3B SCIENTIFIC PHYSICS U17303 Instructions D'utilisation page 10

Fig. 4 The interference pattern of two spherical waves
when the axes of the beams are overlaid or form a small
angle
Light diffraction
5.2.1 Light diffraction on a square and a circle aper-
ture
•
Attach the square or circular aperture slide to
the magnetic stand.
•
Position the stand between the laser and the
screen. The distance between the aperture and
the screen should be at least 50 cm.
•
Observe the diffraction patterns by using differ-
ent apertures.
The equation for diffraction through a circular aperture
λ
ϕ =
sin k
D
where ϕ = diffraction angle, k = diffraction order (0,
1, 2, ...), λ = wavelength of light, D = diameter of
aperture.
Fig. 5 Patterns produced when light is diffracted through
circular and square apertures
5.2.2 Light diffraction on a grating
•
Position the laser and the ground screen oppo-
site and as far as possible from each other on
the metal board (see Fig. 6).
•
Position the grating between the laser and the
screen. The distance between grating and the
screen should be at least 50 cm.
•
Observe the diffraction pattern (see Fig. 7).
The equation for diffraction maxima can be written as
λ
ϕ =
sin m
d
where ϕ = diffraction angle, m = diffraction order (0, 1,
2, ...), λ = wavelength of light, d = grating constant
•
Observe the diffraction on gratings of different
types (G1, G2, G3, G4).
•
Try to insert two gratings into the set-up at once,
one behind the other.
•
Observe the diffraction pattern.
Fig. 6 Diffraction set-up [G = diffraction medium (square aper-
ture, circle aperture, grating,), M = ground screen, L = lens]
Fig. 7 The diffraction pattern of a linear grating
Hologram reconstruction
•
Arrange the components on the metal board as
shown in Figure 8. The lens should be in direct
contact with the laser and the hologram should
be positioned as far as possible from the laser
and turned with the red spot to the la ser.
The larger the area of the illuminated hologram, the
more visible is the reconstructed image.
•
Observe the hologram at an angle of approxi-
mately 30°. Rotate the hologram plate slowly
until a holographic image appears.
•
If you cannot locate the image, try turning the
hologram 180°, or move your head slightly (ob-
servation at 30° can be achieved from two dif-
ferent positions).
Fig. 8 Set-up for hologram reconstruction (L = lens, H =
hologram)
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