Spherical Laser Mirrors: Concave & Convex

Did You Know?

Did you know that for a spherical mirror, the paraxial focal length is exactly f = R/2, but this relation only holds accurately for rays within a few degrees of the optical axis? As the marginal ray height approaches ~0.3–0.5 of the mirror radius, spherical aberration becomes significant, shifting the best-focus position by several percent of f and broadening the focal spot. This is why high-NA imaging systems rarely use bare spherical mirrors and instead rely on aspheric correction or use the spherical mirror only in slow (low-NA) configurations. At normal incidence a spherical mirror's focal length is half its radius of curvature (f = R/2), so an R = 1000 mm mirror focuses at 500 mm. Used off-axis at angle θ, the focal length differs in the tangential (f·cosθ) and sagittal (f/cosθ) planes, which causes astigmatism. Keep the fold angle small in laser cavities.

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Frequently Asked Questions

A spherical mirror is an optical mirror whose reflecting surface forms part of a sphere, characterized by a single radius of curvature and hence a single focal length (in the paraxial approximation). Unlike parabolic mirrors, spherical mirrors introduce spherical aberration for off-axis or large-aperture beams, but they are simpler and more economical to fabricate and are widely used where diffraction-limited performance over large fields is not required.

Overview of Spherical Mirrors

Spherical Mirrors are reflective optical elements with a surface that forms part of a sphere. They are used to focus, collimate, or redirect light in beam delivery, imaging, and diagnostic setups. Unlike parabolic mirrors, Spherical Mirrors are easier to manufacture and are preferred when spherical aberration is acceptable or can be compensated in the system design.

Typical Specifications

On FindLight, Spherical Mirrors can be compared by several key parameters. Radius of curvature (RoC) defines the focal length (approximately f = RoC/2 in air) and determines focusing strength. Surface quality is usually specified as scratch-dig (e.g., 20-10, 40-20) and flatness over the clear aperture (e.g., λ/4, λ/10 at a reference wavelength). Substrate materials commonly include fused silica, BK7, and various optical glasses; metal mirrors may use aluminum or copper substrates.

Coatings on Spherical Mirrors are optimized for different wavelength ranges and applications. Options include protected aluminum, enhanced aluminum, UV-enhanced aluminum, silver, and gold, as well as dielectric high-reflectivity (HR) coatings centered at specific laser lines or broadband regions (UV, visible, NIR, MIR). Reflectance, damage threshold, and incidence angle range are critical when integrating into laser systems.

Use Cases and Applications

Spherical Mirrors are employed in beam expanders, relay telescopes, optical cavities, laser delivery arms, and general-purpose imaging benches. In spectroscopy and metrology, they serve as focusing or collimating elements. In R&D setups, they are frequently used for rapid prototyping where alignment tolerance and cost are more critical than perfect aberration control.

Buyer Guidance on FindLight

When selecting Spherical Mirrors, procurement engineers and scientists should first specify wavelength range and required reflectance to choose an appropriate coating. Next, determine the needed focal length or beam path geometry to select the radius of curvature and mirror diameter. Consider substrate material for thermal stability, coefficient of expansion, and environmental resistance, especially in high-power or vacuum applications.

On FindLight you can browse and compare Spherical Mirrors by RoC, focal length, diameter, coating, substrate, and surface quality. Review datasheets for damage threshold and mounting constraints. Once suitable Spherical Mirrors are identified, you can request quotes or technical clarification directly from suppliers without registration, streamlining component sourcing for both prototype and production builds.