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Exploring the secrets of deformable mirrors: Why does every actuator matter?
In the field of optical technology, deformable mirrors (DM) are widely used in wavefront control and optical aberration correction. These deformable mirrors can rapidly change shape to adapt to dynamic optical environments, which is particularly important in high-speed aerodynamic flow fields. Different deformable mirror designs make them useful in a variety of applications, from adaptive optics to ultrafast pulse shaping techniques. However, the charm lies not only in their functionality, but also in how the individual actuators that make up these mirrors work together to achieve optimal performance.
The shape of a deformable mirror can be precisely controlled by a number of actuators, which enable the mirror to respond quickly to optical errors.
Each deformable mirror typically has multiple actuators, one for each degree of freedom, which allows the mirror to be adjusted for different optical errors. According to statistics, when a deformable mirror with M actors is used for correction, its effect can be approximated by an ideal Zernike corrector with N (usually N < M) degrees of freedom. For the correction of atmospheric turbulence, removing low-order Zernike terms can significantly improve the image quality, while further correcting high-order terms has a relatively small improvement. However, such effects depend on the design and performance of each actuator.
Several key parameters of a deformable mirror include the number of actuators, the actuator spacing, and the actuator travel. The number of actuators directly affects the degrees of freedom of the mirror. The more degrees of freedom there are, the better the mirror's ability to correct the wavefront. Actuator spacing refers to the distance between the actuators, which directly affects the performance and accuracy of the correction. The stroke of the actuator determines the maximum distance the actuator can move, usually between ±1 and ±30 microns.
The travel of the actuator limits the maximum corrective wavefront amplitude; therefore, accurate design of each actuator is critical.
Deformable mirrors of different designs have different response characteristics. For example, a segmented deformable mirror consists of individual flat mirror segments that can move independently to approximate the average value of the light wavefront. The advantage of this design is that the mutual influence between the actuators is very small, but its disadvantage is that it cannot effectively process smooth and continuous light wavefronts. In addition, sharp edges and gaps in the background can cause light scattering, which in turn limits the areas of application. In contrast, the continuous panel concept deformable mirror uses a thin and flexible membrane, which can provide smoother wavefront control.
With the advancement of technology, different types of deformable mirrors are constantly being developed, such as the MEMS concept deformable mirror, which is made using micro-electromechanical system technology and can achieve more efficient wavefront correction at a lower cost. These mirrors respond quickly and have very little hysteresis, allowing them to make adjustments in a very short time. Magnetic deformable mirrors are becoming an emerging option due to their flexible design and excellent optical quality.
Future large space telescopes, such as the Large Ultraviolet Optical Infrared Survey Mission (LUVOIR) in the United States, will also be equipped with segmented primary mirrors, which will improve the performance of direct imaging of planetary systems.
One of the most important challenges in designing and fabricating these advanced deformable mirrors is ensuring precise coordination between the actuators and timely response to control signals. The pressure that each actuator bears during the correction process and the correctness of its adjustment will directly affect the final wavefront correction effect. Maintaining these demanding techniques may be the key to the development of more sophisticated optical systems in the future.
This is not only a technological advancement, but also a profound reflection on the future understanding and application of optical imaging. In your future research or design, facing those unforeseen challenges, do you think the critical thinking mode of each driver can lead you to find the best solution?
