helium -neon laser

1. HELIUM-NEON
LASER
BY-ARPIT SHUKLA
EC ,SRMCEM LUCKNOW

2. INTRODUCTION
 A laser is a device that emits light through a
process of optical amplification based on the
stimulated emission of electromagnetic radiation.
 It can be classified in four basic types-
* SOLID ( ruby laser )
* LIQUID ( dye laser )
* GAS (helium- neon laser)
*PLASMA

3. DISADVANTAGE OF 3 LEVEL LASER
 Occur in non continuous pulses
 High power pumping source req.
 Difficult to maintaie pop. Inversion
 Less efficient
These drawbacks led to dev. of four level
laser

4. EMERGENCE
It was invented by Iranian Physicist Ali Javan &
William R Bennet in 1960.
They worked on the principle of converting electric
energy to a laser light output.

5. CONSTRUCTION
1-Glass envelop
It consist of CAPILARY TUBE
(its main use is to pass electric discharge)

6. 2- Cathode and anode
use to generate electric discharge
3- Reflectors
Combination of mirrors
One is perfectly reflecting and the other is partially
4-Active medium
Mixture of he ne gas which is responsible for
atom excitation

7. WORKING OF THREE LEVEL LASER
o Energy level diagram

8.  Three energy levels required (ie Ground state, Metastable state
and Ordinary excited state).
 Pumping of atom is done from Ground state E1 to ordinary
excitated state E3.
 Energy of photon hv=E3-E1.
 Spontaneous emission take place ie some atoms falls to ground
state E1 and some on metastable state E2.
 Further atoms falls from metastable state to ground state by
stimulated emmision which produces the lasing action.
 A problem arised when the photon responsible for lasing action
also cause indused absorption which severely effect the lasing
action.
 This was 1 of its major drawback!!!

9. WORKINGOF HELIUM-NEONLASER
Energy level diagrams of four level larser
(2 metastable state M1 & M2)

10.  Mixture of He & Ne in ratio 10:1 at 1 torr is kept in a glass tube.
 Due to electric discharge He atom collide with the electrons and
get excited to reach the ordinary excited state(20.61eV).
 These excited He atom transfer their energy through collision to
Ne atoms (unexcited) to reach at an energy level at 20.66eV.
 Due to spontanious emission the Ne atoms falls on metastable
state M2.
 At metastable state 2 stumilated emission takes place and the
neon atoms falls on metastable state 1 (M1).
 This transition results in lasing action of He-Ne laser.

11.  Lasing energy is same as the energy difference of the two
metastable states.
 Further a radiation less transiton takes place due to which
atom at metastable state 1 eaches he ground state.
 Thus the laser light produced in He-Ne laser is Dense,
Non-pulsating & unidirectional.

12. POINTS TO REMEMBER
 Four energy states are required.
 The metastable state should near to ordinary excited state
and ground state.
 The lifetime of metastable state 2(near oes) should be longer
to facilitate population inversion.
 The lifetime of metastable state 1(near gs) should be very
short so as to rapidly get depopulated to avoid re-absoption.
 Purpose of having He atoms in He-Ne laser is to help the
population inversion of Ne atoms.

13. COMPARISION OF THREE & FOUR
LEVEL LASER’S ENERGY DIAGRAM

14. CHARACTERISTIC
The light is extremly monochromatic with
wavelength 632.8nm.
The light has high temporal coherence.
The light is unidirectional and aligned.
The light is spatially coherent.

15. application of he–ne laser
1- He-Ne lasers are produced in large quantities from
many years.
2- Many schools / colleges / universities use this type
of laser in their science programs and experiments.
3- He-Ne lasers also used in super market checkout
counters to read bar codes and QR codes.
4- He-Ne lasers can be use as an alignment tool
5-It is also used in Guns for targeting.

16. ADVANTAGES OF HE –NE LASER
1- It is used in Guns for targeting.
2- He-Ne laser provide inherent safety due
to low power output
3- He-Ne laser tube has very small length
approximately from 10 to 100cm and best
life time of 20.000 hours.

17. DISADVANTAGE OF HE-NE LASER
1- It is relatively low power device means
its output power is low.
2- He-Ne laser is low gain system/ device
3- High voltage requirement can be
considered its disadvantage.
4- Escaping of gas from laser plasma
tube is also its disadvantage