Chemical detection and laser wavelength stabilization employing spectroscopic absorption via laser compliance voltage sensing
Systems and methods are disclosed that provide a direct indication of the presence and concentration of an analyte within the external cavity of a laser device that employ the compliance voltage across the laser device. The systems can provide stabilization of the laser wavelength. The systems and methods can obviate the need for an external optical detector, an external gas cell, or other sensing region and reduce the complexity and size of the sensing configuration.
1. A method for stabilizing a wavelength of an external cavity laser (ECL), comprising:
supplying a drive current to a laser device disposed within the ECL;
modulating the operating wavelength of a laser mode of the ECL at a preselected modulation frequency, waveform, and amplitude when at least one analyte is present in the external cavity of the ECL;
setting an average operating wavelength of the ECL to a value corresponding to an absorption feature of the at least one analyte;
measuring a compliance voltage developed across the laser device;
demodulating the compliance voltage at a preselected demodulation frequency, waveform, and amplitude to obtain an error signal;
passing the error signal to a control member;
applying an output of the control member to at least one wavelength-selective element within the external cavity of the ECL to form a feedback loop that acts on the operating wavelength of the ECL; and
adjusting the gain, phase, and bandwidth of the control member to stabilize the feedback loop and the operating wavelength of the ECL.
2. The method of claim 1 , wherein the control member is a servo-controller that includes at least one member selected from the group consisting of: amplifiers, filters, limiters, integrators, differentiators, filters, notches, computers, delays, and combinations thereof.
3. The method of claim 1 , further including positioning the feedback loop such that the operating wavelength of the ECL is locked to a selected absorption feature of the at least one analyte.
4. The method of claim 1 , wherein the at least one analyte includes a gas, a liquid, a solid, a plasma, or combinations thereof.
5. The method of claim 1 , wherein the at least one analyte fills the external cavity of the ECL.
6. The method of claim 1 , wherein the at least one analyte is contained within a gas cell disposed within the external cavity of the ECL.
7. The method of claim 1 , wherein modulating the wavelength includes modulating the drive current to the laser device within the ECL.
8. The method of claim 1 , wherein modulating the wavelength includes modulating with at least one wavelength-selective element disposed within the external cavity of the ECL.
9. The method of claim 1 , wherein modulating the operating wavelength and setting the operating wavelength employ the same wavelength-selective element within the external cavity of the ECL.
10. The method of claim 1 , wherein modulating the operating wavelength and setting the operating wavelength employ distinct wavelength-selective elements within the external cavity of the ECL.