新模型揭示Raman-Nath声光衍射的时空波动效应

47 浏览量更新于2024-08-27 收藏 409KB PDF 举报

本文主要探讨了拉莫尔-纳特（Raman-Nath）声光衍射模型，这是一种在光与声波相互作用中产生的光学现象。拉莫尔-纳特效应起源于1922年布拉格（Brillouin）对声波散射光的理论预测，他指出声波导致的光散射不仅改变了光的频率，还产生了空间和时间上的光强波动。在传统的声光衍射模型中，主要包括相位栅衍射和多普勒效应两个核心机制。新的Raman-Nath声光衍射模型在此基础上进一步发展，它考虑了光学相位调制和光子-声子散射的共同作用。光学相位调制是指声波通过与光场相互作用，引起光波的相位随时间变化，这种变化直接影响到被散射光的动态特性。这意味着当光波在声场中传播时，其强度不仅在空间上受到周期性分布的声波影响形成衍射图案，而且在时间上也会表现出周期性起伏。模型分析了这两种效应如何交织在一起，即相位格栅衍射导致了空间上的干涉模式，而多普勒效应则引起了光速变化，进而影响了光的频率和波长。同时，由于光子-声子散射的存在，光的强度会随着声波的传播而发生变化，这种过程可能产生额外的光强分布不均匀。这些效应共同作用下，使得逃逸出声场的衍射光具有复杂的时间和空间特性。研究结果对于理解声光相互作用的微观机制，特别是在光纤通信、激光冷却、声光探测器等领域具有重要意义。通过这个新模型，科研人员可以更准确地控制和预测声光系统的动态行为，从而开发出更高效、灵敏的声光设备。这篇论文提供了一个深化对Raman-Nath声光衍射理解的新视角，并可能开启更多基于这一原理的应用创新。

Model of Raman–Nath acousto-optic diffraction

Cuncheng Weng (翁存程)

and Xiaoman Zhang (章小曼)

College of Physics and Energy, Fujian Normal University, Fuzhou 350007, China

College of Photonic and Electronic Engineering, Fujian Normal University, Fuzhou 350007, China

*Corresponding author: xmzhang@fjnu.edu.cn

Received April 16, 2015; accepted August 19, 2015; posted online September 11, 2015

In this Letter, we discuss Raman–Nath acousto-optic diffraction, and a new model of Raman–Nath acousto-optic

diffraction is presented. The model is based on the individual and simultaneous occurrences of phase-grating

diffraction and the Doppler effect and optical phase modulation and photon–phonon scattering. We find that

the optical phase modulation can cause temporal and spatial fluctuations of the diffracted light power escaping

from the acoustic field.

OCIS codes: 170.5120, 290.1350, 290.4210, 290.7050.

doi: 10.3788/COL201513.101701.

Back in 1922, the scattering of light by an sound wave,

known as Brillouin or acousto-optic scattering, was first

predicted by Brillouin

[1]

. He also predicted that the scat-

tered light had shifted in frequency. Brillouin scattering

was first observed by Gross in liquids

[2]

. An acoustic signal

produces regions of compression and rarefactio n as it

propagates through a medium. The induced strains

change the refractive index of the medium. This provides

a moving phase grating that may diffract an incident light

beam into a single diffraction order, the Bragg diffraction,

or multiple diffraction orders, the Raman–Nath diffrac-

tion (RNd)

[1,3–7]

In 1967, Klein and Cook introduced the Q-parameter to

distinguish between the two diffraction regimes

[3]

. It is well

known that the acoustic actions in the RNd simultane-

ously cause the diffraction and phase shift and frequency

shift of the incident light

[1,2,8]

. Conventionally, the RNd is

analyzed independently by using a moving thin-phase gra-

ting diffraction model

[1,3,5]

. According to the model, the in-

cident light is frequency shifted by the Doppler effect and

is diffracted simultaneously by the grating. After the

introduction of laser in the 1960s, the ideas of quantum

mechanics were also employed to el ucidate the RNd

[1,5]

Since then, the RNd has also been regarded independently

as the collision process of a photon and one or more pho-

nons, which are known as photon–phonon scatterings.

This collision process takes two forms: absorption and

emission processes. During the absorption process, one

or more phonons are annihilated by the incoming photon,

and a higher-energy photon leaves the scattering site. In

the emission process, one or more phonons are created

by the incoming photon, and a lower-energy photon leaves

the scattering site.

In the two models, the optical phase shift is ignored. Ad-

ditionally, the acousto-optic interactions can in fact simul-

taneously cause the moving thin-phase grating diffraction

and photon–phonon scattering, especially in an acousto-

optic crystal

[1,5,8]

. Obviously, the conventional models

are insufficient to describe the RNd. But, because of

optical scatterings, the photon–phonon scattering model

can still analyze the RNd in an optically scattering

medium. Additionally, in case of ignoring the optical

phase modulation, the grating diffraction model can still

well explain the RNd in this kind of optically transparent

media such as water, in which the photon–phonon scatter-

ing is very weak

[9]

In this Letter, we present a new RNd model stemming

from the simultaneous occurrences of phase-grating dif-

fraction and the Doppler effect and optical phase modu-

lation and photon–phonon scattering.

The RNd we will deal with is two dimensional. A typical

configuration is seen in Fig.

1. An idealized sound beam

is contained between planes z ¼ 0 and z ¼ l inside an

optically transparent medium of refractive index n

For a plane longitudinal sound wa ve with angular fre-

quency ω and velocity v in the medium, the refractive

index nðt; yÞ at position y and time t obeys

[1–3,5]

nðt; yÞ¼n



1 þ m sin ω



t þ



; (1)

where m is the modulation constant of refractive index

and depends on the acoustic power. From Eq. (

1), the

refractive index is modulated spatially and temporally

by the sound wave.

In order to show the differences between the conven-

tional and presented RNd models, we begin by introduc-

ing the moving thin-phase grating diffraction model.

Based on the grating diffraction model, the diffracted light

Eðl; tÞ is given by

[1–3,5]

Eðl; tÞ¼E

expðjkn

lÞ

þ∞

q¼−∞

ðkn

lmÞ

× exp½jðω

þ qωÞtδ



cos θ

−



; (2)

where E

is the electric field of the incident light; k, ω

and λ are the wave vector, angular frequency, and wave-

length of the incident light in the vacuum, respectively;

COL 13(10), 101701(2015) CHINESE OPTICS LETTERS October 10, 2015

下载后可阅读完整内容，剩余4页未读，立即下载

weixin_38546817

粉丝: 8
资源: 911

新模型揭示Raman-Nath声光衍射的时空波动效应

Microstructure and Raman spectra of Ag-MgF2 cermet films

Carbon turns the tensile surface stress of Ti to be compressive

Fabrication of kW-level chirped and tilted fiber Bragg gratings and filtering of stimulated Raman scattering in high-power CW oscillators

Mitigation of stimulated Raman scattering in kilowatt-level diode-pumped fiber amplifiers with chirped and tilted fiber Bragg gratings

Time evolution of stimulated Raman scattering and two-plasmon decay at laser intensities relevant for shock ignition in a hot plasma

Ultraviolet Raman lidar for high-accuracy profiling of aerosol extinction coefficient

在拉曼-纳特（Raman-Nath）模式下使用光学检测表征脉冲超声

Fiber-optic spectroscopic rotational Raman lidar with visible wavelength fiber Bragg grating for atmospheric temperature measurement

Erythrocyte membrane analysis for type II diabetes detection using Raman spectroscopy in high-wavenumber region

Numerical analysis of Raman amplification and optical signal-to-noise ratio in a photonic crystal fiber

最新资源