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Министерство высшего и среднего специального образования СССР

Московское ордена Ленина, ордена Октябрьской Революции

и ордена Трудового Красного Знамени

высшее техническое училище им. Н. Э. Баумана

Т. И. КУЗНЕЦОВА, Г. В. КИРСАНОВА

Утверждены редсоветом МВТУ

МЕТОДИЧЕСКИЕ УКАЗАНИЯ

ПО ОБУЧЕНИЮ ЧТЕНИЮ ТЕХНИЧЕСКОЙ ЛИТЕРАТУРЫ

НА АНГЛИЙСКОМ ЯЗЫКЕ ПО ОПТИКЕ

Часть 2

(редакция 2008 года,

только для web-сайта факультета «Лингвистика»)

Москва 1988

Данные методические указания издаются в соответствии с учебным планом.

Рассмотрены и одобрены кафедрой иностранных языков 14.10.86 г., методической комиссией факультета ОТ 22.12.86 г. и учебно-методиче­ским управлением 29.01.87 г.

Рецензент к. т. н. доц. Карасик В. Е.

Методические указания предназначены для обучения чтению и пе­реводу научно-технической литературы. Приведены оригинальные тек­сты из английской и американской научно-технической литературы по оптике для развития навыков перевода, аннотирования и реферирова­ния. Разработан терминологический словарь. Тематика методических указаний согласуется с курсом лекций, читаемым на факультете. Реко­мендуется использовать для обучения студентов IV—V семестров днев­ного отделения. Способствует интенсификации учебного процесса.

© Московское высшее техническое училище им. Н. Э. Баумана

MODULE 4 LASERS Texts: A. Types and Comparisons of Laser Sources: Introduction B. Nd:YAG Laser vs. Ruby Laser C. Free Electron Laser

Terminology:

1. to irradiate – облучать, излучать, испускать лучи; irradiation - иррадиация, лучеиспускание, излучение;

2. flashlamp – импульсная лампа, лампа накачки;

3. population inversion – инверсная населенность;

4. technique – метод, способ; excitation technique – способ, метод возбуждения;

5. optical pumping – оптическая накачка;

6. nuclear decay – ядерный распад;

7. dilute electron beam – низкоэнергетический электрон­ный пучок;

8. to scatter – разбрасывать, рассеивать, nonlinear scattering – нелинейное рассеяние;

9. spectral tuning range – спектральный диапазон перестройки;

10. output waveform – волновой фронт, фронт волнового излучения;

11. power scalability – диапазон значений (уровень) выходной мощности

12. gain – усиление, коэффициент усиления; gain medium – усиливающая среда;

13. peak power – пиковая (импульсная) мощность; peak power density – плотность пиковой (импульсной) мощности;

14. pulse energy – энергия в импульсе.

Preliminary exercises

1. Read and translate without a dictionary:

emission, inversion, chromium, ruby, crystal, xenon, decade, substance, neutral, gas, reaction, generate, periodic, spectral, parameter, neon, helium, unique, ensemble, electronic, dynamical, process, structural, kinetic, coherent, scheme, characteristics, ion.

1. Translate the word-combinations that follow:

pulse duration, peak power density, beam quality, chromium ions energy levels, laser sources types, laser action, electron beam kinetic energy, magnetic field periodicity, laser gain medium, pump excitation energy.

1. Find equivalent phrases either in Text 4A or in the right-hand column:

1) усиление света в результате вынужденного излучения	a) this spectacular set of characteristics
2) при облучении (когда кристалл облучается)	b) to generate coherent radiation
3) в течение следующих двух десятилетий	c) the upper laser levels
4) во много раз	d) can be varied
5) чтобы получить (создать) когерентное излучение	e) in the ensuing two decades
6) путем правильного выбора значения кинетической энергии	f) rather than with simple laser oscillators
7) можно изменять	g) listed in this table
8) предельные значения выходных параметров	h) light amplification by stimulated emission of radiation
9) а не с простыми лазерными генераторами	i) the extrema of laser output parameters
10) приведенные в данной таблице	j) when irradiated with
11) этот впечатляющий (замечательный) набор характеристик	k) by properly choosing the kinetic energy
12) верхние лазерные уровни	l) manifold

4. Read Text 4A and answer the following questions:

1) Какие методы используется для создания инверсной населенности?

2) Каким образом можно изменять длину волны излучения лазера на свободных электронах?

TEXT 4A TYPES AND COMPARISONS OF LASER SOURCES: INTRODUCTION

Light Amplification by Stimulated Emission of Radiation was first demonstrated by Maiman in I960, the result of a popu­lation inversion produced between energy levels of chromium ions in a ruby crystal when irradiated with a xenon flashlamp. In the ensuing two decades population inversion and coherent emission have been generated in literally thousands of substances (neutral and ionized gasses, liquids, and solids) using a variety of excitation techniques (optical pumping, electrical discharge, gasdynamic-flow, electron beam, chemical reaction, nuclear decay).

The number and types of laser sources has been further expanded manifold by utilizing one laser source (primary) to generate coherent radiation in a second medium, either by opti­cally producing a population inversion in the second medium or as the result of nonlinear scattering in the second substance. Recently, laser action has even been achieved by passing a di­lute electron beam through a periodic magnetic field (free-elec­tron laser, or FEL). By properly choosing the kinetic energy of the electron beam and the periodicity of the magnetic field, the output wavelength of the FEL can be varied, in principle, from the ultraviolet to the far infrared spectral region.

The extrema of laser output parameters which have been demonstrated to date, and the laser media used are summarized in Table I. Note that the extreme power and energy parameters listed in this table were attained with laser systems (such as a master-oscillator-power-amplifier¹, or MOPА system) rather than with simple laser oscillators.

Table 1 Extrema of Output Parаmеters of Laser Devices and Systems

Parameter	Value	Laser medium
Peak power	2x1013W (collimated)	Nd:glass
Peak power density	1018 W/cm2 (focused)	Nd:glass
Pulse energy	>104J	CO2, Nd:glass
Average power	105W	CO2
Pulse duration	3x10-13sec, cw2	Rh6G dye, various gasses, liquids, solids
Wavelength	60nm ↔385nm	many required
Efficiency (nonlaser-pumped)	70%	CO2
Beam quality	diffraction limited	various gasses, liquids, solids
Spectral linewidth	20Hz (for 10-1sec)	neon-helium
Spatial coherence	10m	ruby

To be sure³, no single laser source can simultaneously provide this spectacular set of characteristics. Each laser gain medium possesses a unique ensemble of energy levels (electronic, vibrational, rotational), which are dynamically coupled to each other through various radiative and nonradiative processes. These structural and kinetic features determine laser's nominal operating wavelength(s), its spectral tuning range, its possible output waveforms, and its energy and power scalability. Laser efficiency is determined by the degree to which appropriate pump excitation energy can be generated, fed selectively into the upper laser level(s), and subsequently ex­tracted coherently before deleterious⁴ decay processes other­wise remove this excitation energy. It is the very richness of energy level schemes and transition probabilities provided in nature that results in such a large number of lasers with such a wide variety of output characteristics.

Given the considerable diversity in laser properties, it is the purpose of this introductory section to order laser sources into basic classes and to describe the principle characte­ristics that define the classes and their subdivisions.

3400 п. зн.

Words to be learnt:

to summarize – суммировать, подводить итоги;

to couple – соединять, сцеплять;

recently – недавно;

to date – до сих пор, до настоящего времени;

otherwise – иначе, в противном случае;

to feed (fed - fed) – подавать, питать, снабжать;

to extract – извлекать, удалять.

Exercises

1. In each group find the word that doesn’t belong:

1. minimum, maximum, datum, phenomenon, medium, extrema, spectrum;

2. coherent, neutral, efficiency, gasdynamic, nuclear, single, kinetic;

3. ultraviolet, unique, various, possible, incoherent, specta­cular, infrared, optical.

2. Find a synonym for each verb below:

a) produce, enumerate, possess, use, expand, remove, link, achieve, vary, give;

b) extract, enlarge, provide, change, attain, utilize, own, list, generate, couple.

1. Complete the sentences below with the appropriate word or word-combination:

1) The output wavelength of the FEL can be varied from the ultraviolet to the far infrared spectral region by...

a) utilizing one laser source to generate coherent radiation in a second medium;

b) properly choosing the kinetic energy of the electron beam and the periodicity of the magnetic field.

2) The extreme power and energy parameters were attained with...

a) simple laser oscillators;

b) laser systems rather than with simple laser oscillators.

4. Point out the statements which do not correspond to Text 4A:

1. A single laser source can simultaneously provide a spectacu­lar set of characteristics.

2. Light amplification by stimulated emission of radiation was first demonstrated in 1970.

3. Recently laser action has been achieved by passing a dilute electron beam through a periodic magnetic field.

5. Translate the sentences below focusing on the underlined words:

1. As the result of nonlinear scattering in the second substance the number of laser sources has been expanded. 2) The richness of energy level schemes results in a large number of lasers with a wide variety of output characteristics. 3) Light amplification by stimulated emission of radiation was the result of a popula­tion inversion produced between energy levels of chromium ions in a ruby crystal. 4) The purpose of this introductory section is to order laser sources into basic classes. 5) One laser source was utilized in order to generate coherent radiation in a second medium. 6) Table I provides the list of the extrema of laser output parameters. 7) The parameters listed in the table were attained with laser systems rather than with simple laser oscillators.

6. In each sentence below find the Subject and Predicate groups. Translate the sentences:

1) Solid state semiconductor laser materials exhibit both high heat capacities and thermal conductivities. 2) To extend the average power output substantially beyond these levels appeal is made to laser – diode arrays (линейки лазерных диодов). 3) Reference 2 is cited in the table as a key literature source dealing with lasers used to illustrate various classes and types of lasers. 4) The costs of lasers and laser systems vary widely and cannot be readily generalized. 5) The major alternative to optical pumping by incoherent sources is pumping by another laser. 6) Excitation into any of these levels decays rapidly down by nonradiative processes because of the relatively small energy gaps (energy gap – энергетическая зона) between various levels. 7) In Table 1 cw stands for continuous wave operation.