SYSTEM FOR MEASURING PHOTO-INDUCED DEFORMATION OF A SAMPLE

Abstract

The invention relates to a system (101) for measuring the photo-induced deformation of a sample, comprising a Michelson interferometer (103) which includes a first light source and means for acquiring and converting the optical interference signal into an electrical signal, a second light source (201), an arbitrary signal generator (205) configured to modulate the intensity of the second light source (201) at a frequency, and an electrical signal processing unit (211). The second beam (203) illuminates the sample, and the processing unit (211) is configured to determine the amplitude of the sample deformation from the electrical signal. Figure 2 is shown in the abstract.

Description

Title of the invention: SYSTEM FOR MEASURING PHOTO-INDUCED DEFORMATION OF A SAMPLE technical field

[0001] The invention relates to the field of characterizing the photomechanical properties of samples. It relates in particular to a system for measuring a photo-induced deformation of a sample. Previous technique

[0002] To characterize the photo-induced deformation of a sample, it is known to use so-called capacitive methods which consist of placing the sample to be characterized between two plates of a capacitor and determining its deformation by measuring the change in capacitance of the capacitor associated with a determined illumination.

[0003] These methods are limited by the fact that the samples to be characterized must be sufficiently rigid to be able to push the capacitor plates when they are deformed.

[0004] Another known approach relies on the use of so-called indirect measurement methods such as spectroscopy (for example, described in the article Photo striction of strontium ruthenate, Wei, TC. et al, Nat Commun 8, 15018 (2017)).

[0005] These methods are said to be indirect insofar as they require prior knowledge of the properties of the material in which the sample is made, which implies carrying out additional measurements and processing complex data in order to determine these properties.

[0006] Another known approach also relies on the use of an atomic force microscope to determine the deformation of the sample by contact of the tip of the microscope with the surface of the sample which is subjected to illumination causing its deformation.

[0007] This approach is however costly and the tip of the microscope disturbs the light source which is used to cause the deformation and can also damage the surface of the sample. Summary of the invention

[0008] The present invention proposes a solution to these drawbacks.

[0009] Thus, an objective of the invention is to propose a system allowing a direct and precise measurement of the photo-induced deformation of a sample, regardless of the material in which the sample is made and without requiring contact with the sample.

[0010] To this end, the invention, according to a first aspect, relates to a system for measuring a photo-induced deformation of a sample comprising:

[0011] - a Michelson interferometer comprising:

[0012] - a first light source configured to emit a first beam at a first wavelength;

[0013] - a first separator configured to separate the first beam into a first part circulating in a first arm of the Michelson interferometer and a second part circulating in a second arm of the Michelson interferometer;

[0014] - the sample, positioned in the first arm, so that the first part of the the first beam is reflected by said sample;

[0015] - a movable support, on which a mirror is mounted, positioned in the second arm, so that the second part of the first beam is reflected on said mirror and the position of said mirror can be modified by means of said movable support;

[0016] - means for acquiring an optical interference signal between the reflection of the first part of the first beam and the reflection of the second part of the first beam and the conversion of said optical signal into an electrical signal,

[0017] said system being characterized in that it further comprises:

[0018] - a second light source configured to emit a second beam at a second wavelength;

[0019] - an arbitrary signal generator configured to modulate the intensity of the second light source at a specific frequency;

[0020] - an electronic card connected to the means and configured to acquire of the electrical signal; and,

[0021] - an electrical signal processing unit for the signal from the electronic board,

[0022] and in that the second beam, the intensity of which is modulated by the arbitrary signal generator, illuminates the sample and the processing unit is configured to determine the amplitude of the deformation of said sample from the electrical signal.

[0023] The system according to the invention may comprise one or more of the following features, taken individually or in combination with each other:

[0024] - the system further comprises a configured synchronous detection amplifier to generate an amplified electrical signal of the component at the frequency of the electrical signal and in which the processing unit is configured to determine the amplitude of the deformation of the sample from said amplified electrical signal.

[0025] - the first wavelength of the first light source is adjustable, and preferably between 600 nanometers and the near infrared, and the second wavelength of the second light source is adjustable, and preferably between the near UV and 600 nanometers.

[0026] - the means for acquiring and converting the optical interference signal are included among a photodiode and a digital camera.

[0027] - in the Michelson interferometer, the first beam splitter is a beam splitter polarization, and said Michelson interferometer further comprises a first quarter-wave plate, positioned in the first arm, between the first separator and the sample, a second quarter-wave plate, positioned in the second arm between the first separator and the mirror, a third quarter-wave plate, positioned after the first separator, and a second separator, of the polarization separator type, positioned after the third quarter-wave plate.

[0028] - the Michelson interferometer includes first means for acquisition and conversion of the optical interference signal and of the second means of acquisition and conversion of the optical interference signal, positioned after the second separator, on the path of the optical interference signal, so that a first part of said optical interference signal is acquired by said first means and a second part of said optical interference signal is acquired by said second means.

[0029] - the system further comprises a half-wave blade, positioned between the first light source and the first separator, on the path of the first beam.

[0030] - the Michelson interferometer further comprises, a bandpass filter, centered on the first wavelength, positioned on the path of the optical interference signal, upstream of the means of acquisition and conversion of said optical interference signal.

[0031] - the electronic board is controlled by the processing unit to generate a signal control of the mobile support based on the optical interference signal, in order to generate a feedback loop for the Michelson interferometer.

[0032] The invention according to a second aspect also relates to a method of using the system according to the first aspect, comprising the following steps:

[0033] - illumination of the sample by the first beam from the first source luminous;

[0034] - illumination of the sample by the second beam of the second light source, modulated in intensity by the arbitrary signal generator;

[0035] - acquisition of the optical interference signal and conversion of said optical signal interference in an electrical signal by means;

[0036] - acquisition, by the electronic card, of the electrical signal;

[0037] - determination, by the processing unit of the amplitude of the deformation of the sample from the electrical signal coming from the electronic board. Brief description of the drawings

[0038] The invention will be better understood with the aid of the following description, given solely by way of example and made with reference to the accompanying drawings in which:

[0039] [Fig.1] is a schematic representation of a Michelson interferometer such as that included in a system for measuring a photo-induced deformation of a sample according to an embodiment of the invention;

[0040] [Fig.2] is a flowchart representing a system for measuring a photo-induced deformation of a sample according to an embodiment of the invention;

[0041] Figure 3 is an example of the evolution, as a function of the path difference, of the amplitude of an optical interference signal converted into an electrical signal; and,

[0042] [Fig.4] is a step diagram of a method of using a system for measuring a photo-induced deformation of a sample according to an embodiment of the invention. Description of the implementation methods

[0043] With reference to [Fig.1] and [Fig.2], we will now describe an embodiment of a system 101 for measuring a photo-induced deformation of a sample 115.

[0044] The invention applies to a sample made of any material, provided that the sample in question is solid and has a flat surface designed to reflect a beam from a first light source (described in more detail below). By way of non-limiting example, the sample 115 can be made of a semiconductor material such as that used in the manufacture of electronic components.

[0045] The system 101 includes a Michelson interferometer 103 which is shown in more detail in [Fig.1].

[0046] The Michelson interferometer 103 comprises a first light source 105 (also referred to as a probe) which is configured to emit a first beam 107 at a wavelength Xp. The emission of the first beam 107 at the wavelength Xi means that the emission is centered on the wavelength Xi and that it has a determined spectral width around this wavelength.

[0047] Furthermore, in the embodiment shown, the first light source 105 is a laser source and therefore has a very small spectral width (on the order of 0.5nm).

[0048] Generally, a person skilled in the art will be able to select a light source whose central wavelength and spectral width are suitable for the sample to be characterized and / or the desired performance of the system. For example, to characterize a sample made of a semiconductor material, the wavelength Xi of the first light source 105 can be chosen between 600 nanometers and the near infrared (down to about 1.6 micrometers) to prevent the first beam 107 from being absorbed by the sample 115.

[0049] In a particular embodiment, the wavelength Xi of the first light source 105 is adjustable. In other words, it is possible to vary the wavelength Xi of the first light source 105 within a predetermined range of values, that is, to adjust the value of the central wavelength of the first light source 105 within this range. Advantageously, it is thus easy to adapt the system (i.e., to optimize it) for different samples made of different materials.

[0050] The Michelson interferometer 103 also includes a first splitter 109 configured to split the first beam 107 into a first part circulating in a first arm 111 of the Michelson interferometer 103 and a second part circulating in a second arm 113 of the Michelson interferometer 103.

[0051] In the non-limiting example shown in [Fig.1], the first splitter 109 is a polarization splitter which separates the first beam 107 according to its polarization and the Michelson interferometer 103 also includes a half-wave plate 127 which is positioned between the first light source 105 and the first splitter 109, on the path of the first beam 107.

[0052] In this configuration, the half-wave plate 127 allows the polarization of the first beam 107 incident on the first separator 109 to be adjusted so as to control the power distribution of the first beam 107 between the first and second parts. Advantageously, this adjustment can be optimized according to the losses related to the sample 115 present in one of the two arms (as described in more detail later).

[0053] Indeed, the sample 115 is positioned in the first arm 111 such that the first part of the first beam 107 is reflected by the sample 115. The level of reflection of the sample 115 depends in particular on its surface condition (i.e., the associated scattering) and its absorption level. The adjustment of the half-wave plate 127 therefore makes it possible to take this level of reflection into account in order to distribute the power of the first beam 107 between the two arms.

[0054] In the example shown in [Fig.1], the polarization of the first beam 107 (incident on the separator 109) is linear and forms an angle α with the vertical (which is perpendicular to the plane of the image) and the power of the first part of the first beam 107 (whose polarization is linear) in the first arm 111 is proportional to the sine of the angle α while the power of the second part of the first beam 107 (whose polarization is also linear and orthogonal to the polarization of the first part of the first beam 107) in the second arm 113 is proportional to the cosine of the angle α.

[0055] The Michelson interferometer 103 also includes a movable support 117, on which a mirror 119 is mounted, positioned in the second arm 113, so that the second part of the first beam 107 is reflected onto the mirror 119 and the position of the mirror 119 can be changed via the movable support 117. In other words, the length of the (optical) path traveled by the second part of the first beam 107 in the second arm 113 can be changed by changing the position of the mirror 119 via the movable support 117. The term "mounted" here implies that the mirror is fixed to a moving portion of the movable support 117.

[0056] In a particular embodiment, the movable support 117 can be a piezoelectric shim. Advantageously, such a piezoelectric shim has a small footprint while offering submicrometer-level adjustment accuracy for the displacement.

[0057] In the non-limiting example shown in [Fig.1], the Michelson interferometer 103 further comprises a first quarter-wave plate 129, positioned in the first arm 111, between the first separator 109 and the sample 115, and a second quarter-wave plate 131, positioned in the second arm 113 between the first separator 109 and the mirror 119.

[0058] The quarter-wave plates 129 and 131 modify the polarization state, respectively of the first part of the first beam 107 and of the second part of the first beam 107, at each passage through said quarter-wave plates 129 and 131 (going from a linear polarization to a circular polarization and vice versa) and advantageously allow, in this configuration where the separator 109 is a polarization separator, to avoid a return of the first beam 107 into the first light source 105.

[0059] The Michelson interferometer further includes means 121 and 123 for acquiring an optical signal 125 of interference between the reflection of the first part of the first beam 107 and the reflection of the second part of the first beam 107 and for converting said optical signal 125 into an electrical signal 127.

[0060] In various embodiments of the invention, the means 121 and 123 may be, for example, a photodiode or a digital camera. In all cases, these means 121 and 123 are positioned in the path of the optical interference signal 125 in order to acquire it and convert it into an electrical signal.

[0061] In the non-limiting example shown in [Fig. 1], the Michelson interferometer 103 also includes a third quarter-wave plate 137 positioned after the first beam splitter 109 (i.e., after the recombination of the two reflected parts of the first beam from the two arms and having passed through the first beam splitter 109) and a second beam splitter 133, positioned after (in the direction of the optical path) the third quarter-wave plate 137 (and before means 121 and 123) which is also a polarization splitter.

[0062] The third quarter-wave plate 137 makes it possible to avoid, in this configuration in which the separator 109 is a polarization separator, that the beams from the two arms which are recombined after their passage through the separator 109, have orthogonal linear polarizations which would prevent them from interfering.

[0063] Furthermore, in this example, the Michelson interferometer 103 includes first means 121 and second means 123 of acquisition which are positioned after the second splitter 133, so that a first part of the optical interference signal 125 is acquired by the first means 121 and a second part of the optical interference signal 125 is acquired by the second means 123.

[0064] Advantageously, this allows, for example by performing a subtraction of the electrical signals generated by each of the means, to improve the signal-to-noise ratio.

[0065] Besides the example shown here in which the interferometer includes first and second means 121 and 123, the invention also relates to a system 101 in which the interferometer 103 includes only (solely) first means 121 for acquiring an optical signal 125 of interference and for converting the optical signal 125 into an electrical signal 127.

[0066] In addition to the Michelson interferometer 103 described above, the system 101 (visible in its entirety in [Fig.2]) also includes a second light source 201 (also referred to as a pump) configured to emit a second beam 203 at a second wavelength X2. The light source 201 is therefore centered in wavelength on the second wavelength X2 and has a determined spectral width.

[0067] The second wavelength X2 differs from the first wavelength Xi because the second light source 201 must generate a photostriction effect on the sample 115 (i.e., photo-induced deformation), which notably involves the absorption of some of the radiation from the second light source 201. For example, the second wavelength X2 of the second light source 201 can be between the near-UV (from approximately 350 nanometers) and 600 nanometers. Furthermore, the second light source 201 can also be a laser source.

[0068] Furthermore, as with the first light source 105, the second wavelength X2 of the second light source 201 can be modulated. Advantageously, the emission wavelength of the second light source 201 can thus be adjusted to the material in which the sample 115 is made in order to optimize the photostriction effect of the sample 115.

[0069] Furthermore, in the embodiment shown in [Fig. 1], the Michelson interferometer 103 further comprises a bandpass filter 135, centered on the first wavelength Xb, positioned in the path of the optical interference signal 125, upstream of the means 121 and 123 for acquiring and converting the optical interference signal 125. Thanks to this bandpass filter 135, the second light source 201 does not interfere with the acquisition of the optical interference signal 125 by the means 121 and 123.

[0070] The system 101 also includes an arbitrary signal generator 205 (also called an ASG) configured to modulate the intensity of the second light source 201 at a predetermined frequency Fi. For example, the frequency Fi can be between 1 MHz and a few MHz. The arbitrary signal generator 205 thus makes it possible to vary the intensity of the second light source 201 periodically (for example, sinusoidally).

[0071] The system 101 further includes an electronic card 213 which is connected to means 121 and 123 and which is configured to acquire the electrical signal 127 and a processing unit 211 for the electrical signal 127 which comes from the electronic card 213.

[0072] In the non-limiting example shown in [Fig.2], the electronic card 213 is controlled by the processing unit 211 to generate a control signal for the mobile support 117 as a function of the optical interference signal 125, so as to generate a servo loop 217 of the Michelson interferometer 103.

[0073] Furthermore, the control loop 217 also includes a voltage amplifier 215 between the electronic board and the moving support 117, which allows the control signal to be amplified, if necessary, according to the displacement of the moving support 117 required by the control system. The presence of this voltage amplifier 215 in the control loop 217 is optional.

[0074] In all cases, the control loop 217 makes it possible to stabilize the path difference (i.e. the optical path difference between the two arms of the Michelson interferometer 103) in order to maintain the electrical signal 127 in a desired area of ​​the evolution of its amplitude.

[0075] In particular, as shown in [Fig. 3], which represents the evolution (in voltage), as a function of the path difference, of the amplitude of the optical interference signal converted into an electrical signal, insofar as the electrical signal 127 is proportional to the optical interference signal 125, its amplitude (as a function of the path difference) evolves as a periodic signal (a cosine in this case) whose period corresponds to half of the first wavelength Xb

[0076] In this case, the control loop aims to maintain the phase difference such that the derivative of the evolution of the amplitude of the electrical signal 127 is maximum (i.e., around the phase <e>(odu cosine). In this way, a photo-induced (periodic) deformation by the second light source 201 causes a variation in voltage Vout of the amplitude of the electrical signal 127 which can be precisely determined.

[0077] Indeed, in the system 101 according to the invention, the second beam 203 (from the second light source 201), the intensity of which is modulated by the arbitrary signal generator 205, is used to illuminate the sample 115 (which causes its periodic photo-induced deformation) and the processing unit 211 is configured to determine the amplitude of the deformation of the sample 115 from the electrical signal 127.

[0078] In concrete terms, as will appear in more detail later with reference to the method of using the system 101, it is the determination of the evolution of the amplitude of the electrical signal 127 as a function of the intensity or frequency of the second beam 203 which allows the processing unit 211 to determine (i.e. to calculate) the amplitude of the photo-induced deformation of the sample 115.

[0079] Finally, in addition to the elements described so far, in the non-limiting example shown in [Fig.2], the system 101 includes a synchronous detection amplifier 207 (or in English “Lock-In Amplifier”) which recovers the electrical signal 127 from the means 121 and 123 and which is configured to generate an amplified electrical signal 209 of the component at the frequency Fidu electrical signal 127 and, as a result, the processing unit 211 is configured to determine the amplitude of the deformation of the sample 115 from the amplified electrical signal 209.

[0080] The presence of this amplifier 207 is optional and in different embodiments, the deformation amplitude of the sample 115 can be determined either directly from the electrical signal 127 or from the amplified electrical signal 209.

[0081] Advantageously, the use of the amplifier 207 with synchronous detection makes it possible to improve the signal-to-noise ratio of the measured electrical signal and thus to increase the accuracy of the measurement.

[0082] With reference to [Fig.4], we will now describe an implementation method of a method 401 of using a system 101 according to the invention.

[0083] Step 403 consists of illuminating the sample 115 with the first beam 107 from the first light source 105, and step 405 consists of illuminating the sample 115 with the second beam 203 from the second light source 201, which is intensity-modulated by the arbitrary signal generator 205. In practice, these two steps are simultaneous so that the Michelson interferometer 103 can to be used to measure the deformations that are induced by the second light source 201.

[0084] Step 407 then consists of acquiring the optical interference signal 125 and converting it into an electrical signal 127 by means 121 and 123. As mentioned above, the means for acquiring and converting the optical signal 125 (which are double in the example shown in [Fig.2]) can also be single.

[0085] Step 409 consists of the acquisition, by the digital card 213, of the electrical signal 127. In practice, the digital card 213 makes it possible to convert the electrical signal 127, from the means 121 and 123, which is analog into a digital electrical signal 127 which is then recovered and processed by the processing unit 211.

[0086] Finally, step 411 consists of the determination, by the processing unit 211, of the amplitude of the deformation of the sample 115 from the electrical signal 127 from the digital card 213.

[0087] In the example shown in [Fig.4], the determination of the amplitude of the deformation of the sample 115 is carried out directly from the electrical signal 127. However, as mentioned above, the determination of the amplitude of the deformation of the sample 115 can be carried out from an amplified electrical signal 209 which itself results from the amplification, by a synchronous detection amplifier, of the electrical signal 127.

[0088] In all cases, the amplitude ô of the photo-induced deformation is calculated using the formula:

[0089] [Math.l] ,S - y 21 ° ~ PP X 2 / r

[0090] where Vpp (as seen in [Fig.3]) corresponds to the peak-to-peak amplitude of the evolution of the electrical signal corresponding to the optical interference signal 125 and Vout corresponds to the value determined (by the processing unit 211) of the amplitude of the electrical signal 127 (or the amplified electrical signal 209) for a determined variation of the intensity of the second beam 203 which is used to illuminate the sample 115.

[0091] Furthermore, in different embodiments, it is possible to vary either the intensity of the second beam 203 (which is then frequency modulated) or its modulation frequency Fi and to follow the evolution of the value ô of the photo-induced deformation accordingly, in order to characterize a sample.

[0092] Furthermore, in the case where sample 115 is not perfectly reflective, this calculation can be adapted to take into account the real part r' and the imaginary part r'' (which must be known beforehand) of the effective reflection factor of sample 115 at the first wavelength Xp

[0093] In this case, the term VPP can be replaced in the above formula by a term VPPjC which takes into account the effective reflection factor of the sample and which is calculated via the formula:

[0094] [Math.2] VPP,C ~^AX PP

[0095] where the term A corresponds to the formula:

[0096] [Math.3] A- ±r'x cos("r2d) + ^^814^2^

[0097] where d is equal to ô / 2.

[0098] Thus, thanks to the invention, it is possible to exploit the precision of a Michelson interferometer to measure a displacement and consequently determine the photo-induced deformation of a sample.

[0099] In addition, the system uses only pump and probe type light sources to determine this deformation and therefore does not involve any contact with the sample, which reduces the risk of sample deterioration.

[0100] Finally, the system is versatile insofar as the choices of types of light sources (wavelength, spectral width...) used can cover a wide variety of samples and it is possible to adapt the measurement to a sample that is not perfectly reflective.< / e>

Claims

1. Demands System (101) for measuring a photo-induced deformation of a sample (115) comprising: - a Michelson interferometer (103) comprising: - a first light source (105) configured to emit a first beam (107) at a first wavelength (XJ; - a first splitter (109) configured to split the first beam (107) into a first part circulating in a first arm (111) of the Michelson interferometer (103) and a second part circulating in a second arm (113) of the Michelson interferometer (103); - the sample (115), positioned in the first arm (111), so that the first part of the first beam (107) is reflected by said sample (115); - a movable support (117), on which is mounted a mirror (119), positioned in the second arm (113), so that the second part of the first beam (107) is reflected on said mirror (119) and the position of said mirror (119) can be modified by means of said movable support (117); - means (121, 123) for acquiring an optical signal (125) of interference between the reflection of the first part of the first beam (107) and the reflection of the second part of the first beam (107) and for converting said optical signal (125) into an electrical signal (127), said system (101) being characterized in that it further comprises: - a second light source (201) configured to emit a second beam (203) at a second wavelength (X2); - an arbitrary signal generator (205) configured to modulate the intensity of the second light source (201) at a determined frequency (Fi); - an electronic card (213) connected to the means (121, 123) and configured to acquire the electrical signal (127); and, - a processing unit (211) for the electrical signal (127) from the electronic card (213), and in that the second beam (203), the intensity of which is modulated by the arbitrary signal generator (205), illuminates the sample (115) and the processing unit (211) is configured to determine the amplitude of the deformation of said sample (115) from the electrical signal (127).

2. System (101) according to claim 1, further comprising a synchronous sensing amplifier (207) configured to generate an amplified electrical signal (209) of the component at frequency (Fi) of the electrical signal (127) and wherein the processing unit (211) is configured to determine the amplitude of the deformation of the sample (115) from said amplified electrical signal (209).

3. System (101) according to claim 1 or claim 2, wherein the first wavelength (Xi) of the first light source (105) is tunable, and preferably between 600 nanometers and the near infrared, and the second wavelength (X2) of the second light source (201) is tunable, and preferably between the near UV and 600 nanometers.

4. System (101) according to any one of the preceding claims, wherein the means (123, 125) for acquiring and converting the optical interference signal (125) are comprised of a photodiode and a digital camera.

5. System (101) according to any one of the preceding claims, wherein, in the Michelson interferometer (103), the first splitter (109) is a polarization splitter, and said Michelson interferometer (103) further comprises a first quarter-wave plate (129), positioned in the first arm (111), between the first splitter (109) and the sample (115), a second quarter-wave plate (131), positioned in the second arm (113) between the first splitter (109) and the mirror (119), a third quarter-wave plate (137), positioned after the first splitter (109), and a second splitter (133), of the polarization splitter type, positioned after the third quarter-wave plate (137).

6. System (101) according to claim 5, wherein the Michelson interferometer (103) comprises first means (121) for acquiring and converting the optical interference signal (125) and second means (123) for acquiring and converting the optical interference signal (125), positioned after the second splitter (133), in the path of the optical interference signal (125), such that a first part of said optical interference signal (125) is acquired by said first means (121) and a second part of said optical interference signal (125) is acquired by said second means (123).

7. System (101) according to claim 5 or claim 6, further comprising a half-wave plate (127), positioned between the first light source (105) and the first separator (109), on the path of the first beam (107).

8. System (101) according to any one of the preceding claims, wherein the Michelson interferometer (103) further comprises, a bandpass filter (135), centered on the first wavelength (Xi), positioned on the path of the optical interference signal (125), upstream of the means (121, 123) for acquiring and converting said optical interference signal (125).

9. System (101) according to any one of the preceding claims, wherein the electronic card (213) is controlled by the processing unit (211) to generate a control signal for the moving support (117) as a function of the optical interference signal (125), so as to generate a servo loop (217) for the Michelson interferometer (103).

10. A method (401) of using a system (101) according to any one of the preceding claims, comprising the following steps: - illumination (403) of the sample (115) by the first beam (107) of the first light source (105); - illumination (405) of the sample (115) by the second beam (203) of the second light source (201), modulated in intensity by the arbitrary signal generator (205); acquisition (407) of the optical interference signal (125) and conversion (407) of said optical interference signal (125) into an electrical signal (127) by means (121, 123); acquisition (409), by the electronic card (213), of the electrical signal (127); determination (411), by the processing unit (211) of the amplitude of the deformation of the sample (115) from the electrical signal (127) from the electronic card (213).

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