Method for generating and for detecting a Raman spectrum
A method and a device for generating and for detecting a Raman spectrum enables an automated, or automatable, and at the same time quantitative SERD spectroscopy (for example concentration measurement series). To this end, during the SERD spectroscopy, a first spectrum and a second spectrum are standardized in relation to one another in terms of intensity values and a first difference spectrum is subsequently calculated, a second difference spectrum is calculated, the first difference spectrum is converted into a first transformation spectrum, the second difference spectrum is converted into a second transformation spectrum, and the Raman spectrum is calculated by adding the first transformation spectrum and the second transformation spectrum.
1. A method for generating and for detecting a Raman spectrum of a medium to be analyzed having the following procedure steps:
exposing the medium to be analyzed to excitation radiation, wherein the medium to be analyzed is exposed in a time-shifted manner to a first excitation radiation having a first wavelength and to a second excitation radiation having a second wavelength, wherein the first wavelength differs from the second wavelength,
spectral analysis of the first excitation radiation scattered by the medium to be analyzed, wherein a first spectrum that assigns one intensity value each to a plurality of wavelengths is detected from the scattered first excitation radiation,
spectral analysis of the second excitation radiation scattered by the medium to be analyzed, wherein a second spectrum that assigns one intensity value each to a plurality of wavelengths is detected from the scattered second excitation radiation,
calculating a Raman spectrum of the medium to be analyzed from the first spectrum and the second spectrum,
wherein
the first spectrum and the second spectrum are normalized to each other with respect to their intensity values, and subsequently:
a) a first difference spectrum is calculated from the difference between the first spectrum and the second spectrum,
b) a second difference spectrum is calculated from the difference between the second spectrum and the first spectrum,
c) the first difference spectrum is converted into a first transformation spectrum, wherein one intensity value each is assigned to a plurality of wavelengths, and the intensity value of a wavelength of the first transformation spectrum is calculated by adding a first intensity value of a first wavelength of the first difference spectrum and the amount of a second intensity value of a second wavelength of the first difference spectrum, wherein the first wavelength of the first difference spectrum is greater than the wavelength of the first transformation spectrum by a predetermined transformation parameter and the second wavelength of the first difference spectrum is smaller than the wavelength of the first transformation spectrum by the transformation parameter,
d) the second difference spectrum is converted into a second transformation spectrum, wherein one intensity value each is assigned to a plurality of wavelengths, and the intensity value of a wavelength of the second transformation spectrum is calculated by adding the amount of a first intensity value of a first wavelength of the second difference spectrum and a second intensity value of a second wavelength of the second difference spectrum, wherein the first wavelength of the second difference spectrum is greater than the wavelength of the second transformation spectrum by the transformation parameter and the second wavelength of the second difference spectrum is smaller than the wavelength of the second transformation spectrum by the transformation parameter, and
e) the Raman spectrum is calculated by adding the first transformation spectrum and the second transformation spectrum.
2. The method of claim 1 , wherein
a value of between 0.2 and 0.8 of the amount of the difference between the first wavelength and the second wavelength is used as a transformation parameter.
3. The method of claim 2 , wherein
a value of between 0.4 and 0.6 of the amount of the difference between the first wavelength and the second wavelength is used as a transformation parameter.
4. The method of claim 3 , wherein
half the amount of the difference between the first wavelength and the second wavelength is used as a transformation parameter.
5. The method of claim 4 , wherein
steps c) and d) are repeated several times before step e) is performed, wherein the transformation parameter is varied with each repetition of steps c) and d), whereby a plurality of first transformation spectra and a plurality of corresponding second transformation spectra are obtained, wherein the Raman spectrum is calculated by adding the first transformation spectra and the second transformation spectra in step e).
6. The method of claim 5 , wherein
the transformation parameter is increased or decreased with each repetition of steps c) and d).
7. The method of claim 6 , wherein
half the amount of the difference between the first wavelength and the second wavelength is used as a transformation parameter when steps c) and d) are performed for the first time, and the transformation parameter is subsequently varied within the interval of 0.2 to 0.8 of the amount of the difference between the first wavelength and the second wavelength.
8. The method of claim 1 , wherein
electromagnetic excitation radiation is generated by means of a laser diode with an internal frequency-selective element.
9. The Method of claim 8 , wherein,
for generating varying excitation wavelengths in an alternating manner, the laser diode is driven with two different excitation conditions in an alternating manner by means of the electric current applied to the laser diode.
10. The method of claim 9 , wherein
toggling between the excitation conditions is performed at a frequency that is higher than 1 Hz.
11. A device for generating an excitation radiation and for detecting a Raman spectrum of a medium to be analyzed, comprising:
an excitation light source,
means for coupling the excitation radiation emitted by the excitation light source into the medium to be analyzed,
means for coupling the radiation scattered by the medium to be analyzed into a spectro-optical system,
a data processing device that is connected to the spectro-optical system, wherein the data processing device calculates a Raman spectrum of the medium to be analyzed from the at least two detected Raman spectra that have varying excitation wavelengths, in which calculated Raman spectrum the fluorescence background has been eliminated by way of calculation, and
wherein
the data processing device is designed to normalize the first spectrum and the second spectrum to each other with respect to their intensity values, and subsequently:
a) a first difference spectrum is calculated from the difference between the first spectrum and the second spectrum,
b) a second difference spectrum is calculated from the difference between the second spectrum and the first spectrum,
c) the first difference spectrum is converted into a first transformation spectrum, wherein one intensity value each is assigned to a plurality of wavelengths, and the intensity value of a wavelength of the first transformation spectrum is calculated by adding a first intensity value of a first wavelength of the first difference spectrum and the amount of a second intensity value of a second wavelength of the first difference spectrum, wherein the first wavelength of the first difference spectrum is greater than the wavelength of the first transformation spectrum by a predetermined transformation parameter and the second wavelength of the first difference spectrum is smaller than the wavelength of the first transformation spectrum by the transformation parameter,
d) the second difference spectrum is converted into a second transformation spectrum, wherein one intensity value each is assigned to a plurality of wavelengths, and the intensity value of a wavelength of the second transformation spectrum is calculated by adding the amount of a first intensity value of a first wavelength of the second difference spectrum and a second intensity value of a second wavelength of the second difference spectrum, wherein the first wavelength of the second difference spectrum is greater than the wavelength of the second transformation spectrum by the transformation parameter and the second wavelength of the second difference spectrum is smaller than the wavelength of the second transformation spectrum by the transformation parameter, and
e) the Raman spectrum is calculated by adding the first transformation spectrum and the second transformation spectrum.
12. The device of claim 11 , wherein the data processing device is designed in such a manner that a value of between 0.2 and 0.8 of the amount of the difference between the first wavelength and the second wavelength is used as a transformation parameter.
13. The device of claim 12 , wherein
the data processing device is designed in such a manner that a value of between 0.4 and 0.6 of the amount of the difference between the first wavelength and the second wavelength is used as a transformation parameter.
14. The device of claim 13 , wherein
the data processing device is designed in such a manner that half the amount of the difference between the first wavelength and the second wavelength is used as a transformation parameter.
15. The device of claim 11 , wherein
the data processing device is designed in such a manner that steps c) and d) are repeated several times before step e) is performed, wherein the transformation parameter is varied with each repetition of steps c) and d), whereby a plurality of first transformation spectra and a plurality of corresponding second transformation spectra are obtained, wherein the Raman spectrum is calculated by adding the obtained first transformation spectra and the obtained second transformation spectra in step e).
16. The device of claim 15 , wherein
the data processing device is designed in such a manner that the transformation parameter is increased or decreased with each repetition of steps c) and d).
17. The device of claim 16 , wherein
the data processing device is designed in such a manner that half the amount of the difference between the first wavelength and the second wavelength is used as a transformation parameter when steps c) and d) are performed for the first time, and the transformation parameter is subsequently varied within the interval of 0.2 to 0.8 of the amount of the difference between the first wavelength and the second wavelength.
18. The device of claim 11 , wherein
the excitation light source is a laser diode with an internal frequency-selective element.
19. The device of claim 11 , wherein
for generating varying excitation wavelengths, the laser diode is connected to a power source modulated by a modulator, wherein the modulator modulates the power source in an alternating manner.
20. The device of claim 19 , wherein
toggling is performed at a frequency that is higher than 1 Hz.
21. The device of claim 11 , wherein
the spectro-optical system is a spectrograph with a CCD detector.
22. The device of claim 11 , wherein
the spectro-optical system and/or the data processing device are/is connected to the modulator, and the detection of the individual Raman spectra that have varying excitation wavelengths is synchronized with the alternating driving of the laser diode.
23. The device of claim 22 , wherein
the modulator is a square-wave generator.