Double Concave Lens

Double-Concave Lens (DCV) Detailed Technical Specifications

A double-concave lens is a diverging lens with two concave surfaces, capable of diverging collimated incident light. 1. Structural Parameters

1. Radius of Curvature (R₁, R₂)

◦ Curvature radii of the two concave surfaces (typically labeled as negative values), in millimeters (mm).

◦ Typical range: R₁ and R₂ may be equal (symmetric DCV) or unequal (asymmetric DCV), e.g., R₁ = -100 mm, R₂ = -200 mm.

2. Center Thickness (CT)

◦ Thickness at the lens center, typically 1–5 mm, depending on application requirements.

3. Edge Thickness (ET)

◦ Thickness at the lens edge, determined by curvature radii and diameter. Must ensure mechanical strength (usually ≥0.5 mm).

4. Diameter (D)

◦ Physical aperture size. Common specifications: 5 mm, 12.7 mm (1/2″), 25.4 mm (1″), 50.8 mm (2″), etc.

2. Material Parameters

1. Optical Material

◦ Glass types: Common optical glasses include BK7 (N-BK7), H-K9L (Chinese grade), fused silica (UV/IR applications), calcium fluoride (CaF₂, low dispersion), etc.

◦ Plastics: PMMA (acrylic), PC (polycarbonate), used for low-cost or lightweight applications.

2. Refractive Index (n)

◦ Material refractive index at a specific wavelength (e.g., 587.6 nm, He-d line). Example: BK7 has n=1.5168.

3. Abbe Number (Vd)

◦ Indicates dispersion characteristics. Higher Vd values imply lower dispersion. BK7 has Vd≈64.2.

3. Optical Parameters

1. Focal Length (f)

◦ Negative value for diverging lenses. Calculated using:

◦ Typical values: -50 mm, -100 mm, -200 mm, etc.

2. Numerical Aperture (NA) & Field of View (FOV)

◦ NA = D/(2|f|), related to light-gathering capability.

◦ FOV depends on lens size and focal length.

3. Image Position

◦ Virtual image position calculated via geometric optics formulas, considering object distance and lens parameters.

4. Coating Parameters

1. Anti-Reflective Coating (AR Coating)

◦ Wavelength range: Visible (400–700 nm), NIR (700–1100 nm), UV (200–400 nm), etc.

◦ Reflectance: ~1.5% for single-layer MgF₂, <0.2% for multilayer coatings.

2. High-Reflective Coating (HR Coating)

◦ Used for specialized applications (e.g., laser reflection), reflectance >99%.

3. Laser-Induced Damage Threshold (LIDT)

◦ Critical for high-power laser systems. Example: Fused silica lenses up to 10 J/cm² (nanosecond pulses).

5. Additional Parameters

1. Surface Quality

◦ Scratch-dig specification: MIL-PRF-13830B standards (e.g., 60-40 or higher, such as 20-10).

2. Surface Figure Accuracy

◦ Flatness: λ/4 (visible light) or better (e.g., λ/10).

3. Tolerances

◦ Radius of curvature: ±0.5%–±2%.

◦ Center thickness: ±0.1 mm–±0.3 mm.

◦ Diameter: ±0.1 mm (precision grade) or ±0.5 mm (standard grade).

6. Typical Applications

• Laser beam expansion, virtual image generation, divergence compensation in optical systems, experimental beam correction, etc.

7. Notes

• Focal length and aberrations (e.g., spherical, chromatic) require optimization via compound lens systems.

• High-precision applications demand low-stress, high-homogeneity materials (e.g., fused silica).