In my prior post I told about components in my CO2 laser’s RF power supply becoming unsoldered when they overheated. After the repair, I needed some way of retuning the RF output stage for maximum laser output. This motivated me to build the power sensor shown in the picture above.
The concept is simple – The laser’s output is directed at a surface that will almost completely absorb it. This will heat a small slab which has constant heat dissipation on its opposite surface. At steady state, a stable temperature gradient will be established on the slab, so temperature increase detected by the thermocouple should track power input.
In my power meter, the laser target is a 1.5″ x 1.5″ x 1/8″ piece of anodized aluminum (cut from a transistor heatsink) that is firmly attached to a CPU fan-cooled heatsink. A K-type thermocouple is placed within the aluminum block, under the laser target area. When the fan operates, the CPU cooler sinks heat very well, keeping one side of the aluminum target at virtually constant temperature. I ran a number of experiments, and found out that steady-state is reached at 1 minute of exposure to the unfocused (so as not to burn the anodization) laser beam. For my sensor, the thermocouple’s temperature change over 1 minute of exposure is related to the laser’s power according to the following graph: