The definition of laser wavelength with using the diffraction grating

Laboratorywork

Topic: The definition of laser wavelength with using the diffraction grating.

Description of device and principle of its work:

Several parallel slits of equal width a, equally spaced a distance d apart, is called a diffraction grating (fig.1).

Fig.1. The diffraction grating

For light rays emerging from each slit at an angle q, there is a path difference of

d sinqbetween each ray and the one directly above it.

The condition for the formation of a bright fringe is:

,               (1)

where m=0, ±1, ±2,…is the order of spectrum (maximum)

Experimental setup (fig.2) consist of:

· He-Ne laser (1)

· Diffraction grating (2)

· Screen for the observation of diffraction pattern (3)

Fig.2. Experimental setup

Work algorithm:

1.  Measure the distance l between the diffraction grating and the screen (fig.2).

2.  Measure the distance k between 0-maximum and 2-maximum (fig.2).

3.  Find the angle q with using formula:

                 (2).

4.  Find the laser wavelength with using the formula (1). Period of diffraction grating d = 10^-5m.

5.  Write the conclusion.