Multipoint photo-acoustic measuring device
A method comprises non-destructive contact-free physical characterization of a sample by repeated excitations of the surface of a sample with a sequence of pulses comprising at least one pump pulse by a first “pump” laser followed by a succession of L temporarily offset pulses by a second “probe” laser, and the analysis of the beam emitted by the surface of the sample by an activated photodetector, for the acquisition of signals delivered by the photodetectors during constant time windows.
1 . A non-destructive and contact-free method for physical characterization of a sample, comprising:
repeatedly exciting a surface of the sample with pump and probe beams comprising a sequence of pulses, the sequence of pulses comprising at least one pump pulse produced by a pump laser followed by a plurality of L probe pulses produced by a probe laser, the plurality of L probe pulses having different temporal offsets with respect to the at least one pump pulse;
receiving, with a photodetector, the plurality of L probe pulses in the sequence of pulses after interacting with the surface of the sample;
wherein:
the photodetector comprises an N-dimensional array of a plurality of M photosensitive elements, wherein N is one or two; and
for each photosensitive element of the plurality of M photosensitive elements, a signal value is determined based on a signal produced by the photosensitive element in response to one probe pulse after the one probe pulse interacts with the surface of the sample;
recording, for each sequence of pulses, an array of MxL signal values delivered by the plurality of M photosensitive elements; and
applying a transformation to the array of M×L signal values to determine a map of a zone of the sample in a form of an array of values of a physical characteristic observed for at least one point of the zone.
2 . The method of claim 1 , further comprising determining the transformation through supervised learning.
3 . The method of claim 1 , further comprising determining a plurality of transformations, each corresponding to a particular physical characteristic.
4 . The method of claim 1 , further comprising automatically optimizing a focus of optics for the pump and probe beams on the sample by controlling a sequence of variation of focusing and measuring a quality factor of the signal values produced by the photodetector, and selecting the focus corresponding to a maximization of the quality factor over the signal values.
5 . A system for non-destructive and contact-free physical characterization of a sample, comprising:
two pulsed laser sources configured to emit respectively a pump beam comprising at least one pump pulse and a probe beam comprising a plurality of L probe pulses, wherein the plurality of L probe pulses have different temporal offsets with respect to the at least one pump pulse;
a detector configured to receive probe pulses after interacting with a surface of the sample, the detector comprising an N-dimensional array of a plurality of M photosensitive elements, wherein N is one or two, and wherein, for each photosensitive element of the plurality of M photosensitive elements, signal values are determined based on signals produced by the photosensitive element in response to the plurality of L probe pulses after interacting with the surface of the sample; and
a computer configured to control a recording of an array of MxL signal values delivered by the plurality of M photosensitive elements and to apply a transformation to the array of MxL signal values to determine a map of a zone of the sample in a form of an array of values of a physical characteristic observed for at least one point of the zone.
6 . The system of claim 5 , wherein the pump beam and the probe beam are coaxial in a zone of interaction with the sample.
7 . The system of claim 5 , wherein the pump beam is perpendicular to a plane of a zone of interaction with the sample, and the probe beam forms an angle other than 90° with the plane of the zone of interaction with the sample.
8 . The system of claim 5 , further comprising memory storing the transformation for applying to the array of MxL signal values to determine the array of values of the physical characteristic observed for the at least one point of the zone.
9 . The method of claim 1 , further comprising determining an N-dimensional mapping of a thickness of a coating layer of a sample, wherein N is 1 or 2.
10 . The method of claim 1 , further comprising determining an N-dimensional mapping of a Young's modulus of a sample, wherein N is 1 or 2.
11 . The method of claim 1 , further comprising determining an N-dimensional mapping of an adhesion strength of a sample, wherein N is 1 or 2.
12 . The method of claim 1 , further comprising determining an N-dimensional mapping of a crystalline state of a sample, wherein N is 1 or 2.
13 . The method of claim 1 , wherein the sequence of pulses comprise a plurality of pump pulses, wherein each pump pulse in the plurality of pump pulses is followed by a single probe pulse and each pair of pump pulse and probe pulse have a different temporal offset.
14 . The method of claim 13 , wherein the pump laser and the probe laser are synchronous and have different repetition frequencies to produce the different temporal offsets.
15 . The method of claim 1 , wherein each pump pulse and each probe pulse has a duration of less than a femtosecond.
16 . The system of claim 5 , wherein the pump beam comprises a plurality of pump pulses, wherein each pump pulse in the plurality of pump pulses is followed by a single probe pulse and each pair of pump pulse and probe pulse have a different temporal offset.
17 . The system of claim 16 , wherein the two pulsed laser sources are synchronous and have different repetition frequencies to produce the different temporal offsets.
18 . The system of claim 5 , wherein each pump pulse and each probe pulse has a duration of less than a femtosecond.