|MadSci Network: Engineering|
Dear Philippe, The explicit answer to your qestion is: No. I'm assuming I won't bore you by examining why, in fact, piezoeletric cryatals and material act like excellent detectors for electromagnetic radiation - although it is not "radiation pressure" which they sense. When I was a graduate student in the last century we had a problem of measuring the spatial profile of our infrared CO2 (carbon dioxide) laser. Our postdoc and I came up with the idea of using piezoelectric crystals made from modified barium titanate (PZT) and piezoelectric materials, such as poly-vinyledene di-fluoride (PVDF) - a plastic. Our reasoning flowed from the need for a material that could withstand high irradiation intensities and still respond with a linear signal output. That is, the measured signal had to be proportional to the laser pulse energy even at 10 Joules/cm^2 fluence. Piezoelectrics to the rescue! So, why do they work? It is not the piezoelectric effect that's active in raidation detection, but the second-order pyroelectric effects common to all piezoelectric materials. They are permanently polarized and acts as a pyroelectric detector because any change in the temperature difference between both the surfaces (front-to-back) generates corresponding change in polarization and as a result a voltage signal across them. A pyroelectric calorimeter has been developed using PVDF foil to measure the energy of x-rays emitted from laser produced plasma which provides two types of signal in pyroelectric calorimeter mode. One of the signal has fast response which is produced due to thermo-elastic effect in foil whereas other one has slow response which is actual time integrated calorimetric signal. However, both the signals are proportional to the absorbed x-ray energy - that is they have a linear response. It's been found that 100% absorption of the x-rays occurs on aluminum- coated detectors. Sensitivity is increase if a gold coating is used, instead. A black coated PVDF detector will enhance the piezoelectric sensitivity for spectral range UV, VIS,IR. Hope this helps! ---* Dr. Ken Beck
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