optics ch1

CHAPTER 1: General Principles and Basics of Light and Optical Surfaces

Geometrical Optics: Treats light as a series of particles (also known as rays).
Physical Optics: Examines the wave motion of light.

Visible Light: A small portion of the electromagnetic spectrum, generally between 380-780 nm, that stimulates the human visual system.
The Electromagnetic Spectrum includes various forms of radiation:
- Gamma rays: Wavelength around $10^{-12}$ m, Frequency: $> 10^{22}$ Hz
- X-rays: Wavelength around $10^{-10}$ m
- Ultraviolet Radiation: Wavelength around $10^{-9}$ m
- Visible Light: Wavelength from 380 nm (violet) to 780 nm (red)
- Infrared: Wavelength from 780 nm to $10^{-5}$ m
- Microwave: Wavelength around $10^{-3}$ m
- FM/AM Radio: Wavelengths from $10^{-2}$ m to $10^{1}$ m

James Clerk Maxwell: Described the universe as consisting of objects exerting electric and magnetic influences on each other, inversely proportional to the distance between them.
This influence can occur over long distances through electromagnetic waves, generated by oscillating electrons.

Electromagnetic Radiation: Involves the oscillation of electrons in atoms and the propagation of electromagnetic waves.
Most electromagnetic radiation from the sun is filtered by the Earth's atmosphere, allowing some to reach the surface:
1. Ultraviolet Rays (UV) (200-380 nm):
  - UV-A (315-380 nm):
  - Tanning effect; absorbed by cornea (35.5%), lens (63%), retina (1.5%).
  - UV-B (280-315 nm):
  - Causes sunburn and ocular disorders (e.g., snow blindness); absorbed by cornea (70%), lens (30%).
  - UV-C (200-280 nm):
  - Dangerous; 99.9% absorbed by the ozone layer.
  - Damaging effects include itching, watering, photophobia, and swelling of the conjunctiva.
2. Visible Light (380-700 nm):
  - Stimulates retinal receptors for image formation; no harmful effects at normal intensity, but excessive diffuse/locally focused light can cause discomfort due to veiling glare.
3. Infrared Radiation (780 nm-2000 nm):
  - Absorbed by ocular tissues leading to thermal lesions; causes sensations of warmth.
4. X-radiation:
  - Used medically and industrially; linked to cataract development and conditions like eyelid dermatitis and conjunctivitis.

Natural Defenses:
- Includes reflex closure of eyelids, reduction in pupil size, filtration by tears and the lens, and adaptation by the retina.
Additional Protection: Filters or tinted lenses may be necessary.

Natural Sources: Sunlight, stars, fire.
Artificial Sources: Tungsten bulbs, gas discharge lights.
- Point Source: Infinitely small or far enough to act as a point (e.g., a star).
- Extended Source: Measurable area (e.g., bulbs, screens).
- Monochromatic Source: Emits a single wavelength (e.g., laser).
- Polychromatic Source: Emits multiple wavelengths (e.g., white light).

Amplitude (A): Maximum displacement of wave vibrations.
Wavelength ($ au$): Distance between identical points on waves (e.g., peak to peak), measured in nanometers (nm).
Cycle (c): Completion of a regular periodic event.
Frequency (f): Number of cycles per unit of time, measured in Hertz (Hz).
Period (P or T): Inverse of frequency, expressed as T = rac{1}{f}; unit is seconds.
Velocity (v): Rate of wave travel, v = f au, with light traveling at approximately 3 imes 10^8 m/s in vacuum.

Optical Medium: Any space light travels through, typically isotropic with consistent properties.
When light starts from a point source in an isotropic medium, it spreads uniformly in all directions.

From a point source, wavefronts can be visualized as arcs, with Huygen's Principle being useful for constructing new wavefronts.
- Huygen's Principle: Each point on a wavefront can be considered a point source of waves, and the new wavefront is the envelope of these secondary wavelets.
Rays: Represent the direction of light travel, perpendicular to wavefronts as per the Law of Malus.

Pencil of Rays: Grouping all rays from a point source or single point on an extended source.
- Divergent Pencil: Formed from a point source, rays spreading out.
- Convergent Pencil: Formed after passing through a convex lens, rays converging to a point.

Light is assumed to travel from LEFT to RIGHT.
- Positive Distances: Measured from left to right.
- Negative Distances: Measured from right to left.
- Wavefront Measurement: Radii of wavefronts are positive for convergent and negative for divergent.

Vergence (v): Defined as the reciprocal of the wavefront radius, V = rac{1}{r}, measured in diopters.
Vergence changes occur in lenses based on the incident rays.

Pinhole Camera Functionality: Utilizes a pinhole instead of a lens, allowing only narrow rays to form an inverted image.
Depth of Field: Distance over which objects can be positioned while maintaining image sharpness, important for bifocals and reading glasses.
Depth of Focus: Distance a screen can move while keeping a sharp image when the object remains fixed.
Field of View: Maximum angular size of an object within the imaged system.

Formed when an opaque object obstructs light, producing a geometric shadow for point sources and having two regions (umbra and penumbra) for extended sources.
Region of Illumination: Pattern of light from an aperture on a screen, varies with source type.
A circular shadow of a sphere is reliably circular, while one of a flat circular body varies depending on positioning.

Convex Lenses:
- Used for hyperopia (far-sightedness).
- Thicker at the center, thinner at the edges, induce pincushion distortion.
Concave Lenses:
- Used for myopia (near-sightedness).
- Thinner at the center, thicker at the edges, induce barrel distortion.

Transparent Medium: Allows light to pass through without distortion (e.g., window pane).
Translucent Medium: Allows light but distorts the image (e.g., frosted glass).
Opaque Medium: Blocks light completely, no visibility through it.