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Scientists use chaos to build the optimal laser beam
Researchers find a way to distort laser light to survive a trip through disordered obstacles.
- Lasers are great for measuring—if they can get a clear view of their target.
- In biomedical applications, there's often disordered stuff in the way of objects needing measurement.
- A new technique leverages that disorder to formulate a custom-made, optimal laser light beam.
Lasers can make amazingly precise measurements. Invaluable for precision construction and manufacturing, they also allow biomedical researchers and doctors to accurately detect the position and movement of microscopic objects, from cells to tissues to tiny biological structures. That is, when the laser can get a direct shot at the target, which is often not possible. In the human body, for example, these objects may be partially obscured by, situated in, or even behind complicated, obfuscating stuff.
Now scientists from Utrecht University (Netherlands) and TU Wien in Austria have devised a cool way to alter lasers so that they can bounce right through such distortion fields, arriving on the other side as an "optimal wave" intact enough to get to work.
Their new system is described in the journal Nature Physics.
Understanding the problem
Credit: gavran333/Adobe Stock
When working with lasers or any other measurement tool, "You always want to achieve the best possible measurement accuracy — that's a central element of all natural sciences," says paper co-author Stefan Rotter of TU Wien in a press release. A highly focused laser beam is an ideal tool for this. However, getting it through a disordered barrier without destroying the integrity of the beam is a challenge.
The researchers describe the problem using the example of the type of frosted glass one might encounter in a bathroom window. Explains Utrecht University's Allan Mosk, another co-author, "Let's imagine a panel of glass that is not perfectly transparent, but rough and unpolished like a bathroom window." To keep people from seeing into the bathroom, "Light can pass through, but not in a straight line. The light waves are altered and scattered, so we can't accurately see an object on the other side of the window with the naked eye."
This is not very different from what happens when a scientist tries to examine some tiny object inside biological tissue. The disordered stuff between the scientist and the object turns the concentrated laser beam into a complex wave pattern that scatters on its way through the visual barrier.
The new solution
Credit: TU Wien
The researchers have found that they can modify a laser's light in anticipation of the way it will travel through the disordered environment so that it hits its target on the other side with sufficient coherence for making accurate measurements.
While that optimal wave may not be a pure, pristine laser light, it's nonetheless just the light wave needed to successfully make its way through that particular barrier. The researchers were able to develop a mathematical procedure that gives them the distortion required to produce such a wave. Says first author Dorian Bouchet, also of Utrecht University, "You can show that for various measurements there are certain waves that deliver a maximum of information as, e.g., on the spatial coordinates at which a certain object is located."
Bouchet adds, "To achieve this, you don't even need to know exactly what the disturbances are. It's enough to first send a set of trial waves through the system to study how they are changed by [it]."
Returning to the glazed bathroom window example, the system would identify an optimal light wave that could travel through the disordered glass and still accurately measure movement of a person behind the glass.
Testing the system
The researchers confirmed that their formula worked in experiments at Utrecht in which they were able to make nano-scale measurements using a laser that successfully transited a turbid plate playing the role of a disordered medium. They also tried simpler and simpler laser beams—reducing the number of photons being used—to see how far they could push their system. They found that it even with the simplest laser possible, it still performed satisfactorily.
Says Mosk, "We see that the precision of our method is only limited by the so-called quantum noise. This noise results from the fact that light consists of photons—nothing can be done about that." Still, he says, "within the limits of what quantum physics allows us to do for a coherent laser beam, we can actually calculate the optimal waves to measure different things. Not only the position, but also the movement or the direction of rotation of objects."
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Physicist Frank Wilczek proposes new methods of searching for extraterrestrial life.
- Nobel Prize-winning physicist Frank Wilczek thinks we are not searching for aliens correctly.
- Instead of sending out and listening for signals, he proposes two new methods of looking for extraterrestrials.
- Spotting anomalies in planet temperature and atmosphere could yield clues of alien life, says the physicist.
1. Atmosphere chemistry<p>Like we found out with our own effect on the Earth's atmosphere, making a <a href="https://ozonewatch.gsfc.nasa.gov/facts/hole_SH.html" target="_blank">hole in the ozone layer</a>, the gases around a planet can be impacted by its inhabitants. "Atmospheres are especially significant in the search for alien life," <a href="https://www.wsj.com/articles/looking-for-signs-of-alien-technology-11581605907" target="_blank">writes Wilczek</a> "because they might be affected by biological processes, the way that photosynthesis on Earth produces nearly all of our planet's atmospheric oxygen."</p><p>But while astrobiology can provide invaluable clues, so can looking for the signs of alien technology, which can also be manifested in the atmosphere. An advanced alien civilization might be colonizing other planets, turning their atmospheres to resemble the home planets. This makes sense considering our own plans to terraform other planets like Mars to allow us to breathe there. Elon Musk even <a href="https://www.space.com/elon-musk-serious-nuke-mars-terraforming.html" target="_blank">wants to nuke the red planet.</a></p>
The Most Beautiful Equation: How Wilczek Got His Nobel<div class="rm-shortcode" data-media_id="ijBZzuI2" data-player_id="FvQKszTI" data-rm-shortcode-id="061a3de613c45f42b05432a2949e7caa"> <div id="botr_ijBZzuI2_FvQKszTI_div" class="jwplayer-media" data-jwplayer-video-src="https://content.jwplatform.com/players/ijBZzuI2-FvQKszTI.js"> <img src="https://cdn.jwplayer.com/thumbs/ijBZzuI2-1920.jpg" class="jwplayer-media-preview" /> </div> <script src="https://content.jwplatform.com/players/ijBZzuI2-FvQKszTI.js"></script> </div>
2. Planet temperatures<p>Wilczek also floats another idea - what if an alien civilization created a greenhouse effect to raise the temperature of a planet? For example, if extraterrestrials were currently researching Earth, they would likely notice the increased levels of carbon dioxide that are <a href="https://www.epa.gov/ghgemissions/overview-greenhouse-gases" target="_blank">heating up</a> our atmosphere. Similarly, we can looks for such signs around the exoplanets.</p><p>An advanced civilization might also be heating up planets to raise their temperatures to uncover resources and make them more habitable. Unfreezing water might be one great reason to turn up the thermostat. </p><p>Unusually high temperatures can also be caused by alien manufacturing and the use of artificial energy sources like nuclear fission or fusion, suggests the scientist. Structures like the hypothetical <a href="https://bigthink.com/paul-ratner/this-mind-bending-scale-predicts-the-power-of-advanced-civilizations" target="_self">Dyson spheres</a>, which could be used to harvest energy from stars, can be particularly noticeable. </p>
Wilczek: Why 'Change without Change' Is One of the Fundamental Principles of the ...<div class="rm-shortcode" data-media_id="KrUgLGWm" data-player_id="FvQKszTI" data-rm-shortcode-id="cc13c3c65924439c1992935c61ab8977"> <div id="botr_KrUgLGWm_FvQKszTI_div" class="jwplayer-media" data-jwplayer-video-src="https://content.jwplatform.com/players/KrUgLGWm-FvQKszTI.js"> <img src="https://cdn.jwplayer.com/thumbs/KrUgLGWm-1920.jpg" class="jwplayer-media-preview" /> </div> <script src="https://content.jwplatform.com/players/KrUgLGWm-FvQKszTI.js"></script> </div>
As patients approached death, many had dreams and visions of deceased loved ones.
One of the most devastating elements of the coronavirus pandemic has been the inability to personally care for loved ones who have fallen ill.
Research reveals a new evolutionary feature that separates humans from other primates.
- Researchers find a new feature of human evolution.
- Humans have evolved to use less water per day than other primates.
- The nose is one of the factors that allows humans to be water efficient.
A model of water turnover for humans and chimpanzees who have similar fat free mass and body water pools.
Credit: Current Biology
Being skeptical isn't just about being contrarian. It's about asking the right questions of ourselves and others to gain understanding.