Dual-modulation-frequency photopyroelectric technique: application to thermophysical investigation of (NH4)HSO4 and (ND4)2TeCl6 crystals at low temperature

Mihai Chirtoc; Dirk Giese; Bertram Arnscheidt; Nikolai Kalevitch; Josef Pelzl

doi:10.1117/1.601209

1 February 1997 Dual-modulation-frequency photopyroelectric technique: application to thermophysical investigation of (NH4)HSO4 and (ND4)2TeCl6 crystals at low temperature

Mihai Chirtoc, Dirk Giese, Bertram Arnscheidt, Nikolai Kalevitch, Josef Pelzl

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Optical Engineering, Vol. 36, Issue 2, (February 1997). https://doi.org/10.1117/1.601209

The photopyroelectric (PPE) method for thermo-optic materials investigation uses a pyroelectric sensor to measure the photothermal heating of the sample. We report on a self-calibrated PPE technique consisting of simultaneous excitation of the PPE cell at two frequencies. The corresponding signals are retrieved from the multiplexed pyroelectric response with two lock-in amplifiers. Their ratio depends only on the sensor’s specific heat and the sample’s thermal effusivity, as temperature-dependent quantities. This scheme has the advantage that it cancels out possible fluctuations of excitation intensity and of the pyroelectric coefficient. Experimental results with (NH4)HSO4 and (ND4)2TeCl6 crystals show that this feature is particularly important when studying structural phase transitions at low temperature (20 to 300 K). Finally it is found that below 240 K epoxy resin is a better coupling medium than silicon grease.

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Mihai Chirtoc, Dirk Giese, Bertram Arnscheidt, Nikolai Kalevitch, and Josef Pelzl "Dual-modulation-frequency photopyroelectric technique: application to thermophysical investigation of (NH4)HSO4 and (ND4)2TeCl6 crystals at low temperature," Optical Engineering 36(2), (1 February 1997). https://doi.org/10.1117/1.601209

Published: 1 February 1997

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