Methods for determining optical power, for power-normalizing laser measurements, and for stabilizing power of lasers via compliance voltage sensing
A method is disclosed for power normalization of spectroscopic signatures obtained from laser based chemical sensors that employs the compliance voltage across a quantum cascade laser device within an external cavity laser. The method obviates the need for a dedicated optical detector used specifically for power normalization purposes. A method is also disclosed that employs the compliance voltage developed across the laser device within an external cavity semiconductor laser to power-stabilize the laser mode of the semiconductor laser by adjusting drive current to the laser such that the output optical power from the external cavity semiconductor laser remains constant.
1. A method for obtaining a power-normalized laser measurement with an external cavity laser, comprising the steps of:
driving a quantum cascade laser device disposed within the external cavity laser with a current through the quantum cascade laser device;
obtaining a laser measurement with the external cavity laser;
measuring a compliance voltage of the quantum cascade laser device; and
combining the laser measurement with the compliance voltage to obtain a power-normalized laser measurement.
2. The method of claim 1 , wherein obtaining the laser measurement is performed while measuring the compliance voltage.
3. The method of claim 1 , wherein the combining includes combining the laser measurement with a value obtained from a mathematical function of the compliance voltage.
4. The method of claim 3 , wherein the mathematical function is a single-valued function that includes the compliance voltage as the input and an optical power as the output.
5. The method of claim 3 , wherein the mathematical function is a binary function that includes the compliance voltage and the current as the inputs and an optical power as the output.
6. The method of claim 1 , further including sweeping a wavelength of the external cavity laser with a sweep signal while obtaining the laser measurement to generate a laser measurement spectrum as a function of the wavelength.
7. The method of claim 1 , further including sweeping a wavelength of the external cavity laser with a sweep signal while measuring the compliance voltage to generate a compliance voltage spectrum as a function of the wavelength.
8. The method of claim 7 , wherein the combining includes combining the laser measurement with a value obtained from a mathematical function of the compliance voltage.
9. The method of claim 8 , wherein the mathematical function is a single-valued function that includes the compliance voltage spectrum as the input and an optical power spectrum as the output.
10. The method of claim 8 , wherein the mathematical function is a binary function that includes the compliance voltage spectrum and the current as the inputs and an optical power spectrum as the output.
11. The method of claim 8 , wherein the mathematical function is a binary function that includes the compliance voltage spectrum and the sweep signal as the inputs and an optical power spectrum as the output.
12. The method of claim 8 , wherein the mathematical function is a ternary function that includes the compliance voltage spectrum, the current, and the sweep signal as the inputs and an optical power spectrum as the output.