Using the Michelson Interferometer

Physical Experiment Center2007 Laboratory

Purpose

（ 1 ） Learn to use Michelson Interferomete

r

（ 2 ） Study the fringe patterns resulting from a point source, and make a precise measurement of the wavelength of the He-Ne laser

Structure of Michelson Interferometer

Experiment Principle

dM1'

M1

Mirror

M2

Mirror

S

G1

Beam splitter

G2

Compensatingplate

Observation screen

Pointolite Non-localized Interference

SG ＝ S'G 2 2 2S'M =M S'

2R2L2R22d)(LΔL

2d

L

d

S

S'

G

E P

R

M 1

M 2

M 1 '

S 1 '

S 2 '

2dcos =k k=0,1,2,

cos2/2 22 dRLLdL

L>>d ， ignore , then2 2d /L

The condition of bright fringe is

d

d

L

measuring laser wavelength

When k 、 are invariable, with the decrease of d, decreases . Then radius of ring fringe of the same k order decreases, as appears that interference circles contract entad. Similarly with the increase of d, interference circles expand forth. If the fringes in the circle center contract entad or expand forth N times, the variation of optical path difference is 2△d=N, then we have

Nd /2

2dcos =k k=0,1,2, d

kd cos2

Experiment Demonstration

Observation screen

Laser

Adjustment screw

Experimental Procedure

Convex lens

Data Reading

Graduated scale Reading data window Fine adjustment drum wheel

xx ． xx xxx Graduated scale Reading data window Fine adjustment drum wheel

36.71503mm

Data recordingd0 d50 d100 d150 d200

mm

d250 d300 d350 d400 d450

mm

△d250

△d250

Experimental Procedure 1 ． Let laser irradiate directly in the middle of beam spli

tter, and adjust adjustment screws to make the two biggest and brightest faculae on the observation screen coincide with each other completely.

2 ． Put the convex lens on the bracket and let the light irradiate on the beam splitter uniformly. Then adjust tension spring screws to move the circle center of the rings to the center of the observation screen.

3 ． Rotate the fine adjustment drum wheel in the same direction for some cycles until fringes on the observation screen contract entad or expand forth. Then record the position of M1, which is designated as d0

4. Continue to rotate the fine adjustment drum wheel in the same direction. When contracting entad or expanding forth every 50 fringes, record the position of M1. Ten records should be got.

Notice

Never touch any optical surfaceNever touch any optical surface

Before measuring data, null-space must be eliminBefore measuring data, null-space must be eliminated. ated.

When measuring, rotate the fine adjustment drum When measuring, rotate the fine adjustment drum wheel only in the same direction, never rotate rewheel only in the same direction, never rotate reversely. versely.