Method for spectroscopically or spectrometrically examining a sample, and interferometric device
A method and an interferometric device for spectroscopically or spectrometrically examining a sample, comprising: a) generating a laser beam having a wavelength, b) splitting the laser beam into a measurement beam and a reference beam, c) interacting the sample with the measurement beam, d) interacting a reference with the reference beam, e) overlaying the measurement beam and the reference beam, f) detecting a first output beam, g) detecting a second output beam, h) forming a differential signal between the first output signal and the second output signal, i) controlling the differential signal to a predefined target value, j) determining a refractive index of the sample from the adjustment of the phase difference between the measurement beam and the reference beam, k) repeating steps a) to j) for additional wavelengths of the laser beam.
1. A method for spectroscopic or spectrometric analysis of a sample, with steps of:
a) generating a laser beam with a wavelength,
b) splitting the laser beam into a measurement beam and a reference beam,
c) interaction of the sample with the measurement beam,
d) interaction of a reference with the reference beam,
e) superposing the measurement beam and the reference beam so that a first output beam and a second output beam are respectively obtained, the phases of which are shifted by 180° with respect to one another,
f) detecting the first output beam,
g) detecting the second output beam,
h) forming a differential signal between the first output beam and the second output beam,
i) adjusting the differential signal to a predetermined setpoint by setting a phase difference between the measurement beam and the reference beam,
j) deducing a refractive index of the sample from the setting of the phase difference between the measurement beam and the reference beam,
k) repeating the steps a) to j) for further wavelengths of the laser beam for capturing a spectrum of a refractive index of the sample.
2. The method according to claim 1 , wherein the differential signal between the first output beam and the second output beam is adjusted to a setpoint of zero.
3. The method of claim 1 , wherein the laser beam is generated with the wavelength in an infrared spectral range.
4. The method of claim 1 , wherein, for repeating the steps a) to j), the further wavelengths of the laser beam are in an infrared spectral range.
5. An interferometric device for spectroscopic analysis of a liquid sample, comprising:
a tunable laser for emitting a laser beam,
a beam-splitter for splitting the laser beam into a measurement beam and a reference beam,
a measurement chamber for interaction between a sample and the measurement beam,
a reference chamber for interaction between a reference and the reference beam,
a beam-combiner with a first output port for interferometric superposition of the measurement beam and the reference beam as a first output beam and with a second output port for interferometric superposition of the measurement beam and the reference beam as a second output beam,
a first detector for capturing the first output beam,
a second detector for capturing the second output beam,
a phase-controller for setting a phase between the measurement beam and the reference beam,
a subtractor for forming a differential signal between the first output beam and the second output beam, and
a control unit which adjusts the differential signal via the phase-controller to a predetermined setpoint and tunes a wavelength of the laser beam in order to deduce a spectrum of a refractive index of the sample from a position of the phase-controller depending on the wavelength of the laser beam.
6. The interferometric device according to claim 5 , wherein an input optical waveguide is provided for the laser beam, a measurement-beam optical waveguide is provided for the measurement beam and a reference-beam optical waveguide is provided for the reference beam.
7. The interferometric device according to claim 6 , wherein the measurement chamber includes a first microfluidic channel adjacent to the measurement-beam optical waveguide and/or wherein the reference chamber includes a second microfluidic channel adjacent to the reference-beam optical waveguide.
8. The interferometric device according to claim 6 wherein the phase-controller includes a heating element for the measurement-beam optical waveguide or for the reference-beam optical waveguide.
9. The interferometric device of claim 8 , wherein the heating element is a resistance heating element.
10. The interferometric device according to claim 6 wherein the beam-splitter includes a 1×2 coupler and the beam-combiner includes a 2×2 coupler.
11. The interferometric device according to claim 5 , wherein the measurement chamber is configured as a first flow cell in a beam path of the measurement beam and the reference chamber is configured as a second flow cell in a beam path of the reference beam.
12. The interferometric device according to claim 11 , wherein the phase-controller comprises a mirror and a piezo actuator for adjusting the mirror.
13. The interferometric device according to claim 11 wherein the beam-splitter comprises a first beam splitter and the beam-splitter comprises a second beam splitter.
14. The interferometric device of claim 5 , wherein the laser beam is emitted in an infrared spectral range.