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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.

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The spatial pattern scales with increased projection magnification.When the projection distance = 140 mm and LED to ultrasound focal zone distance = 10 mm (A), the distant pattern displays alternating peaks with an average peak to peak distance of 10.5 mm. This can be used to calculate an expected 0.75 mm average width of the alternating regions within the ultrasound focal zone. This suggests the pattern scales with expected projection magnification. Similar to figure 5, 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.
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pone-0104268-g006: The spatial pattern scales with increased projection magnification.When the projection distance = 140 mm and LED to ultrasound focal zone distance = 10 mm (A), the distant pattern displays alternating peaks with an average peak to peak distance of 10.5 mm. This can be used to calculate an expected 0.75 mm average width of the alternating regions within the ultrasound focal zone. This suggests the pattern scales with expected projection magnification. Similar to figure 5, 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.

Mentions: Figure 6 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 but with an increased distance between the ultrasound focal zone and PMT of 130 mm. Similar to the above, the distant projections display small shifts decreasing the distance between the peaks, which also become narrower, with increasing LED to ultrasound focal zone distance (average distance between peaks was 10.5, 10.25, 10, and 8.75 mm for the LED to US focal zone distances of 10, 12, 14, and 16 mm respectively).


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

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

The spatial pattern scales with increased projection magnification.When the projection distance = 140 mm and LED to ultrasound focal zone distance = 10 mm (A), the distant pattern displays alternating peaks with an average peak to peak distance of 10.5 mm. This can be used to calculate an expected 0.75 mm average width of the alternating regions within the ultrasound focal zone. This suggests the pattern scales with expected projection magnification. Similar to figure 5, 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.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0104268-g006: The spatial pattern scales with increased projection magnification.When the projection distance = 140 mm and LED to ultrasound focal zone distance = 10 mm (A), the distant pattern displays alternating peaks with an average peak to peak distance of 10.5 mm. This can be used to calculate an expected 0.75 mm average width of the alternating regions within the ultrasound focal zone. This suggests the pattern scales with expected projection magnification. Similar to figure 5, 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.
Mentions: Figure 6 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 but with an increased distance between the ultrasound focal zone and PMT of 130 mm. Similar to the above, the distant projections display small shifts decreasing the distance between the peaks, which also become narrower, with increasing LED to ultrasound focal zone distance (average distance between peaks was 10.5, 10.25, 10, and 8.75 mm for the LED to US focal zone distances of 10, 12, 14, and 16 mm respectively).

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