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Deformable Mirrors

 


Fig. 1


Fig. 2


Fig. 3


Fig. 4

 

 A bimorph (unimorph) deformable mirror (fig. 1, 2) is constructed of two (one) thin plate(s) of piezoelectric material coupled with a substrate plate. The electrode pattern is deposited on the piezo-plates, which are then glued together to form a sandwich of electrodes. The ground plane is the common middle surface of the bimorph or the back surface of the substrate in the unimorph. An optical surface is formed on the front surface of the substrate plate. The polarization of the piezoelectric plate is chosen so that to make the plate expand or contract when voltage is applied to the electrode. The differential expansion/contraction of the substrate and piezo-plates causes the bimorph (unimorph) to bend, much in the same way as a bi-metallic strip will bend when heated.

The typical arrangement of mirror electrodes is shown in fig. 3. As a result of such an arrangement, the mirrors are capable of forming complex surface reliefs, the shape of which is computer-controlled. Measured response functions of deformable mirror electrodes shown in fig. 4.

The deformable mirrors of this type are designed to be applied in medical imaging, laser beam control and shaping, optical communications, and astronomy.

 

TECHNICAL SPECIFICATION:

 

substrate

quartz, glass

 

clear aperture diameter

30-60 mm

 

stroke

15-40 m

 

number
of control electrodes

13-24

 

control voltage (max)

300 V

 

resonance frequency

>2000 Hz

 

reflective coatings

protected Al, Ag, Cu,
multilayer dielectric
coating of reflectivity >99%

 

optical damage threshold

in CW operation
in pulsed operation

 

up to 0.1 kW/cm
up to 4 J/cm

 

surface quality
(scratch-dig)

60-40

 

hysteresis

<15%

 

operating
temperature range

+10..+40 C

 

storage
temperature range

-30..+70 C

 

weight (max)

0.15 kg

 

size

55×55 mm

 

 

These deformable mirrors have been designed in close collaboration with the Institute on laser and information technologies of the Russian Academy of Sciences (ILIT RAS). More detailed information on the mirrors and control units for these can be found [ here ].