Label: Grating Dry Film Divergent Mirror Double-seam White Screen Education
The design experiment seems terrible, and the actual operation is relatively simple ~
My experimental report is for reference only ~
Cover of experimental report
Fabrication of holographic grating
I. Experimental tasks
Design and fabricate holographic grating, and measure its grating constant. The number of gratings required to be manufactured shall not be less than 0/00 per millimeter/kloc.
Second, the experimental requirements
1. Design more than three methods to make holographic gratings and compare them.
2. Design and manufacture complete steps of holographic grating (including parameters and precautions during shooting and developing), and shoot holographic grating.
3. The grating constant value of holographic grating is given, the uncertainty is calculated, the error is analyzed and the experiment is summarized.
Third, the basic physical principles of the experiment
1, principle of grating generation
Grating, also known as diffraction grating, is an optical element that uses the principle of multi-slit diffraction to disperse light (decompose it into spectrum). It is a flat glass or metal plate engraved with a large number of parallel equal-width equidistant slits (scribed lines). The number of slits in the grating is very large, generally tens to thousands per millimeter. The diffraction of monochromatic parallel light through the slits of the grating and the interference between the slits form patterns of wide dark stripes and thin bright stripes, which are called spectral lines. The position of the spectral line varies with the wavelength. When polychromatic light passes through the grating, spectral lines with different wavelengths appear in different positions, forming spectra. The spectrum formed by light passing through the grating is the same result of single-slit diffraction and multi-slit interference (as shown in figure 1).
Figure 1
2, the method of measuring grating constant:
Measure with a measuring microscope;
Using a spectrometer, it is measured according to the grating equation d sin = k;
By diffraction measurement. The laser is diffracted by a grating, and the distance △x between the zero-order diffraction spot and the first-order diffraction spot and the distance L between the screen and the grating are measured on the far screen, so the grating constant d = l/△ x.
Fourth, the specific scheme and comparison of the experiment
1, the improved method of Lloyd's mirror:
Basic physical principle: The characteristic of Lowell mirror is that some direct light interferes with the reflected light of another mirror. If the original beam is parallel light, a total reflector can be added, and part of the direct light can interfere with part of the specular reflection light, thus making a holographic grating.
Advantages: This method saves the step of making double seams.
Disadvantages: the light source must be very close to the plane mirror.
Schematic diagram of the experiment:
Figure 2
2. Young's double-slit interference method;
Basic physical principles: S 1, S2 is the same linear light source, p is any point on the screen, the intersection point s' from the middle vertical line connecting S 1 and S2 is X, the distance S 1 is R 1 and r2, the distance between two seams is D, and the distance between two seams and the screen is L. ..
Because the distance d between the double seams is much smaller than the distance l from the seam to the screen, the optical path difference at point p:
Figure 3
δ= R2-r 1 = dsinθ= DTGθ= dx/L sinθ= TGθ
This is because when the θ angle is small, it can be approximately considered equal.
The position of interference bright fringe can be obtained by the interference maximum condition δ=kλ:
x=(L/d)kλ，
The position of the interference dark fringe can be obtained by the interference minimum condition δ=(k+ 1/2)λ:
x=(D/d)(k+ 1/2)λ
The distance between bright stripes and dark stripes is
δx =λ(D/D)
Therefore, the interference fringes are equidistantly distributed.
And note that the above formulas all have wavelength parameters in them, and the longer the wavelength, the greater the difference.
Fringe shape: it is a group of straight lines (interference fringe characteristics) parallel to the slit at equal intervals, d = l/△ x.
Advantages: The coherence condition of laser light source is easy to meet.
Disadvantages: The required experimental instruments are complex and difficult to obtain.
Schematic diagram of the experiment:
Figure 4
3. Mach-Zehnder interferometer method;
Basic physical principle: As long as the azimuth angle of a beam splitter in the optical path is adjusted, the included angle between transmitted light and reflected light can be changed, thus changing the spacing of interference fringes.
Advantages: This method has low requirements for optical path accuracy, good experimental effect and is convenient for students to operate.
Disadvantages: this method does not require high optical path accuracy, and the experiment may not be accurate enough.
Schematic diagram of the experiment:
Figure 5
Verb (abbreviation of verb) Selection and matching of instruments
Considering all kinds of conditions, Mach-Zehnder interferometer method is adopted in this experiment. The required experimental instruments include 1 He-Ne laser emitter, 1 diverging mirror, 1 convex lens, 2 semi-reflecting mirrors, 2 total reflecting mirrors, 1 white screen and 1 diaphragm, several dry films of shooting grating, and shelves.
Sixth, the experimental steps
(1) Making Holographic Grating
1. Turn on the He-Ne laser transmitter and use a white screen to make the laser beam parallel to the horizontal plane.
2. Adjust the distance between the divergence mirror and the laser transmitter to make the laser diverge.
3. Adjust the distance between the convex lens and the divergent lens to make it equal to the focal length of the convex lens to obtain parallel light.
4. Adjust the positions and heights of the double-sided half mirror and the double-sided total mirror to form a parallelogram (as shown in Figure 5).
5. Adjust the fine adjustment knobs on the half mirror and the total mirror, so that the two obtained light spots have the same height and the spacing is 4-6cm.
6. Measure the optical path difference △l of the optical path in the experiment.
(Experimental optical path difference △l= 1.5cm)
(2) shooting a holographic grating
1. Stop the laser beam, put the dry film on the shelf, let the laser beam shine on the dry film for 1-2 seconds, stop the laser beam, and take the dry film down and put it in the darkroom.
2. Soak the dry film in the developer for a proper time (the length of time depends on the concentration of the developer), take it out and rinse it with clear water, and then soak it in the fixing solution for about 5 minutes. Take out, rinse and dry.
3. The laser beam is used to test the developed dry film. If the zero-order and first-order light spots can be seen, it means that the dry film can be used to determine the grating constant.
(3) Measuring the grating constant of the manufactured grating.
Actual map:
This picture is based on the picture in the experiment report given by the teacher.
Figure 6
Original data table:
x
1
2
three
four
five
six
centimetre
23.8 1
24. 12
23.93
24.24
23.65
23.66
Height (cm)
144.36
144.65
143.84
144.03
144.52
144. 1 1
Calculation process:
Seven, the experimental matters needing attention
1, don't look directly at the laser beam to avoid eye damage.
2. The working voltage of the semiconductor laser is 3V DC, and it works with a special 220V/3V DC power supply (this power supply can avoid the function of generating high voltage due to instantaneous inductance effect when the power supply is turned on), thus prolonging the working life of the semiconductor laser.
Eight. Experimental summary
Design-oriented experiment, which has never been touched before. The previous experiments were done in strict accordance with the detailed steps in the book after understanding the experimental principles introduced in the book, and there was no need to think and study too much by yourself. This time, I prepared a design-oriented experiment, which made me exercise a lot of abilities. First of all, the book only gives simple and general guidance, and everything should be checked and solved by yourself. If you don't even know what the experiment is about, go to the internet to get a general understanding of the content and principle of the experiment, then consult the relevant literature and study the experimental scheme in detail. Especially in this experiment, we are required to provide more than three different experimental schemes and choose one after careful comparison. This requires us to be familiar with and master the principle, specific operation steps and corresponding advantages and disadvantages of each scheme, and then expand our chosen scheme after analyzing and comparing them one by one. This series of processes will take most of the time in the library, because it is really difficult for me, a student who has not finished the course of scientific and technological literature retrieval, to find what I need in the vast literature. In my report, some information comes from the internet, but things on the internet do not completely meet my requirements. After revision, it is almost finished. In fact, I understand the principle and carry out the experiment according to my pre-designed scheme. In the specific operation process, the problem is not big. It can be said that what bothers people is the writing of experimental reports in preview. Now, the experiment has been basically completed, but I feel great gains. You can design experiments more skillfully in the future.
I want to say that a scientific and rigorous attitude is the most important in the whole experiment process. You can't do experiments without understanding, and you can't continue experiments with data problems. We should also take seriously the later experimental data processing.