wire into a 60 mm loop with a handle.
Materiales para este paso:
Detergente suave20 ml
Glicerina (vegetal)20 ml
Alambre de cobre1 metroHerramientas necesarias:
Tarro de vidrio
Juego de alicates3
3
Watch a film thin
Watch a film thin
Dip the loop and hold it upright in front of black card, lit by a window behind you. Colour bands slide down as the film drains; at the top a black band appears - a film too thin to reflect.
Materiales para este paso:
Cartulina negra1 hoja4
4
Fresnel, coating design, soap film
Fresnel, coating design, soap film
Cargando el cuaderno de Jupyter…
5
5
History & Context
History & Context
**What the patent specifies:** a surface layer of quarter-wave optical thickness with a refractive index between those of the surrounding medium and the glass. **Modern build (derived):** measurement and design only - production coatings are evaporated in vacuum.
Blodgett's stearate films were too soft to wipe clean. Alexander Smakula at Zeiss had developed coatings evaporated in vacuum in 1935; that durable route won, and today almost every camera lens and eyeglass is coated, often with many layers. Their limits: a single layer is perfect at only one wavelength, and coatings scratch.
Materiales
6- 1 paqueteMarcador de posición
- Solar Cell Mini - 350mV10% de comisión1 piezaMX$38.00
- 20 mlMarcador de posición
- 20 mlMarcador de posición
- 1 metroMarcador de posición
- 1 hojaMarcador de posición
Herramientas requeridas
5- Marcador de posición
- Marcador de posición
- Alligator to Alligator Cables10% de comisiónMX$61.39
- Marcador de posición
- Marcador de posición
Total estimado
Lo que compró quien lo hizo. Los materiales sin precio se consiguen donde tú los compres.
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