Unit 4 word-study

Exercise 1. Check up the transcription in the dictionary and read the words and expressions listed below. Translate them.

Suitable, operate, conventional, frequency generator, internal discharge, beam of coherent infra-red light, mixture, remarkable monochromaticity, stability.

Exercise 2. Find the equivalents.

Electrical discharge, conventional tube, energy level, internal discharge, collision process, continuous stream, infrared light, inside diameter, simplified diagram, experimental conditions, end mirror, chemically stable, flowing nitrogen, large amounts of power.

Процесс столкновений, поток азота, инфракрасный свет, экспериментальные условия, электрический разряд, большая мощность, упрощенная диаграмма, обычная трубка, торцовое зеркало, внутренний разряд, энергетический уровень, непрерывный поток, внутренний диаметр, химически стабильный.

Understanding a printed text

List of Terms:

continuously operating source – источник непрерывного действия

energy level – энергетический уровень

excitation – возбуждение

collide - сталкиваться

monochromaticity – монохроматичность

output beam – выходящий луч

output power – выходная мощность

carbon dioxide laser – лазер на двуокиси углерода (углекислом газе )

electric discharge – электрический разряд

fold – сгибать

ground state – основное состояние

isolated atom – изолированный атом

molecular laser – молекулярный лазер

neutral atom laser – лазер на нейтральных атомах

vibrational energy – энергия колебания

Comprehensive reading Gas and Molecular Lasers Gas Lasers

Gases offer interesting possibilities as laser materials because their atoms are more suitable for excitation. The neon lasers were the first to be discovered and studied and are the easiest to construct and to оperate. They use a mixture of helium and neon gases through which an electrical discharge flows, in the same way as in a conventional neon tube.

The discharge is provided by the radio-frequency generator which is usually operated in the 25-to-30 mс region. It serves to establish an electric discharge in the gas, although a d-c discharge may serve the purpose as well.

The energy from the internal discharge excites the helium atoms to a very high energy level, from which they normally would not radiate energy. However, the neon atoms in the mixture collide with the excited helium atoms, and the energy is transferred to them through the collision process. The neon atoms themselves can then be stimulated to radiate their energy in a continuous stream.

The beam is reflected back and forth through the length of gas-filled tube by semi-reflecting end plates, growing in intensity with each trip. Some part of the beam is transmitted through the plates, and forms a very narrow output beam of coherent infra-red light (Fig.1).

reflecting end plates

electrodes

Fig.1. Construction of He-Ne laser

The first such 1аsег was built in I960 at Bеll Telephone Laboratories. It consists of a discharge tube 100 cm long with an inside diameter of 1,5 cm filled with helium at 1 torr pressure and with neon at 0.1 torr. Flat reflector plates, which must be adjusted parallel within a few seconds of arc, are included in the gas filled section of the tube.

A simplified diagram of this laser is given in Fig.1.

The power required to excite the laser action is in the tens-of-watts range. The output роwer is in the 1/100-th watt range. At this level of operation, the tube is so cool that it can be held in the hand without discomfort.

Thе great value of helium-neon lasers is their remarkable monochromaticity and stability under carefully controlled experimental conditions.

To communication engineers such a continuously operating source is an important device.