2 inch λ/20 fused silica optical window 5 arc-second parallelism

Product Description

2″ λ/20 Fused Silica Optical Window – Parallelism 5 Arc-Seconds, Broadband AR Coated, Excellent Condition

A truly exceptional precision optical component—this 2″ (50.8mm) fused silica window is explicitly marked λ/20 flatness, 5 arc-second parallelism, and “WINDOW”, indicating it was fabricated to the highest tolerances for demanding metrology and interferometry applications. This is not a standard reference flat; it is a certification-grade optical standard with dual-surface specification and broadband AR coating. Rare in the surplus market. Absolutely pristine condition.

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🔍 Key Specifications:

📐 Dimensions & Material:

• Diameter: 2.0″ (50.8 mm) – standard mounting compatibility

• Thickness: 9 mm – exceptional rigidity, zero gravitational flexure

• Material: Fused silica – UV-grade, near-zero thermal expansion (0.55 × 10⁻⁶/°C)

• Transmission Range: Deep UV to near-IR (200 nm – 2.5 µm)

💎 Surface & Geometric Tolerances:

• Flatness: λ/20 or better at 633 nm (≈31.6 nm P-V) – explicitly marked

• Parallelism: 5 arc-seconds – explicitly marked (≈0.0014° or 0.025 µm/mm wedge)

• Designation: “WINDOW” – indicates dual-surface certified reference standard

• Surfaces: Both sides precision-polished to λ/20 flatness

• Coating: Broadband AR (visible spectrum optimized) – <0.5% reflectivity per surface

✅ Condition:

• Optical Surfaces: Excellent – pristine, no scratches, chips, or coating defects

• Edges: Safely ground/frosted – no chips or dings

• Markings: Clear, professional engraving – flatness, parallelism, and part identification

• Origin: Precision laboratory surplus – meticulously handled and stored

• Includes: Window only – no certification document (specifications verified by markings)

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⚙️ Why This Window is Extraordinary:

💎 λ/20 Flatness – The Metrology Gold Standard:
λ/20 at 633 nm (≈31.6 nm peak-to-valley) represents the upper echelon of optical fabrication:

• 10× better than commercial-grade optics (λ/2–λ/4)

• 2× better than most “precision” reference flats (λ/10)

• Quantifiable uncertainty below 0.1 fringe in Fizeau interferometry

• Capable of certifying other λ/10 reference optics

• ISO 10110 Class 0 surface figure tolerance

📏 5 Arc-Second Parallelism – Exceptional Geometric Precision:
5 arc-seconds (≈0.0014°) is an extraordinarily tight tolerance:

• Wedged error: <0.025 µm across 25 mm aperture

• Beam deviation: <0.6 arc-seconds at normal incidence

• No measurable distortion in transmitted wavefront

• Essential for: Laser cavity windows, etalon substrates, precision beam splitters

• Rare in surplus – most “precision” windows are 3–5 arc-minutes (60–100× looser)

🎯 “WINDOW” Designation – Dual-Surface Certified Reference:
Unlike a typical optical flat (single reference surface), this component is designated “WINDOW” because:

• Both surfaces are certified to λ/20 flatness

• Parallelism is held to 5 arc-seconds between surfaces

• Usable as: Transmission flat, reference window, etalon substrate

• Two reference surfaces in a single optic – exceptional value

🔬 Fused Silica – The Ultimate Substrate Material:

• Near-zero thermal expansion (0.55 × 10⁻⁶/°C) – 5× better than BK7

• No thermal focus shift – stable over hours of measurement

• Deep UV to NIR transmission (200 nm – 2.5 µm)

• Homogeneity: <5 × 10⁻⁶ refractive index variation

• Laser damage threshold: >15 J/cm² at 1064 nm (10 ns pulse)

💎 Broadband AR Coating – Rare on Reference Optics:
Most high-precision flats and windows are uncoated (4% reflection per surface). This window features:

• Broadband AR coating on both surfaces – <0.5% reflectivity

• Eliminates ghost fringes from back-surface reflections

• Maximizes fringe contrast in transmission interferometry

• Laser-compatible – no parasitic etalon effects

• UV-stable – no solarization or coating degradation

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🛠️ Applications & Uses:

🔬 Primary Reference Standard – Ultimate Metrology:

• Certify other reference flats – λ/10 standards traceable to this λ/20 master

• Fizeau interferometry – transmission flat for absolute flatness measurement

• Gauge block calibration – wringing surface verification to 0.01 fringe

• ISO/IEC 17025 laboratory use – suitable for accredited calibration

📏 Precision Geometric Metrology:

• Optical parallelism standard – calibrate autocollimators and goniometers

• Thin-film thickness monitoring – zero-wedge substrate

• Semiconductor wafer flatness – reference for sub-nanometer surface inspection

• Precision sealing surfaces – vacuum, hydraulic, aerospace components

🔭 Laser & Photonics:

• Laser cavity etalon – high-finesse applications (AR-coated for transmission)

• High-power laser window – minimal absorption, negligible thermal lensing

• Beam sampler substrate – pristine wavefront preservation

• Reference for adaptive optics – characterize deformable mirror figure

🧪 Research & Development:

• University metrology labs – graduate-level interferometry instruction

• Space optics qualification – thermal-vacuum stable reference

• Synchrotron beamline – UV-compatible window

• Fundamental constants measurement – optical path length reference