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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.
Olùbẹ̀rẹ̀
90 minutes
Ìlànà
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.
Àwọn ohun èlò fún ìgbésẹ̀ yìí:
Dígí máìkíróskópù pẹ̀lú ìbòrí1 àkópọ̀
Solar Cell Mini - 350mV1 ẹyọÀwọn irinṣẹ́ tí a nílò:
Atọ́ka Leser
Òǹwọ̀n iná mànàmáná onírúurú
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.
Àwọn ohun èlò fún ìgbésẹ̀ yìí:
Ọṣẹ pẹ̀lẹ́20 ml
Glycerin (ti ewéko)20 ml
Okùn Bàbà1 mítàÀwọn irinṣẹ́ tí a nílò:
Ìgò Gílásì
Ìdìpọ̀ ẹmú3
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.
Àwọn ohun èlò fún ìgbésẹ̀ yìí:
Káàdì dúdú tí ó nípọn1 ewé4
4
Fresnel, coating design, soap film
Fresnel, coating design, soap film
Ń ṣí ìwé 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.
Àwọn ohun-èlò
6- 1 àkópọ̀Àyè
- Solar Cell Mini - 350mVìdá 10%1 ẹyọ$2.22
- 20 mlÀyè
- 20 mlÀyè
- 1 mítàÀyè
- Àyè
Àwọn irinṣẹ́ tó nílò
5- Àyè
- $3.58
- Àyè
- Àyè
Àpapọ̀ Ìfojúsùn
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