Apparatus, method and computer-readable storage medium for determining the ring-down time in a spectrometer system

1. A system comprising:

a cavity ring-down spectrometer comprising:

a transmitter configured to transmit a continuous-wave electromagnetic signal at each of one or more selectable, transmission frequencies in the Terahertz region of the electromagnetic spectrum;

a modulator configured to modulate the electromagnetic signal at a modulation frequency;

a cavity resonator configured to receive the modulated electromagnetic signal and pass at least a portion of the modulated electromagnetic signal, wherein the transmitter and cavity resonator are configured so as to excite a single resonant mode of the cavity resonator; and

a receiver configured to receive the portion of the modulated electromagnetic signal passing the cavity resonator; and

a processor configured to receive a measurement of the portion of the modulated electromagnetic signal received by the receiver, and determine a phase shift of the modulated electromagnetic signal at the modulation frequency based upon the measurement, and wherein the processor is configured to calculate a ring-down time of the cavity resonator as a function of the phase shift.

2. The system of claim 1 , wherein the processor being configured to calculate a ring-down time includes being configured to calculate an intensity ring-down time τ in accordance with the following:

tan(φ m′n′ )=2ω md τ

wherein φ m′n′ represents the phase shift at the modulation frequency for the single resonant mode m′n′, and ω md represents the modulation frequency.

3. The system of claim 1 , wherein the processor being configured to calculate a ring-down time includes being configured to calculate an amplitude ring-down time τ amp in accordance with the following:

tan(φ m′n′ )=ω md τ amp

wherein φ m′n′ represents the phase shift at the modulation frequency for the single resonant mode m′n′, and ω md represents the modulation frequency.

4. The system of claim 1 , wherein the cavity resonator is configured to house a sample, and

wherein the processor is configured to determine an absorption signature for the sample medium as a function of the ring-down time and transmission frequency.

5. The system of claim 1 , wherein the transmitter comprises a photomixer transmitter, and the receiver comprises a photomixer receiver.

6. The system of claim 1 , wherein the transmitter comprises a terahertz or millimeter wave transmitter, and the receiver comprises a terahertz or millimeter wave receiver.

7. A method comprising:

transmitting a continuous-wave electromagnetic signal at each of one or more selectable, transmission frequencies in the Terahertz region of the electromagnetic spectrum, the electromagnetic signal being transmitted from a transmitter in a cavity ring-down spectrometer;

modulating the electromagnetic signal at a modulation frequency;

passing at least a portion of the modulated electromagnetic signal through a cavity resonator, wherein the transmitter and cavity resonator are configured so as to excite a single resonant mode of the cavity resonator;

receiving a measurement of the portion of the modulated electromagnetic signal passing the cavity resonator;

determining a phase shift of the modulated electromagnetic signal at the modulation frequency based upon the measurement; and

calculating a ring-down time of the cavity resonator as a function of the phase shift.

8. The method of claim 7 , wherein calculating a ring-down time comprises calculating an intensity ring-down time τ in accordance with the following:

tan(φ m′n′ )=2ω md τ

wherein φ m′n′ represents the phase shift at the modulation frequency for the single resonant mode m′n′, and ω md represents the modulation frequency.

9. The method of claim 7 , wherein calculating a ring-down time comprises calculating an amplitude ring-down time τ amp in accordance with the following:

tan(φ m′n′ )=ω md τ amp

wherein φ m′n′ represents the phase shift at the modulation frequency for the single resonant mode m′n′, and ω md represents the modulation frequency.

10. The method of claim 7 , wherein the cavity resonator houses a sample, and

wherein the method further comprises determining an absorption signature for the sample medium as a function of the ring-down time and transmission frequency.

11. The method of claim 7 , wherein transmitting a continuous-wave electromagnetic signal comprises transmitting a continuous-wave electromagnetic signal from a photomixer transmitter, and wherein receiving a measurement comprises receiving a measurement from a photomixer receiver.

12. The method of claim 7 , wherein transmitting a continuous-wave electromagnetic signal comprises transmitting a continuous-wave electromagnetic signal from a terahertz or millimeter wave transmitter, and wherein receiving a measurement comprises receiving a measurement from a terahertz or millimeter wave receiver.

13. A non-transitory computer-readable storage medium having computer-readable program code portions stored therein, the computer-readable program portions comprising:

a first executable portion configured to receive a measurement, the measurement having been received from a spectrometer system configured to:

transmit a continuous-wave electromagnetic signal at each of one or more selectable, transmission frequencies in the Terahertz region of the electromagnetic spectrum, the electromagnetic signal being transmitted from a transmitter in a cavity ring-down spectrometer;

modulate the electromagnetic signal at a modulation frequency; and

pass at least a portion of the modulated electromagnetic signal through a cavity resonator, wherein the transmitter and cavity resonator are configured so as to excite a single resonant mode of the cavity resonator, the measurement comprising a measurement of the portion of the modulated electromagnetic signal passing the cavity resonator;

a second executable portion configured to determine a phase shift of the modulated electromagnetic signal at the modulation frequency based upon the measurement; and

a third executable portion configured to calculate a ring-down time of the cavity resonator as a function of the phase shift.

14. The computer-readable storage medium of claim 13 , wherein the third executable portion being configured to calculate a ring-down time includes being configured to calculate an intensity ring-down time τ in accordance with the following:

tan(φ m′n′ )=2ω md τ

wherein φ m′n′ represents the phase shift at the modulation frequency for the single resonant mode m′n′, and ω md represents the modulation frequency.

15. The computer-readable storage medium of claim 13 , wherein the third executable portion being configured to calculate a ring-down time includes being configured to calculate an amplitude ring-down time τ amp in accordance with the following:

tan(φ m′n′ )=2ω md τ

wherein φ m′n′ represents the phase shift at the modulation frequency for the single resonant mode m′n′, and ω md represents the modulation frequency.

16. The computer-readable storage medium of claim 13 , wherein the cavity resonator houses a sample, and

wherein the computer-readable program portions further comprise a fourth executable portion configured to determine an absorption signature for the sample medium as a function of the ring-down time and transmission frequency.

17. The computer-readable storage medium of claim 13 , wherein the spectrometer system being configured to transmit a continuous-wave electromagnetic signal includes being configured to transmit a continuous-wave electromagnetic signal from a photomixer transmitter, and wherein the spectrometer system being configured to receive a measurement includes being configured to receive a measurement from a photomixer receiver.

18. The computer-readable storage medium of claim 13 , wherein the spectrometer system being configured to transmit a continuous-wave electromagnetic signal includes being configured to transmit a continuous-wave electromagnetic signal from a terahertz or millimeter wave transmitter, and wherein the spectrometer system being configured to receive a measurement includes being configured to receive a measurement from a terahertz or millimeter wave receiver.