λ/20 fused silica reference mirror protected silver

Product Description

Precision λ/20 Fused Silica Reference Mirror – 50mm Diameter, Ex-US Defense Lab Surplus

This elite single-surface reference mirror is constructed from premium fused silica, a high-purity synthetic quartz glass acclaimed for its ultra-low thermal expansion (5.5 × 10⁻⁷/°C) , broad spectral transmission from UV to IR (185nm–2.5μm), and outstanding resistance to thermal shock, chemical agents, and environmental stressors . Boasting a 50mm diameter and robust 16mm thickness, it delivers superior structural integrity, reducing flexure and maintaining stability in high-precision or variable-temperature setups—critical for defense and aerospace environments.

The front surface is enhanced with a defense-grade protected silver coating, featuring advanced multi-layer dielectric overcoats to prevent oxidation, tarnishing, and degradation while achieving exceptional reflectivity of 97–99% (or higher) across the visible spectrum (0.4–0.7μm) , with averages often exceeding 98% at low angles of incidence . This optimized coating, compliant with MIL-C-48497 standards for durability, ensures near-total light reflection without measurable transmission, producing razor-sharp, vivid images. The back surface, inscribed with “λ/20” (denoting the front’s flatness spec), incorporates a matte or commercial polish to suppress stray reflections and avoid measurement artifacts.

The λ/20 flatness tolerance—verified at 632.8nm (HeNe laser wavelength)—signifies a peak-to-valley surface deviation of just 31.6nm, embodying cutting-edge precision through sophisticated polishing and interferometric certification . This level outstrips standard λ/4 or λ/10 optics, enabling sub-wavelength resolution in rigorous applications .

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Key Specifications

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Material Advantages – Premium Fused Silica

Fused silica is the substrate of choice for precision reference optics due to its exceptional properties :

• Ultra-Low Thermal Expansion (5.5 × 10⁻⁷/°C): Maintains figure across temperature variations – critical for metrology applications

• Broad Spectral Transmission: 185nm to 2.5μm, covering UV through IR

• High Homogeneity: Minimizes wavefront distortion

• Superior Durability: Resists chemical attack and environmental degradation

• Proven Performance: Industry standard for precision optics (Corning 7980 or equivalent)

The 16mm thickness is a significant differentiator from standard 5mm commercial mirrors . This extra thickness provides:

• Enhanced structural rigidity – minimizes flexure under mounting stress

• Superior thermal mass – dampens rapid temperature fluctuations

• Reduced mounting-induced distortion – maintains λ/20 flatness in fixtures

• Long-term stability – ideal for reference standards

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Defense-Grade Protected Silver Coating

Silver coatings offer the highest reflectivity in the visible spectrum but are prone to tarnishing without proper protection . This mirror features an advanced protected silver coating with dielectric overcoats that:

• Prevents oxidation and tarnishing – maintains performance over decades

• Achieves >98% average reflectivity across 450-700nm

• Complies with MIL-C-48497 for durability, including abrasion, adhesion, and humidity resistance

• Enables safe handling and cleaning – the protective overcoat allows for careful cleaning without damaging the reflective layer

• Minimizes scatter for clean interferometric fringes

The coating specification is consistent with Edmund Optics’ TECHSPEC® protected silver mirrors, which achieve Ravg >98% across the visible spectrum .

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λ/20 Flatness – What It Means

The λ/20 surface flatness specification (peak-to-valley at 632.8nm) represents a surface deviation of just 31.6 nanometers – approximately 1/2000th the thickness of a human hair. This level of precision:

• Exceeds standard λ/10 or λ/4 optics, enabling diffraction-limited performance

• Minimizes reflected wavefront error for accurate interferometric measurements

• Ensures reliable calibration of metrology instruments

• Certifies the mirror as a true reference standard

Surface flatness is measured before coating, ensuring the underlying substrate meets the specification . The coating process maintains this figure without degradation.

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Applications and Uses

Reflection Interferometry:

• Ideal for Fizeau, Twyman-Green, or Michelson interferometers to evaluate wavefront integrity, surface flatness, or aberrations in reflective optics like mirrors, lenses, or prisms

• The superior coating enhances fringe contrast for unmatched measurement accuracy

• λ/20 flatness ensures reference-quality wavefronts

Metrological Precision:

• Serves as a reference standard in optical and dimensional metrology for calibrating autocollimators, profilometers, or CMMs

• Quantifies flatness via interference fringes (e.g., Newton’s rings) to sub-wavelength levels, ensuring ISO 17025/NIST-traceable results in quality assurance labs

Laser and Photonics Systems:

• Crucial for beam alignment, cavity tuning, and mode profiling in high-energy lasers, fiber optics, or telecom gear

• Low-expansion substrate and high-reflectivity coating prevent thermal-induced errors

Aerospace and Defense Metrology:

• Employed in inspecting satellite components, targeting optics, or avionics for parallelism and surface quality

• Leverages MIL-spec ruggedness for reliable performance in vibration-prone or extreme conditions

Semiconductor and Precision Manufacturing:

• Verifies wafer flatness, photomasks, or gauge blocks with sub-micron precision

• Supports advanced fabrication in chips or CNC processes

Scientific Research:

• Facilitates holography, spectroscopy, or adaptive optics experiments

• Capitalizes on fused silica’s broadband capabilities and λ/20 accuracy for precise wavefront analysis and correction

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Condition

EXCELLENT – MINIMAL USE
OPTICALLY PRISTINE
NO VISIBLE SCRATCHES, COATING DAMAGE, OR DEFECTS
“λ/20” INSCRIPTION CLEARLY VISIBLE ON BACK SURFACE
STORED AND HANDLED WITH CARE
READY FOR IMMEDIATE INTEGRATION

⚠ HANDLING NOTE: This is a precision reference mirror with a delicate protected silver coating. While the dielectric overcoat improves durability , always handle only by edges with clean gloves. Never touch coated surfaces. Clean only with approved optical methods if absolutely necessary. Store in clean, dry environment when not in use.