2. Translate the following groups of words of the same root and memorize them:

to expand — expansion; infinite — infinitely; to install — installation; to locate — location — locality — local; precision — precise; to desire — desire — desirable; to measure — measure — measure — ment — measurable; happy— happiness— happier— happiest— unhappy.

3. Arrange antonyms in pairs and memorize them. Choose 4-6 words and make up your own sentences with them.

many, always , reflect, intelligent, much, direct, new, ignorance, small, common, negatively, charge, to succeed, outer, conductor, poor, knowledge, thin, uneconomic, attract, cool, often, to raise, little, inner, old, stupid, uncommon, non-conductor, indirect, few, to lower, opaque, good, economic, warm, thick, positively, fluid, large, discharge, never, seldom, to fail, solid, transparent.

4. Match up the words in column a with the words in column b to form meaningful phrases, translate them into Ukrainian.

Column A Column B

1. stimulated emission of a) beam power

2. light of b) transitions

3. pass through c) photons

4. the probability of d) the medium

5. the rate of e) stimulated emission

6. the process of f) the atom

7. reduce the gain of g) the gain medium

8. increasing h) specific wavelength

5. Try to remind all information that you know from the previous years. Write down 15 words related to the topic Laser and make up your own sentences.

6. Read the text and translate it into Ukrainian.Use a dictionary if necessary. Laser

A laser is a device that emits light (electromagnetic radiation) through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation. The emitted laser light is notable for its high degree of spatial and temporal coherence. Spatial coherence typically is expressed through the output being a narrow beam which is diffraction-limited, often a so-called "pencil beam."

Laser beams can be focused to very tiny spots, achieving a very high irradiance. Or they can be launched into a beam of very low divergence in order to concentrate their power at a large distance. Temporal coherence implies a polarized wave at a single frequency whose phase is correlated over a relatively large distance along the beam. A beam produced by a thermal or other incoherent light source has an instantaneous amplitude and phase which vary randomly with respect to time and position, and thus a very short coherence length.

A laser which produces light by itself is technically an optical oscillator rather than an optical amplifier as suggested by the acronym. It has been humorously noted that the acronym LOSER, for "light oscillation by stimulated emission of radiation," would have been more correct. With the widespread use of the original acronym as a common noun, actual optical amplifiers have come to be referred to as "laser amplifiers", notwithstanding the apparent redundancy in that designation.

A laser consists of a gain medium inside a highly reflective optical cavity, as well as a means to supply energy to the gain medium. The gain medium is a material with properties that allow it to amplify light by stimulated emission. In its simplest form, a cavity consists of two mirrors arranged such that light bounces back and forth, each time passing through the gain medium. Typically one of the two mirrors, the output coupler, is partially transparent. The gain medium is excited by an external source of energy into an excited state. The gain medium of a laser is normally a material of controlled purity, size, concentration, and shape, which amplifies the beam by the process of stimulated emission.

The output laser beam is emitted through this mirror. Light of a specific wavelength that passes through the gain medium is amplified (increases in power); the surrounding mirrors ensure that most of the light makes many passes through the gain medium, being amplified repeatedly. Part of the light that is between the mirrors passes through the partially transparent mirror and escapes as a beam of light. The process of supplying the energy required for the amplification is called pumping.

The energy is typically supplied as an electrical current or as light at a different wavelength. Such light may be provided by a flash lamp or perhaps another laser. Most practical lasers contain additional elements that affect properties such as the wavelength of the emitted light and the shape of the beam. The gain medium of a laser is a material of controlled purity, size, concentration, and shape, which amplifies the beam by the process of stimulated emission. It can be of any state: gas, liquid, solid or plasma. The gain medium absorbs pump energy, which raises some electrons into higher-energy quantum states. Particles can interact with light by either absorbing or emitting photons. Emission can be spontaneous or stimulated. In the latter case, the photon is emitted in the same direction as the light that is passing by. When the number of particles in one excited state exceeds the number of particles in some lower-energy state, population inversion is achieved and the amount of stimulated emission due to light that passes through is larger than the amount of absorption. Hence, the light is amplified. By itself, this makes an optical amplifier. When an optical amplifier is placed inside a resonant optical cavity, one obtains a laser.