# School of PhysicsLecture Demonstration Manual

## Oh-5 Optical Crystals

Published: Wednesday 15 March 2006 - Updated: Monday 28 March 2011

### Aim

To demonstrate diffraction from a crystal lattice using optical apparatus.

### Apparatus

•  Laser
•  Optical bench
•  Optical carriers
•  Slide projector
•  PASCO® "Optical Crystals

### Diagrams

Click on pictures to enlarge.

### Description

The Pasco optical crystals consists of 28 photographic emulsion patterns positioned on seven individual plates. These allow diffraction patterns to be observed due to 1, 2 and 3 dimensional crystals. The laser is directed onto the slide which is mounted on a short optical bench and the resulting pattern is then displayed on a ground glass screen. Alternatively a T.V. monitor may be used for enlargement.

Each plate has four optical crystals as follows

PLATE 1. a) dots. Random array.

b) c) d) Single row of dots with various spacings

PLATE 2. a) Two parallel rows of dots

b) Three parallel rows of dots

c) Four parallel rows of dots

d) Rectangular lattice of dots

PLATE 3. a) One row of dots

b) Two rows of dots at a 60degree angle

c) Three rows of dots each at a 60 degree angle

d) Full hexagonal array of dots.

PLATE 4. a) Two identical layers of dots in random array

b) Two layers of dots in hexagonal array

c) d) Two rows of dots in rectangle array (various spacings)

PLATE 5. a) b) Random array of asterisks (two sizes)

c) d) Random array of S's (two sizes)

PLATE 6. a) Random array of A's

b) One row of A's

c) Rectangular array of A's

d) Hexagonal array of A's

PLATE 7. a) Rectangular array of dots

b) Face centred rectangular array

c) Side centred rectangular array

d) Array of dots in sets of three