This lecture briefly describes the construction and working of the Ruby LASER, the first laser system.

1. By
Dr. Arpana Agrawal
Assistant Professor
Department of Physics
(For Master’s students)
Shri Neelkantheshwar Government PostGraduate College, Khandwa, India
UNIT III: Types of LASERS

2. Types of LASERS: Introduction
On the basis of Active medium
-depending on the state of active medium
-(solid/liquid/gas)
On the basis of mode of operation
-Continuous wave mode (CW)
-Pulsed mode
On the basis of laser levels
-3-level laser system
-4-level laser system

3. Types of LASERS on the basis of active medium
 Solid State lasers: Active medium-Solid form
eg. Ruby laser; Nd:YAG laser etc
 Gas lasers: Active medium-Gaseous form
e.g. He-Ne laser; Carbon-di-oxide (CO2) laser etc
 Liquid lasers: Active medium-Liquid form
e.g. Dye lasers-Rhodamine laser; Polymethene laser etc
 Semiconductor lasers: Active medium-Semiconductors
e.g. GaAs laser; InP laseretc.
 Chemical lasers: based on chemical reactions
e.g. HCl; HF etc.
Types of LASERS: Introduction

4. Lecture I: Solid state laser: Ruby laser
Lecture II: Solid state laser: Nd:YAG laser
Lecture III: Gas laser: He-Ne laser
Lecture IV: Gas laser: CO2 laser
Lecture V: Semiconductor laser: GaAs
Lecture VI: Liquid/Dye lasers
Lecture VII: Chemical lasers: HCl and HF
Lecture VIII: Summary (Recapitulation of UNIT IV)
Content of UNIT-IV

5. Lecture I: Solid state laser: Ruby laser
Topics to be covered under Lecture I
• Introduction and Construction
-Active medium
-Pumping method
-Optical resonator
• Working: Energy level diagram
• Advantage and Disadvantages of Ruby LASER
• Applications
• Summary

6. Ruby rod
Xenon flash tube
Laser
(Coherent)
(694.3 nm)
M2
M1
Electrode
Electrode
Power
supply
Solid-state laser, three-level laser system, and first laser invented and operated by Theodore H
Maiman at Hughes Research Laboratories on 16th May 1960
Cross-sectional view
Construction
-Active medium: Single crystal of Al2O3:Cr3+ in the form of cylindrical rod
-Pumping method: Optical pumping using Xenon flash lamp (Helical); rolled over ruby rod
-Optical resonator: Ends of the ruby rod are kept in between two optically coated mirrors,
silvered differently.
Introduction and Construction
M1: Fully reflecting mirror (100%); M2: Partially reflecting mirror (99%)

7. Metastable state
(10-3 sec)
Ground state
(10-8 sec)
Excited state (4F1)
Excited
state (4F2)
Laser Output
(red ; 694.3 nm)
Working: Energy level diagram of Cr3+ ions in Ruby
Pumping
region
Laser transition
400λ(nm)500600700

8. Disadvantages
• The laser requires high pumping power because the laser transition
terminates at the ground state and more than half of ground state atoms
must be pumped to higher state to achieve population inversion.
• The efficiency of ruby laser is very low because only green component of
the pumping light is used while the rest of components are left unused.
• The laser output is not continuous but occurs in the form of pulses of
microseconds duration.
• The defects due to crystalline imperfection are also present in this laser.
Advantages-
• Ruby lasers are economical.
• Construction and function of ruby laser is self explanatory.
Advantages and Disadvantages of Ruby LASER

9. • Ruby lasers have declined in use with the discovery of better lasing media.
They are still used in a number of applications where short pulses of red light
are required.
• Low output power, so are used as toys for children.
• Used in schools, colleges, universities for science programs.
• Used as decoration piece & artistic display.
• Holographers around the world produce holographic portraits with ruby
lasers, in sizes up to a metre squared.
• Many non-destructive testing labs use ruby lasers to create holograms of
large objects such as aircraft tires to look for weaknesses in the lining.
• Ruby lasers were used extensively in tattoo and hair removal
Applications

10. Summary
Type Solid state laser;
Three- level laser system
Active medium Ruby rod (Cr: Al2O3)
Active centre Cr3+ ion
Pumping method Optical pumping
Pumping source Helical flash lamp of filled with Xenon
Optical resonator The ends of the ruby rod are kept in between two
optically coated mirrors, silvered differently.
Output power Low
Nature of the output Pulsed (Spiked)
Wavelength emitted 693.4 nm
Summary
Thank you
Lecture II-to be contd…