EM Spectrum Flashcards
1
Q
EM Spectrum
A
- Electro-magnetic (EM) spectrum includes few zones
- The first two ranges form ionizing radiation (the left part of the spectrum)
- The optical range is spread from UV to IR region
- The third range of EM waves includes microwaves and radio waves. The VISIBLE light is narrow region of EM waves which can be perceived of human eye.
2
Q
Wave-particle duality
A
- The most important feature of light
- represents simultaneously manifestation of properties as both wave and flux of particles by light
- light behavior as wave is described by means of quantities: λ , c , ν , and T
- The propagation of wave responses to following relation
λ = c / ν
- Otherwise – the light is emitted and interacts with matter as energy portions quants/photons – each photon carries energy of
E= h . ν
- light related quantities in the formula E= h . c / λ
3
Q
How does light propagate?
A
- The light propagates with velocity which depends only on the properties of the given matter medium (similarly to the mechanical waves)
- The velocity is directly estimated by quantity of refractive index – the RI is determined by electric permittivity and magnetic permeability
V is max in vacuum (there n = 1) velocity C = 300000 km per sec.
In other media the speed is lower.
4
Q
Nature of light
A
- light is transversal EM wave consisting of two perpendicular fields – electric with strength E and magnetic with strength H
- These fields vibrate simultaneously in two perpendicular planes
- The vibration is harmonic – it means that vectors alter the magnitude in sinus manner
5
Q
Alteration of light during propagation
A
- When during its spreading, the light passes through different matter media
- it causes alteration of the direction of propagation
- Encountering a borderline between two matter media, the light will change its direction due to the difference in optical density
- The reflected light turns back to the first medium
- The part of light may pass into the second medium with some change of direction.
6
Q
2 laws of reflected light
A
- the incident ray, the reflected ray and normal (perpendicular), form a plane
- the angle of reflection is equal to the angle of incidence
7
Q
Specular (mirror) reflection
A
- light hits smooth surface
- irregularities of the surface are smaller than wavelength
- typical for glass, mirror
8
Q
Diffuse reflection
A
- light hits rough surface
- irregularities are consistent or bigger than the wavelength
9
Q
Snellius law
A
- product of refractive index and sinus of angle in two media are equal
- light crosses the borderline between two media it changes the direction of propagation
- The relation which determines the manner of further propagation is called Snellius law
- Such as in the case of reflection, the incident ray, the refracted ray as well as the normal (perpendicular), form a plane (lie on one and the same plane).
- the angle of refraction is smaller than the angle of incidence if the second medium is more dense
10
Q
Total internal reflection
A
- occurs when the light propagates from optically high dense medium to optically low dense medium
- Let the light propagates through a glass toward air with gradually increased angle
- Initially both refraction and reflection occur
- But when the angle of incidence reaches a certain value a reflection of light occurs only. It can be explained by means of Snellius law:
at a given angle of incidence (called critical angle) the angle of refraction acquire the value of 90 degree which means that the light refracted skims along the surface.
Further increase of the angle of incidence causes complete return of the light in the first glass medium (the angle of refraction acquire a value bigger than 90 degree).
11
Q
Conditions for TIR occurrence
A
- Light passage from optically high-density medium to optically low-density medium
- The angle of incidence – bigger than the critical angle
12
Q
Applications of TIR: Optical Fiber
A
- The single optical fiber is built up of few glass layers with particular refractive indexes
- the inner core possesses the higher n and it is covered with less dense coating
- The bundle of many single optical fibers is formed in order to transmit the light. The light beam transmitted passes at angle bigger than critical and propagates along the fiber
13
Q
Applications of TIR: Endoscope
A
- Optical fiber device for examination of hollow body structures/organs (GI tract, airway paths, and other)
- The endoscope is designed as composition of illuminating optical fiber, OF transmitted the image obtained, laser fiber.
14
Q
Beer-Lambert-Bouger law
A
- during light propagation through a given matter, a loss of light energy occurs due to absorption of EM energy from medium particles
- The radiant light flux decreases in exponential manner during the passage through medium with linear absorption coefficient α and thickness d
- Ψ is passed radiant flux, Ψ0 is incident flux
Ψ = Ψ0e–αd
15
Q
α in Beer-lambert-bouger law
A
- α is determined by molar absorptivity coefficient ε and concentration: α= ε.c
- Evaluation of light absorption from body liquids is performed in some diagnostics
- methods based on evaluation of α
- α is specific for the given substance and its dependence on the light wavelength is called absorption spectrum
16
Q
Spectrophotometry
A
- Light absorption based method for identification and investigation of dissolved substances
17
Q
Light diffraction
A
- fundamental phenomenon which determines the manner of light propagation
- a part of photons interact with particles of medium and the latter begin to vibrate due to transfer of energy
- Reemission of photon energy is launched randomly and the light is scattered
- Generally it resulting in change of wave front direction – the light rays appear at angles
18
Q
Why does diffraction occur?
A
- if the light encounters small optical non-homogeneitities i.e. particles with refractive index different from that of the surrounding medium
19
Q
What is diffraction dependent on?
A
- The diffraction depends on wavelength and on dimension of particles:
d << λ (~0,05 μm) - Diffracted flux Ψ~ λ-4 d ~ λ (~ 1⁄4 λ) - Diffracted flux Ψ~ λ-2
d > λ - Diffracted flux
20
Q
Ultraviolet radiation
A
- (10 - 400 nm)
- UV radiation includes electromagnetic waves with wavelength shorter than that of the visible light
- UV photons carry more energy compared to visible light photons.
- UV waves with wavelength of 200 – 400 nm are important for medicine
- UV radiation interacts with skin and eye. In human eye cornea, lens and retina are mostly involved.
The range is divided into UV bands:
zone А 315–400nm
zone B 280 – 315 nm
zone C 200–280nm
21
Q
most significant UV source
A
- sunlight
- due to filtering action of atomosphere, only UV long-wave >200nm pass through the atmosphere
- thunderbolts
- artifical - lamps with gas mixture (mercury etc.)
22
Q
Positive UV radiation effects
A
- A-type and B-type UV radiation have positive influence
- A - catalyzes the vitamin D synthesis
- B - causes improvement of fluorite and calcium assimilation which has eventually anti-rachitic effect
23
Q
High dose of A/B UV: negative effects
A
A-Type UV produces:
- skin sensitization in terms of harmful action of B-zone UV radiation 2. Skin photo-aging effect due to damaging of collagen by photons.
- Burn skin (weak effect), skin cancer induction, cataract of the eye.
- B-band radiation is many times more aggressive than A-band
- It produces the most active photochemical effect at 297 nm - skin erythema, and skin burning, photo-aging of the skin – strongly quicken degenerative processes within the skin; the skin becomes harden and rough. Immunosuppressive effect – decrease white blood cell functionality
- Eye lens cataract
24
Q
Skin cancer induction
A
- C-band UV radiation does not reach the earth surface
- produced by lamps
- C-UV photons are powerful sufficient to damage bacteria
- It is used for sterilization of laboratory, vessels, instruments
- But if C-UV light is absorbed from the transparent tissues in human eye and it causes strong damage
- B-UV light can cause direct DNA damage
25
DNA damage by B-UV
- The radiation excites DNA molecules in skin cells, causing aberrant/abnormal covalent bonds to form between adjacent cytosine bases, producing a dimer
- This is a mutation, which can result in cancerous growths and is known as a "classical C-T mutation"
26
Protection from UV
- The harmful action of UV-B radiation (because of its more marked effect) can be diminished by use of protectors
- In order to protect the skin, absorbing filters are used– substances that interact chemically with UV photons and abolish it
- A quantity called SUN PROTECTION FACTOR is a major characteristic which determine effectiveness of a given filter
- SPF is estimated by ratio of time for appearance of erythema with filter over the time for appearing of erythema without filter
27
Infrared radiation
- 0.76 μm- 1000 μm
- IR waves have wavelength longer than that of visible light and respectively low energy
А /near/ - 0,76 μm- 2,5 μm
В /middle/ - 2,5 μm- 50 μm
С /far/- 50 μm- 1000 μm
- All physical bodies in the nature possessing temperature higher than 0K emit IR radiation with a particular spectrum determined of temperature value.
For example – human body (T = 310 K) emits radiation with 9.6 mkm wavelength
28
Natural sources of IR
- Sun, stars, galaxy, burning bodies (coals)
29
Application of IR
- long wavelength IR rays diffracts less than visible light
– application in detection and possessing of images without light.
- IR radiation divided into two groups – therapeutic and image diagnostics
- The first application is in physiotherapy as a method for stimulation of blood circulation and metabolic rate enhancement
- The second is base for thermograph imaging – thermo vision uses receiving of IR radiation from human body to produce image of temperature distribution
- As an indicator is estimated alteration of temperature in terms of the normal assumed for the given region.
- Increase of temperature is indication for inflammatory processes or tumor appearing
- But decrease of T is indication for vascular disorder.
30
Advantages and Disadvantages of IR
Advantages: noninvasive fast and cheap
Disadvantages: low resolution (due to long wavelength)
31
Luminescence
- Emission of light as a result of strongly determined conversions in atoms
- Electron transitions between a certain levels are possible only and these transitions can be provoked only by particular energy carriers.
32
Different types of luminescence
photoluminescence
roentgenoluminescence
electrono-luminescence
electroluminescence
radioluminescenc
hemiluminescence (bioluminescence)
33
How can electrons change their energy state
- Electrons in atom can posses only certain energy states
– each state is characterized by energy and spin number
- Electrons can absorb photons and emits photons
- When an electron absorbs or emits photons it alters its energy state.
34
Photoluminescence
- an electron in ground state S0 has compensated spin
- this state is called singlet
- if the incoming photon appears (with strongly determined energy) it is absorbed by electron and the latter transits to higher S1 state (S1 is a singled level too)
35
What happens when an e- goes from S0 to S1 (photoluminescence)
- The higher levels are unstable
- Further two types of conversion are possible
- 1. the electron makes direct return transition to basic level emitting photon (with lower energy due to structure of S1)
2. the electron makes transition to INTERMEDIATE level T (triplet level in which electrons have non-compensated spin) After that electron generates photon with energy equal to difference T- S0, the photon emitted carries this energy.
- Depending on the time-duration of emission luminescence can be: fluorescence and phosphorescence
- The transitions between singlet levels are supported with short duration emission - called fluorescence.
t = 10-9- 10-6 s
36
Phosphorescence
- This type of emission has long duration due to specificity of energy conversion
- Transition between triplet and singlet levels sometimes takes sec, min. or even hours.
37
Luminescence laws: Stokes law
λlum \> λex
- This basic law of photoluminescence states the luminescent spectrum is right shifted in terms of the excited spectrum (The luminescent photons have lower energy than exciting photons)
38
Luminescence laws: Vavilov's law
- The number of luminescent photons is proportional to the number of exciting photons
39
Application of Luminescence
- The phenomenon of luminescence is used in many scientific methods for analyzing substance's structures and bioprocesses
- Atoms and molecules can be detected by means of luminescent photons emitted
- A presence of particular chemical bonds in a given bio-structure can be detected
- Fluorescent markers are used – specific molecules which are integrated with structure investigated. Marker-molecule is bounded to strongly determined bio-structure and absorbs a particular wavelength. It causes luminescence and detection of light emitted allows the image to be obtained.
- As an example it can be discussed fluorescent antibodies which are bonded with membrane receptors, DNA, blood cells
- The diagnostics of some physiological phenomena and diseases is provided by use of luminescent analysis.
