concave first surface mirror fused silica enhanced aluminum

Product Description

Precision Concave First-Surface Mirror – 3″ Diameter, 20m Radius of Curvature, Fused Silica Substrate – US Defense Lab Surplus

This high-precision concave first-surface mirror is a rare find from a US Defense laboratory surplus inventory. Measuring 3 inches (76mm) in diameter and 0.5 inches thick, it features an exceptionally shallow curvature with a 20-meter radius of curvature (approximate focal length of 10 meters), making it ideal for applications requiring near-flat performance with subtle convergence. The mirror surface is arrow-marked for proper orientation. Condition is excellent, with a pristine reflective surface showing no scratches or defects—ready for immediate use in demanding optical setups.

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Key Specifications

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Material Advantages – UV-Grade Fused Silica

UV-grade fused silica offers exceptional properties for precision optical mirrors:

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Coating Technology – Enhanced Aluminum (AlSiO Protected)

Enhanced aluminum consists of an aluminum layer overcoated with a dielectric material (such as silicon monoxide) that increases reflection in certain regions of the spectrum and greatly improves durability . The coating is sensitive to wavelength, angle of incidence, and polarization, with reflectance values that can be optimized further by adding more layers to the enhancing overcoat .

Key characteristics of enhanced aluminum :

• Higher Reflectivity: Enhanced aluminum provides higher reflectivity in the visible spectrum compared to standard protected aluminum, with typical reflection of 95% average over 450-650nm . Peak reflectance can exceed 93%, with average reflectivity >95% .

• Broadband Performance: 85-95% reflectivity across the visible spectrum, suitable for general-purpose applications.

• Improved Durability: The dielectric overcoat improves abrasion resistance, enabling the product to be handled and cleaned while being less susceptible to damage . The coating meets adhesion, abrasion, temperature, and humidity specifications of various military and ISO standards .

• Protection Against Oxidation: The dielectric overcoat slows oxidation and increases abrasion resistance while enhancing reflectivity . It acts as a protective barrier, preventing oxidation of the underlying aluminum .

• Laser Damage Threshold: 0.4 J/cm² pulsed at 532 nm, higher than UV enhanced aluminum mirrors, though still limiting pulsed laser applications .

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Understanding the 20-Meter Radius of Curvature

This mirror’s exceptionally shallow concave curvature (20m ROC) provides:

• Subtle Convergence: Focal length of approximately 10 meters (f = R/2), enabling long-radius beam focusing or collimation

• Near-Flat Performance: Ideal for applications requiring minimal wavefront modification

• Long Working Distances: Perfect for large optical systems or long-path setups

• Reduced Aberrations: Shallow curvature minimizes spherical aberration in long-focal-length systems

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Applications

Interferometry and Metrology:

• Reference optic for wavefront testing in Michelson or Twyman-Green interferometers

• Alignment and calibration standards

• Long-radius test plates for optical fabrication

Laser Systems:

• Beam collimation, expansion, or focusing in directed energy, rangefinding, or communication systems

• Defense and aerospace laser applications requiring high stability

• Long-path laser beam delivery

Optical Testing and Simulation:

• Sensor calibration and testing

• Adaptive optics and atmospheric compensation simulation

• Military/aerospace prototyping environments

Astronomy and Research:

• Secondary mirror or component in custom telescopes

• Spectrometer calibration and alignment

• Lab experiments requiring long focal lengths for minimal aberration

Industrial and Scientific Labs:

• Microscopy illumination systems

• Photonics R&D prototypes

• Applications where thermal stability and high reflectivity are essential

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Condition & Provenance

This is a rare authentic high-end optics find at a surplus price.

⚠ HANDLING NOTE: This is a precision optical component with an enhanced aluminum coating. Handle only by edges with clean gloves. Never touch coated surfaces. The dielectric overcoat improves durability, but careful handling is still essential .