Chirped laser dispersion spectrometer and method
The invention provides a chirped laser dispersion spectrometer having two tunable lasers each with a bias current supply, a chirp signal source to provide a matching chirp pattern, a beam splitter to produce a single beam from the two first and second tunable lasers and active-phase locking means to render the two beams phase coherent and to produce a radio frequency carrier signal capable of programmable phase modulation by means of an optical beat signal. The invention also provides a method for generating at least two optical frequency signals for use in a frequency modulation spectroscopy (FMS) process for the detection and/or measurement of molecular species in a gas mixture and a method for generating at least two optical frequency signals for use in a chirped laser dispersion spectroscopy (CLaDS) process for the detection and/or measurement of molecular species in a gas mixture. The invention provides an efficient and cost-effective CLaDS system which maintains optical modulation whilst enabling greater change of the modulation frequency.
1. A chirped laser dispersion spectrometer comprising:
a first tunable laser for providing a first beam at a first wavelength;
a second tunable laser for providing a second beam at a second wavelength;
a bias current supply for the first tunable laser and a bias current supply for the second tunable laser and chirp signal source for the first and second tunable lasers to provide a matching chirp pattern;
a beam combining optical element to produce a single beam from the first and second tunable lasers; and
active-phase locking means to render the phases of the first and second beams coherent with each other and to produce at least one radio frequency carrier signal capable of programmable phase modulation by means of an optical beat signal wherein the phase locking means comprises negative electronic feedback.
2. The chirped laser dispersion spectrometer of claim 1 wherein the bias current supply for the first tunable laser and the bias current supply for the second tunable laser are provided by a common bias current supply.
3. The chirped laser dispersion spectrometer of claim 1 comprising a field programmable logic array (FPGA) device to provide the negative electronic feedback.
4. The chirped laser dispersion spectrometer of claim 1 where the phase locking technique comprises optical injection.
5. The chirped laser dispersion spectrometer of claim 1 which is polarization sensitive and is configured to produce modulation of the combined beam polarization state.
6. The chirped laser dispersion spectrometer of claim 1 comprising a radio frequency reference source that demodulates an optical heterodyne beat signal from a photodetector to create a radio frequency carrier signal.
7. The chirped laser dispersion spectrometer of claim 1 comprising a second modulation source.
8. The chirped laser dispersion spectrometer of claim 7 where the phase locking means comprises negative electronic feedback and wherein the second modulation source has a frequency less than the noise bandwidth of the negative electronic feedback loop and which second modulation source modulates the radio frequency reference.
9. The chirped laser dispersion spectrometer of claim 1 where the radio frequency carrier signal is modulated to produce a phase shift key modulation scheme.
10. The chirped laser dispersion spectrometer of claim 1 where the radio frequency carrier signal is modulated to produce an alternate modulation scheme comprising at least two modulation sidebands.
11. The chirped laser dispersion spectrometer of claim 1 comprising at least one mechanically actuated mirror allowing modulation of the beam path length between the master laser and beam combining optical element.
12. The chirped laser dispersion spectrometer of claim 1 comprising at least one deformable mirror allowing spatial modulation of the combined beam phase wave front.
13. The chirped laser dispersion spectrometer of claim 1 wherein the first tunable laser is adapted to be modulated at a frequency much less than the carrier radio frequency resulting in a comb of sideband frequencies, and further comprising a photodetector that detects an optical homodyne beat signal for negative electronic feedback.
14. The chirped laser dispersion spectrometer of claim 4 wherein the said first tunable laser is an optically isolated master laser that is modulated at a frequency much less than the carrier radio frequency resulting in a comb of sideband frequencies and wherein the second tunable laser is a slave laser that is tuned to optically injection lock onto one of the master laser sideband frequencies or that generated in combination with nonlinear mixing effects within the slave laser.
15. The chirped laser dispersion spectrometer of claim 1 comprising at least one further tunable laser and an arrangement of beam combining optical elements arranged to combine part of the first laser beam with the second slave laser beam and a part of the first laser beam with the further tunable laser beam to produce separate beams.
16. The chirped laser dispersion spectrometer of claim 1 where active phase locking is provided by any combination of negative electronic feedback and optical injection locking.
17. The chirped laser dispersion spectrometer of claim 1 further comprising a reference gas cell and photodetector.
18. The chirped laser dispersion spectrometer of claim 1 further comprising a laser modulation system using optical injection of non-interfering light.
19. The chirped laser dispersion spectrometer of claim 1 further comprising a substrate forming a photonic integrated circuit with waveguide like structures.
20. The chirped laser dispersion spectrometer of claim 1 comprising an optical amplifier.
21. A method for generating at least two optical frequency signals for use in a chirped laser dispersion spectroscopy (CLaDS) process for the detection and/or measurement of molecular species in a gas mixture, the method comprising:
providing a first laser beam at a first wavelength from a first tunable laser and a second laser beam at a second wavelength from a second tunable laser;
providing a bias current supply for the first tunable laser and a bias current supply for the second tunable laser and a chirp signal source for the first and second tunable lasers to provide a matching chirp pattern; and
actively-phase locking the first and second tunable lasers with a phase locking means so as to render the phases of the first and second beams coherent with each other and to produce at least one radio frequency carrier signal capable of programmable phase modulation by means of an optical beat signal wherein the phase locking means comprises negative electronic feedback.
22. A method for generating at least two optical frequency signals for use in a frequency modulation spectroscopy (FMS) process for the detection and/or measurement of molecular species in a gas mixture, the method comprising:
providing a first laser beam at a first wavelength from a first tunable laser and a second laser beam at a second wavelength from a second tunable laser;
providing a bias current supply for the first tunable laser and a bias current supply for the second tunable laser and a chirp signal source for the first and second tunable lasers to provide a matching chirp pattern; and
actively-phase locking the first and second tunable lasers with a phase locking means so as to render the phases of the first and second beams coherent with each other and to produce at least one radio frequency carrier signal capable of programmable phase modulation by means of an optical beat signal wherein the phase locking means comprises negative electronic feedback.
23. A method according to claim 21 wherein the bias current supply for the first tunable laser and the bias current supply for the second tunable laser is provided by a common bias current supply.
24. The chirped laser dispersion spectrometer of claim 1 being used in at least one of Zeeman spectroscopy, Faraday spectroscopy or Stark Effect spectroscopy wherein the beam combining optical element is polarization sensitive and is configured to produce modulation of the combined beam polarization state.