PHYSICS EXPERIMENT 5

EXPERIMENT NO. 5

Object:-  To determine the wavelength of laser light using Diffraction Grating.

Apparatus Required: 

Semi-Conductor Laser, a different grating, an optical bench and a screen.

Theory And Formula Used: A diffraction grating is an optical device which produces spectra to diffraction. It has a large no. of lines grooved on it. The spectra consisting of different orders is governed by the relation-

                                     

The no. of lines on the grating is-

                                     

Wavelength of the laser light is –

Where d= grating constant

m=1, 2,……….(Order of spectra)

Procedure :

1.          Diode laser is mounted on it’s saddle.

2.          A plane transmitting grating is mounted on an upright next to laser.

3.          The position of x of the spot of 1^st order on either side of central maxima is marked.

4.          The distance D between the grating and screen.

         

Observation Table:

S. No.	D in cm.	Order	Distance x cm.		Mean x cm.
			L.H.S	R.H.S
1. 2. 3.

Calculation:

Where d= grating constant

m=1, 2,……….(Order of spectra)

Result:      

1.       The wavelength of the given LASER beam is …………………

Percentage Error:-

                                    (Standard value ~ Observed Value) X 100

                  % ERROR =

                                                           Standard Value

Precautions:     

1.            Direct viewing of laser light should be avoided.

2.            Proper alignment of the laser diode must be done.

3.            Before switching any other source, switch on the laser diode.

Viva-voice

Q1.    What is the full form of laser?

Ans.   Light amplification by stimulated emission of radiation.

Q2.    How laser light is different from the ordinary light

Ans.   It is a monochromatic, convergent, coherent and high intense beam of light. While ordinary light is incoherent, divergent and low intense beam of light.

Q3.    What is population inversion?

Ans.   When the no. of atoms are more in higher energy state than the lower energy state, known as population inversion. it is essential for stimulated emission.

Q4.    What is pumping?

Ans.   It is process to achieve population inversion.

Q5.    What is laser?

Ans.   It is a device which is used to convert ordinary light into laser light

Q6.    What is meant by the term coherency?

Ans.   When the light waves are in same phase and with all most same wavelength in light beam known as coherent.

Q7.    What is diffraction?

Ans.   When the light bends or deviate from path due to obstacle known as diffraction.

Q8.    Define Grating

Ans.  It is an arrangement in which there is a fine quality of glass on which parallel lines are ruled equidistant with diamond point by an automatic shifting machine. The ruled lines works as opaque and spacing works as transparent.

Q9.    What is active medium?

Ans. it may be solid, liquid, or gas which achieves population inversion.

Q10. What is the action of the optical resonator?

Ans.   It is the combination of two reflecting mirror which is used to increase the intensity of laser light.