Working principle of acousto-optic modulator

1. Working principle of acousto-optic modulator
The core of an acousto-optic modulator(AOM modulator)is the acousto-optic effect. Its basic structure includes acousto-optic crystals, transducers, absorption devices, and drivers. The electrical signal output by the driver is converted into ultrasonic waves by the transducer. When the ultrasonic waves propagate in the acousto-optic medium, they cause periodic changes in the medium density, forming a structure similar to a phase grating. When light passes through this medium, diffraction occurs, achieving modulation of the optical carrier wave. There are mainly two types of diffraction modes: Raman Ness diffraction and Bragg diffraction. The commonly used AOM modulator usually operates in Bragg diffraction mode, where the incident light is incident at a specific Bragg angle and the output light contains undeflected zero order light and first-order diffraction light with a deflection angle.
2. Main technical parameters of acousto-optic modulator
2.1 Diffraction efficiency and modulation loss: measures the ability of a device to convert incident light into first-order diffracted light and the accompanying optical loss.
2.2 Bragg angle: The specific incident angle that achieves the best diffraction efficiency, which is related to the laser wavelength, radio frequency, and sound velocity inside the crystal.
2.3 Optimal RF power: i.e. saturation power, the RF driving power required to achieve maximum diffraction efficiency. The specific calculation formula is given in the article.
2.4 Divergence angle adaptation: To ensure optimal performance, the divergence angle of the incident laser needs to match the characteristics of the acousto-optic medium.
2.5 Modulation speed: usually represented by the rise time of light, depending on the transmission time of sound waves through the beam, and related to the beam diameter and sound velocity.
3. Main applications of acousto-optic modulators
The five main applications of acousto-optic technology are:
3.1 Acousto optic Q-switch: placed inside the laser cavity, it generates high peak power pulsed laser by rapidly modulating cavity losses.
3.2 Acousto optic modulator/switch: used for intensity modulation or fast on-off control of laser outside the laser cavity, and can be used as a shutter or variable attenuator.
3.3 Acoustic optic deflector: By changing the radio frequency to deflect the laser beam, fast beam scanning is achieved, suitable for random access or continuous scanning.
3.4 Acousto optic frequency shifter: specifically designed to move the laser frequency up or down, and can be cascaded to achieve more complex frequency shift combinations.
3.5 Acousto optic Adjustable Filter: A solid-state electronic adjustable optical filter that can quickly and dynamically select specific wavelengths from a wide spectrum light source.