Abstract

Control and manipulation of sound is of critical importance to many different scientific and engineering fields, requiring the design of rigid physical structures with precise geometries and material properties for the desired acoustics. In this work, we demonstrate the ability to manipulate the direction and magnitude of sound waves traveling in air using laser light, without the need for physical interfaces associated with different materials. Efficient reflection of sound waves off of transient, optically generated, abrupt air density barriers is demonstrated, with acoustic reflections greater than 25% of the incident acoustic wave amplitude. Implementation of multiple barriers, can result in complete suppress the transmission of incident acoustic signals as great as 70 dB. Additionally, shaping the laser beam acoustic waveguides can be generated with dramatically reduced transmission losses.

© 2017 Optical Society of America

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References

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  1. J. Tyndall, Sound (Longmans, Green and Company, 1867).
  2. J. W. Strutt, “The scientific work of Tyndall,” Proc. Royal Inst.of Great Britain 14, 216–224 (1894).
  3. A. G. Bell, “On the production and reproduction of sound by light,” Am. J. Sci. 20(118), 305–324 (1880).
    [Crossref]
  4. A. G. Bell, “The production of sound by radiant energy,” Science 2(49), 242–253 (1881).
    [Crossref] [PubMed]
  5. C. Haisch and R. Niessner, “Light and sound-photoacoustic spectroscopy,” Spectrosc. Eur. 14(5), 10–15 (2002).
  6. A. Rosencwaig, Photoacoustics and Photoacoustic Spectroscopy (R. E. Krieger Publishing Company, 1980).
  7. S. E. Bialkowski, Photothermal Spectroscopy Methods for Chemical Analysis (Wiley & Sons, 1996), p 488.
  8. S. Dahal and B. M. Cullum, “Characterization of multiphoton photoacoustic spectroscopy for sub-surface brain tissue diagnosis and imaging,” J. Biomed. Opt. 21(4), 47001 (2016).
    [Crossref] [PubMed]
  9. A. A. Oraevsky and A. A. Karabutov, “Optoacoustic tomography,” in Biomedical Photonics Handbook, T. Vo-Dinh ed. (CRC Press, 2003)
  10. M. H. Xu and L. V. Wang, “Photoacoustic imaging in biomedicine,” Rev. Sci. Instrum. 77(4), 041101 (2006).
    [Crossref]
  11. L. V. Wang and J. Yao, “A practical guide to photoacoustic tomography in the life sciences,” Nat. Methods 13(8), 627–638 (2016).
    [Crossref] [PubMed]
  12. A. P. Jathou, J. Laufer, O. Ogunlade, B. Treeby, B. Cox, E. Zhang, P. Johnson, A. R. Peezy, B. Philip, T. Marafioti, M. F. Lythgoe, R. B. Pedley, M. A. Pule, and P. Beard, “Deep in vivo photoacoustic imaging of mammalian tissues using a tyrosinase-based genetic reporter,” Nat. Photonics 9, 239–246 (2015).
  13. C. W. VanNeste, L. R. Senesac, and T. Thundat, “Standoff photoacoustic spectroscopy,” Appl. Phys. Lett. 92(23), 234102 (2008).
    [Crossref]
  14. E. Holthoff, J. Bender, P. Pellegrino, and A. Fisher, “Quantum cascade laser-based photoacoustic spectroscopy for trace vapor detection and molecular discrimination,” Sensors (Basel) 10(3), 1986–2002 (2010).
    [Crossref] [PubMed]
  15. P. Patimisco, G. Scamarcio, F. K. Tittel, and V. Spagnolo, “Quartz-enhanced photoacoustic spectroscopy: a review,” Sensors (Basel) 14(4), 6165–6206 (2014).
    [Crossref] [PubMed]
  16. L. A. Skvortsov and E. M. Maksimov, “Review: application of laser photothermal spectroscopy for standoff detection of trace explosive residues on surfaces,” Quantum Electron. 40(7), 565–578 (2010).
    [Crossref]
  17. R. B. Lindsay, “Relaxation processes in sound propagation in fluids: a historical survey,” in Physical Acoustics, W. P. Mason and R. N. Thurston eds. (Academic Press, 1982).

2016 (2)

S. Dahal and B. M. Cullum, “Characterization of multiphoton photoacoustic spectroscopy for sub-surface brain tissue diagnosis and imaging,” J. Biomed. Opt. 21(4), 47001 (2016).
[Crossref] [PubMed]

L. V. Wang and J. Yao, “A practical guide to photoacoustic tomography in the life sciences,” Nat. Methods 13(8), 627–638 (2016).
[Crossref] [PubMed]

2015 (1)

A. P. Jathou, J. Laufer, O. Ogunlade, B. Treeby, B. Cox, E. Zhang, P. Johnson, A. R. Peezy, B. Philip, T. Marafioti, M. F. Lythgoe, R. B. Pedley, M. A. Pule, and P. Beard, “Deep in vivo photoacoustic imaging of mammalian tissues using a tyrosinase-based genetic reporter,” Nat. Photonics 9, 239–246 (2015).

2014 (1)

P. Patimisco, G. Scamarcio, F. K. Tittel, and V. Spagnolo, “Quartz-enhanced photoacoustic spectroscopy: a review,” Sensors (Basel) 14(4), 6165–6206 (2014).
[Crossref] [PubMed]

2010 (2)

L. A. Skvortsov and E. M. Maksimov, “Review: application of laser photothermal spectroscopy for standoff detection of trace explosive residues on surfaces,” Quantum Electron. 40(7), 565–578 (2010).
[Crossref]

E. Holthoff, J. Bender, P. Pellegrino, and A. Fisher, “Quantum cascade laser-based photoacoustic spectroscopy for trace vapor detection and molecular discrimination,” Sensors (Basel) 10(3), 1986–2002 (2010).
[Crossref] [PubMed]

2008 (1)

C. W. VanNeste, L. R. Senesac, and T. Thundat, “Standoff photoacoustic spectroscopy,” Appl. Phys. Lett. 92(23), 234102 (2008).
[Crossref]

2006 (1)

M. H. Xu and L. V. Wang, “Photoacoustic imaging in biomedicine,” Rev. Sci. Instrum. 77(4), 041101 (2006).
[Crossref]

2002 (1)

C. Haisch and R. Niessner, “Light and sound-photoacoustic spectroscopy,” Spectrosc. Eur. 14(5), 10–15 (2002).

1894 (1)

J. W. Strutt, “The scientific work of Tyndall,” Proc. Royal Inst.of Great Britain 14, 216–224 (1894).

1881 (1)

A. G. Bell, “The production of sound by radiant energy,” Science 2(49), 242–253 (1881).
[Crossref] [PubMed]

1880 (1)

A. G. Bell, “On the production and reproduction of sound by light,” Am. J. Sci. 20(118), 305–324 (1880).
[Crossref]

Beard, P.

A. P. Jathou, J. Laufer, O. Ogunlade, B. Treeby, B. Cox, E. Zhang, P. Johnson, A. R. Peezy, B. Philip, T. Marafioti, M. F. Lythgoe, R. B. Pedley, M. A. Pule, and P. Beard, “Deep in vivo photoacoustic imaging of mammalian tissues using a tyrosinase-based genetic reporter,” Nat. Photonics 9, 239–246 (2015).

Bell, A. G.

A. G. Bell, “The production of sound by radiant energy,” Science 2(49), 242–253 (1881).
[Crossref] [PubMed]

A. G. Bell, “On the production and reproduction of sound by light,” Am. J. Sci. 20(118), 305–324 (1880).
[Crossref]

Bender, J.

E. Holthoff, J. Bender, P. Pellegrino, and A. Fisher, “Quantum cascade laser-based photoacoustic spectroscopy for trace vapor detection and molecular discrimination,” Sensors (Basel) 10(3), 1986–2002 (2010).
[Crossref] [PubMed]

Cox, B.

A. P. Jathou, J. Laufer, O. Ogunlade, B. Treeby, B. Cox, E. Zhang, P. Johnson, A. R. Peezy, B. Philip, T. Marafioti, M. F. Lythgoe, R. B. Pedley, M. A. Pule, and P. Beard, “Deep in vivo photoacoustic imaging of mammalian tissues using a tyrosinase-based genetic reporter,” Nat. Photonics 9, 239–246 (2015).

Cullum, B. M.

S. Dahal and B. M. Cullum, “Characterization of multiphoton photoacoustic spectroscopy for sub-surface brain tissue diagnosis and imaging,” J. Biomed. Opt. 21(4), 47001 (2016).
[Crossref] [PubMed]

Dahal, S.

S. Dahal and B. M. Cullum, “Characterization of multiphoton photoacoustic spectroscopy for sub-surface brain tissue diagnosis and imaging,” J. Biomed. Opt. 21(4), 47001 (2016).
[Crossref] [PubMed]

Fisher, A.

E. Holthoff, J. Bender, P. Pellegrino, and A. Fisher, “Quantum cascade laser-based photoacoustic spectroscopy for trace vapor detection and molecular discrimination,” Sensors (Basel) 10(3), 1986–2002 (2010).
[Crossref] [PubMed]

Haisch, C.

C. Haisch and R. Niessner, “Light and sound-photoacoustic spectroscopy,” Spectrosc. Eur. 14(5), 10–15 (2002).

Holthoff, E.

E. Holthoff, J. Bender, P. Pellegrino, and A. Fisher, “Quantum cascade laser-based photoacoustic spectroscopy for trace vapor detection and molecular discrimination,” Sensors (Basel) 10(3), 1986–2002 (2010).
[Crossref] [PubMed]

Jathou, A. P.

A. P. Jathou, J. Laufer, O. Ogunlade, B. Treeby, B. Cox, E. Zhang, P. Johnson, A. R. Peezy, B. Philip, T. Marafioti, M. F. Lythgoe, R. B. Pedley, M. A. Pule, and P. Beard, “Deep in vivo photoacoustic imaging of mammalian tissues using a tyrosinase-based genetic reporter,” Nat. Photonics 9, 239–246 (2015).

Johnson, P.

A. P. Jathou, J. Laufer, O. Ogunlade, B. Treeby, B. Cox, E. Zhang, P. Johnson, A. R. Peezy, B. Philip, T. Marafioti, M. F. Lythgoe, R. B. Pedley, M. A. Pule, and P. Beard, “Deep in vivo photoacoustic imaging of mammalian tissues using a tyrosinase-based genetic reporter,” Nat. Photonics 9, 239–246 (2015).

Laufer, J.

A. P. Jathou, J. Laufer, O. Ogunlade, B. Treeby, B. Cox, E. Zhang, P. Johnson, A. R. Peezy, B. Philip, T. Marafioti, M. F. Lythgoe, R. B. Pedley, M. A. Pule, and P. Beard, “Deep in vivo photoacoustic imaging of mammalian tissues using a tyrosinase-based genetic reporter,” Nat. Photonics 9, 239–246 (2015).

Lythgoe, M. F.

A. P. Jathou, J. Laufer, O. Ogunlade, B. Treeby, B. Cox, E. Zhang, P. Johnson, A. R. Peezy, B. Philip, T. Marafioti, M. F. Lythgoe, R. B. Pedley, M. A. Pule, and P. Beard, “Deep in vivo photoacoustic imaging of mammalian tissues using a tyrosinase-based genetic reporter,” Nat. Photonics 9, 239–246 (2015).

Maksimov, E. M.

L. A. Skvortsov and E. M. Maksimov, “Review: application of laser photothermal spectroscopy for standoff detection of trace explosive residues on surfaces,” Quantum Electron. 40(7), 565–578 (2010).
[Crossref]

Marafioti, T.

A. P. Jathou, J. Laufer, O. Ogunlade, B. Treeby, B. Cox, E. Zhang, P. Johnson, A. R. Peezy, B. Philip, T. Marafioti, M. F. Lythgoe, R. B. Pedley, M. A. Pule, and P. Beard, “Deep in vivo photoacoustic imaging of mammalian tissues using a tyrosinase-based genetic reporter,” Nat. Photonics 9, 239–246 (2015).

Niessner, R.

C. Haisch and R. Niessner, “Light and sound-photoacoustic spectroscopy,” Spectrosc. Eur. 14(5), 10–15 (2002).

Ogunlade, O.

A. P. Jathou, J. Laufer, O. Ogunlade, B. Treeby, B. Cox, E. Zhang, P. Johnson, A. R. Peezy, B. Philip, T. Marafioti, M. F. Lythgoe, R. B. Pedley, M. A. Pule, and P. Beard, “Deep in vivo photoacoustic imaging of mammalian tissues using a tyrosinase-based genetic reporter,” Nat. Photonics 9, 239–246 (2015).

Patimisco, P.

P. Patimisco, G. Scamarcio, F. K. Tittel, and V. Spagnolo, “Quartz-enhanced photoacoustic spectroscopy: a review,” Sensors (Basel) 14(4), 6165–6206 (2014).
[Crossref] [PubMed]

Pedley, R. B.

A. P. Jathou, J. Laufer, O. Ogunlade, B. Treeby, B. Cox, E. Zhang, P. Johnson, A. R. Peezy, B. Philip, T. Marafioti, M. F. Lythgoe, R. B. Pedley, M. A. Pule, and P. Beard, “Deep in vivo photoacoustic imaging of mammalian tissues using a tyrosinase-based genetic reporter,” Nat. Photonics 9, 239–246 (2015).

Peezy, A. R.

A. P. Jathou, J. Laufer, O. Ogunlade, B. Treeby, B. Cox, E. Zhang, P. Johnson, A. R. Peezy, B. Philip, T. Marafioti, M. F. Lythgoe, R. B. Pedley, M. A. Pule, and P. Beard, “Deep in vivo photoacoustic imaging of mammalian tissues using a tyrosinase-based genetic reporter,” Nat. Photonics 9, 239–246 (2015).

Pellegrino, P.

E. Holthoff, J. Bender, P. Pellegrino, and A. Fisher, “Quantum cascade laser-based photoacoustic spectroscopy for trace vapor detection and molecular discrimination,” Sensors (Basel) 10(3), 1986–2002 (2010).
[Crossref] [PubMed]

Philip, B.

A. P. Jathou, J. Laufer, O. Ogunlade, B. Treeby, B. Cox, E. Zhang, P. Johnson, A. R. Peezy, B. Philip, T. Marafioti, M. F. Lythgoe, R. B. Pedley, M. A. Pule, and P. Beard, “Deep in vivo photoacoustic imaging of mammalian tissues using a tyrosinase-based genetic reporter,” Nat. Photonics 9, 239–246 (2015).

Pule, M. A.

A. P. Jathou, J. Laufer, O. Ogunlade, B. Treeby, B. Cox, E. Zhang, P. Johnson, A. R. Peezy, B. Philip, T. Marafioti, M. F. Lythgoe, R. B. Pedley, M. A. Pule, and P. Beard, “Deep in vivo photoacoustic imaging of mammalian tissues using a tyrosinase-based genetic reporter,” Nat. Photonics 9, 239–246 (2015).

Scamarcio, G.

P. Patimisco, G. Scamarcio, F. K. Tittel, and V. Spagnolo, “Quartz-enhanced photoacoustic spectroscopy: a review,” Sensors (Basel) 14(4), 6165–6206 (2014).
[Crossref] [PubMed]

Senesac, L. R.

C. W. VanNeste, L. R. Senesac, and T. Thundat, “Standoff photoacoustic spectroscopy,” Appl. Phys. Lett. 92(23), 234102 (2008).
[Crossref]

Skvortsov, L. A.

L. A. Skvortsov and E. M. Maksimov, “Review: application of laser photothermal spectroscopy for standoff detection of trace explosive residues on surfaces,” Quantum Electron. 40(7), 565–578 (2010).
[Crossref]

Spagnolo, V.

P. Patimisco, G. Scamarcio, F. K. Tittel, and V. Spagnolo, “Quartz-enhanced photoacoustic spectroscopy: a review,” Sensors (Basel) 14(4), 6165–6206 (2014).
[Crossref] [PubMed]

Strutt, J. W.

J. W. Strutt, “The scientific work of Tyndall,” Proc. Royal Inst.of Great Britain 14, 216–224 (1894).

Thundat, T.

C. W. VanNeste, L. R. Senesac, and T. Thundat, “Standoff photoacoustic spectroscopy,” Appl. Phys. Lett. 92(23), 234102 (2008).
[Crossref]

Tittel, F. K.

P. Patimisco, G. Scamarcio, F. K. Tittel, and V. Spagnolo, “Quartz-enhanced photoacoustic spectroscopy: a review,” Sensors (Basel) 14(4), 6165–6206 (2014).
[Crossref] [PubMed]

Treeby, B.

A. P. Jathou, J. Laufer, O. Ogunlade, B. Treeby, B. Cox, E. Zhang, P. Johnson, A. R. Peezy, B. Philip, T. Marafioti, M. F. Lythgoe, R. B. Pedley, M. A. Pule, and P. Beard, “Deep in vivo photoacoustic imaging of mammalian tissues using a tyrosinase-based genetic reporter,” Nat. Photonics 9, 239–246 (2015).

VanNeste, C. W.

C. W. VanNeste, L. R. Senesac, and T. Thundat, “Standoff photoacoustic spectroscopy,” Appl. Phys. Lett. 92(23), 234102 (2008).
[Crossref]

Wang, L. V.

L. V. Wang and J. Yao, “A practical guide to photoacoustic tomography in the life sciences,” Nat. Methods 13(8), 627–638 (2016).
[Crossref] [PubMed]

M. H. Xu and L. V. Wang, “Photoacoustic imaging in biomedicine,” Rev. Sci. Instrum. 77(4), 041101 (2006).
[Crossref]

Xu, M. H.

M. H. Xu and L. V. Wang, “Photoacoustic imaging in biomedicine,” Rev. Sci. Instrum. 77(4), 041101 (2006).
[Crossref]

Yao, J.

L. V. Wang and J. Yao, “A practical guide to photoacoustic tomography in the life sciences,” Nat. Methods 13(8), 627–638 (2016).
[Crossref] [PubMed]

Zhang, E.

A. P. Jathou, J. Laufer, O. Ogunlade, B. Treeby, B. Cox, E. Zhang, P. Johnson, A. R. Peezy, B. Philip, T. Marafioti, M. F. Lythgoe, R. B. Pedley, M. A. Pule, and P. Beard, “Deep in vivo photoacoustic imaging of mammalian tissues using a tyrosinase-based genetic reporter,” Nat. Photonics 9, 239–246 (2015).

Am. J. Sci. (1)

A. G. Bell, “On the production and reproduction of sound by light,” Am. J. Sci. 20(118), 305–324 (1880).
[Crossref]

Appl. Phys. Lett. (1)

C. W. VanNeste, L. R. Senesac, and T. Thundat, “Standoff photoacoustic spectroscopy,” Appl. Phys. Lett. 92(23), 234102 (2008).
[Crossref]

J. Biomed. Opt. (1)

S. Dahal and B. M. Cullum, “Characterization of multiphoton photoacoustic spectroscopy for sub-surface brain tissue diagnosis and imaging,” J. Biomed. Opt. 21(4), 47001 (2016).
[Crossref] [PubMed]

Nat. Methods (1)

L. V. Wang and J. Yao, “A practical guide to photoacoustic tomography in the life sciences,” Nat. Methods 13(8), 627–638 (2016).
[Crossref] [PubMed]

Nat. Photonics (1)

A. P. Jathou, J. Laufer, O. Ogunlade, B. Treeby, B. Cox, E. Zhang, P. Johnson, A. R. Peezy, B. Philip, T. Marafioti, M. F. Lythgoe, R. B. Pedley, M. A. Pule, and P. Beard, “Deep in vivo photoacoustic imaging of mammalian tissues using a tyrosinase-based genetic reporter,” Nat. Photonics 9, 239–246 (2015).

Proc. Royal Inst.of Great Britain (1)

J. W. Strutt, “The scientific work of Tyndall,” Proc. Royal Inst.of Great Britain 14, 216–224 (1894).

Quantum Electron. (1)

L. A. Skvortsov and E. M. Maksimov, “Review: application of laser photothermal spectroscopy for standoff detection of trace explosive residues on surfaces,” Quantum Electron. 40(7), 565–578 (2010).
[Crossref]

Rev. Sci. Instrum. (1)

M. H. Xu and L. V. Wang, “Photoacoustic imaging in biomedicine,” Rev. Sci. Instrum. 77(4), 041101 (2006).
[Crossref]

Science (1)

A. G. Bell, “The production of sound by radiant energy,” Science 2(49), 242–253 (1881).
[Crossref] [PubMed]

Sensors (Basel) (2)

E. Holthoff, J. Bender, P. Pellegrino, and A. Fisher, “Quantum cascade laser-based photoacoustic spectroscopy for trace vapor detection and molecular discrimination,” Sensors (Basel) 10(3), 1986–2002 (2010).
[Crossref] [PubMed]

P. Patimisco, G. Scamarcio, F. K. Tittel, and V. Spagnolo, “Quartz-enhanced photoacoustic spectroscopy: a review,” Sensors (Basel) 14(4), 6165–6206 (2014).
[Crossref] [PubMed]

Spectrosc. Eur. (1)

C. Haisch and R. Niessner, “Light and sound-photoacoustic spectroscopy,” Spectrosc. Eur. 14(5), 10–15 (2002).

Other (5)

A. Rosencwaig, Photoacoustics and Photoacoustic Spectroscopy (R. E. Krieger Publishing Company, 1980).

S. E. Bialkowski, Photothermal Spectroscopy Methods for Chemical Analysis (Wiley & Sons, 1996), p 488.

J. Tyndall, Sound (Longmans, Green and Company, 1867).

A. A. Oraevsky and A. A. Karabutov, “Optoacoustic tomography,” in Biomedical Photonics Handbook, T. Vo-Dinh ed. (CRC Press, 2003)

R. B. Lindsay, “Relaxation processes in sound propagation in fluids: a historical survey,” in Physical Acoustics, W. P. Mason and R. N. Thurston eds. (Academic Press, 1982).

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Figures (7)

Fig. 1
Fig. 1 Schematic diagram depicting the optical system employed for optical reflection of acoustic waves. A CO2 laser (9.6 μm) is modulated by an optical chopper before passing through an iris to provide a defined beam diameter. On one side of the laser beam an earbud is located that emits a constant amplitude and frequency acoustic tone based on a sinusoidal voltage applied by a frequency generator. On the opposite side the laser beam from the earbud is a microphone (microphone #1) for measuring the acoustic signal transmitted through the optically excited barrier and a second microphone (microphone #2) is located on the same side as the earbud to monitor acoustic reflections from the optically excited barrier.
Fig. 2
Fig. 2 Efficiency of optically-induced acoustic reflection. (A) Optical excitation and photo-thermal expansion generates a transient acoustic impedance barrier in the air that results in suppression in the amplitude of acoustic waves passing through this barrier as well as a corresponding increase in acoustic amplitude reflected off of the optically-induced barrier. (B) The efficiency of the optically-induced barrier for suppression/reflection of acoustic waves of different audible frequencies is nearly constant with the exception of enhanced acoustic suppression/reflection when the optical modulation frequency of the barrier is one half of the acoustic frequency transmitted. (C) Barrier stability and acoustic wave suppression efficiency is stable over incident acoustic waves ranging from 0 dB to 70 dB. Error bars represent ± one standard deviation of the average (N = 15).
Fig. 3
Fig. 3 Spatial dependence of the acoustic source from the optically induced barrier for different frequency acoustic tones. (A) Acoustic signal suppression of a 5.05 kHz acoustic wave transmitted through an optically-induced barrier as a function of distance between the acoustic source and the barrier. (B) Acoustic signal reflection of the same 5.05 kHz acoustic source off of an optically-induced barrier as a function of distance between the source and the barrier. (C) Acoustic signal suppression of a 4.05 kHz acoustic wave transmitted through an optically-induced barrier as a function of distance between the acoustic source and the barrier. (D) Acoustic signal reflection of the same 4.05 kHz acoustic source off of an optically-induced barrier as a function of distance between the source and the barrier. Data points correspond to five averaged measurements for each distance with the dashed sigmoidal trend lines revealing that in order to achieve significant reflection/suppression from the barriers, the acoustic source must be located at least one acoustic wavelength from the optically depleted acoustic barrier zone.
Fig. 4
Fig. 4 Optical multipass barrier for enhanced acoustic suppression. (A) Schematic diagram of the multiple optical barriers employed sequential dampening of the amplitude of the emitted acoustic tone. The reflected laser beam generated four non-overlapping barriers in space arranged in a single z-plane with the acoustic source located on the opposite side of the barriers than the transmission microphone. (B) Acoustic amplitude of the fixed frequency acoustic tone measured by the transmission microphone in the presence (solid black line) and absence (dashed blue line) of the laser used to generate the acoustic barrier (high square wave = laser on; low square wave = laser off).
Fig. 5
Fig. 5 Optical channeling of acoustic waves. (A) Cross sectional schematic representation of the optically-induced channel acoustic channel. The acoustic source is surrounded by a donut shaped optical beam that generates a cylindrical acoustic barrier for enhanced propagation of the sound. (B) A schematic diagram of the system employed for optical channeling of acoustic signals. A CO2 laser is modulated by an optical chopper before passing through the ZnSe window of on a plexiglass chamber saturated with alcohol vapor. A metallic earbud (driven by the sinusoidal output of a variable function generator) is suspended by its cord in the center of the laser beam, masking the central region and generating a donut shaped laser beam. Two movable microphones are placed downfield of the earbud (one inside the channel and one outside) to allow for monitoring of the acoustic amplitude at different distances.
Fig. 6
Fig. 6 Acoustic amplitude decay profile as a function of distance from the source; with (red triangles) and without (blue circles) an optical channel present. The solid blue and the dashed red curves represent power function fits to the data revealing the expected 1/r distance dependent signal decay for non-channeled sound and a slower 1/r 0.6 decay for the optically channeled sound.
Fig. 7
Fig. 7 Laser Power Dependence of Acoustic Barrier Efficiency. The percent acoustic suppression as a function of CO2 laser power is shown by the red dots (left axis) with a dashed red trend line revealing the non-linear power dependence of the barrier efficiency. The photoacoustic background signal from the alcohol vapor used to generate the acoustic barrier as a function of laser power (right axis) is shown by black + , with a solid black trend line showing the linear power dependence.

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