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J.P. Waclawek, B. Lendl:
"Photothermal interferometry apparatus and method";
Patent: USA, Nr. US201716310261; eingereicht: 18.01.2018, erteilt: 04.08.2020.

Photothermal interferometry apparatus (1) for detecting a molecule in a sample, in particular for detecting a trace gas
species, comprising: - a Fabry-Perot interferometer (4) with a first mirror (5), a second mirror (6) and a first cavity (7) for
containing the sample extending between the first (5) and the second mirror (6), - a probe laser arrangement with at least
one probe laser (3) for providing a first probe laser beam (8a) and a second probe laser beam (8b), - an excitation laser
(2) for passing an excitation laser beam (2a) through the first cavity (7) of the Fabry-Perot interferometer (4) for exciting
the molecule in the sample, - the Fabry-Perot interferometer (4) comprising a third mirror (39), a fourth mirror (40) and a
second cavity (41) for containing the sample extending between the third (39) and the fourth mirror (40), - the first (7) and
the second cavity (41) of the Fabry-Perot interferometer (4) being arranged such that the first probe laser beam (8a)
intersects with the excitation laser beam (2a) in the first cavity (7) and the second probe laser (8b) beam does not
intersect with the excitation laser beam (2a) in the second cavity, - a photodetector unit (9) comprising a first photo
detector (44) for detecting the transmitted first probe laser beam (8a) and a second photo detector (45) for detecting the
transmitted second probe laser beam (8b).