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Kinematic Mirror Mounts with Piezoelectric Adjusters
For Ø7.0 mm Mirrors
Ø1" Mirror Mount and
For Ø1" Mirrors
The three-axis mirror mounts sold on this page contain manual and piezo adjusters in series, enabling coarse and fine adjustment of the tip, tilt, and translation of a mounted mirror. We manufacture a Ø7.0 mm mirror mount whose compact size is ideal for use in laser cavities, as well as a Ø1" (Ø25 mm) mirror mount with through holes for integration into a 30 mm cage assembly. The bore in the Ø1" mount is available with an optional internal SM1 (1.035"-40) thread, which allows a mirror to be mounted with SM1RR Retaining Rings as opposed to a setscrew. We also offer the Ø1" mirror mounts in bundles with the MDT693B Three-Channel Piezo Controller, which provides electronic control for all three axes.
For applications requiring an exceptional level of thermal stability, Thorlabs manufactures the Polaris™ Kinematic Mirror Mount with Piezoelectric Adjusters.
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Piezo Controller as Part of a Closed-Loop System
Piezo Controller in a Beam Stabilization Setup
Active beam stabilization is often used to compensate for beam drift (unintended beam pointing deviations) in experimental setups. Drift can be caused by insecurely mounted optics, laser source instabilities, and thermal fluctuations within an optomechanical setup. In addition to correcting for setup errors, active stabilization is frequently used in laser cavities to maintain a high output power or used on an optical table to ensure that long measurements will take place under constant illumination conditions. Setups with long beam paths also benefit from active stabilization, since small angular deviations in a long path will lead to significant displacements downstream.
An example of a beam stabilization setup is shown in the schematic to the left. A beamsplitter inserted in the optical path sends a sample of the beam to a quadrant position sensor that monitors the displacement of the beam relative to the detector's center. (For optimal stabilization, the beamsplitter should be as close as possible to the measurement.) The quadrant detector outputs an error signal in X and Y that is proportional to the beam's position. Each error signal is fed into a channel of a piezoelectric controller that steers the beam back to the center of the quadrant sensor.
The setup illustrated here stabilizes the beam to a point in space. In order to stabilize the beam over a beam path, four independent output channels are required (i.e., at least two piezoelectric controllers), as are two mirror mounts with piezo adjusters, two position sensors, and two position sensor controllers. Suggested electronics for a beam stabilization setup are given in the table below.
ASM003 Kinematic Mirror Mount
KC1(-T)-PZ Kinematic Mirror Mount
MDT693B Three-Channel Piezo Controller
Output Voltage: 0 - 150 V
External Voltage Control
Input Voltage: 0 - 10 V
External Computer Control
Type B USB Female
Piezo Driver Bandwidth Tutorial
Knowing the rate at which a piezo is capable of changing lengths is essential in many high-speed applications. The bandwidth of a piezo controller and stack can be estimated if the following is known:
To drive the output capacitor, current is needed to charge it and to discharge it. The change in charge, dV/dt, is called the slew rate. The larger the capacitance, the more current needed:
So, for example, for a 100 µm stack, having a capacitance of 20 µF, being driven by a BPC Series piezo controller with a maximum current of 0.5 A, the slew rate is given by
Hence, for an instantaneous voltage change from 0 V to 75 V, it would take 3 ms for the output voltage to reach 75 V.
Note: For these calculations, it is assumed that the absolute maximum bandwidth of the driver is much higher than the bandwidths calculated, and thus, driver bandwidth is not a limiting factor. Also please note that these calculations only apply for open-loop systems. In closed-loop mode, the slow response of the feedback loop puts another limit on the bandwidth.
The bandwidth of the system usually refers to the system's response to a sinusoidal signal of a given amplitude. For a piezo element driven by a sinusoidal signal of peak amplitude A, peak-to-peak voltage Vpp, and frequency f, we have:
A diagram of voltage as a function of time is shown to the right. The maximum slew rate, or voltage change, is reached at t = 2nπ, (n=0, 1, 2,...) at point a in the diagram to the right:
From the first equation, above:
For the example above, the maximum full-range (75 V) bandwidth would be
For a smaller piezo stack with 10 times lower capacitance, the results would be 10 times better, or about 1060 Hz. Or, if the peak-to-peak signal is reduced to 7.5 V (10% max amplitude) with the 100 µm stack, again, the result would be 10 times better at about 1060 Hz.
Triangle Wave Signal
For a piezo actuator driven by a triangle wave of max voltage Vpeak and minimum voltage of 0, the slew rate is equal to the slope:
Or, since f = 1/T:
Square Wave Signal
For a piezo actuator driven by a square wave of maximum voltage Vpeak and minimum voltage 0, the slew rate limits the minimum rise and fall times. In this case, the slew rate is equal to the slope while the signal is rising or falling. If tr is the minimum rise time, then
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The shaded region in the graph above denotes the range over which we recommend using our protected silver coating. Click here to download the raw data used to make this plot, as well as data at a 45° AOI.
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Schematic of ASM003 Mirror Mount
This piezo-driven mirror mount provides an angular resolution of better than 1 arcsec (<5 µrad). Each of the three adjustable axes consists of a manual and piezo adjuster in series. Ø7.0 mm optics up to 2.5 mm (0.10") thick are accommodated, and the Ø6.0 mm bore through the entire mount permits use with transmissive optics. A Ø7.0 mm protected silver mirror (Item # PF03-03-P01) is included; the reflectance of protected silver is shown to the right.
The fine-pitch manual adjusters, actuated with a flat head screwdriver (see diagram at right), provide 250 µm/rev and a full translation range of 1 mm (0.04"), for a full angular range of 4° (70 mrad). The piezoelectric elements embedded in the mount allow an additional 7 µm of translation, thereby providing an additional angular range of 2 arcmin (0.6 mrad). Each piezo adjuster is connected to a built-in 200 mm cable with a male SMC connector, and the maximum control voltage is 75 V. When driven by one of our piezoelectric drivers, the piezo elements can operate at up to 2 kHz, making this mirror mount an ideal laser cavity mirror holder when rapid scanning of a resonator cavity length is required.
The bottom of the ASM003 includes a mounting plate with an alignment key for mechanical compatibility with our family of flexure stages. The mounting plate is secured in place by two M2.5 cap screws that can be removed for custom mounting needs.
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These mirror mounts, based upon our KC1 mirror mounts, provide piezo-driven fine adjustments with a minimum angular resolution of 0.06 arcsec (0.3 µrad). Each of the three adjustable axes consists of a manual and piezo adjuster (Item # AE0505D08F) in series. The smooth bore version [Item # KC1-PZ(/M)] secures the mirror with an 8-32 (M4) setscrew and accepts mirrors at least 0.12" (3 mm) thick, while the SM1-threaded version [Item # KC1-T-PZ(/M)] secures the mirror with two included SM1RR Retaining Rings and accepts mirrors up to 0.20" (5 mm) thick.
The 1/4"-80 manual adjusters provide 7 mrad/rev and a full translation range of 6 mm (0.24"), for a full angular range of 10° (174 mrad). The piezoelectric elements embedded in the mount allow an additional 8 µm of translation, thereby providing an additional angular range of 30 arcsec (146 µrad). Each piezo adjuster is connected to a built-in 3' (91.4 cm) cable with a male BNC connector, and the maximum control voltage is 150 V. The knob assignments are shown in the diagram to the right.
Although SM1-threaded optics and lens tubes can be attached to the KC1-T-PZ, we do not recommend it because increasing the distance between the optic and the pivot points of the mount will amplify the movement of the beam. These mounts are also sold bundled with the MDT693B Three-Channel Piezo Controller, providing all the components needed for open-loop control of the mount (see below for details).
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Front Panel of Controller
These bundles provide all the components and cables needed for open-loop control of a three-axis kinematic mirror mount with piezo adjusters. They consist of our MDT693B Three-Channel Piezo Controller, a KC1-PZ(/M) or KC1-T-PZ(/M) mirror mount (see above for details on the mirror mount options), and a region-specific power cord selected at the time of the order.
The MDT693B piezo controller features three precise, low-noise, independently controllable output channels and is capable of supporting the piezo mirror mounts' maximum control voltage of 150 V. The control voltage can be modified using rotary knobs on the front panel and by providing an external signal through BNC or USB 2.0. The driver also includes a Master Scan mode that allows all three axes to be controlled by one signal. For more information, please see the full MDT693B presentation.