Combat helio neon laser color viprominuvannya. Lecture thirteen. gas lasers, helium-neon laser. The laser, which will be examined in more detail later in this robot, is triggered by an electrical discharge

A gas laser is a device that can be connected to optical quantum generators.

The main element of a non-stop helium-neon laser is a gas discharge tube T(Figure 1), which contains the cathode, which is heated, and the anode A. The tube is filled with helium ( Not) (partial vice Not 1 mmHg st) ta neon ( Ne) (partial vice Ne 0.1 mmHg st). The internal diameter of the tube is 1...10 mm, increasing from several tens of centimeters to 1.5...3 m. The ends of the tube are closed with plane-parallel glass or quartz windows P1 and P2, installed under the Brewster cut to the axis. For linearly polarized coupling with the electric vector at the falling plane, the coefficient of variation between them is equal to zero. Therefore, Brewster windows ensure linear polarization and laser propagation and reduce energy consumption when expanding the light from the active zone to the mirrors and back. The tube is placed in a resonator made of mirrors 1 and 2 with multi-spherical dielectric coatings. Such mirrors have a high reflection coefficient in the operating spectral range and practically do not fade the light. The throughput of the mirror, where it is important to improve the laser performance, should be 1...2%, otherwise less than 1%.

A voltage of 1...2 kV is supplied to the electrode of the tube. When the cathode is overheated and the voltage in the gases increases, a smoldering electrical discharge may occur. The smoldering discharge creates the minds for the inversion of the population of the regions in neon. The typical strength of a stream in a gas discharge is tens of milliamps.

Apparently, neon gives a boost to the discharge, but the necessary destruction of atoms occurs with the help of helium atoms. The schematic picture of the energy levels of atoms has been simplified Notі Ne baby 2 is shown.

For rakhunok shut up with electrons atoms Not cross at the awakening camp (2 3 S that 2 1 S). These are equally metastable with energies of 19.82 and 20.61 eV. Spontaneous radiation transition from these levels to the main level is prohibited by selection rules, then. It comes out with even little confidence.

Malyunok 2

The hour of life of an atom on the plains 2 1 S that 2 3 S It is great in the course of time of living on the primary awakening levels, that even a lot of atoms will accumulate on these metastable levels Not. Ale equal to neon 3 S i 2 S Practical avoidance of metastable levels 2 1 S that 2 3 S helium. What is it like when the awakened atoms are closed? Not with atoms Ne atomic transitions occur Ne awakenings with the resonant transfer of energy from helium atoms to neon atoms.

The process of awakening atoms Ne depicted by horizontal dotted arrows (Figure 2). As a result of the concentration of neon atoms at levels 3 S i 2 S grow strongly, and the inverse population of energy levels begins to arise compared to level 2 R. The tube has an active core that is made up of atoms Ne, which may invert the population of energy levels of electrons.

Spontaneous vibration of nearby excited atoms leads to expansion in the active middle of photons, which indicates electronic transitions in atoms of neon from the ranks of 3 S on the level 2 P.

Under the infusion of an electromagnetic field, a discharge of photons (which are initially spontaneously propagated by excited atoms to neon) is induced to coherently propagate the other excited atoms to neon, then. active medium that fills the laser tube. The massive growth of this process will be ensured by a large number of changes between mirrors. U 1 i U 2 resonators that lead to the formation of a pressure-induced flow of a direct coherent vibrating laser. The minimum cut-off width of the laser light beam is determined by diffraction, which occurs around the transverse cross-section of the beam, then. It’s less than light with the Khvil’s authorities. This most important situation distinguishes the laser beam from the other light beam.

4 PRILADI AND PRILADDYA

1 Gas laser LG78.

2 Optical lava.

3 Life block.

4 Diffraction effects.

5 Glass plates with microparticles filed between them.

6 Screen with millimeter scale.

5 Working with a gas laser

Turn down the Merezha toggle switch. Peremikach "Regulation of the flow" of the settings assigned to the worker by the doctor or laboratory assistant. They are categorically opposed to transferring them to another institution.

During the hour of working with the laser, the trace is remembered, which exposure to direct laser radiation is not safe for the eyes .

Therefore, when working with a laser, beware of light after displaying on the screen a surface that is glowing.

6 ORDER OF WYCONANNY ROBOTI

Right 1

Laser dimming

diffraction grating

The directness and spacious coherence of laser propagation allows it to be set in a series of settings without further colimation.

The installation for carrying out this procedure includes a laser, a rater with diffraction graters, and a screen with a millimeter scale to monitor the diffraction pattern (Figure 3).

Malyunok 3

The diffraction grating is installed perpendicular to the axis of the light exchanger, which extends from the laser. For this purpose, the light beam, raised from the surface of the grating, must be placed exactly in the middle of the laser window, then. avoid the light beam coming out of the laser from being reflected across the grating surface.

Due to the monochromatic nature of the laser propagation, the screen is careful not to display diffraction spectra that do not overlap, of different positive and negative orders. These spectra create a series of red shadows on the screen, which repeat the retina of the primary light beam that falls on the surface.

The screen is installed perpendicular to the light beam, and the orders of the spectra are in their order symmetrically to the zero scale of the screen.

When standing between the diffraction spectra and the zero-order spectrum, it is necessary to understand the midpoints of the guarded spectra (smoke).

Rozrakhunok has been following the formula for a long time

de d- permanent benefits (in our opinion d= 0.01 mm);
- Cut of diffraction;

k- spectrum order;

l – the last minute of laser vibration.

Malyunok 4

The diffraction rate is determined from the relationship

(2)

de - stand between the left and the right maxima in order k;

L- Position the area of ​​the diffraction grating up to the area of ​​the screen (Figure 4).

Substituting (2) to (1), removable

Order Vikonanny right 1

1 Vymiryat vіstan u spectra pershogo ( k= 1), other ( k= 2) that of the third ( k= 3) orders for different parts of the screen from the diffraction grating.

2 Enter the results of the experiments in Table 1.

3 Calculate the amount of energy that indicates laser output.

Table 1

Compilation of experimental data

1 Calculate the amount of skin cancer using formula (3).

2. Calculate the average value n- Number of vimiryuvan.

3 Calculate the absolute pardons of several extinct worlds

5 Set the reliability value a (behind the insertion box).

6 Use the Student's table to calculate the boundaries between the confidence intervals

7 Calculate the apparent loss The value of the found value is to be used in the developments necessary for attacks on the right.

Right 2

Fraunhofer diffraction laser vibration analysis

on small round particles

Monochromatic, well-coloured and spatially coherent laser beam makes it possible to completely prevent diffraction of light on round particles.

In order for diffraction on particles to be significant, the size of the particles must be small. However, if you place one small particle near the light beam, then the diffraction pattern that appears on the remote screen will be important to watch out for. The picture is projected on a light surface, created by a part of the light beam, which did not suffer from diffraction.

To obtain a clearly visible diffraction pattern, it is necessary to place randomly distributed particles across the light beam. In fact, Fraunhofer diffraction is observed from the fragments, whether the edge of the part is independent of its position in the cross-sectional area of ​​the light beam, but gives a different distribution of the diffracted light.

With the presence of a large number of particles in the cross-section of the beam, the cut-out section of the diffracted light, closed by the skin part of the rim, is not destroyed, since there is no systematic interference effect between the light beams, which is the diffract they sang on loose particles.

If in the cross-sectional area of ​​the light beam the particles are randomly scattered, then due to the uniformity of all the values ​​of the phases of the light diffracted behind different directions, only the intensity of the light beams will be formed, diffracted particles. Diffraction pattern N parts to strive for intensity N Once the surface has a diffraction pattern, the surrounding parts do not change their structure. This is the setting for this experiment.

The installation is removed from the right 1, and instead of the diffraction grating on the rater, frames with glass plates are installed, between which there are particles of lycopodium (moss moss spores), which are balls when close to the same small size.

On the screen, after turning on the laser, you can see a system of concentric light and dark diffraction rings, which will give off a light color.

Kutovy radius a i dark rings are subservient to relationships:

Kutovy radius a i light rings

(5)

de r- The radius of the part that caused the light diffraction.

Significance sina i get your health insurance

(6)

de D i- Linear diameter of the line diffraction ring on the screen;

L- Stand in front of the glass plate to the screen.

Order Vikonanny right 2

that collection of experimental data

1 Change the diameter of the first ( D 1) that other ( D 3) dark rings behind different parts L. Enter the results in the table. 2.

2 Create a work schedule D=f(L) to the skin at diffraction minimums, then. D 1 = f(L)і D 3 = f(L).

3 Calculate the tangent of the diffraction cutoffs, which indicate the first and the other dark ring, using formula (6), and the average value of the radius of the particle using additional relation (4).

4 Significantly the destruction of the extinction. Record the residual result from the view r = <r> ± r>(m).

5 Zrobiti visnovki shodo roboti.

The helium-neon laser - along with one or another conductor - is one of the most commonly used and most affordable lasers for the visible region of the spectrum. The power of such laser systems, mainly used for commercial purposes, ranges from 1 mW to several tens of mW. Particularly popular are non-pressurized He-Ne lasers of approximately 1 mW, which are used for vicorization, main purpose, as valuation devices, as well as for other advanced tasks in the field of virtualization technology. In the infrared and dark wavelength ranges, helium-neon lasers are increasingly being compared to one laser. He-Ne lasers are available, with blue lines, and also orange, yellow, and green, which are accessible to all types of selective mirrors.

Scheme of energy levels

The most important energy sources for the function of He-Ne lasers are helium and neon, shown in Fig. 1. Laser transitions occur in the neon atom, and the most intense lines appear as a result of transitions with long lines 633, 1153 and 3391 (div. table 1).

The electronic configuration of neon in the main state looks like this: 1s22s22p6, with the first shell (n = 1) and the other shell (n = 2) filled with two and eight electrons. Vishchi stand for rice. 1 is due to the fact that there is a 1s22s22p5 shell, and an electron that lights up (optical) is generated according to the scheme: 3s, 4s, 5s,..., Zp, 4p,... etc. Let's talk about the single-electronic system, which has a connection with the shell. In the LS (Russell - Saunders) scheme, for the energy levels of neon, a single-electron state is indicated (for example, 5s), as well as the resulting additional orbital momentum L (= S, P, D ...). In the notations S, P, D, the lower index shows the higher orbital momentum J, and the upper index shows the multiplicity 2S + 1, for example, 5s1P1. The phenomenological meaning behind Paschen is often discussed (Fig. 1). In this case, the order of the current wake-up electronic stations is from 2 to 5 (for s-stations) and from 1 to 10 (for p-stations).

Small 1. Scheme of the energy levels of a He-Ne laser. In neon, the equals are designated after Paschen, then: 3s2, 3s3, 3s4, 3s5, etc.

Table 1. Designations of transitions of intense lines of the He-Ne laser

Ruined

The active core of the helium-neon laser is a gas mixture, to which the necessary energy is supplied to the electrical discharge. The upper laser levels (2s and 2p after Paschen) are selectively populated based on the presence of metastable helium atoms (23S1, 21S0). During this process, there is an exchange of kinetic energy and a transfer of the energy of the excited helium atoms to the neon atoms. This process is called a different kind of process:

Not * + Ne -> Not + Ne * + ΔE, (1)

The star (*) symbolizes awakening. The difference in energy becomes at the time of destruction of the 2s-level: & DeltaE = 0.05 eV. When closed, the apparent difference is converted into kinetic energy, which is then distributed as heat. For 3s-level, identical numbers are placed. This resonant transfer of energy from helium to neon is the main process of pumping during the inversion of populations. This is a difficult time in the life of a metastable state. The selectivity of the population of the upper laser level is not favorable.

The destruction of non-atoms occurs on the basis of the connection of electrons - either directly, or through additional cascade transitions from the levels that lie higher. Due to long-lived metastable conditions, the density of helium atoms in these conditions is even greater. The upper laser levels 2s and 3s can - subject to the rules of selection for electrical Doppler transitions - only pass into the lower levels. For successful laser generation, it is important that the lifetime of s-stations (upper laser level) = approximately 100 ns, and the lifetime of p-stans (lower laser level) = 10 ns.

Dovzhyni hvil

Next, we will take a closer look at the most important laser transitions, vikoryst and Fig. 1 and data from Table 1. The most prominent line in the red region of the spectrum (0.63 μm) results from the transition 3s2 → 2р4. The lower rhubarb splits as a result of spontaneous vibration lasting 10 ns into the 1s-rubble (Fig. 1). Remains resistant to splitting due to the electric dipole vibration, which is also characteristic of long-term natural life. Therefore, atoms are concentrated in this country, which is highly populated. In a gas discharge, atoms in such a state collide with electrons, and this again awakens the 2nd part of the 3s-ribs. In this case, the population inversion changes, which reduces the intensity of the laser. The depletion of ls occurs in helium-neon lasers mainly through the connection with the wall of the gas discharge tube, due to which, with an increase in the diameter of the tube, a decrease in intensity and a decrease in efficiency are indicated . Therefore, it is practical to set the diameter to approximately 1 mm, which, in turn, can result in a reduction in the output power of He-Ne lasers of several tens of mW.

Electronic configurations 2s, 3s, 2p and 3p, which take part in the laser transition, split into numerical counterparts. This leads, for example, to further transitions in the visible region of the spectrum, as can be seen from Table 2. For all visible lines of the He-Ne laser, the quantum efficiency becomes close to 10%, which is not so much. The level diagram (Fig. 1) shows that the upper laser levels extend approximately 20 eV more than the main value. The energy of the red laser radiation becomes less than 2 eV.

Table 2. Maximum voltage λ, output voltage and line width Δ ƒ of the He-Ne laser (designated transitions according to Paschen)

Vibration in the infrared range around 1.157 µm results from additional transitions 2s → 2p. These also extend to a very weak line of approximately 1.512 µm. These infrared lines are found in commercial lasers.

A characteristic feature of the line in the HF range at 3391 µm is its high intensity. In the weak signal zone, with a one-time passage of weak light signals, it becomes close to 20 dB/m. This corresponds to a coefficient of 100 for a 1 meter laser. The upper laser level is the same as at the visible red junction (0.63 µm). Highly settled, on one side, decorate the viklycans with a short hour of life on the lower 3p-river. On the other hand, this is explained by the apparently great duration of the noise, apparently by the low frequency of vibration. Due to the interaction between forced and spontaneous vibration, the prominence increases for low frequencies. The amplification of weak signals g is usually proportional to g ~2.

Without selective elements, the helium-neon laser was emitted at a line of 3.39 µm, and not in the red region at 0.63 µm. A damaged infrared line skips either the selective mirror of the resonator or the clay in the Brewster windows of the gas discharge tube. Therefore, the laser generation threshold can be moved up to a level sufficient for 3.39 µm generation, so that there is no weaker line here.

Structurally not vikonannya

Necessary electronic activations are created in a gas discharge (Fig. 2), which can be generated with a voltage of approximately 12 kV with flow rates of 5 to 10 mA. The typical discharge depth is 10 cm or more, the diameter of the discharge capillaries becomes close to 1 mm and corresponds to the diameter of the transmitted laser beam. With an increase in the diameter of the gas-discharge tube, the corrosive action coefficient decreases, leaving waste to be emptied of the ls-level required by the wall of the tube. For optimal output tension, a high pressure (p) filling is applied: p D = 500 Pa mm, where D is the diameter of the tube. The relationship of the madness He/Ne to lie under the important line of laser stimulation. For the visible red line we have He: Ne = 5:l, and the infrared line is close to 1.15 µm - He:Ne=10:l. An important aspect is also the optimization of the thickness of the stream. The coefficient of action for the 633 nm line is close to 0.1%, since the wake-up process in this case is not very effective. The service life of a helium-neon laser is approximately 20,000 working years.

Small 2. Design of the He-Ne laser for polarized vibration in the mW range

The strength for such minds is equal to g=0.1 m-1, so it is necessary to use mirrors with a high value. For the laser beam to exit, a partial mirror is installed on one side that transmits (like a viewer) (for example, with R = 98%), and on the other side - a mirror with the highest possible transmission (~ 100%). The intensification of other visible transitions is significantly less (div. Table 2). For commercial purposes, this line was eliminated with the remaining resources behind the help of mirrors, which are supported by extremely small expenses.

Previously, with a helium-neon laser, the output windows of the gas discharge tube were fixed with epoxy resin, and the mirrors were mounted separately. This caused the helium to diffuse through the glue and water vapor to enter the laser. Today, the windows are fastened using the method of direct soldering of the metal to the glass, which reduces the helium flow to approximately 1 Pa per river. For small mass generation lasers, mirror coating is applied directly to the exit windows, which will significantly simplify the entire structure.

The power of the bundle

To select direct polarization, the gas-discharge lamp is provided with two or more rotating windows, as shown in Fig. 2, the resonator is inserted into a Brewster plate. The intensity on the optical surface is reduced to zero when the light falls under the so-called Brewster cut and polarizations are parallel to the incident plane. In this way, the promotion of such direct polarization passes through the Brewster window without any expense. At the same time, the intensity of the component, polarized perpendicularly to the surface of the surface, is high and bends in the laser.

The polarization coefficient (stage) (the degree of polarization is set to be perpendicular to the direction) is 1000:1 for standard commercial systems. When operating a laser without Brewster plates, non-polarized vibrations are generated from internal mirrors.

The laser primarily generates on the transverse TEM00 mode (lower-order mode), and a series of later (axial) modes is created. At the distance between the mirrors (below the laser resonator) L = 30 cm, the intermode frequency interval becomes Δ ƒ` = c/2L = 500 MHz. The central frequency becomes 4.7·1014 Hz. Segments of light amplification can be generated within the range Δ ƒ = 1500 MHz (Doppler width), at L = 30CM three different frequencies are produced: Δ ƒ/Δ ƒ`= 3. With viconicity less stand between the mirrors (<= 10см) может быть получена одночастотная генерация. При короткой длине мощность будет весьма незначительной. Если требуется одночастотная генерация и более высокая мощность, можно использовать лазер большей длины и с оснащением частотно-селективными элементами.

Helium-neon lasers around 10 mW are often used in interferometry and holography. The maximum coherence of such serial generation lasers is 20 to 30 cm, which is completely sufficient for holography of small objects. Greater coherence values ​​come from the distortion of serial frequency-selective elements.

When changing the optical distance between the mirrors, as a result of thermal or other influx, the sound of high axial frequencies of the laser resonator is generated. With single-frequency generation, a stable frequency is produced here and it moves uncontrollably in the line width range of 1500 MHz. By using additional electronic regulation, frequency stabilization can be achieved around the center of the line (commercial systems can achieve frequency stability of a few MHz). In previous laboratories, it is possible to stabilize a helium-neon laser at a range of less than 1 Hz.

By using the different lines of the mirrors in Table 4.2, the different lines in Table 4.2 can be activated to generate laser vibration. It is most common to find a visible line around 633 nm with typical outputs of a few milliwatts. After suppression of the intense laser line near 633 nm, the distortion of selective mirrors or prisms in the resonator may reveal other lines in the visible range (see Table 2). However, the output tension of these lines becomes less than 10% of the output tension of the intensive line or less.

Helium-neon lasers for commercial use are available in a variety of industries. In addition to them, there are also lasers that generate on rich lines and different combinations. At the end of the He-Ne lasers, which are reawakened, reawakened, rotating the prism, select the necessary supply of energy.

As a practical example, let’s look at the device and operating principle of the helium-neon laser, which is being tested in our laboratory. Robocha speech - atomy neon ( Ne). Vikorist is electrically pumped: electrons flow through the gas discharge tube; When liquid electrons connect with neon atoms, the remaining electrons are forced to move to the upper energy levels. However, for neon atoms, direct pumping with electron impact turned out to be ineffective. To speed up the transfer of energy, helium was added to neon ( He).

The pumping diagram is shown in Fig. 4.2. Afterwards, the connection between electrons and helium atoms moves from the main level to the level 2 S. These awakened helium atoms collide with neon atoms and provide them with stored energy. As a result, atoms and neon move from the main level to the level, which is close to the level 2 S helium. The results are on
equal to neon is created with the population is significant. At the same time there is rhubarb
It is sparsely populated, and the fragments are quickly cleared by spontaneous transitions to the lower plains. At the crossing
the population appears to be inverted. Transition of atom to neon from the upper
level to lower level
bring to laser viprominuvaniya with dozhina hvili
µm, which resembles a red light.

P There is a middle ground in which an inverse population has been created, then. umova (4.7) has a place. In such a middle-ground, the vibration is stronger, less polished. Therefore, the middle is more light with frequency ν (dowzhinyu hvili λ) , which indicates a transition between levels with an inverted population (extraordinary formula (4.2)). However, the power is small: the helium-neon laser has light, having passed through the active medium 1 m, try everything on 2 %. Therefore, in order to remove the bright vibration, it is necessary for the light to remain in the active middle for a long time. You can reach out for help optical resonator. An active center with inverse population and an optical resonator are the two main parts of any laser.

In Fig. 4.3 schematically shows a helium-neon laser device. In the middle there is a gas discharge tube (GDT) with an active core - a helium-neon mixture. Partial pressure to helium - 1 mmHg. ( 133 Pa), and neon - 0,1 mmHg. ( 13,3 Pa). The tube contains the cathode Before that anode A. When the cathode is heated and high voltage gases are supplied between the cathode and anode, the gases that energize the tube may generate an electrical discharge and cause the light to glow. During the hour of discharge, the drop in anode voltage at the pipe reaches 1,5 kV, the stream reaches through the tube 30 mA. When the stream passes through the sumish, an inverse population occurs.

Optical resonator - two high-accuracy mirrors Z1і Z2(flat or spherical), one of these ( Z2) napіvprozor. The mirrors are installed at the end of the gas discharge tube parallel to each other. The light, emerging from the resonator mirrors, passes through the gas discharge tube. As a result, the light flows into the active middle of the table, so that the intensity of the light reaches a great value. Before the beginning of laser generation in the middle there is a sprout of spontaneous generation. This transformation, going through the mirrors, often passes through the active middle. On the cutaneous passage it is forced with the help of a forced vipper of the middle. The result is a bright laser beam that emerges from the transparent mirror.

However, only a small part of spontaneous generation is generated by laser generation. The optical resonator has high vibrancy: in the middle of spontaneous vibration it selects vibrations from the song directly. Indeed, a large number of reflections will be detected only by the elements that are distributed throughout the optical axis of the resonator. Spontaneous vibration that goes under the cut to the axis, coming from the resonator and laser generation does not take part. For this reason, the laser generates a narrow, low-spread beam of light.

The vibration of the helium-neon laser is eliptically polarized. This is due to the fact that the window of the gas discharge tube is installed under the Brewster cut.
. The light that passes through the window of the gas discharge tube suppresses laser generation. Installing windows under the Brewster cut, they ask for what is light, in which vector E oscillates at the plane of the valley, passes through the window practically without distortion. As a result, only such polarized light is generated by the laser.

Thus, a narrow beam of red, eliptically polarized light emerges from the helium-neon laser. This light is the result of forced vibration. The order of interference is spontaneous, as it is not polarized and comes out of the laser in all directions. This modification does not take the same place with laser generation. The spontaneous generation of the laser is much weaker than the stimulated one, and its brightness is approximately the same as that of a conventional gas discharge tube.

The helium-neon laser - along with one or another conductor - is one of the most commonly used and most affordable lasers for the visible region of the spectrum. The power of such laser systems, mainly used for commercial purposes, ranges from 1 mW to several tens of mW. Particularly popular are non-pressurized He-Ne lasers of approximately 1 mW, which are used for vicorization, main purpose, as valuation devices, as well as for other advanced tasks in the field of virtualization technology. In the infrared and dark wavelength ranges, helium-neon lasers are increasingly being compared to one laser. He-Ne lasers are available, with blue lines, and also orange, yellow, and green, which are accessible to all types of selective mirrors.

Scheme of energy levels

The most important energy sources for the function of He-Ne lasers are helium and neon, shown in Fig. 1. Laser transitions occur in the neon atom, and the most intense lines appear as a result of transitions with long lines 633, 1153 and 3391 (div. table 1).

The electronic configuration of neon basically looks like this: 1 s 2 2s 2 2p 6 Why is it a first-rate obolonka ( n= 1) that friend's shell ( n= 2) filled with two and eight electrons. Vishchi stand for rice. 1 blame for what is here 1 s 2 2s 2 2p 5 - shell, and the electron that lights up (optical) is connected to the circuit: 3 s, 4s, 5s,..., Z R, 4R,... etc. Let's talk about the single-electronic system, which has a connection with the shell. The LS (Russell - Saunders) scheme for energy levels of neon has one electronic stage (for example, 5 s), and indicate the resulting final orbital moment L (= S, P, D...). In the notations S, P, D, the lower index shows the higher orbital momentum J, and the upper index shows the multiplicity 2S + 1, for example, 5 s 1 P 1 . The phenomenological meaning behind Paschen is often discussed (Fig. 1). In this case, the order of the current wake-up electronic stations is from 2 to 5 (for s-stations) and from 1 to 10 (for p-stations).

Ruined

The active core of the helium-neon laser is a gas mixture, to which the necessary energy is supplied to the electrical discharge. The upper laser levels (2s and 2p behind Paschen) are selectively populated based on the interaction with metastable helium atoms (2 3 S 1, 2 1 S 0). During this process, there is an exchange of kinetic energy and a transfer of the energy of the excited helium atoms to the neon atoms. This process is called a different kind of process:

Not * + Ne -> Not + Ne * + ΔE, (1)

The star (*) symbolizes awakening. The difference in energy becomes at the time of destruction of the 2s-level: & DeltaE = 0.05 eV. When closed, the apparent difference is converted into kinetic energy, which is then distributed as heat. For 3s-level, identical numbers are placed. This resonant transfer of energy from helium to neon is the main process of pumping during the inversion of populations. This is a difficult time in the life of a metastable state. The selectivity of the population of the upper laser level is not favorable.

The destruction of non-atoms occurs on the basis of the connection of electrons - either directly, or through additional cascade transitions from the levels that lie higher. Due to long-lived metastable conditions, the density of helium atoms in these conditions is even greater. The upper laser levels 2s and 3s can - subject to the rules of selection for electrical Doppler transitions - only pass into the lower levels. For successful laser generation, it is important that the lifetime of s-stations (upper laser level) = approximately 100 ns, and the lifetime of p-stans (lower laser level) = 10 ns.

Dovzhyni hvil

Next, we will take a closer look at the most important laser transitions, vikoryst and Fig. 1 and data from Table 1. The most prominent line in the red region of the spectrum (0.63 μm) is a successor to the transition 3s 2 → 2p 4. The lower rhubarb splits as a result of spontaneous vibration lasting 10 ns into the 1s-rubble (Fig. 1). Remains resistant to splitting due to the electric dipole vibration, which is also characteristic of long-term natural life. Therefore, atoms are concentrated in this country, which is highly populated. In a gas discharge, atoms in such a state collide with electrons, and this again awakens the 2nd part of the 3s-ribs. In this case, the population inversion changes, which reduces the intensity of the laser. The depletion of ls occurs in helium-neon lasers mainly through the connection with the wall of the gas discharge tube, due to which, with an increase in the diameter of the tube, a decrease in intensity and a decrease in efficiency are indicated . Therefore, it is practical to set the diameter to approximately 1 mm, which, in turn, can result in a reduction in the output power of He-Ne lasers of several tens of mW.

Electronic configurations 2s, 3s, 2p and 3p, which take part in the laser transition, split into numerical counterparts. This leads, for example, to further transitions in the visible region of the spectrum, as can be seen from Table 2. For all visible lines of the He-Ne laser, the quantum efficiency becomes close to 10%, which is not so much. The level diagram (Fig. 1) shows that the upper laser levels extend approximately 20 eV more than the main value. The energy of the red laser radiation becomes less than 2 eV.

Table 2. Maximum voltage λ, output voltage and line width Δ ƒ of the He-Ne laser (designated transitions according to Paschen)

Vibration in the infrared range around 1.157 µm results from additional transitions 2s → 2p. These also extend to a very weak line of approximately 1.512 µm. These infrared lines are found in commercial lasers.

A characteristic feature of the line in the HF range at 3391 µm is its high intensity. In the weak signal zone, with a one-time passage of weak light signals, it becomes close to 20 dB/m. This corresponds to a coefficient of 100 for a 1 meter laser. The upper laser level is the same as at the visible red junction (0.63 µm). Highly settled, on one side, decorate the viklycans with a short hour of life on the lower 3p-river. On the other hand, this is explained by the apparently great duration of the noise, apparently by the low frequency of vibration. Due to the interaction between forced and spontaneous vibration, the prominence increases for low frequencies. The amplification of weak signals g is usually proportional to g ~ 2.

Without selective elements, the helium-neon laser was emitted at a line of 3.39 µm, and not in the red region at 0.63 µm. A damaged infrared line skips either the selective mirror of the resonator or the clay in the Brewster windows of the gas discharge tube. Therefore, the laser generation threshold can be moved up to a level sufficient for 3.39 µm generation, so that there is no weaker line here.

Structurally not vikonannya

Necessary electronic activations are created in a gas discharge (Fig. 2), which can be generated with a voltage of approximately 12 kV with flow rates of 5 to 10 mA. The typical discharge depth is 10 cm or more, the diameter of the discharge capillaries becomes close to 1 mm and corresponds to the diameter of the transmitted laser beam. With an increase in the diameter of the gas-discharge tube, the corrosive action coefficient decreases, leaving waste to be emptied of the ls-level required by the wall of the tube. For optimal output tension, a high pressure (p) filling is applied: p D = 500 Pa mm, where D is the diameter of the tube. The relationship of the madness He/Ne to lie under the important line of laser stimulation. For the visible red line we have He: Ne = 5:l, and the infrared line is close to 1.15 µm - He:Ne=10:l. An important aspect is also the optimization of the thickness of the stream. The coefficient of action for the 633 nm line is close to 0.1%, since the wake-up process in this case is not very effective. The service life of a helium-neon laser is approximately 20,000 working years.

Small 2. Design of the He-Ne laser for polarized vibration in the mW range

The strength for such minds is at the level of g = 0.1 m -1, so it is necessary to select mirrors with a high value. For the laser beam to exit, a partial mirror is installed on one side that transmits (like a viewer) (for example, with R = 98%), and on the other side - a mirror with the highest possible transmission (~ 100%). The intensification of other visible transitions is significantly less (div. Table 2). For commercial purposes, this line was eliminated with the remaining resources behind the help of mirrors, which are supported by extremely small expenses.

Previously, with a helium-neon laser, the output windows of the gas discharge tube were fixed with epoxy resin, and the mirrors were mounted separately. This caused the helium to diffuse through the glue and water vapor to enter the laser. Today, the windows are fastened using the method of direct soldering of the metal to the glass, which reduces the helium flow to approximately 1 Pa per river. For small mass generation lasers, mirror coating is applied directly to the exit windows, which will significantly simplify the entire structure.

The power of the bundle

To select direct polarization, the gas-discharge lamp is provided with two or more rotating windows, as shown in Fig. 2, the resonator is inserted into a Brewster plate. The intensity on the optical surface is reduced to zero when the light falls under the so-called Brewster cut and polarizations are parallel to the incident plane. In this way, the promotion of such direct polarization passes through the Brewster window without any expense. At the same time, the intensity of the component, polarized perpendicularly to the surface of the surface, is high and bends in the laser.

The polarization coefficient (stage) (the degree of polarization is set to be perpendicular to the direction) is 1000:1 for standard commercial systems. When operating a laser without Brewster plates, non-polarized vibrations are generated from internal mirrors.

The laser generates light on the transverse TEM 00 mode (lower order mode), and a series of later (axial) modes is created. At the distance between the mirrors (below the laser resonator) L = 30 cm, the intermode frequency interval becomes Δ ƒ` = c/2L = 500 MHz. The central frequency becomes 4.7·10 14 Hz. Segments of light amplification can be generated within the range Δ ƒ = 1500 MHz (Doppler width), at L = 30CM three different frequencies are produced: Δ ƒ/Δ ƒ`= 3. With viconicity less stand between the mirrors (<= 10см) может быть получена одночастотная генерация. При короткой длине мощность будет весьма незначительной. Если требуется одночастотная генерация и более высокая мощность, можно использовать лазер большей длины и с оснащением частотно-селективными элементами.

Helium-neon lasers around 10 mW are often used in interferometry and holography. The maximum coherence of such serial generation lasers is 20 to 30 cm, which is completely sufficient for holography of small objects. Greater coherence values ​​come from the distortion of serial frequency-selective elements.

When changing the optical distance between the mirrors, as a result of thermal or other influx, the sound of high axial frequencies of the laser resonator is generated. With single-frequency generation, a stable frequency is produced here and it moves uncontrollably in the line width range of 1500 MHz. By using additional electronic regulation, frequency stabilization can be achieved around the center of the line (commercial systems can achieve frequency stability of a few MHz). In previous laboratories, it is possible to stabilize a helium-neon laser at a range of less than 1 Hz.

By using the different lines of the mirrors in Table 4.2, the different lines in Table 4.2 can be activated to generate laser vibration. It is most common to find a visible line around 633 nm with typical outputs of a few milliwatts. After suppression of the intense laser line near 633 nm, the distortion of selective mirrors or prisms in the resonator may reveal other lines in the visible range (see Table 2). However, the output tension of these lines becomes less than 10% of the output tension of the intensive line or less.

Helium-neon lasers for commercial use are available in a variety of industries. In addition to them, there are also lasers that generate on rich lines and different combinations. At the end of the He-Ne lasers, which are reawakened, reawakened, rotating the prism, select the necessary supply of energy.

The broadest gas laser is helium-neon ( He-Ne) laser (neutral atom laser), which operates on a mixture of helium and neon at a ratio of 10:1. This laser is also the first non-stop laser.

Let's take a look at the energy diagram of helium and neon (Fig. 3.4). Generation occurs between the levels of neon, and helium is added to the implementation of the pumping process. As can be seen from Malyunka, Rivni 2 3 S 1і 2 1 S 0 rubbed with helium, similar, close to equal 2sі 3s neon. The fragments are equal to helium 2 3 S 1і 2 1 S 0 If they are metastable, then when metastable excitations of helium atoms and neon atoms are connected, there will be a resonant transfer of energy to the neon atoms (compared to another type).

In this manner, equals 2sі 3s Neons can be populated and, therefore, generation can take place from these rivals. Hour of life s-staniv ( ts»100 ns) more than an hour of life R-staniv ( t r"10 ns), then the brain for the laser operation is based on the following circuit:

1 1 S Þ (3s, 2s) Þ(3p,2p) Þ 1s .

Laser generation is possible at one of the transitions a, b, c daily until Dovzhin Khvil l a=3.39 µm, l b=0.633 µm, l z=1.15 µm, which can be achieved by selecting the coefficient of reflection of the resonator mirrors or by introducing dispersive elements into the resonator.

Small 3.4. Scheme of energy sources for helium and neon.

Let's take a look at the lasing characteristics of such a laser.

Fig.3.5. Lasing characteristics of a helium-neon laser

The gradual increase in the output pressure due to increased pumping is explained by the population inversion. Once the maximum pressure is reached, with further increase in pressure, the inflation curve begins to decrease. This means that 2p and 1s levels do not allow you to relax, then. electrons are not able to switch to a low energy level and the number of electrons on the current 2p and 1s levels remains the same. And here is the daily inversion.

The CCD of helium-neon lasers is on the order of 0.1%, which is explained by the low volume density of the excited particles. The tension of the typical He-Ne-laser P~5-50 mW, power supply q~1 mrad.

Argon laser

These most powerful lasers operate continuously in the visible and near ultraviolet regions of the spectrum, which extend to ion gas lasers. The upper laser level of the working gas is populated with two subsequent electron connections during an electrical discharge. With the first connection, ions from neutral atoms are created, and with the other, these ions are awakened. Also, pumping is a two-part process, the effectiveness of the skin is proportional to the thickness of the struma. To achieve effective pumping, it is necessary to reach a high-strength stream.

Diagram of laser energy levels Ar+ shown in Fig. 3.3. Vibration of the laser in the lines between 454.5 nm and 528.7 nm is observed when the group of peers is populated 4p path of destruction by electronic impact of the main and metastable stations Ar+.

3.5 CO 2 laser

Molecular CO 2-Lasers are among gas lasers, the most powerful non-stop lasers, due to the highest CCD conversion of electrical energy into vibration energy (15-20%). Laser generation is generated at the collival-obertal junctions and the propagation lines of these lasers are located in the far IR region, which are located on the doves of 9.4 µm and 10.4 µm.

U CO 2- the laser vicorizes the sum of gases CO 2, N 2і He. Pumping occurs without interruption when the molecules are closed CO 2 with electrons and collectively awakened molecules N 2. High thermal conductivity does not absorb cooling CO 2 What should be done to deplete the lower laser level, which is populated as a result of thermal excitation. In this manner, presence N 2 the sumya has a high population of the upper laser level, and the presence He– the collapse of the lower level, and the results of the stench lead to an increased inversion of populations. Diagram of energy levels CO 2-laser is shown in Fig. 3.4. Laser generation occurs during the transition of molecules between chopping mills CO 2 n 3 Þn 1 or else n 3 Þn 2 I will become a substitute for the universal.

CO 2 The laser can be operated either continuously or in pulsed modes. In a continuous mode, the output pressure can reach several kilowatts.