94mm N-BK7 plano-plano optical window military surplus

Product Description

Large 94mm Diameter Military Surplus Optical Window – N-BK7 Plano-Plano with Broadband AR Coating & Orientation Markings

A premium US military surplus plano-plano optical window in pristine new old stock (NOS) condition. This substantial 94mm aperture window combines N-BK7 optical glass, λ/10 surface flatness, and broadband multi-layer AR coating—originally designed for a 4x magnification military optical system such as a periscope, fire control sight, or armored vehicle commander’s viewer.

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🔍 Key Specifications:

• Diameter: ~94mm (3.70 inches)

• Thickness: 0.5 inch (12.7mm)

• Material: N-BK7 borosilicate crown glass – excellent homogeneity, low bubble content

• Surface Figure: Plano-plano (zero power) with λ/10 flatness or better over clear aperture

• Parallelism: Precision-polished – negligible wedge, no beam deviation

• Coating: Broadband multi-layer AR on both surfaces – >99% transmission, <0.5% reflectivity per surface

• Coating Range: Optimized for visible spectrum (400–700nm typical)

• Edge: Ground/frosted with orientation markings (professional mil-spec edge work)

• Condition: Excellent – Pristine NOS, carefully stored

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✅ Provenance & Condition:

• Origin: US military optical system surplus – likely from a 4x magnification sighting device, periscope, or fire control instrument

• Visual: Absolutely clean – no scratches, coating defects, edge chips, or haze

• Markings: Professional edge markings indicate orientation and mil-spec pedigree

• Storage: Kept in protective wrapping; never field-deployed or handled

• Includes: Window only (no mounting cell or hardware)

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⚙️ Why This Window is Exceptional:

🇺🇸 Authentic Military Heritage:
Not a commercial catalog item—this window was engineered to stringent mil-spec tolerances for mission-critical optical systems. The combination of large aperture, λ/10 flatness, and broadband AR coating reflects defense-grade quality rarely found in surplus.

🔬 Precision Optical Performance:

• λ/10 surface accuracy enables use in interferometry and wavefront-sensitive applications

• Plano-parallel design transmits image-forming rays without introducing focus shift or distortion

• Broadband AR coating maximizes transmission and eliminates ghost reflections

🛡️ Rugged & Ready:
Robust 0.5″ thickness and ground edge make this window suitable for protective/sealing applications in demanding environments. The N-BK7 substrate offers excellent thermal stability and scratch resistance.

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🛠️ Applications & Uses:

🔭 Optical Instrumentation:

• Protective window for sensors, cameras, or laser systems requiring environmental sealing

• Exit viewport in telescopic sights, periscopes, or observation ports

• Reference flat for interferometric testing and metrology

💡 Laser & Photonics:

• Debris shield in high-power beam lines (AR-coated for minimal loss)

• Beam sampler or pick-off window in diagnostic setups

• Substrate for custom filter coatings or polarizing optics

🏭 Industrial & Research:

• Machine vision enclosure window – optical clarity without beam deviation

• Vacuum chamber viewport for visible-wavelength experiments

• Educational demonstration of mil-spec optical fabrication standards

📚 Collector & Historian:

• Authentic artifact of US military optical technology

• Representative component from armored vehicle, naval, or aviation sighting systems