Adaptive as name suggest is having an ability to change to suit changing conditions. Human eye is a wonderful example to adaptive optics in which the eye lens adjusts itself to see objects located at both infinite distance as well as close to 25 cm. Eye lens adjusts its focal length to form image of stars as well as lines in our hand on retina. The ability to adjust its optical properties i.e. focal length in this case, is a subject of “Adaptive optics”.

Let’s take another example, where a departmental cloth store plans to make their customers feel good about their body shapes. They install a long mirror with tunable curvature. When the mirror senses person standing before it is fat, it adjusts its curvature to ensure image appear slim, whereas for extremely thin person, it does opposite to make them feel good, as shown in Fig. 1. In other words, it applies a correction factor to correct the things automatically, setting another example of adaptive optics.

Fig. 1 Convex mirror shows slim body shapes of overweight people. [Image from site of https://mirrorsdirect.com.au/ ]

The design and implementation of adaptive optics involve a complex interplay of physics, engineering and computational algorithm. It is a dynamic and vibrant field that continues to evolve and find new applications. The key component of Adaptive optics are deformable mirrors and wavefront sensors. It is a dynamic technology designed to correct distortions in the wavefronts, allowing astronomers to see clearer images.

It has been present in the nature inherently and species like crane and pelican, who have been applying this modern concept of optics, unknowingly through natural evolution. We know that a coin placed at the bottom of a transparent container appear to be located upwards. Similarly, the fish would appear to be located at different height than its actual position. But birds like crane and pelican can catch fish easily by estimating the exact position of fish in their brain. This requires calculation of their real position by applying the correction to the apparent position as shown in Fig. 2.

Fig. 2 Appearance of fish at different location than actual position. This requires calculation by pelican birds to catch in single strive while diving.

Adaptive optics for retinal imagining

Ophthalmic imaging is typically used to assess retinal health images of the back of the eye. It can be captured with cameras or by simply looking into the eye. The visualization of the back of the eye at the cellular level is potentially revolutionary because it enables monitoring of small changes associated with disease progressions. Therefore, it is very important to have a clear and precise images of these structures. Adaptive optics helps in correcting every minute feature on the retina and helps in a very precise surgery.

Adaptive optics in Laser weapons

It is wonderful to understand how laser weapons maintain their precision even in challenging situation. The answer lies again in this fascinating technology of adaptive optics. It plays a vital role in ensuring that the laser beam remains focused and effective in real time during military operations. Adaptive optics takes care of the distortions in a laser beam caused by atmospheric turbulence which occurs when layers of air with different temperatures and densities interact.

Further, the laser beam traveling through the atmosphere can scatter, bend or fluctuate. This can reduce the weapons effectiveness by changing the focus of the beam. To combat this issue adaptive optics systems continues to monitor the laser beams wavefronts. They analyze how the beam propagates and identifies any distortion, using this real time data the system can dynamically adjust deformable mirrors or other optical elements. Such features become important in today’s era where warfare are being planned and executed through drones and unmanned armed vehicles for automatic targeting of enemy objects.

Adaptive Optics in Astronomy

We have been taught from school days that stars twinkle due to the earth’s atmosphere, which distorts the light from celestial objects. This is where adaptive optics comes into play. The basic principle behind this technique is measuring the distortion in the light wave as they enter a telescope. Light travels in the form of waves and when these waves pass through various air densities and temperatures in the atmosphere, they get distorted. To fix this a wavefront sensor is used to detect the distortion. This sensor is crucial because the system knows how much correction is needed. Another key component of adaptive optics is a deformable mirror.

It is very fascinating to know that the mirror can change its shape hundred or even thousands of times each second. A computer controls the mirror based on the data from the wavefront’s sensors. By adjusting the mirror, the system corrects the incoming light resulting in a clearer image. Another important part of adaptive optics is a controlled system. This system processes the information from the waveform sensors and instruct the deformable mirror on how to adjust itself.

The combination of these components allows telescopes to achieve resolutions that were once only possible with space-based telescopes like the Hubble’s space telescope. In astronomy, adaptive optics has many applications. It enables telescopes to observe fainter objects that would otherwise be lost in the atmospheric distortion. This improved resolution is essential for detailed research on various celestial bodies.

Additionally, adaptive optics can help with atmospheric refraction correction. Atmospheric refraction is the bending of light as it passes through the different layers of the atmosphere while adaptive optics mainly corrects for turbulence it also indirectly aids in managing the effects of refraction by providing clearer images by which astronomers can analyze and account for refractional effects. Adaptive optics is a powerful tool in astronomy.

Interestingly, with advancement in the implementation of algorithms for artificial intelligence and machine learning, processing capabilities of computers and ultrasensitive and ultrafast switching sensors, the reach of the adaptive optics has come to realization in our day today life without realizing its presence around us. We never realize that the mobile phone we are carrying, it uses a form of adaptive optics typically in the digital or software sense rather than the mechanical systems used in giant astronomical telescopes.

Instead of physically warping mirrors, modern phones use computational photography and artificial intelligence driven hybrid optics to adjust and optimize images in real time. Tomorrow, it may happen that we should be able to see through opaque objects using adaptive optics: a situation similar to pasting a cello tape on roughened (frosted or, etched) glass partition making it transparent.

Author
The author Dr. Satchi Singh is a researcher in the field of optics and photonics. She has obtained Ph.D in Photonics from IIT Guwahati and have taught at University of Delhi and Central University of Jharkhand.