C. Properties of Light
Light is a special kind of electromagnetic energy which propagates in a vacuum at
c = 2.99*108 [m/s]. The speed of light is in a non vacuum medium such as air (0.03%) and glass
(30.0%) slower. Two key properties of light interaction with the surface of a medium are Reflection
(bounced off a surface) and Refraction (passing from one to another medium). The field of detection
and measurement of light energy is called radiometry.
Dual Nature of Light
The models of the properties were developed through the observation of the effects of light. Scientists
observed that light can act like a wave, and like particle with a discrete amount of energy. Both
models are helpful.
Concept of a photon
A photon is a carrier of electromagnetic energy that interacts with other discrete particles. A beam of
light is a stream of photons.
When UV light shines on some metal surfaces, it causes electrons to be emitted. This is the
photoelectric effect. Two concerns: More intense radiation did not cause electrons to have more
energy and the energy of the emitted electron was dependent on the wavelength, not the amplitude.
If light were a continuous wave, it might wash over the metal surface and interact with the
electrons to give them the needed energy to escape at lower light levels (intensities), but only after
long delays. However, faint light at high frequencies (short wavelengths) caused the immediate
release of electrons. Thus, light knocked the electrons out of the metal surface as if the light were
made of particles—photons
Wave Model
The propagation of light or electromagnetic energy through space can be described in terms of a
traveling wave motion. the wave moves energy-without moving mass-from one place to another at a
speed independent of its intensity or wavelength.
Characteristics of Light Waves
The directions of the electric and magnetic field are at
right angles (perpendicular) to the direction of the wave
moving. The maximum value of wave displacement is
called the amplitude (A) and the distance between each
cycle of waves is called the wavelength (\lambda). The
inverse of the wavelength is the wave number expressed
in 1/m. The wave also propagates at a wave speed ( v)
which equals c in a vacuum and is less than c in a medium. which also means
Polarization and Huygens’ Priciple
The tilted E-vector can be described by its components, Ex and Ey. When
it happens, as in some cases, that Ex and Ey are not in the same
phase—that is, they do not reach their maxima and minima at the same
time—the E-field does not remain oriented in a fixed, linear direction.
Rather, the amplitude maxima of the two components do not occur at the
,same time and so-called elliptically polarized light is exhibited and thus light exhibits differing
polarization orientations over time. A special case of elliptical polarization—called circular
polarization—occurs when Ex equals Ey and they are out of phase by 90°.
The intensity of light passing through a linear polarizer:
Huygens’ principle assumes that each point along a wave can be considered a point source for
production of secondary spherical wavelets. The new position of the wavefront will be surface tangent
to these secondary wavelets.
Superposition
Two or more waves can traverse the same space and time independently of each other. This is the
superposition principle. Thus given multiple waves, the field at any given point can be calculated by
summing each of the individual wave vectors. Superposition of waves with almost similar wavelength
and phase is called constructive interference. Superposition of waves with opposing phases is called
destructive interference.
Reflection and Refraction
When a ray of light reflects off a surface, it’s new direction only depends on the angle if incidence.
Angle of incidence equals angle of reflection.
When a ray of lights transfers to another medium it changes direction at the interface because of the
difference in speed of the two media. The ratio of speed is called the
index of refraction (n). Snell’s law states:
Diffraction and Interference
, 1. Non Laser Light Sources
Monochromaticity : Laser light consists of a single color of light that occurs within a very
narrow range of wavelength. Laser light is very directional and does not diverge a lot
Incoherent: Light waves produced by ordinary sources that don't form an orderly pattern.
They combine in a random fashion and don't produce a wave larger than any of the
single various waves. Coherent: Waves produced by a laser travel through space in phase with one
another. When all the separate waves in the beam remain in phase with one another the result is a
wave much stronger than that of any single wave. — A very intense,
coherent beam is generated.
B.Fluorescent Light Sources : Low pressure discharge lamps with a fluorescent phosphor
○ Consist of mercury discharge lamps that emit 90% of their energy at 253.7-nm
wavelength. Ultraviolet photons can excite a number of phosphors, producing wavelengths
from infrared to ultraviolet. Visible wavelengths are characterized as white, warm white, cool white.
Cold or hot cathode electrodes: Cold electrodes are used when a rapid start is necessary. Hot
electrodes give greater luminous efficiency.
C.High Intensity Discharge Lamps (HID): Can be made of mercury, sodium or metal halides. Gas
pressures inside are usually 2-4 atmospheres.mercury: two envelopes.
D.Flashlamps and Arc Lamps
High intensity discharge devices commonly used in photography and laser
technology. Usually contains gases such as xenon and krypton. Flash or arc is initiated by a high
voltage across the discharge tube — ionizes the gas — produces high intensity light with output peaks
in both the visible and infrared regions of the electromagnetic spectrum
E. Light Emitting Diodes (LED)
Semiconductor devices that are directly modulated by varying input current. Made of
aluminum-gallium-arsenide (AIGaAs). Dopants may be added to vary wavelength. Common in fiber
optics communication, calculators. Can emit light in both the visible and infrared regions of the
spectrum. Operate with pn junctions. Two slabs are put together with the n material having an excess
of electron and the p material having a deficiency of electrons or an excess of holes. Each time an
electron falls into a hole (recombination) a photon of light is emitted — produce incoherent beam of
light. When current flows across a pn junction, free electrons from the n -type material are forced to
combine with holes in the p -type material and release energy.
II. Concepts of Laser Safety
A. Eye Hazards
Most vulnerable part of the body to laser hazards. Changes to the eye can
occur at much lower laser power levels than changes to the skin. Eye is designed to transmit, focus
and detect light. Aqueous humor: Absorbs heat so it protects the internal portion of the eye from
thermal (heat) radiation. Refraction index=1.33 (same as water). Cornea: Front portion of the eye
where light passes through. Outermost transparent layer. Can withstand dust, sand and other assaults
from the environment. Lens : Flexible tissue that changes shape. In conjunction with the cornea, the
lens focuses light on the back of the eye. When the lens changes shape, its focal length changes. This
lets the eye focus on both near and far objects. Iris: Controls the amount of light that enters the eye. Its
pigmented/colored part of the eye. Responds to light intensity by adjusting its size, this size change
controls the amount of light admitted into the eye. Pupil : Opening in the center of the iris through
which light passes. Size changes from 2mm to 7mm, according to the brightness of light in the
Light is a special kind of electromagnetic energy which propagates in a vacuum at
c = 2.99*108 [m/s]. The speed of light is in a non vacuum medium such as air (0.03%) and glass
(30.0%) slower. Two key properties of light interaction with the surface of a medium are Reflection
(bounced off a surface) and Refraction (passing from one to another medium). The field of detection
and measurement of light energy is called radiometry.
Dual Nature of Light
The models of the properties were developed through the observation of the effects of light. Scientists
observed that light can act like a wave, and like particle with a discrete amount of energy. Both
models are helpful.
Concept of a photon
A photon is a carrier of electromagnetic energy that interacts with other discrete particles. A beam of
light is a stream of photons.
When UV light shines on some metal surfaces, it causes electrons to be emitted. This is the
photoelectric effect. Two concerns: More intense radiation did not cause electrons to have more
energy and the energy of the emitted electron was dependent on the wavelength, not the amplitude.
If light were a continuous wave, it might wash over the metal surface and interact with the
electrons to give them the needed energy to escape at lower light levels (intensities), but only after
long delays. However, faint light at high frequencies (short wavelengths) caused the immediate
release of electrons. Thus, light knocked the electrons out of the metal surface as if the light were
made of particles—photons
Wave Model
The propagation of light or electromagnetic energy through space can be described in terms of a
traveling wave motion. the wave moves energy-without moving mass-from one place to another at a
speed independent of its intensity or wavelength.
Characteristics of Light Waves
The directions of the electric and magnetic field are at
right angles (perpendicular) to the direction of the wave
moving. The maximum value of wave displacement is
called the amplitude (A) and the distance between each
cycle of waves is called the wavelength (\lambda). The
inverse of the wavelength is the wave number expressed
in 1/m. The wave also propagates at a wave speed ( v)
which equals c in a vacuum and is less than c in a medium. which also means
Polarization and Huygens’ Priciple
The tilted E-vector can be described by its components, Ex and Ey. When
it happens, as in some cases, that Ex and Ey are not in the same
phase—that is, they do not reach their maxima and minima at the same
time—the E-field does not remain oriented in a fixed, linear direction.
Rather, the amplitude maxima of the two components do not occur at the
,same time and so-called elliptically polarized light is exhibited and thus light exhibits differing
polarization orientations over time. A special case of elliptical polarization—called circular
polarization—occurs when Ex equals Ey and they are out of phase by 90°.
The intensity of light passing through a linear polarizer:
Huygens’ principle assumes that each point along a wave can be considered a point source for
production of secondary spherical wavelets. The new position of the wavefront will be surface tangent
to these secondary wavelets.
Superposition
Two or more waves can traverse the same space and time independently of each other. This is the
superposition principle. Thus given multiple waves, the field at any given point can be calculated by
summing each of the individual wave vectors. Superposition of waves with almost similar wavelength
and phase is called constructive interference. Superposition of waves with opposing phases is called
destructive interference.
Reflection and Refraction
When a ray of light reflects off a surface, it’s new direction only depends on the angle if incidence.
Angle of incidence equals angle of reflection.
When a ray of lights transfers to another medium it changes direction at the interface because of the
difference in speed of the two media. The ratio of speed is called the
index of refraction (n). Snell’s law states:
Diffraction and Interference
, 1. Non Laser Light Sources
Monochromaticity : Laser light consists of a single color of light that occurs within a very
narrow range of wavelength. Laser light is very directional and does not diverge a lot
Incoherent: Light waves produced by ordinary sources that don't form an orderly pattern.
They combine in a random fashion and don't produce a wave larger than any of the
single various waves. Coherent: Waves produced by a laser travel through space in phase with one
another. When all the separate waves in the beam remain in phase with one another the result is a
wave much stronger than that of any single wave. — A very intense,
coherent beam is generated.
B.Fluorescent Light Sources : Low pressure discharge lamps with a fluorescent phosphor
○ Consist of mercury discharge lamps that emit 90% of their energy at 253.7-nm
wavelength. Ultraviolet photons can excite a number of phosphors, producing wavelengths
from infrared to ultraviolet. Visible wavelengths are characterized as white, warm white, cool white.
Cold or hot cathode electrodes: Cold electrodes are used when a rapid start is necessary. Hot
electrodes give greater luminous efficiency.
C.High Intensity Discharge Lamps (HID): Can be made of mercury, sodium or metal halides. Gas
pressures inside are usually 2-4 atmospheres.mercury: two envelopes.
D.Flashlamps and Arc Lamps
High intensity discharge devices commonly used in photography and laser
technology. Usually contains gases such as xenon and krypton. Flash or arc is initiated by a high
voltage across the discharge tube — ionizes the gas — produces high intensity light with output peaks
in both the visible and infrared regions of the electromagnetic spectrum
E. Light Emitting Diodes (LED)
Semiconductor devices that are directly modulated by varying input current. Made of
aluminum-gallium-arsenide (AIGaAs). Dopants may be added to vary wavelength. Common in fiber
optics communication, calculators. Can emit light in both the visible and infrared regions of the
spectrum. Operate with pn junctions. Two slabs are put together with the n material having an excess
of electron and the p material having a deficiency of electrons or an excess of holes. Each time an
electron falls into a hole (recombination) a photon of light is emitted — produce incoherent beam of
light. When current flows across a pn junction, free electrons from the n -type material are forced to
combine with holes in the p -type material and release energy.
II. Concepts of Laser Safety
A. Eye Hazards
Most vulnerable part of the body to laser hazards. Changes to the eye can
occur at much lower laser power levels than changes to the skin. Eye is designed to transmit, focus
and detect light. Aqueous humor: Absorbs heat so it protects the internal portion of the eye from
thermal (heat) radiation. Refraction index=1.33 (same as water). Cornea: Front portion of the eye
where light passes through. Outermost transparent layer. Can withstand dust, sand and other assaults
from the environment. Lens : Flexible tissue that changes shape. In conjunction with the cornea, the
lens focuses light on the back of the eye. When the lens changes shape, its focal length changes. This
lets the eye focus on both near and far objects. Iris: Controls the amount of light that enters the eye. Its
pigmented/colored part of the eye. Responds to light intensity by adjusting its size, this size change
controls the amount of light admitted into the eye. Pupil : Opening in the center of the iris through
which light passes. Size changes from 2mm to 7mm, according to the brightness of light in the
