38 Chapter 1. Properties and Sources of Radiation
gas atom (such as argon, krypton, or xenon) with a halogen atom (chlorine,
flourine, bromine, iodine). Such molecules can only be produced in a short-
lived excited state with a lifetime of less than 10ns. These lasers are also
referred to as Exiplex (excited complex).
Ions:The lasing medium of such a laser is generally an ionized noble gas such
asAr+orKr+. Since most of the wavelengths of these low power lasers fall
within the visible region of spectrum, they are extensively used in entertain-
ment industry to produce laser light shows.
Metal Vapors: Lasing action can also be produced in metal vapors such as
those of gold, silver, and copper. These lasers are very efficient and capable of
delivering high pulsed power.Liquid Lasers
Using liquid as a lasing material is best demonstrated by the so called dye lasers.
These lasers use a combination of liquid organic dyes to produce laser light with
wavelengths that can be tuned over a specific region of the spectrum. The dyes used
in such systems are fluorescent materials. To force the population inversion another
light source is used, which may simply be a lamp or another laser. Nd-YAG laser
is commonly used to pump dye lasers. Other Excimer or continuous wave lasers are
also extensively used for the purpose. Both pulsed and continuous mode of oper-
ation are available in dye lasers. A commonly used dye is Rhodamine-6G, which
produces a spectrum of light centered at 590nm. When pumped with a continuous
wave laser, it can produce a power of about 1kW h. The main advantage of dye
lasers is that they can be selectively tuned to output laser in a specific wavelengths
range. Another advantage of using dyes as lasing media is the very broad range of
laser wavelengths that can be produced.
Solid State Lasers
The solid lasing media can be conveniently categorized according to their electri-
cal conduction properties.
Insulators:The first lasing material successfully used to generate laser light
was Ruby crystal (Al 2 O 3 withCr+3as low level impurity). Since then a large
number of electrically insulated solids have been identified as efficient lasing
media. Common examples of such materials are Nd-YAG and Ti-Sapphire.Semiconductors:Semiconductors have been found to be extremely cost ef-
fective in producing low power laser light. Because of their small size and ease
in production these lasers are widely used in consumer products, such as laser
printers and CD writers.New Developments
During the past two decades a lot of research has been carried out to develop
highly intense and powerful lasers. Most of these research activities have focused on
producing lasers in the ultraviolet and x-ray regions of the electromagnetic spectrum.
Production of coherent light in these regions was first successfully demonstrated in