Baltic State Technical University
"Voenmekh" named after. D. F. Ustinova
Department I4
"Radio-electronic control systems"

Devices for receiving and converting signals
Coursework on the topic
« Quantum generators »

Completed:
Peredelsky Oleg
Group I471
Checked:
Tarasov A.I.

Saint Petersburg
2010

1. Introduction
This paper discusses the principles of operation of quantum generators, generator circuits, their design features, issues of frequency stability of generators and principles of modulation in quantum generators.
1.1 General information
The operating principle of quantum generators is based on the interaction of a high-frequency field with atoms or molecules of matter. They allow the generation of oscillations of significantly higher frequency and high stability.
Using quantum generators, it is possible to create frequency standards that exceed all existing standards in accuracy. Long-term frequency stability, i.e. Stability over a long period is estimated at 10 -9 – 10 -10, and short-term stability (minutes) can reach 10 -11.

Currently in time quantum generators are widely used as frequency standards in time service systems. Quantum amplifiers used in receiving devices of various radio systems, can significantly increase the sensitivity of the equipment and reduce the level of internal noise.
One of the features of quantum generators, which determines their rapid improvement, is their ability to operate effectively at very high frequencies, including the optical range, i.e., almost up to frequencies of the order of 10 9 MHz
Optical range generators make it possible to obtain high radiation directivity and high energy density in the light beam (about 10 12 -10 13 W/M 2 ) and a huge frequency range, allowing for the transmission of a large amount of information.
The use of optical range generators in communication, location and navigation systems opens up new prospects for significantly increasing the range and reliability of communications, the resolution of radar systems in range and angle, as well as the prospects for creating high-precision navigation systems.
Optical range generators are used in scientific research
research and industry. The extremely high concentration of energy in a narrow beam makes it possible, for example, to burn holes of very small diameter in superhard alloys and minerals, including the hardest mineral, diamond.
Quantum generators are usually distinguished:

by nature active substance(solid or gaseous), quantum phenomena in which determine the operation of devices.

by operating frequency range (centimeter and millimeter range, optical range - infrared and visible parts of the spectrum)

by the method of excitation of the active substance or separation of molecules by energy levels.

Based on the operating frequency range, quantum generators are divided into masers And lasers. Name maser- abbreviation of the phrase “microwave amplification by stimulated emission of radiation MASER”. Name laser- abbreviation of the phrase “light amplification by stimulated emission of radiation LASER”

1.2 History of creation
The history of the creation of the maser should begin in 1917, when Albert Einstein first introduced the concept of stimulated emission. This was the first step towards the laser. The next step was taken by the Soviet physicist V.A. A manufacturer who pointed out in 1939 the possibility of using stimulated emission to amplify electromagnetic radiation as it passes through matter. The idea expressed by V.A. Fabrikant, assumed the use of microsystems with inverse population of levels. Later, after the end of the Great Patriotic War, V.A. The manufacturer returned to this idea and, based on his research, submitted in 1951 (together with M.M. Vudynsky and F.A. Butaeva) an application for the invention of a method for amplifying radiation using stimulated emission. A certificate was issued for this application, in which, under the heading “Subject of the invention,” it is written: “A method of amplifying electromagnetic radiation (ultraviolet, visible, infrared and radio wavelengths), characterized in that the amplified radiation is passed through a medium in which, with the help of auxiliary radiation or in another way they create an excess concentration of atoms, other particles or their systems in the upper energy levels, corresponding to excited states.”
Initially, this method of amplifying radiation was implemented in the radio range, or more precisely in the ultrahigh frequency range (microwave range). In May 1952, at the All-Union Conference on Radio Spectroscopy, Soviet physicists (now academicians) N.G. Basov and A.M. Prokhorov made a report on the fundamental possibility of creating a radiation amplifier in the microwave range. They called it a “molecular generator” (it was supposed to use a beam of ammonia molecules). Almost simultaneously, the proposal to use stimulated emission to amplify and generate millimeter waves was put forward at Columbia University in the USA by the American physicist Charles Townes. In 1954, a molecular oscillator, soon called a maser, became a reality. It was developed and created independently and simultaneously in two places on the globe - in Physical Institute named after P.N. Lebedev Academy of Sciences of the USSR (group led by N.G. Basov and A.M. Prokhorov) and at Columbia University in the USA (group led by C. Townes). Subsequently, the term “laser” came from the term “maser” as a result of replacing the letter “M” ( initial the words Microwave - microwave) with the letter “L” (the initial letter of the word Light - light). The operation of both a maser and a laser is based on the same principle - the principle formulated in 1951 by V.A. Manufacturer. The appearance of the maser meant that a new direction in science and technology was born. At first it was called quantum radiophysics, and later it became known as quantum electronics.

2. Operating principles of quantum generators.

In quantum generators, under certain conditions, a direct conversion of the internal energy of atoms or molecules into the energy of electromagnetic radiation is observed. This energy transformation occurs as a result of quantum transitions - energy transitions accompanied by the release of quanta (portions) of energy.
In the absence external influence Energy is exchanged between molecules (or atoms) of a substance. Some molecules emit electromagnetic vibrations, moving from a higher energy level to a lower one, part of it is absorbed, making the reverse transition. In general, under stationary conditions, a system consisting of a huge number of molecules is in dynamic equilibrium, i.e. As a result of a continuous exchange of energy, the amount of energy emitted is equal to the amount absorbed.
The population of energy levels, i.e. number of atoms or molecules present on various levels, is determined by the temperature of the substance. The population of levels N 1 and N 2 with energies W 1 and W 2 is determined by the Boltzmann distribution:

(1)

Where k– Boltzmann constant;
T– absolute temperature of the substance.

In a state of thermal equilibrium, quantum systems have fewer molecules at higher energy levels, and therefore they do not emit, but only absorb energy when exposed to external irradiation. At the same time, molecules (or atoms) move to higher energy levels.
In molecular oscillators and amplifiers that use transitions between energy levels, it is obviously necessary to create artificial conditions under which the population of a higher energy level will be higher. In this case, under the influence of an external high-frequency field of a certain frequency, close to the frequency of the quantum transition, intense radiation associated with the transition from a high to a low energy level can be observed. This radiation caused external field, is called induced.
An external high-frequency field of the fundamental frequency corresponding to the quantum transition frequency (this frequency is called the resonant frequency) not only causes intense stimulated radiation, but also phases the radiation of individual molecules, which provides the addition of vibrations and the manifestation of the amplification effect.
Quantum transition state when the population top level exceeds the population of the lower transition level is called inverted.
There are several ways to obtain a high population of the upper energy levels (population inversion).
In gaseous substances, such as ammonia, it is possible to separate (sort) molecules into different energy states using an external constant electric field.
In solids, such separation is difficult, so various methods of excitation of molecules are used, i.e. methods of redistributing molecules across energy levels by irradiation with an external high-frequency field.

A change in the population of levels (inversion of the population of levels) can be produced by pulsed irradiation with a high-frequency field of a resonant frequency of sufficient intensity. With the correct selection of the pulse duration (the pulse duration should be much less than the relaxation time, i.e., the time to restore dynamic equilibrium), after irradiation it is possible to amplify the external high-frequency signal for some time.
The most convenient excitation method, currently widely used in generators, is the method of irradiation with an external high-frequency field, which differs significantly in frequency from the generated vibrations, under the influence of which the necessary redistribution of molecules across energy levels occurs.
The operation of most quantum generators is based on the use of three or four energy levels (although in principle a different number of levels can be used). Let us assume that generation occurs due to an induced transition from the level 3 per level 2 (see Fig. 1).
In order for the active substance to enhance at the transition frequency 3 -> 2, need to make population level 3 above population level 2. This task is performed by an auxiliary high-frequency field with a frequency ? vsp which “throws” some of the molecules from the level 1 per level 3. Population inversion is possible under certain parameters quantum system and sufficient auxiliary radiation power.
A generator that creates an auxiliary high-frequency field to increase the population of a higher energy level is called a pump or backlight generator. The last term is associated with generators of visible and infrared spectra in which light sources are used for pumping.
Thus, to carry out the effective operation of a quantum generator, it is necessary to select an active substance that has a certain system of energy levels between which an energy transition could occur, and also to select the most appropriate method of excitation or separation of molecules into energy levels.

Figure 1. Diagram of energy transitions
in quantum generators

3. Circuits of quantum generators
Quantum generators and amplifiers are distinguished by the type of active substance used in them. Currently, mainly two types of quantum devices have been developed, which use gaseous and solid active substances
capable of intense induced radiation.

3.1 Molecular generators with separation of molecules by energy levels.

Let us first consider a quantum generator with a gaseous active substance, in which, using an electric fields, separation (sorting) of molecules located at high and low energy levels is carried out. This type of quantum oscillator is usually called a molecular beam oscillator.

Figure 2. Diagram of a molecular generator using an ammonia beam
1 – source of ammonia; 2- mesh; 3 – diaphragm; 4 – resonator; 5 – sorting device

In practically implemented molecular generators, ammonia gas (chemical formula NH 3) is used, in which molecular radiation associated with the transition between different energy levels is very pronounced. In the ultrahigh frequency range, the most intense radiation is observed during the energy transition corresponding to the frequency f n= 23,870 MHz ( ? n=1.26 cm). Simplified diagram of a generator running on ammonia in gaseous state shown in Figure 2.
The main elements of the device, outlined in Figure 2 by a dotted line, in some cases are placed in special system, cooled with liquid nitrogen, which ensures the low temperature of the active substance and all elements necessary to obtain a low noise level and high frequency stability of the generator.
Ammonia molecules leave the reservoir at very low pressure, measured in units of millimeters of mercury.
To obtain a beam of molecules moving almost parallel in the longitudinal direction, ammonia is passed through a diaphragm with a large number narrow axially directed channels. The diameter of these channels is chosen to be quite small compared to medium length free path of molecules. To reduce the speed of movement of molecules and, therefore, reduce the likelihood of collisions and spontaneous, i.e., uninduced, radiation leading to fluctuation noise, the diaphragm is cooled with liquid helium or nitrogen.
To reduce the probability of collisions of molecules, one could go not along the path of decreasing temperature, but along the path of decreasing pressure, however, this would reduce the number of molecules in the resonator that simultaneously interact with the high-frequency field of the latter, and the power given off by excited molecules to the high-frequency field of the resonator would decrease.
To use gas as an active substance in a molecular generator, it is necessary to increase the number of molecules located at a higher energy level against their number determined by dynamic equilibrium at a given temperature.
In a generator of this type, this is achieved by sorting out low energy level molecules from the molecular beam using a so-called quadrupole capacitor.
A quadrupole capacitor is formed by four metal longitudinal rods of a special profile (Figure 3a), connected in pairs through one to a high-voltage rectifier, which have the same potential but alternating in sign. The resulting electric field of such a capacitor on the longitudinal axis of the generator is equal to zero due to the symmetry of the system and reaches its maximum value in the space between adjacent rods (Figure 3b).

Figure 3. Quadrupole capacitor circuit

The process of sorting molecules proceeds as follows. It has been established that molecules located in an electric field change their internal energy with increasing electric field strength; the energy of the upper levels increases and the lower levels decrease (Figure 4).

Figure 4. Dependence of energy levels on electric field strength:

upper energy level

lower energy level

This phenomenon is called the Stark effect. Due to the Stark effect, ammonia molecules, when moving in the field of a quadrupole capacitor, trying to reduce their energy, i.e., acquire a more stable state, are separated: molecules of the upper energylevels tend to leave the region of a strong electric field, i.e., they move towards the axis of the capacitor, where the field is zero, and the molecules of the lower level, on the contrary, move into the region of a strong field, i.e., they move away from the axis of the capacitor, approaching the plates of the latter. As a result, the molecular beam is not only largely freed from molecules of the lower energy level, but also quite well focused.
After passing through the sorting device, the molecular beam enters a resonator tuned to the frequency of the energy transition used in the generator f n= 23,870 MHz .
The high-frequency field of a cavity resonator causes stimulated emission of molecules associated with a transition from an upper energy level to a lower one. If the energy emitted by the molecules is equal to the energy consumed in the resonator and transferred to the external load, then a stationary state is established in the system oscillatory process and the considered device can be used as a frequency-stable oscillation generator.

The process of establishing oscillations in the generator proceeds as follows.
Molecules entering the resonator, which are predominantly at the upper energy level, spontaneously (spontaneously) make a transition to the lower level, emitting energy quanta of electromagnetic energy and exciting the resonator. Initially, this excitation of the resonator is very weak, since the energy transition of the molecules is random. The electromagnetic field of the resonator, acting on the molecules of the beam, causes induced transitions, which in turn increase the field of the resonator. Thus, gradually increasing, the resonator field will increasingly influence the molecular beam, and the energy released during induced transitions will strengthen the resonator field. The process of increasing the intensity of oscillations will continue until saturation occurs, at which point the resonator field will be so large that during the passage of molecules through the resonator it will cause not only induced transitions from the upper level to the lower one, but partially also reverse transitions associated with absorption of electromagnetic energy. In this case, the power released by the ammonia molecules no longer increases and, therefore, a further increase in the amplitude of vibrations becomes impossible. A stationary generation mode is established.
Therefore, this is not a simple excitation of the resonator, but a self-oscillatory system, including feedback, which is carried out through the high-frequency field of the resonator. The radiation of molecules flying through the resonator excites a high-frequency field, which in turn determines the stimulated emission of molecules, the phasing and coherence of this radiation.
In cases where the self-excitation conditions are not met (for example, the density of the molecular flux passing through the resonator is insufficient), this device can be used as an amplifier with a very low level of internal noise. The gain of such a device can be adjusted by changing the molecular flux density.
The cavity resonator of a molecular generator has a very high quality factor, measured in tens of thousands. To obtain such a high quality factor, the resonator walls are carefully processed and silver-plated. The holes for the entry and exit of molecules, which have a very small diameter, simultaneously serve as high-frequency filters. They are short waveguides, the critical wavelength of which is less than the natural wavelength of the resonator, and therefore the high-frequency energy of the resonator practically does not escape through them.
To fine-tune the resonator to the transition frequency, the latter uses some kind of tuning element. In the simplest case, it is a screw, the immersion of which into the resonator slightly changes the frequency of the latter.
In the future, it will be shown that the frequency of the molecular oscillator is somewhat “delayed” when the resonator tuning frequency changes. True, the frequency delay is small and is estimated at values of the order of 10 -11, but they cannot be neglected due to the high requirements placed on molecular generators. For this reason, in a number of molecular generators, only the diaphragm and the sorting system are cooled with liquid nitrogen (or liquid air), and the resonator is placed in a thermostat, the temperature in which is maintained constant by an automatic device with an accuracy of fractions of a degree. Figure 5 schematically shows a device of this type of generator.
The power of molecular generators using ammonia usually does not exceed 10 -7 W,
Therefore, in practice they are used mainly as highly stable frequency standards. The frequency stability of such a generator is estimated by the value
10 -8 – 10 -10. Within one second, the generator provides frequency stability of the order of 10 -13.
One of the significant disadvantages of the considered generator design is the need for continuous pumping and maintenance of the molecular flow.

Figure 5. Design of a molecular generator
with automatic stabilization of the resonator temperature:
1- source of ammonia; 2 – capillary system; 3- liquid nitrogen; 4 – resonator; 5 – water temperature control system; 6 – quadrupole capacitor.

3.2 Quantum generators with external pumping

In the type of quantum generators under consideration, both solids and gases can be used as active substances, in which the ability for energy-induced transitions of atoms or molecules excited by an external high-frequency field is clearly expressed. In the optical range, they are used to excite (pump) the active substance. various sources light radiation.
Optical range generators have a range of positive qualities, and have found wide application in various radio communication systems, navigation, etc.
As in centimeter- and millimeter-wave quantum generators, lasers usually use three-level systems, that is, active substances in which a transition between three energy levels occurs.
However, one feature should be noted that must be taken into account when choosing an active substance for generators and amplifiers of the optical range.
From the relation W 2 –W 1 =h? It follows that as the operating frequency increases? in oscillators and amplifiers it is necessary to use a higher difference in energy levels. For optical range generators approximately corresponding to the frequency range 2 10 7 -9 10 8 MHz(wavelength 15-0.33 mk), energy level difference W 2 –W 1 should be 2-4 orders of magnitude higher than for centimeter range generators.
Both solids and gases are used as active substances in optical range generators.
Artificial ruby is widely used as a solid active substance - corundum crystals (A1 2 O 3) with an admixture of chromium ions (Cr). In addition to ruby, glasses activated with neodymium (Nd), crystals of calcium tungstate (CaWO 4) with an admixture of neodymium ions, crystals of calcium fluoride (CaF 2) with an admixture of dysprosium (Dy) or uranium ions and other materials are also widely used.
Gas lasers typically use mixtures of two or more gases.

3.2.1 Generators with solid active substance

The most widespread type of optical range generator are generators in which ruby with an admixture of chromium (0.05%) is used as the active substance. Figure 6 shows a simplified diagram of the arrangement of energy levels of chromium ions in ruby. The absorption bands at which it is necessary to pump (excite) correspond to the green and blue parts of the spectrum (wavelength 5600 and 4100A). Typically, pumping is carried out using a gas-discharge xenon lamp, the emission spectrum of which is close to that of the sun. Chromium ions, absorbing photons of green and blue light, move from level I to levels III and IV. Some of the excited ions from these levels return to the ground state (to level I), and most of them pass without emitting energy to the metastable level P, increasing the population of the latter. Chromium ions that have moved to level II long time remain in this excited state. Therefore, on the second level
it is possible to accumulate a larger number of active particles than at level I. When the population of level II exceeds the population of level I, the substance is able to enhance electromagnetic oscillations at the frequency of the II-I transition. If a substance is placed in a resonator, it becomes possible to generate coherent, monochromatic vibrations in the red part of the visible spectrum (? = 6943 A ). The role of a resonator in the optical range is performed by reflective surfaces parallel to each other.

Figure 6. Energy levels of chromium ions in ruby

absorption bands under optical pumping

non-radiative transitions

metastable level

The process of laser self-excitation proceeds qualitatively in the same way as in a molecular generator. Some of the excited chromium ions spontaneously (spontaneously) transfer to level I, emitting photons. Photons that propagate perpendicular to reflective surfaces experience multiple reflections and repeatedly pass through the active medium and are amplified in it. The intensity of oscillations increases to a stationary value.
In the pulsed mode, the envelope of the radiation pulse of the ruby generator has the character of short-term flashes lasting on the order of tenths of a microsecond and with a period of the order of several microseconds (Fig. 7, V).
The relaxation (intermittent) nature of the generator radiation is explained by different speeds the entry of ions into level II due to pumping and a decrease in their number during induced transitions from level II to level I.
Figure 7 shows oscillograms that qualitatively explain the process
generation in a ruby laser. Under the influence of pump radiation (Fig. 7, A) accumulation of excited ions occurs at level II. After some time the population N 2 will exceed the threshold value and self-excitation of the generator will become possible. During the period of coherent emission, the replenishment of level II ions due to pumping lags behind their consumption as a result of induced transitions, and the population of level II decreases. In this case, the radiation either sharply weakens or even stops (as in this case) until, due to pumping, level II is enriched to a value exceeding the threshold (Fig. 7, b), and excitation of oscillations again becomes possible. As a result of the process considered, a series of short-term flashes will be observed at the laser output (Fig. 7, c).

Figure 7. Oscillograms explaining the operation of a ruby laser:
a) power of the pumping source
b) level II population
c) generator output power

In addition to ruby, other substances are used in optical range generators, for example, calcium tungstate crystal and neodymium-activated glass.
A simplified structure of the energy levels of neodymium ions in a calcium tungstate crystal is shown in Figure 8.
Under the influence of light from a pumping lamp, ions from level I are transferred to excited states indicated in diagram III. Then they move to level P without radiation. Level II is metastable, and excited ions accumulate on it. Coherent radiation in the infrared range with wavelength ?= 1,06 mk occurs when ions move from level II to level IV. Ions make the transition from level IV to the ground state without radiation. The fact that radiation occurs
when ions move to level IV, which lies above the ground level, it is significantly
facilitates the excitation of the generator. The population of level IV is significantly less than level P [this follows from formula 1] and thus, to achieve the excitation threshold to level II, fewer ions must be transferred, and therefore less pumping energy must be expended.

Figure 8. Simplified structure of neodymium ion levels in calcium tungstate (CaWO 4 )

Glass doped with neodymium also has a similar energy level diagram. Lasers using activated glass emit at the same wavelength? = 1.06 microns.
Active solids are made in the form of long round (less often rectangular) rods, the ends of which are carefully polished and reflective coatings are applied to them in the form of special dielectric multilayer films. The plane-parallel end walls form a resonator in which a regime of multiple reflection of emitted oscillations is established (close to the regime of standing waves), which enhances the induced radiation and ensures its coherence. The resonator can also be formed by external mirrors.
Multilayer dielectric mirrors have low intrinsic absorption and make it possible to obtain the highest quality factor of the resonator. Compared to metal mirrors formed thin layer silver or other metal, multilayer dielectric mirrors are much more difficult to manufacture, but are much superior in durability. Metal mirrors fail after several flashes, and therefore modern models They don't use lasers.
The first laser models used spiral-shaped pulsed xenon lamps as a pumping source. Inside the lamp there was a rod of the active substance.
A serious disadvantage of this generator design is the low utilization rate of the light energy of the pumping source. In order to eliminate this drawback, generators use focusing of the light energy of the pumping source using special lenses or reflectors. The second method is simpler. The reflector is usually made in the form of an elliptical cylinder.
Figure 9 shows the circuit of a ruby oscillator. The backlight lamp, operating in pulse mode, is located inside an elliptical reflector that focuses the lamp light on the ruby rod. The lamp is powered by a high-voltage rectifier. In the intervals between pulses, the energy of the high-voltage source is accumulated in a capacitor with a capacity of about 400 mkf. At the moment of applying a starting ignition pulse with a voltage of 15 kV, removed from the secondary winding of the step-up transformer, the lamp lights up and continues to burn until the energy accumulated in the capacitor of the high-voltage rectifier is used up.
To increase the pumping power, several xenon lamps can be installed around the ruby rod, the light of which is concentrated onto the ruby rod using reflectors.
For the one shown in Fig. 23.10 generator threshold pumping energy, i.e. the energy at which generation begins, is about 150 J. With the storage capacity indicated on the diagram WITH = 400 mkf such energy is provided at a source voltage of about 900 IN.

Figure 9. Ruby oscillator with elliptical reflector for focusing the light of the pumping lamp:

xenon lamp

Due to the fact that the spectrum of pumping sources is much wider than the useful absorption band of the crystal, the energy of the pumping source is used very poorly and therefore it is necessary to significantly increase the power of the source in order to provide sufficient pumping power for generation in a narrow absorption band. Naturally, this leads to a strong increase in the temperature of the crystal. To prevent overheating, you can use filters whose bandwidth approximately coincides with the absorption band of the active substance, or use a forced cooling system for the crystal, for example, using liquid nitrogen.
Inefficient use of pump energy is the main reason for the relatively low efficiency of lasers. Generators based on ruby in pulse mode make it possible to obtain an efficiency of the order of 1%, generators based on glass - up to 3-5%.
Ruby lasers operate primarily in pulsed mode. The transition to continuous mode is limited by the resulting overheating of the ruby crystal and pumping sources, as well as burnout of the mirrors.
Research into lasers using semiconductor materials is currently underway. They use a semiconductor diode made of gallium arsenide as an active element, the excitation (pumping) of which is carried out not by light energy, but by a high-density current passed through the diode.
The design of the laser active element is very simple (see Figure 10) It consists of two halves of semiconductor material p- And n-type. The lower half of n-type material is separated from the upper half of p-type material by a plane р-n transition. Each of the plates is equipped with a contact for connecting a diode to a pumping source, which is used as a source DC. The end faces of the diode, strictly parallel and carefully polished, form a resonator tuned to the frequency of the generated oscillations corresponding to a wavelength of 8400 A. The dimensions of the diode are 0.1 x 0.1 x 1,25 mm. The diode is placed in a cryostat with liquid nitrogen or helium and a pump current is passed through it, the density of which is р-n transition reaches values of 10 4 -10 6 a/cm 2 In this case, coherent oscillations of the infrared range with a wavelength of ? = 8400A.

Figure 10. The structure of the active element of a semiconductor diode laser.

polished edges

contact

pn junction plane

contact

The emission of energy quanta in a semiconductor is possible when electrons move from the conduction band to free levels in the valence band - from higher energy levels to lower ones. In this case, two current carriers “disappear” - an electron and a hole.
When an energy quantum is absorbed, an electron moves from the valence band to the conduction band and two current carriers are formed.
In order for amplification (as well as generation) of oscillations to be possible, it is necessary that the number of transitions with energy release prevail over transitions with energy absorption. This is achieved in a semiconductor diode with heavily doped r- And n-regions when a forward voltage is applied to it, as indicated in Figure 10. When the junction is biased in the forward direction, electrons from n- areas diffuse into p- region. Due to these electrons, the population of the conduction band sharply increases r-conductor, and it can exceed the concentration of electrons in the valence band.
The diffusion of holes from p- V n- region.
Since the diffusion of carriers occurs to a small depth (on the order of a few microns), not the entire surface of the end of the semiconductor diode participates in the radiation, but only the areas immediately adjacent to the interface plane p- And n- regions.
In a pulsed mode of this type, lasers operating in liquid helium have a power of about 300 W with a duration of about 50 ns and about 15 W with duration 1 mks. In continuous mode, the output power can reach 10-20 mW with a pump power of about 50 mW.
Radiation of oscillations occurs only from the moment when the current density in the junction reaches threshold value, which for arsenic gallium is about 10 4 a/cm 2 . So high density achieved by choosing a small area р-n transitions usually corresponds to a current through the diode of the order of several amperes.

3.2.2 Generators with gaseous active substance

In optical quantum generators, the active substance is usually a mixture of two gases. The most common is a gas laser using a mixture of helium (He) and neon (Ne).
The location of the energy levels of helium and neon is shown in Figure 11. The sequence of quantum transitions in a gas laser is as follows. Under the influence of electromagnetic oscillations of a high-frequency generator in gas mixture, enclosed in a quartz glass tube, an electrical discharge occurs, leading to the transition of helium atoms from the ground state I to states II (2 3 S) and III (2 1 S). When excited helium atoms collide with neon atoms, an energy exchange occurs between them, as a result of which the excited helium atoms transfer energy to neon atoms and the population of the 2S and 3S levels of neon increases significantly.
etc.............

electromagnetic coherent source radiation(optical or radio range), in which the phenomenon is used stimulated emission excited atoms, molecules, ions, etc. Gases, liquids, solid dielectrics, and PP crystals are used as working materials in carbon dioxide. The excitation of the worker, i.e., the supply of energy necessary for the work of the generator, is carried out by a strong electric current. field, light from external source, electron beams, etc. Radiation of K. g., in addition to high monochromaticity and coherence, has a narrow focus and means. power. See also Laser, Maser, Molecular Generator.

- the same as Laser...
Beginnings modern Natural Science
- quantum generator a device for generating coherent electromagnetic radiation...
Encyclopedia of technology
- an optical quantum generator is the same as a laser...
Encyclopedia of technology
- source of coherent electromagnetic radiation, the action of which is based on the stimulated emission of photons by atoms, ions and molecules. K. g. radio range is called. masers, K. g. optical. range - lasers...
- the same as a laser...
Natural science. Encyclopedic Dictionary
- a technical device for pulsed or continuous generation of monochromatic coherent radiation in the optical range of the spectrum...
Big medical dictionary
- a source of electromagnetic coherent radiation, which uses the phenomenon of induced radiation of excited atoms, molecules, ions, etc. Gases, liquids,...
Big Encyclopedic Polytechnic Dictionary
- an electromagnetic wave generator that uses the phenomenon of stimulated emission...
- the same as Laser...
Great Soviet Encyclopedia
- the same as a laser...
Modern encyclopedia
- a source of coherent electromagnetic radiation, the action of which is based on the stimulated emission of photons by atoms, ions and molecules...
- the same as a laser...
Big encyclopedic dictionary
- QUANTUM, -a, m. In physics: the smallest amount of energy given off or absorbed by a physical quantity in its non-stationary state. K. energy. K. light...
Ozhegov's Explanatory Dictionary
- QUANTUM, quantum, quantum. adj. to quantum Quantum rays. Quantum mechanics...
Ushakov's Explanatory Dictionary
- quantum adj. 1. ratio with noun quantum associated with it 2...
Explanatory Dictionary by Efremova
- kv"...
Russian spelling dictionary

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The Quantum God While working on this book, I took one day off from quantum physics and went to Lichfield, Staffordshire. I had a wonderful time in the beautiful, esoteric feeling of Lichfield Cathedral, looking at its amazing façade

QUANTUM LEAP

From the book The Sixth Race and Nibiru author Byazyrev Georgy

QUANTUM LEAP When you achieve samadhi, the soul turns into Divine Light Dear readers, you already know that in 2011 the twelfth planet of the solar system, Nibiru, will be visible in our sky. In February 2013, Planet X will make its closest approach to Earth

Appendix III. MINDS: Quantum Mind

From the book The Power of Silence author Mindell Arnold

Appendix III. MINDS: The Quantum Mind In the following pages I summarize some of the many meanings I associate with the term "quantum mind". A technical - yet popularly stated - description quantum mind can be found in Nick Herbert's books

Quantum dualism

From the book The End of Science: A Look at the Limits of Knowledge at the Twilight of the Age of Science by Horgan John

Quantum Dualism There is one point on which Crick, Edelman, and almost all neuroscientists agree: the properties of the mind do not depend significantly on quantum mechanics. Physicists, philosophers, and other scientists have speculated about the connections between quantum mechanics and consciousness, at least

Quantum Mind and Process Mind

From the book The Process Mind. A Guide to Connecting with the Mind of God author Mindell Arnold

The Quantum Mind and the Process Mind The Process Mind is a development of all my previous work and, in particular, the book “The Quantum Mind”, written about ten years ago. In this book I discussed the quantum-like characteristics of our psychology and showed how

ELECTRONS - QUANTUM GAS

From the book Living Crystal author Geguzin Yakov Evseevich

ELECTRONS - QUANTUM GAS In the history of the study of crystals at the beginning of our century, there was a period when, among others, the problem of “electrons in metal” was very mysterious, intriguing, and seemed to be a dead end. Judge for yourself. Experimenters studying electrical properties

Quantum generator

From the book Great Soviet Encyclopedia (KB) by the author TSB

Optical quantum generator

From the book Great Soviet Encyclopedia (OP) by the author TSB

Quantum generator

Quantum generator- a general name for sources of electromagnetic radiation operating on the basis of stimulated emission of atoms and molecules. Depending on what wavelength a quantum generator emits, it can be called differently: laser, maser, razer, gaser.

History of creation

A quantum generator is based on the principle of stimulated emission proposed by A. Einstein: when a quantum system is excited and at the same time there is radiation of a frequency corresponding to a quantum transition, the probability of the system jumping to a lower energy level increases in proportion to the density of radiation photons already present. The possibility of creating a quantum generator on this basis was pointed out by the Soviet physicist V. A. Fabrikant in the late 40s.

Literature

Landsberg G.S. Elementary textbook physics. Volume 3. Oscillations and waves. Optics. Atomic and nuclear physics. - 1985.

Herman J., Wilhelmi B. "Lasers for the generation of ultrashort light pulses" - 1986.

Wikimedia Foundation. 2010.

Notker Stutterer
Resynthesis

See what a “Quantum Generator” is in other dictionaries:

QUANTUM GENERATOR- electric generator mag. waves, in which the phenomenon of stimulated emission is used (see QUANTUM ELECTRONICS). K. g. radio range, as well as a quantum amplifier, called. maser. The first K. g. was created in the microwave range in 1955. The active medium in it ... Physical encyclopedia

QUANTUM GENERATOR- a source of coherent electromagnetic radiation, the action of which is based on the stimulated emission of photons by atoms, ions and molecules. Quantum generators in the radio range are called masers, quantum generators in the optical range... ... Big Encyclopedic Dictionary

quantum generator- A source of coherent radiation based on the use of stimulated emission and feedback. Note Quantum generators are divided according to the type of active substance, method of excitation and other characteristics, for example, beam, gas... Technical Translator's Guide

QUANTUM GENERATOR- a source of monochromatic coherent electromagnetic radiation (optical or radio range), operating on the basis of stimulated emission of excited atoms, molecules, ions. Gases, crystalline... Big Polytechnic Encyclopedia

quantum generator- a device for generating coherent electromagnetic radiation. Coherence is the coordinated flow in time and space of several vibrational or wave processes, which appears when they are added, for example. in case of interference... Encyclopedia of technology

quantum generator- a source of coherent electromagnetic radiation, the action of which is based on the stimulated emission of photons by atoms, ions and molecules. Quantum generators in the radio range are called masers, quantum generators in the optical range ... ... Encyclopedic Dictionary

quantum generator- kvantinis generatorius statusas T sritis Standartizacija ir metrologija apibrėžtis Elektromagnetinių bangų generatorius, kurio veikimas pagrįstas sužadintųjų atomų, molekulių, jonų priverstinio spinduliavimo reiškiniu. atitikmenys: engl. quantum... ... Penkiakalbis aiškinamasis metrologijos terminų žodynas

quantum generator- kvantinis generatorius statusas T sritis fizika atitikmenys: engl. quantum generator vok. Quantengenerator, m rus. quantum generator, m pranc. oscillateur quantique, m … Fizikos terminų žodynas

Quantum generator- a generator of electromagnetic waves that uses the phenomenon of stimulated emission (See Stimulated emission) (See Quantum electronics). K. g. radio range of ultra-high frequencies (microwave), as well as the Quantum amplifier of this ... ... Great Soviet Encyclopedia

Meaning of QUANTUM GENERATORS AND AMPLIFIERS in Collier's Dictionary

QUANTUM GENERATORS AND AMPLIFIERS

generators and amplifiers of electromagnetic waves based on the phenomenon of forced (induced) radiation. The operating principle of a microwave quantum generator called a maser (an abbreviation for English words Microwave Amplification by Stimulated Emission of Radiation, meaning “microwave amplification due to stimulated radiation”), was proposed in 1954 by Charles Townes. (The same principle underlies optical quantum amplifiers and laser generators.) Since the frequency of radiation at the output of a quantum generator is determined by strictly fixed, discrete energy levels of atoms or molecules of the active medium used in such a generator, it has a precisely defined and constant value.

Spontaneous and stimulated emission. The energy of electromagnetic radiation is released or absorbed in the form of separate “portions” called quanta or photons, and the energy of one quantum is equal to h?, where h is Planck’s constant, and? - radiation frequency. When an atom absorbs an energy quantum, it moves to a higher energy level, i.e. one of its electrons jumps to an orbit further from the nucleus. It is customary to say that the atom in this case goes into an excited state.

An atom that finds itself in an excited state can release its stored energy in different ways. One possible way is to spontaneously emit a quantum with the same frequency, after which it returns to its original state. This is the process of spontaneous radiation (emission), schematically depicted in Fig. 1, b. At high frequencies, i.e. At short wavelengths corresponding to visible light, spontaneous emission occurs very quickly. Excited atom having absorbed a photon visible light, typically loses its acquired energy by spontaneous emission in less than one millionth of a second. The process of spontaneous emission at lower frequencies is delayed. In addition, an atom can go into some intermediate state, losing only part of its energy in the form of a photon of lower energy emitted by it.

There is another process that causes the excited atom to release this stored energy. If radiation of a certain frequency falls on an atom (as in Fig. 1, c), then it forces the atom to emit a photon and move to a lower level. Thus, one photon arrives and two leave. Stimulated emission always occurs at the same frequency and with the same phase as the incoming wave, and therefore, passing by the excited atom, the wave increases its intensity.

So, a wave of the corresponding frequency, passing through a medium in which there is an excess of excited atoms, is amplified due to the energy of stimulated emission of these atoms. However, if there are unexcited atoms in the medium, they can absorb the energy of the wave. It is obvious that amplification due to stimulated emission is opposite to absorption, and the predominance of one of the processes over the other depends on which atoms are more in the path of the wave - excited or unexcited.

The fact that along with spontaneous emission there must also be forced emission was postulated by Albert Einstein in 1916, accepting that all three processes occur - absorption, stimulated and spontaneous emission. Based on statistical considerations, he derived a formula describing the frequency spectrum of radiation emitted by a substance. The use of stimulated emission to create electromagnetic wave generators was proposed by Charles Townes in the USA and, independently of him, by Russian physicists N.G. Basov and A.M. Prokhorov. All three were awarded for this work Nobel Prize in physics (1964).

Quantum amplifier. As discussed above, radiation can be amplified simply by passing it through a suitable active medium. However, the gain is often insignificant - about 1%. To increase the gain, it is necessary to keep the radiation in contact with the active medium longer. To do this, you can enclose the active medium in a chamber with reflective walls. Then the transverse wave will be reflected from wall to wall, increasing slightly with each pass. When it is sufficiently intensified, part of the radiation can be released from the chamber as an output.

In the microwave (super high frequency) range, i.e. when the wavelength is in the range of 0.1 to 100 cm, the camera dimensions are usually comparable to the wavelength. A chamber that is tuned to the desired frequency by changing its dimensions (its length must be equal to the wavelength) is called a cavity resonator.

If the radiation wavelength is approximately 1 mm or less, then such a resonator is even difficult to manufacture. However, it is possible to make a cavity resonator for infrared or short-wave visible light so that its length is much longer than the wavelength, for example, in the form of two parallel mirror plates (Fig. 2). In such a device, a wave transverse to the plates, alternately reflected from the mirrors, will remain in the active medium and grow due to stimulated emission. A wave propagating in any other direction quickly leaves the resonator with almost no amplification.

This directional action of a system of two parallel plates is especially important for quantum generators of electromagnetic radiation with very short wavelengths. In this case, the gain in the active medium must be large enough so that when a wave passes from one plate to another, it more than compensates for the inevitable losses it suffers when reflected from the mirror. The continuous growth of the wave leads to the establishment of resonant electromagnetic oscillations in the gap between the mirrors. Waves propagating in any other direction are not amplified enough to compensate for the losses. And although in closed chamber this size could install and support millions different types vibrations and their rapidly changing combinations, a system of two parallel plates selects only transverse waves(the rest fade out). Since such a system is especially suitable for isolating oscillations with a specific short wavelength, it is widely used in quantum generators in the infrared and visible light range - lasers.

In order for some of the light to escape from the laser cavity, one of the plates must be translucent, i.e. transmitting part of the light incident on it and reflecting light with other wavelengths. Light passing through the translucent plate forms a narrowly directed beam. Such a laser device was proposed by Townes and A. Shavlov.

It is also possible to output radiation through a small hole in one of the reflecting walls. This circuit is often used in centimeter-wavelength (microwave) quantum oscillators. In lasers, it does not provide such a high directivity of the output beam.

Active environment. For resonant absorption and amplification due to stimulated emission, it is necessary that the wave passes through a material whose atoms or systems of atoms are “tuned” to the desired frequency. In other words, the difference in energy levels E2 - E1 for the atoms of the material must be equal to the frequency of the electromagnetic wave multiplied by Planck’s constant:

Further, in order for stimulated emission to prevail over absorption, there must be more atoms at the upper energy level than at the lower one. This usually doesn't happen. Moreover, any system of atoms, left to itself for a sufficiently long time, comes into equilibrium with its environment at a low temperature, i.e. reaches a state of lowest energy. At elevated temperatures, some of the atoms of the system are excited by thermal motion. At infinitely high temperature all quantum states would be equally filled. But since the temperature is always finite, the predominant proportion of atoms are in the lowest state, and the higher the states, the less filled they are. If at absolute temperature T there are n0 atoms in the lowest state, then the number of atoms in the excited state, the energy of which exceeds the energy of the lowest state by an amount E, is given by the Boltzmann distribution:

where k is Boltzmann's constant.

Since there are always more atoms in lower states under equilibrium conditions than in higher ones, under such conditions absorption always predominates rather than amplification due to stimulated emission. An excess of atoms in a certain excited state can be created and maintained only by artificially transferring them to this state, and faster than they return to thermal equilibrium. A system in which there is an excess of excited atoms tends to thermal equilibrium, and it must be maintained in a nonequilibrium state by creating such atoms in it.

Three-level quantum generator. The method of creating and maintaining an excess of atoms in an excited state for gases (three-level system method) was proposed by N.G. Basov and A.M. Prokhorov, and for hard materials- N. Blombergen. The first three-level quantum amplifier was created by D. Scovil, J. Feer and G. Seidel. The three-level system is schematically presented in Fig. 3. Initially, all atoms are at the lowest level E1, and levels E2 and E3 are empty. The energy distance between levels E2 and E3 is not equal to the distance between levels E1 and E2. A “pumping” lamp or generator (depending on what range we are talking about - optical or radio frequency) produces radiation with a frequency corresponding to the transition from the lower level to the upper one. By absorbing this radiation, atoms become excited and move from the lower level to the upper one. Since initially there are no atoms at the intermediate level E2, there are more of them at the E3 level. When quite a lot of atoms have accumulated at the E3 level, generation begins at a frequency corresponding to the transition from the upper level to the intermediate one. In order for quantum generation to occur continuously, the E2 level must quickly become empty, i.e. atoms must be removed from it faster than they are created due to stimulated emission from the E3 level. The E2 level can be emptied by various processes, such as collisions with other atoms and energy transfer crystal lattice(if the active medium is solid). In all cases, the energy is converted into heat, so cooling of the device is necessary.

By pumping, no more than half of the atoms can be transferred from level E1 to E3, since then the effect of stimulated emission forces them to return to the lower level. But if, due to collisions or other processes, atoms from the E3 level quickly move to the E2 level, then pumping them to the upper level with a subsequent transition to the intermediate level can continue. In this way, more than half of the atoms (and even all) can be pumped to the E3 level. Then at the intermediate level it turns out more atoms, than at the lower one, and generation begins at the frequency corresponding to the transition. Both circuits of a three-level quantum oscillator and amplifier are used, and one or the other is selected depending on the properties of the available material with resonances at the desired frequencies. Generally speaking, it is desirable that the active medium, while satisfying all other requirements, should have high resonances. If a quantum generator is supposed to be used as a frequency standard, then the resonances must also be sharp. Such resonances are characteristic of the spectra of free atoms and molecules in gases. The resonances of solid materials are usually quite broad, although ions of rare earth elements and transition metals, such as chromium, in crystals have suitable spectra. Some materials of this kind have high and sharp resonances in both the microwave and optical ranges. For example, ruby (aluminum oxide), in which a certain percentage of aluminum ions are replaced by chromium ions, can serve as an active medium for a three-level quantum generator in the microwave range. Maiman showed that ruby is also suitable for making lasers. In both cases, the energy levels of chromium ions are used.

Laser. Lasers are optical quantum generators that produce radiation in the visible and infrared regions of the spectrum (where wavelengths are less than 1 mm). In intensity, such generators are much superior to all other types of sources of similar radiation. In addition, their output radiation falls on a very narrow frequency band and has the form of an almost non-divergent beam. In addition, laser beams can be focused into a very small spot, in which the light power density and electric field strength are colossal compared to what other light sources can produce. The output radiation is almost completely monochromatic and, more importantly, coherent, i.e. completely phase-matched and free of the chaotic disorder of ordinary light. See also LASER.

Molecular quantum generator. The first quantum generator, developed by Gordon, Zeiger and Townes, used an evacuated chamber containing a beam of ammonia molecules. Molecules of the beam, which were in a lower energy state, were removed from the beam by deflecting them in a nonuniform electric field. Molecules in the highest energy state were focused in a cavity resonator, where stimulated emission occurred (Fig. 4).

A quantum generator with a molecular beam produces radiation with a sharply selected output frequency. This is partly due to the fact that there are relatively few molecules in the beam and they cannot influence each other. Due to the small number of molecules, the output power is also small.

Gas discharge laser. The active medium of a gas-discharge laser is a mixture of noble gases such as helium and neon. The helium atom has an excited state with a long lifetime, and atoms excited to this “metastable” state cannot give up their excitation energy by spontaneous emission. However, they can transfer it in atomic collisions to unexcited neon atoms. After such a collision, the helium atom finds itself in its ground state, and the neon atom in its excited state. Generation occurs due to forced transitions from this energy level to an empty lower level of neon atoms.

Application. Quantum- electronic devices with atomic and molecular systems as active media are used as amplifiers and generators. At lower frequencies, such functions are performed by vacuum tubes and transistors. It is not surprising that the family of quantum electronic devices can already rival the number and diversity of older electronic devices. Quantum electronic devices have found a number of applications for which other electronic devices are poorly suited or not suitable at all. These are the functions of low-noise microwave amplifiers, primary frequency and time standards, as well as generators and amplifiers of infrared and visible radiation.

Low noise microwave amplifiers. The purpose of an amplifier is to amplify weak signals without distorting them or introducing noise (chaotic component). Electronic amplifiers always add their own noise to the signal. When working with extremely weak radio signals, it is important that the amplifier contributes as much as possible less noise. These are radio signals received from celestial objects, and radar signals reflected from objects located over long distances. In these two cases, the signal is observed against the sky, which introduces only minor noise. This allows you to detect a very weak signal if it is not masked by the noise of the receiver itself. Conventional amplifiers do not meet the requirements of such a task, and quantum amplifiers come to the rescue, introducing almost no noise. By replacing a vacuum tube amplifier at the receiver input with a quantum amplifier, you can increase the sensitivity of the receiver in the microwave range by a hundred times. Microwave receivers with quantum amplifiers are so sensitive that they can detect the thermal radiation of other planets and determine the temperature of their surface.

Frequency standards and atomic clocks. Atoms and systems of atoms, as already mentioned, can absorb and emit radiation only at certain specific frequencies or wavelengths. These resonances are often shaped like peaks, allowing their frequency to be measured with high precision. The corresponding frequencies are characteristic of certain atoms and molecules and, unlike man-made standards, do not change over time. Therefore, such resonances can serve as standards of frequency, wavelength and time. The frequency of the external electronic oscillator can be checked for calibration even against absorption resonances. Quantum generators directly produce radiation of a reference frequency. When a quantum generator is properly configured, the frequency at its output is constant. It can be used to monitor the progress of a precision clock or a more complex device designed to measure time intervals with high accuracy. The active medium of one of the most precise quantum generators is atomic hydrogen(the system is similar to the device of the first quantum generator - a maser - with a molecular beam of ammonia). The accuracy of its frequency is 10-10%, which corresponds to an error in the “clock rate” equal to one second in 30,000 years.

Collier. Collier's Dictionary. 2012