Lec 3-4 Flashcards
Chemiluminescence vs Fluorescence vs Phosphorescence
Chemiluminescence: e- excitation from chem rxn
Fluorescence: e- excitation from photon absorption
Phosphorescence: e- excitation from photon absorption, with triplet intermediate step
Bioluminescence vs Thermal Radiation
Bioluminescence: e- excitation from chem rxn of luciferin
Thermal Radiation: Light emitted
Evolutionary Pressure to create bioluminescence
Predation, evading predators, communication
Continuum Wave (CW) Lasers
Continuous wave, lower power
Pulsed Lasers
Short pulses, higher power
Properties of lasers
Coherent, monochromatic, polarized and directional
Applications of lasers
Cutting, communication, printing, scanning
Types of waves
- Spherical Waves
- Planar Waves
Huygen-Fresnel’s Principle
All points on a wavefront are the source of a new wave.
Superposition Principle
Because waves can interfere constructively or destructively,
the result of superpositioned waves is their sum.
Refraction
When crossing into another medium, light takes the path of shortest time, not the path of shortest distance
- (light is slower if index of refraction is high)
Diffraction
Interference or bending of waves around obstacle
Optical components for light manipulation
- Pinholes and Irises
- Mirrors
- Beam Splitters
- Filters
- Lenses
- Prisms
- Gratings
- Polarizers
- Optic Fibers`
Pinholes
- Control amount of light entering a system
- Allows for formation of an image on a screen
Pinhole examples
- Human iris
- Pinhole eyes of some animals
- Pinhole camera
Mirrors
- Reflect light
- Flat or Curved
- Metallic or Dielectric
Dielectric mirror
Are made from systems of thin lenses.
Layers of oil, water and air allow light to interfere constructively/destructively.
Snell’s Law
n1sinθ_1=n2 sinθ_2
Total internal reflection
- When
- n1 > n2
- θ_1 > 90
- As light θ_1 increases, more light is reflected than refracted
Critical angle (θ_c)
θ_1 when θ_2 is 90°
(angle of incidence when angle of refraction is 90°)
Filters
Selective for specific wavelengths
Edge filters
Long Pass/Short Pass
Long Pass Filters
Allow passage of long wavelengths, block short wavelengths
Short Pass Filters
Allow passage of short wavelengths, block long wavelengths
Lens equations
1/f=1/d_i +1/d_o
M = -d_i/d_o = hi/ho
Multiple Lens Equations
1/f = 1/f_1 + 1/f_2
M = -f_2/f_1
Rayleigh Length
Describes beam waist at focal point
Prisms
Larger refractive index for smaller wavelengths
–> Different wavelengths refracted at different angles –> White light separated
Gratings
Harnesses wave diffraction and interference to separate white light
Polarizers
- Select light based orientation of electrical field
- Total polarization of reflected ray achieved Brewters’s angle
Brewster’s angle (θ_B)
θ_1 when θ_2 = 90° - θ_1
(incident angle when refracted angle equal to 90 - incident angle) or (angle between refracted ray and reflected ray)
Brewster angle formula (derived from Snell’s Law)
θ_B = arctan(n2/n1), n1 small and n2 large
Critical angle formula (derived from Snell’s Law)
θ_c = arcsin(n2/n1), n1 large and n2 small
Optical fibers
- Harnesses total internal reflection to transport light
- Incident angle larger or equal to critical angle
Optical fiber types
- Step index (aka multimode): Multiple incident angles allowed
- Graded index: refractive index dependent on distance from central axis
- Single mode: Single incident angle allowed to preserve signal purity
Examples of Light manipulation in biology
ex: Gratings in butterflies
ex: Algae as lenses
ex: Optical fibers in sea sponge
ex: Animals with pinhole vision
ex: Animals with bifocal lenses
Describe how can optical components
be used to measure ballistic
photons through tissue.
Mirrors, lenses, beam splitters, optical fibers and filters are used together to use measure ballistic photons.
ex: Optical Coherence Tomography (OCT)
Strength: High resolution
Weakness: Can’t penetrate through deep tissues
Define Structural Coloration
Colour visible on an object due to its structure, not luminescence.
ex: Butterfly wings using gratings
Incident Angle of Acceptance in optical fibers
sinθ = √ (n1^2 - n2^2 )
