CAVITY RING DOWN SYSTEM HAVING A COMMON INPUT/OUTPUT PORT

• US 20090185175A1
• Filed: 09/18/2008
• Published: 07/23/2009
• Est. Priority Date: 09/28/2004
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Thorland, Rodney, Cox, James Allen, Marta, Terry, Cole, Barrett E., Anderson, Carl
• Granted Patent: US 7,902,534 B2
• Time in Patent Office: Days
• US Class Current: 356/213
• CPC Class Codes: G01J 1/44 Electric circuits for command of an exposure part G03B7/02
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01N 2021/0378 Shapes
• CPC Class Codes: G01N 2021/399 Diode laser
• CPC Class Codes: G01N 21/03 Cuvette constructions
• CPC Class Codes: G01N 21/0303 Optical path conditioning in cuvettes, e.g. windows; adapted optical elements or systems; path modifying or adjustment G01N21/031 - G01N21/15 take precedence
• CPC Class Codes: G01N 21/031 Multipass arrangements
• CPC Class Codes: G01N 21/39 using tunable lasers

Abstract

A system having a multiple-mirror ring-down cavity with one mirror where light may be input into the cavity and light from the cavity may be detected. A valve may permit light to enter or not to enter the cavity. An amplifier may be connected to a detector for detecting light from the cavity. The amplifier may be off or set at a low gain when light is entering the cavity and be on at a medium or high gain at a time when light is not entering the cavity.

Claims

1. A cavity ring down system comprising:

a cavity; and

at least two mirrors situated in the cavity for reflecting light from one mirror to another in a ring-down manner; and

wherein a first mirror of the at least two mirrors permits light to enter the cavity, and to exit the cavity for detection.

2. The system of claim 1, comprising:

a detector proximate to the first mirror; and

an amplifier connected to the detector; and

wherein the amplifier is for amplifying signals from the detector; and

the signals are indicative of light from the first mirror.

3. The system of claim 2, further comprising a light valve which is switched on to permit light to go through the valve to the first mirror or is switched off to prevent light from going through the valve to the first mirror.

4. The system of claim 3, wherein:

the amplifier is switched on at a time when the light valve is switched off; and

the amplifier is switched off when the light valve is switched on.

5. The system of claim 4, wherein the light valve is an acousto-optic modulator.

6. The system of claim 3, wherein the amplifier has a low gain mode and a high gain mode.

7. The system of claim 6, wherein:

the amplifier is in a low gain mode at a time when the light valve is switched on; and

the amplifier is in a high gain mode at a time when the light valve is switched off.

8. The system of claim 7, wherein the amplifier comprises:

a first amplifier for the low gain mode; and

a second amplifier for the high gain mode.

9. A method for cavity ring-down measurement comprising:

inputting light through a first mirror of a cavity having at least two mirrors for reflecting light from one mirror to another in a ring-down manner; and

measuring light leaking out of the cavity through the first mirror.

10. The method of claim 9, wherein inputting the light through the first mirror does not occur while measuring the light leaking out of the cavity through the first mirror.

11. The method of claim 9, wherein:

measuring the light is accomplished with a detector and an amplifier connected to the detector;

the amplifier is off during the inputting light through the first mirror;

the amplifier is on at a time when light is not inputted through the first mirror.

12. The method of claim 9 wherein:

measuring the light is accomplished with a detector and a multiple-gain amplifier connected to the detector;

the amplifier has a low gain during the inputting of light through the first mirror;

the amplifier has a high gain at a time when not inputting light through the first mirror.

13. The method of claim 12, wherein the inputting and not inputting light through the first mirror is effected with a light valve situated between a light source and the first mirror.

14. A sensor system comprising:

a cavity;

at least two mirrors situated in the cavity for reflecting light to one another;

a source for providing light into the cavity through a first mirror of the at least two mirrors; and

a detector for detecting light from the cavity through the first mirror.

15. The system of claim 14, further comprising a mechanism for controlling an amount of light from the source to the first mirror.

16. The system of claim 15, further comprising an amplifier connected to the detector.

17. The system of claim 16, wherein the amplifier has a selectable gain.

18. The system of claim 16, wherein the mechanism for controlling an amount of light from the source to the first mirror can prevent virtually any light from going to the first mirror.

19. The system of claim 18, wherein the mechanism for controlling an amount of light from the source to the first mirror is an acoustic-optic light modulator.

20. The system of claim 18, further comprising:

a controller connected to the amplifier and the mechanism for controlling an amount of light from the source to the first mirror; and

wherein;

the controller selects a high gain of the amplifier at a time when virtually no light is going to the first mirror; and

the controller selects a low gain of the amplifier when light is going to the first mirror.