$diffraction with sound$

$diffraction with sound$

B) The reflected acoustic wave returns to the surface, where a second pulse is used to probe both reflection (R) and diffraction (D).

$diffraction with sound$

A) A pump pulse generates acoustic waves (in red, arrows indicate direction of propagation) at the surface of the grating. Schematic view of the segmented grating, the pump and probe pulses. Van den Hooven: “A former PhD student in our group, Guido de Haan, showed that a grating on the metal surface induces a plasmonic resonance that is very sensitive to changes in the reflection signal caused by laser-induced acoustic waves from a sample.” (see news item) The wavelength of the light and its angle of incidence are important, but so are the material properties and shape of the metal. When light hits a metal-semiconductor interface, it can transfer part of its energy to electrons that start to oscillate in the metal, forming a surface plasmon resonance, but only under very specific conditions. Van den Hooven and his colleagues use a layer of gold to induce a phenomenon called plasmonic resonance. That is why our group sought for ways to enhance them and thus improve our previous work.” “Unfortunately these signals are very weak. A second light pulse can diffract off the acoustic-wave copy of the grating, when the wave reaches the surface”, PhD student Thomas van den Hooven explains. “The sound waves coming from the surface, reflect off the hidden grating and copy their shape in the process. In 2020 group leader Paul Planken and his colleagues showed that they could detect a hidden nanostructure using very high frequency sound waves induced by light. The Light Matter Interaction group at ARCNL develops techniques to overcome this problem.

$diffraction with sound$

Detecting these alignment gratings is not always straightforward, because they get buried under many layers of material, some of which can be opaque to light. To make sure consecutive layers are aligned accurately, wafers contain grating lines that act as markers. Nanolithography machines print several layers of nano-sized structures on a wafer to produce state-of-the art computer chips and components. The researchers have published their findings in Photoacoustics on May 9th 2023. The relative enhancement of the diffraction signal is even two to three times larger than the enhancement of the reflection signal. This amplifies reflection and diffraction changes caused by laser-induced acoustic waves in the sample. With a gold-covered segmented grating they can induce a so-called plasmonic resonance. Leaves on trees, and even the tree trunks themselves, have a small impact on sounds below 1,000 Hz, while mountains have can a significant impact.ARCNL researchers Thomas van den Hooven and Paul Planken have found a way to enhance acoustic-wave-induced diffraction changes from a sample similar to those used for wafer alignment in nanolithography.

$diffraction with sound$

And if the object is much larger than the wavelength, it will tend to block the sound entirely. If an object is about the same size as the wavelength, the sound will tend to bend around the object, with large changes in the propagation. For example, a 1,000 Hz signal (with a wavelength of about 1 foot) will not be affected by power lines (with a diameter of less than an inch). If an object is much smaller than the wavelength of sound it is interacting with, then the sound will be unaffected by the object. Sounds at 100 Hz have a wavelength of about 10 feet, sounds at 1,000 Hz have a wavelength of about 1 foot, and sounds at 10,000 Hz have a wave length of about 0.1 foot. The wavelength is the length of the sound wave, and is inversely related to the frequency. However, some of the basics are easy to understand.įirst and foremost, diffraction is frequency dependent, or more precisely, dependent on the wavelength of the sound. As with most aspects of acoustics, this is a complex phenomena, governed by equally complex equations. Diffraction is the process of sound ‘bending’ around objects.

$diffraction with sound$

Diffraction with sound