Acousto-optical deflectors (AOD)

 

An acousto-optic deflectors (AOD) primary goal was laser beam deflection to realize a large number of resolvable spots so that it may be used to replace mechanical scanners such as the rotating polygons.

In recent years most of the effort was directed toward Bragg cells for optical signal processing applications.

But finally nowadays Acousto-optic deflectors have many advantages over electro-mechanical devices, such as fast response time, high precision, and stability of a raster obtained.

Acousto-optic deflectors provide a simple solid state scanner which eliminates the inherent drawbacks of mechanical scanners due to moving parts such as facet errors and the requirement of realignment because of bearing wear.

 

Acousto-optic deflectors find many applications based on continuous laser beam deflection (one axle (1D) as well as 2 axis (2D)) and vector (random) scanning.

The most interesting, demanded and important applications are:

- scanners;

- laser tweezers;

- RGB systems for laser projectors;

- laser scanning microscopy and profilometry;

- measurements of surfaces of specimens over some predefined grid of points.

 

Main deflector principles

As a rule, light diffraction on the wave of slow shear acoustic mode in crystallographic surface (110) is used in paratellurite to provide most efficiency of acousto-optical interaction. 

Typical construction acousto-optic cell made on the basis of paratellurite is shown on picture. The phase velocity of the sound wave is normal to the plane of transducer and directed at the angle α with respect to crystallographic direction [110]. The sound energy flow vector does not coincide with the corresponding wave vector, due to high acoustic anisotropy present in the paratellurite crystals. Angle of sound energy drift A is quiet big and can reach 70 degrees that should be taken into consideration for cell geometrical sizes calculations.

 

In a deflector, the most important performance parameters are resolution and speed.

Resolution, or the maximum number of resolvable spots, is defined as the ratio of the range of deflection angle divided by the angular spread of the diffracted beam, i.e.,

where where D is the width of the incident beam and  ξ  is the a factor (near unity) that depends on the incident beam’s amplitude distribution.

For a nontruncated gaussian beam ξ =4/π.

Where is the acoustic-transit time across the optical aperture. Notice that the acoustic-transit time also represents the (random) access time and is a measure of the speed of the deflector. Equation shows that the resolution is equal to time (aperture) bandwidth product. This is the basic trade of f relation between resolution and speed (or bandwidth) of AO deflectors. In the design of AO deflectors, the primary goal is to obtain the highest diffraction efficiency for the specified bandwidth and resolution (or time aperture)

 

АОD main characteristics

Typical values for TeO2 deflectors

Optical Wavelength Range

540nm-530nm, 630nm-850nm, 700nm-1100nm, 1064nm, 1330nm

Optical Aperture

1 mm - 10 mm

Operating Mode

Shear Wave, 3-15 degrees of axis (110)

Center frequency

20- 200 MHz

Bandwidth

20-100 MHz

Diffraction efficiency

60-95%

Time aperture

1-15 μs

Resolution (T.BW product)

200-2000

Optical Rise Time

9-200 nsec on beam diameter

Deflection Angle

10-100 mrad

ΔDeflection Angle

5-50 mrad

RF input power

0,1- 2 Wt

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The most commonly used geometry shown in Fig. a is more preferable for the visible region, whereas the geometry displayed in Fig. b is more suitable for the infrared region. Polarization of the incident light is shown in the figures.

Under angle β beam is normally fall on incoming edge and corresponds to the angle of Bragg interaction with acoustical column. One of the methods to select angle γ - outgoing diffracted beam is parallel to the incoming.

 

We offer cells’ blanks for deflectors according to your specific requirements.


We can also manufacture pair of blanks (manufactured from one piece or manufacture identical two pieces with all characteristics high repeatability) for 2D deflectors.

Also we’d like to offer elements with AR coating and one golden electrode ready for bounding.

Note

- Upon your request we can supply blanks with any linear dimensions up to 70mm

- Upon your request we can offer AR or protective coating.

- Blanks for AOM & AOTF are also available

- Blanks for transducers from LiNbO3 crystals with different orientations are also available

 

Reference list:

[1] Xu J and Stroud R 1992 Acousto-Optic Devices (New York:Wiley)

[2] Handbook of optics. CHAPTER 12 ACOUSTO-OPTIC DEVICES AND APPLICATIONS I. C. Chang

[3] Goutzoulis A and Pape D 1994 Design and Fabrication of Acousto-Optic Devices (New York: Dekker)

Events/News

14th - 16th March 2017 - visit us at "Laser World of Photonics China 2017" fair in Shanghai, China. Hall 1 Booth 1735.

22 - 25 June 2015

June 2015 - visit us at "Laser World of Photonics 2015" fair in Munich, Germany.

Booth B1.439.

 

January 2015 - new edition of OptoIndex catalogue was published. You can find our company page here.