Ion laser

Argon- ion laser (Ar laser) are gas lasers in which the lasing medium is comprised of the ionized argon gas, cf oxygen -ion laser.

Argon - ion lasers can be next to copper vapor lasers currently the highest radiation power generated directly in the visible spectral range.

Argon has up to ten laser lines in the blue, green and yellow-green region of the optical spectrum.

Typical parameters

• Optical output power: 10 mW to 100 W ( typically 50 mW to several watts )
• Beam quality: very high, single -mode operation
• Beam diameter: 1 mm
• Coherence length: up to 100 m
• Efficiency: 0.05-2.5 % ( depending on version)
• Lifetime of a gas filling to regeneration: about 500-2000 hours depending on the tube type (wear by diffusion, leakage occurs, contamination )
• Dimensions for 50 mW optical power: Laser head: (150 × 150 × 300 ) mm ³ ​​, supply part: (350 × 350 × 150 ) mm ³ ​​( power input 1.5 kW)
• Performance typical: 1-5 watts to 100W to high and more

Applications

Argon ion lasers are widely used in electro-optical research, where they serve among other things as optical pump source for other lasers.

Besides its use in research and development argon -ion lasers are also in the conversation (eg, laser shows), for the structured production of objects, usually in high-speed printing machines, plotters or holography, and medicine ( dermatology, ophthalmology and dentistry ) is used.

Construction

Argon- ion laser with an argon -filled consist of a vacuum-tight welded to the plasma tube. This tube is usually an existing beryllium oxide (BeO ) ceramic tube. BeO ceramic has a high thermal conductivity and excellent thermal shock resistance, which is necessary to the cope with the enormous temperatures in her burning plasma and dissipating the heat released in the process. Depending on the model and power flow in the plasma 3-60 A at voltages up to 500 V. While small argon lasers produce only about 1-2 kW of heat, bring it to the bigger ones to more than 13 kW. This high heat output generated in the interior of the plasma tube and must be removed therefrom, for which purpose BeO has proven to be a suitable material. However, these excellent features is offset by the extreme toxicity of BeO. While smaller laser to 1 W can usually be cooled with air, for larger equipment water cooling is required. Due to the high power demand argon lasers are used today in many areas by frequency-doubled Nd: YAG laser replaced ( DPSS ), which can deliver only one wavelength while, but at the same optical output power less than a tenth of the power demand.

Typically emit argon laser in the visible spectral range. The power rating of this usually refers to the total power of the six strongest lines from 514.5 nm to 457.9 nm, the strongest and most frequently used laser lines of an argon laser, the green 514.5 nm and 488.0 nm, the turquoise line.

Depending on the optics used, argon laser can be constructed either as a single-line laser, which then generate only a single frequency, and thus, monochromatic light, or as a multi-line laser. The latter will be able to work at different frequencies, so that - depending on the construction of the laser - either a free selection of the desired line is possible, or more spectral lines are produced at the same time.

The wavelengths outside the visible range, including the stable infrared line at 1090 nm may be generated by the optical components will be replaced by specific IR or UV optics.

The UV - lines are created by double - ionized transitions that require substantially higher currents in the plasma discharge. Therefore, only the large high-power laser to UV operation it rebuilt.

Single-line laser configuration

The majority of applications, such as interferometry, holography, or require that the laser only a single frequency, and thus generates monochromatic light. This can be accomplished by the highly reflective back mirror, which reflects all frequencies normally again back into the laser tube through a so-called Littrow prism (see Littrow spectrometer ) is replaced. This prism works as a wavelength selector, also features a fully mirrored side.

The light enters the prism and is thereby spectrally decomposed before it is reached the reflective layer and reflected back. Thus, only a single wavelength can be reflected into the tube, namely those for which, due to the angular position of the prism, the distraction is exactly 0 °.

Another possibility for monochromatic light provides when the partially transparent output mirror is coated reflective only for the desired wavelength ( dichroic interference mirror ). All other frequencies can then generate any vibrations in the laser, because for them there is no sufficient feedback.

The radiation which is produced by such a single-line laser, has a very small line width and good coherence extremely in comparison with other light sources, or frequency-doubled DPSS. But in fact it is not a single frequency but by several, very close to each other within the laser line of the argon -lying frequencies. The width of this frequency band is approximately 5 GHz. The spacing of the individual frequencies to each other is determined by the speed of light in the plasma tube and the distance between the two mirrors forming the cavity to each other. For a 1 m long resonator, this results in a difference of the frequencies of about 150 MHz. This is called a mode spacing of the longitudinal modes.

Power control and stabilization

The output power of a gas ion laser may be adjusted to any value between the maximum laser power and laser threshold is changed by the discharge current in the plasma.

Plasmas have a negative differential resistance, i.e., with increasing discharge current decreases, the internal resistance of the plasma, resulting in a rise of the avalanche current would result. Without current limiting, the laser would therefore destroy themselves.

The electronics of the flow control, therefore, requires a counter- coupling: as a control variable can be used in this case the current flowing through the plasma, or the optical power of the laser beam generated either. The electronics then either keeps the current in the plasma, or the radiation power of the laser constant. Older power supplies are built on the principle of the linear regulator. These are very large and heavy. They also produce a very high heat loss and often have to be cooled with water. Newer devices are built as a switching regulator, which they would be much smaller and lighter, with comparable performance. They can be cooled with air at higher output powers yet.