Optics — 54 Terms Defined

Acceptance Angle Optics Degrees (°) The maximum angle relative to the fiber axis at which incident light can enter the fiber core and undergo total internal reflection. θ_a = arcsin(NA) = arcsin(√(n1² - n2²))

Accommodation of the Eye Optics Diopters (D) The automatic adjustment process by which ciliary muscles alter crystalline lens focal length to focus objects at varying distances onto the retina. Power range ΔP = P_near - P_far

Angle of Deviation Optics Degrees (°) The angle between the direction of an incident light ray entering an optical element (like a prism) and its emerging direction. δ = i1 + i2 - A

Astigmatism Optics Diopters (D) A visual defect caused by non-spherical, asymmetric curvature of the cornea or lens, preventing rays in different planes from focusing at a single point. Power difference = P_vertical - P_horizontal

Astronomical Telescope Optics Dimensionless (×) A refracting optical instrument consisting of a long-focal-length objective lens and short-focal-length eyepiece used to observe distant celestial bodies. M = -f_obj / f_eye, Tube Length L = f_obj + f_eye

Attenuation Optics dB/km The loss of optical power or signal strength as light propagates through a medium or optical fiber. α = (10 / L) log10(P_in / P_out)

Brewster's Law Optics Degrees (°) The law stating that reflected light is 100% linearly polarized when the angle of incidence equals the polarizing angle, where reflected and refracted rays are perpendicular. tan θ_p = n2 / n1

Cartesian Sign Convention Optics N/A A standardized coordinate rule used in geometric optics to assign consistent algebraic signs to distances, heights, and focal lengths. Origin at optical center/pole; light travels left to right (+x)

Cassegrain Telescope Optics Dimensionless A compact reflecting telescope design combining a concave parabolic primary mirror and a convex hyperbolic secondary mirror. f_effective = f_primary × (Magnification of secondary)

Chromatic Aberration Optics m An optical distortion in lenses caused by material dispersion, where different wavelengths of light focus at different spatial positions. f_blue < f_red (v = c/n(λ))

Compound Microscope Optics Dimensionless (×) A two-stage optical instrument utilizing a short-focal-length objective lens and a longer-focal-length eyepiece to achieve high magnification. M_total = m_obj × M_eye ≈ (L / f_obj) × (D / f_eye)

Critical Angle Optics Degrees (°) The specific angle of incidence in an optically denser medium for which the angle of refraction in the rarer medium is exactly 90 degrees. θ_c = arcsin(n2 / n1)

Diffraction Optics m The bending, spreading, and interference of light waves around the edges of an obstacle or through a narrow aperture. a sin θ = m λ (Single Slit Minima)

Diffraction Grating Optics m (slits per mm) An optical element with a periodic structure of thousands of closely spaced parallel rulings or lines that disperses light into its component spectral wavelengths. d sin θ = m λ (m = 0, ±1, ±2, ...)

Dispersive Power Optics Dimensionless A dimensionless material property measuring a prism or lens material's ability to separate different spectral wavelengths. ω = (n_v - n_r) / (n_y - 1)

Fermat's Principle Optics s (or m) The fundamental principle stating that light traveling between two points follows the path that requires the stationary (usually minimum) optical path time. Optical Path Length L = ∫ n(s) ds = extremum

Fraunhofer Diffraction Optics m Far-field wave diffraction where both incident and observed wavefronts are planar, achieved using lenses or large distances. a sin θ = m λ

Fraunhofer Lines Optics nm A set of dark absorption lines in the solar spectrum caused by chemical element absorption in the Sun's outer atmosphere. E = h ν = E_upper - E_lower

Fresnel Diffraction Optics N/A Near-field wave diffraction where source or observation screen is close to the diffracting aperture, requiring spherical wavefront curvature analysis. Fresnel Number F = a² / (λ L) ≳ 1

Graded-index Fiber Optics N/A An optical fiber whose core refractive index decreases continuously from the central axis outward toward the cladding. n(r) = n0 √(1 - 2 Δ (r/a)^g)

Holography Optics N/A A technique for recording and reconstructing 3D wavefields by recording phase and amplitude interference patterns between object and reference laser beams. I(x,y) = |E_ref + E_obj|²

Laser Optics W (or J) Light Amplification by Stimulated Emission of Radiation—a device producing coherent, monochromatic, highly directional, high-intensity light. E = h ν, Population Inversion N2 > N1

Lens Maker's Formula Optics m⁻¹ (Diopters) An equation relating a thin lens's focal length to its material refractive index and the radii of curvature of its two spherical surfaces. 1/f = (n - 1) [ (1/R1) - (1/R2) ]

Luminous Flux Optics Lumens (lm) A photometric quantity measuring total perceived power of light emitted by a source, weighted by human eye spectral sensitivity. Φ_v = 683 ∫ P(λ) V(λ) dλ