AO Modulator

An acousto-optic modulator (AOM) uses sound waves within a crystal to create a diffraction grating. As the power of the applied RF signal is varied, the amount of diffracted light varies proportionally. Acousto-optic modulators can be used like a shutter, or as a variable attenuator.

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     An acousto-optic modulator (AOM) uses sound waves within a crystal to create a diffraction grating. As the power of the applied RF signal is varied, the amount of diffracted light varies proportionally. Acousto-optic modulators can be used like a shutter, or as a variable attenuator.


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◆ High efficiency






1064 nm

Transmission Single pass


Damage threshold


Diffraction efficiency

Nom 80%





Crystal length

A, B

Operating mode


Diffraction angle

25.2 mrad

RF Frequency


RF power rating (Maximum)

2.5 W

RF connector


Rise time

120 ns

Input impedance

50 Ω



Operating temperature


Storage temperature






1064 nm

TransmissionSingle pass


Average optical power handling


Peak optical power handling


Insertion loss


Polarization dependent loss

0.5 dB

Extinction ratio

50 dB

Rise-time/fall-time: (10% - 90%)

50 ns



RF power ratingMaximum

2 W

RF connector


Input impedance

50 Ω



Fiber type


Fiber length

1.5 m

Fiber termination

 Bare fiber





Aperture (mm)

RF Frequency


Acousto-Optic Modulators


Tellurium Dioxide

1064 nm



Tellurium Dioxide

1064 nm




Bragg cell: A device using a bulk acousto-optic interaction (eg. deflectors, modulators, etc...).


“Zero” order,”1st” order: The zero order is the beam directly transmitted through the cell. The first order is the diffracted beam generated when the laser beam interacts with the acoustic wave.


Bragg angle (QB): The particular angle of incidence (between the incident beam and the acoustic wave) which gives efficient diffraction into a single diffracted order. This angle will depend on the wavelength and the RF frequency.


Separation angle (Q): The angle between the zero order and the first order.


RF Bandwidth (DF): For a given orientation and optical wavelength there is a particular RF frequency which matches the Bragg criteria. However, there will be a range of frequencies for which the situation is still close enough to optimum for diffraction still to be efficient. This RF bandwidth determines, for instance, the scan angle of a deflector or the tuning range of an AOTF.


Maximum deflection angle (DQ): The angle through which the first order beam will scan when the RF frequency is varied across the full RF bandwidth.


Rise time (TR): Proportional to the time the acoustic wave takes to cross the laser beam and, therefore, the time it takes the beam to respond to a change in the RF signal. The rise time can be reduced by reducing the beam’s width.


Modulation bandwidth (DFmod): The maximum frequency at which the light beam can be amplitude modulated. It is related to the rise time - and can be increased by reducing the diameter of the laser beam.


Efficiency (h): The fraction of the zero order beam which can be diffracted into the “1st” order beam.


Extinction ratio (ER): The ratio between maximum and minimum light intensity in the “1st” order beam, when the acoustic wave is “on” and “off” respectively.


Frequency shift (F): The difference in frequency between the diffracted and incident light beams. This shift is equal to the acoustic frequency and can be a shift up or down depending on orientation.


Resolution (N): The number of resolvable points, which a deflector can generate - corresponding to the maximum number of separate positions of the diffracted light beam - as defined by the Rayleigh criterion.


RF Power (PRF): The electrical power delivered by the driver.


Acoustic power (Pa ): The acoustic power generated in the crystal by the piezoelectric transducer. This will be lower than the RF power as the electro-mechanical conversion ratio is lower than 1.


2.Physical Principles

    An RF signal applied to a piezo-electric transducer, bonded to a suitable crystal, will generate an acoustic wave. This acts like a “phase grating”, traveling through the crystal at the acoustic velocity of the material and with an acoustic wave-length dependent on the frequency of the RF signal. Any incident laser beam will be diffracted by this grating, generally giving a number of diffracted beams.


3.Acousto-Optic Q-Switches

    When placed inside a laser cavity, an acousto-optic Q-switch (AOQS) can be used to control the amount of light circulating within the resonator via the acousto-optic effect. When turned on, an AOQS diffracts light out of the optical beam path within the cavity, thus increasing losses and reducing the Q-factor. While loss in the cavity is high and pumping continues, lasing cannot occur, but a population inversion can build up within the gain medium. Once the gain is saturated, the RF power to the acousto-optic Q-switch is turned off, reducing loss within the cavity very quickly. This increases the Q-factor and allows rapid amplification to create a very high intensity, short pulse.


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