For most applications, the slight change of optical frequency is irrelevant. (The change in direction is smaller than shown in Figure 1 because the wavenumber of the sound wave is very small compared with that of the light beam.) The frequency and direction of the diffracted beam depend on the frequency of the sound wave, whereas the acoustic power is the control for the diffracted optical power. The optical frequency of the diffracted beam is increased or decreased by the frequency of the sound wave (depending on the propagation direction of the acoustic wave relative to the beam) and propagates in a slightly different direction. However, most AOMs operate in the Bragg regime, where there is a substantial diffraction efficiency for the first diffraction order and hardly any diffraction into other orders. The diffraction angle is exaggerated it is normally only of the order of 1°.įor a very short interaction length in the modulator, one would operate in the Raman–Nath regime, where multiple diffraction orders are obtained. Figure 1: Schematic setup of a non-resonant acousto-optic modulator.Ī transducer generates a sound wave, at which a light beam is partially diffracted. Through the photo-elastic effect, that leads to a traveling refractive index grating, at which light can experience Bragg diffraction therefore, AOMs are sometimes called Bragg cells. The intense sound wave generates a traveling strain wave in the material. The piezo transducer excites a sound wave with a frequency of the order of 100 MHz and with an acoustic wavelength which is typically between 10 μm and 100 μm and an acoustic power e.g.
Sound diffraction materials driver#
A piezoelectric transducer attached to the crystal obtains a strong oscillating electrical signal from an RF driver (often via an impedance matching device). The key element of an AOM is a transparent crystal (or piece of glass) through which the light propagates. Usually, an AOM is understood to be an intensity modulator other acousto-optic devices are suitable for shifting the optical frequency (→ acousto-optic frequency shifter) or the spatial direction ( acousto-optic deflectors). the modification of the refractive index of some crystal or glass material by the oscillating mechanical strain of a sound wave ( photoelastic effect). It is based on the acousto-optic effect, i.e. bulk, fiber-coupled and integrated-optical AOMs,Īn acousto-optic modulator (AOM) is a device which can be used for controlling the transmitted power of a laser beam with an electrical drive signal.the used acousto-optic materials and their characteristics,.
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