Research and analysis

Yang Guihong

(08 Physics Class Two, 200802050253)

Introduction:

We can't live without sunshine. Generally, we think that sunlight is a monochromatic light (light with a single wavelength). In fact, the light around us is polychromatic light (light composed of two or more monochromatic lights), which is composed of monochromatic lights with different wavelengths.

Broadly speaking, diffraction screens with periodic spatial structure or optical properties (such as transmittance and refractive index) are collectively called gratings. There are many kinds of gratings, such as transmission grating and reflection grating, plane grating and concave grating, black-and-white grating and sine grating, one-dimensional grating, two-dimensional grating and three-dimensional grating, etc. The grating used in this experiment is a holographic transmission grating shot by holographic technology. If the grating surface is not easy to clean after being polluted, special attention should be paid when using it.

Spectrometer is an optical instrument that can accurately measure angles. It is often used to measure the refractive index, dispersion rate, wavelength of light wave and spectral observation of materials. Because the equipment is precise and has many complicated control parts, it must be adjusted in strict accordance with certain rules and procedures in order to measure accurate results.

Absrtact: Spectrometer is a typical optical instrument that can accurately measure the refraction angle. It is often used to measure the refractive index, dispersion rate, wavelength of light wave and spectral observation of materials. Because of the precision, many control parts and complicated operation, the device must be adjusted strictly according to certain rules and procedures to obtain high-precision measurement results.

Keywords: spectrometer, prism, refractive index

Abstract: Spectrometer is a typical optical instrument that can accurately measure the refraction angle. It is often used to measure the refractive index, dispersion rate, wavelength and spectral observation of substances. Because the more precise the equipment is, the more complicated the control elements and operations are, so it must be adjusted in strict accordance with certain rules and procedures to get high-precision measurement results.

Keywords: spectrometer, prism, refractive index

Second, the purpose of the experiment:

1, understand the structure of spectrometer, and learn how to adjust and use the forward solution of spectrometer;

2. Measure the top angle of prism with spectrometer;

3. Learn to measure the refractive index of prism with the minimum deflection angle method.

Third, the experimental instruments:

The spectrometer is mainly composed of five parts: triangular base, collimator, telescope, calibration disk and stage. See table 1 for the name and function of the regulating device in the figure.

Figure 1 Schematic diagram of basic structure of spectrometer

Table 1 Name and function of spectrometer adjusting device

Code function

1 slit width adjustment screw adjusts the slit width to change the incident light width.

2 slit device

3 When loosening the locking screw of the slit device, pull the slit device back and forth to adjust the parallel light. After adjustment, lock it to fix the slit device.

Collimator produces parallel light.

5. The optical element is placed on the stage. Three fine-tooth screws 7 are installed under the table top for adjusting the inclination of the table top. Loosen screw 8 to lift and rotate the stage.

6. Clamp the reed of the object to be measured and clamp the optical element on the stage.

Seven stage adjustment screws (3) are used to adjust the level of the stage.

8 Loosen the locking screw of the stage, and the stage can rotate and lift independently; After locking, the stage can rotate synchronously with the reading cursor disk.

9 telescope to observe the light after the action of optical elements.

When the locking screw of 10 eyepiece device is loosened, the eyepiece device can be extended and rotated (telescope focusing); After locking, fix the eyepiece device.

1 1 abbe autocollimator eyepiece device can be telescopic and rotated (telescope focusing).

12 eyepiece focusing handwheel adjusts the eyepiece focal length, so that the crosshairs and forks are clear.

13 telescope optical axis elevation adjustment screw adjusts the elevation of the telescope.

14 telescope optical axis horizontal adjustment screw Adjust this screw to make the telescope rotate in the horizontal plane.

15 telescope bracket

The two cursors are symmetrically arranged on the 16 cursor disk.

17 The cursor is divided into 30 cells, and each cell corresponds to an angle 1'.

18 telescope fine-tuning screw This screw is located on the reverse side of figure 14- 1. After locking the brake screw 2 1 of the telescopic bracket, adjust the screw 18 to slightly rotate the telescopic bracket.

19 dial is divided into 360 degrees, and the minimum scale is half a degree (30'). If it is less than half a degree, read it with the cursor.

20 Eyepiece Lighting Power Turn on the power 20, and a green dot and a black cross can be seen from the eyepiece.

2 1 telescopic bracket brake screw This screw is located on the reverse side of Figure 14- 1. After locking, the telescope bracket can only rotate slightly with the telescope fine-tuning screw 18.

After the telescope bracket is locked with the dial locking screw, the telescope rotates synchronously with the dial.

23 spectrometer power socket

The triangular base of the spectrometer is the base of the whole spectrometer. The center of the base is provided with a rotating shaft sleeve along the vertical direction, and the whole telescope assembly, dial and vernier disk can rotate independently around the central axis. The collimator is fixed on one foot of the triangular base.

25 collimator bracket

26 After the vernier caliper adjusting screw locks the vernier caliper braking screw 27, the adjusting screw 26 can make the vernier caliper rotate slightly.

27 After locking the screw of the disc brake, the disc brake can only rotate slightly with the fine adjustment screw of the disc 26.

28 collimator optical axis horizontal adjustment screw, so that the collimator rotates in the horizontal plane.

Adjust the elevation angle of the optical axis of the collimator by adjusting the screw.

Fourth, the experimental principle:

The prism is shown in figure 1. AB and AC are transparent optical surfaces, also called refractive surfaces, and their included angle is called prism vertex angle. BC is the ground glass surface, which is called the bottom surface of the prism.

Fig. 2 schematic diagram of prism

1. Measure the prism vertex angle by reflection method.

As shown in fig. 2, a beam of parallel light is incident on the prism, and the light reflected by the AB plane and the AC plane exits along the direction respectively, and the included angle with the direction is recorded as, which can be known from the geometric relationship:



Fig. 3 Measurement of Vertex Angle by Reflection Method

2. Measure the refractive index of prism glass by minimum deflection angle method.

Assuming that a monochromatic parallel light LD is incident on the prism and refracted twice and then exits in the direction of ER, the included angle between the incident light LD and the outgoing light ER is called the deflection angle, as shown in Figure 3.

Figure 4 Determination of Minimum Deviation Angle

When the prism rotates, the incident angle of the incident light on the optical surface AC changes, and the direction ER of the outgoing light also changes, that is, the deflection angle changes. Continue to slowly rotate the prism along the direction where the deflection angle decreases, so that the deflection angle gradually decreases; When turning to a certain position, if you continue to turn in this direction, the deflection angle will gradually increase. At this position, the deflection angle reaches the minimum value, and the minimum deflection angle is measured. It can be proved that the relationship between refractive index of prism material and vertex angle and minimum deflection angle is as follows.

In the experiment, the vertex angle and minimum deflection angle of prism are measured by spectroscope, and the refractive index of prism material can be calculated by the above formula.

Experimental contents and steps:

1. Adjustment of spectrometer (the spectrometer structure is shown in the right figure)

Before adjustment, you should be familiar with the positions of the following screws in the spectrometer used:

(1) Eyepiece focusing (see reticle alignment) handwheel; ② Adjust the handwheel (or screw) when focusing the telescope (see the object clearly); ③ screws for adjusting the high and low inclination of the telescope; (4) Brake screw (together with dial) for controlling the rotation of telescope; ⑤ Screw for adjusting the horizontal state of the stage; ⑥ Brake screw for controlling the rotation of the stage; ⑦ Screws for adjusting the slit width on the collimator; ⑧ Tuning

Screws for adjusting the height and inclination of the collimator; Figure 5

Pet-name ruby collimator focusing slot sleeve brake screw.

(1) Visual coarse adjustment. Roughly adjust the telescope, stage and collimator to be horizontal and vertical to the central axis by visual inspection (rough adjustment is the premise and guarantee of fine adjustment in the later stage).

(2) Adjust the telescope with autocollimation method to focus on infinity.

(1) Adjust the eyepiece focusing handwheel until the crosshairs can be clearly seen to be "aligned".

② Turn on the power supply of the small lighting lamp and turn on the switch. In the field of view of the eyepiece, you can see the "alignment" and the window with a small green cross as shown in Figure 4.

Fig. 6 Eyepiece field of view

③ Place the double mirror on the stage according to the direction shown in Figure 5. This placement is based on the consideration that if the pitch of the plane mirror is to be adjusted, only the screws a 1 or a2 under the stage need to be adjusted, and the adjustment of the screw a3 has nothing to do with the pitch of the plane mirror.

Fig. 7 Placement of Plane Mirror

(4) Looking along the outside of the telescope, you can see a bright cross in the plane mirror. When you gently rotate the stage, the bright cross will also rotate. But if you look at the plane mirror with a telescope, you often can't see this bright cross, which means that the light emitted by the telescope is not reflected by the plane mirror into the telescope.

We still aim the telescope at the plane mirror on the stage, adjust the pitch of the mirror, rotate the stage to let the reflected light return to the telescope, let the light from the transparent cross pass through the objective lens (at this time, the light from the objective lens is not necessarily parallel light), then be reflected by the plane mirror, and then be refocused by the objective lens, thus forming a blurred image spot on the cross line (note: the above steps are the key to smooth adjustment). Then adjust the distance between the objective lens and the reticle, and then adjust the distance between the reticle and the eyepiece, so that you can see both the reticle and the clear reflection image of the cross from the eyepiece. Pay attention to make the difference between the line of sight and the reflection image of the bright cross be ignored. If there is parallax, it needs to be adjusted repeatedly to eliminate it. If there is no parallax, it means that the telescope has focused to infinity.

(3) Adjust the optical axis of the telescope to be perpendicular to the central axis of the spectrometer.

The optical axes of collimator and telescope represent the directions of incident light and emergent light respectively. In order to measure the angle accurately, their optical axes must be parallel to the dial respectively. During manufacture, the dial is perpendicular to the central axis of the spectrometer. Therefore, when the telescope is perpendicular to the central axis of the spectrometer, it meets the requirement of being parallel to the dial.

The specific adjustment method is: the plane mirror is still placed vertically on the object stage, so that the telescope is aimed at the front and rear mirrors of the plane mirror respectively, and the reflection images of two bright crosses can be observed respectively by using the self-collimation method. If the optical axis of the telescope is perpendicular to the central axis of the spectrometer and the reflecting surface of the plane mirror is parallel to the central axis, when the stage rotates, it can be observed from the telescope that the bright cross images reflected by the front and rear surfaces of the plane mirror twice completely coincide with the upper cross line of the reticle, as shown in Figure 6(c). If the optical axis of the telescope is not perpendicular to the central axis of the spectrometer and the reflecting surface of the plane mirror is not parallel to the central axis, then the two bright cross reflected images observed from the telescope will not coincide with the cross on the reticle at the same time, but one is lower and one is higher, or even only one can be seen. At this time, it is necessary to carefully analyze and determine the adjustment measures, and we must not blindly adjust them. It is important to make a rough adjustment first: first, observe visually from the outside of the telescope, and adjust it to two bright cross images from the outside of the telescope; Then fine-tune: when the bright cross can be observed from the field of view of the telescope, no matter which reflector of the plane mirror faces the telescope, if the sight line seen from the telescope does not coincide with the bright cross image, their intersection points are different by a certain distance in height, as shown in Figure 6(a). At this time, adjust the telescope tilt screw to reduce the gap to h/2, as shown in Figure 6(b). Then adjust the horizontal adjustment screw below the stage to eliminate the other half distance, so that the aligned upper reticle coincides with the bright reticle, as shown in Figure 6(c). Then, rotate the stage 180o, so that the telescope faces the other side of the flat mirror, and make the same adjustment. This adjustment is repeated until the bright cross images reflected from the front and back surfaces of the plane mirror can coincide with the upper cross line of the reticle when the stage is rotated. At this time, the optical axis of the telescope is perpendicular to the central axis of the spectrometer, which is commonly called the successive approximation halftoning method.

Fig. 8 the positional relationship between the bright cross image and the reticle alignment.

(4) Adjust the collimator

Adjust the collimator with the previously adjusted telescope. When the collimator emits parallel light, the slit is imaged on the focal plane of the telescope objective, and the slit image can be clearly seen in the telescope, which is no different from the quasi-straight line.

① Adjust the collimator to produce parallel light. Take the flat mirror on the stage, turn off the small lamp in the telescope, illuminate the slit with sodium lamp, observe the slit image from the collimator through the telescope, adjust the distance between the collimator slit and the lens until a clear slit image can be seen in the telescope, and then adjust the slit width to make the slit width in the field of view of the telescope about 65438 0 mm. ..

② Adjust the optical axis of the collimator to make it perpendicular to the central axis of the spectrometer. When a clear slit image is seen in the telescope, rotate the slit (but it cannot move back and forth) to a horizontal state, and adjust the tilt screw of the collimator so that the horizontal image of the slit is equally divided up and down on the central cross line of the reticle, as shown in Figure 7(a). At this time, the optical axis of the collimator is perpendicular to the central axis of the spectrometer. Then rotate the slit to the vertical position to keep the slit image clearest and ignore the difference, as shown in Figure 7(b).

Fig. 9 Location of slit image and reticle

At this point, the spectrometer has been completely adjusted. When using, it must be noted that other screws on the spectrometer cannot be rotated at will, otherwise it will destroy the working conditions of the spectrometer and need to be readjusted.

measure

Before the formal measurement, please find out the positions of the following screws in the spectrometer you use: ① the brake screw (together with the dial) that controls the rotation of the telescope; (2) screws to control the micro-motion of the telescope.

Measurement of Prism Vertex Angle by (1) Reflection Method

As shown in Figure 2, align the top corner of the prism with the collimator, turn on the sodium lamp to make parallel light shine on the AC and AB faces of the prism, tighten the brake screw of the vernier disk, fix the position of the vernier disk, loosen the brake screw of the telescope, rotate the telescope (together with the dial) to find the slit image reflected by the AB face, then tighten the telescope screw, and use the fine-tuning screw of the telescope to make the vertical line and the slit completely overlap, and record both at this time. Turn the telescope to the AC surface and make the same measurement. free

The vertex angle of the prism is

Repeat the measurement three times and take the average.

(2) Determination of refractive index of prism glass

Loosen the brake screws of the vernier dial and the telescope respectively, and turn the vernier dial (together with the prism) to make parallel light enter the AC surface of the prism, as shown in Figure 3. Turn the telescope and find the image of the slit in the collimator in the AB plane. Then slowly turn the cursor disk (together with the prism) in one direction to observe the movement of the slit image in the telescope. When the slit image moving in one direction with the rotation of the cursor disk will start to move in the opposite direction, fix the cursor disk. Gently rotate the telescope to align the vertical line on the crosshair with the slit image, and record the readings indicated by the two cursors as: Then take off the prism, rotate the telescope to make it directly aim at the collimator, aim the vertical line on the cross line at the slit image, and record the readings indicated by the symmetrical two cursors.

Repeat the measurement three times and take the average. Use the above formula to find the refraction of prism.

Five, the experimental matters needing attention:

1. The lenses, prisms and mirrors on telescopes and collimators cannot be touched or wiped by hand. If dust is found, gently wipe it with lens paper. Prism and flat mirror are not allowed to collide or fall to avoid damage.

Spectrometer is a relatively precise optical instrument, so you should take care of it more. When the brake screw is locked, do not forcibly turn the telescope or twist the slit at will.

3. Before measuring data, be sure to check whether several brake screws of spectrometer are locked. If they are not locked, the obtained data will be unreliable.

4. When measuring, the fine-tuning screw rotated by the telescope should be used correctly to improve work efficiency and measurement accuracy.

5. In the process of reading the cursor, since the telescope may be located in any direction, we should pay attention to whether the telescope has passed the zero point of the scale during the rotation.

6. Adjust one direction when adjusting. At this time, some screws that have been adjusted can no longer be screwed casually, otherwise the previous efforts will be in vain.

7. The adjustment of the telescope is a key point. First turn the eyepiece handwheel to see the crosshair, and then enlarge the eyepiece barrel to see the crosshair clearly.

Six, thinking about the problem:

1. What are the requirements for spectrometer adjustment? What is the standard of prosecution?

Answer: ① Geometric requirements: "three verticals". That is, the plane of the stage, the main optical axis of the telescope and the main optical axis of the collimator must be perpendicular to the central axis of the spectrometer.

② Physical requirements: "triple focus". That is, the crossed wire focuses on the eyepiece, the telescope focuses on infinity, and the slit focuses on the collimating objective.

③ The standard for testing the three verticals: "Four Parallels". That is, the plane of the loading platform, the main optical axis of the telescope, the main optical axis of the collimator and the reading disk are parallel to each other.

(4) Test the standard of triple focusing: "triple clarity". That is to say, the fork wire in the eyepiece is clear, the bright cross (green cross) image is clear, and the slit in the telescope is clear.

2. How to adjust the telescope system is the key and difficult content.

Answer: ① Visual rough adjustment.

(2) Turn on the small lamp to adjust the eyepiece, and see the fork wire clearly.

(3) Put a biplane mirror on the stage (the position is as shown in the picture, why? ), adjust the objective (tilt angle and expansion) and the objective table (screw) to make the green cross images on both sides of the double mirror clear and ignore the differences. At this time, the telescope has been infinitely focused.

④ Adjust the optical axis of the telescope to make it perpendicular to the rotation axis of the spectrometer. Make both sides of the double mirror have green cross images. Then, the optical axis of the telescope is perpendicular to the central axis of the spectrometer by using the "half-step approximation method" (refer to the film description and demonstrate if necessary), that is, the cross-stitch image completely coincides with the adjustment cross-stitch.

3. How to adjust the collimator?

Answer: ① Based on the adjusted telescope, adjust the tilt screw at the lower part of the collimator to make it emit parallel light.

② Adjust the slit width of the collimator (emphasis: don't damage the knife edge! )

③ Make the optical axis of the collimator perpendicular to the rotation axis of the spectrometer. Center the horizontal and vertical slit images seen in the eyepiece.

Seven, error analysis:

In the experiment of measuring the refractive index of prism, when the collimator optical axis of spectrometer and the telescope optical axis are perpendicular to the central axis, it can be seen from the experiment that the inclination of the stage plane has no effect on the measurement of the minimum deflection angle, but the measurement of the vertex angle has different effects with the inclination of the stage plane.

Eight, experimental experience:

1, which improves our comprehensive analysis ability. When facing a problem, we should first consider how to solve it, and then start to consider the specific methods to solve it. You must preview in advance before the experiment, and master the principle, process and matters needing attention of the whole experiment clearly, so as to ensure that your experiment can be completed quickly and well. When previewing, you should have a purpose, knowing clearly in your heart where the key points of the experiment are and where the problems that must be paid attention to are. Design the experimental steps. Analyze every detail of the experiment to minimize the experimental error. All these have enabled us to initially cultivate the quality and ability of experiments.

2. Cultivate a scientific and rigorous attitude in the experiment, respect objective facts, and treat any experiment objectively and seriously. Before the official start of the experiment, the experimental instruments and materials should be checked to ensure the smooth progress of the experiment. Before we begin, we should compare the experimental knowledge in our hearts before we begin. In the course of the experiment, a meticulous attitude and a realistic attitude are needed to start again. Pay attention to every step and every detail.

We have formed the habit of being careful and patient. In the experiment, you must be patient, because every change in the experiment may be subtle, and you must concentrate on it before you can find it, and you can't rush for success. If the experimental data is too different from the correct data, it is necessary to recall the whole experimental process, find out the problems in each step and do it again.

4. I know how to use many instruments, get a good exercise under the good environment and equipment in the optical laboratory, and have a clear understanding of the debugging and measurement of many instruments and how to reduce experimental errors. I think this will be very useful in our future experiments.

I was deeply impressed by the patience and earnest attitude of the experimental teacher. Every teacher who guides our experiment is very serious about his work. Before the experiment, the teacher usually explains the matters needing attention in the experiment and patiently explains the problems in our experiment. Moreover, during and after our experiment, the teachers inspired us to think about some extended contents of the experiment, which will help us to closely link the contents of the experiment with the textbooks and master the knowledge more comprehensively.

Nine, test summary:

First of all, the instrument measurement of optical experiment is very precise, and a very small link in the experiment may lead to the failure of the experiment. Take "measuring the refractive index of prism by total reflection critical angle method" as an example, it should be noted that the spectrometer is calibrated in this experiment, so it should be noted that only the tilt adjustment screws of the stage can be adjusted, but not the tilt adjustment screws of the collimator and telescope, otherwise it will lead to.

Secondly, optical experiments also have higher requirements for data processing. Data requires not only high precision, but also high precision. Usually, multiple groups of data are recorded and finally averaged.

Thirdly, the measuring instruments in optical experiments usually need a stable experimental environment when measuring. When there is a light source, it is usually necessary to turn on the light source before the start of the experiment, so that the light source has reached stability during the experiment. For "holographic photography", the stability of the environment is required to be higher. The experimental instrument is placed on the shockproof table. After arranging the optical path of the instrument, tap the table with your hand to see if the optical path has changed. Before exposure, indoor experimenters should not talk loudly, because the change of air density caused by sound wave vibration may lead to the failure of the experiment. After the film is installed, there must be a period of time for all components on the table to stabilize naturally. Even if the interference fringe is stabilized, time is not allowed. It can be said that this experiment has the highest stability requirement among the six experiments I have done.

Fourth: I always think that it is the most important to do a good preview of the experiment. Before doing the experiment, we can understand the principle of the experiment and the purpose of the instrument to be used, so that we can have a general understanding of the experiment before the experiment, and then we can quickly master the use of the instrument through the teacher's explanation in class, so that we can be handy when doing the experiment, and at the same time we can reduce the situation that the experiment fails or even damages the instrument because we don't know the purpose of the experimental instrument.

Nine, references:

[1], general physics experiment 3, edited by Yang and Zhao, Higher Education Press, etc.

2008 edition;

[2] College Physics Experiment, edited by Zhang, Southwest Jiaotong University Press, June 2009, 5438+ 10;

[3], College Physics Experiment Course (2nd Edition) He Chunjuan edited by Northwestern Polytechnical University Press.

April 2009