helium neon laser

1. Helium-neon Lazer

2. Presented BY
NAME : ROHINI YADUWANSHI
CLASS: BSC VI SEM (C.S)
COLLEGE: RAI SAHEB BHANWAR
SINGH COLLEGE
NASRULLAGANJ
SUBMITTED TO: GYANRAO DHOTE SIR

4. Historical facts
• The Helium-Neon laser was the first continuous
laser.
• It was invented by Javan et. al. in 1961. But
how did Javan manage to do this?
• This shows that it is no coincidence that Javan's
first He-Ne laser oscillated at a
• Wavelength of 1.5μm, since the amplification at
this wavelength is considerably

5. •Higher than the 632 nm line which is reached at what is
now commonly known as the red line, which was made to
oscillate only one year later by White and Ridgen.
•The similarity between the manufacturing techniques of
He-Ne lasers and electron valves helped in the mass
production and distribution of He-Ne lasers..
•It is now clear that He-Ne lasers will have to increasingly
compete with laser diodes in the future. But He-Ne lasers
are still unequalled as far as beam geometry and the purity
of the modes are concerned.
•Laser diodes will have to be improve to a great extent
before they pose a serious threat to helium-neon laser

6. Introduction
• A helium-neon laser, usually called a He-Ne
laser, is a type of small gas laser. HeNe lasers
have many industrial and scientific uses, and are
often used in laboratory demonstrations of
optics.
• He-Ne laser is a four-level laser.
• Its usual operation wavelength is 632.8 nm, in
the red portion of the visible spectrum.
• It operates in Continuous Working (CW) mode.

7. Construction of He-Ne laser
• The setup consists of a discharge tube of length
80 cm and bore diameter of 1.5cm.
• The gain medium of the laser, as suggested by
its name, is a mixture of helium and neon gases,
in a 5:1 to 20:1 ratio, contained at low pressure
(an average 50 Pa per cm of cavity length ) in a
glass envelope.

8. • The energy or pump source of the laser is provided by
an electrical discharge of around 1000 volts through an
anode and cathode at each end of the glass tube. A
current of 5 to 100 mA is typical for CW operation.
• The optical cavity of the laser typically consists of a
plane, high-reflecting mirror at one end of the laser
tube, and a concave output coupler mirror of
approximately 1% transmission at the other end.
• HeNe lasers are normally small, with cavity lengths of
around 15 cm up to 0.5 m, and optical output powers
ranging from 1 mW to 100 mW.

10. He-Ne Energy level diagram
• The left side of the representation shows the lower levels of the helium
atoms.The energy scale is interrupted and that there is a larger
difference in energy in the recombination process than is evident in the
diagram.
• A characteristic of helium is that its first states to be excited, 21S1 and
21S0 are metastable, i.e. optical transitions to the ground state 11S0
are not allowed, because this would violate the selection rules for
optical transitions. As a result of gas discharge, these states are
populated by electron collisions

11. A collision is called a collision of the second type if one
of the colliding bodies transfers energy to the other so
that a transition from the previous energy state to the
next higher or lower takes place. Apart from the electron
collision of the second type there is also the atomic
collision of the second type. In the latter, an excited
helium atom reaches the initial state because its energy
has been used in the excitation of a Ne atom. Both
these processes form the basis for the production of a
population inversion in the Ne system.

13. Working of He-Ne laser
• A description of the rather complex HeNe excitation
process can be given in terms of the following four
steps.
• (a)When the power is switched on, An energetic electron
collisionally excites a He atom to the state labeled 21So .
A He atom in this excited state is often written
He*(21So), where the asterisk means that the He atom
is in an excited state.

14. (b) The excited He*(21So) atom collides with an
unexcited Ne atom and the atoms exchange
internal energy, with an unexcited He atom and
excited Ne atom, written Ne*(3s2), resulting.
This energy exchange process occurs with high
probability only because of the accidental near
equality of the two excitation energies of the two
levels in these atoms. Thus, the purpose of
population inversion is fulfilled.

15. • When the excited Ne atom passes from metastable state(3s) to lower
level(2p), it emits photon of wavelength 632 nm.
• This photon travels through the gas mixture parallel to the axis of tube,
it is reflected back and forth by the mirror ends until it stimulates an
excited Ne atom and causes it to emit a photon of 632nm with the
stimulating photon.

17. The stimulated transition from (3s) level to
(2p) level is laser transition.
This process is continued and when a
beam of coherent radiation becomes
sufficiently strong, a portion of it escape
through partially silvered end.
The Ne atom passes to lower level 1s
emitting spontaneous emission. and
finally the Ne atom comes to ground state
through collision with tube wall and
undergoes radiationless transition.

18. Applications of He-Ne laser
• The Narrow red beam of He-Ne laser is
used in supermarkets to read bar codes.
• The He- Ne Laser is used in Holography in
producing the 3D images of objects.
• He-Ne lasers have many industrial and
scientific uses, and are often used in
laboratory demonstrations of optics.

19. Thanks For
Your
Attention