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
Ultrasound modulation causes a spatial pattern in the projection of incoherent LED light in water.When the unmodulated LED light propagation (RF off) is sampled at a projected distance of 113 mm, the normalized incoherent light distribution is relatively smooth and uniform over the detection window. However when the light passes through an ultrasound focal zone (1 MHz, located 10 mm from the LED and 103 mm from the projection plane), the light displays a pattern having a central peak with smaller maxima or side lobes on either side with an average peak spacing of 8.5 mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0104268-g003: Ultrasound modulation causes a spatial pattern in the projection of incoherent LED light in water.When the unmodulated LED light propagation (RF off) is sampled at a projected distance of 113 mm, the normalized incoherent light distribution is relatively smooth and uniform over the detection window. However when the light passes through an ultrasound focal zone (1 MHz, located 10 mm from the LED and 103 mm from the projection plane), the light displays a pattern having a central peak with smaller maxima or side lobes on either side with an average peak spacing of 8.5 mm.

Mentions: Figure 3 (top) shows the light distribution incident on the detector after passage through an optically clear medium (water) without ultrasound modulation, measured by scanning the PMT and slit with the LED to focal zone distance (d) = 10 mm and the LED to PMT projection distance (D) = 113 mm. The light pattern peaks about the principal axis of the LED at the center of the optical window, is reasonably uniform over approximately 30 mm of travel, but it then decreases monotonically as the slit moves further from the center of the LED and optical window. The limited size of the optical window and the geometry of the LED reduce the extent of the projection of the light at the plane of the detector. Figure 3 (bottom) shows the corresponding AOM signal pattern when the ultrasound is on. The overall pattern extends over approximately the same extent but there is a main narrow central peak with adjacent smaller maxima or side lobes on either side. The smaller maxima are located an average 8.5 mm from the main central peak. This pattern at first is suggestive of a far-field diffraction pattern, but as shown below, the pattern is in reality a simple projection of the variation of absorption of the light as it passes through the focal zone.


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

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

Ultrasound modulation causes a spatial pattern in the projection of incoherent LED light in water.When the unmodulated LED light propagation (RF off) is sampled at a projected distance of 113 mm, the normalized incoherent light distribution is relatively smooth and uniform over the detection window. However when the light passes through an ultrasound focal zone (1 MHz, located 10 mm from the LED and 103 mm from the projection plane), the light displays a pattern having a central peak with smaller maxima or side lobes on either side with an average peak spacing of 8.5 mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0104268-g003: Ultrasound modulation causes a spatial pattern in the projection of incoherent LED light in water.When the unmodulated LED light propagation (RF off) is sampled at a projected distance of 113 mm, the normalized incoherent light distribution is relatively smooth and uniform over the detection window. However when the light passes through an ultrasound focal zone (1 MHz, located 10 mm from the LED and 103 mm from the projection plane), the light displays a pattern having a central peak with smaller maxima or side lobes on either side with an average peak spacing of 8.5 mm.
Mentions: Figure 3 (top) shows the light distribution incident on the detector after passage through an optically clear medium (water) without ultrasound modulation, measured by scanning the PMT and slit with the LED to focal zone distance (d) = 10 mm and the LED to PMT projection distance (D) = 113 mm. The light pattern peaks about the principal axis of the LED at the center of the optical window, is reasonably uniform over approximately 30 mm of travel, but it then decreases monotonically as the slit moves further from the center of the LED and optical window. The limited size of the optical window and the geometry of the LED reduce the extent of the projection of the light at the plane of the detector. Figure 3 (bottom) shows the corresponding AOM signal pattern when the ultrasound is on. The overall pattern extends over approximately the same extent but there is a main narrow central peak with adjacent smaller maxima or side lobes on either side. The smaller maxima are located an average 8.5 mm from the main central peak. This pattern at first is suggestive of a far-field diffraction pattern, but as shown below, the pattern is in reality a simple projection of the variation of absorption of the light as it passes through the focal zone.

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