Device and method for observing a sample with a chromatic optical system

1. A method for observing a fluorescent sample, lying in a sample plane, the sample comprising a fluorescent agent configured to emit a fluorescence light wave, in a fluorescence spectral band, when it is illuminated by an excitation light wave, in an excitation spectral band, the method comprising:

a) illuminating the sample using a first light source, in a first illumination spectral band, the first illumination spectral band lying in the excitation spectral band, and acquiring a first image of the sample, in the fluorescence spectral band, using an image sensor, the image sensor defining a detection plane;

b) illuminating the sample using a second light source, in a second spectral band, outside of the fluorescence spectral band, the sample lying between the second light source and the image sensor, and acquiring a second image of the sample, in the second spectral band, using the image sensor;

the image sensor being coupled to an optical system placed between the image sensor and the sample, the optical system being such that:

in the fluorescence spectral band, the object plane of the optical system is coincident with the sample plane; and

in the second spectral band, at least one of

the object plane of the optical system is offset with respect to the sample plane, and

the image plane, of the optical system is offset with respect to the detection plane,

the offset being larger than 20 μm;

wherein:

the first image is a focused image of the sample, which image is representative of a fluorescence of the sample;

the second image is a defocused image of the sample, which image is representative of a structure of the sample; and

the image sensor, the optical system and the sample remain stationary between the acquisition of the first image and the acquisition of the second image.

2. The method according to claim 1 , comprising:

c) applying a holographic reconstruction operator to the second image, so as to obtain a reconstructed image of the sample in a reconstruction plane.

3. The method according to claim 1 , wherein the second spectral band is offset, with respect to the fluorescence spectral band, by at least 150 nm and preferably by at least 200 nm.

4. The method according to claim 1 , wherein, in the second spectral band, the object focal plane is offset from the sample plane by a distance smaller than 1 mm, and preferably by a distance smaller than 500 μm.

5. The method according to claim 1 , wherein:

the first light source is placed in a half-space bounded by the sample plane and comprising the image sensor; or the first light source is placed in a half-space bounded by the sample plane and comprising the second light source.

6. The method according to claim 1 , wherein a) and b) are carried out successively, a) being carried out before b) or vice versa.

7. The method according to claim 1 , wherein the second spectral band is at least 150 nm or at least 200 nm wide, so as to include fluorescence peaks of different fluorescent agents.

8. A device for observing a fluorescent sample, the sample being configured to emit a light wave in a fluorescence spectral band when it is illuminated in an excitation spectral band, the device comprising:

a first light source configured to emit a light wave in a first spectral band lying in an excitation spectral band of the sample;

a second light source configured to emit a light wave in a second spectral band outside of the fluorescence spectral band of the sample;

an image sensor that is optically coupled to an optical system, the image sensor defining a detection plane; and

a holder intended to receive the sample, such that the sample lies in a sample plane, the latter lying between the optical system and the second light source;

the optical system defining:

in the fluorescence spectral band, a first object plane that is coincident with the sample plane; and

in the second spectral band, at least one of a second object plane that is distant from the sample plane by at least 20 μm and a second image plane that is distant from the detection plane by at least 20 μm;

wherein the image sensor is configured to acquire, without moving the sample or the image sensor or the optical system:

a clear image of the sample, in the fluorescence spectral band, when the sample is illuminated by the first light source; and

a defocused image of the sample, in the second spectral band, when the sample is illuminated by the second light source.

9. The device according to claim 8 , wherein the distance between the first object plane and the second object plane is smaller than 1 mm, and preferably smaller than 500 μm.

10. The device according to claim 8 , comprising a processor configured to apply a holographic reconstruction operator to an image acquired by the image sensor, so as to reconstruct an image representative of the sample, in a reconstruction plane distant from a detection plane in which the image sensor lies, and preferably in the sample plane.

11. The device according to claim 8 , comprising a filter, lying between the sample and the image sensor, having a fluorescent pass band, corresponding to the fluorescence spectral band.

12. The device according to claim 11 , wherein the filter has an auxiliary passband, distinct from the fluorescence passband, corresponding to the second spectral band.

13. The device according to claim 11 , wherein the fluorescence passband of the filter has a bandwidth narrower than 100 nm.

14. The device according to claim 8 , wherein:

the first light source is placed in a half-space bounded by the sample plane and comprising the image sensor; or

the first light source is placed in a half-space bounded by the sample plane and comprising the second light source.

15. The device according to claim 8 , wherein the device is configured to form an in-focus image of the sample in a spectral band which is at least 150 nm or at least 200 nm wide.