# Training Videos

## Acousto-optic diffraction

This is a continuation from the previous tutorial - photoelastic effect. We see from the preceding two tutorials that the space- and time-dependent periodic permittivity changes induced by a traveling plane acoustic wave of the form given in (8-1) [refer to the elastic waves tutorial] can be generally expressed as $\tag{8-34}\Delta\boldsymbol{\epsilon}=\Delta\tilde{\boldsymbol{\epsilon}}\sin(\mathbf{K}\cdot\mathbf{r}-\Omega{t})$ where $$\mathbf{K}$$ depends on both the polarization and the propagation direction of the acoustic wave. In general, $$\Delta\tilde{\boldsymbol{\epsilon}}$$ is a function of the strain and the rotation generated by the acoustic wave in the medium, the elasto-optic coefficients of the medium, the mode and direction of the acoustic wave,...

## Photoelastic effect

This is a continuation from the previous tutorial - elastic waves. Mechanical strain in a medium causes changes in the optical property of the medium due to the photoelastic effect.  The basis of acousto-optic interaction is the dynamic photoelastic effect in which the periodic time-dependent mechanical strain caused by an acoustic wave induces periodic time-dependent variations in the optical properties of the medium. The photoelastic effect is traditionally defined in terms of changes in the elements of the relative impermeability tensor caused by strain: $\tag{8-7}\eta_{ij}(\mathbf{S})=\eta_{ij}+\Delta\eta_{ij}(\mathbf{S})=\eta_{ij}+\sum_{k,l}p_{ijkl}S_{kl}$ where $$p_{ijkl}$$ are dimensionless elasto-optic coefficients, also called strain-optic coefficients or photoelastic coefficients, and they...

## Elastic Waves

This is a continuation from the previous tutorial - guided-wave magneto-optic devices.   Introduction Scattering of light by acoustic waves was first investigated by Brillouin. The acoustic frequencies involved in Brillouin scattering fall in the ultrasonic and hypersonic regions. Hypersonic waves in a medium are caused by thermal excitation, whereas ultrasonic waves can be excited electronically using piezoelectric transducers. The acoustic waves used in acousto-optics are generally ultrasonic waves that have frequencies in the range between about 100 kHz and a few gigahertz. The basic principles of acousto-optic devices are based on the scattering of light by the periodic index...