Covert laser remote sensing and vibrometry

• US 8,210,044 B1
• Filed: 10/14/2008
• Issued: 07/03/2012
• Est. Priority Date: 10/12/2007
• Status: Active Grant

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Maleki, Lutfollah, Yu, Nan, Matsko, Andrey B., Savchenkov, Anatoliy
• Primary Examiner(s): Williams, Hezron E
• Assistant Examiner(s): Miller, Rose M
• Application Number:
  US12/288,011
• Time in Patent Office: 1,358 Days
• Field of Search: 736/43
• US Class Current: 73/643
• CPC Class Codes: G01N 29/2418 using optoacoustic interaction with the material, e.g. laser radiation, photoacoustics photoacoustic cells G01N21/1702; measuring characteristics of vibrations by using radiation-sensitive means G01H9/00; acousto-optical conversion techniques for short-range imaging G01S15/8965; sound-producing devices using laser bundle G10K15/046
• CPC Class Codes: G01N 29/46 by spectral analysis, e.g. Fourier analysis or wavelet analysis spectral signal processing per se G06F17/14

Abstract

Designs of single-beam laser vibrometry systems and methods. For example, a method for detecting vibrations of a target based on optical sensing is provided to include operating a laser to produce a laser probe beam at a laser frequency and modulated at a modulation frequency onto a target; collecting light at or near the laser to collect light from the target while the target is being illuminated by the laser probe beam through an optical receiver aperture; using a narrow-band optical filter centered at the laser frequency to filter light collected from the optical receiver aperture to transmit light at the laser frequency while blocking light at other frequencies; using an optical detector to convert filtered light from the narrow-band optical filter to produce a receiver electrical signal; using a lock-in amplifier to detect and amplify the receiver electrical signal at the modulation frequency while rejecting signal components at other frequencies to produce an amplified receiver electrical signal; processing the amplified receiver electrical signal to extract information on vibrations of the target carried by reflected laser probe beam in the collected light; and controlling optical power of the laser probe beam at the target to follow optical power of background illumination at the target.

Claims

1. A method for detecting vibrations of a target based on optical sensing, comprising:

operating a laser to produce a laser probe beam at a laser frequency and modulated at a modulation frequency onto a target;

collecting light at or near the laser to collect light from the target while the target is being illuminated by the laser probe beam through an optical receiver aperture;

using a narrow-band optical filter centered at the laser frequency to filter light collected from the optical receiver aperture to transmit light at the laser frequency while blocking light at other frequencies;

using an optical detector to convert filtered light from the narrow-band optical filter to produce a receiver electrical signal;

using a lock-in amplifier to detect and amplify the receiver electrical signal at the modulation frequency while rejecting signal components at other frequencies to produce an amplified receiver electrical signal;

processing the amplified receiver electrical signal to extract information on vibrations of the target carried by reflected laser probe beam in the collected light; and

controlling optical power of the laser probe beam at the target to follow optical power of background illumination at the target.

2. The method as in claim 1, comprising:

setting the optical receiver aperture to be equal to or greater than an optical aperture of the laser probe beam at the laser.

3. The method as in claim 1, wherein:

the optical power of the laser probe beam at the target is comparable to the optical power of background illumination at the target.

4. The method as in claim 1, wherein:

the optical power of the laser probe beam at the target is controlled so that the laser probe beam at the target is covert in the background illumination at the target.

5. The method as in claim 1, comprising:

measuring optical power of the background illumination at the target; and

using a feedback control in response to the measured optical power to control the laser so that the optical power of the laser probe beam at the target is covert in the background illumination at the target.

6. The method as in claim 1, comprising:

controlling the laser probe beam at the laser frequency to have a spectral linewidth of around one kilohertz.

7. A method for detecting vibrations of a target based on optical sensing, comprising:

operating a laser to produce a laser probe beam at a laser frequency and modulated at a modulation frequency onto a target;

collecting light at or near the laser to collect light from the target while the target is being illuminated by the laser probe beam through an optical receiver aperture;

using a narrow-band optical filter centered at the laser frequency to filter light collected from the optical receiver aperture to transmit light at the laser frequency while blocking light at other frequencies;

using an optical detector to convert filtered light from the narrow-band optical filter to produce a receiver electrical signal;

using a lock-in amplifier to detect and amplify the receiver electrical signal at the modulation frequency while rejecting signal components at other frequencies to produce an amplified receiver electrical signal; and

processing the amplified receiver electrical signal to extract information on vibrations of the target carried by reflected laser probe beam in the collected light,

wherein;

the processing of the amplified receiver electrical signal to extract information on vibrations of the target carried by reflected laser probe beam in the collected light comprises generating an acoustic signal indicating the vibrations of the target.

8. The method as in claim 7, comprising:

controlling the laser probe beam at the laser frequency to have a spectral linewidth of around one kilohertz.

9. The method as in claim 7, comprising:

setting the optical receiver aperture to be equal to or greater than an optical aperture of the laser probe beam at the laser.

10. A method for detecting vibrations of a target based on optical sensing, comprising:

directing a laser probe beam at a laser frequency, which is modulated at a modulation frequency, onto a target;

measuring optical power of the background illumination at the target;

using a feedback control in response to the measured optical power to control the optical power of the laser probe beam at the target to be covert in the background illumination at the target;

collecting light at or near the laser to collect light from the target while the target is being illuminated by the laser probe beam through an optical receiver aperture;

using a narrow-band optical filter centered at the laser frequency to filter light collected from the optical receiver aperture to transmit light at the laser frequency while blocking light at other frequencies;

converting the filtered light from the narrow-band optical filter into a receiver electrical signal;

detecting and amplifying the receiver electrical signal at the modulation frequency, while rejecting signal components at other frequencies, to produce an amplified receiver electrical signal; and

extracting from the amplified receiver electrical signal an acoustic signature of the target.

11. The method as in claim 10, comprising:

setting the optical receiver aperture to be equal to or greater than an optical aperture of the laser probe beam at the laser.

12. The method as in claim 10, comprising:

controlling the laser probe beam at the laser frequency to have a spectral linewidth of around one kilohertz.

13. A device for detecting vibrations of a target based on optical sensing, comprising:

a laser module to produce a laser probe beam at a laser frequency, which is modulated at a modulation frequency;

means for directing the laser probe beam onto a target;

means for measuring background illumination at the target;

a feedback control that is responsive to the measured background illumination at the target and controls the optical power of the laser probe beam at the target to be covert in the background illumination at the target;

an antenna collecting light from the target to produce collected light;

a narrow-band optical filter centered at the laser frequency to filter the collected light from the antenna to produce filtered light at the laser frequency while blocking light at other frequencies;

an optical detector to convert the filtered light from the narrow-band optical filter into a receiver electrical signal;

an amplifier that detects and amplifies the receiver electrical signal at the modulation frequency, while rejecting signal components at other frequencies, to produce an amplified receiver electrical signal; and

means for extracting from the amplified receiver electrical signal an acoustic signature of the target.

14. The device as in claim 13, wherein:

the antenna has an optical receiver aperture that is equal to or greater than an optical aperture for projecting the laser probe beam of the device onto the project.

15. The device as in claim 13, comprising:

means for controlling the laser probe beam at the laser frequency to have a spectral linewidth of around one kilohertz.

16. A device for detecting vibrations of a target based on optical sensing, comprising:

a laser module to produce a laser probe beam at a laser frequency, which is modulated at a modulation frequency;

means for directing the laser probe beam onto a target;

means for measuring background illumination at the target;

a feedback control that is responsive to the measured background illumination at the target and controls the optical power of the laser probe beam at the target to be covert in the background illumination at the target;

an antenna collecting light from the target to produce collected light;

an optical detector to convert the collected light into a receiver electrical signal;

an amplifier that detects and amplifies the receiver electrical signal at the modulation frequency, while rejecting signal components at other frequencies, to produce an amplified receiver electrical signal; and

means for extracting from the amplified receiver electrical signal an acoustic signature of the target.

17. The device as in claim 16, wherein:

the antenna has an optical receiver aperture that is equal to or greater than an optical aperture for projecting the laser probe beam of the device onto the project.

18. A method for detecting vibrations of a target based on optical sensing, comprising:

directing a laser probe beam at a laser frequency, which is modulated at a modulation frequency, onto a target;

measuring optical power of the background illumination at the target;

using a feedback control in response to the measured optical power to control the optical power of the laser probe beam at the target to be covert in the background illumination at the target;

collecting light at or near the laser to collect light from the target while the target is being illuminated by the laser probe beam through an optical receiver aperture;

converting the collected light into a receiver electrical signal;

detecting and amplifying the receiver electrical signal at the modulation frequency, while rejecting signal components at other frequencies, to produce an amplified receiver electrical signal; and

extracting from the amplified receiver electrical signal an acoustic signature of the target.

19. The method as in claim 18, comprising:

setting the optical receiver aperture to be equal to or greater than an optical aperture of the laser probe beam at the laser.