1

Laser Physics I PH481/581-VTA (Mirov)

Introduction to Two Practical Laser Systems. The Ruby Laser. The Helium-Neon Laser

Lecture 5 chapter 3

Fall 2017C. Davis, “Lasers and Electro-optics”

2

Schematic Energy level Diagram of Three and Four Level Lasers

3

Threshold inversion in three and four-level lasers

3 2 1 0

If th e to ta l n u m b er o f p a rtic le s p e r u n it vo lu m e p a rtic ip a tin g in th e p u m p in g an d la s in gp ro cess is w e can w rite

, (3 .1 )In a th ree -leve l la se r, leve l 1 is e ssen tia lly th e g ro u n d

NN N N N N

3 2 1

2 1

s ta te , so, (3 .2 )

In a g o o d th ree -leve l la se r, leve l 3 sh o u ld tran sfe r its ex c ita tio n ve ry rap id ly to leve l 2 , so. (3 .3 )

T h e th resh o ld in vers io

N N N N

N N N

22 1

1

2

12 3

2

1

2 1 2

n is

. (3 .4 )

F ro m E q s . (3 .3 ) an d (3 .4 ),

( ) , (3 .5 )1

w h ich , if , g ives .2F o r a g o o d fo u r-leve l la se r in w h ich th e lo w er la se r leve l r

t

t

leve l

gN N Ng

g N NgN g

gNg g N

2 4

2

2 13

22 41

em ain s re la tive ly d ep o p u la ted .

, th e ra ltive ra te a t w h ich leve l 2 m u s t b e ex c ited to p ro d u ce an in vers io n is

. (3 .6 )1

U su a lly , , an d fo r

tleve l

tleve l

leve l t

t

N N

g N NN ggN Ng

N N

2 1

4

th e s im p le case th e ra tio o f p u m p in g ra te s b eco m es

. T h is n u m b er can eas ily b e 1 0 o r m o re .2 t

g gN

N

4

Introduction to Two Practical Laser Systems

The Ruby Laser

5

6

7

Simple Electrical Circuit for Driving a Flashlamp

8

9

Schematic Arrangement of Maiman’s Original Ruby Laser

Elliptical reflector for optical pumping of a laser crystal by a linear flashlamp

10

The Helium-Neon Laser

11

Energy level Diagram for the Helium-Neon Laser

12

Schematic Arrangement of the First Gas Laser

13

Typical Schematic Design of a Modern Gas Laser