Experiment on acousto-optic modulation effect using a He-Ne laser

The proposed experiments are pedagogically rich as they allow not only the study of the different physical phenomena involved in acousto-optic interaction but also provide an overview of potential applications in both intensity modulation and deflection.

Acousto-optic systems are or have been used in various fields: laser printers, scanners, projectors, pulsed lasers, tunable filters, etc...

An equivalent product is presented in the chapter dedicated to waves: it involves an interaction between an optical wave and an acoustic network generated by ultrasonics in a liquid.

Topics covered:
- Bragg Cell / Determination of Bragg diffraction angle
- Study of diffracted beams based on the frequency of the acoustic wave
- Evaluation of the speed of the acoustic wave in the material
- Measurement of diffraction intensity based on the power of the acoustic wave
- Calculation of diffraction efficiency and medium absorption
- Study of acousto-optic modulation and application to the recording and transport of an audio signal on an optical carrier
- Study of acousto-optic deflection and application to projection and optical addressing

Principles and objectives:
The acousto-optic effect involves the interaction between an ultrasonic wave and an optical wave in a solid or liquid medium. The acoustic wave causes the propagation of a deformation and consequently a variation in the refractive index in the medium. The acoustic wave is generated, for example, by a piezoelectric transducer. The refractive index variation has spatial and temporal periodicity. The index network moves parallel to itself at the speed of the acoustic wave. As this speed is much lower than that of light, the acoustic wave can be considered stationary and the network fixed with respect to the incident light beam. The refractive index network formed by acousto-optic interaction is then used to cause the diffraction of an optical wave.

Composition:
▪ 1 prism bench of 1 m with adjustable feet set (ref.202519)
▪ 2 standard prism riders (ref.202234)
▪ 1 prism rider with angular adjustment (ref.202514)
▪ 1 optical foot (ref.203212)
▪ 1 He-Ne laser 632.8 nm <1mW, polarized with power supply (ref.204886)
▪ 1 laser support on rod (ref.202674)
▪ 1 polarizer in graduated mount (ref.202374)
▪ 1 acousto-optic modulator / deflector (Bragg cell)
▪ 1 control power supply for acousto-optic cell
▪ 1 object holder plate with horizontal adjustment
▪ 1 amplified detector with adjustable gain (ref.204888)
▪ 1 white and gridded metal screen 20x20 cm (ref.202368)
▪ 1 digital CCD/CMOS sensor + OD1, OD3 filters, polarizer + software (ref.204354)
▪ 1 multimedia kit (radio + speakers + all necessary connections for proper operation)
▪ 1 experimental manual