New technology regarding manufacturing of micro cooling systems and selective laser melting was presented at
Photonics West 2005; at Photonics West 2006 the first non-corrosive active micro coolers manufactured by this
procedure were introduced to the auditorium. This presentation shows the latest results regarding active micro cooling
systems for high power diode laser with a matched CTE.
After the first non corrosive micro coolers passed the tests regarding cooling performance, there were still two tasks
which had to be accomplished:
First one was the homogeneity of cooling. In order to achieve the homogeneity, the design of the supporting structure in
front of the micro cooling structures was modified. Measurements of cooling performance and the range of the
wavelength along the laser bar showed that with the modified structure a homogeneous inflow was achieved as well as
homogeneous cooling along the laser bar. The presentation highlights the measurements and results.
Second point of development was the quest for a material combination with an adequate thermal conductivity for
keeping the cooling performance, but with a coefficient of thermal expansion that matches with the CTE of diode laser
bar material. After testing several materials fitting to these requirements, only one material was left, which was capable
to machine workable micro coolers with the SLM procedure. The presentation contains the first results of the micro
coolers with a matched CTE regarding thermal resistance, CTE and packaging with gold - tin solder.
At Photonics West 2005 a new technology was described for building a new, non corrosive micro cooling heat sink for diode lasers made of stainless steel with the procedure of three dimensional laser melting. Due to the thermal conductivity, which is 20 times worse than the conductivity of copper, first test leads to the result, that it is not possible to compensate the worst thermal conductivity by an optimized inner structure, regarding wall thicknesses and flow rate. So the solution was searching a different material, with a better thermal conductivity to achieve a thermal over all resistance that is usable for the cooling of high power laser diodes. Searching that material leads to a special nickel alloy in the field of nuclear industry. The new generation of micro coolers are named TEX series. All TEX Series coolers were made out of a special nickel alloy, specially developed as a corrosion protection material. Therefore, the TEX coolers have excellent corrosion resistance. In addition, due to the manner and way of using three dimensional laser melting, the surface of the inner structure was hardened. The hardening HV1 is 380, so that there is no danger regarding erosion or a combination of erosion and corrosion. Metallization and soldering the semi conductor also had been tested. The commonly used structure with Nickel and Gold is possible as well as the metallization only with gold. With both variations the semi conductor can be soldered and the connection to the cooler surface is very strong.
Cooling high power laser diodes with micro channel heat sinks is state of the art. But latterly also states of the art are problems with leaks, based on corrosion. As a user of high power diode lasers we can badly confirm that point. We observed, that the major part of the collapsed heat sinks was made by using direct copper bonding. Due to that, ProLas decided to get forward in there own development of micro cooling systems and the protection of corrosion. In a first step the joining procedure was switched to diffusion welding. This procedure uses only a vacuum surrounding, pressure and heat, no oxygen. In a second step the micro coolers will be covered at the inside using a special gas during the aeration of the vacuum oven. This cover is only a few nm thick, so that the cooling performance will not be impaired. Additionally the cover is so stabile, that particles or cavitations are not able to destroy it. Only in a few regions of very high flow rate we still have erosion, but the passivation is not able to build a local element with the copper. So erosion will not leads to corrosion in these cases. In addition to the improved copper cooler types we developed a complete new generation of micro coolers, using alternative materials and a different manufacturing method, to achieve non-corrosive monolithic heat sinks with a more suitable CTE.
Basis of the developments discussed in the presentation are 10 mm GaAs diode laser bars mounted on copper micro channel heat sinks. Optimizing the micro channel heat sinks leads to decreased thermal resistance and decreased pressure drop. In the presentation the steps to ten times reduced pressure drop and optical power output of the diode lasers of over 100 Watts will be described.
Basis of the developments discussed in the presentation are 10 mm GaAs diode laser bars mounted on copper micro channel heat sinks. Optimizing the micro channel heat sinks leads to decreased thermal resistance and decreased pressure drop. In the presentation the steps to ten times reduced pressure drop and optical power output of the diode lasers of over 100 Watts will be described.
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