The Nature of Light. Light and Energy

Size: px

Start display at page:

Download "The Nature of Light. Light and Energy"

Baldwin Carson
5 years ago
Views:

indirectly - solar energy intimately associated

dissipate as heat emitted at longer wavelength

light - CO 2 +H 2 O = Glc + O 2 - chlorophyll:

1 The Nature of Light Light and Energy - dependent on energy from the sun, directly and indirectly - solar energy intimately associated with existence of life -light absorption: dissipate as heat emitted at longer wavelength trigger chemical reaction - putting together by light - CO 2 +H 2 O = Glc + O 2 - chlorophyll: reflects green, absorbs violet-blue and redorange, emits red 1

Electromagnetic Radiation Atoms Electron microscope Amino acids Proteins Viruses Light microscope Bacteria Red blood cells Epithelial cells Human eye

2 Electromagnetic Radiation Atoms Electron microscope Amino acids Proteins Viruses Light microscope Bacteria Red blood cells Epithelial cells Human eye Sources of Visible Light - Body. all organisms do not visible = 1000x weaker than eyes by-product of biochemical processes related to circadian rhythm 2

3 - Sun energy production in form of thermal radiation = superheated - Bioluminescence yellow-green light produced by insects, blue-green in marine organisms luciferase, luciferin and oxygen Uses? 3

4 - Chemiluminescence emission of light as a result of chemical reaction Liquid or gas reaction - Visible light source = incandescent light Electrical current passing through until light filaments glow 4

5 - Fluorescent light = mercury or LED lights EPA concerns Use of Light in Microscopy Detector Filter Mirror Filter Light Source Incandescence Traditional light source Filament becomes hot = light emission Specimen Fluorescence Fluorescent light + filters + mirrors = stained specimen Bioluminescence Fluorescent light + filters + mirrors = autofluorescence 5

Lasers -conceptualized in the late 1950 s - Light

optical amplification => photon perturbation of any

photon not disturbed in process - in optical microscopy:

6 Lasers -conceptualized in the late 1950 s - Light Amplification by the Stimulated Emission of Radiation - optical amplification => photon perturbation of any matter leads to creation of a new photo - perturbing photon not disturbed in process - in optical microscopy: high density monochromatic light sources Light Concepts and the Microscope 6

Speed of Light - in 45 years episodes of your favorite TV show

miles/sec in a vacuum -slows down when in a dense medium =>

$etc. Refraction - when light passes from one medium into$ $another refraction = manifested in bending of light - object$ $characteristic of microscope lenses - refractive index = law of$ = c/v where c=speed of light; n=velocity of light - RI vacuum =

= c/v where c=speed of light; n=velocity of light - RI vacuum =

7 Speed of Light - in 45 years episodes of your favorite TV show will be broadcasting somewhere in deep space - 186,000 miles/sec in a vacuum -slows down when in a dense medium => reason why lenses work - speed of light changes with every transfer into a different medium = specimen, objectives, air etc. Refraction - when light passes from one medium into another refraction = manifested in bending of light - object submersed in water and mirages in the desert - important characteristic of microscope lenses - refractive index = law of the ratio of incident and refracted Angles n (refractive index) = c/v where c=speed of light; n=velocity of light - RI vacuum = 1, air = higher index, slower speed of light - relationship between bending angles and waves 7

$Refraction and Microscopy - ability to magnify and resolve depends on refractive index - determines the focal length of objective - refractive indices: Air = 1.003 Water = 1.33 Immersion Oil = 1.$

8 Refraction and Microscopy - ability to magnify and resolve depends on refractive index - determines the focal length of objective - refractive indices: Air = Water = 1.33 Immersion Oil = Crown Glass = exact RI varies with color of light ability of prism to separate colors Image made by single lens can therefore suffer aberrations => multi-lens systems Aberrations: The trouble with refraction Chromatic aberration: different colors (wavelengths) focus at different distances Coma: resulting in the images of structures out from the center being smeared outwards Spherical aberration: resulting in light passing through lens center being focused at different distance to light passing through the outer portion 8

9 Lenses - lens: component of glass or transparent plastic, circular in diameter, with two primary surfaces that are ground and polished Planoconvex Biconvex Planococave Planar 9

$In your Student Microscopes Refraction$ chromatic = more than 4 colors generally 11

defect/ produce sharp images = complex lenses

flat - plan achromat = corrected for spherical

10 In your Student Microscopes Refraction requires high degrees of corrections spherical chromatic = more than 4 colors generally 11 lens elements Compensation: Lens - combat defect/ produce sharp images = complex lenses achromat apochromat plan achromat - achromat = corrected for red and blue, 65% flat - apochromat = corrected for three colors, 80% flat - plan achromat = corrected for spherical aberration, 95% flat highest degree of correction, often 4 colors 10

11 Diffraction particles of light travel in straight lines objects in the path of light will cast shadows - when passing close to edge of an object (i.e. slit, aperture) = spreading at oblique angle => DIFFRACTION, similar to dispersion Diffraction and Microscopy - image composed of overlapping points of light from specimen plane - image forming light rays are diffracted point seen as diffraction pattern - image never exact representation - importance of apertures = size determines reaction of light small wavelength = straight line large wavelength = diffraction of bright center and darker circles around it 11

$Diffraction and the Airy Disk - diffraction causes pattern with a bright$ $eye similar pattern: bright disk surrounded by diffraction rings - proper$ $secondary diffraction maxima and central spot remain Diffraction and the$

12 Diffraction and the Airy Disk - diffraction causes pattern with a bright central area = primary maximum - bounded on each side by secondary maxima separated by dark areas = minima - circular aperture = microscope, human eye similar pattern: bright disk surrounded by diffraction rings - proper focus: light intensity at lowest minimum is 0 no matter how perfect, secondary diffraction maxima and central spot remain Diffraction and the Microscope 12

$Diffraction requires correct estimation of numerical aperture and condenser setting NA = expression of the$ objective NA => Dimensionless number that characterizes the angle of light accepted into lens Reflection -

objective NA => Dimensionless number that characterizes the angle of light accepted into lens Reflection -

reflected wave law of reflection - concept for all electromagnetic waves - wave theory: reflected at angle

13 Diffraction requires correct estimation of numerical aperture and condenser setting NA = expression of the ability of an objective to collect these image forming rays; the large the NA, the better able the objective NA => Dimensionless number that characterizes the angle of light accepted into lens Reflection - wave hits non-absorptive surface surface of a smooth water pool - incident vs. reflected wave law of reflection - concept for all electromagnetic waves - wave theory: reflected at angle determined by incident angle - particle theory: travel close, bounce from different pts - texture of surface => specular vs. diffuse reflection 13

Reflection and Virtual Image - formation of a virtual image (mirror image) behind mirror does not exist light rays don t pass through it, could not be projected onto screen - image is the same size

14 Reflection and Virtual Image - formation of a virtual image (mirror image) behind mirror does not exist light rays don t pass through it, could not be projected onto screen - image is the same size as original - upright Spherical Mirrors plane yet not so so simple - piece cut out of sphere - focal point = 1/2 distance F = R/2, with R = radius of curvature (shown as C) - ray diagrams = 3 rays (2 are necessary) 1st: tip of object, parallel then through focal point (F) 2nd: tip of object through curvature center (C) 3rd: parallel to first from bottom of object C F 14

Spherical Mirrors Concave = converging mirror - image is inverted - when object beyond center of curvature C => image between focal pt (F) and C I C O F O F C Convex = fish eye/diverging mirror -

15 Spherical Mirrors Concave = converging mirror - image is inverted - when object beyond center of curvature C => image between focal pt (F) and C I C O F O F C Convex = fish eye/diverging mirror - reflective surface bulges towards light - F and C = imaginary - image diminished and upright Mirror Application - directing light through pathways of optical systems and onto specimen - flat mirrors for folding light at precise angles with minimum distortion - What mirrors are used in microscopy? 15

16 Mirrors - different mirrors in microscopy, dependent on type of microscope => generally planar in shape Specimen Microscope Objective Excitation Mirror Dichroic Mirror Emission Regular upright microscope Fluorescent inverted microscope Reflection and the Microscope 16

cut/ground to specific angles Beamsplitters -

continues on path DIC Prism - light dispersal

rotation, deviation & displacement - lucite

17 Prisms and Beamsplitters - essential components - glass/ transparent materials - cut/ground to specific angles Beamsplitters - redirect portion of light - remainder continues on path DIC Prism - light dispersal => dissection into components - image rotation, deviation & displacement - lucite prism = true color illumination Beamsplitters/Prisms in the Microscope 17

Light Filters/Lenses - most are absorbing or reflecting unwanted

fluorescence - polarizing filter (changes the orientation of

density filters limit intensity of all wavelength = not used in

18 Light Filters/Lenses - most are absorbing or reflecting unwanted light = remove chromatic abberrations - dichroic filter = fluorescence - polarizing filter (changes the orientation of oscillation) - heat absorbing filters limit infrared - neutral density filters limit intensity of all wavelength = not used in microscopy, computer settings instead => synthetic gels and colored filter glass Filters in the Microscope 18

Reflection! Reflection and Virtual Image!

Reflection! Reflection and Virtual Image! 1/30/14 Reflection - wave hits non-absorptive surface surface of a smooth water pool - incident vs. reflected wave law of reflection - concept for all electromagnetic waves - wave theory: reflected back