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Katharine B. Blodgett · Public domain (expired patent)

أنشأه

Charlie

22. سبتمبر 2026

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.

مبتدئ

90 minutes

التعليمات

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.

المواد لهذه الخطوة:

شرائح مجهرية مع أغطية1 عبوة

Solar Cell Mini - 350mV1 قطعة

الأدوات المطلوبة:

مؤشّر ليزر

جهاز قياس متعدد

Alligator to Alligator Cables

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.

المواد لهذه الخطوة:

منظّف لطيف20 مل

غليسرين (نباتي)20 مل

سلك نحاسي1 متر

الأدوات المطلوبة:

مرطبان زجاجي

طقم زرّاديات

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.

المواد لهذه الخطوة:

مقوّى أسود1 ورقة

Fresnel, coating design, soap film

جارٍ تحميل دفتر Jupyter…

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.