# 15.3 Lasers

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## Lasers

A laser is a device that produces a special type of light: all the laser photons are identical! They all have the same wavelength (and frequency), amplitude and phase. Since they all have the same wavelength, this means they all have the same colour and the light is called monochromatic . ( Note: mono means "one" or "single" and chromatic means "colour".) This is very different to most other light sources which produce light with a range of wavelengths (e.g. white light from the sun consists of all the visible wavelengths.)

Laser light is highly directional and can be focused very well. This focus allows laser beams to be used over long distances, and to pack a lot of energy into the beam while still requiring reasonably small amounts of energy to be generated. Each centimetre of a typical laser beam contains many billions of photons. These special properties of laser light come from the way in which the laser photons are created and the energy levels of the material that makes up the laser. These properties make laser light extremely useful in many applications from CD players to eye surgery.

The term LASER stands for L ight A mplification by the S timulated E mission of R adiation. This stimulated emission is different to the spontaneous emission already discussed earlier. Let's review the absorption and emission processes which can occur in atoms.

• Absorption : As you can see in the picture above, absorption happens when an electron jumps up to a higher energy level by absorbing a photon which has an energy equal to the energy difference between the two energy levels.
• Spontaneous emission : Spontaneous emission is when an electron in a higher energy level drops down to a lower energy level and a photon is emitted with an energy equal to the energy difference between the two levels. There is no interference in this process from outside factors. Usually spontaneous emission happens very quickly after an electron gets into an excited state. In other words, the lifetime of the excited state is very short (the electron only stays in the high energy level for a very short time). However, there are some excited states where an electron can remain in the higher energy level for a longer time than usual before dropping down to a lower level. These excited states are called metastable states.
• Stimulated emission : As the picture above shows, stimulated emission happens when a photon with an energy equal to the energy difference between two levels interacts with an electron in the higher level. This stimulates the electron to emit an identical photon and drop down to the lower energy level. This process results in two photons at the end.
Spontaneous Emission

Spontaneous emission occurs when an atom is in an unstable excited state and randomly decays to a less energetic state, emitting a photon to carry off the excess energy. The unstable state decays in a characteristic time, called the lifetime.

Meta-stable state

A meta-stable state is an excited atomic state that has an unusually long lifetime, compared to the lifetimes of other excited states of that atom. While most excited states have lifetimes measured in microseconds and nanoseconds ( ${10}^{-6}$ s and ${10}^{-9}$ s), meta-stable states can have lifetimes of milliseconds ( ${10}^{-3}$ s) or even seconds.

Do polymers form restrictedly only if compound is saturated, only?
what is a free fall?
is when The Only Force acting On an Object is Gravitational Force
Thats right
Beyanca
She's just helping those who forgot it...bro
Thato
guys I need help on Getting ready for a last minute test
Neil
we'll I'm in grade 12 so we doing this topic about upac thing
Kenelioe
on What?
the organic molecule section
Kenelioe
IUPAC NAMING WHICH FUNCTIONAL GROUP YOU CANNOT NAME?SO I COULD HELP YOU
ester
Sboniso
you should also look at structural isomers. Its crucial that they might add that one. also try and write down the structural formula of all the given compounds on the table
milani
hi guys i can explain everything in terms of physics and chemistry
😂😂😂😂😂
yes
Lucky
yea
Kenelioe
guys 2mrrow I'm writing a test in chemistry I need help
Kenelioe
Hi guys. Can anyone please tell me what a functional group is?
Samukelo
a functional group depends on how many bonds there are between carbon atoms, if there are single bonds all the way it's an alkane, if there is a presence of at least one double bond it's a Alkene and if there's at least one triple bond it's an alkyne.
Olive
which quantity is measured in Watt?
work
Absai
explain for me absai
Sboniso
is Power Not Work work is Measured In Joules it has Energy
thanks
Saara
Pleasure
what is galvanic cell ?
is an electrochemical cell that derives electrical energy from spontaneous redox reactions taking place within the cell.
Hope
how to understand alkane names
suffix Ane in the IUPAC NAMING
elaborate a little more plz
Kenelioe
Alkanes are Saturated Meaning they don't have Multiple Bonds between Carbon Atoms and When you are Naming THEM THEY MUST END WITH (-ANE ) GET ME?
What are hydrocarbons
are organic Compounds with only Carbon and Hydrogen Atoms
whats the difference between aldehydes and ketones
definition of chain parent
what is wave?
when butane burns in an excess of oxygen ,the products are
Slay
CO2 and H2O
GARY
Carbon dioxide and Water...
Thato
what is hydrocarbon
Hydrocarbon is a compostion of mainy carbon and hydrogen
Tsion
hydrocarbon compound made up of carbon and hydrogen only
Thembelani
25 element of physics
an object will remain at rest or move at a constant velocity unless acted upon a net force
thank you
Thabiso
law of inertia
Joan
an object resisting the change in velocity.
Thabiso
newton first law of motion
Tshepo
An object will remain at rest, unless an unbalanced force acts on it.
Anga
or uniform motion
Thato
What is a molecule
a molecule is a simplest structure unite of an elements
Else
thank you
Thabiso
Plz remind me the 1st Newton's law
Thabiso