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Optics

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Optics

Acceptance Angle

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)) Degrees (°)
Optics

Accommodation of the Eye

The automatic adjustment process by which ciliary muscles alter crystalline lens focal length to focus objects at varying distances onto…

Power range ΔP = P_near - P_far Diopters (D)
Optics

Angle of Deviation

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 Degrees (°)
Optics

Astigmatism

A visual defect caused by non-spherical, asymmetric curvature of the cornea or lens, preventing rays in different planes from focusing at a…

Power difference = P_vertical - P_horizontal Diopters (D)
Optics

Astronomical Telescope

A refracting optical instrument consisting of a long-focal-length objective lens and short-focal-length eyepiece used to observe distant…

M = -f_obj / f_eye, Tube Length L = f_obj + f_eye Dimensionless (×)
Optics

Attenuation

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) dB/km
Optics

Brewster's Law

The law stating that reflected light is 100% linearly polarized when the angle of incidence equals the polarizing angle, where reflected…

tan θ_p = n2 / n1 Degrees (°)
Optics

Cartesian Sign Convention

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) N/A
Optics

Cassegrain Telescope

A compact reflecting telescope design combining a concave parabolic primary mirror and a convex hyperbolic secondary mirror.

f_effective = f_primary × (Magnification of secondary) Dimensionless
Optics

Chromatic Aberration

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)) m
Optics

Compound Microscope

A two-stage optical instrument utilizing a short-focal-length objective lens and a longer-focal-length eyepiece to achieve high…

M_total = m_obj × M_eye ≈ (L / f_obj) × (D / f_eye) Dimensionless (×)
Optics

Critical Angle

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) Degrees (°)
Optics

Diffraction

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) m
Optics

Diffraction Grating

An optical element with a periodic structure of thousands of closely spaced parallel rulings or lines that disperses light into its…

d sin θ = m λ (m = 0, ±1, ±2, ...) m (slits per mm)
Optics

Dispersive Power

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) Dimensionless
Optics

Fermat's Principle

The fundamental principle stating that light traveling between two points follows the path that requires the stationary (usually minimum)…

Optical Path Length L = ∫ n(s) ds = extremum s (or m)
Optics

Fraunhofer Diffraction

Far-field wave diffraction where both incident and observed wavefronts are planar, achieved using lenses or large distances.

a sin θ = m λ m
Optics

Fraunhofer Lines

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 nm
Optics

Fresnel Diffraction

Near-field wave diffraction where source or observation screen is close to the diffracting aperture, requiring spherical wavefront…

Fresnel Number F = a² / (λ L) ≳ 1 N/A
Optics

Graded-index Fiber

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) N/A
Optics

Holography

A technique for recording and reconstructing 3D wavefields by recording phase and amplitude interference patterns between object and…

I(x,y) = |E_ref + E_obj|² N/A
Optics

Laser

Light Amplification by Stimulated Emission of Radiation—a device producing coherent, monochromatic, highly directional, high-intensity…

E = h ν, Population Inversion N2 > N1 W (or J)
Optics

Lens Maker's Formula

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) ] m⁻¹ (Diopters)
Optics

Luminous Flux

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 Lumens (lm)