R. M. R. Calorimeter Idea
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Rene M. Rogers


Central Research at Varian Associates had several active LASER projects underway in the early 1960s.  One of these involved a Light Emitting Diode (LED) with Sol Miller as the principal investigator.  I did not know any of the details, but Sol asked me to think about an instrument capable of measuring small amounts of pulse energy.  After thinking about it for a day or so, it seemed intuitive to me that a small amount of energy absorbed in a liquid would produce a small change in the volume of the liquid without regard to how the energy was distributed.  I went to the glass lathe and made several prototype devices illustrated in schematic form above.  I explained to Sol that I would fill the main bulb with a black liquid through the capillary by filling the outer tube to the top and alternately heating and cooling the bulb to drive out all of the air.   Then I would fill the region between the outer protective tube and the capillary with a clear liquid that would greatly reduce the reflected light from those surfaces.  The top of the black liquid inside the capillary would be clearly visible either directly or under a microscope if necessary.  The laser light would be directed into the reentrant device in the main bulb and be absorbed by the liquid.  Some small effort might be required to make the entry point a “black hole” and thus minimize any heat loss by reflection.  If Sol liked the idea, I could build any number of these devices in short order and include a small resistor in the bulb for calibration purposes.  By discharging a small capacitor through the resistor, a precisely known amount of energy would be delivered into the liquid and the instrument could be considered as a Primary device.   Perhaps 2 or 3 of these instruments with calibrating resistors included were built before my friend Ken Rogers came up with a far superior instrument even as I was explaining to him how this one would work.  He reasoned that the resistance of a length of wire would change in a precise way when the energy content was changed without regard to the distribution of the energy.  The resistor, a length of fine black copper wire, connected as one leg of a bridge gave an electrical readout in a far simpler device than my glass contraption.  It was a fun idea anyway.

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