Limits...
Detection of a novel mechanism of acousto-optic modulation of incoherent light.

Jarrett CW, Caskey CF, Gore JC - PLoS ONE (2014)

Bottom Line: This pattern differs from previous reports of acousto-optical interactions that produce diffraction effects that rely on phase shifts and changes in light directions caused by the acoustic modulation.Moreover, previous studies of acousto-optic interactions have mainly reported the effects of sound on coherent light sources via photon tagging, and/or the production of diffraction phenomena from phase effects that give rise to discrete sidebands.These effects potentially provide a novel method for visualizing sound fields and may assist the interpretation of other hybrid imaging methods.

View Article: PubMed Central - PubMed

Affiliation: Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, United States of America; Program in Chemical and Physical Biology, Vanderbilt University, Nashville, Tennessee, United States of America.

ABSTRACT
A novel form of acoustic modulation of light from an incoherent source has been detected in water as well as in turbid media. We demonstrate that patterns of modulated light intensity appear to propagate as the optical shadow of the density variations caused by ultrasound within an illuminated ultrasonic focal zone. This pattern differs from previous reports of acousto-optical interactions that produce diffraction effects that rely on phase shifts and changes in light directions caused by the acoustic modulation. Moreover, previous studies of acousto-optic interactions have mainly reported the effects of sound on coherent light sources via photon tagging, and/or the production of diffraction phenomena from phase effects that give rise to discrete sidebands. We aimed to assess whether the effects of ultrasound modulation of the intensity of light from an incoherent light source could be detected directly, and how the acoustically modulated (AOM) light signal depended on experimental parameters. Our observations suggest that ultrasound at moderate intensities can induce sufficiently large density variations within a uniform medium to cause measurable modulation of the intensity of an incoherent light source by absorption. Light passing through a region of high intensity ultrasound then produces a pattern that is the projection of the density variations within the region of their interaction. The patterns exhibit distinct maxima and minima that are observed at locations much different from those predicted by Raman-Nath, Bragg, or other diffraction theory. The observed patterns scaled appropriately with the geometrical magnification and sound wavelength. We conclude that these observed patterns are simple projections of the ultrasound induced density changes which cause spatial and temporal variations of the optical absorption within the illuminated sound field. These effects potentially provide a novel method for visualizing sound fields and may assist the interpretation of other hybrid imaging methods.

Show MeSH

Related in: MedlinePlus

The spatial pattern is suggestive of the alternating regions of optical absorption caused by ultrasound.Increasing the distance between the LED and the ultrasound focal zone causes a narrowing of the overall pattern as well as reduction of the average peak to peak distance. At a projection distance of 113 mm and LED to ultrasound focal zone distance of 10 mm (A), the distant pattern displays alternating peaks with an average peak to peak distance of 8.67 mm. This can be used to calculate an expected 0.77 mm average width of the alternating regions within the ultrasound focal zone. This is precisely the expected value of a half-wavelength of sound in water. As the LED was positioned further from the ultrasound focal zone, (B), (C), and (D), the observed pattern narrowed with additional peaks being added on the fringes of the pattern. In addition, the individual peaks narrow. The pattern is suggestive of the alternating region of optical absorption caused by the ultrasound.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4126715&req=5

pone-0104268-g005: The spatial pattern is suggestive of the alternating regions of optical absorption caused by ultrasound.Increasing the distance between the LED and the ultrasound focal zone causes a narrowing of the overall pattern as well as reduction of the average peak to peak distance. At a projection distance of 113 mm and LED to ultrasound focal zone distance of 10 mm (A), the distant pattern displays alternating peaks with an average peak to peak distance of 8.67 mm. This can be used to calculate an expected 0.77 mm average width of the alternating regions within the ultrasound focal zone. This is precisely the expected value of a half-wavelength of sound in water. As the LED was positioned further from the ultrasound focal zone, (B), (C), and (D), the observed pattern narrowed with additional peaks being added on the fringes of the pattern. In addition, the individual peaks narrow. The pattern is suggestive of the alternating region of optical absorption caused by the ultrasound.

Mentions: Figure 5 shows the measured projections (for 1 MHz AOM light, within 0.25% volume, whole milk) for various distances (10, 12, 14, and 16 mm) between the LED source and the ultrasound focal zone, with a fixed ultrasound focal zone to PMT distance of 103 mm. As the LED was positioned further away from the focal zone, the peaks in the distant projections undergo shifts that decrease the distance between them, and additional peaks become more clear at the edge of the window. The average distance between peaks decreased as the LED to US focal zone increased (separations of 8.67, 8, 7.5, and 7.33 mm for 10, 12, 14, and 16 mm respectively), consistent with a change in the geometrical magnification of the focal zone by the light source.


Detection of a novel mechanism of acousto-optic modulation of incoherent light.

Jarrett CW, Caskey CF, Gore JC - PLoS ONE (2014)

The spatial pattern is suggestive of the alternating regions of optical absorption caused by ultrasound.Increasing the distance between the LED and the ultrasound focal zone causes a narrowing of the overall pattern as well as reduction of the average peak to peak distance. At a projection distance of 113 mm and LED to ultrasound focal zone distance of 10 mm (A), the distant pattern displays alternating peaks with an average peak to peak distance of 8.67 mm. This can be used to calculate an expected 0.77 mm average width of the alternating regions within the ultrasound focal zone. This is precisely the expected value of a half-wavelength of sound in water. As the LED was positioned further from the ultrasound focal zone, (B), (C), and (D), the observed pattern narrowed with additional peaks being added on the fringes of the pattern. In addition, the individual peaks narrow. The pattern is suggestive of the alternating region of optical absorption caused by the ultrasound.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4126715&req=5

pone-0104268-g005: The spatial pattern is suggestive of the alternating regions of optical absorption caused by ultrasound.Increasing the distance between the LED and the ultrasound focal zone causes a narrowing of the overall pattern as well as reduction of the average peak to peak distance. At a projection distance of 113 mm and LED to ultrasound focal zone distance of 10 mm (A), the distant pattern displays alternating peaks with an average peak to peak distance of 8.67 mm. This can be used to calculate an expected 0.77 mm average width of the alternating regions within the ultrasound focal zone. This is precisely the expected value of a half-wavelength of sound in water. As the LED was positioned further from the ultrasound focal zone, (B), (C), and (D), the observed pattern narrowed with additional peaks being added on the fringes of the pattern. In addition, the individual peaks narrow. The pattern is suggestive of the alternating region of optical absorption caused by the ultrasound.
Mentions: Figure 5 shows the measured projections (for 1 MHz AOM light, within 0.25% volume, whole milk) for various distances (10, 12, 14, and 16 mm) between the LED source and the ultrasound focal zone, with a fixed ultrasound focal zone to PMT distance of 103 mm. As the LED was positioned further away from the focal zone, the peaks in the distant projections undergo shifts that decrease the distance between them, and additional peaks become more clear at the edge of the window. The average distance between peaks decreased as the LED to US focal zone increased (separations of 8.67, 8, 7.5, and 7.33 mm for 10, 12, 14, and 16 mm respectively), consistent with a change in the geometrical magnification of the focal zone by the light source.

Bottom Line: This pattern differs from previous reports of acousto-optical interactions that produce diffraction effects that rely on phase shifts and changes in light directions caused by the acoustic modulation.Moreover, previous studies of acousto-optic interactions have mainly reported the effects of sound on coherent light sources via photon tagging, and/or the production of diffraction phenomena from phase effects that give rise to discrete sidebands.These effects potentially provide a novel method for visualizing sound fields and may assist the interpretation of other hybrid imaging methods.

View Article: PubMed Central - PubMed

Affiliation: Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, United States of America; Program in Chemical and Physical Biology, Vanderbilt University, Nashville, Tennessee, United States of America.

ABSTRACT
A novel form of acoustic modulation of light from an incoherent source has been detected in water as well as in turbid media. We demonstrate that patterns of modulated light intensity appear to propagate as the optical shadow of the density variations caused by ultrasound within an illuminated ultrasonic focal zone. This pattern differs from previous reports of acousto-optical interactions that produce diffraction effects that rely on phase shifts and changes in light directions caused by the acoustic modulation. Moreover, previous studies of acousto-optic interactions have mainly reported the effects of sound on coherent light sources via photon tagging, and/or the production of diffraction phenomena from phase effects that give rise to discrete sidebands. We aimed to assess whether the effects of ultrasound modulation of the intensity of light from an incoherent light source could be detected directly, and how the acoustically modulated (AOM) light signal depended on experimental parameters. Our observations suggest that ultrasound at moderate intensities can induce sufficiently large density variations within a uniform medium to cause measurable modulation of the intensity of an incoherent light source by absorption. Light passing through a region of high intensity ultrasound then produces a pattern that is the projection of the density variations within the region of their interaction. The patterns exhibit distinct maxima and minima that are observed at locations much different from those predicted by Raman-Nath, Bragg, or other diffraction theory. The observed patterns scaled appropriately with the geometrical magnification and sound wavelength. We conclude that these observed patterns are simple projections of the ultrasound induced density changes which cause spatial and temporal variations of the optical absorption within the illuminated sound field. These effects potentially provide a novel method for visualizing sound fields and may assist the interpretation of other hybrid imaging methods.

Show MeSH
Related in: MedlinePlus