Free-Electron Lasers

Lasers using beams of electrons unattached to atoms and spiralling around magnetic field lines to produce laser radiation were first developed in 1977 and are now becoming important research instruments. They are tunable, as are dye lasers, and in theory a small number could cover the entire spectrum from infrared to X-rays. Free-electron lasers should also become capable of generating very high-power radiation, which is currently too expensive to produce.

Liquid Lasers (Dye Lasers)

The liquid lasers are those in which the active medium consists of solutions of certain organic dye compounds in liquid solvents such as ethyl alcohol, methyl alcohol, or water.

Due to their wavelength tunability, wide spectral coverage, and the possibility of generating very short pulses, organic dye lasers have found an important role in various fields. In particular, these lasers are widely used in scientific applications. Other applications include the biometrical field (e.g., retinal treatment or photodynamic therapy) and applications in the field of laser photochemistry.

Chemical Lasers

A chemical laser is usually defined as one in which the population inversion is “directly” produced by a chemical reaction. According to this definition, the gas-dynamic CO₂ laser should not be regarded as a chemical laser even though the upper state population arises ultimately from a combustion reaction (e.g., combustion of CO with O₂ ). Chemical lasers usually involve a chemical reaction between gaseous elements, and often involve either an associative or a dissociative exothermal chemical reaction.

Chemical lasers are interesting for two main reasons: (1) They provide an interesting example of direct conversion of chemical energy into electromagnetic energy. (2) They are potentially able to provide either large output power (in CW operation) or large output energy ( in pulsed operation). This is because the amount of energy available in an exothermal chemical reaction is usually quite large.

Chemical lasers of the HF type can give large output powers (or energies) with good chemical efficiency. The most important area of these lasers seems to be for high-power military applications.

Check your understanding

Exercise 1. Read the text and answer the questions.

1. What types of lasers can you name?

2. What are the most common solid laser media?

3. What are common uses for semiconductor lasers?

4. Where are liquid lasers used?

5. What is the most important area of chemical lasers applications?

6. What are the advantages of free-electron lasers?

Exercise 2. Complete the sentences.

1. Solid-state lasers offer … . They are usually operated in a pulsed manner…

2. The laser medium of a gas laser can be …

3. The helium neon laser is known for its high frequency stability, …

4. Gallium arsenide is …

5. … were first developed in 1977 and are now becoming important research instruments.

6. The active medium of the liquid lasers consists of …

7. A chemical laser is usually defined as one …

Exercise 3. True or false?

1. The laser medium of a gas laser can be a pure gas, a mixture of gases or even metal vapour.

2. Solid state lasers offer the lowest power output.

3. Liquid lasers have the active medium consisting of solutions of organic dyes compounds in liquid solvents.

4. Chemical lasers don’t involve a chemical reaction between gaseous elements.