An acousto-optic modulator is made to vary the intensity of the incoming laser beam (Amplitude Modulation, AM). The modulation can be digital (ON/OFF) or analog (sine, square, linear, random…).
The key parameter of a modulator is its rise/fall time, which defines the achievable « speed » of the modulation, or amplitude modulation bandwidth. The rise/fall time is proportional to the beam diameter inside the modulator. As a consequence, the laser beam must be focused inside the modulator to reach a fast rise time.
● Fixed Frequency Shifters:
An acousto-optic frequency shifter uses the frequency shift of the laser beam inherent to the acousto-optic interaction. The laser wavelength is frequency shifted by the amount of the carrier RF frequency. The frequency shift can be positive or negative, depending on the angular sketch configuration. Modulators are used as fixed frequency shifters.
● Deflectors & Variable Frequency Shifters:
A Bragg configuration gives a single first order output beam, which intensity is directly linked to the power of RF control signal, and which angle is directly linked to the RF frequency.
By varying the frequency, the output laser beam angle is modified. A deflector is used to scan a laser beam over a range of angles, or to control with accuracy the output angle of the laser beam. By varying the frequency, the first order beam is also frequency shifted by the amount of the RF carrier frequency: it acts like a variable frequency shifter.
The main parameters to qualify a deflector are 1. Deflection angle range and 2. Resolution.
The deflection angle range is the maximum angle variation of the laser beam: it is linked to the frequency range of the device. The resolution of a deflector is the number of distinct directions which can be ad- dressed by the deflector: it is linked to the deflection angle range and laser divergence.
Two deflectors can be used in serie and at right angles to give full two-dimensional scanning.
● Pulse Pickers:
A pulse picker is an electrically controlled optical switch used to extract single pulses from a fast pulse train. Short and Ultrashort pulses are in most cases generated by a mode-locked laser in the form of a pulse train with a pulse repetition rate of the order of 10 MHz – few GHz. For various reasons, it is often necessary to pick certain pulses from such a pulse train, i.e., to transmit only certain pulses and block all the others. This can be done with a pulse picker, which is essentially an electrically controlled optical gate.
● AO Tunable Filters:
An AOTF is a solid-state, electronically tunable bandpass filter, which uses the acousto-optic interaction inside an anisotropic medium. These filters can be used with multi-lines sources (mixed gas lasers, Laser diodes…) or with broadband light sources (Xenon,Halogen lamps…). They allow to select and transmit a single or multiple wavelengths from the incoming light.
AA proposes a whole range of AOTFs based on TeO2 with shear acoustic mode. The filters are designed so as to get the best performances in each wavelength range and to satisfy most of the applications: resolution down to 1 nm, Field of view up to 20 degrees, apertures up to 10 mm…
In most cases, the filtered output from the tunable filter is made collinear to make easier the use of these devices, and to satisfy fiber pigtailing conditions. A random input polarization will be separated into two orthogonal polarizations (order -1 and +1).
● Polychromatic Modulators:
The AOTFnC is a special acousto-optic tunable filter which uses the anisotropic interaction inside a Tellurium dioxide crystal (TeO2) to control independently or simultaneously different lines from an incoming UV or VISIBLE laser light (White laser, Ar+, Kr+, HeNe, DPSS, Dye…).
Up to 8 distinct lines can be mixed and separately modulated in order to generate different colorimetric patterns. The specific crystal cut of the AOTFnC produces good diffraction efficiency (> 90%), narrow resolution (1-2 nm), a low cross-talk between lines, and high extinction ratio.
The large separation angle between 0 and 1st orders, as well as the excellent output chromatic colinearity (<0.2 to <0.3 mrd ) make this AOTF a powerful tool for free space or fibre pigtailed applications. Its associated thermal stabilization maintains stable diffraction efficiency and reduces dramatically beam drift with single mode fibre pigtailing. This is a major advantage for high sensitivity applications.
AA propose a line of Acousto-optic Q-switches and associated RF drivers, for a wide range of applications. They are manufactured from the highest quality materials, with optimized hard coatings for high damage threshold and long term operation. All AA Q-switches are designed so as to optimize heat dissipation and beam stability with a unique glueing and mechanical technology which reduces stress during operation.
● Fiber Pigtailed Modulators: ● Fiber Pulse Picker:
These fiber pigtailed devices can be used depending on the models as modulators, fixed frequency shifters, Q-switches or Pulse pickers. Our standard versions are proposed with a single mode fiber with polarization maintaining. However on request, we can offer different types of fibers or connectors. These devices are dedicated for telecommunication applications, as well as for printing, microscopy, lidars, remote sensing, Q-switching or any other scientific application.
AA propose a selection of fiber pigtailed pulse pickers for 1030-1080nm, 1300-1600nm and 1900-2100nm with compact or VSF packages.
Other models for different wavelengths, type of fibers and connectors are available on request.