How Lasers Work - A Complete Guide

Summary

This script delves into the fascinating world of lasers, explaining their ubiquitous presence in both scientific research and industry. It begins with the history of the laser, from Einstein's concept of stimulated emission in 1917 to the first working laser in 1960. The script highlights lasers' unique properties: their narrow line width for monochromatic light, coherence for synchronized photon behavior, and the ability to focus high intensity light into a small area. It then breaks down the complex quantum mechanics behind laser operation, including stimulated absorption, spontaneous emission, and the crucial stimulated emission process. The explanation of how a laser cavity supports specific frequencies and the role of the gain medium in determining the emitted light's color complete this comprehensive overview.

Takeaways

• 🌟 Lasers are widely used in both scientific research and industry for their unique properties.
• 🔤 The term 'laser' is an acronym for 'Light Amplification by Stimulated Emission of Radiation'.
• 📚 The concept of the laser was introduced by Einstein in 1917, with the first working laser being developed by Theodor Maiman in 1960.
• 🔴 The first laser used synthetic Ruby to excite atoms to higher energy levels, creating a powerful beam of light.
• 🎯 Lasers are characterized by three main properties: narrow line width (monochromaticity), coherence, and the ability to focus high intensity light into a small area.
• 🔬 The purity of a laser's light, known as line width, is much narrower than other light sources, making it ideal for scientific experiments requiring specific energies.
• 🌀 Coherent light from a laser is polarized and in phase, similar to an orchestra playing in sync, allowing for the concentration of light energy over a distance.
• 💡 The high intensity of lasers is useful in applications such as military targeting and medical procedures like laser eye surgery.
• 🤔 The functioning of a laser involves complex quantum mechanics, including stimulated absorption, spontaneous emission, and stimulated emission.
• 🔄 To create a laser, a population inversion is necessary where there are more electrons in the excited state than the ground state, favoring stimulated emission.
• 🔍 A laser cavity with mirrors helps to create standing waves through constructive interference, amplifying the light waves and producing a coherent beam.
• 📏 The allowed frequencies in a laser cavity are determined by the cavity's length and the speed of light, with imperfections in the mirrors broadening these frequencies slightly.

Q & A

What does the acronym LASER stand for?

LASER stands for Light Amplification by Stimulated Emission of Radiation.

When was the concept of stimulated emission introduced by Einstein?

The concept of stimulated emission was introduced by Einstein in 1917.

What was the first device based on Einstein's predictions that achieved amplification and generation of electromagnetic waves?

The first device was the MASER (Microwave Amplification by Stimulated Emission of Radiation), demonstrated by Charles Townes in 1954.

Who developed the first working laser and when was it developed?

Theodor Maiman developed the first working laser at Hughes Research Lab in 1960.

What are the three unique properties of a laser?

The three unique properties of a laser are line width (monochromaticity), coherence, and the ability to deliver high-intensity light to a small area.

What is the significance of a laser's narrow line width?

A narrow line width signifies that the emitted light is close to a single frequency, which is useful for scientific experiments that require analysis with specific energies.

How does coherence in a laser differ from the light emitted by an LED?

Coherent light from a laser is polarized in the same direction and is in phase, whereas an LED emits incoherent light where the light waves are not synchronized.

What is the process called when an electron in an excited state falls back down to a lower energy state and emits a photon?

This process is called spontaneous emission.

What is stimulated emission and why is it important for lasers?

Stimulated emission is when an excited electron is forced to fall back to a lower energy state by a photon, emitting an identical photon in the process. It is important for lasers because it allows for the creation of a beam of identical, coherent photons.

What is a population inversion and why is it necessary for a laser to operate?

A population inversion is a condition where there are more electrons in the excited state (metastable state) than in the ground state. It is necessary for a laser to operate because it allows for the continuous stimulated emission of photons.

How does a laser cavity contribute to the amplification of light?

A laser cavity, with a mirror on one side and a partial mirror on the other, allows light waves to reflect back and forth, creating standing waves through constructive interference, which amplifies the light through stimulated emission.

What is the role of the gain medium in a laser?

The gain medium is the material in a laser that provides the energy levels necessary for stimulated emission. Different materials will emit photons of different energies, determining the laser's output frequency.

How do the allowed frequencies in a laser cavity relate to the laser's output frequency?

The allowed frequencies in a laser cavity are the frequencies that can resonate within the cavity and produce standing waves. The laser's output frequency must be one of these allowed frequencies that also falls within the gain medium's emission range.

What factors cause the broadening of the frequency range emitted by a laser?

Factors such as the Doppler effect, Stark effect, and other quantum mechanical behaviors cause the broadening of the frequency range emitted by a laser, resulting in a gain curve rather than a single frequency.

Outlines

00:00

🌌 Introduction to Lasers and Their History

This paragraph introduces the ubiquity of lasers in both scientific research and industry. It explains the acronym LASER, which stands for 'Light Amplification by Stimulated Emission of Radiation', and provides a brief historical context starting with Einstein's introduction of stimulated emission in 1917. The first working laser was developed by Theodor Maiman in 1960 using a synthetic ruby. The paragraph also outlines the collaborative nature of the laser's development and hints at the unique properties of lasers that make them so useful.

05:01

🔍 The Unique Properties and Utility of Lasers

This section delves into the three main properties that make lasers so versatile: line width, coherence, and power. Line width refers to the purity of the laser light, which is much narrower than any other light source, making it monochromatic. Coherence describes the laser light's uniform polarization and phase, akin to an orchestra playing in sync. Lastly, the power of lasers allows for the concentration of high-intensity light in a small area, which is beneficial for various applications, including military and medical uses such as laser eye surgery.

10:01

🔬 Quantum Mechanics Behind Laser Operation

This paragraph explains the complex workings of a laser, grounded in quantum mechanics. It discusses the fundamental processes of stimulated absorption, spontaneous emission, and stimulated emission. Stimulated absorption occurs when a photon boosts an electron to a higher energy state. Spontaneous emission is the natural decay of an excited electron back to a lower state, releasing a photon. Stimulated emission is pivotal for lasers, where an incoming photon triggers an excited electron to emit an identical photon, leading to a coherent light beam. The paragraph also introduces the concept of metastable states, which are essential for creating the population inversion necessary for laser action.

15:02

🏗️ Constructing a Laser: The Laser Cavity and Resonance

This section describes the construction of a laser cavity, which is crucial for amplifying light waves through constructive interference. The cavity typically consists of a fully reflective mirror and a partially reflective mirror, allowing some light to escape as the laser beam. The paragraph explains how light waves are amplified through stimulated emission within the cavity, leading to the formation of standing waves due to resonance. These standing waves are the result of multiple light waves interfering constructively, and the conditions for their formation are governed by an equation relating the cavity's length, the mode number, and the speed of light.

20:04

📊 Laser Cavity Frequencies and Gain Medium

The final paragraph discusses the allowed frequencies within a laser cavity and how they are determined by the cavity's dimensions and the speed of light. It explains that not all frequencies can resonate within the cavity, and the specific frequencies are influenced by the cavity's imperfections. The paragraph also introduces the concept of the gain medium, which is the material used in a laser to produce light through stimulated emission. Different materials are used for different laser frequencies, and the emitted frequencies are influenced by various quantum mechanical effects, resulting in a gain curve that represents the range of frequencies the laser can emit.

🌈 Conclusion: The Variety of Laser Materials

Concluding the script, this paragraph highlights the wide variety of laser materials available, including gases, solids, and even liquids, which enable the creation of lasers emitting a broad spectrum of frequencies. The paragraph wraps up by encouraging viewers to engage with the content and supporting the channel, reinforcing the educational value of the video.

Keywords

💡Laser

A laser is a device that emits light through a process of optical amplification based on the stimulated emission of radiation. In the video, lasers are discussed as ubiquitous tools in both scientific research and industry, known for their powerful and coherent beams of light. The acronym 'laser' stands for 'light amplification by stimulated emission of radiation,' highlighting the core principle of its operation.

💡Stimulated Emission

Stimulated emission is a quantum mechanical process where an excited electron drops to a lower energy state under the influence of an external photon, emitting a photon with identical properties. This concept, introduced by Einstein in 1917, is fundamental to the operation of a laser, as it is the basis for the amplification of light. The script explains how stimulated emission leads to the production of coherent light, which is a key feature of lasers.

💡Line Width

Line width, in the context of the video, refers to the purity of the laser light, which can be quite narrow, indicating a closeness to a single frequency or color. This property is important for scientific experiments that require analysis with specific energies, as different wavelengths of light correspond to different energies. The script uses the term to contrast the monochromatic nature of laser light with the broad spectrum emitted by an incandescent bulb.

💡Coherence

Coherence, in the script, describes the property of laser light where all emitted photons are polarized in the same direction and are in phase with each other. This results in highly coherent monochromatic light, which is different from the incoherent light emitted by LEDs. Coherence is crucial for focusing the light on a small spot over a distance and is illustrated through the analogy of a synchronized orchestra.

💡Power

Power, in relation to lasers, refers to the ability to deliver a high-intensity light to a small area. The script mentions that this property is of particular interest to military and medical applications, such as laser eye surgery. The power of a laser is what makes it stand out for precision tasks that require intense energy concentration.

💡Quantum Mechanics

Quantum mechanics is the fundamental theory in physics that describes how the physical world operates at the smallest scales. The script requires an understanding of quantum mechanics to explain the workings of a laser, including the processes of stimulated absorption, spontaneous emission, and stimulated emission, which are all quantum phenomena.

💡Metastable State

A metastable state, as discussed in the script, is an excited state of an electron with a longer lifetime than typical excited states, allowing for more time to undergo stimulated emission. The concept is crucial for creating a population inversion, which is necessary for the laser to emit light effectively. The script explains how metastable states facilitate the laser's operation by providing a longer-lived state for electrons before they emit photons.

💡Population Inversion

Population inversion is a condition where a majority of electrons in a laser medium are in a higher energy state (metastable state) than in the ground state. This is essential for a laser to function, as it allows for the stimulated emission process to dominate over spontaneous emission, resulting in a cascade of identical photons that make up the laser beam. The script describes how achieving population inversion is a key step in laser operation.

💡Cavity

In the context of the video, a cavity refers to the resonant space within a laser that contains the gain medium and has mirrors at both ends. The script explains how the cavity, through constructive interference, amplifies the light waves produced by stimulated emission, creating a high-intensity beam. The cavity's design is crucial for determining the frequencies that can resonate and thus be emitted by the laser.

💡Gain Medium

The gain medium is the material within a laser that provides the energy levels necessary for stimulated emission to occur. Different materials are used for different types of lasers, emitting photons of varying energies. The script discusses how the gain medium's properties determine the frequencies of light that can be amplified within the laser cavity.

💡Doppler Effect

The Doppler effect, mentioned in the script, refers to the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. In the context of lasers, it contributes to the broadening of the emitted frequency spectrum, making the laser light not perfectly monochromatic but close enough for most applications.

Highlights

Lasers are ubiquitous in both scientific research and industry, used for various applications from hair removal to popping balloons.

Laser stands for Light Amplification by Stimulated Emission of Radiation, a term coined by Einstein in 1917.

The first laser was developed in 1960 by Theodor Maiman at Hughes Research Lab, using synthetic ruby as the lasing medium.

Lasers are valuable due to their narrow line width, meaning they emit light at a very specific frequency, which makes them monochromatic.

Coherence is a key property of lasers, meaning the emitted light is all polarized in the same direction and in phase.

Lasers can deliver high-intensity light to a small area, which is crucial for applications like laser eye surgery and military uses.

The process of laser operation involves stimulated absorption, spontaneous emission, and stimulated emission.

Stimulated absorption occurs when a photon excites an electron to a higher energy state.

Spontaneous emission happens when an excited electron falls back to a lower energy state, releasing a photon.

Stimulated emission is critical for lasers, where an incoming photon causes an excited electron to emit a second, identical photon.

Lasers require a population inversion, where more electrons are in an excited state than in the ground state.

Laser cavities amplify light by constructive interference, using mirrors to reflect light back and forth.

The gain medium in a laser determines the wavelength of the emitted light, with different materials producing different colors.

Standing waves in the laser cavity produce resonance, amplifying the light to create the laser beam.

Modern lasers can use various materials, including gases, solids, and liquids, to produce a wide range of wavelengths.

Transcripts

everyone has seen them and have probably

teased many cats with them maybe some of

you have had unwanted hair removed or

maybe you have built one and popped some

balloons with it bottom line lasers are

ubiquitous not only in scientific

research but also in Industry just how

do these little devices manage to put

out that nice powerful cated beam of

light all this and more coming up as

some may or may not know laser is

actually an acronym it stands for light

amplification by stimulated emission of

radiation however nowadays it is so

common that people don't bother to

capitalize it and simply write laser a

very brief history of the laser starts

in 1917 when Einstein introduced the

concept of stimulated emission which

will be explained shortly then in 195

before the first Mesa was demonstrated

by Charles towns the M standing for

microwave the ammonia Mesa was the first

device based on Einstein's predictions

and obtained the first amplification and

generation of electromagnetic waves with

a wavelength of about 1 cm which is in

the microwave range this is recognized

as the precursor to the laser it wasn't

until 1960 when Theodor mayam developed

the first working laser at Hughes

research lab mayon's early laser used a

powerful energy source to excite atoms

in a synthetic Ruby to higher energy

levels the development of the laser was

a collaborative effort by scientists and

Engineers who were leaders in Optics and

photonics okay so why are lasers useful

why are they ubiquitous the answer can

be broken down to three unique

properties the laser holds the first

being line width the purity of a laser

referred to as the line width can can be

quite narrow more so than any other

light source in layman's terms this is a

measure of what frequencies are

contained in the emitted light the

narrower the line withd the closer the

emitted light is to a single frequency

single color if you will thus a laser is

said to be monochromatic in reality it

does output a small range of

frequencies the smaller this range the

better the line width and quality of the

laser in contrast an incandescent bulb

has a very large line width and emits

the broad spectrum which is why the

emitted light is white white light is a

superposition of all the colors in the

visible

spectrum having a narrow line width is

useful because many scientific

experiments want to analyze stuff with

certain energies different wavelengths

of light corresponds to different

energies hence having a source with one

energy is helpful the second is

coherence the light emitted by a laser

is coherent light this means it is all

polarized in the same direction as well

as being in Phase the laser is said to

Output highly coherent monochromatic

light and led on the other hand is also

monochromatic one color but it emits

incoherent light an analogy with

synchronization and Harmony can be made

imagine an orchestra playing if the

orchestra is in sync and everyone is

playing the parts correctly it will be

pleasing to the ear the laser if some

players are playing out of sync but

still playing the parts correctly it

won't sound as good the D coherence is

important because all the photons add

their energies together and we can then

focus them on a small spot over some

distance lastly power lasers make it

possible to deliver High intense light

to a small area of course militaries are

particularly interested in this aspect

of the laser as well as medical

applications laser ey surgery for

example now let's take a look at how a

laser works the workings of a laser are

quite complex as it requires an

understanding of quantum mechanics there

are some commonalities behind every

laser the first part can be broken down

to three key pieces stimulated

absorption spontaneous emission and

stimulated emission which is what the SE

part of laser stands for let's take a

look at the first concept stimulated

absorption we will need a nucleus that

is made up of protons and neutrons that

has an overall positive charge and an

electron that has a negative charge

hey there little guy most textbooks show

electrons existing in discrete energy

states of a material but actually

electrons exist in probability density

clouds around the nucleus as they have

wave likee Behavior and the orbitals

represent the average distance one is

likely to find it let's use this average

distance to define the orbital and

ignore the probability distribution for

Simplicity mostly always electrons are

found in the lowest energy state or

ground state everything in nature wants

to be in a low energy State as it is

easier for it to exist at this level in

other words it minimizes energy think of

a ball on a hill and how easy it is for

it to roll down it wants to roll down

because the energy state is lower closer

to the Earth's core than further away in

this case potential

energy however it is possible to excite

electrons by some kind of external means

just like we can exert a force on the

ball that has rolled down and push it

back up light can be this push to excite

electrons if a photon of Light which is

one unit of light comes across an

electron in a low energy state it can

sacrifice itself and push the electron

to a higher energy State the photon is

annihilated but the energy of it is now

part of the excited electron it should

be noted that each material has

different levels of energy in other

words if the ground state is one unit

and the next energy level is 5 units

then the photon of light must have

exactly four units of energy to excise

the electron to that energy level

anything lower will not suffice and

anything higher would not as well as

there is nowhere for that extra energy

to go unless a higher energy State

exists if the incident photon is very

high in energy the electron would be

ionized to continue our analogy it would

be like trying to push the ball up the

hill with not enough Force the ball

would just roll back down too much force

and it would roll down the other side go

to another Plateau or be launched into

space an exact amount of energy is

required to elevate it to a particular

energy State again this process is

called stimulated absorption as we are

stimulating the electron and it absorbs

the photon's energy the next mechanism

we will look at is spontaneous emission

we now have an excited electron what

happens now well again this higher

energy level is quite unstable and after

a very very short time about 100 nond of

being there the electron will eventually

fall for some perspective light travels

about 29 m in 100 NS when it falls back

down it will release a photon with

energy equal to the difference in energy

levels the higher the fall the higher

the energy of the photon will be should

the energy value of the photon that is

released be in the visible range we

would perceive it as color you may be

thinking if the electron reaches the

higher energy level through the

previously mentioned stimulated

absorption mechanism why exactly does it

fall back down well referring back to

the ball example imagine the ball on a

hill but now with the top having zero

friction and a sharp point the ball can

remain there only if it is perfectly

balanced but any tiny little force in

either direction will cause it to start

rolling the electron in this higher

energy state is in a similar situation

the forces that push it are small

perturbations in vacuum energy this is a

quantum mechanical effect space or

vacuum is not as empty as we think

things are popping into and out of

existence constantly it is these vacuum

events that perturb the electron this is

also responsible for why things are

ferromagnetic that's a different story

though again this process is called

spontaneous emission as the process that

the electron falls back down to the

lower energy state is more or less

spontaneous the last Quantum process we

will talk about and the most important

for lasers is stimulated emission this

occurs when a photon interacts with an

electron that is already excited this

Photon can act as a type of pertubation

and force the electron to fall back down

to a lower energy State and emit a

photon we then will have two photons

photons actually like to be together so

if one comes near a situation where

another one could be present such as the

the electron falling back to a lower

energy State the situation usually will

play out the important part is that the

emitted Photon will be identical to the

one that stimulated it meaning same

frequency phase and polarization they

will be coherent with each other so if

we could somehow Avalanche this process

we would have a laser after all that is

basically what a laser is a zip tillan

identical coherent photons being emitted

in contrast if two electrons undergo

spontaneous emission the emitted photons

will unlikely be traveling in the same

direction nor be in Phase but in order

for electrons in the excited energy

level to be able to undergo stimulated

emission and not spontaneous emission

enough time has to be available the

lifetime of an electron in the excited

level is just too short however some

materials have so-called meta stable

States these are excited states with

slightly lower energy than the excited

States States these states allow the

electron to remain there for much longer

lifetimes milliseconds instead of Nan

seconds enough time that a passing

Photon can cause it to undergo

stimulated emission of course an initial

spontaneous emission from the metastable

state to the ground state must occur in

order to have the initial Photon that

can stimulate other excited electrons in

the metastable states to sum up if a

ground state electron is hit with a

photon it will absorb it and move from

the ground state to the excited state

the photon must have the energy equal to

the difference between these levels this

electron will then transition to the

metast stable state if one exists this

transition does not emit a photon and is

said to be a radiationless transition

the energy difference is dissipated in

other ways heat or phons now this

electron if a photon stimulates it will

emit a photon with equal energy phase

and Direction these are the ones that

make up the laser beam it should be

apparent that the photon which pumps the

electron from the ground state to the

excited state has a different energy

than the photons that are being lazed

this is because the energy difference

between the ground state and the excited

state is different than the difference

between the meta stable State and the

ground state the pumping photons are

always higher in energy than the photons

being

lazed we obviously want lots of

electrons in this meta stable State more

so than the ground state in order for

them to be in a situation where

stimulated emission can occur something

known as creating a population inversion

is required if we only had a two levels

we would reach a point of saturation

where 50% of the electrons are excited

and 50% are not the excited electrons

simply spontaneously emit to fast

essentially our medium becomes

transparent to photons by introducing

the metas stable State we force the

pumping photons to excite the ground

state electrons that then transition to

the metastable state so the photons that

are emitted by the transition from the

metastable state to the ground state are

primarily used to stimulate other

electrons in the metastable state enough

time exists for this to happen yes some

of these photons will excite ground

state electrons directly into the

metastable state but the pumping photons

should take care of the majority and

create a situation where there are more

excited electrons in the metast stable

State than ground state electrons a

population

inversion by the way the above is

describing a three-level laser four

level lasers exist and are more

efficient again we want to create an

avalanche effect where the spontaneously

emitted Photon that was created when an

electron transitioned from the

metastable state to the ground state get

Amplified through the means of

stimulated emission

we don't want just a single puny Photon

we want lots all working together it is

not practical to create a laser that is

extremely long so the solution is to put

the laser medium in a cavity let's take

a closer look at how a cavity will

influence the light waves and how

exactly this will create the

amplification we desire since light is a

wave it will be subject to constructive

and destructive

interference we want constructive

interference in our cavity to take place

in order to have a high intensity beam a

laser cavity has a mirror on one side

and a partial mirror on the other it is

partial because we want some of the beam

to escape that's the beam we see now

when light waves are created through

spontaneous emission they will initially

travel in random directions but the ones

traveling perpendicular to the mirrors

will reflect back and forth let's take a

look at one of these light waves it is

first emitted via spontaneous emission

and quickly becomes large in amplitude

through stimulated emission it travels

towards the mirror and is reflected back

because we continue to stimulate atoms

in the left and right directions we get

two waves in the cavity again one moving

to the left and one moving to the right

waves will add their amplitudes when

interfering with each other in this case

we will get a standing wave meaning

instead of a wave noticeably moving to

the left or right the combin wave will

appear to be going up and down rest sure

this is just an illusion this is the

effect of two waves hitting each other

head on and their left and right

components cancel out but their up and

down components add together so when the

wave looks flat this is a moment when

the two waves are destructively

interfering with each other and at the

maximum they are in a constructive

interference Point here are a few

examples of some standing waves in a

cavity that are resonating resonance is

just a fancy word for having these waves

being in a state where standing waves

are being produced a mode being just

what n you have Nal 1 is a mode Nal 2 is

another one n equal 3 Etc is there an

equation that will tell us what modes

can exist in the cavity sure there is

the left part is the frequency that

exists in the cavity n is the mode which

is always an integer V is the velocity

of the wave and L is the distance

between the two sides of the cavity the

Velocity in our equation is the speed of

light C which is 300,000

km/s the L is just the distance between

the mirrors light traveling from the

left of the cavity will now interfere

with light traveling from the right so

again we have these possible modes where

the light can produce standing waves and

be in resonance not all frequencies are

able to exist in a cavity but a lot are

also let's be clear that the standing

waves produces are a collection of

trillions and trillions of light waves

all working together they are produced

by stimulated emission and the cavity

allows them to keep amplifying each

other they are coherent with each other

recall this was one of the big reasons

why we care about lasers if we didn't

have this Synergy between light waves we

would just have an ugly LED I bet you

can't make your cat go crazy with a red

LED well maybe but you get my point

question what frequencies are allowed to

exist in a red Las a point of cavity

answer a cheap red laser pointer has a

cavity length of about 1 mm and the

speed of light is c 300 million

m/s plugging in these values to our

equation we would get a difference

between allowed frequencies of about

10050

GHz Now red light has a frequency of

about 400.0 5 terz which corresponds to

an N value of

2,667 recall n must be an integer so if

400.0 5 terz is an allowed frequency

then the next one would be when n equal

2,668 which is a frequency of 400.2

terz we can plot all allowed frequencies

as we know 150 GHz will separate them

the plot will look like this here we

have an equal to

2,667 and the corresponding frequency of

400.0 five terz here is

2,668

2,669 and so on these are the

frequencies that are allowed to resonate

in this laser cavity so if you wanted

your laser to have a frequency of 400.1

terz you would first have to change the

cavity length for this to be allowed as

it is not possible in this red Laser's

cavity about 2,600 frequencies in the

visible spectrum would be able to

resonate in this red lasers cavity

now there is slightly more to the story

about these allowed frequency lines we

have assumed the mirrors are perfect

which is practically impossible the

imperfectness of the mirrors and other

slight variations add a thickness to the

frequency lines the actual allowed

frequencies in a laser cavity looks like

this again this is due to

imperfections the last piece of the

puzzle is to mention the gain medium

itself gain medium is just the material

we are using for our laser different

materials will have different energy

levels hence photons of different energy

will be released during stimulated

emission for example different materials

will need to be used to create a blue

laser than that of a red laser since the

energy levels in a material are discrete

one would think that exactly one

frequency would be emitted out of a

laser but only if this is also a

frequency allowed in our laser cavity we

can superimpose these ideas on this

graph

we assume here that indeed the

stimulated emitted photon is a frequency

that is allowed in the cavity however

there is much more to the story The

frequencies being emitted out of the

laser actually takes a shape like this

this was briefly mentioned at the

beginning of this video when discussing

L width what is going on here are

complicated events such as the Doppler

effect Stark effect and other quantum

mechanical Behavior the takeaway is that

the gain medium does output a small

range of frequencies and has this gain

curve it is still extremely narrow and

said to be monochromatic it's not but

it's close enough to sum up certain

frequencies are allowed to exist in a

laser cavity there is some relaxation to

these frequencies as the mirrors and

such are not perfect the laser game

medium emits photons in a certain

frequency as well but again there is

some broadness to this as certain

effects influence this we can

superimpose these two frequency Plus

spots and get the following the

frequencies under the game curve that

have enough intensity to overcome other

cavity losses are the ones the laser

emits there are plenty of laser active

medium these days any frequency you wish

to lace is pretty much possible here is

a picture of different laser material

and the frequency they output some are

in the gas State Some solid and it is

even possible to use a liquid as a

Lessing

material this concludes this episode on

the laser if you enjoyed the content and

learned something please consider doing

all that stuff every other video asks

you to do you know what I am talking

about