laser light. Reflection and refraction of light

A person who knows the elementary laws of optics will laugh heartily at a plot in which a superhero repels a villain's laser attack with the help of a shiny surface. A mirror cannot reflect a laser beam without scattering its beam. To reflect or redirect a laser beam, you need to work hard and have quite sophisticated equipment for this.
And the superhero's hand is in great danger. After all, when a powerful beam hits, a mirror with insufficient surface quality will either collapse or melt.

This is a considerable problem for modern specialists in the field of laser optics. They are faced with the need to reflect the laser beam constantly. Until recently, no matter how many tricks were taken by scientists, their mirrors did not satisfy the tasks set. No matter how ideal the surface of the mirror is, it heats up at the point of contact with the beam, heats up and deforms. The laser beam is not completely reflected, most of his energy is lost.

Traditionally, scientists have looked for new heat-resistant materials to make mirrors. Some materials are better, some are worse, some materials are expensive, while others require complex processing. The search for suitable material is not over to this day. Most likely, these searches will drag on indefinitely.

Opticians from the Fraunhofer Institute went the other way. They applied the well-known saying "if the mountain does not come to Mohammed, then Mohammed goes to the mountain." They changed their approach to the problem and decided to create a smart mirror that compensates for energy losses and "adjusts" to each laser beam individually. This became possible due to the fact that the mirror does not absorb heat and deform, but simply compensates for thermal deformation. For compensation, high-precision artificial heating of the desired areas of the mirror and the piezoelectric effect are used.
The mirror, made of special ceramics and coated with a layer of copper, can change its surface automatically. This is due to thermal sensors that instruct the heating device to heat up the area of ​​the mirror that compensates for the deformation from the heat of the laser beam.

The use of smart mirrors gives scope for wide application laser. These can be installations for cutting large-sized space debris into small pieces that can burn up in the Earth's atmosphere. This does not require significant energy costs and work can be carried out from a long distance.

The use of such mirrors will help overcome atmospheric distortions of the laser beam and transmit large amounts of information without loss over distances of thousands of kilometers. This project holds excellent prospects for the development of laser communications.

Of course, such a mirror will not fit in a superhero's pocket. He needs to find other ways to counter the laser weapons. Who knows, maybe such methods will be found in the future?!

Researchers have learned to bend the surface of the water using sources of optical radiation as early as 1973, but then powerful lasers were used for this, which acted due to high photon pressure. This phenomenon was then surprising in itself, because. water has a fairly high surface tension (and light exerts a relatively low pressure).

Until now, it was believed that curvature could be achieved with lasers with a power of at least 10 W (this is the class of lasers used in micro-machining or surgery). Therefore, no one even tried to get similar results with less powerful equipment. But a group of scientists from the University of Rennes (France) decided to conduct an experiment with a weak laser in a configuration known as full internal reflection, within which the forces are distributed in a slightly different way than in the case of direct irradiation. Detailed results of their work are published in the journal Physical Review Letters.

When you illuminate water with light at some random angle, the total force of light pressure will be the sum of the effects of three rays: the initial one that passed through the surface and reflected from the surface. As a result, the pressure force will be vertical (the horizontal component of the total force will be equal to zero). But when light hits the surface of the water from its thickness at an angle of more than 49 degrees, it is almost completely reflected back. In this case, the horizontal component of the force is preserved (according to the Gauss Henchen effect) and acts on the water in the direction of the center of the beam. A curvature of the surface is formed, similar to what occurs if the edges of a sheet of paper are shifted towards each other.

In the experiment, the team used a green 20-milliwatt argon laser beamed at an angle to the surface from a shallow container of water with a mirror along the bottom. The laser beam reflected several times from the mirror and the surface, eventually hitting the sensor. The elongated image of the beam showed the curvature of the water surface (just like a curved mirror, depending on its shape, distorts the proportions of the person reflected in it). Scientists were puzzled by the fact that in this case, not the bulges they expected, but, on the contrary, depressions were formed on the surface. However, their explanation shows that all this is fully consistent with the influence of the Henchen Gauss effect. The team bases its opinion on why such a surprise is possible on the presence of a small electric field extending about one micron above the surface of the water. They believe that the gradient of this field is so great that it significantly changes the air pressure in the immediate vicinity of the surface (pressing it down).

Colleagues of scientists, however, do not fully accept this explanation, although they do not question the results of the experiment. In their opinion, the model is too simple. But, regardless of the details of this model, the detected effect could well be used to create small, tunable optical lenses.

This project is devoted to the study of the properties and features of laser radiation in practice, the use of a laser to create simple physical devices. The paper outlines and describes the device and physical principles laser operation is shown wide area applications of lasers, in particular in the space industry.

Ministry of General and vocational education Sverdlovsk region

local government

"Department of Education of Kamensk-Uralsky"

Municipal Autonomous General Educational Institution

"Secondary school No. 40"

Second Youth Space Forum "Semikhatov Readings"

Section 1. Physics and knowledge of the world

Project

"Homemade laser devices"

Executor:

Zherebyatiev Ilya Vladimirovich,

9th grade student

Supervisor:

Balashova Marina Eduardovna,

Physics teacher

Kamensk-Uralsky – Yekaterinburg

Introduction

For many centuries, astronomy has been the leader of natural science. Astronomical observations served as the initial foundation for the discovery of many laws of physics. A few years ago, radio astronomers made a curious discovery. It turned out that in the interstellar medium there are groups of OH molecules (hydroxyl groups). Hydroxide radiation is similar to laser radiation. So nature created lasers before man invented them.

In 2015, the scientific community celebrates the 55th anniversary of the invention of the laser.

Laser radiation has amazing properties. No wonder science fiction anticipated its creation.

The work on the project included the study of the history of the invention of the laser, the principle of its operation, familiarity in practice with the properties of radiation and consideration of the use of laser devices in various fields human activities, familiarization of the school community (students of grades 1-11, parents) with the laser.

The purpose of this work: to make devices using a laser: the simplest scanner and resonator.

Tasks:

• study the literature on the topic (laser theory, history, applications);
• to study the properties and features of laser radiation in practice;
• select materials for the manufacture of devices.

The relevance of this topic is due to the constant growth in the rate of development of laser technologies and their implementation in our lives, including in the space industry.

Object of study: laser radiation.

Subject of study: the possibility of using a laser to create simple physical devices.

Main part

What is a laser. Basic properties of laser radiation

The word "laser" is made up of the initial letters in the English phrase Light Amplification by Stimulated Emission of Radiation, which in translation into Russian means: amplification of light by stimulated emission.

Laser (optical quantum generator) is a device that converts pump energy (light, electrical, thermal, chemical, etc.) into the energy of a consistent, monochromatic, polarized and narrowly directed radiation flux.

Main properties of laser radiation: monochromatic (monochrome) - all electromagnetic flow oscillations have the same frequency and wavelength. Characterizes the width of the radiation spectrum. The smaller the spectrum width, the higher the monochromaticity of the radiation. coherence – phase coincidence electromagnetic oscillations. It characterizes the degree of agreement between the phases of the waves that form this radiation. Two beams are called coherent if the phase difference between the waves remains constant during the observation time. The property of temporal coherence of laser radiation is used in optoelectronic devices for receiving and transmitting information. The shorter the wave, the more information can be transmitted. Polarization – fixed orientation of vectors electromagnetic radiation in space relative to the direction of its propagation. Orientation – low divergence of the radiation flux, propagates within a small solid angle. High directivity provides maximum energy density at the output of the device.

Thanks to its properties, the laser has become one of the most significant inventions of the 20th century. Unique properties laser radiation have made quantum generators an indispensable tool in various fields of science and technology.

From the history of the laser

1900 The German scientist Max Planck puts forward the bold hypothesis of the quantization of radiation: matter emits and absorbs light in separate portions (quanta). quantum energy Е = h∙ν, wherehis Planck's constant.

1913 Niels Bohr, trying to explain E. Rutherford's planetary model of the atom, will formulate two postulates:

• The energy of an atom is quantized, that is, it can take on a number of discrete values: E 1, E 2, E 3, ... En
• When an atom passes from a level with energy E 2 to a level with energy E 1, a quantum (photon) is emitted with energyh∙ ν \u003d E 2 - E 1

1916 Albert Einstein created the theory of the interaction of radiation with matter, and in 1917. predicts the possibility of induced (forced) emission by atoms, which implies the fundamental possibility of creating quantum amplifiers and generators electromagnetic waves.

1940 The Soviet physicist V. A. Fabrikant shows the possibility of using the phenomenon of stimulated emission to amplify electromagnetic waves.

1954 Scientists Nikolai Gennadievich Basov and Alexander Mikhailovich Prokhorov and, independently of them, the American physicist Charles Towns create a microwave quantum generator of radio waves with a wavelength of 1.27 cm ("MASER"). They were awarded the Nobel Prize for this invention.

1960 American physicist Theodore Maiman designed the first ruby ​​laser with a wavelength of 0.69 microns. Peter Sorokin and Mirek Stevenson built a calcium fluoride infrared laser doped with uranium ions. Ali Javan, William Bennett, and Donald Harriot demonstrated the world's first helium-neon gas laser, which is still in widespread use today.

The invention of lasers and their improvement continues to this day.

Theorylaser

Lasers usually consist of three parts (Fig. 1):

Energy source or pumping mechanism;

working body;

What each of these parts is responsible for: A system of mirrors or an optical resonator.

Energy source supplies the energy needed to operate the device. Such initial energy can be another source of light, as well as an electric discharge, chemical reaction etc.

working body- a substance (gas, solid, liquid and even plasma), in which there are atoms that emit coherent photons. Defines all the most important characteristic laser, such as power, wavelength, etc., which ultimately determines its practical application.

Optical resonator is a system of mirrors for collecting radiation into one narrow beam.

Operating principle

In order for the process of emission of coherent photons to occur, the working body is subjected to energy pumping, which leads to the fact that most of the atoms that make up the working body have passed into an excited energy state. In this state, the transition to the reverse - the ground (not excited) state will occur if a photon passes through the atom, corresponding in energy to the difference between these two states of the atom. Thus, an excited atom, upon transition to the ground state, adds to the photon “flying through it” its exact copy. Thus, light amplification occurs.

Application of lasers

From the very moment of its development, the laser was called a device that itself is looking for tasks to be solved. Lasers have found application in a wide variety of fields - from vision correction to control vehicles, from space flights of pre-thermonuclear fusion. Examples of laser use: industry: cutting, welding, drilling, engraving; medicine: surgery, laser therapy; military affairs: sights, light locators, SDI; household: printer, DVD, data transfer; science: level, holography, autofocus.

Application of lasersin the space industry

Scientists are developing innovative ways transmitting data in space using a laser.

The first step in this program NASA will be the launch of the LCRD project scheduled for 2017. The main task this mission is to test and demonstrate the capabilities new technology with 6 times faster data transfer rate.

In astronautics and aviation, pulsed laser locators(Fig. 2) to determine the distance to the target.

Laser altimeters(Fig. 3) were used in spaceship"Apollo" for photographing the surface of the Moon, on the Interplanetary Probe "Messenger" for high-precision topographic survey of the surface of Mercury.

Energy i probl ema for k

osmonautics is no less important. One solution is to use managed onesnuclear fusion. But there are a number of technological problems that do not allow to bring the work to practical use. One of these problems is the confinement of a heated plasma in nuclear reactor. One way to solve this problem may be to use lasers.

The time is not far off when mankind will begin to break away from the Earth and fly to other planets. At the same time, astronauts will have to take with them many technologies that are now used in areas far from astronautics. Including laser: laser scalpel, laser cutting and welding, holography, etc.

Space systems designer Boris Chertok, academician of the Russian Academy of Sciences, does not rule out the possibility that damaging laser and high-frequency space weapons may appear in space in the future.

Practical part

1. Study of some properties of laser radiation

Determining the wavelength of laser radiation

Purpose: to determine the wavelengths of red and green laser radiation.

Equipment required for measurement: In this work, a diffraction grating with a known period is used to determine the wavelength of a light wave (the period is indicated on the grating).

If a laser beam is passed through the grating, then on the dark background of the screen one can observe diffraction maxima of the 0th, 1st, 2nd, etc. orders.

Wavelength λ, is determined by the formula: , where a is the distance from the grating to the screen, b is the distance on the screen from the 0th order maximum to the 1st or 2nd order diffraction maximum, d- period grating, k is the order of the spectrum.

Wavelength calculationred laser beam. Grating with a period of 1/50 mm:

Wavelength calculationred

Wavelength calculationgreen laser beam. Grating with a period of 1/75 mm:

Wavelength calculationgreen laser beam. Grating with a period of 1/300 mm:

To compare the results obtained, use the table below.

Table. Wavelengths of laser radiation in laser pointers

Conclusion: Taking into account the measurement error in the experiment, and also taking into account that laser pointers differ in the spectral range, they have a different manufacturer, the results are practically close to those given in the table.

Reflection of the laser beam

Purpose: to observe the reflection of a laser beam from a mirror surface.

Equipment: optical bench, mirror, protractor, laser.

A laser beam is incident on a reflecting surface (mirror) in a given direction. The beam, reflected from the mirror, changes its direction. Regardless of how the beam falls on the mirror, the angle of incidence is always equal to the angle of reflection and the rays are in the same plane with the perpendicular drawn at the point of incidence of the beam.

The photographs show the reflection of the beam from the mirror at angles of incidence 304) and 60 (Fig. 5).

Conclusion: experience proves the validity of the law of reflection of light.

Determining the divergence angle of the laser beam

Purpose: to observe the divergence of the laser beam and determine the angle of divergence.

Equipment: laser, ruler.

To determine the angle of divergence of the laser beam, I placed the source of laser radiation at a distance of 67230 mm from the wall (the experiment was carried out in the recreation of the school). The diameter of the light spot on the wall turned out to be 90 mm (Fig. 8). The beam diameter at the output of the device is approximately 3 mm. This size can be neglected, since it is much smaller than the obtained value of the spot diameter on the wall and the distance to the wall (Fig. 9).

Simple calculations allow you to determine the angle of divergence of the beam:

Conclusion: the angle of divergence of the laser beam is approximately 4.824 "".

In the work, experiments were also carried out on refraction, diffraction, scattering, polarization of the laser beam and measurement of the surface temperature under the action of the laser beam.

2. Manufacturing of a laser spirograph

The spectacle of spiral patterns that are reproduced on the walls with this device fascinates and attracts attention. Most of the people to whom I showed the patterns of the spirograph were simply delighted with what they saw.

The idea of ​​creation came to me at a disco, when I saw with my own eyes what a real laser show and laser color music are, and how it all works. I spied on the principle of operation of the device in a Chinese light and music device, which changes patterns depending on the sound. It uses stepper motors controlled by a microcontroller, with this construction, the drawn pictures are unstable, due to the synchronous operation of the motors.

I made a device similar in principle, with simple controls and using available parts. The laser beam is directed at the first mirror, which is rotated by the first motor and reflects the beam onto the next mirror, and due to the slight inclination of the mirrors relative to the motor axis, the beam is reflected with circular rotation and the stain is obtained in the form of a clear pattern.

My device uses two laser beams, four motors, five mirrors, and three rheostat motor speed controllers. Thus, a "laser show" is obtained.

3. Manufacturing of a laser scanner

Resonance is a phenomenon of a sharp increase in the amplitude of forced oscillations, which occurs when the frequency of an external action coincides with certain values ​​(resonant frequencies) determined by the properties of the system. An increase in amplitude is only a consequence of resonance, and the cause is the coincidence of the external (exciting) frequency with some other frequency determined from the parameters of the oscillatory system, such as internal (natural) frequency, viscosity coefficient, etc.

The scanner is designed to obtain uncomplicated optical figures. The whole device is based on magnetic resonance. The device is made of a motor, a plastic plate and magnets. An increase in the amplitude of oscillations of the plate at resonance can be observed along the light line. By changing the position of the motor and the speed of its rotation, you can get not only different figures on the screen, but also find the resonant frequencies.

Conclusion

This work allowed me not only to understand in detail the selected material on this topic, but also to learn how to analyze information from a variety of sources, as well as present it to the audience. The experiments carried out confirming some laws of physics and the properties of laser radiation also contributed to the study of the material. Project activity contributes to the development of the ability to independent work, the formation of self-organization skills.

My practical achievements include the significance of my (not the first, similar) work, which lies in the fact that it helps propaedeutics physical education in primary school, where I go regularly with my projects in physics. And I already have followers in this business. AT design work in physics, the kids themselves are also included, which will undoubtedly help them in education, including with the choice future profession. I do not rule out the possibility that some of them will connect their activities with astronautics.

Event

Subscribe to news

What is a laser?

Isaac Newton believed that light is made up of smallest particles- corpuscle, and his opponent Christian Huygens believed that from the waves. More than three hundred years have passed, and people still do not know the answer. Without resolving the dispute, pundits came to a compromise - the corpuscular-wave theory of light. The corpuscle was called a photon, the wave - a quantum, they studied the properties of light, but the dispute was not resolved.

In the process of studying electromagnetic waves (from the centimeter to micrometer wavelength range), it was found that some substances (solid, liquid or gaseous) under the influence of external exciting radiation or electricity emit structured light having one wavelength, direction of propagation and phase.

Simply put, this is the same resonance phenomenon that we know from school course physics. Remember the bridge example? A company of soldiers is marching across the bridge. They go in step, in a certain rhythm. And this ever-increasing oscillation leads to the collapse of the bridge, which in principle is designed even for the passage of trucks. The same thing happens with light. Great amount light waves of different lengths, phases and directions do not have a significant impact on us and are sometimes even useful.

Under the influence of the impulse of an external source of energy in the active medium, the atoms pass into an excited state, that is, their electrons occupy an energetically higher position. Then the electrons themselves return to their old position, while emitting a quantum of light. This quantum passes through the neighboring atom, exciting it. It turns out already two quanta of light. A chain reaction begins, intensified by the fact that the active medium is surrounded by mirror surfaces. Light quanta reflected from them stimulate further development chain reaction, leading to an increase in the radiation power level up to required dimensions. In this case, all quanta have one direction, one phase and wavelength, since they were generated by atoms of one substance.

It was this kind of radiation that was first called optical masers (a maser is a quantum generator of electromagnetic radiation in the centimeter range), then optical quantum generators, and now lasers. Laser- amplification of light by stimulated emission(Light Amplification by Stimulated Emission of Radiation).

2. Automatic system for tracking the movements of the patient's eye.

In terms of speed and quality of reaction, computers not only overtook world chess champions, but also practically caught up with the human eye. Previously, during the operation, the surgeon corrected the place where the beam hit the cornea, depending on the movements of the patient's eyeball. Now autotracking is doing this - automatic system tracking. Her reaction is faster than a human. It moves the "head" of the excimer apparatus, which includes an operating microscope and a part of the radiation delivery system, following the small movements of the patient's eye, and if the movement is too fast or sweeping, it automatically interrupts the laser.

Autotracking sharply reduces the possibility of such a complication as decentering of the laser exposure zone, that is, the appearance of irregular astigmatism in a patient after correction. Also, this system helps the surgeon to aim the laser at the optical center of the cornea before laser correction.

3. Air evacuation system with laser evaporation products from the area of ​​the surgical field.

This is such a small vacuum cleaner that removes microdust from the air above the patient's eye, into which the corneal tissue turns under the action of a laser. This dust interferes with the passage of radiation through the air, which reduces the predictability of the result of laser correction.

If the device satisfies the listed requirements, then laser correction on it can be carried out at the modern level.

Are there domestic excimer lasers

IRTC Eye Microsurgery in cooperation with the Institute general physics The Academy of Sciences of the USSR in 1986 created the excimer laser Profile-500, and recently, together with the Center for Physical Instrumentation of the Institute of General Physics Russian Academy sciences improved it and called it MicroScan-2000. MicroScan complies with world standards, but is used in a few clinics. I hope this situation will change in the future.

How much does a laser system cost?

Expensive, although prices are constantly decreasing. There was a time when the cost exceeded one million US dollars. Now it is several hundred thousand dollars. In addition, consumables for the laser and its maintenance are quite expensive. Periodically, it is necessary to clean the mirrors, change gas cylinders, and diagnose other systems of the apparatus. And no one is immune from wear and tear of parts. Permanent work with the laser by a specialized engineer is necessary. All this increases the cost of laser correction.

laser operating room

Twelve years ago, information appeared that in one of the US cities, laser correction was being carried out on the territory of a department store and without the participation of a doctor. The experience did not take root, laser correction could not be reduced to the level of wiping glasses. On the contrary, with the development of laser correction methods, the requirements for the room in which it is carried out have become more stringent. Sterile conditions, control of temperature, humidity, air purity are necessary.

The surfaces in the operating room should not be mirrored, which excludes the use of shiny tiles and blinds, glasses, mirrors, because the reflected laser radiation is dangerous.

Our air

The air must be clean. Any dust or volatile compounds can affect the quality of the beam through the air. Therefore, the patient should refrain from smoking and the use of perfumes and deodorants before correction. The ventilation system must have high-quality filters. In addition, the volume of air outflow should be less than the inflow. Then, when the door is opened, clean air will escape from the operating room under some pressure, not letting in dirty air from the preoperative room and blowing dust out. The same is true for possible gaps. High-quality ventilation contributes to stable and long work excimer laser facility. But it is undesirable to open the door to the operating room during laser operation, even with good ventilation.

The main parameter of high-quality ventilation is a tenfold air exchange. That is, in an hour the volume of air should change ten times. For example, in a room with a volume of 500 cubic meters, ventilation should deliver 5,000 cubic meters of air in one hour. This can be easily checked with an anemometer.

Our electricity

Our electricity is like our roads - smooth ones are extremely rare. So is electricity. Voltage fluctuations are not so bad. Many have heard about this. But about the structure of our alternating current not everyone remembers in the power grid. The graph reflecting the structure of the Russian alternating current is, to put it mildly, very uneven. And any "irregularities" of the alternating current can disrupt the stability of the laser, turn it off or break it. Not to mention the possibility of a sudden power outage during the operation.

Therefore, an uninterruptible switch should be an integral attribute of a laser installation.

Its functions:

In the event of a sudden drop in voltage in the mains, allow all electrical appliances in the operating room to work for another half an hour on average;

Avoid voltage fluctuations;

Align the AC structure. This is achieved by transforming the alternating current received from the mains into direct current, and then again forming an alternating current, but already even in structure.

Temperature and Humidity

Stable positive temperature and low humidity- a guarantee of the quality of medical manipulations. The recommended operating temperature for the laser is 19 to 23 °C. Therefore, the air conditioner must also be of high quality and provide full climate control.

Humidity- no more than 70%. No sudden fluctuations during the operating day, especially between laser calibrations. Accordingly, the doors to the operating room should be opened as rarely as possible, the number of people in it should be limited and not changed during the operating day, because everyone new person raises the temperature, and especially the humidity.

Article from the book: .