|M.Sc Thesis||Department of Mechanical Engineering|
|Supervisor:||Prof. Emeritus Hetsroni Gad|
In this work we compared the heat generated in Nd:YAG following pumping with 885nm (‘direct’ pumping) and 803nm (‘standard’) diode lasers under similar conditions.
Two laser heads were used, one made of stainless steel, the other of quartz. In both cases water was used as the cooling fluid. The temperatures at the laser head inlet and outlet were measured, together with the volumetric flow rate. These measured quantities allowed direct calculation of the heat transferred by the water.
In the stainless steel head, the coolant temperature increased due to the heat generated directly in the rod and due to the fluorescence created in the rod and absorbed by the stainless steel. The heat measured in this way was then used to measure the absorbed power in the rod for each diodes current.
The second head allowed much of the fluorescence light to escape. The coolant temperature increase here could be used to directly calculate the heat created in the rod.
Measurements had shown, that heat fraction, when pumping at 803nm under non-lasing conditions, is around 50%, while according to theory, the heat fraction, under same conditions, should be between 30 to 35%. Thus, probably part of the fluorescence was still being converted into heat that contributed to DT (~30% at no lasing condition). This contribution was reduced when the lasing fraction increased, reaching minimum effeect when the lasing fraction was maximal. Assuming that the fluorescence contribution is similar for 803 and 885nm pumping, an upper limit of 82±7% for heat generated with the 885 wave length as compared to 803nm pumping was found experimentally for maximum lasing fraction at hL~0.6.