Elliptical photo-acoustic sensor
An elliptical photo-acoustic spectrometer chamber design will result in a larger intensity signal at the pick-up microphone and allow high frequency light modulation. This makes the spectrometer have a lower limit of detection threshold, and will increase the signal to noise ratio in general for the instrument, resulting in a more sensitive instrument allowing more precise measurements.
1. A photo-acoustic sensor comprising:
an elliptically shaped chamber having its two foci positioned along its longitudinal axis;
a light excitation path oriented along a first focus of the chamber; and
an acoustic sensor oriented along a second focus of the chamber.
2. The sensor as recited in claim 1 , further comprising a trace gas inside of the chamber to be sensed.
3. The sensor as recited in claim 2 , further comprising a laser for transmitting a laser pulse along the light excitation path.
4. The sensor as recited in claim 3 , wherein a frequency of the laser pulse is modulated to resonate with the gas.
5. The sensor as recited in claim 1 , wherein the acoustic sensor comprises a flexible tube oriented along the second focus with its ends connected to microphones.
6. The sensor as recited in claim 1 , wherein the acoustic sensor comprises a rigid mechanical pick-up substantially oriented along the second focus and coupled to microphones.
7. The sensor as recited in claim 1 , wherein the acoustic sensor comprises a probing laser signal aimed along the second focus, wherein a frequency of the probing laser signal is resonant with a background gas containing a trace gas to be sensed, the probing laser signal aimed to strike a photodiode positioned on an end wall of the chamber.
8. The sensor as recited in claim 1 , wherein the elliptically shaped chamber comprises a cylinder having a cross-section that is in a shape of an ellipse, wherein the two foci are positioned along the longitudinal axis of the cylinder.
9. The sensor as recited in claim 1 , wherein the elliptically shaped chamber comprises an elliptical cylinder.
10. The sensor as recited in claim 2 , wherein the trace gas is present along the first focus of the chamber.
11. The sensor as recited in claim 1 , wherein for a cross-section of the chamber perpendicular to the longitudinal axis of the chamber, a path length measured from the first focus to any position along a wall of the chamber to the second focus is constant.
12. A photo-acoustic sensor comprising:
an axially extended elliptical chamber having first and second axially extended foci;
a light excitation path oriented along a length of the first axially extended focus of the chamber; and
an extended acoustic sensor positioned along a length of the second axially extended focus of the chamber.
13. The sensor as recited in claim 12 , further comprising a trace gas present along the first axially extended focus of the chamber.
14. The sensor as recited in claim 13 , further comprising a laser for transmitting a laser pulse along the light excitation path.
15. The sensor as recited in claim 12 , wherein the acoustic sensor comprises a flexible tube oriented along the second axially extended focus with its ends connected to microphones.
16. The sensor as recited in claim 12 , wherein the acoustic sensor comprises a rigid mechanical pick-up substantially oriented along the second axially extended focus and coupled to microphones.
17. The sensor as recited in claim 12 , wherein the acoustic sensor comprises a probing laser signal aimed along the second axially extended focus, wherein a frequency of the probing laser signal is resonant with a background gas containing a trace gas to be sensed, the probing laser signal aimed to strike a photodiode positioned on an end wall of the chamber.
18. The sensor as recited in claim 12 , wherein for a cross-section of the chamber perpendicular to the longitudinal axis of the chamber, a path length measured from the first focus to any position along a wall of the chamber to the second focus is constant.