FEATURE COOLING TECHNOLOGY
The final amplification stages of the Vulcan laser at Rutherford Appleton Laboratory, in which disks of laser glass are mounted into cavities and pumped with flash lamps. There is no active cooling of the laser glass, with the heat generated in the flash lamps extracted by air-cooling
at the University of Oxford. This relatively old method of liquid cooling is still extremely important and widely used in many different systems.
When the laser material is cooled in this way, it is generally mounted in a chamber that allows the cooling liquid to come into contact with the laser material; the cooling liquid then flows into a chiller where the heat is removed by exchange with the air or a secondary cooling loop. It is important to make sure that the liquid does not create scaling or other corrosion of the tubing that would limit the efficiency of the heat exchange or limit the flow, noted Arrigoni. Where the cooling liquid, usually water, is in direct contact with electrical connections,
www.electrooptics.com | @electrooptics
the purity of the water is critical, he added, as impurities cause the water to conduct, and this can lead to serious electrical problems. Improvements in techniques for removing dissolved materials and ions from water have contributed to the increase in laser systems’ lifetime.
Going cutting-edge Higher power lasers need greater cooling and advances in cooling technology have increased the lifespan of these lasers. ‘Very small patterned conduits called micro-channel plates are used to cool very high power laser diode arrays that can produce kilowatts of power,’ said Arrigoni. ‘Even though these laser diodes are very efficient,
considerable amounts of heat need to be removed from a very small device, with a cooling area of a few centimetres squared or even less. The overall quality of the micro-channel plate is an enabling element.’
Also, he added, it is important to look for smarter ways to provide an efficient path from the laser medium, where the heat is first produced or deposited, to the cooling plate or fluids. ‘Liquid nitrogen or cryogenic cooling is the most extreme method but also the most complex and costly. It should only be used where absolutely necessary. Although some companies producing Ti:S lasers cool them cryogenically, at Coherent we use cryogenic cooling only with the most extreme systems, like ones operating at 20W level of
➤ MARCH 2014 l ELECTRO OPTICS 27
Monty Rakusen
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40