Lasers (1982)

The frame shows a special device, a red laser beam coming out of it, a panorama of devices and equipment, working scientists.

The frame shows quantum electronics devices that emit laser beams.

Induced radiation.

Photograph of Albert Einstein.

Close-up - device, lens, hands adjusting, installing equipment.

Einstein explained the regularities of the spectrum of an absolutely black body, based on the concept of induced radiation (in the frame - a graph).

Experiment - passing a beam through a container with liquid (it is shown that the beam intensity decreases over the entire range of wavelengths.

Large - experiment, in the frame the device, the burner is lit, sodium vapor is released, a panorama of a scientist who is looking into the device and observing how sodium vapor selectively absorbs light in the yellow part of the spectrum.

Such absorption is called resonant.

Formula for the frequency of resonant absorption.

In the frame - the simplest energy two-level model (formulas, graphs, etc.).

During resonant absorption of a photon, the atom moves to a higher energy level, and during spontaneous emission - to a lower level.

An atom can emit a photon under the influence of an external electromagnetic field - such radiation is called induced.

The frequency of stimulated emission is the same as the frequency of the external electromagnetic field.

The intensity of induced emission is proportional to the intensity of the external electromagnetic field.

Strict quantum theory of radiation.

Photograph of the English scientist Paul Dirac.

Dirac showed that both photons have not only the same frequency, but also the same polarization and move in the same direction.

Both photons are strictly coherent.

Spontaneous emission is isotropic and unpolarized.

Under normal conditions, the upper energy levels are less populated than the lower ones, which corresponds to Boltzmann statistics.

Such a medium will always absorb light.

If we achieve a population inversion of the levels, then such a medium will be able to amplify light.

The inversion in them can be formally described if we consider the absolute temperature to be negative (a formula was derived).

Photograph by Soviet scientist Valentin Fabrikant.

Fabrikant predicted that population inversion can be obtained if molecular impurities are used.

Due to their resonant excitation and inelastic collisions with gas molecules, one of the energy levels can become depleted.

Fabrikant predicted the possibility of amplifying light.

Photographs by American scientists Edward Purcell and Robert Pound.

Purcell and Pound obtained the population inversion of the energy levels of the magnetic moments of lithium atoms using rapid changes in the direction of the magnetic field.

Photograph of Albert Einstein.

Photographs of various physicists who laid the foundations necessary for the creation of quantum generators, masers and lasers.

Close-up - a large stationary household radio receiver.

A television tower for transmitting a signal.

One of the first television models from the 50s.

In the frame - a modern radio spectrometer, a panorama of the equipment, an employee who monitors the readings of the devices and makes notes.

An employee watches the readings of the devices.

In the frame - a device, an oscilloscope, a signal in the form of a moving dot is visible on the screen.

Close-up - curved lines are automatically drawn on a sheet of paper.

When an atom or molecule is removed, the radiation frequency decreases due to the Doppler effect, and when approaching it increases.

Therefore, thermal motion always leads to a broadening of the spectral lines.

In many cases, the broadening of the lines exceeded the distance between them and did not allow them to be resolved.

To get rid of the Doppler broadening of lines, Academician Alexander Prokhorov suggested using molecular beams.

The resolving power of beam spectrometers increased, but the spectral lines were too weak.

Photos by Academicians N. Basov and A. Prokhorov.

Basov and Prokhorov put forward an important idea - it is necessary to artificially change the population of levels and study not absorption, but induced emission.

This led to the creation of paramagnetic amplifiers, and then masers and lasers.

In the frame - one of the first masers, created on a beam of ammonia molecules (the animated diagram shows the structure and operating principle).

The flow of molecules is sorted by a quadrupole capacitor - it deflects unexcited molecules, and fixes excited ones along its axis, directing them into a resonator.

In the resonator, excited molecules, due to induced emission, support electromagnetic oscillations, and part of the radiation energy leaves the resonator in the form of coherent electromagnetic waves.

Spatial separation of excited and unexcited molecules is good only for molecular beams.

After developing a maser on ammonia, Basov and Prokhorov proposed a three-level method of creating an inverse population - due to pumping by an external source, molecules from the ground state move to the third level, and from there they spontaneously move to the second metastable level with a long lifetime and accumulate on it.

A population inversion occurs between the second and ground energy levels, which makes it possible to obtain maser radiation.

An avalanche of quanta can now develop due to forced transitions between these levels.

A large radio telescope in the form of a plate, space, starry sky.

Image of the Horseshoe Nebula in the constellation Sagittarius.

The operating principle of the first maser, acting from a cloud of hydroxyl molecules in the Horseshoe Nebula in the constellation Sagittarius, is shown.

Pumping in such a natural maser is carried out due to the collision of hydroxyl molecules or external radiation.

Invisible quanta emitted by the maser are conventionally depicted in red.

Examples of maser radiation of hydroxyl molecules are shown (in the frame, special large round structures and other constructions are shown).

The maser effect was discovered in the shells of red variable stars.

An important stage in the creation of lasers were paramagnetic amplifiers, in which the splitting of energy levels was carried out under the action of a magnetic field.

Population inversion in them was carried out due to the pumping field, and liquid helium prevented spontaneous transitions.

One of the first paramagnetic amplifiers was an amplifier on ruby.

Thanks to the work of various scientists in the USSR and the USA, all the prerequisites for constructing a quantum generator of the optical range were created.

The first laser was created in 1960 by Neumann in the USA. Red spectral line pulses were emitted.

Quantum electronics as a science was born when a quantum system was placed in a resonator.

The scientist shows how a modern ruby laser is arranged and disassembles the device.

For wavelengths of the optical range, the role of the resonator is played by a Fabry-Perot interferometer.

A system of two parallel mirrors - opaque and translucent.

Chromium atoms are transferred to a state with an inverted population according to a three-level scheme using a pump lamp.

Forced transitions are accompanied by the development of an avalanche of photons.

When the energy influx due to forced transitions exceeds the losses in the crystal, a laser flash occurs.

As soon as the energy supply falls below the threshold value, the flash stops.

The scientist turns on the device, a red laser beam appears.

The duration of the ruby laser pulse is about a thousandth of a second.

The pulse consists of many individual pulses.

The frame shows a quantum generator, a red laser beam is visible.

The power of the laser beam can be increased by reducing the pulse duration.

Experiment, experience - the frame shows a scientist at a table with devices and equipment.

To reduce the pulse duration, the scientist places a Pockels shutter between a ruby crystal and a mirror.

When the shutter is closed, the light does not reach the reflecting mirror, there is no feedback in the laser and there is no generation.

The scientist opens the Pockels shutter, close-up - the arrow is moving on the device.

Close-up - it is shown how generation occurs, a red laser beam appears.

When the shutter is open, only slightly more than half of the chromium atoms are in an excited state, when closed - almost all.

When the Pockels shutter is opened, a powerful pulse develops during its operation for one millionth of a second.

To prevent the crystal itself from becoming an optical resonator, the ends are made oblique at the Brewster angle.

By applying an alternating voltage to the Pockels shutter, a series of pulses can be obtained.

Close-up - hands switching switches and buttons on the equipment.

The scientist is standing near a table with devices and equipment.

The device is turned on, a red laser beam appears.

This operating mode is called "Q-modulated".

The use of this mode, as well as a number of other methods, made it possible to achieve a pulse power of tens of millions of kilowatts.

In the frame - the construction of a hydroelectric power station.

The picture shows the equipment of the power station.

A ruby laser is shown in operation.

In the frame - an image of the sun.

The first continuous-action laser was invented in 1960 by the American physicist Javan.

The scientist disassembles the design of the laser.

The working substance in the gas laser was a mixture of helium and neon.

Close-up - hands switching buttons and levers on the device.

Under the influence of voltage, with the optical resonator turned off, a glow discharge is excited in the tube, the glow of which is similar to the glow of neon advertising tubes.

The scientist looks into a special magnifying tube.

The mixture emits many spectral lines.

Helium-neon laser emits coherent light in the red region of the spectrum and two spectral lines in the infrared region.

In neon atoms, the laser transition occurs from the metastable upper laser level not to the ground level, but to the intermediate (lower laser level).

Helium in the gas mixture is used only for resonant excitation of neon atoms.

A helium atom is excited by a plasma electron.

When colliding with a neon atom, the helium atom transfers excitation energy to it.

Under the action of an external photon, the neon atom emits a coherent photon and passes to the lower laser level.

Infrared forced transitions occur between laser levels E3 and E4, as well as E2 and E1. Panorama of different models of helium-neon lasers.

The power of helium-neon lasers is small (up to one tenth of a Watt), but they have an insignificant beam divergence close to the diffraction limit.

In the frame - semiconductor lasers.

The laser is based on a pn junction between p- and n-type gallium arsenide.

The active medium is created by injecting free charge carriers into the pn junction region.

Coherent radiation is generated by forced recombination of excess carriers in the vicinity of the pn junction.

The laser's optical resonator is two parallel faces cleaved along crystallographic planes.

The advantage of semiconductor lasers is their miniature size and high efficiency.

The power of such lasers is low.

In the frame - a liquid laser (was created in 1966).

Panorama of lasers, devices.

In dye lasers, solutions of various organic dyes are used as an active medium.

During laser operation, the dye is pumped.

Close-up - a hand turns the key on the dashboard, presses a button, etc.

A dye laser can be pumped with a gas laser.

In the frame - lasers.

Energy scheme of dye laser radiation.

In solutions, each energy level consists of a series of vibrational and rotational sublevels.

A dye laser operates on a four-level energy scheme.

Population inversion is created between the excited level with the lowest energy and the vibrational-rotational sublevels of the ground state.

The generation line is very wide - this allows the laser frequency to be tuned.

A scientist employee near the lasers removes the cover of the device.

The required wavelength is adjusted by introducing a dispersive prism or diffraction grating into the optical resonator.

Close-up - an employee performs manipulations, closes the lid of the device, turns the laser handle.

Dye lasers can also operate in pulse mode.

Their power is the same as that of solid-state lasers.

The frame shows the laser in operation, the laser beam is visible.

The laser beam has a high degree of spatial coherence.

Young's experiment is reproduced - first with a regular beam, and then with a laser beam.

A regular beam of light gives a not very clear interference pattern.

The pattern from a coherent laser beam is clearer.

Close-up - a hand turns the handle of the device, a red laser beam is visible.

An employee near the laser installation, turns on the device.

Distribution of intensity over the cross-section of the laser beam.

Close-up - a hand prepares the equipment, adjusts the device.

On a special white screen - a red dot from the projected laser beam.

The distribution of the laser beam intensity is non-uniform and is determined by the condition for the emergence of standing waves.

Close-up - a red dot from the laser (vibrates, oscillates).

The frame shows a radio telescope for planetary location.

Its antenna is 22 meters in diameter and is made in the form of a mirror bowl.

At a wavelength of 1 meter, the beam divergence caused by diffraction is 2.6 degrees.

The size of the radio spot on the Moon is 30,000 km, which is much larger than its diameter.

When using a laser with a wavelength of 1 micron and an optical resonator mirror with a diameter of 10 cm, the laser beam spot can have a diameter of only 3 km.

Only for gas lasers is the beam divergence close to the diffraction limit and is 1 ... 2 minutes.

For ruby lasers, the divergence is 7 ... 9 minutes.

And for semiconductor lasers - 1 ... 2 degrees.

Panorama of tables with laser installations, devices, etc.

The frame shows different models of industrial lasers.

Such lasers develop a power of up to 1 kW in continuous mode, and up to 100 MW in pulsed mode.

The frame shows miniature semiconductor lasers (their efficiency exceeds 50%).

Dye lasers make it possible to cover the entire range of visible light waves.

LED strips are also used as a pumping source, which makes it possible to reduce the mass of the laser by 10-20 times.

A scientist works with lasers.

High-quality holograms are created using a laser beam.

An object is exposed to a laser beam.

The scientist sets up and adjusts the equipment, looks at the laser beam.

The frame shows a dot from the laser beam on the mirror of the device.

The frame shows a hologram of an image in a laser beam (a figure on a horse).

The use of lasers in mine surveying, geodetic, and topographic work (in the frame, a man is working with a level-type device).

A man is standing with a huge geodetic ruler.

Using a laser to create a reference direction.

The frame shows laser sights that provide geodetic control when planning the bed of highways and railways, laying pipelines.

A river, a ship, a panorama of the shore, where a man is standing with a laser device.

The direction of the ship's movement is provided by laser equipment - the laser beam is captured by a receiving device on the ship.

It is shown how special laser devices are used to treat eye diseases (the frame shows doctors and patients).

A doctor at a table conducts laser treatment using a special device, a panorama of the office, equipment, etc.

Treatment and vision correction is carried out using a corneal infrared laser.

Various shots of the use of high-tech medical laser equipment, eye treatment, etc.

The frame shows an operating room, an operation in progress, a surgeon makes an incision using a laser.

Panorama of laser installations in production.

Such installations are used for welding (the frame shows welding work using a laser).

Cutting various workpieces using a laser.

The frame shows a workshop, laser equipment, various devices.