![sound beam diffraction sound beam diffraction](https://i.ytimg.com/vi/DjEKHdKH75A/maxresdefault.jpg)
In other words, the intensity is not also related to the origin y even though one or many orders of diffracted light, escaping from outside the small defined region, is also collected.Īdditionally, if only the qth-order of diffracted light is collected, the collected light intensity will beįrom Eq. Additionally, even though the values of a and d are increased, the collected light intensity is not also related to its origin y. ( 4) and ( 5), the collected light intensity fluctuates with the sound wave but is not related to its origin y inside the acoustic field.
![sound beam diffraction sound beam diffraction](https://images.fineartamerica.com/images-medium-large-5/laser-diffraction-giphotostock.jpg)
In which F( t) is a periodic function with acoustic period 2 π / ω and obeysįrom Eqs. Then, the collected light intensity I( t) is Consequently, we can assume that only the diffracted light of the absolute diffraction order less than five is collected. Generally, the diffracted light with the absolute diffraction order more than five is very weak. Then, all collected light can be considered to originate from the same location (0, y, 0) inside the acoustic field. Additionally, the regional sizes are much shorter than the acoustic wavelength in the medium. The regional center is a point (0, y, 0). The region is assumed a rectangle with the 2 a and 2 d sizes along the X- and Y-axes respectively. To reveal the relationship between the sound-modulated light and its origin (a specific location inside the acoustic field from which the modulated light originates), only the light escaping from a very small defined region inside the acoustic field is collected. Additionally, the optical phase of each order of diffracted light is not shifted by the sound wave and does not fluctuate with the sound wave and is not related to the location y. ( 2) that the qth-order of diffracted light is shifted in frequency by qω and its diffraction angle θ q obeysĪnd each order of diffracted light has the same optical phase exp(j kn 0 l) and is a plane light wave. Where E 0 is the electric field of incident light, k, ω 0, and λ are the wave vector, angular frequency, and the wavelength of incident light in vacuum, respectively, q is an integer, J q denotes the qth-order Bessel function, and λ u is the acoustic wavelength in the medium. For Raman– Nath diffraction, the diffracted light E( t) was still expressed as A plane wave for each order of diffracted light in Raman– Nath diffractionĪ light wave getting into the acoustic field will be diffracted. As a result, the wavefront of each order of diffracted light is modulated to fluctuate spatially and temporally with the sound wave.Ģ.1. In this paper, we find that each order of diffracted light is not a plane light wave, and that its optical phase is shifted by the sound wave and fluctuates with the sound wave and is the function of the location inside the acoustic field from which the diffracted light originates. However, each order of diffracted light was still considered as a plane light wave. Each order of diffracted light has a specific frequency shift and a diffraction angle.
![sound beam diffraction sound beam diffraction](https://www.mdpi.com/sensors/sensors-20-06148/article_deploy/html/images/sensors-20-06148-g001.png)
The Raman– Nath diffraction includes multiple diffraction orders. In the paper, only the Raman– Nath diffraction in acousto– optic effect is studied. Additionally, the diffracted light is frequency-shifted by an integer multiple of the acoustic frequency. The Klein– Cook parameter Q obeys ), where λ and λ u are the wavelength of incident light in vacuum and sound in the medium respectively, l is the acousto– optic interaction length, and n 0 is the refractive index of the medium in the absence of sound. When the Klein– Cook parameter is less than 1, only the Raman– Nath diffraction occurs. The diffraction is divided into two distinct diffraction types: Raman– Nath and Bragg diffraction. The incident light on the grating is diffracted. When an acoustic wave is launched into an optical medium, it generates a phase grating. So far, acousto– optic effects have been applied to a wide range of optical system applications. Acousto– optic effects occur in all optical media.