Pasco OS-8501 Interferometer Manuel d'utilisateur télécharger pdf (Page 7)

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012-02675B Interferometer

In this way the original beam of light splits, and

portions of the resulting beams are brought back

together. The beams are from the same source and

their phases highly correlate. When a lens is placed

between the laser source and the beam-splitter, the

light ray spreads out. An interference pattern of dark

➦ NOTE: Do not be concerned if your pattern

shows irregularities or has fewer fringes. As

long as fringes are clearly visible, measurements

will be accurate.

Since the two interfering beams of light were split

from the same initial beam, they were initially in

phase. Their relative phase when they meet at any

point on the viewing screen, therefore, depends on the

difference in the length of their optical paths in reach-

ing that point.

By moving mirror M

, the path length of one of the

beams can be varied. Since the beam traverses the

path between M

and the beam-splitter twice, moving

1/4 wavelength nearer the beam-splitter will reduce

the optical path of that beam by 1/2 wavelength. The

interference pattern will change; the radii of the

maxima will be reduced so they now occupy the

position of the former minima. If M

is moved an

additional 1/4 wavelength closer to the beam-splitter,

the radii of the maxima will again be reduced so

maxima and minima trade positions. However, this

new arrangement will be indistinguishable from the

original pattern.

By slowly moving M

a measured distance d

, and

counting m, the number of times the fringe pattern is

restored to its original state, the wavelength of the light

(λ) can be calculated as:

λ =

If the wavelength of the light is known, the same

procedure can be used to measure d

Figure 2 INTERFERENCE PATTERN

and bright rings, or fringes, is seen on the viewing

screen, as shown in Figure 2.

1 2 3 4 5 6 7 8 9 10 11 12 ... 17 18

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Pasco OS-8501 Interferometer Manuel d'utilisateur Page 7

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