Device and method for stimulated Raman detection
According to one aspect, the invention relates to a device for detecting a resonant non-linear optical signal of Stimulated Raman Scattering (SRS) type induced in a sample. The device comprises electro-optical means for making interact in the sample, at a first modulation frequency, trains of light pulses of angular frequencies ω 1 and ω 2 and, at a second modulation frequency, trains of light pulses of angular frequencies ω 2 and ω 3 , such that ω 2 −ω 1 =ω 3 −ω 2 =Ω R where Ω R is a molecular vibrational resonant angular frequency of the sample. Moreover, the device comprises means for synchronous detection at the first and second modulation frequencies of non-linear optical signals resulting from the interaction of the light pulses in the sample, and electronic processing means making it possible to obtain, from electronic signals resulting from the synchronous detection, a signal characterizing the molecular vibrational resonance of the sample.
1. A device for detecting a resonant non-linear optical signal of Stimulated Raman Scattering (SRS) type induced in a sample, the device comprising:
electro-optical means for making interact in the sample, at a first modulation frequency, trains of light pulses of angular frequencies ω 1 and ω 2 and, at a second modulation frequency, trains of light pulses of angular frequencies ω 2 and ω 3 , such that ω 2 −ω 1 =ω 3 −ω 2 =Ω R where Ω R is a molecular vibrational resonant angular frequency of the sample;
means for synchronous detection at the first and second modulation frequencies of non-linear optical signals resulting from the interaction of the light pulses in the sample; and
electronic processing means making it possible to obtain, from electronic signals resulting from the synchronous detection, a signal characterizing the molecular vibrational resonance of the sample.
2. The device according to claim 1 , in which the electro-optical means comprise an optical source for emitting trains of pulses at the angular frequencies ω 1 , ω 2 and ω 3 , and means for amplitude modulating the trains of pulses at the angular frequencies ω 1 and ω 3 at the first and second modulation frequencies, respectively.
3. The device according to claim 2 , in which the electro-optical means comprise means for amplitude modulating the trains of pulses at the angular frequencies ω 1 and ω 3 at the same modulation frequency but in phase opposition.
4. The device according to claim 2 , in which the electro-optical means comprise means for amplitude modulating the trains of pulses at the angular frequencies ω 1 and ω 3 at two separate modulation frequencies that are not multiples of each other.
5. The device according to claim 1 , in which the first and second modulation frequencies are identical, and the electro-optical means comprise an optical source for emitting trains of pulses at the angular frequencies ω 1 , ω 2 and ω 3 , and means for amplitude modulating the train of pulses at the angular frequency ω 2 at the modulation frequency.
6. The device according to claim 1 , in which the first and second modulation frequencies are identical, and the electro-optical means comprise an optical source for emitting trains of pulses at the angular frequencies ω 1 , ω 2 and ω 3 , and at least one delay line making it possible to generate between the trains of pulses at the angular frequencies ω 1 and ω 3 and the trains of pulses at the angular frequency ω 2 , a time delay modulated at the modulation frequency.
7. The device accordingly to claim 1 , in which the electro-optical means comprise an optical source for emitting trains of frequency chirped pulses centered on the angular frequencies ω 1 , ω 2 and ω 3 , respectively.
8. The device according to claim 7 , in which the emitting optical source furthermore comprises a delay line allowing an identical time shift to be generated between the pulses at the angular frequencies ω 1 and ω 2 , on the one hand, and the pulses at the angular frequencies ω 2 and ω 3 , on the other hand, in such a way as to make the molecular vibrational resonant frequency of the sample at which the non-linear optical signal is detected vary.
9. The device according to claim 7 in that it depends on claim 6 , in which the emitting optical source comprises a generator of trains of frequency chirped pulses centered on the angular frequency ω 2 and a dichroic beam splitter making it possible to separate pulses centered on the angular frequency ω 2 , on the one hand, and pulses centered on the angular frequencies ω 1 and ω 3 , respectively, on the other hand.
10. The device according to claim 1 , is at least partially fibered.
11. A method for detecting a resonant non-linear optical signal of Stimulated Raman Scattering (SRS) type induced in a sample, comprising:
interacting in the sample, at a first modulation frequency, trains of light pulses of angular frequencies ω 1 and ω 2 and, at a second modulation frequency, trains of light pulses of angular frequencies ω 2 and ω 3 , such that ω 1 −ω 1 =ω 3 −ω 2 =Ω R where Ω R is a molecular vibrational resonant angular frequency of the sample;
synchronous detection at the first and second modulation frequencies of non-linear optical signals resulting from the interaction of the light pulses in the sample; and
electronic processing making it possible to obtain, from electronic signals resulting from the synchronous detection, a signal characterizing the molecular vibrational resonance of the sample.
12. The method according to claim 11 comprising the emission of trains of pulses at the angular frequencies ω 1 , ω 2 et ω 3 and the amplitude modulation of the trains of pulses at the angular frequencies ω 1 and ω 3 at the first and second modulation frequencies, respectively.
13. The method according to claim 12 , in which the trains of pulses at the angular frequencies ω 1 and ω 3 are amplitude modulated at the same modulation frequency but in phase opposition.
14. The method according to claim 12 , in which the trains of pulses at the angular frequencies ω 1 and ω 3 are amplitude modulated at two separate modulation frequencies that are not multiples of each other.
15. The method according to claim 11 , in which, the first and second modulation frequencies being identical, it comprises emitting trains of pulses at the angular frequencies ω 1 , ω 2 and ω 3 , and amplitude modulating the trains of pulses at the angular frequency ω 2 at the modulation frequency.
16. The method according to claim 11 , in which, the first and second modulation frequencies being identical, it comprises emitting trains of pulses at the angular frequencies ω 1 , ω 2 and ω 3 , and generating between the trains of pulses at the angular frequencies ω 1 and ω 3 and the trains of pulses at the angular frequency ω 2 , a time delay modulated at the modulation frequency.
17. The method according to claim 11 , in which the pulses are frequency chirped pulses centered on the angular frequencies ω 1 , ω 2 and ω 3 , respectively.
18. The method according to claim 17 , furthermore comprising generating an identical time shift between the pulses at the angular frequencies ω 1 and ω 2 , on the one hand, and the pulses at the angular frequencies ω 2 and ω 3 , on the other hand, in such a way as to detect a non-linear optical signal characterizing another molecular vibrational resonant frequency of the sample.
19. The method according to claim 16 , in which the pulses are frequency chirped pulses centered on the angular frequencies ω 1 , ω 2 and ω 3 , respectively.
20. The method according to claim 19 , comprising generating trains of frequency chirped pulses centered on the angular frequency ω 2 , and separating the pulses into pulses centered on the angular frequency ω 2 , on the one hand, and pulses centered on the angular frequencies ω 1 and ω 3 , respectively, on the other hand.