Demonstration experiment of college physics

Experimental report 23 Michelson interference experiment

The purpose of the experiment

1, to understand the structure of Michelson interferometer;

2. Master the structure of Michelson interferometer;

3. Observe the phenomenon of equal inclination interference of light and the method of mastering wavelength;

4, master the difference method to process data.

Second, experimental instruments.

He-Ne laser, beam expander lens, Michelson interferometer

Three experimental principles

The optical system of Michelson interferometer is shown in the figure. It consists of a beam splitter G, a compensation plate H, a fixed mirror M 1 and a moving mirror M2. M 1 and M2 are perpendicular to each other. The beam splitter and compensation plate are a pair of plane optical glasses with the same material and appearance. They are parallel to each other and form an angle of about 45 degrees with M 1 M2, respectively. Optical path difference caused by different times of beam splitter. The light from the point light source (or extended light source) is incident on the spectroscope and divided into "1" and "2" coherent light with the same intensity, which are reflected by M 1 and M2 respectively and projected on the light screen (for extended light source, the eyes are facing the observation) to produce interference phenomenon. Since M 1 is perpendicular to M2, it can be equivalently considered that the virtual images of M2 and M 1 form an air gap with a thickness of d, and the size of d varies with the position of M2, so the optical path difference between the two rays can be determined by the following formula:

( 1)

Where Iˇ is the incident angle of the light "1" to M2. When d is constant, δ is determined by iˊ, and the optical path difference in the same direction of iˊ is equal, forming equal inclination interference fringes. And satisfy:

k=0、 1、2、3…… (2)

Bright stripes:

k=0、 1、2、3…… (3)

Dark stripes. The fringe is a concentric ring with alternating light and dark, which is similar to Newton's ring interference fringe, but the difference is that the interference level outside this concentric ring is lower, and the closer it is to the center of the circle, the higher the interference level is. The center interference level is the highest. Now analyze formula (2). For the first bright stripe, there are:

(4)

When D increases, in order to ensure that Equation (4) still holds, IK' must also increase, that is, the K-level bright stripes expand outward, and conversely, when D decreases, IK' must also decrease, and the K-level bright stripes shrink inward. Iˊ=0 (that is, the center of the circle) is specially considered. Satisfy:

(5)

This is a bright stripe. Then, when d increases, the grade k of the central bright stripe increases, and the bright stripe appears outward from the center; When d decreases, the level of the central bright stripe decreases and the bright stripe converges to the center. Whenever d changes, interference fringes appear or close at the center. When d changes, n interference fringes appear or enter the center. According to this phenomenon, the wavelength of light wave can be determined.

Assuming that the moving mirror M2 was originally at the position of D 1, move the position of M2 now, and observe and calculate the number of central bright stripes coming out or coming in at the same time. When M2 moves to position D2, correspondingly, the number of bright stripes coming out or coming in is n.. There are:

(6)

Fourth, the experimental steps

1. Remove the beam expander, turn on the laser power supply to emit laser, and adjust the laser direction to make the incident light and reflected light coincide.

2. Observe the two groups of light spots reflected by M 1 and M2 on the screen or wall, and repeatedly adjust the three screws on the back to make the light spots reflected by M 1 and M2 coincide one by one.

3. Put the beam expander lens into the laser beam to expand the laser beam and project it onto the beam splitter, and adjust the irradiation position until concentric circles are observed on the screen.

4. Turn the micro handwheel to observe the change of interference pattern, and turn the handwheel clockwise or counterclockwise to observe the appearance or income of the center of interference pattern.

Verb (abbreviation of verb) data recording and processing

DN (mm) M DM (mm) DM-DN (mm)

10 44.99455 4 10 44.86692 0. 12763

60 44.97835 460 44.85 109 0. 12726

1 10 44.96242 5 10 44.83525 0. 127 13

160 44.94655 560 44.8 1958 0. 12697

2 10 44.93072 6 10 44.80370 0. 12702

260 44.9 1450 660 44.78765 0. 12685

3 10 44.89865 7 10 44.77 175 0. 12690

360 44.88280 760 44.75585 0. 12695

; s = 2.384× 10-4； SC8=4.44× 10-4

After checking that 0. 12763 is a bad value, remove it;