Carbon di oxide Laser

Features :
Active Medium : mixture of CO2+ N2+He
Active centre : CO2 molecule
Pumping method : Inelastic collision of N2 with CO2
Resonators : Concave reflecting mirrors are provided at both
the ends of laser rod.
Output nature : continuous at 10.6 micrometre
Output power : 70 K watts
Wavelength : 9.6 micron and 10.6 microns

Modes of vibration of CO2 molecules :


i) Stretched symmetric mode (100)

In this mode, the carbon atom and oxygen atoms are in the same plane and oxygen atoms vibrate along the axis of the molecule.

ii) Bending mode (010)(020)
In this mode, the oxygen atoms and carbon atom vibrate perpendicular to the axis of the molecule.

iii) Antisymmetric mode (001)(002)
In this mode, the oxygen atoms vibrate asymmetrically with carbon atom . When oxygen atoms move in one direction, the carbon atom moves in opposite direction.

Construction :



It consists of a quartz discharge tube of length 5 m and 2.5 cm in diameter. The terminals of discharge tube are connected to dc power supply. Two concave mirrors are provided to give laser oscillations the necessary optical gain. Two Brewster windows made up of NaCl are provided to make the output beam a polarized one.

Working :

Mixture of gases, CO2, N2, and He are taken into the discharge tube in appropriate proportions. When the dc supply is switched on, the nitrogen atoms are first excited by the accelerated electrons.

e* + N2 = N2* + e



The excited Nitrogen atoms collide with co2 atoms and resonant collision energy transfer takes place and CO2 molecule is excited now.

N2* + Co2 = Co2* + N2

Among the excited energy levels of CO2 atoms, laser transitions take place . From the asymmetric mode vibrational energy level(001) to bending mode (020), laser emission takes place with wavelength of 9.6 μm and another laser emission of 10.6 μm is from asymmetric mode(001) to symmetric mode (100).

Advantages :

1. Output of the laser is continuous
2. It has high efficiency
3. It has high output power
Disadvantages :
1. Contamination of oxygen by CO affects laser action
2. Operating temperature may influence output power
3. corrosion may occur in reflecting plates.