Application of light interference. Diffraction of light. (Presentation). Interference. presentation for a physics lesson (grade 11) on the topic Phenomena of interference and diffraction of waves download the presentation

To view the presentation with pictures, design and slides, download its file and open it in PowerPoint on your computer.
Text content of presentation slides: Presentation by the teacher of Municipal Educational Institution “Secondary School No. 56 with UIOP” in Saratov Sukhova Tatyana Mikhailovna Interference of light. Interference is the addition of two (or several) light waves, in which the light intensity increases at some points in space and weakens at others. Conditions for the coherence of light waves. Waves whose phase difference does not depend on time are called coherent. Manifestations in nature. Application of interference. The phenomenon of light interference is widely used in modern technology. One such application is the creation of “coated” optics. The phenomenon of mechanical waves bending around obstacles is observed when river waves freely bend around objects protruding from the water and spread as if these objects were not there at all. A phenomenon characteristic of all wave processes. Sound waves also bend around obstacles and we can hear a car signal around the corner of the house when the car itself is not visible. Lesson plan.1. Jung's experience.2. What is diffraction.3. Hugens' principle.4. Hugens-Fresnel principle.5. Diffraction patterns from various obstacles.6. Limits of applicability of geometric optics.7. Resolution of optical devices.8. Conclusion. In the mid-17th century, the Italian scientist F. Grimaldi observed strange shadows from small objects placed in a narrow beam of light. These shadows did not have clear boundaries and were bordered by colored stripes. Diffraction of light is the bending of a light wave around opaque bodies with penetration into the region of a geometric shadow and the formation of an interference pattern there. Christiaan Huygens played a major role in the development of the idea that the propagation of light is a wave process. Each point on the surface reached by a light wave is a secondary source of light waves. The envelope of the secondary waves becomes a wave surface at the next moment in time. Augustin Fresnel laid the foundations of wave optics, supplementing Huygens' principle with the idea of ​​interference of secondary waves: he constructed a quantitative theory of diffraction. Each element of the wave front can be considered as the center of a secondary disturbance generating secondary spherical waves, and the resulting light field at each point in space will be determined by the interference of these waves. The diffraction of light manifests itself most clearly when this condition is met (diffraction observation condition). Where D is the size of the obstacle or hole,  is the light wavelength, L is the distance from the obstacle to the place where the diffraction pattern is observed. l 2 D L Diffraction also places a limit on the resolving power of a telescope. The maximum angular distance () between luminous points at which they can be distinguished is determined by the ratio of the wavelength () to the lens diameter (D). Light diffraction is used to create sensitive spectral devices. Diffraction phenomena bring not only benefits, but also harm, limiting the resolution of optical instruments. II OPTION 1. B2. AT 3. B4. D5.6. D 7. G 1. A2. B3. A4. G5. 6. A7.A 1. What is diffraction?2. Formulate the Huygens principle.3.Formulate the Huygens-Fresnel principle.4. How to get a dark or light spot in the center of the diffraction pattern of a hole?5. Limits of applicability of geometric optics.6. Resolution of optical instruments. There is no separate interference and separate diffraction - this is a single phenomenon, but in certain conditions the interference properties are more prominent, in others - the diffraction properties of light. Myakishev G.Ya., Bukhovtsev B.B. Physics: textbook for 11th grade. – M.: Education Zhelezovsky B.Ya. Lectures on optics for SSU studentsEducational complexes. Physics, 7-11 grades, Library of visual aids Physikon programs, Physics 7-11 grades, Local version Kirill and Mifodiy, Educational electronic publications BENP Physics

Interference of mechanical waves. Wave addition
What happens to sound waves when
a conversation between several people while an orchestra is playing,
sings a choir, etc.?
What do we observe when we enter the water at the same time?
two stones fall
or drops?

Let's trace this on a mechanical model

Interference.

Coherent waves.

Interference of light

Interference in thin films.

Jung's experiment diagram

Observing interference in laboratory conditions

Interference maxima and minima

Bubble

Newton's rings

Diffraction is a deviation from the rectilinear propagation of waves.

Diffraction of light waves

Fresnel's theory.

The distance through which the lines on the grating are repeated is called the period of the diffraction grating. Denoted by the letter d. If

• A thin film is applied to the glass surface

Coated optics

The reflection of light for the extreme parts of the spectrum - red and violet - will be less. The lens has a lilac tint.

• Deviation of the direction of wave propagation from straight line at the boundary of an obstacle (waves bending around obstacles)
• Condition: the dimensions of the obstacle must be comparable to the wavelength

Grimaldi experience

• In the mid-17th century, Italian scientist Francesca Maria Grimaldi observed strange shadows from small objects placed in a very narrow beam of light. To the scientist’s surprise, these shadows did not have sharp boundaries, but for some reason were bordered by colored stripes.

Observation conditions

• - the size of the obstacle must be commensurate with the length of the light wave
• - the distance from the obstacle to the observation point must be much greater than the size of the obstacle

As a result of diffraction, light waves coming from different points are superimposed (coherent waves), and it is observed interference waves

Diffraction manifests itself in a violation of the straightness of light propagation!

Huygens' principle Fresnel

• Each point on the wave front is a source of secondary waves, and all secondary sources are coherent.

• Fresnel proved the linear propagation of light and quantitatively examined diffraction by various types of obstacles.

Peculiarities

diffraction pattern

Explanation

Slit image dimensions

more sizes,

received through

geometric

constructions

Secondary waves go behind

edges of the slit

Peculiarities

diffraction pattern

Explanation

In the center of the picture appears

light stripe

Secondary waves in

direction,

perpendicular to the slit,

have the same

phase. Therefore, when they

superimposed amplitude

fluctuations increase

Features of diffraction

Explanation

Along the edges of the picture - alternation

light and dark stripes

Secondary waves interfere

in a direction at an angle to

perpendicular to the slot,

having a certain phase difference, from

which the resulting

vibration amplitude

• Diffraction prevents clear images of small objects because light bends around objects.
• Images appear blurry. This occurs when the linear dimensions of objects are less than the wavelength of light.

Resolution of microscope and telescope

If two stars are at a small angular distance from each other, then these rings overlap each other, and the eye cannot distinguish whether there are two luminous points or one.

The phenomenon of interference occurs when two or more waves of the same frequency, propagating in different directions, interact. Moreover, it is observed both in waves propagating in media and in electromagnetic waves. That is, interference is a property of waves as such and does not depend either on the properties of the medium or on its presence. Interference

A stable pattern of alternating maxima and minima of oscillations of points in the medium when coherent waves are superimposed Coherent waves are waves of the same frequency with a constant phase difference Interference We encounter interference phenomena quite often: the rainbow color of oil stains on asphalt, the color of freezing window glass, fancy colored patterns on the wings Some butterflies and beetles are all manifestations of light interference.

Diffraction The phenomenon of diffraction occurs when complex light is decomposed. The position of the maxima and minima that make up the diffraction pattern depends on the wavelength of the light. Therefore, when observing in complex light, for example in white, where different wavelengths are represented, the diffraction maxima for different colors will be in different places.

Diffraction The phenomenon of diffraction imposes restrictions on the application of the laws of geometric optics: The law of rectilinear propagation of light, the laws of reflection and refraction of light are satisfied quite accurately only if the size of the obstacles is much larger than the light wavelength. Diffraction imposes a limit on the resolution of optical instruments: - in a microscope, when observing very small objects, the image turns out to be blurry - in a telescope, when observing stars, instead of an image of a point, we get a system of light and dark stripes.

Dispersion Wave dispersion is the difference in phase velocities of waves depending on their frequency. Wave dispersion leads to the fact that a wave disturbance of an arbitrary non-harmonic shape undergoes changes (disperses) as it propagates. Sometimes wave dispersion is understood as the process of decomposing a broadband signal into a spectrum, for example, using diffraction gratings.

Dispersion Red sunset, one of the results of the decomposition of light in the Earth's atmosphere. The reason for this phenomenon is the dependence of the refractive index of the gases that make up the earth's atmosphere on the wavelength of light. The rainbow, whose colors are determined by dispersion, is one of the key images of culture and art. Thanks to light dispersion, it is possible to observe the colored “play of light” on the facets of a diamond and other transparent faceted objects or materials. To one degree or another, rainbow effects are found quite often when light passes through almost any transparent object. In art they can be specifically intensified and emphasized.

Polarization A polarized wave is a transverse wave in which all particles oscillate in the same plane. Such a wave can be obtained using a rubber cord if a barrier with a thin slit is placed in its path. The slit will only allow vibrations that occur along it.

Malus's Law Linearly polarized light can be observed, for example, in laser radiation. Another way to produce linearly polarized light is to pass natural light through a Polaroid (polarizing filter), which freely transmits the component of light polarized along the selected direction and completely absorbs light with perpendicular polarization. If a linearly polarized wave is incident on such a polaroid, then the intensity I of the transmitted light will depend on the angle a between the direction of polarization of the incident light and the selected direction of the polaroid itself as follows: I = I 0 cos 2 a

Ellipsometry Ellipsometry is a set of methods for studying the surfaces of liquid and solid bodies based on the state of polarization of the light beam reflected by this surface and refracted on it. Plane polarized light incident on the surface acquires elliptical polarization upon reflection and refraction due to the presence of a thin transition layer at the interface. The relationship between the optical constants of the layer and the parameters of elliptically polarized light is established based on Fresnel formulas. Methods for sensitive non-contact studies of the surface of liquids or solids, adsorption processes, corrosion, etc. are based on the principles of ellipsometry.

Slide 2

Interference of light

• Interference is one of the most convincing evidence of wave properties.
• Interference is inherent in waves of any nature.
• Interference of light waves is the addition of two coherent waves, as a result of which an increase or decrease in the resulting light vibrations is observed at different points in space.