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The active medium is a dye solution. Below is an example of a dye laser used at a university. We have the laser unit resting on the table and the dye is continuously circulated through pipes. This specific laser is a tuneable laser capable of emitting wavelengths between 530nm and 590 nm. (nm – nanometres)

The active medium of a laser is the part that is excited by an external energy source. Gas lasers have an active medium that is a gas. They can be filled with different gases whether this is argon, helium or carbon dioxide. (CO2.)

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This picture has been shown for reference and should not be copied, there are a number of bad habits here. We have a class 4 laser with open beam paths. The dye has obviously been leaking as we can see by the residue on the side of the table and, underneath, is the high voltage power supply potentially catching the drips. This has been shown to highlight the dangers that need to be considered.

The frequency can even be tripled or even quadrupled to give a wavelength of 355 nm and 266 nm. These would be invisible.

Semiconductors like the ones found in laser pointers are typically small hand held lasers that are battery operated. The main problem is that the output powers of these lasers have been steadily increasing leading to potentially dangerous situations in the wrong hands.

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The type of gas that is used affects the wavelength of the laser and different wavelengths have different colours. But remember, not all wavelengths are visible to our eyes.

The active medium is a solid, transparent material. The cavity is filled with a crystalline material traditionally based around a gemstone such as a ruby, sapphire or emerald. But these days they are composed of man made materials such as the Nd:YAG (neodymium-doped, yttrium aluminium garnet). These lasers emit light with a wavelength of 1064 nm, which is the near infrared. But with the use of clever optics the frequency can be doubled (this will halve the wavelength to 532 nm). This now produces a green laser emission as seen in hand held laser pointers.