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Chia sẻ tài liệu: cách tử quang thuộc Vật lí 9
Nội dung tài liệu:
Team:
Dinh Cong Huy
Nguyen Thai Long
Bui Viet Hung
Nguyen Duc Nam
HUT- 17/10/2008
Gratings and application
Mechatronics Engineering- Advanced Training Program
Grating: a system of multi close equidistant and parallel lines or bars, especially lines ruled on a polished surface, used for producing spectra by diffraction--- called also diffraction grating.
Diffraction grating: is an optical device used to learn the different wavelength or color contained in a beam of light. The device usually consist of thousand of narrow, closely spaced parallel slits (or grooves).
Figure 1:
- Diffraction grating: is an
optical device used to learn
the different wavelength or
color contained in a beam of light.
The device usually consist of thousands of
narrow, closely spaced parallel slits (or grooves).
- Used for producing spectra.(Fig 1)
I- INTRODUCTION
Fig 2: The first diffraction grating was made by Fraunhofer (which is called Fraunhofer diffraction).
II- Background of topic
1. Single – slit diffraction.
2. Double- slits diffraction.
3. Multi- slits diffraction.
4. Diffraction gratings.
5. Quiz.
II- Background
The smaller the slit, the broader the entire the diffraction pattern.
Single slit diffraction:
Phenomena: the beam spreads out
vertically after passing through the slit.
Denote:
a- the width of the slit
d- the distance between slit and screen
θ - the angle between the perpendicular to the slit a line from the center of the slit to a point P on the screen
Condition for dark fringe:
m= 1,2,3…
Position of the mth dark fringe:
The phase difference between the phase of light of the upper and lower trip:
The intensity :
2.Double slits diffraction:
Diffraction envelope
Inference fringe
- must consider not only diffraction due to the individual slits but also the interference of wave coming form different source.
-intensity:
Where: is the phase difference at point P of 2 incident lights, and is calculated by the formula:
And : is the phase difference of wave at P from the top trip with respect to the wave received from the bottom trip:
3.Multiple slits diffraction:
Constructive interference occurs for rays at angle θ satisfy: d.sinθ=mλ
(m= 0,±1,±2,±3…)
- The maxima are the same position as for two slits diffraction with the same spacing d.
Q: Why occurs such this coincidence ?
Interference patterns for N equally spaced very narrow slits.
The greater the value of N, the narrower the principle maxima become and the smaller the intensity of secondary maxima is.
4.Diffraction grating:
Thousands of very narrow and close slits.
The phenomena seen on the screen is similar to multi slits diffraction.
Positions of the maxima are given by: d.sinθ= mλ
(m = 0,±1,±2,..)
m=±1: first order lines
m=±2: second order lines
…..
5. Quiz:
1. The pattern of double diffraction.
2. The pattern of interference.
Q:What is the difference?
A: No fundamental distinsion
III- APPLICATION OF DIFFRACTION
For instrument analytical chemistry.
In laser system
In astronomical application
In synchrotron radiation beam lines
Some special uses for grating : gratings as filters, gratings in fiber- optic telecommunication, gratings as beam splitters, gratings as optical couplers….
Resolving power, scattering and stray.
1. Resolving power:
Disperse a spectrum into its wavelength components.
2 wavelengths:
The resolving power:
Where:
And:
N: the number slits of Diffraction grating, m-th order diffraction.
R= N.m
2. Spectrograph
Structure of a slit spectrograph
Sunlight spectrum
The important of this technique is to astronomy.For example,to measure sunlight spectrum.
With sunlight, people obtain spectrum produced by a diffraction grating has dark absorption lines.
The resolution of grating spectrograph:
The greater the number of slits N,the better the resolution;also,the higher the order m of the diffration-pattern maximum tthat we use,the better the resolution.
3. Spectrometer:
Explanation about spectometer:
The light to be analyzed passes through a slit, and a collimated beam of light is incident on the grating.
The diffracted light leaves the grating at angles that satisfy Equation:
a telescope is used to view the image of the slit.
The wavelength can be determined by measuring the precise angles at which the images of the slit appear for the various orders
4. Some pictures in real life:
Rain-bow colors reflection and diffraction on the surface of CD/DVD.
Fresnel mirror.
Dispersion through a prism.
Data soures:
1. University Physics with mordern physics 12th edition- Young
2.Fundamentals of Physics 7th edtion– Halliday, Resnick, Walker.
3. http://www.wikipedia.org
4. http://www.google.com.vn
Thanks for your attention!!!
Have a nice day!
Dinh Cong Huy
Nguyen Thai Long
Bui Viet Hung
Nguyen Duc Nam
HUT- 17/10/2008
Gratings and application
Mechatronics Engineering- Advanced Training Program
Grating: a system of multi close equidistant and parallel lines or bars, especially lines ruled on a polished surface, used for producing spectra by diffraction--- called also diffraction grating.
Diffraction grating: is an optical device used to learn the different wavelength or color contained in a beam of light. The device usually consist of thousand of narrow, closely spaced parallel slits (or grooves).
Figure 1:
- Diffraction grating: is an
optical device used to learn
the different wavelength or
color contained in a beam of light.
The device usually consist of thousands of
narrow, closely spaced parallel slits (or grooves).
- Used for producing spectra.(Fig 1)
I- INTRODUCTION
Fig 2: The first diffraction grating was made by Fraunhofer (which is called Fraunhofer diffraction).
II- Background of topic
1. Single – slit diffraction.
2. Double- slits diffraction.
3. Multi- slits diffraction.
4. Diffraction gratings.
5. Quiz.
II- Background
The smaller the slit, the broader the entire the diffraction pattern.
Single slit diffraction:
Phenomena: the beam spreads out
vertically after passing through the slit.
Denote:
a- the width of the slit
d- the distance between slit and screen
θ - the angle between the perpendicular to the slit a line from the center of the slit to a point P on the screen
Condition for dark fringe:
m= 1,2,3…
Position of the mth dark fringe:
The phase difference between the phase of light of the upper and lower trip:
The intensity :
2.Double slits diffraction:
Diffraction envelope
Inference fringe
- must consider not only diffraction due to the individual slits but also the interference of wave coming form different source.
-intensity:
Where: is the phase difference at point P of 2 incident lights, and is calculated by the formula:
And : is the phase difference of wave at P from the top trip with respect to the wave received from the bottom trip:
3.Multiple slits diffraction:
Constructive interference occurs for rays at angle θ satisfy: d.sinθ=mλ
(m= 0,±1,±2,±3…)
- The maxima are the same position as for two slits diffraction with the same spacing d.
Q: Why occurs such this coincidence ?
Interference patterns for N equally spaced very narrow slits.
The greater the value of N, the narrower the principle maxima become and the smaller the intensity of secondary maxima is.
4.Diffraction grating:
Thousands of very narrow and close slits.
The phenomena seen on the screen is similar to multi slits diffraction.
Positions of the maxima are given by: d.sinθ= mλ
(m = 0,±1,±2,..)
m=±1: first order lines
m=±2: second order lines
…..
5. Quiz:
1. The pattern of double diffraction.
2. The pattern of interference.
Q:What is the difference?
A: No fundamental distinsion
III- APPLICATION OF DIFFRACTION
For instrument analytical chemistry.
In laser system
In astronomical application
In synchrotron radiation beam lines
Some special uses for grating : gratings as filters, gratings in fiber- optic telecommunication, gratings as beam splitters, gratings as optical couplers….
Resolving power, scattering and stray.
1. Resolving power:
Disperse a spectrum into its wavelength components.
2 wavelengths:
The resolving power:
Where:
And:
N: the number slits of Diffraction grating, m-th order diffraction.
R= N.m
2. Spectrograph
Structure of a slit spectrograph
Sunlight spectrum
The important of this technique is to astronomy.For example,to measure sunlight spectrum.
With sunlight, people obtain spectrum produced by a diffraction grating has dark absorption lines.
The resolution of grating spectrograph:
The greater the number of slits N,the better the resolution;also,the higher the order m of the diffration-pattern maximum tthat we use,the better the resolution.
3. Spectrometer:
Explanation about spectometer:
The light to be analyzed passes through a slit, and a collimated beam of light is incident on the grating.
The diffracted light leaves the grating at angles that satisfy Equation:
a telescope is used to view the image of the slit.
The wavelength can be determined by measuring the precise angles at which the images of the slit appear for the various orders
4. Some pictures in real life:
Rain-bow colors reflection and diffraction on the surface of CD/DVD.
Fresnel mirror.
Dispersion through a prism.
Data soures:
1. University Physics with mordern physics 12th edition- Young
2.Fundamentals of Physics 7th edtion– Halliday, Resnick, Walker.
3. http://www.wikipedia.org
4. http://www.google.com.vn
Thanks for your attention!!!
Have a nice day!
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