Laser 101: What Is Laser And How Is Laser Produced

I will introduce you the basic principle of laser.

By dismantling a He Ne laser generator and a laser pen, we can vividly see how the magical laser is produced.

We will introduce the characteristics of laser light source to pave the way for other related production in the future.

We will also talk about some of the latest developments of laser and interesting laser sources in unexpected places in nature.

On January 20, 1968, the last unmanned lunar exploration spacecraft, surveyor 7, launched by NASA, pointed its TV camera at the earth.

At this time, America is in the dark, and the whole earth is like a crescent moon hanging in the dark cosmic background.

However, in the spacecraft’s camera, there are two bright spots on the dark American continent (see Figure 1). Is this a UFO? Or urban lights that consume millions of kilowatts? None of them.

These two points are from KITT peak Observatory in Arizona and the observatory in California.

They are laser light sources produced by two lasers invented a few years ago, with a power of only 2W.

Seen from the moon 300000 kilometers away, the brightly lit cities are dim, but a light source with 2W intensity is still clear. This is the magical laser.

photos of the earth taken by the surveyor 7 lunar spacecraft

(photo provided by NASA Jet Propulsion Laboratory)

Fig.1 Photos of the earth taken by the surveyor 7 lunar spacecraft.

Notice the two bright spots on the left, which is the southwest of the United States.

After long-distance propagation and disturbance of the earth’s atmosphere, the laser appears to become two large spots.

The English name of laser is called laser. It was originally the abbreviation of “light amplification by stimulated emission of radiation”, that is, “light amplification device generated by stimulated radiation”.

Now laser has been widely used as an independent word.

Before the 1980s, the laser may still be something that researchers and “ashes” enthusiasts can afford to play.

Since the 1990s, a large number of cheap red semiconductor lasers have appeared on the market, and lasers began to enter ordinary people’s homes.

In this article, we will use this cheap laser to carry out several interesting experiments and production.

In this chapter, we will first understand the story of lasers.

Our most direct feeling about laser is that its color is very pure and the light is very concentrated.

At night, the light from a small laser pen still shines a bright spot on the building hundreds of meters away.

These two points just reflect the difference between laser and light sources such as ordinary flashlight.

The simple color indicates that the frequency of the laser is very single, and the concentration of light indicates that the direction of the laser is very good.

The reason why we can still see the laser on the earth on the moon is an excellent embodiment of its good directivity.

Although the power is only 2W, the 2W light is very “United and go hand in hand”.

Up to 300000 kilometers away, they still “don’t give up”, so they look very bright from the moon.

Why does laser have such characteristics? This has to start with the structure of the laser.

The configuration of a typical laser can be shown in Fig. 2.

structure of laser

Fig. 2 Structure of laser

The most obvious difference between a laser and a general light source is that it has two mirrors. As shown in Fig.2, there is a slightly transparent mirror on the left and an almost completely opaque mirror on the right (as the saying goes, there is no opaque mirror in the world, so it is only “almost completely opaque”).

The laser is emitted from the slightly transparent mirror on the left, and between the two mirrors is the luminous material that produces the laser.

Here, I want to apologize to non physics readers first, because I have to talk about the quantum theory of matter luminescence, which is very helpful for everyone to understand lasers and more natural phenomena.

In the early 20th century, people summarized a set of theories describing the motion of micro particles from the observation of the spectrum of matter luminescence, which is called “quantum theory”.

This theory holds that light travels like particles, one by one (called “photons”) in the form of waves.

This sentence sounds awkward, but just such a stubborn temper is the so-called “wave particle duality”.

It doesn’t matter if you don’t understand it for the time being, because according to master Feynman, no one in the world knows why microscopic particles are like this.

We can also safely think that light is an electromagnetic wave, and a photon is a weak electromagnetic wave.

The light we usually see is a strong electromagnetic wave composed of many photons.

Quantum theory also holds that electrons have some discrete “energy levels” in the atom, that is, the arrangement of electrons in the atom is not arbitrary, but has a strict hierarchy. The higher the level of electrons, the greater the energy.

When an electron at a high energy level jumps to a low energy level, according to the law of conservation of energy, some energy will be released and incarnated into a “photon”.

This luminescence process is shown in Fig.3, which physicists call “spontaneous emission”.

luminous process

Fig.3 Luminous process

It is easy to understand that when an electron is at the low energy level, it can also absorb a photon with energy of E1-E2 and jump to the high energy level.

As shown in Fig.4, this process is called “excitation”.

Of course, if the electron is “tired” at the high energy level, it can also jump back and emit an E1-E2 photon.

process of absorbing light

Fig.4 process of absorbing light

The story is not as like as two peas. Mr. Einstein realizes that the process of luminescence should have another situation.

When an electron at high energy level happens to encounter a photon of E1 E2, it will jump to the low energy level with a big slip and emit a photon that is exactly the same as the external photon.

As like as two peas, it is not just energy, because photon is a weak electromagnetic wave, and since it is fluctuating, there are frequency, phase and polarization state mentioned in the previous chapter.

In quantum theory, the energy of photons = constant ×  Photons with the same frequency and energy naturally have the same frequency, which is nothing strange.

But the phase and polarization are not simple.

This shows that the electromagnetic wave (photon) emitted by the electron is completely synchronized with the electromagnetic field vibration stimulating the electromagnetic wave (photon), and the vibration direction is the same, as shown in Fig.5.

Physicists call this luminescence process “stimulated radiation”.

stimulated emission process

Fig.5 stimulated emission process

Imagine that we have many atoms whose electrons are at a high energy level E1.

At this time, an electron can’t stay and jumps back to the low energy level to produce a photon of E1-E2.

Go forward with great strength and vigour, and as like as two peas, the photon can generate the stimulated radiation in the local electron.

The photon will become the two identical, two to 4, 4 to 8… Soon, we have a mighty photon team, they are all alike, with the same frequency, polarization and phase.

Isn’t this light amplification by stimulated emission of radiation? The generation of laser is close at hand!

So far, we have mastered the necessary tool for generating laser – “stimulated radiation”.

But it is strange that Mr. Einstein put forward this concept at the beginning of the 20th century. Why did the laser wait until the 1960s?

This is because of common sense.

This common-sense says that under normal circumstances, electrons in matter always like to stay at low energy level.

This is indisputable. Just as water flows downward, everything in the world naturally tends to be in a state of low energy.

So if there are many atoms, only a small number of atoms have electrons at the high energy level.

At this time, if a high-energy electron can’t stay still, jump back to the low-energy level and produce a photon.

In the process of propagation, this photon is likely to encounter another electron at the low-energy level and absorb it (see Fig.4), so we can’t get more photons.

For this reason, stimulated radiation is considered useless for a long time.

This situation finally changed in the morning of April 26, 1951.

The young American physicist, Mr. Charles Townes, suddenly had a wonderful idea of using stimulated radiation in the quiet and fresh air in the morning.

If we can continuously provide many atoms at the high energy level, we can ensure that more and more photons can be obtained from the source (the term is called particle number inversion, that is, there are more atoms at the high energy level than at the low energy level).

In order to ensure that a photon can encounter more high-energy atoms to produce stimulated radiation, he envisages placing these high-energy atoms between two reflecting surfaces (see Fig.2), so that a photon can shuttle back and forth between high-energy atoms to produce many identical photons.

Then it is emitted from the slightly transparent side (the details I describe are greatly simplified. Readers can refer to “how laser accidentally found” to obtain first-hand accurate information).

Later experiments proved that Mr. Townes’s two great ideas were indispensable.

Only a lot of atoms at high energy level are not enough to produce laser.

Two mirrors must be added to make a photon induce enough stimulated radiation and make full use of it.

Stimulated radiation and the addition of these two mirrors directly determine the characteristics of the laser we are familiar with today.

As mentioned above, stimulated radiation produces a large number of identical photons, so the laser has a very good monochromaticity (containing only one frequency).

Two mirrors lead to excellent directivity of the laser. Why? Let’s look at fig.6.

reflector determines the directivity of laser

Fig.6 reflector determines the directivity of laser

In Fig.6, we first assume that the electron of the atom in the upper left corner jumps back from the high energy level to the low energy level, emitting a photon moving horizontally to the right.

This photon induces stimulated radiation, and the “popularity” soars all the way.

Until it touches the mirror on the right, their propagation direction becomes horizontal to the left, and then continue to induce stimulated radiation (note that we make the atoms in the working material in a high-energy state by some means.

Even if it emits a photon, we can quickly excite it to a high-energy level by other means).

When the “mighty” photons meet the left mirror, a small part is transmitted out, and most of the rest remains in the laser working material to continue amplification.

Some of these photons become familiar lasers. Do you notice?

They all move in the same direction and have no intention of diffusion.

Readers will say that this is because the original “seed” photon happened to move in a horizontal direction.

What would happen if it deviated a little? As shown in Fig.6, this photon will also cause stimulated radiation and be amplified.

Unfortunately, because they follow the “heresy”, they quickly leave the laser working material and cannot be reflected back and forth many times and amplified repeatedly like photons moving in the horizontal direction.

Therefore, the existence of two mirrors leads to the excellent directivity of the laser.

Of course, when Mr. Townes designed such a device, his starting point was only to obtain enough amplification to produce relatively strong stimulated radiation.

The two mirrors not only enhance the stimulated radiation, but also play a role in shaping the slim shape of the laser.

At this point, the long-awaited laser finally began to become clear in human thinking.

After having this excellent idea, Mr. Townes made a lot of careful calculations and was sure that his idea could be realized.

So he and his graduate students began a long way to put their ideas into practice.

Their goal at that time was to create a device to produce a “microwave laser”, that is, the generated laser was in the microwave band rather than the visible band (to be exact, the device was called maser rather than laser).

Where “m” stands for microwave (microwave).

To create a new thing, no matter how simple it is later, the process of creation is full of ups and downs.

For a long time, there was no progress in Mr. Townes’ research.

At that time, Professor Rabi and Professor Kusch, two Nobel Laureates in physics in the Department of physics at Columbia University, saw it in their eyes and were worried.

They found Mr. Townes and had a conversation (see “how laser accidentally found it”).

The two professors said earnestly, “Xiao Tang, we don’t think your idea will work! You’re wasting money and time!”

Mr. Townes didn’t believe in this evil. He politely rejected the advice of the two great physicists and planned to go to the black together.

He is very confident in his calculation and believes that since it is completely feasible in principle, it should be realized.

The two professors said earnestly, “Xiao Tang, we don’t think your idea will work! You’re wasting money and time!”

Mr. Townes didn’t believe in this evil. He politely rejected the advice of the two great physicists and planned to go to the black together.

He is very confident in his calculation and believes that since it is completely feasible in principle, it should be realized.

In life, from the DVD drive in the computer to the bar code scanner in the supermarket, there are traces of laser everywhere.

Laser is also a regular guest of science fiction. The first science fiction novel in China, the dead light on the coral island, takes laser as the main clue.

The nickname of “dead light”, a laser, may date back to the time when the laser was just discovered. Gossip reporters asked scientists whether this magical and powerful beam of light could be used to shoot down enemy planes, so they gave it the glorious title of “death ray”.

But now the use of laser in medical treatment is far more than that in military. It should be said that laser is the divine light of “hanging pot to help the world”.

After talking about so many stories about lasers, readers as amateur scientists must want to move their hands. That’s what we’re going to do next.

Hands on practice

To have a deeper understanding of the previous theory on laser, the best way is to take apart the two lasers to see what happened. Let’s first dismantle a big laser.

The first experiment encountered a He Ne laser

Materials required

He Ne laser tube

He Ne laser tube (and its high voltage power supply)

He Ne laser is a kind of gas laser that produces red light. Its appearance makes the laser enter daily life.

Early laser printers and bar code scanners used this kind of bulky laser.

Now, many second-hand He Ne laser tubes can be bought online, most of which are disassembled from some old equipment in those years.

Readers who have 100 yuan spare money may as well buy one. It is also very interesting as a collection.

More importantly, it can clearly show the internal structure of the laser.

I was lucky to pick up a 1977 helium neon laser tube (see Fig.7) and its power supply from a pile of waste instruments.

He Ne laser tube

Fig.7 He Ne laser tube

He-Ne laser is actually the family relative of our common neon lamp.

Neon lamp is transliterated from English “neon”.

When we fill a vacuum tube with low-pressure neon and apply high voltage at both ends of the tube, a large number of neon atoms are excited to a high-energy state, and then emit bright red light in all directions mainly through the aforementioned “spontaneous emission”.

He Ne laser can as like as two peas on a pair of neon lights (see Fig.8), so that the photons produced by spontaneous radiation can be reflected back and forth in the lamp tube, and generate a large number of identical photons through the continuous generation of “stimulated radiation”, and they all propagate along the direction of the lamp tube, thus forming laser.

He Ne laser

Fig.8 shows the almost complete mirror on the left;

On the right is a slightly transparent mirror.

If a reader decides to buy such a laser tube, it’s best to buy another laser power supply. Its price is similar to that of a laser tube on Taobao.

This power supply should be able to generate a DC voltage of 7000 ~ 9 000v (high voltage danger, please use after being guided by professionals) to discharge the gas and emit light.

I carefully connected the power output terminal to both ends of the laser tube, and then turned on the power (never touch the electrode with your hand when the power is turned on), and a very bright red laser tube appeared in front of me (see Fig.9).

If you look carefully, you can find a slender light path in the central glass tube.

It can be imagined that the atoms on this optical path are constantly excited to the high energy level by the 7000v voltage applied at both ends, and then continuously induced to produce stimulated radiation by the photons already existing in the laser to form a laser.

lighting up He Ne laser tube

Fig.9 lighting up He Ne laser tube

On the side of the slightly transparent mirror, we can see a strong laser bright spot, while on the side of the almost opaque mirror, we can only see a relatively dim laser bright spot (see Fig.10).

From fig.9 and fig.10, readers can also notice an interesting phenomenon, that is, we can see the dazzling light emitted from the laser tube, but we can’t see the track of the laser in the air after it is emitted from the tube.

We can’t see a bright laser spot until it is reflected by other objects, which is the vivid embodiment of fig.6.

In the laser tube, those photons that do not propagate along the horizontal direction leave the laser working material after a few times of amplification and emit to the side to become the dazzling light we can see.

The real laser only propagates along the horizontal direction, and the photons in it will not enter the eyes of the observer, so we can’t feel its existence in the air, even though its brightness is very high.

We can’t see it until it is reflected in all directions by a rough surface.

laser emitted from two mirrors

Fig.10 laser emitted from two mirrors

Here, I would like to remind readers about laser safety.

Never let a laser beam directly into your eyes.

Even a 5MW laser (for example, many of our laser pens produce 5MW laser, and the helium neon laser I use is 4MW) may lead to permanent blindness after being directly injected into the eyes for a certain time.

Other lasers with higher power can cause blindness as long as they are injected into the eye for 0.1s or less.

For specific information about laser safety, please inquire online.

Readers may feel that the price of He-Ne laser is a little expensive, and it is not easy to deal with 7000v power supply.

Don’t worry. Next, let’s look at another high-quality and cheap laser – red laser pen.

The second experiment dissected the red laser pen

Materials required

5mW red laser pen

Cheap 5mW red laser pen

Generally, the more expensive the instrument is, the better, but the cheaper the instrument (laser pen) is, such as the ugly red laser pen in the material list.

Note that the whole pen holder is connected as a whole. The battery is inserted from the left and the laser is emitted from the right.

Some expensive laser pens are unscrewed from the middle and loaded into the battery, which is generally not suitable for this experiment.

If readers can meet a laser pen with extremely rough workmanship like me, they will be really lucky!

Because in this way, we can explore the core components of the laser diode.

Generally, the light-emitting element of this laser pen – Laser Diode – is located on the silver white part of the pen head.

Its production process is probably to install the laser diode and switching circuit on the silver pen head, then apply glue and insert it into the pen tube for fixation.

Therefore, to get the laser diode, you need to pull out the pen head with pliers.

If all goes well, we will see the components shown in Fig.11.

internal components of laser pen

Fig.11 internal components of laser pen

The laser pen is simple.

We can separate the core of the laser diode, that is, the semiconductor devices that really participate in light-emitting, as shown in Fig.12 (I have welded two wires on it to apply voltage).

core of laser diode (light emitting semiconductor)

Fig.12 core of laser diode (light emitting semiconductor)

In fact, what we see in Fig.12 is not all light-emitting semiconductors, most of which are just copper sheets convenient for welding electrodes.

The part that finally emits the laser is a small crystal on the middle bulge (inside the red dotted circle in Fig.12).

People whose eyes are not as good as mine are not easy to see. We can turn to the microscope for a closer look, as shown in Fig.13.

laser diode under microscope

Fig.13 laser diode under microscope

Further magnification can see the fine structure of the light-emitting crystal (see Fig.14).

further enlarged light emitting crystal

Fig.14 further enlarged light emitting crystal

As can be seen from fig.14, the size of the light-emitting crystal is actually only about 0.1mm, 2, or so.

We have to sincerely lament the progress of nanotechnology, which enables us to create such a complex structure on an object the size of a needle tip.

After knowing its appearance, we can apply voltage to it and make it produce laser.

Note that since we don’t know how much voltage will damage the light-emitting crystal (from the laser pen using two 1.5V batteries, its working voltage is about 3V), I use an adjustable DC regulated power supply to supply power to it, so that we can apply voltage to it bit by bit until it emits light.

Such a power supply will be used in future experiments and production. It is a right-hand assistant worthy of investment (you can buy it for less than 100 yuan online).

In addition, we don’t know how to connect the positive and negative poles (the positive and negative poles in Fig.13 are marked after trying).

Therefore, when the voltage is applied to 2V in one direction, if it does not emit light, it indicates that the positive and negative electrodes are connected reversely.

After these details are clear, slowly increase the voltage, and we can see that the crystal emits a dazzling red laser (see Fig.15).

laser generated by luminous crystal

Fig.15 laser generated by luminous crystal

Seeing this, readers must be wondering if I’m mistaken. Is it really a laser shown in Fig.15? Why is the spot so large?

In addition, in the “basic principles” section, we emphasized the importance of the role of two mirrors.

From this small luminous crystal, we can’t see these two mirrors at all!

All these doubts can be solved from the structure of the laser diode.

Laser diode and general LED are relatives of our family.

They all belong to the LED family, and this family is the most glorious one in the diode family.

The basic structure of all diodes is to connect two semiconductors (such as silicon crystals mixed with different impurities) (see Fig.16).

One is called p-type semiconductor and the other is called n-type semiconductor.

Just as electrons have separate energy levels in gas atoms, when atoms form semiconductors, the electrons in them can also be divided into high-energy level and low-energy level.

When p-type and n-type semiconductors are combined, their energy levels will bend at the intersection (called PN node region).

It is this small bend that determines the nature of the diode conducting only in one direction and cutting off in the other direction (when we add a positive voltage to the p-type semiconductor and a negative voltage to the n-type semiconductor, the diode resistance is very small;

If the voltage is applied in reverse, the resistance will be very large.

The former is called forward bias and the latter is called reverse bias).

basic structure of diode

Fig.16 basic structure of diode

When we add forward bias, the electron flow process is shown in Figure 17.

Note that in the PN junction region, electrons jump from the high energy level to the low energy level.

According to our discussion in “basic principles”, electrons jump from high energy level to low energy level to release energy.

For atoms, this part of the energy can only be released in the form of photons.

However, when atoms form crystals, the ways to release energy are diversified.

Ordinary diodes do not emit light because they turn this part of energy into heat energy.

The reason why our computers are so hot is that there are hundreds of millions of PN junctions working in the world.

But not all diodes generate heat, and some semiconductor materials are more inclined to emit light (such as gallium arsenide).

The diode made of these materials is our familiar LED (light-emitting diode).

electron flow under forward bias

Fig.17 electron flow under forward bias

Since the diode can emit light, we should be able to make it emit laser.

After the invention of the first laser, scientists immediately began to study how to make the diode produce laser.

According to the previous description, to generate laser, there must be two mirrors to make photons reflect back and forth in the PN junction and induce “stimulated radiation”.

But where can I find such a small mirror that can be installed at both ends of a PN junction less than 0.1mm?

Smart researchers came up with a good way to use local materials without a single soldier.

They found that when the surface of semiconductor crystal is accurately cut and polished, it has high reflectivity like a mirror.

In this way, both ends of a diode can be made into two natural mirrors (see Fig.18).

The photons transmitted as like as two peas in the PN junction perpendicular to the two ends will be reflected back and forth, and more electrons will be stimulated in the PN junction to jump from the high energy level to the lower energy level, and more and more photons will be emitted to form laser.

Generally speaking, the refractive index of these two “mirrors” is almost high, so the laser with the same intensity can be emitted from two directions. We usually see only one of them.

how diodes generate lasers

Fig.18 how diodes generate lasers

Similarly, the structure of the laser diode can also explain why the laser it emits is not a common thin beam of light, but a very large spot.

We learned the diffraction of light in high school physics class and know that light waves have a strange temper (in fact, all fluctuations have this strange temper).

That is, when we let a beam of light pass through a small hole, the smaller the aperture, the more the light spreads.

It seems that the stronger the oppression, the stronger the resistance.

We can see that the size of a laser diode is less than 0.1mm, and the area in which the laser is actually generated is much smaller (see Fig.19).

When the laser is emitted from this small area, a large spot will naturally be generated according to the diffraction of light.

In the helium neon laser mentioned at the beginning, the size of the laser generation area is equivalent to the diameter of the central glass tube containing low-pressure helium neon gas mixture (about 0.5 cm).

The laser does not feel any constraints, so it produces a perfect beam of thin lines.

From fig.19, we can also see that the laser generated by the diode is more constrained in the direction perpendicular to the PN junction, so the spot in that direction diffuses more seriously.

This is exactly what we see in Fig.15.

why is the laser generated by the laser diode a spot

Fig.19 why is the laser generated by the laser diode a spot

Readers may wonder why the light emitted by the laser pen we usually buy is a thin beam, and the size of the spot does not become large even if it shines on the building hundreds of meters away?

This is because when the laser is just emitted from the diode and has not diffused very much, it encounters a convex lens with a very short focal length (a few millimeters), which turns the originally divergent laser into parallel light.

If you pay attention, you can still see the convex lens in front of the diode when you disassemble the laser pen.

Some readers say that if I didn’t have such good luck and couldn’t buy such a poor quality laser pen, could I still observe the internal structure of the laser diode so closely?

Don’t worry about it. There is a cheap “focusing laser diode” (pay attention to the 5MW one) on the Internet. Its convex lens is installed on a copper sleeve.

The distance between the convex lens and the light-emitting crystal can be adjusted by rotation, or the convex lens can be completely removed.

We can use such a laser diode to experience the phenomenon described in Fig.19.

In the later production of hologram, we also need to use this kind of focusing laser diode, so we’ll be familiar with it here first, and we’ll be familiar with it in the future.

In the “basic principles” section, we also mentioned that photons produced by stimulated radiation have the same polarization.

With the knowledge and material preparation of the previous chapter, we can easily verify this point (see Fig.20).

Generally, non stimulated radiation light sources (such as fluorescent lamps) will not have polarization.

checking the polarization of laser diode

Fig.20 checking the polarization of laser diode

Exploration and discovery

Mr. Lu Xun said that the first person to eat crabs was a hero.

This is often the case in the world. It is always difficult for pioneers to open up the right road from the thorns, but once this road is proved, later people can be familiar with the road.

The laser is the same. With the efforts of a large number of scientists and engineers such as Mr. towns and Mr. Maiman, the theory and practice of laser have been very mature.

Later, people can easily create some strange laser sources.

Physicist Arthur Schawlow, one of the pioneers of laser mentioned earlier, created an edible laser (“edible laser”).

He added fluorescent material into a jelly, put the jelly between two mirrors, induced the fluorescent material to emit light through an external light source, and formed a laser through the reflection of the mirror.

Imagine that there is a laser emitting light in front of us, and we can scoop a spoonful of light-emitting material from time to time and put it into our mouth to chew.

This may be the innocence of a good physicist!

In addition to this edible laser source, some other strange laser sources are of great significance to scientific research.

In 2011, several biomedical researchers made some human kidney cells emit green lasers (please search “single cell biological lasers”).

They injected some fluorescent proteins into the cells, placed the cells between two tiny mirrors, and then excited fluorescent chromosomes to produce lasers.

These cells have been living, indicating that the laser emission process did not damage them.

This technology can make the cell structure attached to fluorescent proteins very obvious, so it has important application prospects for biological microscopic imaging and observing the internal structure of cells.

So far, the laser sources we mentioned are all created by human beings.

However, the laser sources in the universe actually exist for a long time and only wait for the eye to identify them.

Mr. towns and his colleagues were the first to have these eyes (Mr. towns later turned to studying the material composition of gas clusters in galaxies).

Generally speaking, astronomers judge the material composition of the area through observing the absorption line in the spectrum, but Mr. towns found that the light of a certain frequency that should have been absorbed has been greatly strengthened in one of his observations.

With his in-depth understanding of maser and laser, Mr. towns soon realized that this must be a process of laser emission.

But did the creator buy two huge mirrors from somewhere, put them away tens of thousands of light-years apart, and then put some luminous gas clusters in them?

This possibility is relatively low.

Mr. towns’s theory is that the molecules in these gases are excited to a high-energy state by cosmic rays, and because the size of the gas cluster is huge, there is no need to reflect at all.

A photon has to go through a long (light-years) distance in the luminous gas to induce many times of stimulated radiation, resulting in a very strong laser.

Because there is no mirror, this laser is emitted evenly in all directions (this so-called 3D laser is a research frontier in the laser field.

For more details, please search “Beyond the beam: a history of multidimensional lasers”).

We should thank the creator. If he really made two mirrors and made these lasers shoot towards the earth, it might be a disaster for mankind.

Laser has many interesting properties. For example, it has excellent coherence, which we will leave for later experiments and production to explore and taste.

Scroll to Top