Introduction to quantum electronics Quantum electronics

Quantum optics is a branch of atomic, molecular, and optical physics dealing with how individual quanta of light, known as photons, interact with atoms and molecules. It includes the study of the particle-like properties of photons. Photons have been used to test many of the counter-intuitive predictions of quantum mechanics, such as entanglement and teleportation, and are a useful resource for quantum information processing.

According to quantum theory, light may be considered not only to be as an electro-magnetic wave but also as a "stream" of particles called photons which travel with c, the vacuum speed of light. These particles should not be considered to be classical billiard balls, but as quantum mechanical particles described by a wavefunction spread over a finite region.

Each particle carries one quantum of energy, equal to hf, where h is Planck's constant and f is the frequency of the light. That energy possessed by a single photon corresponds exactly to the transition between discrete energy levels in an atom (or other system) that emitted the photon; material absorption of a photon is the reverse process. Einstein's explanation of spontaneous emission also predicted the existence of stimulated emission, the principle upon which the laser rests. However, the actual invention of the maser (and laser) many years later was dependent on a method to produce a population inversion.

The use of statistical mechanics is fundamental to the concepts of quantum optics: light is described in terms of field operators for creation and annihilation of photons—i.e. in the language of quantum electrodynamics.

A frequently encountered state of the light field is the coherent state, as introduced by E.C. George Sudarshan in 1960. This state, which can be used to approximately describe the output of a single-frequency laser well above the laser threshold, exhibits Poissonian photon number statistics. Via certain nonlinear interactions, a coherent state can be transformed into a squeezed coherent state, by applying a squeezing operator which can exhibit super- or sub-Poissonian photon statistics. Such light is called squeezed light. Other important quantum aspects are related to correlations of photon statistics between different beams. For example, spontaneous parametric down-conversion can generate so-called 'twin beams', where (ideally) each photon of one beam is associated with a photon in the other beam.

Atoms are considered as quantum mechanical oscillators with a discrete energy spectrum, with the transitions between the energy eigenstates being driven by the absorption or emission of light according to Einstein's theory.

For solid state matter, one uses the energy band models of solid state physics. This is important for understanding how light is detected by solid-state devices, commonly used in experiments.

Laser - induced amplification of light (microwave waves) using the effect of induced emission of radiation.

Laser radiation is the result of the conversion of various forms of energy into a coherent light wave (monochromatic, with a constant radiation phase).

Monochromatic laser radiation is the ability to maintain a constant radiation frequency.

Properties of laser radiation.

1. The wave process is characterized by polarization. Introduction to quantum electronics .

2. Describes the function: Introduction to quantum electronics .

3. Wave number: Introduction to quantum electronics .

4. In practice, the levels have a finite value. The nature of the transition from one level to another has a stochastic nature.

Introduction to quantum electronics

Picture 1.

Introduction to quantum electronics .

5. In quantum electronics, you can change the width of the lines. For this, the Zeyman and Stark effect is used. Stark effect - the width of the zone changes under the action of an electric field The width of the emission lines is indicated by Introduction to quantum electronics :

Introduction to quantum electronics , .

6. A quantum source is characterized by a good quality (monochromaticity):

Introduction to quantum electronics ,

so the quartz resonator has: Introduction to quantum electronics .

7. Temporal coherence - the time during which the phase of the wave in the passband remains unchanged:

Introduction to quantum electronics .

8. Coherence duration - the distance over which the phase velocity (phase front) remains unchanged:

Introduction to quantum electronics .

This property is used to measure slow displacements and for holographies.

9. The directivity of the laser radiation d.

Introduction to quantum electronics

Figure 2.

10. Diffraction divergence:

Introduction to quantum electronics .

Laser radiation is characterized by the dependence of the wavelength on the source of the beam divergence. Small angular divergence is used for target designation (a system with laser radiation), space communications, in technology allows to obtain a high radiation density.

Introduction to quantum electronics

Figure 3.

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Introduction to quantum electronics , because .

Laser radiation is divided into 3 positions:

Introduction to quantum electronics

Figure 4.

I - near zone Introduction to quantum electronics ;

II - middle zone Introduction to quantum electronics ;

III - far zone Introduction to quantum electronics .

In the far zone, there is a radiation pattern representing the Fourier decomposition into transverse components. The number of modes must be equal to 1, i.e.

Introduction to quantum electronics

Figure 5.

11. Focusing laser radiation.

For a simple increase in power, a lens (lens) is placed in front of the beam. In an ordinary physical lens, there is no aberration operation.

Introduction to quantum electronics

Figure 6.

If the diameter of the lens and the beam is not the same Introduction to quantum electronics then

Introduction to quantum electronics .

12. Power density Introduction to quantum electronics where - radiated power - spot area.

13. In practice, the laser field distribution is approximated by a fairly simple Gaussian characteristic:

Introduction to quantum electronics

Figure 7.

J ( p ) = Introduction to quantum electronics , (one).

Introduction to quantum electronics - average level: ,

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Where Introduction to quantum electronics , , .

14. Coherence allows the creation of periodic structures in the material. For this, a system with surface acoustic waves is used.

Introduction to quantum electronics

Figure 8.

Polarization property and coherence allow bundling Introduction to quantum electronics , in amplitude, which allows to significantly increase power.

Introduction to quantum electronics

Figure 9.

Introduction to quantum electronics

Figure 10.

Introduction to quantum electronics .

The field strength of two beams:

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Where Introduction to quantum electronics and - phase shift.

If the beams are coherent, the field intensity Introduction to quantum electronics and at

Introduction to quantum electronics , .

15. Full field intensity: Introduction to quantum electronics where n is the number of rays. If the beams are not coherent, then where - the average value of the i - th beam.

16. The polarization of laser radiation is either circular or linear, and may also contain elliptical components.

These properties of laser radiation are used for focusing laser radiation, in guidance systems, in fiber communication lines, in engineering and medicine.

Introduction to quantum electronics

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