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Adaptive optics have become a key way of improving the performance of various optical systems by manipulating the waves of light that pass through them. Many light waves suffer from distortions that can cause inaccuracies when measuring, imaging or cutting using optical instruments; and adaptive optics are a way of negating these inaccuracies. In this article, we look at what adaptive optics are and the applications where they are used.
What is Adaptive Optics
Adaptive optics is a class of components that can be added to optical systems to improve their performance. They do this by reducing the incoming wave distortions which can arise due to natural effects, such as air turbulence, and changes in the local temperature and atmosphere, as well as from systematic errors such as those which arise due to the misalignment of components, imperfections in elements and aberrations.
Adaptive optics do this by manipulating the optical wavefront—a surface which contains the propagating wave that passes through all points within the same phase—so that it can be controlled. Most optical wavefronts are spherical or planar in nature, and if undistorted, can be changed using common optical elements. However, when the wavefront is distorted, complex adaptive optic components are required to improve the performance of the optical system. Whilst there are many different types of adaptive optics, the most common include deformable mirrors, actuators, and optical cavities.
Applications of Adaptive Optics
There are many areas where adaptive optics have found useful and here, we look at some of the key areas where adaptive optics are used.
Lasers are perhaps the biggest application area where adaptive optics can be used, and this ranges from applications in manufacturing to high-powered lasers, and femtosecond lasers that can be used on delicate materials. The addition of adaptive optics has been known to increase the efficiency of many lasers, and in turn, this has led to an increase in the performance of the applications they are used in. Some common applications that utilize lasers with adaptive optics include atomic trapping, understanding light-matter interactions at the atomic level, laser cutting, quantum computing, and free-form metrology. Many of these laser applications are possible because the adaptive optics enables the laser’s beam shape and size to be controlled, which makes it more accurate—especially in the cutting and manufacturing of materials.
Another big application area is astronomy. Many optical systems can be used to image celestial objects. However, given that the distance of these objects is far away, the wavefront can become distorted. Additionally, if the imaging is being performed from Earth (and not from a platform in space), disturbances can arise from the different temperature layers and wind speeds within the Earth’s atmosphere. All these factors contribute to turbulence which affects the imaging quality of the telescope. The use of adaptive optics can recover a lot of the information that is lost due to these disturbances by correcting the issues that arise from both low photon flux and atmospheric turbulence.
There are many different areas to vision science where adaptive optics are applied. One area is in robotic vision for surveillance cameras to provide real-time and long-distance imaging. Whilst these applications are on the machine side, there are also applications for humans where adaptive optics are useful. One of the key ways in imaging of the retina within the eye. One of the causes for the use of glasses is that aberrations can cause distortions in the wavefront that passes through the eye. However, for an ophthalmologist to see why vision is becoming impaired, they need to image the eye, and these distortions passing through the eye can not only distort the imaging of the eye itself, but also the imaging equipment. Adaptive optics can be employed in retina imaging equipment to identify the wavefront distortion and correct it so that a clear image of the eye can be taken.
Adaptive optics are used in microscopy applications to correct the aberrations that arise from the sample, as well as for correcting the aberrations caused by index mismatching in the microscope. The correction of these aberrations enables the resolution of the microscope to be high and is widely used in multi-photon microscopy, confocal microscopy, and fluorescence microscopy. Another area where adaptive optics have been found to be useful, is in imaging depth; and their use can help to better facilitate the depth of focus, without moving the objective of the microscope closer to the sample.
Free Space Optical Communications
Free space optical communications—which the transmission of light through an area of free space to transmit data—use horizontally propagating waves between optic components, and this often leads to a high degree of turbulence and distortion (of the light waves) in the free space region. Adaptive optics can be used to correct these disturbances, and this improves the transmission of data over long distances. The use of adaptive optics can also provide a decrease in the bit error rate and an increase in the speed of the telecommunication system.
Adaptive optics have also gained a small amount of usage in microelectronics to correct the wavefront at the sub-nm level, and this enables semiconductors to be fabricated with the highest spatial resolution possible. Additionally, lasers with adaptive optics can be combined with microelectronics to correct the masks in the top-down microfabrication processes used for creating semiconductors and microelectronic devices.
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